JP2012195289A - Composition for lithium secondary battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for a lithium secondary battery electrode, excellent in dispersibility and adhesiveness of an active material, and capable of manufacturing a high-capacity lithium secondary battery even when an additive amount of a binder is small.SOLUTION: A composition for a lithium secondary battery electrode contains an active material, a binder and a solvent. The binder contains a polyvinyl acetal resin, and the polyvinyl acetal resin contains 33-55 mol% of a hydroxyl group.

Description

The present invention relates to a composition for a lithium secondary battery electrode that is excellent in dispersibility and adhesiveness of an active material, and can produce a high-capacity lithium secondary battery even when the amount of binder added is small.

In recent years, with the widespread use of portable electronic devices such as portable video cameras and portable personal computers, the demand for secondary batteries as mobile power sources has increased rapidly. In addition, there are very high demands for such secondary batteries to be reduced in size, weight, and energy density.
Thus, as secondary batteries that can be repeatedly charged and discharged, conventionally, water-based batteries such as lead batteries and nickel-cadmium batteries have been mainstream, but these water-based batteries have excellent charge / discharge characteristics. However, in terms of battery weight and energy density, it cannot be said that the battery has sufficient characteristics as a power source for moving portable electronic devices.

Therefore, research and development of lithium secondary batteries using lithium or a lithium alloy as a negative electrode as a secondary battery has been actively conducted. This lithium secondary battery has excellent characteristics such as high energy density, low self-discharge, and light weight.
An electrode of a lithium secondary battery is usually a thin film obtained by kneading an active material and a binder together with a solvent, dispersing the active material into a slurry, applying the slurry on a current collector by a doctor blade method or the like, and drying the slurry. It is formed by forming.

Currently, in particular, fluorine-based resins represented by polyvinylidene fluoride (PVDF) are most widely used as binders for electrodes (negative electrodes) of lithium secondary batteries.
However, when a fluororesin is used as a binder, a flexible negative electrode thin film can be produced, but the binding property between the current collector and the negative electrode active material is inferior. There was a risk that some or all of the part would peel off or fall off from the current collector. In addition, when the battery is charged / discharged, lithium ions are repeatedly inserted and released in the negative electrode active material, and there is a problem that the negative electrode active material may be peeled off or dropped off from the current collector. .
In order to solve such a problem, an attempt has been made to add an excessive amount of a binder. However, along with this, the amount of the negative electrode active material added is relatively reduced, and the problem that the battery capacity is reduced is newly introduced. Had occurred.

On the other hand, Patent Document 1 discloses a technique using a mixture of a polymer insoluble in an electrolytic solution and a polymer soluble in the electrolytic solution as a binder used for a positive electrode and a negative electrode.
However, in such a technique, by using a polymer that is soluble in the electrolytic solution, the binder flows out to the electrolytic solution, and eventually, peeling and dropping of the negative electrode active material from the current collector cannot be suppressed. It was.

JP-A-10-214629

The present invention provides a composition for a lithium secondary battery electrode that is excellent in dispersibility and adhesiveness of an active material and capable of producing a high-capacity lithium secondary battery even when the amount of binder added is small. Objective.

The present invention is a composition for a lithium secondary battery electrode containing an active material, a binder, and a solvent, wherein the binder contains a polyvinyl acetal resin, and the polyvinyl acetal resin has a hydroxyl group content of 33 to 55 mol%. It is a composition for lithium secondary battery electrodes.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have used a polyvinyl acetal resin as a binder for forming a lithium secondary battery electrode, and the amount of hydroxyl group of the polyvinyl acetal resin is within a predetermined range. The present inventors have found that a high-capacity lithium secondary battery can be produced even in the case where the dispersibility and adhesiveness are excellent and the amount of the binder added is small, and the present invention has been completed.

The composition for a lithium secondary battery electrode of the present invention has an active material.
The composition for a lithium secondary battery electrode of the present invention may be used for either a positive electrode or a negative electrode, or may be used for both a positive electrode and a negative electrode. Accordingly, the active material includes a positive electrode active material and a negative electrode active material.

Examples of the positive electrode active material include lithium-containing composite metal oxides such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. Specifically, for _{example, LiNiO 2, LiCoO 2, LiMn} 2 O 4 and the like.
In addition, these may be used independently and may use 2 or more types together.
Moreover, you may add conductive support agents, such as flake graphite and carbon black, to the said positive electrode active material as needed.

