JPH11339851A - Nonaqueous electrolyte and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve charge/discharge characteristic from a low temperature to normal temperature by allowing a nonaqueous solvent contain a vinylene carbonate derivative or the like expressed by a prescribed formula, and setting the ratio of the vinylene carbonate in the nonaqueous solvent to be within a specified volume range. SOLUTION: This nonaqueous solvent contains at least a vinylene carbonate derivative expressed by formula I (R<1> , R<2> , a hydrogen atom or a 1-3C alkyl group are the same or different), one kind of cyclic carbonate selected from propylene carbonate, ethylene carbonate and butylene carbonate or a mixture of them, and an ester derivative expressed by formula II (R<3> indicates a hydrogen atom and the alkyl group, methoxy group, ethoxy group or propoxy group having 1-3C, and R<4> indicates the alkyl group of 1-4C). The ratio of the vinyl carbonate in the nonaqueous solvent is set within the range of 0.1-4 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte having excellent battery charge / discharge performance at low to normal temperatures, and the non-aqueous electrolyte And a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art Conventionally, as a general secondary battery, a nickel cadmium battery or a lead battery using an aqueous electrolyte has been widely used. However, camera-integrated VTRs, mobile phones, laptop computers, etc.
As new portable electronic devices appear one after another in recent years, in order to further reduce the size and weight of these electronic devices, there is a demand for a higher energy density of a secondary battery which is a portable power source. Conventionally used nickel cadmium batteries and lead batteries have insufficient energy density for these applications, and cadmium and lead are not preferable from the viewpoint of environmental protection, and legally regulate cadmium and lead. Since some countries have begun, the development of secondary batteries using alternative materials is desired.

In recent years, as such a secondary battery, a battery using carbon for the negative electrode and a lithium-cobalt composite oxide for the positive electrode has been developed, and has rapidly spread as a lithium ion battery.

[0004] As a carbon material used as a negative electrode,
It is roughly classified into what is called a graphitic carbon material and an amorphous carbon material. Graphite carbon material has a (002) plane spacing,
It is made of carbon having good crystallinity of 0.340 nm or less, and the amorphous carbon material has a (002) plane spacing.
It exceeds 0.340 nm. Among the above carbon materials, a lithium ion battery using a graphitic carbon material is:
Since the change in charge / discharge voltage is small and the specific gravity is large, there are advantages such as a large discharge capacity per volume.

In order to exchange lithium ions between a positive electrode and a negative electrode, such a lithium ion battery has
Electrolyte is used. In a lithium ion battery, a non-aqueous electrolyte composed of a non-aqueous solvent and an electrolyte is usually used because an electrode has a high potential and an electrolytic solution using water as a solvent is electrolyzed.

As such a non-aqueous electrolyte, propylene carbonate, γ-butyrolactone, sulfolane, or dimethyl carbonate, which is a low-viscosity organic solvent, is used as a non-aqueous solvent. Diethyl carbonate, dimethoxyethane, tetrahydrofuran, 1,3-dioxolan, and the like have been used. As the electrolyte, LiPF ₆ , LiBF ₄ , LiClO ₄ , L
iN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (S
O ₂ CF ₂ CF ₃ ) ₂ and LiN (SO ₃ CH ₂ CF ₃ ) ₂ are used.

For example, in a lithium ion battery using an amorphous carbon material for a negative electrode, a lithium ion battery obtained by dissolving LiPF ₆ or LiBF ₄ in a mixed solvent of propylene carbonate as a cyclic carbonate and diethyl carbonate as a chain ester is used. I have. In a lithium ion battery using a graphite carbon material for the negative electrode, since the electrolyte is easily decomposed on the negative electrode, a non-aqueous electrolyte containing ethylene carbonate is used to suppress the decomposition of the electrolyte on the negative electrode. ing.

By the way, such a lithium ion battery is small and lightweight, and has excellent cycle characteristics. Therefore, such a lithium ion battery is mounted on portable electronic devices such as a camera-integrated VTR, a mobile phone, a laptop computer, etc., and is in demand. It is stretched. However, as the applications of these devices are expanded and their functions are advanced, power consumption is increased, long-term use is desired, and use in various environments is also desired. For this reason, there is a demand for a battery having a higher capacity and an excellent charge / discharge characteristic under a high load in a wide temperature range from a low temperature to a normal temperature.

