JP2003086249A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe and high-performance lithium secondary battery wherein swelling of the lithium secondary battery in a high-temperature storage is suppressed, which especially becomes a problem when a case to house a battery element is shape-variable. SOLUTION: In the lithium secondary battery having the battery element to possess a positive electrode, a negative electrode, and an electrolyte to contain a non-aqueous solvent and a solute, and the shape-variable case, and in case that the difference: Esol (A)-Esol (N) between an enthalpy: Esol (N) of a neutral molecule of the non-aqueous solvent obtained by a prescribed calculation method and the enthalpy: Esol (A) of an anion radical generated by giving one electron to the neutral molecule is shown as ΔEsol (AN), that the battery element contains the additive α, and that the difference: Eadd (A)-Eadd (N) between the enthalpy: Eadd (N) of the neutral molecule of the additive α calculated by a prescribed calculation method and the enthalpy: Eadd (A) of the anion radical generated by giving one electron to the neutral molecule is taken as ΔEadd (AN), ΔEadd (AN) is less than ΔEsol (AN).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery (in this specification, it may be simply referred to as a battery).
More specifically, the present invention relates to a lithium secondary battery that is highly safe even when stored at high temperatures.

[0002]

2. Description of the Related Art A lithium secondary battery is known in which a battery element having a positive electrode, a negative electrode, and an electrolyte containing a non-aqueous solvent and a solute is hermetically sealed in a case. The most common lithium secondary battery uses a rigid metal can made of metal such as SUS (stainless steel) as a case.

In recent years, instead of a lithium secondary battery using such a metal can, an outer packaging material having a shape-variable property, such as a laminate film having resin layers on both sides of a gas barrier layer, has been used for a case. Lithium secondary batteries have been put to practical use. The exterior material having the shape changeability has an advantage that the degree of freedom in designing the shape of the case is higher than that of the metal can, and thus the degree of freedom in designing the shape of the lithium secondary battery is improved. Further, in a lithium secondary battery using a case having a shape-changing exterior material, the weight and thickness of the exterior material can be reduced, which further reduces the size and weight of the battery and further improves volume energy density and It is possible to improve the weight energy density.

In addition to the selection of the case, research and development have also been conducted to improve the volume energy density and weight energy density of the lithium secondary battery by increasing the capacity of the battery element itself. As a technique for increasing the capacity of the battery element itself, the use of a lithium nickel composite oxide as a positive electrode active material has been studied. This is useful from the viewpoint of high capacity, since the lithium nickel composite oxide has a large current capacity per unit weight as compared with the lithium cobalt composite oxide (LiCoO ₂ ) generally used as a positive electrode active material. This is because it is a positive electrode material.

[0005]

However, a lithium secondary battery using a case having shape changeability has a mechanical strength higher than that of a conventional lithium secondary battery using a metal can as a case. weak. Therefore, when the internal pressure of the case of the lithium secondary battery rises due to storage under a high temperature environment, the lithium secondary battery may swell.
The swelling of the lithium secondary battery due to this increase in internal pressure is
This causes deterioration of battery performance, deterioration of safety, and deterioration of shape stability of the lithium secondary battery. That is, when a metal can is used for the case, the metal can has sufficiently high mechanical strength against an increase in internal pressure generated during high temperature storage, and therefore the case does not swell due to the increase in internal pressure. On the other hand, since the material having the shape changeability has a weak mechanical strength, the lithium secondary battery swells as the internal pressure of the case rises.

The bulge of the lithium secondary battery causes deterioration of battery performance. That is, the swelling of the lithium secondary battery lowers the adhesion between the electrode and the electrolyte in the battery element housed in the case, resulting in a decrease in discharge capacity and deterioration in cycle characteristics. Furthermore, when a case made of a laminated film is used as the case having shape variability, the swelling of the lithium secondary battery may cause a part of the joint part of the film to leak. As a result, the battery characteristics may deteriorate.

The bulge of this lithium secondary battery is
This will expose the lithium secondary battery to dangerous conditions. That is, when a case made of a laminated film is used as the shape-variable case, the swelling of the lithium secondary battery may cause a part of the film joint to leak, and when the electrolyte leaks from this leak part. There is. Further, when the internal pressure rises rapidly or is large, there is a risk of the case bursting.

Further, the swelling of the lithium secondary battery causes deterioration of the shape stability of the lithium secondary battery and hinders downsizing of electric equipment. In other words, electronic devices in which lithium secondary batteries are housed are becoming smaller and smaller in recent years, so there is a demand to make the battery housing space as small as possible. Therefore, when the lithium secondary battery swells due to an increase in the internal pressure of the case during high temperature storage, it is necessary to design the battery storage space in consideration of the amount of the swelling. Therefore, the bulge of the lithium secondary battery also becomes an obstacle to downsizing of electronic devices.

Actually, a mobile phone or the like in which a lithium secondary battery is used as a power source may be left in an extremely hot car. In this case, the lithium secondary battery is 60 to 8
It will be exposed to a high temperature environment of 5 ° C. From this situation as well, suppressing the rise of the internal pressure of the case when stored at the high temperature must be solved for the lithium secondary battery in which the battery element is housed in the case having shape changeability. This is a technical issue that must be addressed.

According to the study by the present inventors, it has been found that the increase in the internal pressure becomes particularly remarkable when the lithium nickel composite oxide is used as the positive electrode active material.
Lithium nickel composite oxide is a very promising positive electrode active material because it has a higher battery capacity per unit weight than other lithium transition metal composite oxides such as lithium cobalt composite oxide and lithium manganese composite oxide. is there.
However, when the lithium nickel composite oxide is used, the increase in the internal pressure tends to be more remarkable as compared with other lithium transition metal oxides. The fact is that this problem hinders the practical application of a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material.

The present invention has been made in view of the above problems. An object of the present invention is to suppress swelling of a lithium secondary battery due to an increase in internal pressure of the case during high temperature storage, which is a problem when using a case having shape variability, and to improve battery performance and safety of the lithium secondary battery. , And improving the shape stability.

[0012]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the inventors of the present invention have taken into consideration the swelling of a lithium secondary battery during high temperature storage, which is a problem in a lithium secondary battery using a case having a shape changeability. We have diligently studied suppression. As a result, by adding the additive α to the battery element and controlling the relationship between the non-aqueous solvent contained in the electrolyte and the additive α as shown below, it is possible to increase the case internal pressure during high temperature storage. The present invention has been completed with the finding that swelling of a lithium secondary battery can be suppressed. That is, the difference between the enthalpy of the neutral molecule of the non-aqueous solvent: Esol (N) and the enthalpy of the anion radical produced by giving one electron to the neutral molecule: Esol (A): Esol (A)- Esol (N)
With respect to the enthalpy of neutral molecules of the additive α: E
The difference between add (N) and the enthalpy of anion radical Eadd (A) generated by giving one electron to the neutral molecule: Eadd (A) -Eadd (N) has been found to be small. is there.

That is, the gist of the present invention is to provide a lithium secondary battery having a battery element having a positive electrode, a negative electrode, an electrolyte containing a non-aqueous solvent and a solute, and a shape-variable case accommodating the battery element. The enthalpy of the neutral molecule of the non-aqueous solvent: Esol (N), and the enthalpy of anion radical generated by giving one electron to the neutral molecule, which is determined by the following calculation method (#):
Difference from Esol (A): Esol (A) -Esol (N) is ΔEs
ol (AN), the battery element contains the additive α, and the enthalpy of the neutral molecule of the additive α is Eadd (N), which is determined by the following calculation method (#), and the neutral molecule has electrons. Difference between the enthalpy of the anion radical generated by giving one of the following: Eadd (A): Eadd (A) -Eadd
If (N) is ΔEadd (AN), then ΔEadd (A
N) is smaller than ΔEsol (AN) in a lithium secondary battery.

Calculation Method (#) The enthalpy of the neutral molecule and the enthalpy of the anion radical are respectively obtained by quantum chemical calculation by the ab initio restricted Hartree-Fock molecular orbital method using the 6-31G * basis set.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium secondary battery of the present invention will be described in detail below. [1] Additive α The lithium secondary battery of the present invention has a positive electrode, a negative electrode, a battery element having an electrolyte containing a non-aqueous solvent and a solute, and a shape-variable case housing the battery element. In a lithium secondary battery, the enthalpy of the neutral molecule Esol (N) of the non-aqueous solvent and the enthalpy of anion radicals produced by giving one electron to the neutral molecule, which is determined by the following calculation method (#): : Esol (A)
Difference with: Esol (A) -Esol (N) is ΔEsol (AN)
The battery element contains the additive α, and the enthalpy of the neutral molecule of the additive α: Eadd (N), which is obtained by the following calculation method (#), and one electron is given to the neutral molecule. Enthalpy of generated anion radicals: E
Difference from add (A): Eadd (A) -Eadd (N) is ΔEadd
If (AN), then ΔEadd (AN) is ΔEsol (A
It is smaller than N).

Calculation Method (#) The enthalpy of the neutral molecule and the enthalpy of the anion radical are obtained by quantum chemical calculation by the ab initio restricted Hartree-Fock molecular orbital method using the 6-31G * basis set. In other words, the enthalpies of neutral molecules and anion radicals are 6-
The molecular structure is optimized by the ab initio Hartree-Fork molecular orbital method using a 31G * basis set. However, the restricted open shell molecular orbital method is used for the evaluation of anion radicals.

In the present invention, as a general notation, the enthalpy of a neutral molecule is E (N), the enthalpy of an anion radical is E (A), and the difference between the enthalpy of an anion radical and the enthalpy of a neutral molecule. : E (A)
-E (N) may be represented as ΔE (AN). The reason why the swelling of the lithium secondary battery during high temperature storage is suppressed by making ΔEadd (AN) of the additive α smaller than ΔEsol (AN) of the non-aqueous solvent will be described below. .

That is, when the lithium secondary battery is maintained in a high temperature environment in a charged state, the surface of the positive electrode active material acts as a catalyst and the non-aqueous solvent contained in the electrolyte decomposes into a component containing gas such as carbon dioxide gas. To be done. Then, since this gas raises the internal pressure of the case of the lithium secondary battery, swelling of the lithium secondary battery using the shape-variable case occurs.

Here, the surface of the positive electrode active material acts as a catalyst when, for example, the positive electrode active material is a lithium transition metal composite oxide such as a lithium cobalt composite oxide or a lithium nickel composite oxide. In a metal oxide such as cobalt oxide or nickel oxide, the basicity of the oxygen atom is increased due to the polarization in the bond between the metal atom and the oxygen atom. Particularly in the charged state, a large amount of positive atom lithium is released from the positive electrode active material, and there are few factors that neutralize the negative charge in the positive electrode active material. Sex is even higher. Then, in a high temperature environment, the site of the oxygen atom having high basicity serves as a basic point, and a nonaqueous solvent contained in an electrolyte such as a carbonate is decomposed by a nucleophilic reaction to generate a gas such as carbon dioxide gas. Let them do it.

Therefore, as a method of suppressing the decomposition reaction of the non-aqueous solvent, a method of passivating the surface of the oxygen atom of the metal oxide constituting the positive electrode active material to reduce its basicity is effective. Here, in order to reduce the basicity, a method of combining with an acidic additive can be considered. However, according to the study by the present inventors, even if a large amount of mobile ions such as protic acids and Bronsted acids are present in the battery element, the effect of suppressing the swelling of the lithium secondary battery during high temperature storage is still high. It has been found that not only is it insufficient, but it also causes an increase in the resistance of the battery and is likely to cause deterioration in charge and discharge performance. That is, in order to suppress the swelling of the lithium secondary battery that occurs during high temperature storage, any additive that has acidity may be used as the additive that is included in the battery element. The additive must be capable of sufficiently suppressing the swelling without deteriorating the battery characteristics.

Under such circumstances, the present inventors have found that in order to reduce the basicity of the surface of the positive electrode active material, the component, particularly the electrolyte, which is likely to be compatible with the electric charge derived from the basic points present on the surface of the positive electrode active material. It was thought that the battery element should be allowed to contain a component that is more likely to have an affinity for the electric charge derived from the base point than the non-aqueous solvent contained in (3). Because, if the basicity of the surface of the positive electrode active material can be lowered in preference to the decomposition reaction of the non-aqueous solvent, the decomposition reaction of the non-aqueous solvent can be suppressed, and thus the gas generation during storage at high temperature can be suppressed. Because you can

Based on the above assumptions, the present inventors prefer the electron derived from the base point rather than the non-aqueous solvent as the component which has a higher affinity for the electric charge derived from the base point on the surface of the positive electrode active material in preference to the non-aqueous solvent. It was considered effective to use the additive α which is easily accepted and easily resonates. Such an additive α needs to have a property of more easily changing from a neutral molecule to an anion radical than in a non-aqueous solvent. The present inventors used the energy gap when changing from a neutral molecule to an anion radical as an index showing the ease of this change. Then, the energy gap of the additive α (ΔE
It has been considered that add (AN)) should be smaller than the energy gap (ΔEsol (AN)) of the non-aqueous solvent. The reason is that, when the energy gap is small, the neutral molecule easily accepts an electron and thus easily resonates with the electron at the base point.

As the additive α, a Lewis acid that accepts an electron at a base point on the surface of the positive electrode active material and easily resonates is preferable. Then, the energy gap (ΔEadd when this Lewis acid changes from a neutral molecule to an anion radical)
(AN)) is the energy gap (Δ) of the non-aqueous solvent.
It may be smaller than Esol (AN)). In the present invention, the difference between the ΔEsol (AN) and the ΔEadd (AN): ΔEsol (AN) −ΔEadd (AN) is usually 0.
It is 1 eV or more, preferably 0.2 eV or more, more preferably 0.3 eV or more, particularly preferably 0.7 eV or more, and most preferably 0.95 eV or more. When it is 0.2 eV or more, even if the oxidation state of the metal oxide forming the positive electrode active material is non-uniform depending on the state of the electrode, the effect becomes remarkable. If the voltage is 0.3 eV or more, a voltage distribution may easily occur inside the positive electrode depending on the battery element, but even in that case, the swelling suppressing effect at high temperature becomes clear. On the other hand, ΔEsol (AN) −ΔEadd (AN)
Is usually 4 eV or less, preferably 3.5 eV or less, and more preferably 3 eV or less. If it is 3.5 eV or less, the additive α is more likely to accept electrons properly than the non-aqueous solvent contained in the electrolyte and selectively acts only on the Lewis base point on the surface of the positive electrode active material. Become.

In the present invention, the additive α is preferably a sulfur compound having one or more double bonds of sulfur and oxygen. That is, the additive α has a double bond of sulfur and oxygen, and its ΔEadd (AN) is ΔEso of a general non-aqueous solvent used as an electrolyte of a lithium secondary battery.
It is preferably smaller than l (AN). By using such an additive α, the charge at the base point of the positive electrode is accepted and resonance is facilitated, and the surface of the positive electrode is passivated in preference to the non-aqueous solvent. The reaction is suppressed and the swelling of the case is effectively prevented.

The properties of the sulfur compound used in the present invention are preferably liquid or solid at room temperature and normal humidity. Here, normal temperature and normal humidity means an environment of 25 ° C./50% RH. Here, in general, a sulfur compound having a plurality of sulfur atoms and an oxygen atom has a smaller ΔEadd (AN) value than a sulfur compound having one double bond, and ΔEadd (AN) has a smaller value.
The difference from l (AN) tends to be large, and a resonant structure that accepts electrons is structurally easy to be stably obtained.
Therefore, when a sulfur compound having a plurality of double bonds of a sulfur atom and an oxygen atom is used, interaction with the surface of the positive electrode is facilitated, and swelling of the lithium secondary battery can be prevented more effectively. Further, a sulfur compound in which an oxygen atom is further bonded with a single bond to a sulfur atom forming a double bond with an oxygen atom,
For the same reason as above, it is preferable in that the swelling of the lithium secondary battery can be prevented more effectively.

