JP2001035495A - Positive electrode paste composition for lithium secondary battery, positive electrode, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode paste composition for lithium secondary battery excellent in the performance as required of lithium secondary battery and also suitable for mass-production, provide a positive electrode using the paste composition, and offer a method for manufacturing such positive electrodes. SOLUTION: A positive electrode active material consisting of lithium-nickel series compound oxide having a stratified crystalline structure, a conductive substance to give conductivity to this active material, and a binder to couple them together are dispersed in a solvent, and thereto 0.1-3 pts.wt. organic acid of divalent or more is added relative to 100 pts.wt. positive electrode active material. This paste composition is applied to an electricity collector followed by drying so that an intended positive electrode for lithium secondary battery is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly, to a positive electrode suitable as a positive electrode material for a lithium secondary battery using a lithium nickel composite oxide having a layered rock salt type crystal structure as a positive electrode active material. The present invention relates to a paste composition, a positive electrode for a lithium secondary battery using the same, and a method for producing the same.

[0002]

2. Description of the Related Art A lithium secondary battery of this type has a high voltage and a high voltage.
High energy density can be obtained and it can be made smaller and lighter, so it has already been put into practical use in the field of information and communication equipment such as personal computers and mobile phones. It is also used in electric vehicles and hybrid electric vehicles due to resource and environmental issues. Practical use has also been advanced considerably for power supplies.

In such a situation, various studies have been made on a positive electrode paste composition for a lithium secondary battery. For example, regarding a positive electrode active material in the composition, a lithium cobalt composite oxide (LiCoO ₂ ), A lithium manganese-based composite oxide (LiMn ₂ O ₄ ) having a spinel-type crystal structure due to cost and resource issues, and a layered rock-salt-type crystal structure having excellent charge-discharge cycle characteristics at high temperatures. lithium-nickel-based composite oxide having a (LiNiO ₂₎ has also been noted.

This positive electrode paste composition is generally prepared by mixing a positive electrode active material as described above and a conductive material (for example, acetylene black or the like) for imparting conductivity to the positive electrode active material. The material is dispersed in a binder solution obtained by dissolving an organic binder resin in a solvent to form a positive electrode mixture slurry, and the positive electrode mixture slurry is collected from a metal electrode foil (for example, Al foil) or a metal mesh. The positive electrode sheet is formed by applying and drying the material on a current collector and pressing the applied material onto the current collector by pressing.

In the negative electrode sheet, a negative electrode active material is similarly dispersed in a binder solution obtained by dissolving an organic binder resin in a solvent to form a negative electrode mixture slurry, which is coated on a current collector, dried and pressed. It is made by doing. Then, a lithium secondary battery is formed by immersing the battery in a non-aqueous organic electrolyte with a porous separator sheet having insulation and ion mobility interposed between the positive electrode sheet and the negative electrode sheet. Things.

In such a technical background, examples of the binder solution used in the positive electrode paste composition include, for example, JP-A-6-93025 and JP-A-6-1724.
As shown in Japanese Patent Publication No. 52, various kinds of vinylidene fluoride polymers (PVDF) are excellent in chemical resistance, weather resistance, stain resistance, etc., and are stable with respect to non-aqueous electrolytes. Attention was paid to this, and N-methyl-2-pyrrolidone (NM
Those dissolved in a polar solvent such as P) and dimethylformamide are known.

For example, as disclosed in Japanese Patent Application Laid-Open No. 10-255808, when a vinylidene fluoride polymer is dissolved in an organic solvent to produce a binder solution, the vinylidene fluoride polymer is heated or treated with an alkaline substance. In addition, there is also a method of improving the adhesion between the electrode paste composition and the current collector by adding an acid (organic acid) other than hydrofluoric acid by removing hydrofluoric acid by adding hydrofluoric acid, and further adding an acid (organic acid) other than hydrofluoric acid. is there.