As said negative electrode active material, the material conventionally used as a negative electrode active material of a lithium secondary battery can be used, for example, natural graphite, artificial graphite, amorphous carbon, carbon black, or these components And the like in which different elements are added.
Moreover, you may add conductive support agents, such as flake graphite, to the said negative electrode active material as needed.

The composition for a lithium secondary battery electrode of the present invention contains a polyvinyl acetal resin. In the present invention, by using a polyvinyl acetal resin as a binder (binder), an attractive interaction works between the hydroxyl group of the polyvinyl acetal resin and the oxygen atom of the positive electrode active material, and the positive electrode active material is surrounded by the polyvinyl acetal resin. Take. In addition, another hydroxyl group in the same molecule has an attractive interaction with the conductive additive, and the distance between the active material and the conductive additive can be kept within a certain range. Thus, the dispersibility of an active material is improved significantly by taking a characteristic structure with a moderate distance between an active material and a conductive additive. Moreover, compared with the case where resin, such as PVDF, is used, adhesiveness with a collector can be improved. Furthermore, there is an advantage that the solvent solubility is excellent and the range of solvent selection is widened.

The minimum of the amount of hydroxyl groups of the said polyvinyl acetal resin is 33 mol%, and an upper limit is 55 mol%. When the amount of the hydroxyl group is less than 33 mol%, the resistance to the electrolytic solution becomes insufficient, and when the electrode is immersed in the electrolytic solution, the resin component may be eluted in the electrolytic solution. If it exceeds, not only is it difficult to synthesize industrially, but also the solution viscosity becomes high, and it becomes difficult to sufficiently disperse the active material.
The preferable lower limit of the amount of the hydroxyl group is 35 mol%, and the preferable upper limit is 50 mol%.

The minimum with a preferable polymerization degree of the said polyvinyl acetal resin is 250, and a preferable upper limit is 4000. If the degree of polymerization is less than 250, it may be difficult to obtain industrially. When the polymerization degree exceeds 4000, the solution viscosity becomes high and it may be difficult to sufficiently disperse the active material. The more preferable lower limit of the degree of polymerization is 280, and the more preferable upper limit is 800.

In the present invention, particularly when the amount of hydroxyl groups in the polyvinyl acetal resin is 33 mol% or more and less than 42 mol%, the degree of polymerization is preferably 500 to 4000, and the amount of hydroxyl groups in the polyvinyl acetal resin is 42 mol% or more. When the content is 55 mol% or less, the degree of polymerization is preferably 250 to 500.
When the amount of hydroxyl groups in the polyvinyl acetal resin is 33 mol% or more and less than 42 mol%, if the degree of polymerization is less than 500, the resistance to the electrolytic solution is insufficient, and the resin is obtained when the electrode is immersed in the electrolytic solution. Components may elute into the electrolyte.
Moreover, when the amount of hydroxyl groups of the polyvinyl acetal resin is 42 mol% or more and 55 mol% or less, if the polymerization degree exceeds 500, the solution viscosity becomes high and it is difficult to sufficiently disperse the active material. It becomes.

The polyvinyl acetal resin preferably has an acetalization degree of 40 to 65 mol%. When the degree of acetalization is less than 40 mol%, the solubility in a solvent is lowered, so that it is difficult to use the composition. When the degree of acetalization exceeds 65 mol%, the resistance to the electrolytic solution becomes insufficient, and the resin component may be eluted in the electrolytic solution when the electrode is immersed in the electrolytic solution. More preferably, it is 45-60 mol%.
In the present specification, the degree of acetalization is the ratio of the number of hydroxyl groups acetalized with butyraldehyde out of the number of hydroxyl groups of polyvinyl alcohol. Since the acetal group is formed by acetalization from two hydroxyl groups, a method of counting the two acetal hydroxyl groups is employed to calculate the mol% of the degree of acetalization.

In the polyvinyl acetal resin, the ratio of the portion acetalized with acetaldehyde and the portion acetalized with butyraldehyde is preferably 0/100 to 50/50. Thereby, a polyvinyl acetal resin becomes flexible and the adhesive force to a collector becomes favorable. More preferably, the ratio of the portion acetalized with acetaldehyde and the portion acetalized with butyraldehyde is 0/100 to 20/80.

