JPH08148141A - Manufacture of electrode for lithium secondary battery - Google Patents

Abstract

PURPOSE: To improve the electron conductivity and charging/discharging characteristics without adding a conductive material by baking an active material layer obtained by applying the slurry containing an active material and a binder on a current collector board. CONSTITUTION: The slurry containing an active material having the grain size of 5μm or below and a binder is applied on a current collector board by the doctor blade method to obtain an active material layer. This active material layer is baked, and the active material layer is formed on the current collector board to obtain a positive electrode 3. The positive electrode 3 is arranged in a bottomed cylinder case 1, a separator 5 and a negative electrode 4 are laminated on it, then a seal plate 2 fitted with an insulating gasket 6 is inserted, and the edge section of the case 1 is integrally caulked to obtain a lithium secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode for a lithium secondary battery.

[0002]

2. Description of the Related Art Generally, in an electrode of a lithium battery, a carbon-based conductive agent such as acetylene black and a binder such as polytetrafluoroethylene are added to the active material, and the mixture is formed into a sheet. It is manufactured by a method of molding, coating on a current collector substrate such as a mesh, and pressure bonding.

[0003]

However, in the above method for manufacturing an electrode, a conductive agent, a binder, etc. are added to the active material. Therefore, in addition to the active material, electrochemical stability and mixing of these materials are added. It is necessary to take measures in consideration of the conditions, etc., which inevitably leads to an increase in manufacturing cost. In addition, since the conductive agent, the binder and the like are added, an extra electrolytic solution must be added, which also causes a decrease in the battery capacity per unit weight due to a decrease in the packing density of the active material. On the other hand, it is conceivable that the electrode is composed of only the powdered active material without adding a conductive agent or a binder, but a transition metal composite oxide (for example, LiCoO ₂ , LiNiO ₂₎ that does not have very high conductivity as an active material. , LiMnO ₂ ) is used, even if the capacity per unit weight becomes large,
It became clear that there is a problem that the overvoltage is large and the charge capacity is reduced.

Therefore, according to the present invention, sufficient electronic conductivity can be obtained even when the active material alone is used without using a conductive agent or the like which reduces the battery capacity per unit weight, and excellent charge / discharge characteristics are obtained. The purpose of the present invention is to make it possible to inexpensively manufacture a battery included in the battery.

[0005]

Means for Solving the Problems As a means for achieving the above object, the present invention is to make an active material into a slurry together with a binder so that a film thickness after firing on a current collector substrate by a doctor blade method becomes 20 μm or less. After the active material layer is formed on the substrate, the active material layer is baked.

As the material of the collector substrate, metals such as stainless steel, aluminum, copper and nickel, ceramics, synthetic resins and the like can be used, and these are any conventionally known materials such as plates, films, foils and screens. A form can be adopted.

Examples of the active material include Fe ₂ O ₃ , MnO ₂ ,
CuO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , LiOH-MnO ₂ , LiCo
Oxide active materials such as O ₂ , LiNiO ₂ and LiMn ₂ O ₄ may be mentioned. Among them, LiMn ₂ O ₄ and the general formula:
LiNi _x Co _1-x O ₂ (0 ≦ x ≦ 1), that is, a lithium-based composite oxide, that is, LiCoO ₂ , LiNiO ₂ and LiNi _x
It is preferred to use Co _1- xO ₂ (0 <x <1).
In a preferred embodiment, the active material used has a particle size of 5 μm or less.

[0008]

In the present invention, in the case of an oxide-based active material, a conductive agent must be added in order to give conductivity in a usual use method, but the electrode is very thin, specifically, 20 μm.
When the film thickness is less than or equal to m, a current collecting effect can be obtained without adding a conductive agent, and sufficient electronic conductivity can be obtained only with the active material.

[0009]

Example 1 Lithium carbonate and manganese dioxide were prepared as raw materials for the active material, and these were weighed and mixed so as to be LiMn ₂ O _4, and calcined at 800 ° C. for 10 hours. Next, toluene was added to this calcined powder and the mixture was pulverized by a ball mill to obtain an active material slurry having a D50 of 1 μm in Microtrac analysis. After adding 3% by weight of polybutyral to this slurry and mixing, a thickness of 30% was obtained by the doctor blade method.
The active material layer having a thickness of 30, 20, 10, and 5 μm was formed by directly coating the current collector substrate made of μm stainless steel (SUS316).

