JP2007095570A - Lithium secondary battery and negative electrode used in that battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of improving by leaps and bounds cycle characteristics by suppressing cut-off of the conductive network in a negative electrode by improving an active material layer of the negative electrode, even if the negative electrode active material is separated from the negative electrode current collector. <P>SOLUTION: The lithium ion secondary battery comprises a negative electrode 2 including a negative electrode active material, a conductive agent, and a binder, a positive electrode 1 including a transition metal compound oxide as a positive electrode active material, and a non-aqueous electrolyte. As the negative electrode active material, an alloy containing Sn having a charging capacity of 1200 mAh/g or less is used, and as the conductive agent, carbon material having a particle size of primary particle of 100 nm or less is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery and a negative electrode used for the battery.

  In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and batteries as drive power sources are required to have higher capacities. A lithium secondary battery that performs charging / discharging by moving lithium ions between the positive and negative electrodes along with charging / discharging has a high energy density and high capacity. As widely used. In the future, with further miniaturization and higher functionality of these mobile information terminals, it is expected that the load on the lithium secondary battery as a power source will increase, and there is a demand for higher energy density of the lithium secondary battery. Will be very expensive.

  Here, to increase the energy density of the battery, it is an effective means to use a material having a larger energy density as the active material, and the use of graphite as a negative electrode material for the lithium secondary battery has been put into practical use. Has been. However, the theoretical capacity of graphite is 372 mAh / g, which is insufficient to sufficiently achieve the high energy density of the battery. Therefore, it is necessary to use lithium metal having a theoretical capacity larger than that of graphite as the negative electrode material. Conceivable. As described above, when lithium metal is used as the negative electrode material of the lithium secondary battery, a high charge / discharge capacity can be obtained. However, since lithium metal is deposited in a dendrite shape on the negative electrode during charging, the battery is short-circuited internally. Has a problem that it is easy to occur.

Therefore, in recent lithium secondary batteries, aluminum, tin, and silicon that occlude lithium by an alloying reaction with lithium have been proposed and studied as negative electrode active materials that can suppress dendrite and have a high energy density. ing.
However, when a material alloyed with lithium is used as the negative electrode active material of the lithium secondary battery, the negative electrode active material expands and contracts during charge and discharge, and the volume changes rapidly. For this reason, with the progress of the charge / discharge cycle, the negative electrode active material was pulverized and had a problem of causing peeling from the negative electrode current collector.

  In consideration of the above, by applying a slurry containing Sn alloy, a binder and a diluting solvent to the surface of the negative electrode current collector and drying, by electroplating a metal having a low lithium compound forming ability, A method for suppressing the separation of the negative electrode active material from the negative electrode current collector has been proposed (see Patent Document 1 below).

  In addition, a mixture of active material particles containing silicon and / or a silicon alloy and a conductive metal powder such as copper is placed on a current collector and then sintered in an inert atmosphere to achieve a fusion effect. Thus, a method has been proposed in which the adhesion between the negative electrode current collector and the negative electrode active material is improved to prevent peeling of the negative electrode active material (see Patent Document 2 below).

JP 2004-241329 A

Japanese Patent Laid-Open No. 2002-260637

  However, when the active material having a large expansion and contraction is used, it is difficult to completely prevent the negative electrode active material from peeling from the negative electrode current collector, even if the above-described conventional invention is used. Once such delamination occurs, the conductive network in the negative electrode is cut, so that there is a problem that the cycle characteristics are greatly deteriorated.

  Therefore, the present invention suppresses the disconnection of the conductive network in the negative electrode by improving the active material layer of the negative electrode, for example, even when the negative electrode active material is separated from the negative electrode current collector. Accordingly, an object of the present invention is to provide a lithium secondary battery capable of dramatically improving cycle characteristics.

  In order to achieve the above object, the invention according to claim 1 of the present invention includes a negative electrode including a negative electrode active material, a conductive agent, and a binder, a positive electrode including a transition metal composite oxide as a positive electrode active material, A lithium ion secondary battery comprising a non-aqueous electrolyte, wherein an alloy containing Sn having a theoretical charge capacity of 1200 mAh / g or less is used as the negative electrode active material, and the particle size of primary particles is used as the conductive agent. Is a carbon material having a thickness of 100 nm or less.