The sulfur compound is preferably a compound represented by the following general formula (1).

[0027]

[Chemical 4]

[0028] In the above general formula (1), R ¹ and R ² each independently represents X ¹ or O-X ^1,, X ¹ is 1-9 carbon chain or cyclic saturated hydrocarbon Base, carbon number 1
~ 9 chain or cyclic unsaturated hydrocarbon group, or 6 carbon atoms
The aromatic hydrocarbon groups of 9 to 9 may be combined with each other, and R ¹ and R ² may be linked to each other to form a 5- or 6-membered ring containing a sulfur atom. Here, by setting R ¹ and R ² to be a functional group in which oxygen is bonded to X ¹ , that is, O—X ¹ , it is possible to effectively suppress an increase in the internal pressure of the case.

Examples of the chain or cyclic saturated hydrocarbon group having 1 to 9 carbon atoms include, for example, methyl group, ethyl group and n-
Propyl group, t-propyl group, n-butyl group, sec-
Examples thereof include a butyl group and a cyclohexyl group. Of these, a methyl group and an ethyl group are preferable from the viewpoint that the effects of the present invention can be more exerted. Examples of the chain or cyclic unsaturated hydrocarbon group having 1 to 9 carbon atoms include a vinyl group, an allyl group, a butynyl group and a pentynyl group. Of these, a vinyl group is preferable because the effect of the present invention can be further exhibited.

Examples of the aromatic hydrocarbon group having 6 to 9 carbon atoms include phenyl group and 4-methylphenyl group. Of these, a phenyl group is preferred from the viewpoint that the effects of the present invention can be more exerted. The total carbon number of R ¹ and R ² is more preferably 2 to 7. This is because the smaller the steric hindrance of the substituent bonded to the sulfur atom, the more effectively the rise in the internal pressure of the case is suppressed.

R ¹ and R ² may be connected to each other to form a 5- or 6-membered ring containing a sulfur atom. Examples of such compounds include divalent free radicals 1,
4-butylene group, 1,5-pentylene group, -O- (CH
_{2) n -, - O- (} CH 2) m -O- , and the like (n, m are usually each 2-4 integer.
n is preferably 3 or 4 and m is 2 or 3
Is preferable). Among these, more preferable from the viewpoint that the effect of the present invention is exerted more is that there are many oxygen atoms bonded to sulfur atoms, and steric hindrance is small.
_{(CH 2) 3 -, -} O- (CH 2) a ₂ -O-.

The sulfur compound is preferably a compound represented by the following general formula (2).

[0033]

[Chemical 5]

[0034] In the general formula (2), the R ³ and R ⁴ each independently represent X ² or O-X ^2,, X ² is 1 to 9 carbon atoms chain or cyclic saturated hydrocarbon Base, carbon number 1
~ 9 chain or cyclic unsaturated hydrocarbon group, or 6 carbon atoms
It represents a to 9 aromatic hydrocarbon group, linked together and R ³ and R ^4, may form a 5- or 6-membered ring containing a sulfur atom. Here, by making R ³ and R ⁴ functional groups in which oxygen is bonded to X ² , that is, O—X ² , it is possible to effectively suppress an increase in internal pressure of the case.

As X ² , the same ^one as X ¹ described in the general formula (1) can be used. The preferable range of the total carbon number of R ³ and R ⁴ is the same as the preferable range of the total carbon number of R ¹ and R ² . And R ³ and R ⁴
When and are bonded to each other to form a ring, the same groups as those used when R ¹ and R ² are bonded to each other to form a ring can be used.

Examples of the sulfur compound include dimethyl sulfoxide, diethyl sulfoxide, diphenyl sulfoxide, tetramethylene sulfoxide, methyl methanesulfinate, ethyl ethanesulfinate, dimethylsulfite, diethylsulfite, 1,2-propylene glycol sulfite. , 1,3-butylene glycol sulfite, diphenyl sulfite, ethylene sulfite, vinylene sulfite, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, diphenyl sulfone, dibenzyl sulfone, sulfolane, 3-
Methylsulfolane, 3-methylsulfolene, methyl methanesulfonate, ethyl methanesulfonate, acetyl methanesulfonate, tetrahydrofurfuryl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, methyl propanesulfonate, methyl benzenesulfonate , 1,3-propane sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, ethyl methyl sulfate, methylphenyl sulfate, ethylene glycol sulfate, 1,3-propanediol sulfate, and 1,4-butanediol sulfate. Mention may be made of esters. For some of these sulfur compounds, E
Difference between add (A) and Eadd (N): Table 1 shows the values of ΔEadd (AN).

[0037]

[Table 1]

What is important in the present invention is the value of ΔEsol (AN) of the non-aqueous solvent contained in the electrolyte, and the above table-
It is a comparison with the value of ΔEadd (AN) in 1. For example,
When the value of ΔEsol (AN) of the non-aqueous solvent contained in the electrolyte is 4, the effect of the present invention can be obtained by using any of the sulfur compounds shown in Table-1. on the other hand,
For example, when the value of ΔEsol (AN) is 2, the effect of the present invention can be obtained by using one having ΔEadd (AN) of 2 or less in Table-1.

However, among these sulfur compounds, ΔEad
If a sulfur compound with a small d (AN) is used, ΔEsol (A
Since the difference between the value of N) and the value of ΔEadd (AN) tends to be large, the swelling of the lithium secondary battery during high temperature storage can be suppressed more effectively. From the above viewpoint, ΔE
What is preferable in that add (AN) is 3 or less is that
Diethyl sulfoxide (1.49 eV), diphenyl sulfoxide (1.83 eV), tetramethylene sulfoxide (1.7 eV), dimethyl sulfite (1.85)
eV), diethyl sulfite (2.15 eV), 1,
2-Propylene glycol sulfite (1.99e
V), 1,3-butylene glycol sulfite (1.
86 eV), ethylene sulfite (2.01 eV),
Dimethyl sulfone (1.37eV), diethyl sulfone (2.58eV), diphenyl sulfone (1.41e)
V), dibenzyl sulfone (0.45 eV), sulfolane (1.48 eV), 3-methylsulfolane (1.46)
eV), 3-methylsulfolene (0.93 eV), methyl methanesulfonate (0.25 eV), ethyl methanesulfonate (0.24 eV), acetyl methanesulfonate (0.94 eV), tetrahydrofurfuryl methanesulfonate (-0.12 eV), methyl benzenesulfonate (1.44 eV), 1,3-propane sultone (-0.
17 eV), 1,4-butane sultone (0.29 e
V), dimethyl sulfate (2.04 eV), diethyl sulfate (2.07 eV), ethylene glycol sulfate (-0.59 eV), and 1,3-butylene glycol sulfate (-0.103 eV).

Further, in view of ΔEadd (AN) of 2 or less, diethyl sulfoxide (1.
49 eV), diphenyl sulfoxide (1.83 e)
V), tetramethylene sulfoxide (1.7 eV), dimethyl sulfite (1.85 eV), 1,2-propylene glycol sulfite (1.99 eV), 1,3
-Butylene glycol sulfite (1.86 eV),
Dimethyl sulfone (1.37eV), diphenyl sulfone (1.41eV), dibenzyl sulfone (0.45eV)
V), sulfolane (1.48 eV), 3-methylsulfolane (1.46 eV), 3-methylsulfolene (0.9
3 eV), methyl methanesulfonate (0.25 eV),
Ethyl methanesulfonate (0.24 eV), acetyl methanesulfonate (0.94 eV), tetrahydrofurfuryl methanesulfonate (-0.12 eV), methyl benzenesulfonate (1.44 eV), 1,3-propane sultone ( -0.17 eV), 1,4-butane sultone (0.29 eV), ethylene glycol sulfate (-0.59 eV), and 1,3-butylene glycol sulfate (-0.103 eV).

Most preferable in terms of ΔEadd (AN) of 1.5 or less are diethyl sulfoxide (1.49 eV) and dimethyl sulfone (1.37 e).
V), diphenyl sulfone (1.41 eV), dibenzyl sulfone (0.45 eV), sulfolane (1.48 eV)
V), 3-methylsulfolane (1.46 eV), 3-methylsulfolene (0.93 eV), methyl methanesulfonate (0.25 eV), ethyl methanesulfonate (0.
24eV), acetyl methanesulfonate (0.94e
V), tetrahydrofurfuryl methanesulfonate (-
0.12 eV), methyl benzenesulfonate (1.44
eV), 1,3-propane sultone (-0.17e
V), 1,4-butane sultone (0.29 eV), ethylene glycol sulfate (-0.59 eV), and 1,3-butylene glycol sulfate (-0.10).
3 eV).

The sulfur compound may be contained in any part of the battery element, but since it is preferable to exist on the surface of the positive electrode active material from the viewpoint of preventing the case from swelling, the sulfur compound should be contained in the positive electrode or the electrolyte. Is preferable, and it is particularly preferable to include it in the electrolyte. By including it in the positive electrode or the electrolyte, the basicity can be lowered by interacting with the surface of the oxygen atom of the metal oxide on the surface of the positive electrode active material in preference to the non-aqueous solvent contained in the electrolyte. ,
Swelling of the case during storage at high temperature can be effectively suppressed.

When the sulfur compound is contained in the electrolyte, it is usually contained in an amount of 0.001 part by weight or more per 100 parts by weight of the non-aqueous solvent and solute contained in the electrolyte, but 0.1 part by weight is contained. It is preferable to contain at least 0.5 part by weight, more preferably at least 0.5 part by weight,
It is particularly preferable to contain 1 part by weight or more, and most preferably 5 parts by weight or more. The content of the non-aqueous solvent and solute is usually 30 parts by weight or less, preferably 15 parts by weight or less, more preferably 10 parts by weight or less, based on 100 parts by weight. If the amount added is less than this range, the swelling of the case during high temperature storage may be insufficient, and if the amount added is more than this range, the conductivity of the electrolyte decreases and the internal resistance of the battery increases. There is.

Incidentally, JP-A-8-241731, JP-A-8-241732, JP-A-8-321312, JP-A-2000-133305, and JP-A-27.
No. 34978, Japanese Patent No. 2766018, and Japanese Patent No. 2804591 each disclose a compound similar to the sulfur compound in the additive α used in the present invention.

However, in these documents, by making a predetermined relationship between ΔEsol (AN) of the non-aqueous solvent contained in the electrolyte and ΔEadd (AN) of the additive α contained in the battery element, the documents are described. There is no description or suggestion of suppressing the rise of the internal pressure of the case in the lithium secondary battery. [2] Non-Aqueous Solvent The electrolyte used in the lithium secondary battery of the present invention contains a non-aqueous solvent and a solute (in the present specification, the solute and the non-aqueous solvent are combined to form an electrolytic solution or non-aqueous electrolysis). Sometimes called liquid).

The non-aqueous solvent used in the present invention has a ΔEsol larger than the ΔEadd (AN) of the additive α described above.
It is necessary to have (AN). Examples of such a non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate and vinylene carbonate; non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate; furan such as tetrahydrofuran and 2-methyltetrahydrofuran. And glymes such as dimethoxyethane; lactones such as γ-butyl lactone; nitriles such as acetonitrile; Among these, a mixed solution of one or more selected from cyclic carbonates, acyclic carbonates and lactones is preferable.

For some of the non-aqueous solvents specifically exemplified above, E obtained by the above-described calculation method was used.
Difference between sol (A) and Esol (N): Table 2 shows the numerical values of ΔEsol (AN).

[0048]

[Table 2]

As described above, what is important in the present invention is that
ΔEso of the non-aqueous solvent contained in the electrolyte in Table 2 above
Value of l (AN) and Δ of additive α contained in the battery element
This is a comparison with the value of Eadd (AN). For example, when propylene carbonate is used as the non-aqueous solvent, 2.39
The effect of the present invention is remarkably exhibited by using the additive α having ΔEadd (AN) of eV or less.

When a plurality of non-aqueous solvents are used, the amount of the non-aqueous solvent is 2 with respect to the whole non-aqueous solvent (100% by volume).
In a solvent containing 0% by volume or more, ΔEsol (A
The value of ΔEsol (AN) of the solvent with the smallest value of N),
Compare the value of ΔEadd (AN) for additive α. This is because, in the present invention, the additive α needs to accept the electron at the base point on the surface of the positive electrode active material and resonate in preference to all the solvents constituting the non-aqueous solvent. For example,
When an equal amount mixed solvent of ethylene carbonate and propylene carbonate is used as the non-aqueous solvent, the additive α
ΔEsol used to compare with the value of ΔEadd (AN)
The value of (AN) is 2.37 eV of ethylene carbonate.
Becomes Further, for example, vinylene carbonate: ethylene carbonate: propylene carbonate = 10: 4
In the non-aqueous solvent having a composition of 5:45, the value of ΔEsol (AN) used is 2.
It becomes 37 eV.

In the present invention, it is more preferable to add a high-boiling solvent to the non-aqueous solvent from the viewpoint of more effectively suppressing swelling of the case during storage at high temperature. A high-boiling solvent has a boiling point of usually 150 ° C or higher, preferably 180 ° C or higher, more preferably 200 ° C or higher, while usually 300 ° C.
Or less, preferably 270 ° C. or less, more preferably 250
It is a solvent in the range of ℃ or less. By using a solvent having a boiling point in the above range, the safety of the battery during high temperature storage can be further ensured. Examples of such a solvent include ethylene carbonate (boiling point 243 ° C.),
Examples thereof include propylene carbonate (boiling point 240 ° C.) and γ-butyrolactone (boiling point 204 ° C.).
These high boiling point solvents may be used alone or in combination of two or more, and further used in combination with a low boiling point solvent (in the present invention, one having a boiling point of 150 ° C. or lower). May be. The phrase "boiling point is X ° C" means that the vapor pressure does not exceed 1 atm even when heated from room temperature to X ° C under a pressure of 1 atm. [3] Other members of lithium secondary battery The lithium secondary battery of the present invention includes a battery element having a positive electrode, a negative electrode, and an electrolyte containing a non-aqueous solvent and a solute, and a variable shape for housing the battery element. And a sex case. [3-1] Positive Electrode / Negative Electrode [A] Positive Electrode Active Material The positive electrode of the lithium secondary battery of the present invention usually has a structure in which a positive electrode material layer is formed on a current collector, and the positive electrode material layer is formed in the positive electrode material layer. Usually, it contains a positive electrode active material capable of inserting and extracting Li.

Examples of the positive electrode active material used for the positive electrode include various inorganic compounds such as transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Here, Fe, Co, Ni, Mn or the like is used as the transition metal. Specifically, MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂
Such as transition metal oxide powder, lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide and other composite oxide powder of lithium and transition metal, transition metal sulfide such as TiS ₂ , FeS, MoS ₂ Powder and the like. These compounds may be partially element-substituted to improve their properties. In addition, polyaniline, polypyrrole, polyacene,
Disulfide compound, polysulfide compound, N-
Organic compounds such as fluoropyridinium salts can also be used. You may mix and use these inorganic compounds and organic compounds. The particle size of these positive electrode active materials is usually 1 to 3.
The thickness is 0 μm, preferably 1 to 10 μm. If the particle size is too large or too small, battery characteristics such as rate characteristics and cycle characteristics tend to deteriorate.

