JPH11162450A - Electrode for nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a nonaqueous electrolyte battery allowing the battery to have good bonding between an electrode active material and a conductive material, a good flow of electrolyte ions and a high charge/ discharge capacity. SOLUTION: An electrode layer constituted of at least an electrode active material, a conductive material and a binder is provided on an electrode current collector, and the electrode active material Lix Niy O2 in the range of 2.5-3.2 g/cm<3> is contained in the electrode layer, where 0.8<x<1.2, 0.8<y+z<1.2, 0<=z<=0.35, M is one or more kinds of Co, Al, Mn, Fe. The binder in the range of 1-5 wt.% is contained in the electrode layer, and slice-like graphite having the center grain size larger than the center grain size of the electrode active material is used for the conductive material to form an electrode for a nonaqueous electrolyte battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to electrode for a nonaqueous electrolyte battery, in particular _{Li x Ni y M z O 2} ( where 0.8 <
x <1.2, 0.8 <y + z <1.2, 0 ≦ z ≦ 0.3
5, M is one or more of Co, Al, Mn, and Fe)
The present invention relates to an electrode for a non-aqueous electrolyte battery having a high discharge potential and a high discharge capacity using the electrode active material.

[0002]

2. Description of the Related Art Among non-aqueous electrolyte batteries having a high discharge potential and a high discharge capacity, lithium ion secondary batteries that occlude and release lithium have been put to practical use. The electrode of this battery is coated with a paint composed of an electrode active material and a binder on the electrode current collector,
The electrode layer is formed by drying, and the electrode is thereafter compressed and cut by a roller press or the like as necessary.
In a conventional lithium ion secondary battery, lithium cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material. In addition, lithium nickel oxide (LiNiO)
_{When 2} ) is used as the positive electrode active material, the above LiCo
Although the capacity of the battery is larger than that of O ₂ , there is a problem in safety, and LiNiO ₂ to which Co or the like is added is being studied. JP-A-7-29606 discloses that the positive electrode active material is a lithium-containing transition metal oxide, and the density of the positive electrode mixture (electrode layer) is 2.5 g / cm ³ or more and 3.5 g / cm ^3.
The following non-aqueous secondary batteries are described. Further, JP-A-8-17471 discloses a lithium manganese oxide (LiM
It is shown that the battery capacity is improved by defining the specific surface area and the density of the active material layer using n ₂ O ₄ ).

Here, one of the methods for increasing the capacity of a battery is to improve the flow of electrons by improving the connection between the electrode active material and the conductive material in the electrode layer, and to improve the contact between the electrode active material and the electrolyte. There is a method for improving the transfer of electrolyte ions by improving the quality. When the connection between the electrode active material in the electrode layer and the conductive material is poor, an unused electrode active material is generated, and the battery capacity is reduced. In addition, if the electrode active material and the electrolyte are not in good contact, the movement of the electrolyte ions is hindered, and the capacity is reduced. As a means for enhancing the connection between the electrode active material and the conductive material, compression is usually performed by a roller press or the like, but when the degree of compression is increased, the penetration of the electrolyte becomes poor, and the contact between the electrode active material and the electrolyte becomes poor. turn into.
On the other hand, when the degree of compression is small, the situation is reversed, and it is necessary to increase the connection between the electrode active material and the conductive material by, for example, increasing the content of the conductive material. And the battery capacity is reduced.

[0004]

The above LiCoO ₂ as a positive electrode active material is dry-mixed, calcined and crushed, so that its shape becomes angular. It is easy to secure a space for liquid to permeate. However, LiNiO ₂ to which Co or the like is added is generally made by a wet method of synthesis and firing, and the shape tends to be spherical, and an electrode using such a spherical electrode active material is compressed. Then, there is a problem that the electrode layer is too clogged, the flow of electrolyte ions is deteriorated, the capacity is reduced, and the efficiency is deteriorated. On the other hand, when the compression is weakened, the flow of electrolyte ions is improved, but there is a problem that an electrode active material not in contact with the conductive material is generated and the capacity is reduced.

In the above-mentioned Japanese Patent Application Laid-Open No. 8-17471, there is shown an embodiment in which acetylene black and graphite are used in combination as a conductive material. However, when acetylene black is used, the electrode layer adheres to the electrode current collector. Worse,
When the amount of the binder is increased to improve the adhesiveness, there is a problem that the flow of electrolyte ions is deteriorated and the capacity is reduced.

[0006] The present invention has been made in view of such circumstances, and a non-aqueous solution that enables a battery having a good connection between an electrode active material and a conductive material, a high flow of electrolyte ions, and a high charge / discharge capacity. An object of the present invention is to provide an electrode for an electrolyte battery.