[0008]

However, for example, an electrode sheet used for a lithium secondary battery for an electric vehicle, which is as thin as tens of μm to several hundred μm and has a large area, may be used. It is becoming mandatory. In such a case, as a method for industrially and inexpensively manufacturing such a thin-film and large-area electrode sheet, an electrode mixture slurry (described above) is conveyed on a sheet surface while a current collector sheet is transported on a continuous production line. A method in which a powder electrode material or the like is dispersed in a binder solution) is applied and dried, and the applied material is pressed against the surface of the current collector sheet by a roll press.

When such a production method is adopted, the vinylidene fluoride polymer used for the binder solution of the above-mentioned positive electrode paste composition has a low binding force to the powder electrode material and a low adhesion force to the current collector. Since the powder electrode material is relatively weak, phenomena such as dropping of the powdered electrode material such as the active material during use and separation of the electrode mixture layer containing the powdered electrode material from the current collector were observed. In particular, when a layered lithium nickel composite oxide having excellent battery performance at high temperatures is used as the positive electrode active material, the binding force with the vinylidene fluoride-based polymer is very weak.
At the time of pressing after coating, there is a problem that the active material falls off and adheres to the rolls or peels off from the current collector due to the stress generated by the pressing, making it impossible to press the large area. In a lithium secondary battery using a nickel composite oxide as a positive electrode active material, a large battery such as an automobile battery could not be manufactured in large quantities.

In order to solve the above-mentioned problem, it is conceivable to increase the amount of a vinylidene fluoride-based polymer as a binder. However, the amount of vinylidene fluoride polymer increased,
Although the binding force and the adhesive force are certainly improved, there is a problem that the concentration of the active material in the electrode mixture layer is reduced, and the electric capacity per unit area is reduced. Moreover, in the case of the layered lithium nickel composite oxide, even if the amount of the binder was increased, sufficient improvement in the binding force and the adhesive force could not be obtained.

[0011] The reason why the positive electrode paste composition using the layered lithium nickel composite oxide is inferior in the binding force or the adhesive force is a bond between the three members of the positive electrode active material particles, the binder and the current collector. Since the bonding force between the material particles and the active material particles, between the active material particles and the binder, between the active material particles and the current collector, and between the binder and the current collector is weak, the active material particles fall off during roll pressing and the roll It is considered that it adheres to the surface or peels off from the current collector.

According to the binder solution disclosed in Japanese Patent Application Laid-Open No. 10-255808, since the amount of the organic acid added is very small, the active material particles also fall off during roll pressing and adhere to the roll, The problem of peeling off from the electrical sheet is not solved, and the production of this binder solution requires a step of heating the vinylidene fluoride-based polymer or removing hydrofluoric acid by adding an alkali substance. There is also a problem that the production cost of the electrode sheet increases.

The present inventors believe that if the bonding force between the layered lithium-nickel composite oxide particles, the binder, and the current collector is further increased, the above-described problem that occurs during roll pressing can be solved. Thought. As a result of intensive studies, it was found that by mixing a divalent or higher valent organic acid into the positive electrode paste composition and adjusting the amount of the organic acid, the layered lithium-nickel composite oxide particles, the binder, and the current collector were mixed. It has been found that the bonding force between the members is increased and the problem of the adhesion of the active material particles to the roll is solved, and the present invention has been reached.

An object of the present invention is to provide a lithium-nickel composite which is excellent in battery performance as a positive electrode active material, and which can exhibit high charge / discharge cycle characteristics even in a high-temperature use environment such as an automobile power supply. It is an object of the present invention to provide a positive electrode paste composition which has good bonding strength between active materials and fixability of the active materials to a current collector even when an oxide is used, and is suitable for mass-producing large batteries. Another object of the present invention is to provide a lithium secondary battery using the paste composition and a method for manufacturing the same.

[0015]

According to the present invention, there is provided a positive electrode paste composition for a lithium secondary battery according to the present invention, which comprises a lithium nickel composite oxide having a layered crystal structure. The material as a positive electrode active material, this positive electrode active material, a conductive material that imparts conductivity to the active material,
A binder that binds both substances is dispersed in a solvent, and 2
Organic acid having a valency of at least 0.1 part by weight per 100 parts by weight of the positive electrode active material
The gist of the invention is that 1 to 3 parts by weight are blended.