If it is the said structure, even if it is a case where a negative electrode collector and a negative mix layer peel, the electrically conductive network which can collect current between a negative electrode collector and a negative mix layer only with the structural pressure of a battery Thus, it is possible to suppress a decrease in cycle characteristics due to an increase in internal resistance. This is due to the following reason.
That is, in order to construct a conductive network capable of collecting current between the negative electrode current collector and the negative electrode mixture layer only with the constituent pressure of the battery even when the negative electrode current collector and the negative electrode mixture layer are separated. It is necessary to dispose a conductive agent in the negative electrode mixture layer.

However, even if a conductive agent is disposed in the negative electrode mixture layer, it is difficult to form a conductive network in the negative electrode if the negative electrode active material itself has poor conductivity. Therefore, when an alloy containing Sn is used as the negative electrode active material as in the above configuration, the alloy has a conductivity about 10 ⁴ times larger than that of Si (that is, the resistivity is about 10 ⁴ times smaller). The conductivity of the active material itself can be improved, and a conductive network can be formed in the negative electrode.

  Further, even if a conductive agent is arranged in the negative electrode mixture layer and an alloy containing Sn is used as the negative electrode active material, if the primary particle size of the conductive agent is too large, the specific surface area becomes small, It is difficult to form a conductive network in the negative electrode. Therefore, if the particle size of the primary particles of the conductive agent is regulated to 100 nm or less as in the above configuration, the specific surface area of the conductive agent is increased, and the conductive agent is uniformly present on the surface of the alloy containing Sn. Therefore, the effect as a conductive agent is sufficiently exhibited, and an excellent conductive network can be formed in the negative electrode.

  In addition, even if a conductive agent having a primary particle size of 100 nm or less is disposed in the negative electrode mixture layer and an alloy containing Sn is used as the negative electrode active material, the expansion amount of the alloy active material is large, The conductive network may be destroyed by the expansion and contraction that occurs at each charge and discharge. Here, when an alloy containing Sn is used as the negative electrode active material, the theoretical charge capacity and the expansion amount of the negative electrode active material are basically in a proportional relationship. Therefore, if the theoretical charge capacity is regulated to 1200 mAh / g or less, the expansion and contraction that occurs each time charging / discharging is less than the specified amount, so that it is possible to suppress the destruction of the conductive network.

  In this way, even when the negative electrode active material is peeled off from the negative electrode current collector, it is possible to suppress the disconnection of the conductive network in the negative electrode. The decrease can be suppressed.

  In addition, in this specification, an average particle diameter shall mean a median diameter (D50). The theoretical charge capacity refers to the capacity per unit mass until the potential is reduced to 1 mV with respect to Li when Li is occluded in the negative electrode active material.

  Further, the alloy containing Sn includes a solid solution of Sn and one or more other elements, an intermetallic compound of Sn and one or more other elements, and a eutectic of Sn and one or more other elements. An alloy etc. are mentioned. Examples of the method for producing the alloy include an arc melting method, a liquid quenching method, a mechanical alloying method, a sputtering method, a chemical vapor deposition method, and a firing method. In particular, examples of the liquid quenching method include a single roll quenching method, a twin roll quenching method, and various atomizing methods such as a gas atomizing method, a water atomizing method, and a disk atomizing method.

  In addition, the amount of the conductive agent in the present invention is preferably 0.1 to 20% by mass, particularly 1 to 10% by mass with respect to the total mass of the negative electrode mixture layer. Because, if the amount of the conductive agent is too small, the addition effect of the conductive agent cannot be exhibited, while if the amount of the conductive agent is too large, the amount of the negative electrode active material is reduced and the capacity of the battery is reduced. This is because the slurry gels during the production of the negative electrode, and thus the negative electrode cannot be produced smoothly.

The invention according to claim 2 is the invention according to claim 1, wherein the carbon material is amorphous carbon.
If amorphous carbon is used as the carbon material, the amorphous carbon is bulky and has a very large specific surface area. Therefore, the effect of claim 1 can be further exhibited.

The invention described in claim 3 is the invention described in claim 2, characterized in that the amorphous carbon is acetylene black or ketjen black.
The amorphous carbon is exemplified by the above acetylene black, but is not limited thereto, and may be coke or the like.