[0007]

In order to achieve such an object, the present invention provides at least Li _x Ni _y M _z O
₂ (provided that 0.8 <x <1.2, 0.8 <y + z <1.
2, 0 ≦ z ≦ 0.35, and M is Co, Al, Mn,
In an electrode for a non-aqueous electrolyte battery in which an electrode layer made of an electrode active material, a conductive material, and a binder (one or more types of Fe) is formed on an electrode current collector, the amount of the electrode active material per unit volume of the electrode layer is 2.5 g / cm ³ in the range of ~3.2g / cm ^3, amount of binder in the electrode layer is 1 to 5 wt%
And the conductive material was a flaky graphite having a center particle size larger than the center particle size of the electrode active material.

In the present invention, the amount of the binder in the electrode layer, the kind of the conductive material, and the amount per unit volume of the electrode active material are defined, so that the connection between the electrode active material and the conductive material is good and the electrolyte The flow of ions becomes extremely good.

[0009]

Embodiments of the present invention will be described below.

[0010] The electrode for a non-aqueous electrolyte battery according to the present invention comprises an electrode current collector provided with at least an electrode layer comprising an electrode active material, a conductive material, and a binder. The electrode active material and its amount per unit volume in the electrode layer, the blending amount of the binder, and the kind of the conductive material are defined as follows.

The electrode active material in the electrode for a non-aqueous electrolyte battery of the present invention is Co, Al, M
Li _x Ni _y M _z O doped with at least one of n and Fe
₂ (however, 0.8 <x <1.2, 0.8 <y
+ Z <1.2, 0 ≦ z ≦ 0.35). The amount of the electrode active material per unit volume of the electrode layer is set to 2.5 g / cm.
^{It is} within the range of ^{3 to} 3.2 g / cm ³ . Specifying the amount of the electrode active material per unit volume of the electrode layer as described above means that the state of the electrode active material in the electrode layer (the degree of clogging).
It is important to define the degree of clogging of the electrode active material as described above with respect to the flow of electrons and the flow of electrolyte ions in the electrode layer. If the amount of the electrode active material per unit volume of the electrode layer is out of the above range, the charge / discharge capacity of the electrode decreases, which is not preferable.

The amount of the binder in the electrode layer of the electrode for a non-aqueous electrolyte battery of the present invention is 1 to 5% by weight, preferably 2 to 4% by weight. When the amount of the binder is less than 1% by weight, the coating film is difficult to form, the adhesion to the electrode current collector is low and the film easily peels off, and when the amount exceeds 5% by weight, the charge / discharge capacity of the electrode is reduced. I will.

As the binder constituting the electrode layer, a thermoplastic resin or a polymer having rubber elasticity can be used singly or as a mixture. Specifically, a fluorine-based polymer, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl Cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene,
Ethylene-propylene-diene terpolymer (EPD
M), sulfonated EPDM, styrene butadiene rubber,
Examples thereof include polybutadiene and polyethylene oxide. Among them, the atomic ratio of fluorine atom / carbon atom is 0.75 to 1.5, preferably 0.75 to 1.3.
Can be particularly preferably used. When the atomic ratio exceeds 1.5, the battery capacity cannot be sufficiently obtained, and when the atomic ratio is less than 0.75, the binder dissolves in the electrolytic solution. It is not preferable. Examples of such a fluorine-based polymer include polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-ethylene trifluoride copolymer, ethylene-tetrafluoroethylene copolymer, propylene-tetrafluoroethylene copolymer, and the like. Further, a fluorine-based polymer in which hydrogen in the main chain is substituted with an alkyl group can also be used. Selective solubility among these fluoropolymers (low solubility in electrolyte,
(A soluble solvent is present) is preferable.For example, in the case of a vinylidene fluoride-based polymer, it is difficult to dissolve in a carbonate-based solvent used for an electrolytic solution,
It can be dissolved in solvents such as N, N-dimethylformamide and N-methylpyrrolidone.

Further, the conductive material in the electrode for a non-aqueous electrolyte battery of the present invention is required to be flaky graphite. The flaky shape means that the thickness is thin and the surface has a spread. Artificial graphite, natural graphite having a small thickness, and pulverized products of expanded graphite fall into this category. Specifically, LF series manufactured by Chuetsu Graphite Industry Co., Ltd., UFG series manufactured by Showa Denko KK, KS manufactured by LONZA
Series, MICROCARBO manufactured by Kansai Thermochemical Co., Ltd.
-G series, Ecos carbon series manufactured by Ecos Giken Co., Ltd. and the like. The central particle size of the graphite needs to be larger than the central particle size of the electrode active material.
If the center particle size of the flaky graphite is smaller than the center particle size of the electrode active material, problems such as poor connection between conductive materials and deterioration of the charge and discharge cycle life occur.