Among the above positive electrode active materials, from the viewpoint of obtaining a high-performance lithium secondary battery, the positive electrode active material is a lithium transition metal composite oxide such as lithium cobalt composite oxide, lithium nickel composite oxide or lithium manganese composite oxide. It is preferably an oxide. In the present invention, it is particularly preferable that the positive electrode active material contains a lithium nickel composite oxide. The lithium nickel composite oxide has a large current capacity per unit weight, and the battery using this can increase the capacity, while the lithium secondary battery easily swells during high temperature storage. By controlling the relationship with the additive α, the effect of the present invention becomes remarkable.

The lithium-nickel composite oxide is an oxide containing at least lithium and nickel. Examples of the lithium nickel composite oxide include α-Na
A lithium nickel composite oxide such as LiNiO ₂ having a layered structure such as FeO ₂ structure is preferable. Specific examples of the composition include LiNiO ₂ and LiNi ₂ O ₄ . In this case, the lithium-nickel composite oxide may be one in which some of the sites occupied by Ni are replaced with an element other than Ni. By substituting a part of the Ni site with another element, the stability of the crystal structure can be improved, and a part of the Ni element moves repeatedly to the Li site during repeated charge / discharge, resulting in a capacity decrease. Since it is suppressed, the cycle characteristics are also improved. Furthermore, by substituting a part of the Ni site with an element other than Ni,
DSC (Differential Scanning)
Calorimetry (differential scanning calorimetry) shifts the heat generation start temperature to the high temperature side, so the thermal runaway reaction of the lithium nickel composite oxide is suppressed when the battery temperature rises, resulting in improved safety during high temperature storage. Leads to.

When substituting a part of the site occupied by Ni with an element other than Ni, the element (hereinafter referred to as a substituting element) is, for example, Al, Ti, V, Cr, Mn,
Fe, Co, Li, Cu, Zn, Mg, Ga, Zr and the like can be mentioned. Of course, the Ni site may be substituted with two or more kinds of other elements. Preferably Al, Cr, Fe, C
O, Li, Mg, Ga and Mn are mentioned, and more preferably Al and Co are mentioned. Part of Ni element is Co, A
Substitution with l enhances the effect of improving cycle characteristics and safety.

When substituting the Ni site with a substituting element, the ratio is usually 2.5 mol% or more of the Ni element, preferably 5 mol% or more, and usually 50 mol% of the Ni element.
It is preferably 30 mol% or less. If the replacement ratio is too small, the effect of improving cycle characteristics may not be sufficient, and if the replacement ratio is too large, the capacity of the battery may decrease.

The above composition may have a small amount of oxygen deficiency and nonstoichiometry. Further, part of the oxygen site may be replaced with sulfur or a halogen element. In the present invention, the lithium-nickel composite oxide has an unsubstituted or Ni site of Co represented by the following general formula (3).
And a compound substituted with Al is preferable.

[0058]

Embedded image Li _a Ni _X Co _Y Al _Z O ₂ (3) In the general formula (3), a is a number that changes depending on the charging and discharging conditions in the battery, and is usually 0 or more, preferably 0.3. that's all,
On the other hand, the number is usually in the range of 1.1 or less. Also, X is
Usually 0.5 or more, preferably 0.7 or more, while usually 1
Hereafter, the number is preferably in the range of 0.9 or less. Y is
Usually 0 or more, preferably 0.1 or more, while usually 0.5
Hereafter, the number is preferably in the range of 0.3 or less. If Y is more than this range, the capacity is lowered, while if it is less than this range, the effect becomes insufficient. Z is a number in the range of usually 0 or more, and usually 0.1 or less, preferably 0.05 or less. If it exceeds this range, the capacity will decrease,
If it is below this range, the effect becomes insufficient. The above X, Y, and Z satisfy the relationship of 0.9 ≦ X + Y + Z ≦ 1.1, but are usually 1.0. In the composition represented by the general formula (3), by substituting a part of the Ni site with Co, the effect of improving the cycle characteristics and safety becomes large as described above. By substituting Al with Al, further improvement in cycle characteristics and safety is achieved.

The specific surface area of the lithium nickel composite oxide used in the present invention is usually 0.01 m ² / g or more, preferably 0.1 m ² / g or more, more preferably 0.5 m ² / g or more, and Usually 10 m ² / g or less, preferably 5 m ²
/ G or less, more preferably 2 m ² / g or less. If the specific surface area is too small, rate characteristics and capacity are deteriorated, and if it is too large, an undesired reaction with the electrolytic solution or the like is caused, and cycle characteristics may be deteriorated. The specific surface area is measured according to the BET method.

The average secondary particle diameter of the lithium nickel composite oxide used in the present invention is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more,
Most preferably 0.5 μm or more, usually 300 μm
Or less, preferably 100 μm or less, more preferably 5
It is 0 μm or less, and most preferably 20 μm or less. If the average secondary particle size is too small, the cycle deterioration of the battery may become large, or a safety problem may occur.

As the positive electrode active material, the lithium nickel composite oxide may be used alone, or may be used in combination with another lithium transition metal composite oxide. An example of such a lithium transition metal composite oxide is a lithium cobalt composite oxide. The lithium-cobalt composite oxide is an oxide containing at least lithium and cobalt. The lithium-cobalt composite oxide is a useful positive electrode material having excellent rate characteristics because the discharge curve is flat. Examples of the lithium-cobalt composite oxide include LiCoO ₂ having a layered structure.
The lithium-cobalt composite oxide may be one in which some of the sites occupied by Co are replaced with an element other than Co. By substituting the Co site with another element, the cycle characteristics and rate characteristics of the battery may be improved. C
When substituting part of the site occupied by o with an element other than Co, the substituting elements are Al, Ti, V, Cr, Mn,
Fe, Li, Ni, Cu, Zn, Mg, Ga, Zr, S
n, Sb, Ge, and the like, and preferably Al, Cr,
Fe, Li, Ni, Mg, Ga, Zr, Sn, Sb, G
e More preferably, Al, Mg, Zr, and Sn. The Co site may be substituted with two or more other elements.

When substituting the Co site with the substituting element, the ratio is usually 0.03 mol% or more, preferably 0.05 mol% or more of the Co element, and usually 3 Co of the Co element.
It is 0 mol% or less, preferably 20 mol% or less. If the substitution ratio is too small, the stability of the crystal structure may not be sufficiently improved, and if it is too large, the capacity of the battery may decrease.

The lithium-cobalt composite oxide is usually represented by LiCoO ₂ as a basic composition before charging,
As described above, part of the Co site may be replaced with another element. In the above composition formula, a small amount of oxygen deficiency,
It may have indefiniteness, and a part of the oxygen site may be replaced with sulfur or a halogen element. Furthermore, in the above composition formula, the amount of lithium can be made excessive or insufficient.

[0064] The specific surface area of the lithium cobalt composite oxide is usually 0.01 m ² / g or more, preferably 0.1 m ² /
g or more, more preferably 0.4 m ² / g or more, and usually 10 m ² / g or less, preferably 5 m ² / g or less, more preferably 2 m ² / g or less. If the specific surface area is too small, rate characteristics and capacity are deteriorated, and if it is too large, an undesired reaction with the electrolytic solution or the like is caused, and cycle characteristics may be deteriorated. The specific surface area is measured by BE
Follow T method.

The average secondary particle diameter of the lithium-cobalt composite oxide is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more, most preferably 0.5 μm or more, and usually 300 μm or less. , Preferably 100 μm or less, more preferably 50 μm or less, most preferably 20 μm or less. If the average secondary particle size is too small, the cycle deterioration of the battery may become large, or safety problems may occur. If it is too large, the internal resistance of the battery may become large, and it may be difficult to output power. [B] Organic acid and / or lithium salt of organic acid In the present invention, the positive electrode preferably contains an organic acid and / or a lithium salt of an organic acid. The positive electrode contains an organic acid and / or a lithium salt of an organic acid, and the additive α
By including the above in the battery element, it becomes possible to more effectively suppress the rise of the internal pressure of the case during high temperature storage.

The above-mentioned organic acid is not particularly limited, and examples thereof include acetic acid, propionic acid, stearic acid, glyoxylic acid, pyruvic acid, acetoacetic acid, levulinic acid, phenylacetic acid, benzoylpropionic acid, benzoic acid and oxalic acid. , Malonic acid, succinic acid, glutaric acid, adipic acid,
Examples thereof include maleic acid, phthalic acid, trimellitic acid, polyacrylic acid, polymethacrylic acid, tricarballylic acid and benzenetricarboxylic acid. Further, the lithium salt of an organic acid is not particularly limited, and examples thereof include lithium salts of the above organic acids.

Among the above organic acids, divalent or higher valent organic acids are preferable. By having a valence of 2 or more, the rise of the internal pressure of the case can be effectively suppressed. Examples of the divalent or higher valent organic acid include a divalent organic acid and a trivalent organic acid. As the divalent organic acid,
For example, aliphatic saturated dicarboxylic acid, aliphatic unsaturated dicarboxylic acid, aromatic dicarboxylic acid, etc. can be mentioned.
Specific examples of the aliphatic saturated dicarboxylic acid compound include oxalic acid, malonic acid, succinic acid, and glutaric acid. Specific examples of the aliphatic unsaturated dicarboxylic acid compound include maleic acid. Specific examples of the aromatic dicarboxylic acid compound include phthalic acid and the like. Examples of the trivalent organic acid include tricarballylic acid and benzenetricarboxylic acid.

The lithium salt of the above organic acid is also preferably a lithium salt of a divalent or higher valent organic acid.
The lithium salt of the above divalent or trivalent organic acid can be mentioned. The organic acid used in the present invention includes oxalic acid,
It is preferable to use succinic acid, and it is more preferable to use oxalic acid. These organic acids have a small molecular size and have a large effect of suppressing an increase in internal pressure. As the lithium salt of an organic acid, it is preferable to use the lithium salt of oxalic acid or succinic acid, and more preferable to use the lithium salt of oxalic acid, for the same reason as the above organic acid. By using the organic acid and / or the lithium salt of the organic acid in combination with the additive α, it becomes possible to more effectively suppress the increase in the internal pressure of the case during high temperature storage.

The organic acid and / or the lithium salt of the organic acid used in the present invention is usually 0. 1 part by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, usually 1 part by weight or less, preferably 0.8 parts by weight or less, more preferably 0.6 parts by weight or less. It If the amount added is less than this range, the increase in internal pressure of the case during high temperature storage may be insufficiently suppressed. On the other hand, if the amount added exceeds this range, the surface of the positive electrode active material will be covered with an excessive lithium ion impermeable coating, which may adversely affect the charge / discharge characteristics of the battery.

Further, the organic acid and / or
Alternatively, the content of the lithium salt of the organic acid is the additive α: 100.
It is usually 1 part by weight or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more with respect to parts by weight, while
It is usually 150 parts by weight or less, 130 parts by weight or less, and more preferably 120 parts by weight or less. Inclusion of the additive α in the battery element has a greater effect of suppressing an increase in internal pressure of the case during high-temperature storage than inclusion of an organic acid and / or a lithium salt of an organic acid in the positive electrode. However, in the case where the content of the additive α in the battery element is limited from the viewpoint of battery characteristics and the like, if the organic acid and / or the lithium salt of the organic acid is contained in the positive electrode within the above range, Therefore, it becomes possible to effectively suppress the pressure rise inside the case during high temperature storage while maintaining the battery characteristics.

A method for allowing the above organic acid and / or the lithium salt of the organic acid to be present in the positive electrode will be described below. As such a method, for example, an organic acid and / or a lithium salt of an organic acid is dissolved in a suitable solvent, the positive electrode active material is moistened with this solution, and then the solvent is removed. The contained positive electrode active material can be obtained, and if the positive electrode active material is contained in the positive electrode, as a result, the organic acid or the like can be present in the positive electrode.

When a positive electrode-producing coating material in which a material constituting the positive electrode is contained in a solvent is used and the positive electrode is produced by applying the coating material to a current collector and drying, the organic solvent is added to the positive electrode-producing coating material. When the lithium salt of an acid and / or an organic acid is contained, as a result, the above organic acid or the like can be present in the positive electrode. The method for incorporating the organic acid or the like into the coating material for producing a positive electrode includes, for example, dissolving the organic acid and / or the lithium salt of the organic acid in a solvent used for the coating material (for example, N-methylpyrrolidone), and then adding the solution to the solution. There may be mentioned a method of passing through the step of wetting the positive electrode active material, and then passing through the step of incorporating the remaining material constituting the positive electrode into a coating material. This method is preferable because the solvent used in the wetting step and the solvent used in the coating step are common, and there is no need to remove the solvent after the wetting step, which improves the production efficiency. As a method for further improving the production efficiency, a method in which a lithium salt of an organic acid and / or an organic acid and another material constituting the positive electrode are put into a solvent at one time and mixed to form a coating material for a positive electrode manufacturing coating material is used. Can be mentioned. In the above charging, the organic acid and / or the lithium salt of the organic acid may be directly charged into the solvent, but the organic acid and / or the lithium salt of the organic acid may be previously dissolved in the solvent used for the positive electrode manufacturing coating material. Then, this solution may be added. When the organic acid and / or the lithium salt of the organic acid is in a solid state, the latter method is effective.

Incidentally, Japanese Patent Laid-Open No. 2001-35495 describes an organic acid similar to the organic acid used in the present invention. However, this document describes that ΔEsol (AN), a non-aqueous solvent contained in the electrolyte, and ΔEadd, the additive α.
There is no description or suggestion that the increase in the internal pressure of the case of the lithium secondary battery during storage at high temperature is suppressed by setting (AN) in a predetermined relationship. [C] Negative Electrode Active Material The negative electrode used in the lithium secondary battery of the present invention is usually
A negative electrode material layer is formed on a current collector, and the negative electrode material layer usually contains a negative electrode active material capable of inserting and extracting Li.

Examples of the negative electrode active material include carbon-based active materials. Examples of the carbon-based active material include graphite, coal-based coke, petroleum-based coke, carbide of coal-based pitch, carbide of petroleum-based pitch, or carbide of these pitches subjected to oxidation treatment, needle coke, pitch coke, phenol resin. , And carbonized materials such as crystalline cellulose, and carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fiber, and the like can be used. Also, these carbon-based active materials can be used in the form of a mixture with a metal, a salt thereof, an oxide, or a coating. In addition to the above carbon-based active material, negative electrode active materials include oxides of silicon, tin, zinc, manganese, iron, nickel, etc., or sulfates, and also metallic lithium, Li-Al, Li-Bi-Cd, Li. A lithium alloy such as —Sn—Cd, a lithium transition metal nitride, a metal such as silicon or tin, and the like can also be used. The particle size of these negative electrode active materials is usually 1 to 50 μm, preferably 5 to 30 μm. If it is too large or too small, the battery characteristics such as initial efficiency, rate characteristics and cycle characteristics tend to deteriorate. Of course, two or more kinds of negative electrode active materials selected from the above may be used in combination. [D] Other Materials Contained in Positive Electrode and Negative Electrode In the positive electrode material layer and the negative electrode material layer, the positive electrode active material and the negative electrode active material (in the present specification, the positive electrode active material and the negative electrode active material are collectively activated). In some cases, a binder may be contained in addition to the substance. The content of the binder relative to 100 parts by weight of the active material is usually 0.01 parts by weight or more, preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, usually 50 parts by weight or less, preferably 30 parts by weight or less,
It is more preferably 15 parts by weight or less. If the amount of the binder is too small, it is difficult to form a strong positive electrode. If the amount of the binder is too large, the energy density and cycle characteristics may deteriorate.