In this case, the layered lithium-nickel-based composite oxide has a layered rock-salt structure, and has the same crystal structure as the lithium-cobalt-based composite oxide. And, it is excellent in charge / discharge cycle characteristics at a higher temperature than a lithium manganese composite oxide having a spinel type crystal structure. This layered lithium nickel-based composite oxide refers to a composite oxide of lithium and a transition metal containing nickel as a main component,
Composition formula _{LiNi 1-X M X O 2} (M is, Ti, Mn, C
It is composed of one or more of o, Al, Mg, Ga and the like. A composite oxide represented by 0 ≦ x <1) can be used. Whichever active material is used, it is preferable to use a fine particle powder, and it is preferable to use one having a particle diameter in the range of 1 to 30 μm.

The conductive material is not particularly limited as long as it can be mixed with an appropriate amount of the positive electrode active material to impart conductivity to the positive electrode layer. For example, one or more of carbon material powders such as carbon black, acetylene black, and graphite can be used in combination. In addition, a metal powder that is stable at the electrode potential used can be used.

As the binder, an organic binder is generally used. The organic binder plays a role of binding the particles of the positive electrode active material and the conductive material, and needs to be stable to a non-aqueous electrolyte, etc., and has weather resistance, chemical resistance, heat resistance, and flame retardancy. Good properties are required. For example, a tetrafluoroethylene polymer, a vinylidene fluoride polymer, a fluoropolymer such as fluororubber,
Thermoplastic polymers such as polypropylene and polyethylene can be used. It is also possible to use synthetic rubber-based latex such as styrene-butadiene rubber latex and carboxy-modified styrene-butadiene rubber latex.

The solvent plays a role of uniformly dispersing the cathode active material, the conductive material, and the organic binder, and also plays a role of adjusting the viscosity of the cathode paste composition obtained by mixing them. As long as the organic binder can be dissolved and can be easily dried, it can be appropriately selected. Specific examples include n-methyl-2-pyrrolidone and dimethylformamide.

The organic acid having a valency of 2 or more is used to strengthen the bonding force between the positive electrode active material particles, the binder, and the current collector. There is no particular limitation. For example, as dicarboxylic acids having two carboxyl groups in the molecule, aromatic saturated dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and glutaric acid; aliphatic unsaturated dicarboxylic acids such as maleic acid; and aromatics such as phthalic acid. Group dicarboxylic acids. Examples of tricarboxylic acids having three carboxyl groups in the molecule include tricarballylic acid and benzenetricarboxylic acid. The mixing ratio of the organic acid is preferably 0.1 part by weight or more with respect to 100 parts by weight of the positive electrode active material in order to sufficiently improve the binding force of the positive electrode active material particles. On the other hand, when the amount of the organic acid exceeds 3 parts by weight, the effect of improving the binding force decreases, and a problem occurs in battery performance such as reduction in battery capacity.

The reason why the organic acid having a valency of 2 or more has a large effect of strengthening the bonding force between the positive electrode active material particles, the binder and the current collector is that the organic acid having a valency of 2 or more binds to another substance in one molecule. Since there are two or more possible sites, when an appropriate amount of a divalent or higher valent organic acid is added to the positive electrode paste composition, one bonding site is formed into a layered lithium nickel composite oxide, which is a positive electrode active material in the composition. Material particles, conductive material particles, and a binder, and the remaining bonding sites are bonded to other layered lithium-nickel composite oxide particles, conductive material particles, and a binder to improve the binding force between the positive electrode materials, When applied to the current collector, it is considered that the remaining bonding site is bonded to the surface of the current collector, and the adhesion between the positive electrode material and the current collector is improved.

Further, the positive electrode for a lithium secondary battery of the present invention comprises:
The gist is that the paste composition according to claim 1 is applied to a current collector and dried. According to this positive electrode for a lithium secondary battery, high charge / discharge cycle characteristics can be obtained even when used in a high-temperature environment when incorporated in a battery.