As an attempt to improve the discharge characteristics of a lithium ion battery depending on the type of the non-aqueous electrolyte, a conventionally used diethyl carbonate is replaced with dimethyl carbonate to improve the conductivity of the electrolyte (JP-A-5-21).
However, dimethyl carbonate has a problem that the freezing point is as high as 3 ° C. and the electrolytic solution solidifies at a low temperature. Also, in batteries using a graphite carbon material for the negative electrode, in an attempt to improve the charge / discharge characteristics at low temperatures, part of ethylene carbonate in which the electrolyte easily solidifies at low temperatures was replaced with propylene carbonate, which hardly solidifies at low temperatures. It has been proposed to replace (Japanese Patent Laid-Open No. 6-84)
542). However, in this method, decomposition on the negative electrode is likely to occur, and the ratio of propylene carbonate in the nonaqueous solvent is 50% by volume or less based on the total amount of cyclic carbonate (ethylene carbonate, propylene carbonate, etc.). For this reason, the effect of suppressing the solidification of the non-aqueous electrolyte at a low temperature was not always sufficient. There is also an attempt to replace ethylene carbonate in a non-aqueous solvent with vinylene carbonate (see JP-A-7-122296 and JP-A-8-96852), but the amount of vinylene carbonate added is 5% by volume.
As described above, or at least 20% by volume, and the freezing point of vinylene carbonate is 22 ° C., the effect of suppressing the freezing of the non-aqueous electrolyte was not satisfactory.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object a non-aqueous electrolyte having excellent charge / discharge characteristics at low to normal temperatures, and a non-aqueous electrolyte secondary using the non-aqueous electrolyte. It is intended to provide a battery.

[0011]

The non-aqueous electrolyte according to the present invention is a non-aqueous electrolyte obtained by dissolving an electrolyte containing Li in a non-aqueous solvent, wherein the non-aqueous solvent contains at least [A] A vinylene carbonate derivative represented by [1], [B] a cyclic carbonate selected from propylene carbonate, ethylene carbonate, and butylene carbonate or a mixture thereof, and [C] an ester represented by the following general formula [2] And a ratio of the vinylene carbonate in the non-aqueous solvent is in the range of 0.1 to 4% by volume.

[0012]

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(Wherein R ¹ and R ² may be the same or different from each other, and represent a hydrogen atom or a carbon atom
3 represents an alkyl group. )

[0014]

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(Wherein R ³ is a hydrogen atom, having 1 to 3 carbon atoms)
Represents an alkyl group, a methoxy group, an ethoxy group, a propoxy group, or an isopropoxy group, and R ⁴ represents an alkyl group having 1 to 4 carbon atoms. A) vinylene carbonate derivative in the non-aqueous solvent, [B]
The ratio of the cyclic carbonate and the [C] ester derivative is [A] vinylene carbonate derivative: 0.1 to 4% by volume, [B] cyclic carbonate: 5 to 45% by volume, and [C] ester derivative: 51 to 94. It is preferably 9% by volume (however, the total of [A] to [C] is 100% by volume).

In the present invention, the [B] cyclic carbonate is ethylene carbonate, propylene carbonate or a mixture thereof, and the [C] ester derivative is dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, Preferably, it is dipropyl carbonate, diisopropyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate or a mixture thereof.

In the present invention, in particular, the [B] cyclic carbonate is a mixture of propylene carbonate and ethylene carbonate, and the content of ethylene carbonate in the mixture is preferably 75% by volume or less.

The non-aqueous electrolyte secondary battery according to the present invention comprises the above-mentioned non-aqueous electrolyte, a negative electrode using a carbon material capable of doping and undoping lithium ions as a negative electrode active material, and a positive electrode. Features.

As the negative electrode active material, a carbon material having a (002) plane spacing of 0.340 nm or less is preferable.

[0020]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the non-aqueous electrolyte according to the present invention,
The non-aqueous electrolyte secondary battery will be specifically described.

[Non-Aqueous Electrolyte] The non-aqueous electrolyte according to the present invention comprises [A] a specific vinylene carbonate derivative and [B] a cyclic carbonate selected from propylene carbonate, ethylene carbonate and butylene carbonate. [C] An electrolyte containing Li is dissolved in a non-aqueous solvent containing a specific ester derivative.

Vinylene carbonate derivative [A] As the vinylene carbonate derivative used in the present invention, those represented by the following general formula [1] are used.