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the binder is polyvinylidene fluoride.
As described above, when an alloy having large expansion and contraction is used as the negative electrode active material, if the mechanical strength and adhesion of the binder is too high, a large stress is applied to the negative electrode current collector due to the expansion and contraction of the negative electrode active material. May cause wrinkles in the negative electrode current collector, resulting in a decrease in cycle characteristics and an increase in electrode plate thickness. Therefore, among the fluororesins and polyimide resins generally used as the binder for the negative electrode, the negative electrode current collector can be obtained by using polyvinylidene fluoride which has a small burden on the negative electrode current collector and has appropriate adhesion. Since generation | occurrence | production of the wrinkles by big stress being added to a body can be suppressed, the fall of cycling characteristics and the electrode plate thickness increase can be suppressed.

  Here, in the present invention, the amount of the negative electrode binder is 5% to 50% of the total mass of the negative electrode mixture layer, and the volume occupied by the negative electrode binder is 5% to 50% of the total volume of the negative electrode mixture layer. % Or less is preferable. When the amount of the negative electrode binder is less than 5% of the total mass of the mixture layer and the volume occupied by the negative electrode binder is less than 5% of the total volume of the mixture layer, As a result, the amount of the negative electrode binder is too small, resulting in insufficient adhesion within the electrode due to the negative electrode binder, while the amount of the negative electrode binder exceeds 50% of the total mass of the negative electrode mixture layer, or This is because if the volume occupied by the adhesive exceeds 50% of the total volume of the negative electrode mixture layer, the resistance in the electrode increases, so that initial charging becomes difficult. The total volume of the negative electrode mixture layer is the sum of the volumes of materials such as the negative electrode active material and the negative electrode binder contained in the negative electrode mixture layer, and there are voids in the negative electrode mixture layer. If present, it does not include the volume occupied by this void.

According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, an electrode body including the positive and negative electrodes and a separator disposed between the positive and negative electrodes has a substantially circular shape.
As in the above configuration, the cross-sectional shape of the electrode body is substantially circular, that is, when the present invention is applied to a cylindrical battery, the constituent pressure of the electrode plate is large in the battery, and the entire electrode body is configured uniformly. Since the pressure is applied, the conductive network is effectively maintained, and the cycle characteristics can be further improved.

In order to achieve the above object, the invention according to claim 6 of the present invention is a negative electrode for a lithium ion secondary battery including a negative electrode active material, a conductive agent, and a binder, and the negative electrode active material As described above, an alloy containing Sn having a theoretical charge capacity of 1200 mAh / g or less is used, and a carbon material having a primary particle size of 100 nm or less is used as the conductive agent.
If it is the said structure, there exists an effect similar to the invention of Claim 1.

A seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, the carbon material is amorphous carbon.
If it is the said structure, there exists an effect similar to the invention of Claim 2.

The invention according to claim 8 is the invention according to claim 7, wherein the amorphous carbon is acetylene black or ketjen black.
If it is the said structure, there exists an effect similar to the invention of Claim 3.

A ninth aspect of the invention is characterized in that, in the sixth to eighth aspects of the invention, the binder is polyvinylidene fluoride.
If it is the said structure, there exists an effect similar to the invention of Claim 4.

(Other matters concerning the main components of the battery)
(1) The average particle diameter of the negative electrode active material particles in the lithium secondary battery of the present invention is not particularly limited, but is preferably 100 μm or less, more preferably 50 μm or less, and most preferably 15 μm or less. This is because when an active material particle having a small particle size is used, the absolute amount of volume expansion and contraction of the active material particle due to insertion and extraction of lithium during charging and discharging is reduced. The absolute amount of distortion between the active material particles is also reduced. For this reason, it is difficult to cause destruction of the negative electrode binder, and it is possible to obtain excellent charge / discharge cycle characteristics as a result of suppressing the decrease in the current collecting ability in the electrode.

(2) The particle size distribution of the negative electrode active material particles in the lithium secondary battery of the present invention is preferably as narrow as possible. This is because, in the case of a wide particle size distribution, there is a large difference in the absolute amount of volume expansion and contraction associated with lithium storage and release between negative electrode active material particles having greatly different particle sizes. Distortion occurs in the agent layer. For this reason, it is because the destruction of the binder occurs and the current collecting property in the electrode is lowered, so that the charge / discharge cycle characteristics are lowered.