This active material layer was heat-treated at 400 ° C. in a natural atmosphere to evaporate and remove the added binder, and then 17 mm
It was punched into a disk shape of φ and dried under reduced pressure at 200 ° C. to obtain an electrode. A cell was assembled using this electrode as a positive electrode.
This cell is a coin-type battery, and as shown in FIG. 1, a positive electrode 3 composed of an active material layer 3b formed on a current collector substrate 3a is placed in a bottomed cylindrical case 1, and a separator 5 is placed thereon.
After the negative electrode 4 and the negative electrode 4 are sequentially laminated, the sealing plate 2 fitted with the insulating gasket 6 is inserted, and the edge portion of the case 1 is caulked to be integrated. It should be noted that as the electrolytic solution, lithium perchlorate (LiClO ₄ ) was dissolved at 1 mol / l in a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1. Celgard 2 as a separator using a protic organic electrolyte
502 (trade name, Daicel Chemical Industries, Ltd.) was used as a negative electrode with a lithium metal having a thickness of 0.24 mm.

A charging / discharging cycle test was conducted on each of the obtained cells under the conditions of a charging / discharging current density: 1 mA / cm ² , a charging / discharging final voltage: 4.5V, and a discharge final voltage: 3.0V. The results are shown in FIG. For simplification, the charge / discharge cycle test result of the first cycle is shown on the upper side of FIG.
The charge / discharge cycle test results of the 0th cycle are shown.

As is apparent from FIG. 2, the cell of the comparative example using the active material layer having a film thickness of 30 μm has a small discharge capacity and poor cycle characteristics, whereas the cell of the present invention has a comparative discharge capacity. It is 150% or more compared with the example, and it can be seen that the cycle characteristics are remarkably improved.

[0013]

Example 2 Lithium carbonate and manganese dioxide were prepared as raw materials for the active material, and these were weighed and mixed so as to be LiMn ₂ O _4, and calcined at 800 ° C. for 10 hours. Next, toluene was added to the calcined powder, and the mixture was pulverized by a ball mill to obtain an active material slurry containing LiMn ₂ O ₄ having D50s of 2 μm, 5 μm and 7 μm in Microtrack analysis. After adding 3% by weight of polybutyral to each slurry and mixing them, a doctor blade method was applied directly on a stainless steel (SUS316) current collector substrate having a thickness of 30 μm to form an active material layer having a thickness of 10 μm. Formed.

A charge / discharge cycle test was conducted on each of the obtained cells under the same conditions as in Example 1. The results are shown in FIG. For simplification, the charge / discharge cycle test result of the first cycle is shown on the upper side of FIG. 3, and the charge / discharge cycle test result of the 100th cycle is shown on the lower side.

As is apparent from FIG. 3, the cell of the comparative example having an active material having a particle size outside the range of the present invention and having a particle size of 7 μm has a small discharge capacity and a poor cycle characteristic, whereas the cell according to the present invention. It can be seen that the discharge capacity and the cycle characteristics are remarkably improved as compared with those of the comparative example.

In the above embodiment, Li was used as the active material.
An example using Mn ₂ O ₄ has been described, but the present invention is not limited to this, and LiCoO ₂ , LiNiO ₂ , LiMn are used.
It is also possible to use O ₂ or LiNix Co _1-x O ₂ (0 <x <1), and, of course, the synthesis temperature and mixed solvent, the kind of binder, the amount of binder added, and the current collector substrate. Needless to say, known materials, negative electrode materials, electrolytic solutions, separators and the like can be arbitrarily used.

[0017]

As is apparent from the above description, according to the present invention, the active material is slurried together with the binder, and the film thickness after firing on the current collector substrate is 2 by the doctor blade method.
Since the active material layer is formed so as to have a thickness of 0 μm or less and is baked, an electrode having sufficient electronic conductivity can be manufactured without adding a conductive agent, and the active material has an average particle diameter of Since it was pulverized to have a particle size of 5 μm or less, a film having a uniform thickness can be formed and the cycle characteristics of the cell can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a cell using an electrode according to the method of the present invention.

FIG. 2 is a voltage capacity characteristic diagram of a cell of a lithium secondary battery using an electrode according to the method of the present invention.

FIG. 3 is a voltage capacity characteristic diagram of a cell of a lithium secondary battery using an electrode according to the method of the present invention.

[Explanation of symbols]

 1 Case 2 Sealing Plate 3 Positive Electrode 3a Current Collector Substrate 3b Active Material Layer 4 Negative Electrode 5 Separator 6 Insulation Gasket

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunizaburo Banno 2 26-10 Tenjin Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. An active material is slurried together with a binder,
Manufacture of an electrode for a lithium secondary battery, which comprises forming an active material layer on a current collector substrate by a doctor blade method so that the film thickness after firing is 20 μm or less, and then firing the active material layer. Method. 2. The active material has the general formula: LiNi _x Co _1-x O _2.
The method for producing an electrode for a lithium secondary battery according to claim 1, which is a lithium-based composite oxide represented by (0 ≦ x ≦ 1). 3. The active material is LiMn ₂ O ₄
A method for producing an electrode for a lithium secondary battery as described above. 4. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the active material has a particle size of 5 μm or less.