Further, in the method of manufacturing a positive electrode for a lithium secondary battery according to the present invention, a lithium alloy-based positive electrode active material, a conductive material, and a binder are dispersed in a solvent, and a divalent or higher valent organic acid is dispersed in the solvent. The gist is that a positive electrode paste is prepared by mixing 0.1 to 3 parts by weight with respect to 100 parts by weight, and this is applied to a current collector and dried to produce the positive electrode paste. As a result, a positive electrode for a lithium secondary battery having excellent battery characteristics is manufactured.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. <Configuration and Preparation Method of Positive Electrode Paste Composition> As described above, the positive electrode paste composition of the present invention comprises a layered lithium nickel composite oxide particle which is an active material capable of inserting and extracting lithium, A conductive material that imparts properties, an organic binder that binds these positive electrode active material particles to the conductive material, a solvent that uniformly disperses them, and a divalent or higher valent organic acid that is added to the solvent. It is composed of When producing the positive electrode paste composition, the positive electrode active material and the conductive material are mixed with an organic binder, and the mixture is mixed and dispersed in a solvent. Is prepared.

At this time, the mixing ratio of the positive electrode active material is as follows, assuming that the whole of the prepared positive electrode paste composition is 100%.
In order to obtain a sufficient battery capacity, the content is desirably 30 wt% or more. Further, the mixing ratio of the conductive substance is desirably 2 wt% or more in order to obtain sufficient conductivity.
The mixing ratio of the organic binder is desirably 2 wt% or more in order to obtain sufficient binding properties. As described above, the mixing ratio of the organic acid is 0.1 part by weight or more with respect to 100 parts by weight of the positive electrode active material in order to obtain the effect of improving the binding property of the positive electrode active material particles. It is desirably at least 0.5 wt%.

However, when the amount of the conductive material exceeds 20 wt%, the amount of the organic binder exceeds 10 wt%, or the amount of the organic acid exceeds 3 parts by weight with respect to 100 parts by weight of the positive electrode active material, the battery capacity is reduced. And other problems in battery performance. Further, the compounding ratio of the solvent is desirably 30 wt% or more, in order to uniformly disperse the composition or to prevent problems in uniformity and surface smoothness in coating, and to be 60 wt% or more. %, The viscosity decreases, and problems such as sagging during coating occur.

In the positive electrode paste composition, it is necessary that the above-mentioned respective component substances are sufficiently and uniformly kneaded and dispersed in order to ensure good battery performance. Therefore, the kneading and dispersing step is desirably performed using a stirrer having rotating blades, a ball mill, a medium stirring mill, or the like.

<Method of Producing Positive Electrode> The positive electrode of the lithium secondary battery was prepared by applying the positive electrode paste composition prepared and prepared as described above to the surface of a current collector sheet to form a positive electrode layer. Will be A metal foil such as aluminum is used for the current collector sheet serving as a base material to be coated. As a device used for coating, it is convenient to use a coater-type coating machine that can continuously apply and dry the electrode paste composition on the belt-shaped current collector sheet.

Since the composition to be coated has a relatively high viscosity, it is preferable to adopt a coating method such as a comma coat, a squeeze coat, a die coat, and a lip coat in the coating section of the coating machine. The coating thickness of the positive electrode paste composition is
Any value between 50 and 500 μm can be used.

The drying section of the coating machine is a continuous furnace in the case of a coater system, and various types of drying such as hot air and infrared rays can be employed for drying. The drying temperature is preferably 80 ° C. or higher. If the temperature is lower than 80 ° C., the drying becomes insufficient, the solvent may remain in the positive electrode layer, and the battery performance may be reduced. However, care must be taken because if the drying temperature is too high, drying proceeds only on the surface and uniform drying cannot be achieved. Then, in order to make the thickness of the electrode layer a predetermined thickness, increase the electrode density, and further enhance the surface smoothness, pressing is performed after drying. This is effective in increasing the energy density of the battery.
As a device used for pressing, a roll press capable of continuously pressing after applying and drying an electrode paste on a belt-shaped current collector sheet is generally used.

<Structure of Lithium Secondary Battery> A lithium secondary battery using the electrode manufactured as described above will be described. A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Hereinafter, components except for the above-described positive electrode will be sequentially described.