(3) Examples of the negative electrode current collector used in the present invention include metals such as copper, nickel, iron, titanium, cobalt, and alloys made of combinations thereof. In particular, a metal foil containing a copper element is preferable, and a copper foil or a copper alloy foil is more preferable.

(4) As the positive electrode active material of the lithium secondary battery of the present invention, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Examples include lithium-containing transition metal oxides such as Mn _0.1 O ₂ and metal oxides such as MnO ₂ that do not contain lithium. In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation.

(5) The solvent of the nonaqueous electrolyte used in the present invention is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc. Chain carbonates, esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1 , 2-dioxane, ethers such as 2-methyltetrahydrofuran, nitriles such as acetonitrile, amides such as dimethylformamide, etc. can be used alone or in combination. It can be. In particular, a mixed solvent of a cyclic carbonate and a chain carbonate can be preferably used.

(6) The solute of the nonaqueous electrolyte used in the present invention is not particularly limited, but is a chemical formula LiXF _y such as LiPF ₆ , LiBF ₄ , LiAsF ₆ (wherein X is P, As, Sb, B) , Bi, Al, Ga, or In, and when X is P, As, or Sb, y is 6, and when X is B, Bi, Al, Ga, or In, y is 4. And LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO Lithium compounds such as ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ can be used. Among these, LiPF ₆ can be particularly preferably used.

(7) Examples of the nonaqueous electrolyte used in the present invention include gel polymer electrolytes in which a polymer electrolyte such as polyethylene oxide and polyacrylonitrile is impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li ₃ N. The non-aqueous electrolyte in the present invention can be used without limitation as long as the lithium compound as a solute that develops lithium ion conductivity and the solvent that dissolves and retains the lithium compound do not decompose during charge / discharge or storage of the battery.

  According to the present invention, by repeating charging and discharging while improving the energy density, even if the negative electrode active material is peeled off, the current collecting property of the negative electrode active material is ensured only by the constituent pressure. As a result, the cycle characteristics can be remarkably improved.

  Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to the following best modes, and can be appropriately modified and implemented without departing from the scope of the present invention.

(Production of negative electrode)
95 mass ratio of SnCo (mass ratio of Sn and Co: 73.1: 22.1) having an average particle size [median diameter (D50)] of 5 μm as an active material and acetylene black as a conductive agent is 95 A mixture of 95 parts by mass with this mixture and 8% by mass of an N-methylpyrrolidone solution containing 5 parts by mass of polyvinylidene fluoride as a binder A mixture slurry was obtained. Next, this negative electrode mixture slurry was applied to one side of an electrolytic copper foil (thickness 10 μm) as a negative electrode current collector, dried, and then rolled. Finally, the obtained product was cut out to 30 × 30 mm, and then a nickel metal piece serving as a current collecting tab was attached to the end of the negative electrode current collector to produce a negative electrode.

[Production of positive electrode]
First, Li ₂ CO ₃ and CoCO ₃ were used as starting materials, both were weighed so that the atomic ratio of Li: Co was 1: 1, mixed in a mortar, and then pressed with a mold having a diameter of 17 mm. Then, it was pressure-molded, and further fired at 800 ° C. for 24 hours in an air atmosphere to obtain a fired body of lithium cobalt composite oxide (lithium transition metal composite oxide) represented by LiCoO ₂ . Next, this fired body was pulverized in a mortar to prepare an average particle size of about 20 μm.

Next, after adding the LiCoO ₂ powder as the positive electrode active material, the carbon material powder as the positive electrode conductive agent, and polyvinylidene fluoride as the positive electrode binder to N-methyl-2-pyrrolidone as the dispersion medium These were kneaded to prepare a positive electrode mixture slurry. The mass ratio of LiCoO ₂ powder, carbon material powder, and polyvinylidene fluoride was 94: 3: 3.