The center particle size is measured using a laser particle size distribution meter such as a Microtrack manufactured by Nikkiso Co., Ltd.
It means the cumulative percent diameter at which the frequency cumulative is 50%.

The electrode current collector constituting the electrode for a non-aqueous electrolyte battery of the present invention may be any electronic conductor which does not cause a chemical change in the battery thus constituted. For example, aluminum, copper, stainless steel, Nickel, titanium, calcined carbon, and the like can be used, and further, carbon, nickel, titanium, or silver may be treated on the surface thereof. Aluminum foil is desirable if considered.

The electrode for a non-aqueous electrolyte battery of the present invention is manufactured by forming an electrode layer on an electrode current collector, and thereafter compressing and cutting with a roller press or the like.

The formation of the electrode layer on the electrode current collector includes a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure roll method, a bar coating method, a dip method, a kiss coating method, and the like. The coating is performed by applying the electrode active material composition coating by a generally well-known coating method such as a squeeze method. Among them, the extrusion method is preferable, and a good coating film can be obtained by selecting the solvent composition and the drying conditions of the electrode active material composition coating so that the coating can be performed at a speed of 5 to 100 m / min.

The above-mentioned electrode active material composition paint is generally produced by mixing the above-mentioned electrode active material with a conductive material, a binder and a solvent. In order to make electrodes with higher performance, to improve the connection between the electrode active material and the conductive material,
It is preferable to treat before coating. In this case, it is preferable to mix and pulverize the electrode active material and flaky graphite to remove a stack of graphites, and to further pulverize the graphite as necessary to make the flakes thin. For mixing and pulverization, a kneader or an ong mill can be used.

As the solvent for the electrode active material composition coating, general organic solvents can be used. Specifically, saturated hydrocarbons such as hexane and aromatic hydrocarbons such as toluene and xylene can be used. , Methanol, ethanol, alcohols such as propanol and butanol, acetone,
Ketones such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran, dioxane and diethyl ether, N, N-dimethylformamide, N-methylpyrrolidone, N, N- Examples thereof include organic solvents such as amides such as dimethylacetamide and halogenated hydrocarbons such as ethylene chloride and chlorobenzene, and these solvents can be used alone or in combination of two or more. Among these, an amide-based solvent can be preferably used because it can dissolve the fluorine-based polymer.

[0021] The electrode active material weight per unit volume of the electrode layer to the range of 2.5g / cm ³ ~3.2g / cm ³ as the above is to adjust the compression process such as roller press And set the pressure so that it is within the above range. The compression may be performed in the above range once, or may be performed several times in the above range. When compressing several times, the pressure of each time may be changed.

[0022]

Next, the present invention will be described in more detail with reference to examples. (Example 1) An electrode active material composition paint having the following composition was prepared.

Electrode active material composition paint / electrode active material (LiNi _0.8 Co _0.2 O ₂ ) 92 parts by weight Central particle diameter 10 μm Conductive material (Graphite KS25 manufactured by LONZA) 4 parts by weight Flaky, central particle diameter 11 μm Binder (polyvinylidene fluoride (PVDF)) 4 parts by weight KYNAR741 manufactured by Elf Alchem Japan Co., Ltd. Solvent (N-methyl-2-pyrrolidone (NMP)) 67 parts by weight , PVDF
(4 parts by weight) was dissolved in NMP (67 parts by weight) to prepare a binder solution (71 parts by weight). Next, the electrode active material (92 parts by weight) and the conductive material (4 parts by weight) were charged into an ang mill and mixed and pulverized for 20 minutes. The above binder solution (71 parts by weight) was added thereto, and the mixture was stirred and mixed with a hyper mixer for 60 minutes to obtain an electrode active material composition paint.