As the negative electrode active material, metallic lithium, a lithium compound, a lithium alloy or the like can be used, but there is a problem that dendrite is precipitated due to repetition of charge and discharge.
Instead, a negative electrode active material is preferably a powdery carbon material capable of inserting and extracting lithium. When a carbon material is used as a negative electrode active material, a binder is mixed with the carbon material, and an appropriate solvent is added as necessary to form a negative electrode paste composition. It is prepared by coating and drying the surface to form a negative electrode layer.

Examples of the carbon material usable as the negative electrode active material include natural graphite, artificial graphite, coke, carbon black, vapor grown carbon, carbon fiber, a material obtained by carbonizing an organic polymer compound, or a heat treatment of these materials. And mixed materials. In the production of the negative electrode, a binder for binding the negative electrode active material, a solvent, kneading and dispersing the negative electrode paste composition, a coating and drying method, and the like,
The same material as the positive electrode or a similar method can be used.

The separator sandwiched between the positive electrode and the negative electrode has a function of separating the positive electrode and the negative electrode, holding an electrolyte, and passing lithium ions. For this separator, a porous film such as polyethylene or polypropylene, a nonwoven fabric or a woven fabric can be used.
It is preferable that the thickness of the separator be about 10 to 200 μm.

The non-aqueous electrolyte contains a non-aqueous electrolyte which is stable with respect to the positive electrode active material and the negative electrode active material and has ion mobility since lithium ions undergo an electrochemical reaction with the positive electrode active material and the negative electrode active material. Any substance can be used. Usually, a lithium salt as an electrolyte is used by dissolving it in an organic solvent. Salts which can be used for the electrolyte, _{specifically,} LiPF _6, LiAsF _6, LiSb
F ₆ , LiBF ₄ , LiClO ₄ , LiI, LiBr,
LiCl, LiAlCl, LiHF ₂ , LiSCN, L
ISO ₃ CF _2, and the like. Of these,
LiPF ₆ , LiBF ₄ and LiClO ₄ are preferred.

The solvent for dissolving the electrolyte can be arbitrarily selected, but an organic solvent having a relatively high dielectric constant is preferably used. For example, ethylene carbonate, cyclic carbonates such as propylene carbonate, dimethyl carbonate, non-cyclic carbonates such as ethyl methyl carbonate, tetrahydrofuran, glimes such as 2-methyltetrahydrofuran, lactones such as γ-butyl lactone, sulfur such as sulfolane. One or more solvents such as compounds, nitriles such as acetonitrile and the like can be mentioned. Among these, in particular, one or more mixed solvents selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and non-cyclic carbonates such as dimethyl carbonate and ethyl methyl carbonate are preferably used.

Further, the above non-aqueous electrolyte is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, a crosslinked isocyanate of polyethylene oxide, phenylene oxide, or a phenylene sulfide polymer as a solid electrolyte in place of the above non-aqueous electrolyte. Organic solid electrolyte, Li ₃ N, LiBCl ₄ , Li ₄ SiO
₄ , an inorganic solid electrolyte of lithium glass such as Li ₃ BO ₃ can also be used.

As the shape of the lithium secondary battery configured as described above, various shapes such as a cylindrical type, a box type, a paper type, and a card type can be used. Regardless of the shape, an electrode body in which a separator is sandwiched between a positive electrode and a negative electrode, a current collecting lead from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal, etc. The electrode body is sealed in a battery case together with the non-aqueous electrolyte to complete a lithium secondary battery.

Based on the above embodiment, as a working example, a positive electrode paste composition was actually produced. Separately, a cathode paste composition outside the range specified in the present invention was prepared as a comparative example. Using the positive electrode paste compositions of Examples and Comparative Examples, a positive electrode was produced by coating and drying and roll pressing on the surface of the current collector sheet. Furthermore, a cylindrical cell type lithium secondary battery was actually manufactured. Then, the state of attachment of the positive electrode active material to the roll during pressing, the adhesion of the positive electrode layer after pressing, and the battery capacity (initial discharge capacity) and the charge / discharge cycle characteristics at high temperature (60 ° C.) are compared. It was confirmed that the positive electrode paste composition of the present invention was effective.