The minimum with the preferable amount of acetyl groups of the said polyvinyl acetal resin is 1 mol%, and a preferable upper limit is 20 mol%. When the amount of the acetyl group is less than 1 mol%, the flexibility of the resin is insufficient, and the adhesive force to the current collector becomes insufficient, and when the amount of the acetyl group exceeds 20 mol%, the resistance to the electrolytic solution is increased. Significantly decreases, and elution into the electrolyte causes a short circuit. The more preferable lower limit of the acetyl group amount is 3 mol%, and the more preferable upper limit is 10 mol%.

The polyvinyl acetal resin preferably has an anionic group.
By having the anionic group, the polyvinyl acetal resin easily adheres to the surface of the active material, and the dispersibility of the active material can be improved.

Although content of the said polyvinyl acetal resin in the composition for lithium secondary battery electrodes of this invention is not specifically limited, A preferable minimum is 0.5 weight part with respect to 100 weight part of active materials, A preferable upper limit is 12 weight part. It is. When the content of the polyvinyl acetal resin is less than 0.5 parts by weight, the adhesive force to the current collector may be insufficient. When the content exceeds 12 parts by weight, the discharge capacity of the lithium secondary battery is reduced. May end up. More preferably, it is 2 to 5 parts by weight.

The number of hydroxyl groups of the polyvinyl acetal resin is preferably 0.1 to 10% with respect to the number of oxygen atoms of the active material. If the amount of hydroxyl groups in the polyvinyl acetal resin is less than 0.1% of the number of oxygen atoms in the active material, the adsorptive power to the active material may be insufficient, and sufficient dispersibility may not be obtained. As a result, the discharge capacity of the lithium secondary battery may be reduced. More preferably, it is 1 to 3%.
The number of hydroxyl groups of the polyvinyl acetal resin relative to the number of oxygen atoms of the active material is calculated by calculating the number of hydroxyl groups of the polyvinyl acetal resin from the calculated molecular weight of the polyvinyl acetal resin, the weight of the polyvinyl acetal resin, the degree of polymerization, and the amount of hydroxyl groups. The number of hydroxyl groups in the polyvinyl acetal resin / the number of oxygen atoms in the active material) × 100] can be calculated.

The polyvinyl acetal resin is obtained by acetalizing polyvinyl alcohol with an aldehyde.

The polyvinyl alcohol can be obtained, for example, by saponifying a copolymer of vinyl ester and ethylene. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate and the like. Of these, vinyl acetate is preferred from the viewpoint of economy.

The polyvinyl alcohol may be a copolymer of an ethylenically unsaturated monomer as long as the effects of the present invention are not impaired. The ethylenically unsaturated monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, acrylonitrile methacrylonitrile, acrylamide, and methacrylamide. , Trimethyl- (3-acrylamido-3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid and its sodium salt, ethyl vinyl ether, butyl vinyl ether, N-vinyl pyrrolidone, vinyl chloride, vinyl bromide, fluorine Vinyl chloride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, sodium allyl sulfonate and the like. Also use terminal-modified polyvinyl alcohol obtained by copolymerizing vinyl ester monomer such as vinyl acetate with ethylene in the presence of thiol compounds such as thiol acetic acid and mercaptopropionic acid, and saponifying it. Can do.

The polyvinyl alcohol may be a saponified copolymer obtained by copolymerizing the vinyl ester and an α-olefin. Furthermore, it is good also as polyvinyl alcohol which copolymerizes the said ethylenically unsaturated monomer and contains the component originating in an ethylenically unsaturated monomer. Also used is a terminal polyvinyl alcohol obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with an α-olefin in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid, and saponifying it. be able to. The α-olefin is not particularly limited, and examples thereof include methylene, ethylene, propylene, isopropylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, cyclohexylethylene, and cyclohexylpropylene.

In addition to the said polyvinyl acetal resin, the composition for lithium secondary battery electrodes of this invention may contain the polyvinylidene fluoride resin.
By using the polyvinylidene fluoride resin in combination, the resistance to the electrolytic solution can be further improved, and the discharge capacity can be improved.

When the polyvinylidene fluoride resin is contained, the weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is preferably 0.5: 9.5 to 7: 3.
By setting it within such a range, it is possible to impart resistance to the electrolytic solution while having adhesive force to the current collector that is significantly insufficient for polyvinylidene fluoride.
A more preferred weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is 1: 9 to 4: 6.

Although content of the whole binder in the composition for lithium secondary battery electrodes of this invention is not specifically limited, A preferable minimum is 1 weight part and a preferable upper limit is 20 weight part with respect to 100 weight part of active materials. If the content of the binder is less than 1 part by weight, the adhesive force to the current collector may be insufficient, and if it exceeds 20 parts by weight, the discharge capacity of the lithium secondary battery may be reduced. There is.