[0023]

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(Wherein R ¹ and R ² may be the same or different from each other, and represent a hydrogen atom or a carbon atom
3 represents an alkyl group. Specific examples of such vinylene carbonate derivatives include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethylvinylene carbonate, 4,5-diethylvinylene carbonate,
Examples thereof include 4,5-dipropylvinylene carbonate, 4-ethyl-5-methylvinylene carbonate, 4-ethyl-5-propylvinylenecarbonate, and 4-methyl-5-propylvinylene carbonate.

The mechanism of such a vinylene carbonate derivative is unknown, but even if a small amount is added to the electrolyte,
It has an effect of suppressing a decrease in the initial charge / discharge efficiency of lithium ions to the negative electrode graphitic carbon material, which is considered to be caused by decomposition of the electrolytic solution on the graphitic carbon material. For this reason, when such a vinylene carbonate derivative is used as a non-aqueous solvent, the amount of ethylene carbonate used in a non-aqueous electrolyte, which is usually essential for a battery using a graphitic carbon material as a negative electrode, is greatly reduced. Alternatively, the use of ethylene carbonate as a non-aqueous solvent can be eliminated. Therefore, by using the vinylene carbonate derivative as the non-aqueous solvent, the solidification of the electrolyte at a low temperature can be suppressed, and the charge and discharge characteristics of the battery at a low temperature can be improved.

Cyclic Carbonate [B] The non-aqueous electrolyte according to the present invention contains cyclic carbonate [B] in addition to the above vinylene carbonate derivative.

As the cyclic carbonate [B], one of cyclic carbonates selected from propylene carbonate, ethylene carbonate and butylene carbonate or a mixture thereof is used. Particularly, as the cyclic carbonate, propylene carbonate and ethylene carbonate are preferred from the viewpoint of the effect of dissociation of the electrolyte, and a mixture thereof is particularly preferred.

By including such a cyclic carbonate [B] in the non-aqueous solvent, it is possible to increase the dissociation of the electrolyte described later. Ester Derivative [C] In the present invention, one selected from a chain ester or a chain carbonate derivative represented by the following formula [2] or a mixture thereof is used as the ester derivative [C].

[0029]

Embedded image

(Wherein R ³ is a hydrogen atom, carbon number 1 to 3)
Represents an alkyl group, a methoxy group, an ethoxy group, a propoxy group, or an isopropoxy group, and R ⁴ represents an alkyl group having 1 to 4 carbon atoms. Examples of the chain ester or chain carbonate derivative represented by the general formula [2] include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, diisopropyl carbonate, Ethyl propyl carbonate, ethyl isopropyl carbonate, methyl formate, ethyl formate,
Examples include methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate.

By including such a chain ester or chain carbonate derivative in a non-aqueous solvent, the viscosity of the electrolyte can be reduced. Among the above chain ester or chain carbonate derivatives, particularly from the stability to the negative electrode, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, diisopropyl carbonate, ethyl propyl carbonate, Ethyl isopropyl carbonate is desirably used.

In the present invention, since the cyclic carbonate [B] and the ester derivative [C] are contained together with the vinylene carbonate derivative [A], the conductivity of the electrolytic solution is improved and the charge / discharge characteristics of the battery are improved. Can be done.

Solvent Composition of Nonaqueous Solvent In the nonaqueous electrolyte according to the present invention, the above [A] vinylene carbonate derivative, [B] cyclic carbonate, and [C]
A non-aqueous solvent containing an ester derivative is used.

[A] The vinylene carbonate derivative is contained in a nonaqueous solvent in an amount of 0.1 to 4% by volume, preferably 0.1 to 3% by volume, more preferably 0.5 to 2% by volume. Desirably, it is contained in an amount. In such a range,
[A] When the vinylene carbonate derivative is contained, it is possible to sufficiently suppress the decomposition of the electrolytic solution on the negative electrode such as a graphitic carbon material, and the stability and storage stability of the nonaqueous electrolytic solution are also excellent. .

The mixing ratio of the [B] cyclic carbonate in the non-aqueous solvent is determined by the balance between the promotion of dissociation of the electrolyte and the increase in the viscosity of the electrolyte. To increase the dissociation of the electrolyte,
The higher the mixing ratio of [B] the cyclic carbonate, the better, but the viscosity of the non-aqueous electrolyte may increase because the viscosity of the [B] cyclic carbonate is high.