Examples of the binder include alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, polyvinylpyridine and poly-N. -A polymer having a ring such as vinylpyrrolidone; an acrylic derivative system such as polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polymethylacrylate, ethylpolyacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide. Polymers; Fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile, polyvinylidene cyanide; polyvinyl acetate, polyvinyl Polyvinyl alcohol polymers, such as alcohol; polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride; various resins such as a conductive polymer such as polyaniline can be used. Also, a mixture of the above polymers, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer and the like can be used. It is also possible to use an inorganic compound such as silicate or glass. In the present invention, it is preferable to use a fluororesin such as polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene or the like.

The weight average molecular weight of the binder is usually 10
00 or more, preferably 10000 or more, more preferably 20000 or more, usually 5,000,000 or less, preferably 1,000,000 or less, more preferably 300.
It is 000 or less. If it is too low, the mechanical strength of the electrode may decrease. If it is too high, the viscosity of the coating material becomes high when the positive electrode (or the negative electrode) is manufactured by applying the positive electrode manufacturing coating material (or the negative electrode manufacturing coating material) to the current collector, and the positive electrode material layer (or the negative electrode material layer). ) May be difficult to form.

If necessary, the positive electrode material layer and the negative electrode material layer may contain an additive such as a conductive material and a reinforcing material exhibiting various functions, a powder, a filler and the like. The conductive material is not particularly limited as long as it can impart conductivity by mixing an appropriate amount with the active material, but is usually carbon powder such as acetylene black, carbon black, graphite, various metal fibers, foil, etc. Is mentioned. As the reinforcing material, various inorganic or organic spherical or fibrous fillers can be used.

As the material of the current collector used for the positive electrode and the negative electrode, usually, metals such as aluminum, copper, nickel, tin, stainless steel, alloys of these metals and the like can be used. In this case, aluminum is usually used as the current collector of the positive electrode, and copper is usually used as the current collector of the negative electrode. The shape of the current collector is not particularly limited, and examples thereof include a plate shape and a mesh shape. The thickness of the current collector is usually 1 to 50 μm, preferably 1 to 30 μm. If it is too thin, the mechanical strength will be weak, but if it is too thick, the battery will be large and the space occupied in the battery will be large, and the energy density of the battery will be low.

The thickness of each of the positive electrode and the negative electrode is usually 1 μm.
m or more, preferably 10 μm or more, and usually 500
It is not more than μm, preferably not more than 200 μm. If it is too thick or thin, battery performance such as capacity and rate characteristics tends to decrease. The method for producing the positive electrode (or the negative electrode) is not particularly limited, and, for example, a positive electrode (or a negative electrode) in which a solvent (for example, N-methylpyrrolidone) contains an active material and a binder, a conductive material, or the like used as necessary. It can be manufactured by applying a manufacturing coating material to a current collector and drying. Alternatively, for example, it can be produced by kneading an active material and a binder, a conductive material, or the like used as necessary without using a solvent, and then pressure-bonding to a current collector. In the present invention, the positive electrode is preferably produced by the former method using a coating material for producing a positive electrode. If the former method is adopted, the organic acid and / or the lithium salt of the organic acid tends to be uniformly present in the positive electrode. The method of allowing the organic acid and / or the lithium salt of the organic acid to be present in the positive electrode is as described above. [3-2] Electrolyte The electrolyte contains a non-aqueous electrolytic solution containing a non-aqueous solvent and a solute. The non-aqueous solvent is as described in [2].

As the solute, any conventionally known lithium salt can be used. For example, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , C
_{H 3 SO 3 Li, CF 3} SO 3 Li, LiN (SO 2 CF 3)
₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ ,
Examples include LiSbF ₆ and LiSCN, and at least one of them can be used. Among these, from the viewpoint that the effect of the present invention becomes remarkable, Li
ClO ₄ and LiPF ₆ are particularly preferable. The content of these solutes in the non-aqueous electrolyte is usually 0.5 to 2.5 mol /
It is l.

In addition to the solute and the non-aqueous solvent, the non-aqueous electrolytic solution may further contain additives for ensuring safety and battery characteristics (eg cycle characteristics). In the present invention, the electrolyte is not only a non-aqueous solvent and solute,
It is preferable to contain a polymer. By containing the polymer, the electrolyte becomes non-fluid, the liquid retaining property is improved, and the liquid leakage can be prevented, so that the safety during high temperature storage is further improved. On the other hand, the polymer contained in the electrolyte may be peeled off from the electrode surface due to an increase in the internal pressure of the case when the lithium secondary battery is stored at a high temperature. This exfoliation of the polymer will greatly increase the internal resistance of the battery. Therefore, when the polymer is contained in the electrolyte, it becomes particularly necessary to suppress the internal pressure increase in the case during high temperature storage due to the addition of the additive α to the battery element.

The polymer contained in the electrolyte is not particularly limited as long as it can secure the liquid retaining property of the electrolyte to some extent, and for example, an acrylic polymer such as polymethylmethacrylate or an alkylene oxide unit is used. Examples thereof include alkylene oxide-based polymers, fluorine-based polymers such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer. Among these polymers, from the viewpoint of sufficiently securing the liquid retaining property of the electrolyte, it has a bond (crosslinking bond) formed so as to bridge between any two atoms of a molecule composed of chain-bonded atoms. It is preferable to use a polymer (herein, referred to as “crosslinkable polymer”).

Examples of the material forming the basic skeleton of the crosslinkable polymer include those produced by polycondensation of polyester, polyamide, polycarbonate, polyimide and the like, those produced by polyaddition such as polyurethane and polyurea, and polymethacryl. Examples thereof include those produced by addition polymerization of acrylic polymers such as methyl acidate and polyvinyl polymers such as polyvinyl acetate and polyvinyl chloride.

In the present invention, since it is preferable to impregnate a spacer (details will be described later) and then polymerize, a polymer produced by addition polymerization in which the control of the polymerization is easy and a by-product is not generated during the polymerization. It is desirable to use. Examples of such polymers include acrylic polymers. Acrylic polymers are preferable materials in terms of battery characteristics such as battery capacity, rate characteristics, and mechanical strength.

As the acrylic polymer, a polymer obtained by polymerizing a monomer having an acryloyl group is particularly preferable. Examples of the monomer having an acryloyl group include methyl acrylate, ethyl acrylate,
Butyl acrylate, acrylamide, 2-ethoxyethyl acrylate, diethylene glycol ethyl ether acrylate, polyethylene glycol alkyl ether acrylate, polypropylene glycol alkyl ether acrylate, 2-cyanoethyl acrylate and other monoacrylates; 1,2-butanediol diacrylate, 1,3 -Butanediol diacrylate,
Alkanediol diacrylates such as 1,4-butanediol diacrylate, neopentanediol diacrylate and 1,6-hexanediol diacrylate; ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate Polyethylene glycol diacrylates such as acrylates; polypropylene glycol diacrylates such as propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, tetrapropylene glycol diacrylate; bisphenol F ethoxylate diacrylate, bisphenol F ethoxylate Dimethacrylate, bisphenol A ethoxy Diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, isocyanuric acid ethoxylate triacrylate, glycerol ethoxylate triacrylate, glycerol propoxylate triacrylate, pentaerythritol ethoxylate tetra Examples thereof include acrylate, ditrimethylolpropane ethoxylate tetraacrylate, and dipentaerythritol ethoxylate hexaacrylate.

Among these, polyacrylate polymers having an ethylene glycol unit are particularly preferable from the viewpoint of lithium ion conductivity. In the present invention, a copolymer of the above monomer component and another monomer component can be used as the acrylic polymer. That is, as the monomer component, a monomer having a different structure may be coexisted and polymerized in addition to the above monomers. In particular, coexistence of a monomer having a group having an unsaturated double bond such as a methacryloyl group, a vinyl group or an allyl group may improve the strength and liquid retention of the electrolyte. As such a monomer, compounds such as methyl methacrylate, methacrylamide, butadiene, acrylonitrile, styrene, vinyl acetate and vinyl chloride can be used.

When an acrylic polymer is used, the abundance of the acryloyl group-containing monomer is not particularly limited, but is usually 50% by weight or more, preferably 70% by weight or more, particularly preferably 80% by weight or more. Is. A higher abundance ratio is advantageous in that the polymerization rate is faster and the productivity of the electrolyte can be increased. The crosslinkable polymer has crosslinks. The cross-linking can be produced by causing a cross-linking reaction between polymers with a cross-linking agent. Further, it can be produced by using a monomer having a plurality of reaction points (hereinafter, may be referred to as a “polyfunctional monomer”) as a raw material of the polymer. The latter method is preferred.

When the crosslinkable polymer is produced by the latter method, a monomer having one reaction point (hereinafter sometimes referred to as "monofunctional monomer") can be used as a raw material in addition to the polyfunctional monomer. .. When the polyfunctional monomer and the monofunctional monomer are used in combination, the equivalent ratio of the functional groups of the polyfunctional monomer is usually 10% or more, preferably 15% or more, more preferably 20% or more.

The most preferable method for producing a crosslinkable polymer is a method in which a polyfunctional monomer having a plurality of acryloyl groups is polymerized with a monofunctional monomer having one acryloyl group, if necessary. The polymer content in the electrolyte is usually 80 based on the total weight of the electrolyte.
It is not more than 50% by weight, preferably not more than 50% by weight, more preferably not more than 20% by weight. If the polymer content is too large, the concentration of the non-aqueous electrolytic solution is lowered, so that the ionic conductivity is lowered and the battery characteristics such as rate characteristics tend to be lowered. on the other hand,
When the proportion of the polymer is too low, not only may gel formation be difficult and retention of the non-aqueous solvent may be reduced to cause fluidization and liquid leakage, and battery safety may not be ensured. The content of the polymer in the electrolyte is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, and most preferably 5% by weight or more.

The ratio of the polymer to the non-aqueous solvent is appropriately selected according to the molecular weight of the polymer, but is usually 0.1.
% By weight or more, preferably 1% by weight or more, usually 50% by weight
It is preferably 30% by weight or less. If the proportion of the polymer is too low, gel formation becomes difficult and the retention of the non-aqueous electrolytic solution tends to be low, causing problems of fluidization and liquid leakage. If the proportion of the polymer is too high, the viscosity becomes too high, which makes handling difficult, and the concentration of the non-aqueous electrolytic solution tends to lower the ionic conductivity, which tends to lower the battery characteristics such as rate characteristics.

In the present invention, a method is used in which the polymer is formed by filling the voids of the spacer (details will be described later) in the state where the electrolyte contains the monomer as the raw material of the polymer, and then polymerizing the monomer. Is preferred. As a method for polymerizing these monomers, for example, a method using heat, ultraviolet rays, electron beams and the like can be mentioned, but in the present invention, the monomers can be polymerized by heating or ultraviolet irradiation from the viewpoint of ease of production. preferable. In the case of polymerization by heat, a polymerization initiator which reacts with heat may be added to the electrolyte to be impregnated in order to effectively proceed the reaction. The usable thermal polymerization initiators are azobisisobutyronitrile, 2,2 '
-Azo compounds such as dimethyl azobisinbutyrate, benzoyl peroxide, cumene hydroperoxide, peroxides such as t-butylperoxy-2-ethylhexanoate, etc. can be used. From the viewpoint of reactivity, polarity, safety, etc. Preferable ones may be used alone or in combination. still,
In order to obtain a polymer, of all the functional groups of the monomer,
Usually, 30% or more is reacted, preferably 40% or more, more preferably 50% or more.

The electrolyte is preferably impregnated into the positive electrode, the negative electrode, and a spacer that may be disposed between the positive electrode and the negative electrode in order to improve the ionic conductivity due to lithium ions. The spacer is usually used to prevent a short circuit between the positive electrode and the negative electrode. The spacer usually consists of a porous membrane. Examples of the material used as the spacer include polyolefins such as polyethylene and polypropylene, and polyolefins in which some or all of hydrogen atoms of these are substituted with fluorine atoms, polyacrylonitrile, and porous films of resins such as polyaramid. Can be mentioned. From the viewpoint of chemical stability with respect to the electrolyte, stability with respect to the applied voltage, preferably polyolefin or,
It is a fluorine-substituted polyolefin, and specifically,
Examples thereof include polyethylene and polypropylene, and those in which some or all of these hydrogen atoms are replaced with fluorine atoms. Of these, polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride are particularly preferable, and polyolefins such as polyethylene and polypropylene are most preferable. Of course, these copolymers and mixtures can also be used.

The number average molecular weight of the resin used as the material for the spacer is usually 10,000 or more, preferably 100,000 or more, and usually 10 million or less, preferably 3 million or less. If the molecular weight is too small, the mechanical strength will be insufficient and the electrodes will tend to short circuit. When the molecular weight is too large, impregnation of the electrolyte into the voids of the porous membrane tends to be difficult, which tends to reduce the production efficiency of the battery and also the battery performance such as rate characteristics. Further, if the molecular weight is too large, film formation may be difficult in the method of mixing a plasticizer described below and then stretching.

As mentioned above, the spacer is usually a porous film. As the porous film, for example, a porous stretched film,
Nonwoven fabrics and the like can be mentioned, but in the present invention, a stretched film produced by stretching is more preferable. Since the porous stretched film has more uniform resistance in the film than the nonwoven fabric, it is possible to suppress local deposition of lithium, that is, dendrite that causes a short circuit between electrodes.

The stretching of the porous stretched film may be either uniaxial or biaxial stretching, but it is preferable to use biaxial stretching. If the film is biaxially stretched, the mechanical strength in the longitudinal and lateral directions of the film is well balanced, and therefore the handling in battery production becomes easy. The porosity of the spacer is usually 30% or more, preferably 35% or more, usually 80% or less, preferably 75% or less, more preferably 72% or less. If the porosity is too small, the film resistance increases and the rate characteristics deteriorate. In particular, the capacity decreases when used at a high rate. On the other hand, if the porosity is too large, the mechanical strength of the film decreases,
A short circuit is likely to occur when the shape of the battery element changes.
In the present invention, the larger the porosity, the greater the effect of the electrolyte retaining property due to the use of the crosslinkable polymer, and therefore the higher the safety at high temperature storage becomes.

The average pore diameter of the pores present in the spacer is usually 0.2 μm or less, preferably 0.18 μm or less, more preferably 0.15 μm or less, and usually 0.01
It is at least μm, preferably at least 0.07 μm. If the pore size is too large, a short circuit is likely to occur, while if the pore size is too small, the membrane resistance tends to increase, and battery performance such as rate characteristics tends to deteriorate. In the present invention, the larger the average pore size is, the greater the effect of the electrolyte retaining property due to the use of the crosslinkable polymer is, and the higher the safety at high temperature storage is.

The film thickness of the spacer is usually 5 μm or more, preferably 7 μm or more, usually 50 μm or less, preferably 28 μm or less, more preferably 25 μm or less,
Most preferably, it is 20 μm or less. If the film thickness is too small, self-discharge due to the mild short-circuit phenomenon tends to occur. If the film thickness is too large, not only the battery characteristics such as rate characteristics become insufficient, but also the volume energy density tends to decrease. In the present invention, the self-discharge is effectively prevented by using the crosslinkable polymer when the spacer has a small film thickness.

The spacer usually has a withstand voltage of 0.3 kV or more, preferably 0.5 kV or more. Here, "Xk
“Having a withstand voltage of V” means that when a voltage of XkV or more is applied across the spacer, a current of 100 mA or more does not flow between the electrodes. If the withstand voltage is too low, if the resistance partially increases during charging of the battery for some reason, the temperature may rise abnormally as a result. Also,
It tends to be difficult to effectively prevent self-discharge. Withstand voltage is usually 1000k for practical use.
V or less, preferably 100 kV or less, more preferably 10 kV or less.