[0040]

EXAMPLES The positive electrode paste compositions of Examples and Comparative Examples, the production of the positive electrode, the production of the battery, and the results of comparison of the experimental data will be described in order. Table 1 shows a comparison of the components of each test cathode paste composition.

Example 1 The positive electrode paste composition of Example 1 based on the above-described embodiment of the present invention uses lithium nickel composite oxide crystal particles as a positive electrode active material and acetylene black as a conductive material. Using. As the organic binder, a vinylidene fluoride polymer (hereinafter, referred to as PVD) is used.
F), oxalic acid having a divalent valence was used as an organic acid, and n-methyl-2-pyrrolidone (hereinafter abbreviated as “NMP”) was used as a solvent. The mixing ratio of each of the positive electrode paste compositions was adjusted so that oxalic acid was 0.1 part by weight with respect to 100 parts by weight of lithium nickel composite oxide. 45.9 wt%, acetylene black 5.4 wt%,
PVDF 2.7wt%, oxalic acid 0.5wt%, NMP
46.0 wt%.

For the kneading and dispersing of the positive electrode paste composition, a disperser (Ultraviscomil: manufactured by IMEX) was used. The disperser has a capacity of 2.0 liters and a stirring disk of 5 liters.
There are 1.4 liters of zirconia beads having a diameter of 2 mm. Rotating speed of stirring disk 1000r
The mixture was rotated at pm, and the positive electrode paste composition was continuously processed at 150 ml / min and kneaded and dispersed to obtain a positive electrode paste.

Example 2 In the positive electrode paste composition of Example 2 based on the above-described embodiment of the present invention, the amount of oxalic acid was adjusted to 3 parts by weight based on 100 parts by weight of lithium nickel composite oxide. Except for Example 1 and each component material,
The production conditions were the same, and the mixing ratio of each component was 44.8 wt% of lithium nickel composite oxide, 5.3 wt% of acetylene black, 2.6 wt% of PVDF, 1.3 wt% of oxalic acid, and 46.0 wt% of NMP. did.

<Comparative Example 1> The positive electrode paste composition did not contain an organic acid (oxalic acid), and the other components and production conditions were the same as in Example 1 except for the above. The mixing ratio of each component was 45.9 wt% of lithium nickel composite oxide.
%, Acetylene black is 5.4 wt%, PVDF2.
7 wt% and NMP 46.0 wt%.

Comparative Example 2 Example 1 was repeated except that the mixing ratio of the organic acid in the positive electrode paste composition was higher than the prescribed ratio.
Each component material and manufacturing conditions are the same as those of the second and third embodiments. In Comparative Example 2, the amount of oxalic acid was 4 parts by weight with respect to 100 parts by weight of lithium nickel composite oxide. The mixing ratio of each component material is lithium nickel composite oxide 4
4.4 wt%, acetylene black is 5.2 wt%, P
VDF 2.6 wt%, oxalic acid 1.8 wt%, NMP4
6.0 wt%.

Comparative Example 3 An organic acid was added to the positive electrode paste composition, but it was acetic acid having a monovalent valence. 3 parts by weight with respect to parts by weight.
The mixing ratio of each component is as follows.
4.8 wt%, acetylene black 5.3 wt%, P
VDF 2.6 wt%, acetic acid 1.3 wt%, NMP46.
0 wt%.

[0047]

[Table 1]

The positive electrode paste thus prepared was applied to a thickness of 2
On a 0 μm aluminum foil (width 200 mm, length 250 m), apply one side using a comma coater, dry at 80 ° C. for 5 minutes, then apply and dry the back side as well. 200 m length coated with positive electrode material
Was obtained. Next, a linear pressure of 1000 kgf / cm
And then cut into a predetermined shape to form a positive electrode.