The composition for a lithium secondary battery electrode of the present invention contains a solvent.
The solvent is not particularly limited as long as it can dissolve the polyvinyl acetal resin. For example, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, toluene, isopropyl alcohol, N-methylpyrrolidone, ethanol, distilled water. Etc. The said solvent may be used independently and may use 2 or more types together.

In addition to the above-described active material, polyvinyl acetal resin, and solvent, the composition for a lithium secondary battery electrode of the present invention includes a flame retardant aid, a thickener, an antifoaming agent, a leveling agent, and an adhesion as necessary. An additive such as a property-imparting agent may be added.

The method for producing the composition for a lithium secondary battery electrode of the present invention is not particularly limited. For example, the active material, the polyvinyl acetal resin, the solvent, and various additives to be added as necessary may be a ball mill, a blender mill, The method of mixing using various mixers, such as a 3 roll, is mentioned.

The electrode for lithium secondary battery electrode composition of the present invention is formed, for example, through a process of coating on a conductive substrate and drying.
A lithium secondary battery using the composition for a lithium secondary battery electrode of the present invention is also one aspect of the present invention.
As a coating method when the composition for a lithium secondary battery electrode of the present invention is applied to a conductive substrate, various coating methods such as an extrusion coater, a reverse roller, a doctor blade, an applicator and the like can be adopted. it can.

ADVANTAGE OF THE INVENTION According to this invention, the composition for lithium secondary battery electrodes which is excellent in the dispersibility and adhesiveness of an active material, and can produce a high capacity | capacitance lithium secondary battery even when there is little addition amount of a binder can be provided. .

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Synthesis of polyvinyl acetal resins (A) to (H))
350 parts by weight of polyvinyl alcohol having a polymerization degree of 320 and a saponification degree of 99 mol% was added to 3000 parts by weight of pure water, and stirred at a temperature of 90 ° C. for about 2 hours for dissolution. The solution was cooled to 40 ° C., and 230 parts by weight of hydrochloric acid having a concentration of 35% by weight was added thereto. Then, the liquid temperature was lowered to 1 ° C. and 155 parts by weight of n-butyraldehyde was added to maintain the temperature, and the acetal was maintained. The reaction product was precipitated by the reaction. Thereafter, the liquid temperature was maintained at 30 ° C. for 3 hours to complete the reaction, and neutralized, washed with water and dried by a conventional method to obtain a white powder of the polyvinyl acetal resin (A). The obtained polyvinyl acetal resin was dissolved in DMSO-d ₆ (dimethylsulfoxaside), and the degree of butyralization (degree of acetalization), the amount of hydroxyl groups and the amount of acetyl groups were determined using ¹³ C-NMR (nuclear magnetic resonance spectrum). When measured, the degree of butyralization was 49 mol%, the amount of hydroxyl groups was 50 mol%, and the amount of acetyl groups was 1 mol%.
Further, polyvinyl acetal resins (B) to (H) were synthesized in the same manner as the polyvinyl acetal resin (A) except that the conditions shown in Table 1 were used.

Example 1
(Preparation of composition for positive electrode of lithium secondary battery)
95 parts by weight of N-methylpyrrolidone was added to 2 parts by weight of the polyvinyl acetal resin (A) obtained as a binder to prepare a 5% by weight solution of the polyvinyl acetal resin. For 100 parts by weight of this solution, 50 parts by weight of lithium manganate (manufactured by Nippon Chemical Industry Co., Ltd., Cellseed C-5H) as the positive electrode active material and 4 acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) as the conductive assistant A weight part was added and mixed, and the composition for positive electrodes of a lithium secondary battery was obtained.

(Examples 2 to 7)
A composition for a positive electrode of a lithium secondary battery was obtained in the same manner as in Example 1 except that the polyvinyl acetal resin shown in Table 2 was used and the addition amount of N-methylpyrrolidone was changed.

(Example 8)
A mixture of polyvinyl acetal resin and polyvinylidene fluoride (PVDF, manufactured by Kureha, # 1100) shown in Table 2 was used as a binder resin, and the amount of N-methylpyrrolidone was changed. A composition for a secondary battery positive electrode was obtained.