In order to prevent the short circuit more effectively, the pin piercing strength when the spacer is locally pressed is usually 2
The amount is 00 gf or more, preferably 230 gf or more, and more preferably 300 gf or more. However, it is not practical to have too much pin piercing strength, so 20
It is not more than 00 gf, preferably not more than 1500 gf, more preferably not more than 1000 gf.

In addition, the spacer is fixed in a fixed direction of 0.1 kg /
It is preferable to use a spacer that causes a strain of 1% or less when pulled by a force of cm. As a result, it is possible to further effectively prevent a short circuit, and it is easy to maintain the spacer positional accuracy and the like during the spacer transporting step and the stacking step in battery manufacturing, and it is possible to improve the yield.
However, it is practically difficult to obtain a material having such a small strain, so the content is usually 0.01% or more, preferably 0.1% or more.

The thermal shrinkage of the spacer at 100 ° C. is
It is usually 10% or less, preferably 9 in one direction.
% Or less, and more preferably 7% or less. Here, the "heat shrinkage rate in one direction" means, for example, in a stretched film, the heat shrinkage rate in the stretching direction and in the direction perpendicular thereto. If the heat shrinkage rate is too large, a short circuit at the end of the electrode is more likely to occur due to heating during battery production, storage in a high temperature environment, or the like. When a biaxially stretched film is used as the stretched film, it is preferable that the heat shrinkage rates in both stretching directions are close to each other in view of easiness in design and manufacturing. In this case, the difference in thermal shrinkage between the two stretching directions is usually within 7%, but 5%.
It is preferably within the range, and more preferably within 4.5%.

The surface tension of the spacer is usually 40d.
It is yne / cm 2 or more, preferably 46 dyne / cm or more, and particularly preferably 48 dyne / cm 2 or more.
As a result, it becomes easy to sufficiently impregnate the voids in the porous membrane with the electrolyte, and it is possible to improve productivity and rate characteristics. In order to obtain a film having such a surface tension, usually, the spacer, corona discharge treatment,
Surface modification treatment such as plasma treatment or fluorine gas treatment is preferably performed. However, since it is difficult to obtain a film having a too large surface tension, the surface tension is usually 60 dyne / cm or less, preferably 58 dyne / cm or less.

The spacer can be manufactured, for example, as follows. A resin having a number average molecular weight of about 10,000 to 10,000,000, preferably 100,000 to 3,000,000 is mixed with a plasticizer as a heterogeneous dispersion medium, and the mixture is kneaded and then formed into a sheet. Further, a desired spacer can be obtained by further performing a step of extracting the plasticizer with a solvent and a step of stretching the plasticizer in a longitudinal direction or a lateral direction or both at a predetermined ratio. [3-3] Battery Element and Case that Stores Battery Element The lithium secondary battery of the present invention has the battery element housed in a case. The battery element is usually formed on the basis of a unit battery element composed of a positive electrode and a negative electrode containing an active material as a main component, and an electrolyte, and the unit battery element is formed in a long length and wound, It is formed by stacking a plurality of the unit battery elements formed in a flat plate shape. That is,
Examples of the form of the battery element include, for example, a flat plate laminated type in which a plurality of flat plate-shaped unit battery elements are laminated, a flat plate-shaped wound type in which a long unit battery element is wound into a flat plate shape, and further A cylindrical winding type in which a long unit battery element is wound into a cylindrical shape can be used. In the present invention, from the viewpoint of productivity and miniaturization, the form of the battery element is preferably a flat plate wound type or a flat plate laminated type. In the case of a flat-plate wound type or flat-plate laminated type battery element, the case for accommodating the flat-plate type battery element also has a flat-plate shape. The effect of using α is particularly great.

When the battery element takes the form of a flat plate winding type, the number of windings of the unit battery element is usually 2 or more, preferably 3 or more, more preferably 4 or more, usually 20 or less,
It is preferably 15 or less, more preferably 10 or less.
When the number of windings is small, the capacity of the battery as a whole is small, while when the number of windings is too large, it is disadvantageous in terms of downsizing of the battery.

When the battery element has a flat plate type,
The number of laminated unit battery elements is usually 5 or more, preferably 8
The number of layers is 10 or more, more preferably 10 or more, usually 50 or less, preferably 30 or less, more preferably 25 or less. When the number of laminated layers is small, the capacity of the battery as a whole is small, while when the number of laminated layers is too large, it is disadvantageous in terms of downsizing of the battery.

Hereinafter, the specific shape of the lithium secondary battery of the present invention will be described with reference to the drawings by taking as an example a lithium secondary battery in which flat plate type battery elements are hermetically enclosed in a shape-variable case. However, it goes without saying that these are merely examples and the present invention is not limited to these modes. FIG. 1 is an exploded perspective view of a battery according to an embodiment of the present invention, FIG. 2 is a sectional view of a main part of the battery, FIG. 3 is a schematic perspective view of a battery element, and FIG. 4 is a perspective view of the battery. It is a figure.

In this battery, after the battery element 1 is housed in the recess of the exterior material 3, the terminal portions (tabs 4a, 4b) of the battery element 1 are placed.
An insulating material 5 such as an epoxy resin or an acrylic resin is injected in the vicinity, the exterior material 2 is then covered on the exterior material 3, and the peripheral edges 2a, 3a of the exterior materials 2, 3 are joined by vacuum sealing. As shown in FIG. 1, the exterior material 2 has a flat plate shape. The exterior material 3 is a housing portion 3b having a rectangular box-shaped recess, and the housing portion 3b.
And a peripheral edge portion 3a protruding outward from the four peripheral edges in a flange shape.

As shown in FIG. 3, the battery element 1 is formed by stacking a plurality of unit battery elements in the thickness direction. The tab 4a or 4b is pulled out from this unit battery element. The tabs 4a from the positive electrode are bundled (that is, superposed on each other), and the positive electrode lead 21 is joined to form a positive electrode terminal portion. The tabs 4b from the negative electrode are also bundled, and the negative electrode lead 21 is joined to form the negative electrode terminal portion.

The battery element 1 is accommodated in the accommodating portion 3b of the exterior material 3, and the insulating material 5 is injected near the tabs 4a and 4b.
After the side surfaces of the battery element near the positive electrode terminal portion and the negative electrode terminal portion are covered with an insulating material, the exterior material 2 is covered. Battery element 1
The pair of leads 21 extending from the
3 is drawn out to the outside through the mating surfaces of the peripheral portions 2a and 3a of one side portion of 3. Then depressurize (preferably vacuum)
Under the atmosphere, the four peripheral edges 2a, 3a of the outer casings 2, 3 are airtightly joined together by a method such as thermocompression bonding or ultrasonic welding, and the battery element 1 is enclosed in the outer casings 2, 3. After that, the insulating material 5 is subjected to a curing treatment by heating or the like, and the insulating material 5 is completely fixed in the vicinity of the terminal portion. Since the exterior material is sealed before completely fixed, the shape of the battery hardly changes when fixed. Terminal part (tab 4a,
4b) When the insulating material 5 is filled in the vicinity, even if the internal pressure rises during high temperature storage, peeling of the battery element due to the rise of the internal pressure of the outer casing (case) can be effectively prevented, and a short circuit is also effective. To be prevented.

By joining the peripheral edge portions 2a, 3a to each other, the joining piece portions 4A, 4F, 4G are formed. The joining piece portions 4A, 4F, 4G project outward from the encapsulating portion 4B enclosing the battery element 1. Therefore, the joining pieces 4A, 4F, 4G are bent along the covered portion 4B. Furthermore, a method of fastening (fixing) these joining pieces to the side surface of the covered portion 4B with an adhesive or an adhesive tape (not shown) is also suitably used. In the battery configured as described above, peeling of the battery element due to an increase in the internal pressure of the outer casing (case) during high temperature storage can be effectively prevented, and the strength and rigidity of the side surface of the battery can be improved. it can. Of course, it is also prevented that the bent joint piece part separates from the envelope part. Further, since the side surface of the battery has high strength and rigidity, peeling of the active material is prevented even when the side surface is impacted.

As the above-mentioned insulating material 5, synthetic resin is suitable, and epoxy resin, acrylic resin, silicone resin and the like are exemplified, but among them, epoxy resin or acrylic resin is preferable because the curing time is short. In particular, acrylic resin is most preferable because it is unlikely to adversely affect battery performance. The insulating material is supplied in the vicinity of the terminal portion in an uncured and fluid state, and is completely fixed by the curing in the vicinity of the terminal portion.

In FIG. 1, the insulating material is separately supplied to the positive electrode terminal portion and the negative electrode terminal portion. The entire side of the element can be coated. In FIG. 1, the exterior materials 2 and 3 are separate bodies, but in the present invention, the exterior materials 2 and 3 may be integrally formed as shown in FIG. In FIG. 5, one side of the exterior material 3 and one side of the exterior material 2 are connected to each other, and the exterior material 2 has a lid shape that is connected to the exterior material 3 in a bendable manner. The concave portion of the housing portion 3b is formed from one side where the exterior materials 2 and 3 are connected, and has the same configuration as the joining piece portion except that the joining piece portion is not formed on this one side.

In the case of FIG. 5 as well, after the battery element 1 is housed in the housing portion 3b, the insulating material is injected near the tabs 4a and 4b of the battery element 1. 1 and 5, the exterior material 3 having the accommodation portion 3b and the flat exterior material 2 are shown.
In the present invention, as shown in FIG.
The battery element 1 may be encapsulated by the exterior materials 6 and 7 having b and 7b and peripheral portions 6a and 7a protruding from the four peripheral edges of the accommodating portions 6b and 7b. In FIG. 6, the exterior materials 6 and 7 are a continuous body, but they may be separate bodies as in the case of FIG.

In the configurations shown in FIGS. 1, 5, and 6, since the battery element housing portion is formed in advance, the battery element can be housed more compactly and the housing itself is easy.
In the above description, after accommodating the battery element in the accommodating portion, the insulating material is injected in the vicinity of the terminal portion. It may adhere and flow in to hinder the bonding of the peripheral portion, or the battery shape may not be as designed. Therefore, the above problem can be avoided by housing the battery element in the housing portion after supplying the insulating material in the vicinity of the terminal portion of the battery element. In particular, in the case of FIG. 6, even if the insulating material is supplied after accommodating the battery element, the insulating material cannot be supplied to substantially the upper half of the battery element, so this manufacturing method is preferable. On the other hand, in this method, the battery element that is not easy to handle in the state where the insulating material is supplied is transported,
Since it needs to be placed on the exterior material, it must be handled with care during manufacturing. In this respect, the former method is preferable.

In the present invention, as shown in FIG. 7, one flat sheet-like exterior material 8 is folded back in two folds along the central side 8a so that the first piece 8A and the second piece 8B are separated into two pieces. The battery element 1 is formed between the first piece 8A and the second piece 8B, and the peripheral portion 8 of the first piece 8A and the second piece 8B is formed as shown in FIG.
The battery element 1 may be enclosed by joining b. Also,
It is also possible to exemplify a method in which both ends of a film-like exterior material are attached to each other to form a tubular shape, a battery element is housed inside, and then the upper and lower portions of the tube are further attached.

Also in these cases, the tabs 4a, 4 of the battery element 1 are
Before or after the insulating material is attached to the vicinity of b, the first piece 8A and the second piece 8B of the exterior material 8 are overlapped with each other to encapsulate the battery element 1. Further, it is preferable that the joining piece portion is bent and fastened along the envelope portion. In coating the side surface of the battery element in the vicinity of the terminal portion, it is particularly preferable to provide a spacer larger than these between the positive electrode and the negative electrode and fix the protruding portions of the spacers to each other.

That is, in the battery element, for example, as shown in FIG.
As shown in FIG.
A protruding portion 13a is formed by slightly protruding from 2, and a short circuit between the positive electrode 11 and the negative electrode 12 is prevented. Since the battery elements are constrained in the stacking direction by fixing the protruding portions 13a to each other with an insulating material, it is possible to effectively prevent the battery elements from peeling off due to an increase in the internal pressure of the exterior material (case) during high temperature storage. You can Of course, the insulating material can be provided over the sides of the battery element,
It is also preferable.

To inject the insulating material, it is preferable to insert the nozzle 51 of the insulating material injecting device 50 into the exterior material 3 as shown in FIG. 17 and inject the insulating material into the side end surface of the battery element 1. In this case, as shown in FIGS. 14, 15, and 16, both corner portions R _{1 of} the side end surface provided with the tab 4a or 4b,
And R _6, either side of the base of each tab _{4a, 4b R 2, R 3} ,
It is preferable to inject the insulating material into a plurality of places such as R ₄ and R ₅ . The injected insulating material permeates the side surface of the battery element into the entire side including the positive electrode terminal portion and the negative electrode terminal portion by the action of the capillary phenomenon or the like. A plurality of (6
It is possible to inject a plurality of insulating materials at one time.

Further, as shown in FIG. 16, when the insulating material is injected into the root portions on both sides of the tabs 4a and 4b, the injection point (center of the injection nozzle 51) is 2m from the tab 4a or 4b.
It is preferably within m. In this way tabs 4a, 4
When an insulating material is injected into the bases on both sides of b, this insulating material not only fixes the protruding portions 13a to each other but also insulates at least a part of the positive electrode terminal portion and the negative electrode terminal portion as in the case of FIG. A configuration covered with material 5 is also obtained.

In the above-mentioned structure, the joining piece formed by laminating the film-like outer packaging material is bent along the encapsulation portion enclosing the battery element, but more preferably the encapsulation portion. Bend from the base of. In this case, the joining piece portion may be bent only once at the base of the envelope portion, or may be bent a plurality of times. In the case of bending a plurality of times, it is preferable that the tip edge of the joining piece portion is bent so as to be interposed between the joining piece portion and the encapsulating portion. As a result, the leading edge of the joining piece portion is isolated from the outside air, and it is possible to prevent water, air, or the like from entering through the leading edge.

As the adhesive that can be used when the joining piece portion is fastened to the encapsulation portion, an epoxy-based adhesive,
Acrylic adhesives, urethane adhesives, hot melt adhesives, synthetic rubber adhesives, and the like can be mentioned. A hot-melt adhesive that easily cures is preferable.

The preferred structure of the unit battery element will be described below. FIG. 9 shows a preferred example of the unit battery element of this lithium secondary battery element. This unit cell element is formed by stacking a positive electrode including a positive electrode current collector 22 and a positive electrode material layer 23, a spacer 24 impregnated with an electrolyte, and a negative electrode including a negative electrode material layer 25 and a negative electrode current collector 26. To suppress the precipitation of lithium dendrite,
The negative electrode is made larger than the positive electrode. Further, the spacer 24 is made larger than the positive electrode and the negative electrode in order to prevent a short circuit. By making the spacer larger than the positive and negative electrodes,
As described above, the protruding portions of the spacers of the unit cell element can be fixed to each other.

A plurality of the unit battery elements are laminated to form a battery element. At the time of this lamination, the unit battery element in a normal posture (FIG. 9) with the positive electrode on the upper side and the negative electrode on the lower side, and On the contrary, the unit cell elements of the reverse orientation (not shown) with the positive electrode on the lower side and the negative electrode on the upper side are alternately laminated. That is, the unit battery elements adjacent in the stacking direction are stacked so that the same poles (that is, positive electrodes and negative electrodes) face each other.