For the negative electrode paste composition, mesocarbon microbeads were used as a negative electrode active material, mixed with vinylidene fluoride polymer (PVDF) as an organic binder, and n-methyl-2-pyrrolidone (solvent) was used. NM
What was dispersed in P) was used. The mixing ratio in the negative electrode paste composition was 45.0 wt% of mesocarbon microbeads, 5.0 wt% of PVDF, and 5 wt% of NMP5.
0.0 wt%. Then, the negative electrode paste kneaded and dispersed in the same manner as the positive electrode paste composition was applied on one side using a comma coater on a copper foil having a thickness of 20 μm, and then dried at 80 ° C. for 5 minutes. Thus, a negative electrode sheet having both surfaces coated with a negative electrode material was obtained. Next, roll pressing was performed at a linear pressure of 1000 kgf / cm to make the film thickness 100 μm, and then cut into a predetermined shape to produce a negative electrode.

Next, a thickness of 20 mm was provided between the obtained positive electrode and negative electrode.
A separator made of polyethylene having a thickness of μm was sandwiched and wound up on a spiral to form a cylindrical cell, which was then mounted on a battery can filled with a non-aqueous electrolyte. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / l in a mixed solution of equal volumes of ethylene carbonate and diethyl carbonate was used.

<Comparative Results> Adhesion of the positive electrode material to the rolls in a roll press after coating and drying was performed on the positive electrode paste compositions of Examples 1 and 2 of the present invention and Comparative Examples 1, 2 and 3 of the comparative products. The properties were compared and evaluated by a tape peel test. In the tape peeling test, a cellophane tape was adhered to the positive electrode surface and quickly peeled off, and the peeled surface was visually observed to evaluate the adhesion.

Further, the initial discharge capacity and the charge / discharge cycle characteristics at a high temperature (60 ° C.) of the cylindrical cells prepared using the respective positive electrode paste compositions were comparatively evaluated. The initial discharge capacity is a charge current of 500 mA and a discharge current of 5
A constant current charge / discharge of 00 mA was performed in a voltage range of 3.0 to 4.1 V. The charge / discharge cycle characteristics at a high temperature (60 ° C.) were evaluated by repeating the charge / discharge under these conditions and maintaining the discharge capacity after 100 cycles with respect to the initial discharge capacity. Table 2 shows the results.

[0053]

[Table 2]

As shown in Table 2 above, in the positive electrode paste composition of Comparative Example 1, there was a deposit on the roll at the time of 50 m press in a roll press, and the binding property of the positive electrode material was low. The material was peeled off and the adhesion to the current collector surface was low. This is because the positive electrode paste composition of Comparative Example 1 did not contain an organic acid having a valency of 2 or more, so that the binding property and the adhesion of the positive electrode material were reduced.

Further, in the positive electrode paste composition of Comparative Example 2, although the binding property and the adhesion were equal to those of Examples 1 and 2, the initial discharge capacity of the produced battery was as low as 1080 mAh. This is considered to be because the organic acid was mixed in the positive electrode paste of Comparative Example 2 in an amount of more than 3 parts by weight to 4 parts by weight with respect to 100 parts by weight of the positive electrode active material, so that the capacity of the battery itself was reduced.

In the positive electrode paste composition of Comparative Example 3, there was a deposit on the roll at the time of pressing 80 m, the binding property of the positive electrode material was low, and the positive electrode material was peeled off from the current collector surface.
Adhesion to the current collector surface was also low. This is probably because the positive electrode paste of Comparative Example 3 was mixed with monovalent acetic acid as an organic acid, so that the binding property and adhesion of the positive electrode material were reduced.

On the other hand, in the positive electrode paste compositions of Examples 1 and 2 based on the embodiment of the present invention, the binding property and adhesion were improved by the addition of the divalent organic acid, and 200 m
At the time of pressing, the positive electrode material did not adhere to the roll, and the positive electrode material did not peel off from the current collector surface. Also, no decrease in the initial discharge capacity of the manufactured battery was observed.
From this result, it was demonstrated that the positive electrode paste composition of the present invention was a positive electrode paste composition having excellent binding properties and adhesion.