Example 9
(Preparation of composition for negative electrode of lithium secondary battery)
91 parts by weight of N-methylpyrrolidone was added to 9 parts by weight of the polyvinyl acetal resin (A) obtained as a binder to prepare a 4% by weight solution of the polyvinyl acetal resin. With respect to 100 parts by weight of this solution, 43 parts by weight of spherical natural graphite (Nippon Graphite Industries Co., Ltd., CGB-10) as a negative electrode active material, and 4 weights of acetylene black (Denka Black, Denki Kagaku Kogyo Co., Ltd.) as a conductive assistant. Part of the mixture was added and mixed to obtain a lithium secondary battery negative electrode composition.

(Examples 10 to 13)
A composition for a lithium secondary battery negative electrode was obtained in the same manner as in Example 9 except that the polyvinyl acetal resin shown in Table 2 was used and the addition amount of N-methylpyrrolidone was changed.

(Example 14)
A mixture of polyvinyl acetal resin and polyvinylidene fluoride (PVDF, manufactured by Kureha, # 1100) shown in Table 2 was used as a binder resin, and the amount of N-methylpyrrolidone was changed. A composition for a secondary battery negative electrode was obtained.

(Comparative Examples 1-3)
A composition for a positive electrode of a lithium secondary battery was obtained in the same manner as in Example 1 except that the polyvinyl acetal resin shown in Table 2 was used and the addition amount of N-methylpyrrolidone was changed.

(Comparative Example 4)
A lithium secondary battery was obtained in the same manner as in Example 1 except that polyvinylidene fluoride (PVDF, manufactured by Kureha, # 1100) was used instead of the polyvinyl acetal resin (A), and the amount of N-methylpyrrolidone was changed. A positive electrode composition was obtained.

(Comparative Examples 5-7)
A composition for a lithium secondary battery negative electrode was obtained in the same manner as in Example 9 except that the polyvinyl acetal resin shown in Table 2 was used and the addition amount of N-methylpyrrolidone was changed.

(Comparative Example 8)
A lithium secondary battery was obtained in the same manner as in Example 9 except that polyvinylidene fluoride (PVDF, manufactured by Kureha Corporation, # 1100) was used instead of the polyvinyl acetal resin (A), and the addition amount of N-methylpyrrolidone was changed. A negative electrode composition was obtained.

<Evaluation>
The following evaluation was performed about the composition for lithium secondary battery electrodes (for positive electrodes and negative electrodes) obtained by the Example and the comparative example. The results are shown in Table 2.

(1) Adhesiveness About the compositions for lithium secondary battery electrodes obtained in Examples 1 to 8 and Comparative Examples 1 to 4, the adhesiveness to aluminum foil was evaluated, and Examples 9 to 14 and Comparative Examples 5 to 5 were evaluated. About the composition for lithium secondary battery electrodes obtained in 8, the adhesiveness with respect to copper foil was evaluated.

(1-1) Examples 1-8, Comparative Examples 1-4
On the aluminum foil (thickness 20 μm), the electrode composition was applied and dried so that the film thickness after drying was 20 μm, to obtain a test piece in which the electrode was formed in a sheet shape on the aluminum foil.
This sample was cut into a length of 1 cm and a width of 2 cm, and the electrode sheet was pulled up while fixing the test piece using AUTOGRAPH (manufactured by Shimadzu Corporation, “AGS-J”) until the electrode sheet was completely peeled from the aluminum foil. The required peel force (N) was measured.

(1-2) Examples 9 to 14 and Comparative Examples 5 to 8
In the above (1-1), the peel force was measured in exactly the same manner except that the aluminum foil was changed to a copper foil (thickness 20 μm).

(2) Dispersibility After mixing and diluting 10 parts by weight of the obtained composition for a lithium secondary battery electrode and 90 parts by weight of N-methylpyrrolidone, an ultrasonic disperser (manufactured by SNDI, “US-303”) was used. And stirred for 10 minutes. Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution meter (LA-910, manufactured by Horiba, Ltd.), and the average dispersion diameter was measured.

(3) Solvent solubility (production of electrode sheet)
On the polyethylene terephthalate (PET) film subjected to the release treatment, the lithium secondary battery electrode compositions obtained in Examples and Comparative Examples were applied and dried so that the film thickness after drying was 20 μm. A sheet was produced.
The electrode sheet was cut into a 2 cm square to prepare an electrode sheet test piece.