Therefore, the volume ratio of the cyclic carbonate [B] in the non-aqueous solvent is 5 to 45% by volume, preferably 8 to 40% when the total of [A] to [C] is 100% by volume. It is desirable that the amount be in the range of 10% to 30% by volume. When the [B] cyclic carbonate is contained in the non-aqueous solvent in such a range, the dissociation of the electrolyte can be sufficiently increased, and the increase in the viscosity of the non-aqueous electrolyte can be suppressed. In addition, when ethylene carbonate and another cyclic carbonate are used as a mixture of [B] cyclic carbonate, the ethylene carbonate has a high freezing point of 39 ° C. and is easily solidified at a low temperature, so that the charge and discharge characteristics at a low temperature are improved. It is desirable that the content be low. On the other hand, since ethylene carbonate has a large effect of increasing the dissociation of the electrolyte, it is desirable that the content thereof is large in order to improve the conductivity of the electrolyte at room temperature. For this reason, it is desirable that ethylene carbonate is contained in an amount of 75% by volume or less, preferably 50% by volume or less, more preferably 30% by volume or less based on the total amount of the cyclic carbonate [B]. When ethylene carbonate is contained in the cyclic carbonate at this ratio, coagulation of the electrolytic solution at a low temperature can be suppressed, and the dissociation of the electrolyte can be increased.

Further, the volume ratio of the entire solvent of [B] cyclic carbonate other than ethylene carbonate is determined by the degree of the effect of the vinylene carbonate derivative on the decomposition of the electrolytic solution on the negative electrode (hereinafter referred to as the effect of vinylene carbonate). I can decide. The effect of vinylene carbonate is [B]
The larger the volume ratio of the cyclic carbonate in the non-aqueous solvent, and the lower the crystallinity of the carbon material of the negative electrode of the applied battery, the larger the value. For this reason, the volume ratio of the [B] cyclic carbonate in the non-aqueous solvent is 4 when the spacing of the (002) plane, which is an index of crystallinity of carbon, is 0.337 nm or more.
It is preferably 5% by volume or less, and when the spacing of the (002) plane is 0.337 nm or less, it is preferably 40% by volume or less, more preferably 30% by volume or less.
When the [B] cyclic carbonate is contained in the non-aqueous solvent in such a range, the decomposition of the electrolytic solution on the negative electrode is more sufficiently suppressed.

The mixing ratio of the [C] ester derivative in the non-aqueous solvent is determined according to the viscosity of the non-aqueous electrolyte used. Therefore, the volume ratio of the [C] ester derivative in the non-aqueous solvent is 51% when the total of [A] to [C] is 100% by volume.
It is desirable that the content be 94.9% by volume, preferably 55-90% by volume, and more preferably 60-85% by volume.
When the [C] ester derivative is contained in the non-aqueous solvent at such a ratio, the viscosity of the non-aqueous electrolyte can be sufficiently reduced. It is preferable to use a mixture of dimethyl carbonate and another ester derivative as the [C] ester derivative. In this case, dimethyl carbonate accounts for 60% by volume or less, preferably 50% by volume, based on the entire non-aqueous solvent. It is preferable that the content is not more than 40% by volume, more preferably not more than 40% by volume. With this ratio, solidification of the non-aqueous electrolyte at a low temperature can be suppressed.

By setting the mixing ratio of [A] to [C] in the non-aqueous solvent to the above ratio, the dissociation of the electrolyte in the non-aqueous electrolyte can be increased, and the viscosity can be further reduced. .
For this reason, the movement of lithium ions in the non-aqueous electrolyte is likely to occur, and the charge and discharge characteristics of the battery are improved.

In the present invention, the above-mentioned non-aqueous solvent may be used.
In addition to the solvents [A] to [C], chain ethers such as dimethoxyethane, methoxyethoxyethane, diethoxyethane, and diethyl ether used as nonaqueous solvents, cyclic ethers such as tetrahydrofuran, dioxolan, and dioxane, and dimethyl Amides such as formamide, chain carbamates such as methyl-N, N-dimethylcarbamate, cyclic esters such as γ-butyrolactone, cyclic sulfones such as sulfolane, cyclic carbamates such as N-methyloxazolidinone, N Cyclic amides such as -methylpyrrolidone, and cyclic ureas such as N, N-dimethylimidazolidone can be appropriately added within a range that does not affect the effects of the present invention.