A positive electrode tab 4a extends from the positive electrode collector 22 of this unit battery element, and a negative electrode tab 4b extends from the negative electrode collector 26. Instead of the unit cell element in which the positive electrode material layer, the spacer and the negative electrode material layer are laminated between the positive electrode current collector and the negative electrode current collector as shown in FIG. 9, as shown in FIG. 10, the positive electrode current collector 15a or A negative electrode current collector 15b is used as a core material, and a positive electrode 11 and a negative electrode 12 are prepared by laminating a positive electrode material layer 11a or a negative electrode material layer 12a on both surfaces thereof.
1 and the negative electrode 12 may be alternately laminated via the spacer 13 impregnated with the electrolyte as shown in FIG. 11 to form a unit battery element. In this case, a combination of a pair of the positive electrode 11 and the negative electrode 12 (strictly speaking, from the center of the current collector 15a of the positive electrode 11 in the thickness direction to the center of the current collector 15b of the negative electrode 12 in the thickness direction).
Corresponds to a unit battery element.

The planar shape of the electrode is arbitrary and can be a quadrangle, a circle, a polygon, or the like. As shown in FIGS. 9 and 10, the current collectors 22, 26 or 15a, 15b are usually
Tabs 4a and 4b for lead coupling are arranged in series. When the electrode is rectangular, a tab 4a protruding from the positive electrode current collector is usually formed near one side of the electrode as shown in FIG. 3, and a tab 4b of the negative electrode current collector is formed near the other side. To do.

It is effective to stack a plurality of unit battery elements in order to increase the capacity of the battery, but at this time, the tabs 4a and 4b from each unit battery element usually have a different thickness. The positive and negative terminal portions are formed by being coupled in the direction. As a result, a large capacity battery element 1 can be obtained. As shown in FIG. 2, leads 21 made of flaky metal are coupled to the tabs 4a and 4b. as a result,
The lead 21 and the positive and negative electrodes of the battery element are electrically coupled. The tabs 4a are joined together, the tabs 4a are joined together,
The connection between 4b and the lead 21 can be performed by resistance welding such as spot welding, ultrasonic welding or laser welding.

It is preferable to use an annealed metal as at least one of the positive electrode lead 21 and the negative electrode lead 21 and preferably both of them. As a result, not only the strength but also the bending durability can be made excellent. Generally, aluminum, copper, nickel, SUS, or the like can be used as the type of metal used for the leads. The preferred material for the positive electrode lead is aluminum. A preferable material for the negative electrode lead is copper.

The thickness of the lead 21 is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more,
Most preferably, it is 40 μm or more. If it is too thin, the mechanical strength of the lead such as tensile strength tends to be insufficient. The thickness of the lead is usually 1000 μm or less, preferably 500 μm or less, more preferably 100 μm or less. If it is too thick, the bending durability tends to deteriorate, and sealing of the battery element by the case tends to become difficult. The advantage of using the annealed metal described below for the lead is more remarkable as the lead is thicker.

The width of the lead is usually 1 mm or more and 20 mm or less, particularly 1 mm or more and 10 mm or less, and the exposed length of the lead to the outside is usually 1 mm or more and 50 mm or less. In the lithium secondary battery of the present invention, the case accommodating the battery element has variable shape. The shape-variable case has advantages that it is easy to make batteries of various shapes and that the case itself is thin and lightweight, so that the volume energy density and the weight energy density of the battery are improved. The shortage causes swelling of the case during storage at high temperature. Therefore, when the shape-variable case is used, the effect of incorporating the additive α in the battery element is remarkably exhibited.

The case having shape changeability means a case having flexibility. Specifically, it means a case having flexibility and flexibility. More specifically, it means a case that can be flexibly bent by a human hand and that a flat case can be easily changed to an L-shaped or S-shaped shape. As the material of the shape-variable case, aluminum, nickel-plated iron, metal such as copper, synthetic resin, or the like can be used. A laminate film having a gas barrier layer and a resin layer is preferable, and a laminate film having a resin layer on both sides of the gas barrier layer is preferable. Such a laminated film has high gas barrier properties, high shape variability, and thinness. As a result, it is possible to reduce the thickness and weight of the exterior material,
The capacity of the battery as a whole can be improved.

Materials for the gas barrier layer used for the laminate film include aluminum, iron, copper, nickel,
Metals such as titanium, molybdenum, and gold, alloys such as stainless steel and Hastelloy, and metal oxides such as silicon oxide and aluminum oxide can be used. Aluminum is preferable because it is lightweight and excellent in workability. As the resin used for the resin layer, various synthetic resins such as thermoplastics, thermoplastic elastomers, thermosetting resins and plastic alloys can be used. These resins include those in which a filler such as a filler is mixed.

As a concrete structure of the laminate film, as shown in FIG. 12A, a laminate of a gas barrier layer 40 and a resin layer 41 can be used. Further, a more preferable laminated film is shown in FIG.
As shown in (B), a synthetic resin layer 41 for functioning as an outer protective layer is provided on the outer side surface of the gas barrier layer 40, and corrosion on the inner side surface is prevented from being corroded by the electrolyte or contact between the gas barrier layer and the battery element. This is a three-layer structure in which a synthetic resin layer 42 that functions as an inner protective layer for protecting the layers is laminated.

In this case, the resin used for the outer protective layer is
Resins having excellent chemical resistance and mechanical strength such as polyethylene, polypropylene, modified polyolefins, ionomers, amorphous polyolefins, polyethylene terephthalate and polyamides are preferable. As the inner protective layer,
A chemical resistant synthetic resin is used, such as polyethylene,
Polypropylene, modified polyolefin, ionomer,
An ethylene-vinyl acetate copolymer or the like can be used.

As shown in FIG. 13, the laminated film has a gas barrier layer 40 and a synthetic resin layer 4 for forming a protective layer.
1. It is also possible and preferable to provide the adhesive layer 43 between the synthetic resin layers 42 for forming the anticorrosion layer. Furthermore,
An adhesive layer made of a resin such as polyethylene or polypropylene that can be welded may be provided on the innermost surface of the composite material in order to bond the exterior materials to each other. A case is formed using these metals, synthetic resins, or composite materials. The case may be formed by fusing the periphery of the film-like body, or the sheet-like body may be drawn by vacuum forming, pressure forming, press forming or the like. It can also be molded by injection molding a synthetic resin. In injection molding, the gas barrier layer is usually formed by sputtering or the like.

The outer casing material used for the shape-variable case can be provided with a housing portion made of a concave portion by drawing or the like. In addition, it is preferable to use a film-shaped exterior material because it is easy to process. The thickness of the deformable case is usually 0.01 μm or more, preferably 0.0
2 μm or more, more preferably 0.05 μm or more, usually 1 mm or less, preferably 0.5 mm or less, more preferably 0.3 mm or less, further preferably 0.2.
mm or less, most preferably 0.15 mm or less. The thinner the battery, the smaller and lighter the battery becomes, but if it is too thin, not only will there be a greater risk of bursting due to an increase in the internal pressure of the case when stored at high temperatures, but it will not be possible to impart sufficient rigidity or seal tightness. There is a possibility that it will decrease.

The thickness of the entire lithium secondary battery in which the battery element is housed in the case is usually 5 mm or less, preferably 4.5 mm or less, more preferably 4 mm or less.
The effect of the present invention is particularly great for such a thin lithium secondary battery. However, since a too thin battery has a too small capacity and is difficult to manufacture, it is usually 0.
It is 5 mm or more, preferably 1 mm or more, more preferably 2 mm or more.

For the convenience of mounting the battery on a device, etc., the plurality of lithium secondary batteries are further rigidized after encapsulating the battery element in a shape-variable case and molding it into a preferable shape. It can also be stored in an outer case. [4] Uses of lithium secondary battery Examples of electrical equipment in which the lithium secondary battery of the present invention is used as a power source include, for example, a notebook personal computer, a pen input personal computer, a personal digital assistant (Personal Digital Assistant).
nts, PDA), e-book player, mobile phone,
Cordless phone handset, pager, handy terminal, mobile fax, mobile copy, mobile printer,
Headphone stereo, video movie, LCD TV,
Handy cleaner, portable CD, mini disk, electric shaver, transceiver, electronic organizer, calculator, memory card, portable tape recorder, radio,
Examples include backup power supplies, motors, lighting equipment, toys, game machines, road conditioners, watches, strobes, cameras, medical equipment (pacemakers, hearing aids, shoulder massagers, etc.) and the like.

[0138]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications can be made without departing from the scope of the invention. it can. The parts in the composition are parts by weight. A. Effect of Sulfur Compound Type and Presence or Absence of Addition [Reference Example 1] A lithium secondary battery containing dimethylsulfoxide in the electrolyte was produced as follows. [Production of Positive Electrode] A positive electrode coating material was prepared with the following composition.
Lithium nickel composite oxide (LiNi _0.82 Co
The specific surface area of _0.15 Al _0.03 O ₂ ) was adjusted to 0.38 m ² / g by pulverizing and classifying after synthesis. In addition, lithium cobalt composite oxide (LiCoO
₂ ) had a specific surface area of 0.50 m ² / g.

[0139]

[Table 3] Composition of positive electrode coating-Lithium cobalt composite oxide (LiCoO ₂ ) 27 parts-LiNi _0.82 Co _0.15 Al _0.03 O ₂ 63 parts-Acetylene black 5 parts-Polyvinylidene fluoride 5 parts-N-methyl-2-pyrrolidone 80 parts The above raw materials were kneaded for 2 hours with a planetary mixer type kneader to obtain a positive electrode coating material. Next, the above positive electrode coating material was applied onto an aluminum current collector base material having a thickness of 15 μm by extrusion type die coating and dried,
A porous film was prepared in which the active material was bound on the current collector by the binder. Then roll press (calendar)
An electrode sheet was produced by consolidating using the. Then, the electrode was cut out from the electrode sheet to obtain a positive electrode. The weight of the positive electrode active material was 10 mg / cm ² . [Manufacture of Negative Electrode] A negative electrode paint was prepared with the following composition.

[0140]

[Table 4] Composition of Negative Electrode Paint-Graphite (particle size 15 µm) 90 parts-Polyvinylidene fluoride 10 parts-N-methyl-2-pyrrolidone 100 parts The above raw materials were kneaded for 2 hours by a planetary mixer type kneader. It was used as a negative electrode paint. Next, the above negative electrode coating material was applied onto a copper current collector substrate having a thickness of 20 μm by extrusion type die coating and dried to prepare a porous film in which an active material was bound on the current collector by a binder. . Then, an electrode sheet was prepared by compacting using a roll press (calender). Then, the electrode was cut out from the electrode sheet to obtain a negative electrode. [Ratio of positive electrode / negative electrode material layer] In the production example of the positive electrode / negative electrode, (charge capacity of positive electrode) / (charge capacity of negative electrode) =
The film thicknesses of the positive electrode material layer and the negative electrode material layer were adjusted so as to be 0.93. Here, the charge capacity of the negative electrode was based on the capacity per unit weight of the negative electrode (mAh / g) when the counter electrode Li was charged to 1.5 V to 3 mV. [Manufacture of Paint for Forming Electrolyte] The following compositions were mixed, stirred and dissolved to manufacture a paint for forming an electrolyte layer.

[0141]

[Table 5] Composition of paint for forming electrolyte • Electrolyte solution 925 parts Mixture solution of ethylene carbonate and propylene carbonate containing 1M concentration of LiPF ₆ (volume ratio; ethylene carbonate: propylene carbonate = 1: 1) • Tetraethylene Glucol diacrylate 44 parts-Polyethylene oxide triacrylate 22 parts-Dimethyl sulfoxide 9.3 parts (*)-Polymerization initiator 2 parts-Additive (succinic anhydride) 9 parts * ... 1 dimethyl sulfoxide to the electrolyte The content was 0.0 part. [Manufacture of Lithium Secondary Battery] A polymer porous film (spacer) prepared by applying a coating material for forming an electrolyte to the positive electrode and the negative electrode prepared as described above and separately immersing in the coating material for forming an electrolyte layer, After sandwiching this film between the positive electrode and the negative electrode, the film was heated at 90 ° C. for 10 minutes to polymerize tetraethylene glycol diacrylate and polyethylene oxide triacrylate in the coating material for forming the electrolyte. As a result, a flat unit battery element having a positive electrode and a negative electrode formed on a current collector containing an active material and a binder and having a non-fluidized electrolyte between the positive electrode and the negative electrode was manufactured.

Lead wires for taking out a current were connected to the terminal portions of the positive electrode current collector and the negative electrode current collector of the above unit battery element. The battery element thus obtained was charged to a battery voltage of 4.2 V at 0.34 mA / cm ² . Thereafter, the battery element was housed in a bag-shaped case in which a laminate film in which both surfaces of an aluminum film were covered with a resin layer was oppositely formed, and the laminate film was sealed with a vacuum seal to produce a flat lithium secondary battery. . [Swelling test 1 of lithium secondary battery in high temperature storage] The swollenness test of a lithium secondary battery in high temperature storage was performed by storing the lithium secondary battery at 90 ° C for 4 hours and then checking the degree of swelling of the laminated film with the human eyes. Look, "No",
It was relatively evaluated in four grades of "small", "medium", and "large".
The evaluation results are shown in Table-3.

[Measurement of Initial Capacity of Battery] Regarding the initial capacity of the lithium secondary battery, the sample charged to a battery voltage of 4.2 V was discharged to a battery voltage of 3.0 V at 0.34 mA / cm ² ,
The discharge capacity at that time was obtained. Here, the discharge capacity obtained by the lithium secondary battery of Reference Example 1 is set to 100, and the discharge capacity obtained by the above method of the lithium secondary batteries of other Examples and Comparative Examples is compared with the discharge capacity of 100. It was expressed as a relative value. The evaluation results are shown in Table-3. Example 1 A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethylsulfoxide was changed to tetramethylenesulfoxide in the composition of the coating material for forming an electrolyte. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Example 2] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to dimethylsulfite in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Example 3] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethylsulfoxide was changed to ethylene sulfite in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. Example 4 A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to dimethyl sulfone in the composition of the electrolyte-forming coating material in Reference Example 1. Of the lithium secondary battery thus obtained
[Swelling test 1 of lithium secondary battery in high temperature storage] and
[Measurement of initial capacity of battery] was evaluated. The evaluation results are shown in Table-3. Example 5 A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was replaced by sulfolane in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Example 6] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to methyl methanesulfonate in the composition of the electrolyte-forming coating material. The thus obtained lithium secondary battery [swelling test 1 of lithium secondary battery in high temperature storage]
And [measurement of initial capacity of battery] were evaluated. The evaluation results are shown in Table-3. [Example 7] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to 1,3-propane sultone in the composition of the electrolyte forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Example 8] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethylsulfoxide was changed to diethyl sulfate in the composition of the coating material for forming an electrolyte. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. Table 3 shows the evaluation results.
Shown in. [Example 9] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to ethylene glycol sulfate in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Comparative Example 1] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethylsulfoxide was not added to the composition of the electrolyte-forming coating material in Reference Example 1. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Comparative Example 2] A lithium secondary battery was produced in the same manner as in Reference Example 1 except that dimethyl sulfoxide was changed to diphenyl sulfide in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3. [Comparative Example 3] A lithium secondary battery was prepared in the same manner as in Reference Example 1, except that dimethyl sulfoxide was changed to diphenyl sulfide in the composition of the coating material for forming an electrolyte and the addition amount was 47 parts. Was produced. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-3.