  Thereafter, this positive electrode mixture slurry was applied to one surface of an aluminum foil as a positive electrode current collector, dried, and then rolled. Finally, the obtained product was cut out to 20 × 20 mm, and an aluminum metal piece serving as a current collecting tab was attached to the end of the positive electrode current collector to produce a positive electrode.

(Preparation of non-aqueous electrolyte)
First, LiPF ₆ was dissolved at a ratio of 1 mol / liter to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 to prepare a non-aqueous electrolyte.

[Production of battery]
An electrode body is prepared by sandwiching a separator made of a polyethylene porous body between the positive electrode and the negative electrode, and then the electrode body and the non-aqueous electrolyte are made of an aluminum laminate in an argon atmosphere at normal temperature and normal pressure. The lithium secondary battery was produced by inserting and injecting the liquid into the exterior body.

  Here, as shown in FIGS. 1 and 2, the specific structure of the lithium secondary battery is as follows. An electrode body composed of a positive electrode 1, a negative electrode 2, and a separator 3 has a closed portion 7 in which the peripheral edges are heat-sealed. The positive electrode current collection tab 4 and the negative electrode current collection tab 5 are projected outside and are arranged in the storage space of the aluminum laminate exterior body 6 comprising: It has a structure capable of discharging.

[First embodiment]
Example 1
As Example 1, the battery shown in the best mode was used.
The battery thus produced is hereinafter referred to as the present invention battery A1.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that ketjen black (median diameter (D50): 100 nm) was used as the conductive agent.
The battery thus produced is hereinafter referred to as the present invention battery A2.

(Comparative Example 1)
A battery was fabricated in the same manner as in Example 1 except that graphite powder (median diameter (D50): 300 nm) was used as the conductive agent.
The battery thus manufactured is hereinafter referred to as a comparative battery Z1.

(Comparative Example 2)
A battery was fabricated in the same manner as in Example 1 except that graphite powder (median diameter (D50): 5 μm) was used as the conductive agent, and the ratio of the negative electrode active material to the graphite powder was 80:20 by mass ratio. Produced.
The battery thus produced is hereinafter referred to as a comparative battery Z2.

(Comparative Example 3)
A battery was prepared in the same manner as in Example 1 except that graphite powder [median diameter (D50): 20 μm] was used as the conductive agent and the ratio of the negative electrode active material and the graphite powder was 80:20 by mass ratio. Produced.
The battery thus produced is hereinafter referred to as comparative battery Z3.

(Experiment)
Table 1 shows the results of the initial efficiency (first cycle charge / discharge efficiency) and cycle characteristics of the present invention batteries A1 and A2 and the comparative batteries Z1 to Z3. The initial efficiency is calculated by the following formula 1, and the charge / discharge conditions are as described below. In the cycle characteristic test, the cycle life is defined as 70% of the discharge capacity of the first cycle. Further, in Table 1, the cycle life of each battery is an index with the cycle life of the battery A1 as 100. It is represented by

[Charging / discharging conditions]
-Charging conditions The condition of charging at a current of 14 mA and carrying out constant current charging to a battery voltage of 4.2 V, and then charging until the current value reaches 0.7 mA while holding the battery voltage at 4.2 V.
-Discharge condition The condition that constant current discharge is performed up to a battery voltage of 2.75 V at a current of 14 mA.
In addition, the temperature at the time of charging / discharging is 25 degreeC.

  As apparent from Table 1 above, the batteries A1 and A2 of the present invention having an average particle diameter of the conductive agent of 100 nm or less have a lower initial efficiency than the comparative batteries Z1 to Z3 in which the average particle diameter of the conductive agent exceeds 100 nm. It can be seen that the cycle characteristics are remarkably improved without causing them.

  This is because, as in the case of the present invention batteries A1 and A2, if the particle size of the primary particles of the conductive agent is regulated to 100 nm or less, the specific surface area of the conductive agent increases, and the conductive agent is uniformly present on the surface of the Sn alloy. Since the effect as the conductive agent is sufficiently exhibited, an excellent conductive network can be maintained even when the negative electrode active material is peeled off. On the other hand, when the particle size of the primary particles of the conductive agent exceeds 100 nm as in the comparative batteries Z1 to Z3, the specific surface area of the conductive agent is reduced and the conductive agent is uniformly present on the surface of the Sn alloy. Therefore, it is considered that when the negative electrode active material is peeled off, an excellent conductive network cannot be maintained.