Regarding the charge / discharge cycle characteristics at a high temperature (60 ° C.), all the prototypes have a high discharge capacity because the lithium nickel composite oxide is used as the positive electrode active material in the positive electrode paste composition. It was confirmed that the rate was exhibited. The fact that such a result is obtained is considered as a substance reaction mechanism as follows. Since a divalent or higher valent organic acid has two or more sites capable of binding to another substance in one molecule, when a suitable amount of a divalent or higher valent organic acid is added to the positive electrode paste composition, one bonding site However, the layered lithium-nickel composite oxide particles that are the positive electrode active material in the composition, the conductive material particles, bond with the binder, the remaining binding site is another layered lithium-nickel composite oxide particles, conductive material particles, Combines with the binder to improve the binding force between the positive electrode material and, when applied to the current collector, the remaining bonding site binds to the current collector surface, and the adhesion between the positive electrode material and the current collector It is thought that this was improved.

The present invention is not limited to the above-described embodiment at all, and various modifications can be made without departing from the gist of the present invention. For example, in the above examples, oxalic acid was shown as an example of a divalent organic acid, but other dicarboxylic acids such as maleic acid, malonic acid, and succinic acid, or tricarboxylic acids and other various organic compounds having two or more valences are also used. The application of the acid is clear from the utility of the organic acid of the present invention. Further, the conductive material, the binder, and the like are not limited to those of the embodiment. Also for the layered lithium-nickel-based composite oxide, it is of course possible to stabilize battery characteristics by substituting a part of the nickel element with another metal element.

[0060]

According to the positive electrode paste composition of the present invention,
By using a layered lithium-nickel-based composite oxide as the positive electrode active material, a high temperature (6
(0 ° C. or higher), not only excellent in battery characteristics (such as charge-discharge cycle characteristics), but also by collecting an appropriate amount of a divalent or higher polyvalent organic acid into the composition to collect the paste during the production of the electrode sheet. It is possible to improve the adhesiveness to the body and eliminate the adhesion of the coating film to the roll at the time of pressing after coating. Therefore, applying this positive electrode paste composition to a power source of an electric vehicle placed in an environment of use at a high temperature is effective not only in battery performance, but also suitable for mass production and is suitable for a positive electrode active material. This also contributes to stability of battery performance due to less exfoliation from the current collector and reduction of manufacturing cost. The present invention opens up the possibility of using layered lithium nickelate for applications in which a large number of electrode layers need to be produced in a short time, such as a secondary battery for an electric vehicle.

Further, the positive electrode for a lithium secondary battery of the present invention comprises:
Since the paste composition is applied to a current collector and dried, when the positive electrode is incorporated in a lithium secondary battery, excellent battery characteristics such as high-temperature charge / discharge cycle characteristics can be exhibited.

Further, according to the method of manufacturing a positive electrode for a lithium secondary battery according to the present invention, a positive electrode of a lithium secondary battery having excellent battery characteristics as described above can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takuaki Okuda 41-Cho, Yokomichi, Nagakute-machi, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory, Inc. (72) Inventor Hideyuki Nakano Nagakute-cho, Aichi-gun, Aichi Prefecture 41 Chuo-ku Yokomichi 1 Toyota Central Research Laboratory Co., Ltd. (72) Inventor Toshihiko Inoue 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 5H003 AA04 BA03 BB05 BB11 BB14 BC06 BD04 5H014 AA02 BB01 BB06 BB08 EE10 HH01

Claims (3)

[Claims] 1. A lithium nickel composite oxide having a layered crystal structure is used as a positive electrode active material, and the positive electrode active material, a conductive material that imparts conductivity to the active material, and a binder that binds both materials are used. A positive electrode paste composition for a lithium secondary battery, wherein the positive electrode paste composition is dispersed in a solvent and contains 0.1 to 3 parts by weight of a divalent or higher valent organic acid per 100 parts by weight of the positive electrode active material. 2. A positive electrode for a lithium secondary battery, wherein the paste composition according to claim 1 is applied to a current collector and dried. 3. A lithium alloy-based positive electrode active material, a conductive material and a binder are dispersed in a solvent, and 0.1 to 3 parts by weight of a divalent or higher organic acid is mixed with 100 parts by weight of the positive electrode active material. Producing a positive electrode paste for a lithium secondary battery by applying a positive electrode paste to a current collector and drying it.