[0144]

[Table 6]

(Note 1) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". The following can be seen from Table-3.
First, from the results of Reference Example 1, Examples 1 to 9 and Comparative Example 1, when the electrolyte solution does not contain a sulfur compound, the swelling of the lithium secondary battery during high temperature storage is “large”, By containing a sulfur compound having one or more double bonds of sulfur and oxygen in the liquid, the swelling of the lithium secondary battery during high temperature storage can be suppressed to "medium", "small", and "none". You can That is, it is understood that in this lithium secondary battery system, a sulfur compound having one or more double bonds of sulfur and oxygen can serve as the additive α.

Secondly, from the results of Comparative Examples 2 and 3, the compounds containing sulfur in the molecule but not forming a double bond of sulfur and oxygen are not suitable for lithium dinitrate storage at high temperature. Swelling of the secondary battery cannot be suppressed. That is, in this lithium secondary battery system, diphenyl sulfide is
It can be seen that it does not become the additive α. Thirdly, comparing the results of Reference Example 1 and Example 4 with the results of Examples 1 and 5, respectively, the number of double bonds between sulfur and oxygen in the molecule is changed from one to two. By doing so, the swelling of the lithium secondary battery during high temperature storage can be further reduced.

Fourthly, the results of Reference Example 1 and Example 2, and
Comparing the results of Example 5 and Example 9 respectively,
By further combining oxygen with sulfur forming a double bond with sulfur and oxygen, the swelling of the lithium secondary battery during storage at high temperature can be further reduced. Fifthly, based on the measurement results of the initial battery capacities of Reference Example 1, Examples 2 to 9 and Comparative Examples 1 to 3, a sulfur compound having one or more double bonds of sulfur and oxygen was added to a lithium secondary battery. Even if contained in
It can also be seen that the basic characteristics of the lithium secondary battery do not deteriorate. [Blistering Test 2 of Lithium Secondary Battery at High Temperature Storage] In each of the lithium secondary batteries of Reference Example 1, Examples 1 to 9 and Comparative Example 1, lithium was stored at high temperature by adding the additive α to the battery element. In order to determine the limit capacity of the blistering prevention effect of the secondary battery, two (n = 2) or three (n = 3) of the lithium secondary batteries are prepared, and the lithium secondary batteries are Stored at 24 ° C for 24 hours.

The swelling of the lithium secondary battery after storage at high temperature was evaluated as follows. That is, in a laminate film that is an exterior material of a lithium secondary battery, a portion where swelling was observed was marked, and then the lithium secondary battery was disassembled. The laminated film obtained by disassembling was divided into this marking portion and the other portion. Then, the weight of the laminated film in the portion where the swelling was observed was divided by the total weight of the laminated film to obtain the weight ratio of the swelled portion to the whole. Since the density of the laminated film can be considered to be constant, this weight ratio was defined as the area ratio representing the area of the swollen portion with respect to the area of the entire laminated film.

Table 4 shows the additive ΔEadd (AN) (Reference Example 1, Examples 1 to 9) and the non-aqueous solvent ΔEsol (A).
N) (Comparative Example 1) and the value of the area ratio of the swollen portion of the lithium secondary battery are shown. Further, in FIG. 19, the relationship between the value of ΔEadd (AN) of the additive (Reference Example 1, Examples 1 to 9) and ΔEsol (AN) of the non-aqueous solvent (Comparative Example 1) and the area ratio of the swollen portion are shown. Is shown in the graph. In Table 4 and FIG. 19, ΔEsol (AN) is ethylene carbonate (ΔEsol (AN) = 2.3) used as the solvent.
7) and propylene carbonate (ΔEsol (AN) =
Among 2.39), ethylene carbonate having a smaller value of ΔEsol (AN) is used.

[0150]

[Table 7]

In FIG. 19, the swelling area relative values n = 1, 2, and 3 shown in Table 4 are plotted with the marks x, Δ, and ◯, respectively, and the average of the swelling area relative values is shown. A linear approximation line is shown. The following can be seen from the linear approximation line of the average value of n = 1 to 3 in FIG. That is,
Δ of ethylene carbonate (EC) used as a non-aqueous solvent
Based on the value of Esol (AN), smaller than this Δ
It can be seen that when the electrolyte has an additive having a value of Eadd (AN), the relative area value of the swollen portion becomes small (swelling becomes small). In addition, the above ΔEsol
It is understood that when the electrolyte contains an additive having a value larger than (AN), the area relative value of the swollen portion becomes large (swelling becomes large). Specifically, ΔEadd (AN) of dimethylsulfoxide is 3.23 eV, which is larger than Δsol (AN) of 2.37 eV of EC. Therefore, the swollenness of the lithium secondary battery (Reference Example 1) under the extremely severe high temperature storage condition of 90 ° C. for 24 hours is larger than that of the lithium secondary battery containing no additive (Comparative Example 1). .

Incidentally, in the measurement result of the above-mentioned [swelling test 1 of lithium secondary battery in high temperature storage] (hereinafter, may be referred to as “swelling test 1”), the lithium secondary battery containing dimethyl sulfoxide was tested. The blistering evaluation result during high temperature storage was "medium" (see Table 3). That is, the swelling evaluation results of the lithium secondary battery containing dimethyl sulfoxide at high temperature storage are as follows: Swelling test 1 and [Swelling test 2 of lithium secondary battery at high temperature storage] (hereinafter,
It may be referred to as "blister test 2". ) And different results. The results are obtained because the high temperature storage test conditions of the swelling test 1 and the high temperature storage test conditions of the swelling test 2 are different from each other. That is, the high temperature storage condition of the swelling test 2 (90 ° C., 24 hours) is extremely severe compared to the high temperature storage condition of the swelling test 1 (90 ° C., 4 hours). This means that the ultimate capacity of the additive can be determined by high temperature storage in the blistering test 2. Since dimethyl sulfoxide has a double bond of sulfur and oxygen, swelling of the battery during storage at high temperature is suppressed in the swelling test 1, which is sufficient as an index for determining whether or not it can be actually used. However, in the swelling test 2, which is the ultimate evaluation method for determining the presence or absence of swelling of the battery during high temperature storage, swelling of the lithium secondary battery occurs. This result shows that ΔEadd
By using a sulfur compound in which the value of (AN) and the value of ΔEsol (AN) of the non-aqueous solvent have a specific relationship, it is possible to reliably suppress the swelling of the battery during high temperature storage. Then, the ultimate ability of the additive can be determined by the blistering test 2, and in the present invention, the Δ of the non-aqueous solvent is
It can be said that the significance of controlling the relationship between the value of Esol (AN) and the value of ΔEadd (AN) of the additive becomes clearer. B. Examination of Addition Amount of Sulfur Compound [Example 10] Lithium dioxide was added in the same manner as in Example 4 except that the amount of dimethyl sulfone added was changed to 4.7 parts in the composition of the electrolyte-forming coating material. A secondary battery was produced. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. Table of evaluation results
5 shows. [Example 11] A lithium secondary battery was produced in the same manner as in Example 4 except that the amount of dimethyl sulfone added was changed to 47 parts in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. Table-5 shows the evaluation results.
Shown in. Example 12 A lithium secondary battery was produced in the same manner as in Example 4 except that the amount of dimethyl sulfone added was changed to 94 parts in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. Table-5 shows the evaluation results.
Shown in.

[0153]

[Table 8]

(Note 2) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". Table 4 also contains the data of Example 4 in order to study the influence of the addition amount of dimethyl sulfone as an additive in detail.

From the results of Table 4, this lithium secondary battery
In the above system, one double bond between sulfur and oxygen is included in the molecule.
Dimethyl sulfone, which is a sulfur compound having three or more
It can be seen that it functions as an additive α. Especially dimethyls
If more than 5.0 parts of Ruhon is included in the electrolyte,
It is possible to completely suppress the swelling of the thium secondary battery during high temperature storage.
You can see that Also, measure the initial battery capacity.
From the results, if the addition amount is at least 10 parts by weight,
Even if the amount of methyl sulfone added is increased, the lithium secondary
It can also be seen that the basic characteristics of the pond do not deteriorate. C. Effect of positive electrode active material [Comparative Example 4] Lithium-nickel composite acid in Reference Example 1
Compound (LiNi_0.82Co_0.15Al _0.03O₂)
Without the lithium cobalt composite oxide (L
iCoO₂) Was used alone (in the composition of the positive electrode paint)
Lithium cobalt composite oxide (LiCoO₂) 9
0 parts) and dimethyl sulfoxide was added.
Lithium dioxide was prepared in the same manner as in Reference Example 1 except that it was omitted.
A secondary battery was produced. The lithium secondary battery thus obtained
Ikeno [Blistering test 1 of lithium secondary battery in high temperature storage]
And [measurement of initial capacity of battery] were evaluated. Evaluation results
Is shown in Table-6.

[0156]

[Table 9]

(Note 3) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". Table 6 also contains the data of Comparative Example 1 in order to examine the influence of the type of the positive electrode active material in detail.

From the results of Table 6, in the lithium secondary battery systems of Comparative Examples 1 and 4, when the lithium cobalt composite oxide (LiCoO ₂ ) alone was used as the positive electrode active material, the additive α was not contained. Also, it can be seen that swelling during storage at high temperature does not occur as long as it is visually observed. That is, it is understood that when the positive electrode active material contains the lithium nickel composite oxide for the purpose of increasing the battery capacity, the problem of swelling of the shape-variable case during high temperature storage becomes more apparent.

In Comparative Example 4, the swelling of the lithium secondary battery during storage at high temperature was "absent"
In addition, it is considered that the lithium secondary battery system of Comparative Example 4 uses the polymer electrolyte and the high boiling point solvent and has a stable composition for high temperature storage. Secondly, it is considered that the high temperature storage time is relatively short at 4 hours.
Although the high-temperature storage condition of 90 ° C. for 4 hours in the swelling test 1 is a sufficient condition considering the actual use of the lithium secondary battery, like the swelling test 2, the presence or absence of swelling of the lithium secondary battery in the high-temperature storage. It is not the ultimate high temperature storage condition to judge. Therefore, also in the lithium secondary battery of Comparative Example 4, when the presence or absence of swelling of the lithium secondary battery during high temperature storage is evaluated by performing the swelling test 2, it is expected that the lithium secondary battery will swell. To be done.
Therefore, also in the lithium secondary battery of Comparative Example 4, if the additive α is contained in the battery element and the non-aqueous solvent and the additive α are controlled to have a specific relationship, it is possible to ensure even under severer high temperature storage conditions. It is considered that the swelling of the lithium secondary battery can be suppressed. D. Effect of Specific Surface Area of Positive Electrode Active Material [Example 13] In Example 11, a specific surface area of 0.60 m
² / g lithium nickel composite oxide (LiNi _0.82 C
Example 11 except that _0.15 Al _0.03 O ₂ ) was used.
A lithium secondary battery was produced in the same manner as in. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-7. [Example 14] The specific surface area in Example 11 was 0.74 m.
² / g lithium nickel composite oxide (LiNi _0.82 C
Example 11 except that _0.15 Al _0.03 O ₂ ) was used.
A lithium secondary battery was produced in the same manner as in. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-7. [Example 15] The specific surface area of Example 11 is 0.92 m.
² / g lithium nickel composite oxide (LiNi _0.82 C
Example 11 except that _0.15 Al _0.03 O ₂ ) was used.
A lithium secondary battery was produced in the same manner as in. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-7. [Comparative Example 5] In Reference Example 1, a specific surface area of 0.60 m ² /
g of lithium nickel composite acid (LiNi _0.82 Co _0.15
A lithium secondary battery was produced in the same manner as in Reference Example 1 except that Al _0.03 O ₂ ) was used and dimethyl sulfoxide was not added. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-7.

[0160]

[Table 10]

(Note 4) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". From the results of Table-7, the specific surface area of the lithium nickel composite oxide was 0.38 to 0.92 m ² /
If dimethyl sulfone, which is a sulfur compound having one or more double bonds of sulfur and oxygen, is contained even when it is changed to g, the swelling of the lithium secondary battery during high temperature storage is "medium" to
It turns out that "none" can be set. This indicates that dimethyl sulfone serves as the additive α of the present invention in this lithium secondary battery system. On the other hand, when dimethyl sulfone is not contained, 0.38, 0.
It can be seen that the swelling is “large” at any specific surface area of 60 m ² / g. E. Effect of Addition of Organic Acid and / or Lithium Salt of Organic Acid to Positive Electrode [Example 16] A lithium secondary battery was prepared in the same manner as in Reference Example 1 except that the production method of the positive electrode was as follows. It was made. That is, a coating material for producing a positive electrode was prepared with the following composition so that the positive electrode contained oxalic acid.

[0162]

[Table 11] Composition of paint for producing positive electrode-Lithium cobalt composite oxide (LiCoO ₂ ) 27 parts-LiNi _0.82 Co _0.15 Al _0.03 O ₂ 63 parts-Acetylene black 5 parts-Polyvinylidene fluoride 5 parts-Oxalic acid 0.4 Parts-N-methyl-2-pyrrolidone 80 parts The above raw materials were kneaded with a planetary mixer type kneader for 2 hours to obtain a coating material for producing a positive electrode. Next, the above positive electrode-producing coating material is applied onto an aluminum current collector base material having a thickness of 15 μm by extrusion die coating and dried, and a positive electrode material layer in which an active material is bound on the current collector by a binder. It was created. Then, an electrode sheet was prepared by compacting using a roll press (calender). Then, the electrode was cut out from the electrode sheet to obtain a positive electrode. Weight of positive electrode active material is 10 mg / cm
^{Was 2} .

The lithium secondary battery thus obtained was
[Swelling test 1 of lithium secondary battery in high temperature storage] and
[Measurement of initial capacity of battery] was evaluated. The evaluation results are shown in Table-8. [Example 17] In the same manner as in Example 16 except that dimethylsulfoxide was replaced with tetramethylenesulfoxide in the composition of the electrolyte-forming coating material,
A lithium secondary battery was produced. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-8. [Example 18] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to dimethyl sulfite in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-8. [Example 19] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to ethylene sulfite in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-8. Example 20 A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to dimethyl sulfone in the composition of the electrolyte-forming coating material. The thus obtained lithium secondary battery [swelling test 1 of lithium secondary battery in high temperature storage]
And [measurement of initial capacity of battery] were evaluated. The evaluation results are shown in Table-8. Example 21 A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was replaced with sulfolane in the composition of the electrolyte-forming coating material. Of the lithium secondary battery thus obtained
[Swelling test 1 of lithium secondary battery in high temperature storage] and
[Measurement of initial capacity of battery] was evaluated. The evaluation results are shown in Table-8. [Example 22] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to methyl methanesulfonate in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery].
The evaluation results are shown in Table-8. [Example 23] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to 1,3-propane sultone in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-8. [Example 24] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethylsulfoxide was changed to diethyl sulfate in the composition of the electrolyte-forming coating material. Of the lithium secondary battery thus obtained
[Swelling test 1 of lithium secondary battery in high temperature storage] and
[Measurement of initial capacity of battery] was evaluated. The evaluation results are shown in Table-8. [Example 25] A lithium secondary battery was produced in the same manner as in Example 16 except that dimethyl sulfoxide was changed to ethylene glycol sulfate in the composition of the electrolyte-forming coating material. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-8. [Comparative Example 6] A lithium secondary battery was produced in the same manner as in Example 16, except that dimethyl sulfoxide was not added to the composition of the electrolyte-forming coating material in Example 16. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. Table of evaluation results
8 shows.