[Second Embodiment]
Example 1
A battery was fabricated in the same manner as in Example 1 of the first example, except that SnCoC (mass ratio, Sn: Co: C = 42: 30: 28) having an average particle diameter of 5 μm was used as the negative electrode active material.
The battery thus produced is hereinafter referred to as the present invention battery B1.

(Example 2)
Example 1 of the first example was used except that SiSnCuC (mass ratio, Si: Sn: Cu: C = 20: 52.5: 17.5: 10) having an average particle diameter of 5 μm was used as the negative electrode active material. A battery was produced in the same manner.
The battery thus produced is hereinafter referred to as the present invention battery B2.

(Example 3)
Except that SiSnCuCFe (mass ratio, Si: Sn: Cu: C: Fe = 32.2: 34.1: 10.6: 12.8: 4.7) having an average particle diameter of 5 μm was used as the negative electrode active material. A battery was fabricated in the same manner as in Example 1 of the first example.
The battery thus produced is hereinafter referred to as comparative battery Y.

(Experiment)
The initial efficiency and cycle characteristics of the present invention batteries B1 and B2 and the comparative battery Y were examined, and the results are shown in Table 2. In Table 2, the results of the battery A1 of the present invention are also shown. In addition, the experimental conditions, the experimental contents, and the table marking method are the same as those in the experiment of the first embodiment, and Table 2 also describes the theoretical charge capacity at the negative electrode of each battery.

  As apparent from Table 2 above, the present invention batteries A1, B1 and B2 having a theoretical charge capacity of Sn alloy of 1200 mAh / g or less are compared with the comparative battery Y in which the theoretical charge capacity of Sn alloy exceeds 1200 mAh / g. It can be seen that the cycle characteristics are significantly improved without lowering the initial efficiency.

  This is because, if the theoretical charge capacity of the Sn alloy is regulated to 1200 mAh / g or less as in the present invention batteries A1, B1, B2, the expansion and contraction of the electrode plate are reduced, so even if charging and discharging are repeated, The formed conductive network is difficult to be destroyed. On the other hand, when the theoretical charging capacity of the Sn alloy exceeds 1200 mAh / g as in the comparative battery Y, the electrode plate expands and contracts, so that it is formed when charging and discharging are repeated. This is probably because the conductive network is easily destroyed.

  In addition, since the relationship between the expansion coefficient of the electrode plate and the theoretical charge capacity was examined using the negative electrode of the battery A1 of the present invention, the results are shown in FIG. As apparent from FIG. 3 and Table 3, since the expansion rate of the electrode plate and the theoretical charging capacity are in a substantially proportional relationship, the expansion rate of the electrode plate is uniquely determined by regulating the theoretical charging capacity as described above. It can be confirmed that it is determined.

[Third embodiment]
(Example)
A battery was produced in the same manner as in Example 1 of the first example except that polyimide was used as the binder.
The battery thus produced is hereinafter referred to as the present invention battery C.

(Experiment)
Table 4 shows the results obtained by examining the initial efficiency, the cycle characteristics, and the electrode plate expansion coefficient calculated by the following formula 2 in the battery C of the present invention. Table 4 also shows the results of the battery A1 of the present invention. The experimental conditions, the experimental contents, and the table marking method are the same as in the experiment of the first embodiment.

  As is clear from Table 4 above, the present battery A1 using polyvinylidene fluoride as the binder for the negative electrode has an initial efficiency and cycle characteristics as compared with the present battery C using polyimide as the binder for the negative electrode. It is recognized that the electrode plate expansion coefficient is remarkably small.

This is because, when polyvinylidene fluoride is used as a binder as in the present invention battery A1, the binder has an appropriate adhesion, so that the negative electrode current collector is secured while ensuring the adhesion in the negative electrode mixture layer. While it is possible to suppress overloading of the body, when the polyimide is used as the binder as in the present invention battery C, the adhesion between the negative electrode current collector and the negative electrode mixture layer is too strong. It is considered that the electrode plate thickness increased as a result of the occurrence of wrinkles due to an increase in stress applied to the electric body.
If an increase in the electrode plate thickness can be suppressed as in the case of the present invention battery A1, a short circuit can be suppressed inside the battery, and the volume energy density of the battery can be improved.