When ethylene carbonate and dimethyl carbonate are used together with the above-mentioned vinylene carbonate derivative as the non-aqueous solvent, the ratio of ethylene carbonate to dimethyl carbonate, the volume ratio of ethylene carbonate to X, and the volume ratio of dimethyl carbonate to Y,
When the volume ratio of the other solvents including the vinylene carbonate derivative is Z and X + Y + Z = 1, 0.35−X ≦ 0.60Z 0 <X <0.35, 0 <Y, Z By doing so, solidification of the electrolytic solution can be particularly suppressed. Furthermore, it is desirable to have a solvent composition represented by 0.3 ≦ X / (X + Y) ≦ 0.4.

Electrolyte In the non-aqueous electrolyte according to the present invention, an electrolyte containing Li is dissolved in the non-aqueous solvent. Examples of the electrolyte containing Li include LiPF ₆ , LiBF ₄ , and LiCl.
O ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO
₂ CF ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CH
_And lithium salts such as ₂ CF ₃ ) ₂ . These lithium salts may be used alone or as a mixture of two or more lithium salts. Of these lithium salts, L
iPF ₆ and LiBF ₄ are preferably used.

The electrolyte containing Li is 0.1 to 0.1%.
It is desirable that it is contained in the non-aqueous electrolyte in a range of 3 mol / l, preferably 0.5 to 2 mol / l. [Non-aqueous electrolyte secondary battery] The non-aqueous electrolyte secondary battery according to the present invention includes a negative electrode including a carbon material capable of doping / dedoping lithium ions as a negative electrode active material, a positive electrode active material, And a water electrolyte.

Such a non-aqueous electrolyte secondary battery can be applied to, for example, a cylindrical non-aqueous electrolyte secondary battery. As shown in FIG. 1, a cylindrical nonaqueous electrolyte secondary battery has a negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound through a separator 3 into which a non-aqueous electrolyte is injected, and is housed in a battery can 5 with an insulating plate 4 placed above and below the wound body. A battery lid 7 is attached to the battery can 5 by caulking via a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. It is configured to function as. The separator is a porous film.

In this battery, the positive electrode lead 12 may be electrically connected to the battery lid 7 via the current interrupting thin plate 8. In such a battery, when the pressure inside the battery rises, the current interrupting thin plate 8 is pushed up and deformed, and the positive electrode lead 12 is cut leaving a portion welded to the thin plate 8 so that the current is interrupted. Has become.

As the positive electrode active material constituting the positive electrode 2, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ ,
LiNi _x Co _1-x O ₂ lithium and a composite oxide comprising a transition metal such _{as, MoS 2, V 2 O 5} , TiO 2, transition metal oxides such as MnO ₂ or a transition metal sulfide, polyaniline - disulfide compound For example, a conductive polymer such as Among them, a composite oxide composed of lithium and a transition metal is particularly preferable.

As the negative electrode active material constituting the negative electrode 1, a carbon material capable of doping / dedoping lithium ions is used. Graphite carbon materials and amorphous carbon materials are roughly used as such carbon materials. The graphitic carbon material is composed of highly crystalline carbon having a (002) plane spacing of 0.340 nm or less, and the amorphous carbon material has a (002) plane spacing of more than 0.340 nm. A thing.

In the negative electrode made of any of the above carbon materials, the effect of suppressing the decomposition of the nonaqueous electrolyte on the negative electrode by using the nonaqueous electrolyte of the present invention is exhibited. In particular, a graphitic carbon material is preferably used because the effect of suppressing the decomposition of the non-aqueous electrolyte increases. Graphite negative electrode materials, other than natural graphite, mesophase carbon fibers, mesophase carbon microbeads, and other various carbon-containing substrates fired at 2000 ° C or higher,
Examples include pyrolytic graphite. Generally, the crystallinity of a carbon material tends to improve as the temperature of the heat treatment increases,
Since the electrolytic solution of the present invention is particularly effective with a carbon material having high crystallinity, the firing temperature of the nonaqueous electrolyte secondary battery of the present invention is desirably 2800 ° C. or higher. The crystallinity of the carbon material is represented by the distance between the (002) planes of the carbon material obtained from X-ray diffraction. It is desirable that the spacing between the (002) planes is 0.340 nm or less, preferably 0.338 nm or less, and more preferably 0.337 nm or less.