Next, the above-mentioned electrode active material composition paint was applied to one side of an aluminum foil electrode current collector with a blade coater and dried to form an electrode layer. Thereafter, the same coating operation was performed on the other surface of the aluminum foil to form an electrode layer. The electrode current collector having the electrode layers formed on both surfaces is compressed by a roller press so that the amount of the electrode active material per unit volume of the electrode layer is 2.9 g / cm ³ , The electrode of Example 1 was obtained. (Example 2) The amount of the electrode active material per unit volume of the electrode layer was increased to 3.2 by increasing the pressure of the compression by the roller press.
An electrode of Example 2 was obtained in the same manner as in Example 1 except that g / cm ³ was obtained. (Example 3) The pressure of the compression by the roller press was reduced, and the amount of the electrode active material per unit volume of the electrode layer was reduced to 2.5.
An electrode of Example 3 was obtained in the same manner as in Example 1, except that g / cm ³ was obtained. (Comparative Example 1) The amount of the electrode active material in the unit volume of the electrode layer was 3.4 by increasing the pressure of the compression by the roller press.
An electrode of Comparative Example 1 was obtained in the same manner as in Example 1 except that g / cm ³ was obtained. (Comparative Example 2) The amount of the electrode active material per unit volume of the electrode layer was reduced to 2.1 by reducing the pressure of the compression by the roller press.
An electrode of Comparative Example 2 was obtained in the same manner as in Example 1 except that g / cm ³ was obtained. Example 4 An electrode active material composition paint having the following composition was prepared by the same preparation procedure as in Example 1.

Electrode active material composition paint / electrode active material (LiNi _0.8 Co _0.2 O ₂ ): 91 parts by weight, center particle diameter: 10 μm Conductive material (Graphite KS25 manufactured by LONZA): 4 parts by weight, flake, center particle diameter: 11 μm Binder (polyvinylidene fluoride (PVDF)) 5 parts by weight KYNAR741 manufactured by Elf Alchem Japan Co., Ltd. Solvent (N-methyl-2-pyrrolidone (NMP)) 67 parts by weight Next, the above-mentioned electrode active material composition paint is used. An electrode of Example 4 was obtained in the same manner as in Example 1, except that the amount of the electrode active material per unit volume of the electrode layer was 2.8 g / cm ³ . Comparative Example 3 An electrode active material composition paint having the following composition was prepared by the same preparation procedure as in Example 1.

Electrode active material composition paint / electrode active material (LiNi _0.8 Co _0.2 O ₂ ) 89 parts by weight Central particle diameter 10 μm Conductive material (Graphite KS25 manufactured by LONZA) 4 parts by weight Flaky, central particle diameter 11 μm Binder (polyvinylidene fluoride (PVDF)) 7 parts by weight KYNAR741 manufactured by Elf Alchem Japan Co., Ltd. Solvent (N-methyl-2-pyrrolidone (NMP)) 67 parts by weight Next, the above-mentioned electrode active material composition paint is used. Then, an electrode of Comparative Example 3 was obtained in the same manner as in Example 1, except that the amount of the electrode active material per unit volume of the electrode layer was 2.8 g / cm ³ . Comparative Example 4 An electrode active material composition paint having the following composition was prepared by the same preparation procedure as in Example 1.

Electrode active material composition paint / electrode active material (LiNi _0.8 Co _0.2 O ₂ ) 95.5 parts by weight Central particle diameter 10 μm Conductive material (Graphite KS25 manufactured by LONZA) 4 parts by weight Flaky, central particle diameter 11 μm Binder (polyvinylidene fluoride (PVDF)) 0.5 part by weight KYNAR741 manufactured by ELF Alchem Japan Co., Ltd. Solvent (N-methyl-2-pyrrolidone (NMP)) 67 parts by weight Next, the above electrode active material An electrode of Comparative Example 4 was obtained in the same manner as in Example 1, except that the composition paint was used and the amount of the electrode active material per unit volume of the electrode layer was 2.8 g / cm ³ . (Example 5) Graphi manufactured by LONZA as a conductive material
te Instead of KS25, Graph made by LONZA
An electrode of Example 5 was obtained in the same manner as in Example 1, except that item KS44 (flake shape, center particle size: 17 μm) was used. (Comparative Example 5) Graphi manufactured by LONZA as a conductive material
Instead of KS25, flaky acetylene black (Denka Black manufactured by Denki Kagaku Kogyo KK)
An electrode of Comparative Example 5 was obtained in the same manner as in Example 1 except that 1 μm) was used. (Comparative Example 6) Graphi manufactured by LONZA as a conductive material
te Instead of KS25, Graph made by LONZA
An electrode of Comparative Example 6 was obtained in the same manner as in Example 1, except that item KS6 (flake shape, center particle size: 3.8 μm) was used. (Comparative Example 7) Graphi manufactured by LONZA as a conductive material
instead of te KS25, MCMB made by Osaka Gas Co., Ltd.
An electrode of Comparative Example 7 was obtained in the same manner as in Example 1 except that (spherical shape, central particle size: 11 μm) was used. (Evaluation of each electrode) For each of the above-mentioned electrodes (Examples 1 to 5 and Comparative Examples 1 to 7), the electrode characteristics and the adhesion of the electrode layer to the electrode current collector were evaluated by the following methods, and the results were shown in the following table. 1 is shown.