[Fourth embodiment]
Example 1
The negative electrode was cut to 400 × 52 mm and the positive electrode was cut to 340 × 50 mm, and both the positive and negative electrodes were wound into a cylindrical shape with a φ1.5 mm core through a separator and inserted into a cylindrical outer package. A battery was fabricated in the same manner as in Example 1 of the first example except for the above.
The battery thus produced is hereinafter referred to as the present invention battery D1.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that the electrode body wound into a cylindrical shape with a φ20 mm winding core was pressed into a substantially oval cross section and inserted into an exterior body made of an aluminum laminate film. did.
The battery thus produced is hereinafter referred to as the present invention battery D2.

(Experiment)
Since the cycle characteristics of the present invention batteries D1 and D2 were examined, the results are shown in Table 5. The charging / discharging conditions are as follows. Table 5 also shows the results of the battery A1 of the present invention. Further, the cycle number when the discharge capacity reached 70% of the first cycle was defined as the cycle life.

[Charging / discharging conditions]
-Charging conditions The condition of charging at a current of 900 mA and carrying out constant-current charging to a battery voltage of 4.2 V, and then charging until the current value reaches 160 mA while holding the battery voltage at 4.2 V.
-Discharge condition The condition that constant current discharge is performed up to a battery voltage of 2.5 V at a current of 160 mA.
In addition, the temperature at the time of charging / discharging is 25 degreeC.

  As is clear from Table 5 above, it is recognized that the cycle type battery battery D1 has significantly improved cycle characteristics as compared with the single layer planar battery A1 and the thin battery B2. It is done.

  In the present invention battery D1, since the constituent pressure is uniformly applied to the entire electrode body, the conductive network is effectively maintained even after repeated charging and discharging, whereas the present invention battery A1 and the present invention battery. In D2, since the component pressure is not uniformly applied to the entire electrode body, it is considered that the charge network is somewhat inferior in maintaining the effect of the conductive network when charging and discharging are repeated.

  The present invention can be applied not only to a driving power source of a mobile information terminal such as a mobile phone, a notebook computer, and a PDA, but also to a large battery such as an in-vehicle power source of an electric vehicle or a hybrid vehicle.

It is a front view of the lithium secondary battery concerning this invention. It is AA arrow sectional drawing (before charge) of FIG. It is a graph which shows the relationship between the expansion coefficient of an electrode plate, and theoretical charge capacity.

Explanation of symbols

1: Positive electrode 2: Negative electrode 3: Separator 6: Aluminum laminate outer package

Claims (9)

A lithium ion secondary battery comprising a negative electrode including a negative electrode active material, a conductive agent, and a binder, a positive electrode including a transition metal composite oxide as a positive electrode active material, and a non-aqueous electrolyte,
Lithium secondary characterized in that an alloy containing Sn having a theoretical charge capacity of 1200 mAh / g or less is used as the negative electrode active material, and a carbon material having a primary particle size of 100 nm or less is used as the conductive agent. battery.   The lithium secondary battery according to claim 1, wherein the carbon material is amorphous carbon.   The lithium secondary battery according to claim 2, wherein the amorphous carbon is acetylene black or ketjen black.   The lithium secondary battery according to claim 1, wherein the binder is polyvinylidene fluoride.   5. The lithium secondary battery according to claim 1, wherein a cross-sectional shape of an electrode body including the positive and negative electrodes and a separator disposed between the positive and negative electrodes is substantially circular. A negative electrode for a lithium ion secondary battery comprising a negative electrode active material, a conductive agent, and a binder,
Lithium secondary characterized in that an alloy containing Sn having a theoretical charge capacity of 1200 mAh / g or less is used as the negative electrode active material, and a carbon material having a primary particle size of 100 nm or less is used as the conductive agent. Battery negative electrode.   The negative electrode for a lithium secondary battery according to claim 6, wherein the carbon material is amorphous carbon.   The negative electrode for a lithium secondary battery according to claim 7, wherein the amorphous carbon is acetylene black or ketjen black.   The negative electrode for a lithium secondary battery according to claim 6, wherein the binder is polyvinylidene fluoride.