(Elution evaluation)
The weight of the obtained test piece was accurately measured, and the weight of the resin contained in the test piece was calculated from the component weight ratio contained in the sheet. Thereafter, the test piece was put in a bag-like mesh, and the total weight of the mesh bag and the test piece was accurately measured.
Next, the mesh bag containing the test piece was immersed in diethyl carbonate, which is an electrolytic solution, and left overnight at room temperature. After standing, the mesh bag was taken out and dried under conditions of 150 ° C. and 8 hours to completely dry the solvent.
After taking out from the dryer, it was left at room temperature for 1 hour and weighed. The elution amount of the resin was calculated from the weight change before and after the test, and the elution rate of the resin was calculated from the ratio between the elution amount and the resin weight calculated in advance. In addition, it means that resin is easy to elute in electrolyte solution, so that the value of elution rate is high.

(4) Battery performance evaluation (4-1) Examples 1-8, Comparative Examples 1-4
(A) Preparation of coin battery The lithium secondary battery positive electrode compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were applied to an aluminum foil and dried to a thickness of 0.2 mm, which was adjusted to φ12 mm. A positive electrode layer was obtained by punching.
Moreover, the lithium secondary battery negative electrode composition obtained in Example 9 was applied to a copper foil and dried to a thickness of 0.2 mm, which was punched to φ12 mm to obtain a negative electrode layer.
A mixed solvent with ethylene carbonate containing LiPF ₆ (1M) was used as the electrolytic solution, and after impregnating the electrolytic solution into the positive electrode layer, the positive electrode layer was placed on the positive electrode current collector, and further on the electrolytic solution A porous PP membrane (separator) having a thickness of 25 mm impregnated with was placed.
Further, a lithium metal plate serving as a negative electrode layer was placed thereon, and a negative electrode current collector covered with insulating packing was placed thereon. Pressure was applied to the laminate with a caulking machine to obtain a sealed coin battery.

(B) Discharge capacity evaluation and charge / discharge cycle evaluation The obtained coin battery was subjected to discharge capacity evaluation and charge / discharge cycle evaluation using (a charge / discharge test test device manufactured by Hosen Co., Ltd.).
This discharge capacity evaluation and charge / discharge cycle evaluation were performed at a voltage range of 3.0 to 4.5 V and an evaluation temperature of 20 ° C.

(4-2) Examples 9 to 14 and Comparative Examples 5 to 8
The lithium secondary battery positive electrode composition obtained in Example 1 was applied to an aluminum foil and dried to a thickness of 0.2 mm, which was punched into φ12 mm to obtain a positive electrode layer.
Moreover, the lithium secondary battery negative electrode compositions obtained in Examples 9 to 14 and Comparative Examples 5 to 8 were applied to a copper foil and dried to a thickness of 0.2 mm, which was punched out to φ12 mm to form a negative electrode layer. Obtained.
Except for using the obtained positive electrode layer and negative electrode layer, after obtaining a sealed coin battery by the same method as (4-1), discharge capacity evaluation and charge / discharge cycle evaluation were performed.

ADVANTAGE OF THE INVENTION According to this invention, the composition for lithium secondary battery electrodes which is excellent in the dispersibility and adhesiveness of an active material, and can produce a high capacity | capacitance lithium secondary battery even when there is little addition amount of a binder can be provided. .

Claims (9)

A composition for a lithium secondary battery electrode containing an active material, a binder and a solvent,
The binder contains a polyvinyl acetal resin,
The composition for a lithium secondary battery electrode, wherein the polyvinyl acetal resin has a hydroxyl group content of 33 to 55 mol%. The composition for a lithium secondary battery electrode according to claim 1, wherein the polyvinyl acetal resin has a polymerization degree of 250 to 4000. The composition for a lithium secondary battery electrode according to claim 1 or 2, wherein the polyvinyl acetal resin has an anionic group. The composition for lithium secondary battery electrodes according to claim 1, wherein the polyvinyl acetal resin has 1 to 20 mol% of acetyl groups. 5. The composition for a lithium secondary battery electrode according to claim 1, comprising 0.5 to 12 parts by weight of a polyvinyl acetal resin with respect to 100 parts by weight of the active material. Furthermore, the composition for lithium secondary battery electrodes of Claim 1, 2, 3, 4 or 5 characterized by containing a polyvinylidene fluoride resin as a binder. The lithium secondary according to claim 1, 2, 3, 4, 5 or 6, wherein the weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is 0.5: 9.5 to 7: 3. Battery electrode composition. The composition for a lithium secondary battery electrode according to claim 1, wherein the binder is contained in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the active material. A lithium secondary battery comprising the composition for a lithium secondary battery electrode according to claim 1, 2, 3, 4, 5, 6, 7 or 8.