Electrode Characteristics Each electrode was cut to a size of 25 mm in length and 20 mm in width, and the upper end was removed with a width of 5 mm to leave a 20 mm square electrode layer. A stainless wire was spot-welded as a lead to the upper end from which the electrode layer had been removed to form an electrode (working electrode). Next, a charge / discharge capacity measurement cell as shown in FIG. 1 was produced using this electrode (working electrode). That is, in the beaker 1, a pair of counter electrodes 4 using a lithium plate connected to a stainless steel wire, a lugine tube 6 having a similar reference electrode 5, and the above-mentioned electrode (working electrode) 3 between the counter electrodes 4. The electrolyte solution 7 was prepared by dissolving 1 mol / l lithium perchlorate as an electrolyte salt in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1. The cell was sealed with the stopper 2 to produce a cell for charge / discharge capacity measurement. Next, a constant current of 6 mA was applied to the charge / discharge capacity measurement cell from 3 V to 4.2 V.
Charge / discharge was repeated five times in the range up to (Potential vs Li / Li +), and the capacity (initial capacity) at the time of the first Li ion occlusion and the fifth capacity were measured.

Adhesion A test was conducted in accordance with the JIS K 5400 8.5. 1 grid method to examine the adhesion of the electrode to the aluminum foil.
That is, one side of an electrode formed on both sides of an aluminum foil was scratched with a scratch tester (Model 29, manufactured by ERICHSEN).
(5 blades, 11 blades at 1 mm intervals) were cut in a grid pattern and scored according to JIS.

[0030]

[Table 1] As shown in Table 1, the electrodes of Examples 1 to 5 were all maintained at a high level in five charge / discharge cycles,
Also, the adhesion of the electrode layer was good.

[0031] On the contrary, the electrode (Comparative Examples 1 and 2) in which the electrode active material of the electrode layer is outside the range of 2.5g / cm ³ ~3.2g / cm ³ is less capacity in the charge and discharge Was something. An electrode having a binder amount in the electrode layer of more than 5% by weight (Comparative Example 3) has a low capacity in charge and discharge, and an electrode having a binder amount of less than 1% by weight (Comparative Example 4).
Was insufficient in film formation and adhesion was extremely poor, and peeling occurred in the electrolytic solution, making measurement impossible. Further, the electrode using acetylene black as the conductive material (Comparative Example 5) had the same level of capacity as that of the present invention in five charge / discharge cycles, but had poor adhesion of the electrode and could not be put to practical use. . An electrode using flaky graphite having a center particle diameter smaller than the center particle diameter of the electrode active material (Comparative Example 6);
The electrode using the spherical graphite instead of the flaky graphite (Comparative Example 7) had a low capacity in charge and discharge.

[0032]

As described in detail above, according to the present invention, an electrode layer made of at least an electrode active material, a conductive material and a binder is provided on an electrode current collector, and the electrode active material is made of Li _x Ni.
_y M _z O ₂ (provided that 0.8 <x <1.2, 0.8 <y +
z <1.2, 0 ≦ z ≦ 0.35, and M is Co, A
1, at least one of Mn and Fe) in the electrode layer.
g / cm ³ is contained in the range of ~3.2g / cm ^3, the amount of binder in the electrode layer is in the range of 1 to 5 wt%, median particle size of conductive material than the median particle size of the electrode active material The electrode for the non-aqueous electrolyte battery is made of large flaky graphite, so the connection between the electrode active material and the conductive material is good, the flow of electrolyte ions is very good, and the electrode layer adheres to the electrode current collector. An electrode for a non-aqueous electrolyte battery having excellent chargeability and high charge / discharge capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the structure of a charge / discharge capacity measurement cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Beaker 2 ... Silicon stopper 3 ... Electrode (working electrode) 4 ... Counter electrode 5 ... Reference electrode 6 ... Luggin tube 7 ... Electrolyte

Claims (1)

[Claims] At least Li _x Ni _y M _z O ₂ (provided that 0.8 <x <1.2, 0.8 <y + z <1.2, 0
≦ z ≦ 0.35, and M is one or more of Co, Al, Mn, and Fe), and a non-aqueous electrolyte in which an electrode layer made of an electrode active material, a conductive material, and a binder is formed on an electrode current collector. in the battery electrode, in the range the amount of the electrode active material in a unit volume of the electrode layers is ^{2.5g / cm 3 ~3.2g / cm 3} , a range amount of binder in the electrode layer is 1 to 5 wt% Wherein the conductive material is flaky graphite having a central particle diameter larger than the central particle diameter of the electrode active material.