The non-aqueous electrolyte secondary battery according to the present invention includes the above-described non-aqueous electrolyte and a negative electrode material. The shape and form of the battery are not limited to those shown in FIG. It may be a coin type as shown in FIG. 2, a sheet type, a square type, or the like.

In the coin type non-aqueous electrolyte secondary battery shown in FIG.
The disc-shaped negative electrode 13, the disc-shaped positive electrode 14, the separator 15, the stainless steel plate 18, and the flat spring 19 form the negative electrode 13,
The separator 15, the positive electrode 14, the stainless steel plate 18, and the flat spring 19 are stacked in this order and housed in the battery can 16, and the battery can (lid) 17 is attached by caulking via the gasket 20. As the negative electrode 13, the separator 15, and the positive electrode 14, the same as those described above are used. The battery can 16 and the battery can (lid) 17 are made of a material such as stainless steel which is hardly corroded by the electrolytic solution.

[0051]

According to the present invention, a non-aqueous electrolyte having excellent charge / discharge characteristics from a low temperature to a normal temperature can be obtained by containing a vinylene carbonate derivative and having a specific solvent composition. In addition, by using a negative electrode positive carbon material having a specific structure and the above-mentioned electrolyte, a non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics from room temperature to low temperature can be obtained.

[0052]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples.

[0053]

Examples 1 to 10 and Comparative Examples 1 to 6 <Preparation of Nonaqueous Electrolyte> 15.2 g (100 mmol) of LiPF _{6 was} added at 25 ° C. in Table 1
Dissolved in a mixed solvent having a predetermined volume ratio shown in
100 ml of a non-aqueous electrolyte having an F ₆ concentration of 1 mol / l was prepared.

[0054]

[Table 1]

<Preparation of Negative Electrode> As a graphitic carbon material, M
CMB (Osaka Gas, 6-28B) was used. 90 parts by weight of this carbon material powder and polyvinylidene fluoride (PV
DF) was mixed with 10 parts by weight and dispersed in N-methylpyrrolidone as a solvent to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to a 10-μm-thick negative electrode current collector made of a strip-shaped copper foil, dried, and then compression-molded to obtain a diameter of 1 μm.
It was punched out to 6 mm to obtain a coin-shaped negative electrode 13. The thickness of such a carbon electrode mixture was 80 μm.

<Production of Positive Electrode> The positive electrode 14 was produced as follows. A positive electrode mixture was prepared by mixing 90 parts by weight of LiCoO ₂ (HLC-21, Honjo Chemical), 6 parts by weight of graphite as a conductive agent, 1 part by weight of acetylene black, and 3 parts by weight of polyvinylidene fluoride as a binder. And N-methylpyrrolidone to prepare a positive electrode mixture slurry.

This slurry was applied to a 20 μm-thick aluminum foil positive electrode current collector, dried, compression molded, and punched into a 15 mm diameter to obtain a coin-shaped positive electrode 14. The thickness of such a positive electrode mixture was 70 μm.

<Preparation of Battery> The coin-shaped negative electrode 13, coin-shaped positive electrode 14 and separator 1 thus obtained were obtained.
5 was stacked in the order of a negative electrode, a separator, and a positive electrode, and stored in a coin-type battery.

After the nonaqueous electrolyte having the solvent composition shown in Table 1 was immersed in the separator, a spacer 18 and a spring 19 were placed on the positive electrode 14, and the battery lid 17 was closed via a gasket 16. By squeezing, a coin-type lithium ion secondary battery was produced.

<Evaluation of Charge / Discharge Efficiency> The charge / discharge test was performed on the manufactured coin battery at 25 ° C. The charging was performed at 1 mA until the battery voltage reached 4.1 V, and thereafter, the current was reduced so that the battery voltage became 4.1 V, and the charging was terminated when the current value reached 0.05 mA.

Discharging is performed at 1 mA until the battery voltage reaches 2.75 V. Thereafter, the current is reduced so that the battery voltage becomes 2.75 V, and the discharge ends when the current value reaches 0.05 mA. did.

The charge / discharge efficiency is a ratio of the number of discharged coulombs to the number of charged coulombs. In FIG.
The amount of vinylene carbonate added in the non-aqueous solvent is 0.2
The first cycle of the battery at volume% (Examples 1, 3, 5, 7, 9), 1 volume% (Examples 2, 4, 6, 8, 10), and 0 volume% (Comparative Examples 1 to 6) FIG. 3 is a diagram plotting the charge / discharge efficiency of EC with respect to the ratio of EC to PC.