[0164]

[Table 12]

(Note 5) ... [Evaluation result in [Swelling test 1 of lithium secondary battery in high temperature storage]] is shown. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". From the results of Table-8, the following can be said when the amount of oxalic acid in the positive electrode is constant.

First, from the results of Examples 16 to 25 and Comparative Example 6, when the electrolyte does not contain a sulfur compound, the swelling of the lithium secondary battery during high temperature storage becomes “large”, while
Swelling of the lithium secondary battery during high temperature storage is suppressed to "medium", "small", and "none" by containing a sulfur compound having one or more double bonds of sulfur and oxygen in the electrolytic solution. be able to. In other words, it is understood that the swelling of the lithium secondary battery during high temperature storage cannot be sufficiently suppressed only by containing oxalic acid in the positive electrode.

Secondly, from the comparison between Example 16 and Example 20 and the comparison between Example 17 and Example 21, the number of double bonds between sulfur and oxygen in the molecule is 1 to 2. By this, swelling of the lithium secondary battery during high temperature storage can be further reduced. Thirdly, from the comparison between Example 16 and Example 18 and the comparison between Example 21 and Example 25, by further combining oxygen with sulfur forming a double bond with sulfur and oxygen, high temperature The swelling of the lithium secondary battery during storage can be further reduced.

Fourthly, based on the measurement results of the initial battery capacities of Examples 16 to 25 and Comparative Example 6, the lithium secondary battery was made to contain a sulfur compound having one or more double bonds of sulfur and oxygen. However, it can be seen that the basic characteristics of the lithium secondary battery do not deteriorate. [Example 26] A lithium secondary battery was produced in the same manner as in Example 22 except that the content of oxalic acid in the positive electrode was changed to 0.3 part. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-9. [Example 27] A lithium secondary battery was produced in the same manner as in Example 22, except that the content of oxalic acid in the positive electrode was changed to 0.6 part. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-9. [Example 28] A lithium secondary battery was produced in the same manner as in Example 22 except that the content of oxalic acid in the positive electrode was changed to 1.0 part. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-9. [Example 29] Example 22 except that the content of methyl methanesulfonate was 4.7 parts and the addition amount of oxalic acid in the positive electrode was 0.6 part.
A lithium secondary battery was produced in the same manner as in. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-9. Example 30 The same as Example 22 except that the content of methyl methanesulfonate was 47 parts and the amount of oxalic acid added to the positive electrode was 0.6 part. A lithium secondary battery was produced. The lithium secondary battery thus obtained was subjected to [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery].
Was evaluated. The evaluation results are shown in Table-9.

[0169]

[Table 13]

(Note 6) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". Table 9 also contains the data of Example 22 in order to examine the relationship between the addition amount of the sulfur compound as the additive α and the addition amount of oxalic acid in detail.

From the results of Table 9, the following can be said about the relationship between the amount of the sulfur compound added to the electrolyte and the amount of oxalic acid added to the positive electrode. First, Examples 26 and 22,
From the comparison of No. 27 and No. 28, when the content of the sulfur compound in the electrolyte was constant, by increasing the addition amount of oxalic acid in the positive electrode from 0.3 part to 1.0 part, high temperature storage The swelling of the lithium secondary battery at that time can be reduced from “medium” to “none”. On the other hand, Examples 29 and 2
From the comparison of 7 and 30, when the oxalic acid in the positive electrode was kept constant at 0.6 parts and the addition amount of the sulfur compound in the electrolyte was 1.0 part or more, the lithium secondary battery during high temperature storage was obtained. Can be almost completely suppressed. Furthermore, from the results of Examples 26, 22, and 27, when the sulfur compound in the electrolyte was 1.0 part, the oxalic acid content in the positive electrode was 0.3%.
.About.0.6 parts, the results of Examples 29, 27,
From the results of 30, when the oxalic acid in the positive electrode was 0.6 parts, the basic characteristics as a lithium secondary battery deteriorated even if the sulfur compound in the electrolyte was changed to 0.5 to 5.0 parts. I know I won't. The lithium secondary battery (Example 28) in which the sulfur compound was 1.0 part and the oxalic acid in the positive electrode was 1.0 part was compared with the lithium secondary batteries of other examples.
Although the initial battery capacity is low, the swelling of the lithium secondary battery during storage at high temperature can be almost completely suppressed, so that the lithium secondary battery is well balanced. [Comparative Example 7] A lithium secondary battery was prepared in the same manner as in Example 16 except that dimethylsulfoxide was not added and that the oxalic acid content in the positive electrode was 0.8 parts. A battery was made. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-10. [Comparative Example 8] A lithium secondary battery was prepared in the same manner as in Example 16 except that dimethylsulfoxide was not added and that the oxalic acid content in the positive electrode was 1.0 part. A battery was made. The lithium secondary battery thus obtained was evaluated in [Swelling test 1 of lithium secondary battery in high temperature storage] and [Measurement of initial capacity of battery]. The evaluation results are shown in Table-10.

[0172]

[Table 14]

(Note 7) ... Shows the evaluation results in [Swelling test 1 of lithium secondary battery in high temperature storage]. Seen with the human eye, the degree of swelling is "large", "medium", "small",
Classified as "none". In Table-10, the data of Comparative Example 1 and Comparative Example 6 are also shown in order to examine the relationship with the added amount of oxalic acid in detail.

From the results shown in Table 10, when the sulfur compound is not contained in the electrolyte, the swelling of the lithium secondary battery during storage at high temperature can be suppressed when the content of oxalic acid in the positive electrode is up to 0.4 part. Although not seen, the content is 0.8 parts, 1.
When it increases to 0 part, the swelling is suppressed to "medium" and "small". From this result, it is expected that if the oxalic acid content in the positive electrode is further increased, the swelling of the lithium secondary battery during storage at high temperature can be suppressed almost completely. However, focusing on the initial capacity of the battery, it can be seen that an increase in the oxalic acid content leads to a decrease in the initial capacity. Therefore, in this lithium secondary battery system, in order to obtain a high-capacity lithium secondary battery while suppressing swelling of the lithium secondary battery during high-temperature storage, in addition to containing oxalic acid in the positive electrode It can be seen that it is necessary to include the additive α in the inside.

[0175]

According to the present invention, it is possible to control the relationship between the ΔEsol (AN) value of the non-aqueous solvent contained in the electrolyte and the ΔEadd (AN) value of the additive α contained in the battery element. Thus, a lithium secondary battery having excellent safety and storage characteristics can be obtained without impairing the initial capacity, rate characteristics, and cycle characteristics. In particular, it prevents swelling of the lithium secondary battery during high-temperature storage of the lithium secondary battery, which is a problem when the case that accommodates the battery element is a shape-variable case, and is excellent in safety during high-temperature storage. A lithium secondary battery with excellent capacity can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a battery according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of a battery according to an embodiment of the present invention.

FIG. 3 is a perspective view showing a battery element of a battery according to an embodiment of the present invention.

FIG. 4 is a perspective view of a battery according to an exemplary embodiment of the present invention.

FIG. 5 is a perspective view in the process of manufacturing a battery according to another embodiment of the present invention.

FIG. 6 is a perspective view of a battery according to still another embodiment of the present invention during manufacturing.

FIG. 7 is a perspective view of a battery according to still another embodiment of the present invention during manufacturing.

8 is a plan view of the embodiment shown in FIG. 7 during manufacture.

FIG. 9 is a schematic perspective view of a unit battery element.

FIG. 10 is a schematic cross-sectional view of a positive electrode or a negative electrode.

FIG. 11 is a schematic cross-sectional view of a battery element.

12A and 12B are vertical cross-sectional views showing an example of a composite material that constitutes an exterior material.

FIG. 13 is a vertical cross-sectional view showing another example of the composite material that constitutes the exterior material.

FIG. 14 is a perspective view of the battery according to another embodiment of the present invention during manufacturing.

FIG. 15 is a plan view schematically showing the state of FIG.

16 is an enlarged view of a main part of FIG.

FIG. 17 is a cross-sectional view showing a state of injection of an insulating material.

FIG. 18 is an enlarged cross-sectional view of the tab portion of the battery element.

FIG. 19 is a diagram showing a relationship between ΔEadd (AN) of an additive α and ΔEsol (AN) of a non-aqueous solvent, and swelling of a lithium secondary battery during high temperature storage.

[Explanation of symbols]

1 Battery element 2, 3, 6, 7, 8 Exterior material 4a, 4b tabs 4A, 4F, 4G Joint piece part 4B Encapsulation part 5 Insulation material 11 Positive electrode 11a Positive electrode material layer 12 Negative electrode 12b Negative electrode material layer 13 Non-fluidic electrolyte layer 15a Positive electrode current collector 15b Negative electrode current collector 21 lead 22 Positive electrode current collector 23 Positive electrode material layer 24 Spacer (electrolyte layer) 25 Negative electrode material layer 26 Negative electrode current collector 40 metal layer 41, 42 Synthetic resin layer 43 Adhesive layer 50 injection device 51 nozzles

Continued front page    (72) Inventor Hiroyuki Saito             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation (72) Inventor Koji Kobayashi             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation F-term (reference) 5H011 AA01 AA13 CC02 CC05 CC06                       CC10 DD03                 5H029 AJ03 AJ04 AJ05 AJ11 AJ12                       AK03 AK19 AL02 AL06 AL07                       AL08 AL12 AM02 AM03 AM04                       AM05 AM07 AM16 BJ02 BJ04                       DJ02 EJ04 EJ12 HJ00 HJ01                       HJ02 HJ07                 5H050 AA07 AA08 AA10 AA14 AA15                       BA16 BA17 CA08 CA29 CB02                       CB07 CB08 CB09 CB12 DA09                       DA18 EA10 EA22 EA23 EA24                       HA00 HA01 HA02 HA07

Claims (20)

[Claims] 1. A lithium secondary battery comprising a battery element having a positive electrode, a negative electrode, an electrolyte containing a non-aqueous solvent and a solute, and a shape-variable case accommodating the battery element. The difference between the enthalpy: Esol (N) of the neutral molecule of the non-aqueous solvent and the enthalpy of the anion radical produced by giving one electron to the neutral molecule: Esol (A): Esol (A) -Esol
(N) is ΔEsol (AN), the battery element contains the additive α, and the following calculation method (#)
Enthalpy of the neutral molecule of the additive α: Eadd (N), and enthalpy of an anion radical generated by giving one electron to the neutral molecule: Eadd
Difference from (A): Eadd (A) -Eadd (N) is ΔEadd
When (AN), ΔEadd (AN) is smaller than ΔEsol (AN), a lithium secondary battery. Calculation Method (#) The enthalpy of the neutral molecule and the enthalpy of the anion radical are obtained by quantum chemical calculation by the ab initio restricted Hartree-Fock molecular orbital method using the 6-31G * basis set. 2. The ΔEsol (AN) and the ΔEadd (A)
The lithium secondary battery according to claim 1, wherein ΔEsol (AN) −ΔEadd (AN), which is the difference from N), is 0.1 eV or more and 4 eV or less. 3. The additive α is a Lewis acid.
Or the lithium secondary battery according to 2. 4. The lithium secondary battery according to claim 1, wherein the additive α is a sulfur compound having one or more double bonds of sulfur and oxygen. 5. The lithium secondary battery according to claim 4, wherein the sulfur compound is represented by the following general formula (1). [Chemical 1] In (the above general formula (1), R ¹ and R ² each independently represents X ^1, or O-X ^1, X ¹ is 1-9 carbon atoms
Represents a chain or cyclic saturated hydrocarbon group, a chain or cyclic unsaturated hydrocarbon group having 1 to 9 carbon atoms, or an aromatic hydrocarbon group having 6 to 9 carbon atoms, wherein R ¹ and R ² Are connected to each other,
It may form a 5- or 6-membered ring containing a sulfur atom. ) 6. The lithium secondary battery according to claim 4, wherein the sulfur compound is represented by the following general formula (2). [Chemical 2] In (the general formula (2), the R ³ and R ⁴ each independently represent X ^2, or O-X ^2, X ² is 1 to 9 carbon atoms
Represents a chain or cyclic saturated hydrocarbon group, a chain or cyclic unsaturated hydrocarbon group having 1 to 9 carbon atoms, or an aromatic hydrocarbon group having 6 to 9 carbon atoms, and R ³ and R ⁴ Are connected to each other,
It may form a 5- or 6-membered ring containing a sulfur atom. ) 7. The sulfur compound is diethyl sulfoxide, diphenyl sulfoxide, tetramethylene sulfoxide, methyl methanesulfinate, ethyl ethanesulfinate, dimethylsulfite, diethylsulfite, 1,2-propyleneglycolsulfite, 1,
3-butylene glycol sulfite, diphenyl sulfite, ethylene sulfite, vinylene sulfite, dimethyl sulfone, diethyl sulfone, ethylmethyl sulfone, diphenyl sulfone, dibenzyl sulfone, sulfolane, 3-methylsulfolane, 3-methylsulfolene, methane Methyl sulfonate, ethyl methane sulfonate, acetyl methane sulfonate, tetrahydrofurfuryl methane sulfonate, methyl ethane sulfonate, ethyl ethane sulfonate, methyl propane sulfonate, methyl benzene sulfonate, 1,3-propane sultone,
At least selected from the group consisting of 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, ethyl methyl sulfate, methylphenyl sulfate, ethylene glycol sulfate, 1,3-propanediol sulfate, and 1,4-butanediol sulfate. It is one.
7. The lithium secondary battery according to any one of 1 to 6. 8. The lithium secondary battery according to claim 4, wherein the sulfur compound is contained in the electrolyte. 9. The lithium secondary battery according to claim 4, wherein the sulfur compound is contained in an amount of 0.001 part by weight or more and 30 parts by weight or less based on the total amount of the solute and the non-aqueous solvent. Next battery. 10. The lithium secondary battery according to claim 1, wherein the positive electrode contains a lithium nickel composite oxide. 11. The lithium secondary battery according to claim 10, wherein the lithium nickel composite oxide is represented by the following general formula (3). Embedded image Li _a Ni _X Co _Y Al _Z O ₂ (3) (In the general formula (I), a, X, Y, and Z are each 0 ≦.
a ≦ 1.1, 0.5 ≦ X ≦ 1, 0 ≦ Y ≦ 0.5, 0 ≦ Z
The numbers satisfy ≦ 0.1 and 0.9 ≦ X + Y + Z ≦ 1.1. ) 12. The lithium secondary battery according to claim 10, wherein the specific surface area of the lithium nickel composite oxide is in the range of 0.01 to 10 m ² / g. 13. The lithium secondary battery according to claim 1, wherein the positive electrode contains an organic acid and / or a lithium salt of an organic acid. 14. The lithium secondary battery according to claim 13, wherein the organic acid is a divalent or higher valent organic acid. 15. The lithium secondary battery according to claim 13, wherein the lithium salt of the organic acid is a lithium salt of a divalent or higher valent organic acid. 16. The positive electrode is formed by forming a positive electrode material layer on a current collector, and the organic acid and / or the lithium salt of the organic acid is
The content of 0.1 wt% or more and 1 wt% or less based on the total weight of the positive electrode material layer excluding the weight of the organic acid and / or the lithium salt of the organic acid.
16. The lithium secondary battery according to any one of 3 to 15. 17. The lithium secondary battery according to claim 1, wherein the electrolyte further contains a polymer. 18. The lithium secondary battery according to claim 17, wherein the polymer is a crosslinkable polymer. 19. The lithium secondary battery according to claim 18, wherein the crosslinkable polymer is an acrylic polymer. 20. The lithium secondary battery according to claim 1, wherein the shape-variable case is made of a laminate film provided with a gas barrier layer and a resin layer.