When the content of vinylene carbonate was 0.2% by volume, the charge / discharge efficiency in the first cycle was improved even when the content of EC was small. In addition, 1 volume% of vinylene carbonate
When it contained, even if it did not contain EC, the charge / discharge efficiency in the first cycle was hardly reduced. In particular, EC
When the ratio of EC to the total of PC and PC became 75% or less, the effect of suppressing a decrease in charge / discharge efficiency due to the addition of vinylene carbonate was remarkable.

[0064]

Examples 11 to 17 <Preparation of non-aqueous electrolyte> LiPF ₆
15.2 g (100 mmol) was dissolved in a mixed solvent at a predetermined ratio shown in Table 2 at 25 ° C. to prepare 100 ml of a non-aqueous electrolyte having a LiPF ₆ concentration of 1 mol / l.

<Preparation of Negative Electrode> As a graphitic carbon material, natural graphite (CHUETSU GRAPHITE WORKS CO., LTD, LF-18A) and MCMB (Osaka Gas, 6-28B) were used. Parts by weight and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidone as a solvent to prepare a negative electrode mixture slurry.
This negative electrode mixture slurry was applied to a 10-μm thick negative electrode current collector made of a strip-shaped copper foil, dried, compression-molded, and punched into a diameter of 16 mm to obtain a coin-shaped negative electrode 13. The thickness of such a carbon electrode mixture was 80 μm.

<Evaluation of Charge / Discharge Efficiency> A coin battery was prepared using a combination of a negative electrode and a non-aqueous electrolyte as shown in Table 2.
A charge / discharge test was performed at 25 ° C.

[0067]

[Table 2]

FIG. 4 shows the charge / discharge efficiency of the first cycle of the battery using the negative electrode made of natural graphite (Examples 11 to 13) and the battery using the negative electrode made of MCMB (Examples 14 to 17). FIG.

In the case of a negative electrode prepared from MCMB having a (002) plane spacing of 0.337 nm or more, a decrease in charge / discharge efficiency in the first cycle was hardly observed when the proportion of cyclic carbonate was 45 vol% or less. . Also, (00
2) In the case of a negative electrode made of natural graphite having a plane spacing of 0.337 nm or less, the ratio of cyclic carbonate is 40%.
At less than 30% by volume, the charge / discharge efficiency was significantly improved. At 30% by volume or less, little decrease in charge / discharge efficiency was observed, and the effect of suppressing the decrease in charge / discharge efficiency due to the addition of the vinylene carbonate derivative was significant.

[0070]

Examples 18 to 31 and Comparative Examples 7 to 12 <Preparation of non-aqueous electrolyte> 15.2 g (100 mmol) of LiPF _{6 was} added at 25 ° C.
Dissolved in a predetermined ratio of the mixed solvent shown in Table 3
100 ml of a non-aqueous electrolyte having an F ₆ concentration of 1 mol / l was prepared.

<Evaluation of Charge / Discharge Characteristics> Using the obtained non-aqueous electrolyte, a coin battery was prepared in the same manner as in Example 1, and
The following charge / discharge characteristics were evaluated. 1. Charging / discharging characteristics at normal temperature In the charging / discharging characteristics at normal temperature, the battery was charged at a constant current of 4 mA until the voltage of the battery reached 4.2 V, and then 4.2
The battery was charged by maintaining the voltage at V. The total charging time at this time was 150 minutes.

Next, the charged lithium ion battery was discharged at room temperature (25 ° C.) at a constant current of 4 mA or 8 mA until the battery voltage reached 2.75 V, and the discharge capacity at room temperature was measured. 2. Low-temperature charge / discharge characteristics The low-temperature discharge test was performed as follows. First,
The battery was charged at a constant current of 4 mA at 25 ° C. until the voltage of the battery reached 4.1 V, and then charged by holding the battery at 4.1 V. The total charging time at this time was 150 minutes.

Next, the charged lithium ion battery is
After cooling to 20 ° C., at a current of 4 mA or 2 mA, 2.
The battery was discharged to 75 V, and the discharge capacity at a low temperature was measured. Table 3 shows the results.

[0074]

[Table 3]

From Examples 18 to 27, it was found that the electrolytic solution to which vinylene carbonate was added had improved discharge capacity and low-temperature characteristics. Further, according to Example 30, EC and DMC were used.
It has been found that the load characteristics and the low-temperature characteristics can be improved by setting the ratio to a specific ratio.

[0076]

Examples 32 and 33, Comparative Examples 13 and 14 <Preparation of non-aqueous electrolyte> 15.2 g (100 mmol) of LiPF _{6 was} added at 25 ° C.
Then, dissolved in a mixed solvent in a predetermined ratio shown in Table 3,
100 ml of a non-aqueous electrolyte having an iPF ₆ concentration of 1 mol / l was prepared.

[0077]

[Table 4]

<Storage stability test of non-aqueous electrolyte> The non-aqueous electrolyte prepared above was stored at 80 ° C. for 24 hours and 48 hours, and the coloring of the non-aqueous electrolyte was evaluated.

FIG. 5 shows that the amount of vinylene carbonate added was 1% by volume (Example 32) and 3% by volume (Example 3).
3) 5% by volume (Comparative Example 13), 0% by volume (Comparative Example 1)
The figure which plotted coloring of the nonaqueous electrolyte in 4) is shown.

The amount of vinylene carbonate added was 5% by volume.
The non-aqueous electrolyte containing 1% by volume and 3% by volume of vinylene carbonate has less coloring and excellent storage stability as compared with the non-aqueous electrolyte of No.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a cylindrical battery showing one embodiment of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a schematic sectional view of a coin-type battery showing one embodiment of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 3 is a diagram showing first cycle charge and discharge efficiencies in Examples 1 to 10 and Comparative Examples 1 to 6.

FIG. 4 is a diagram showing first cycle charge / discharge efficiency in Examples 11 to 17;

FIG. 5 is a diagram showing storage stability of non-aqueous electrolyte solutions in Examples 32 and 33 and Comparative Examples 13 and 14.

[Explanation of symbols]

 1, 13 ... negative electrode 2, 14 ... positive electrode 3, 15 ... separator 4: insulating plate 5, 16 ... battery can 6, 20 ... gasket 7, 17 ··· Battery cover 8 ··· Thin plate for current interruption 9 ··· Negative electrode current collector 10 ··· Positive electrode current collector 11 ··· Negative electrode lead 12 ··· Positive electrode lead 18 · ... Stainless steel plate 19

Claims (6)

[Claims] 1. A non-aqueous electrolyte obtained by dissolving an electrolyte containing Li in a non-aqueous solvent, wherein the non-aqueous solvent comprises at least [A] a vinylene carbonate derivative represented by the following general formula [1]: And [B] propylene carbonate, ethylene carbonate,
A cyclic carbonate selected from butylene carbonate or a mixture thereof, and [C] an ester derivative represented by the following general formula [2], and the ratio of the vinylene carbonate in a nonaqueous solvent is 0.1 to 0.1; A non-aqueous electrolyte characterized by being in the range of 4% by volume. Embedded image (In the formula, R ¹ and R ² may be the same or different, and represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.) (In the formula, R ³ represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a methoxy group, an ethoxy group, a propoxy group, or an isopropoxy group, and R ⁴ represents an alkyl group having 1 to 4 carbon atoms. ) 2. The ratio of [A] vinylene carbonate derivative, [B] cyclic carbonate and [C] ester derivative in the non-aqueous solvent is as follows: [A] vinylene carbonate derivative: 0.1 to 4% by volume, B] cyclic carbonate: 5 to 45% by volume, [C] ester derivative: 51 to 94.9% by volume (provided that the total of [A] to [C] is 100% by volume) The non-aqueous electrolyte according to claim 1. 3. The [B] cyclic carbonate is ethylene carbonate, propylene carbonate or a mixture thereof, and the [C] ester derivative is dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate,
3. The non-aqueous electrolyte according to claim 1, which is dipropyl carbonate, diisopropyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate or a mixture thereof. 4. The cyclic carbonate [B] is a mixture of propylene carbonate and ethylene carbonate, and the content of ethylene carbonate in the mixture is 75%.
The non-aqueous electrolyte according to any one of claims 1 to 3, which is not more than a volume. 5. A non-aqueous electrolyte according to claim 1, a negative electrode using a carbon material capable of doping / dedoping lithium ions as a negative electrode active material, and a positive electrode. Non-aqueous electrolyte secondary battery. 6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the negative electrode active material is a carbon material having a (002) plane spacing of 0.340 nm or less.