JP2000251938A - Manufacture of all solid lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To retard interface reaction between a solid electrolyte and electrode active materials by interposing solid electrolyte powder between a positive electrode active material body made by mixing positive electrode active material powder and solid electrolyte powder and a negative electrode active material body made by mixing negative electrode active material powder and solid electrolyte powder, heating with microwaves, and then sealing them in a battery can. SOLUTION: A positive electrode active material body 3 of a coin type lithium battery is prepared by mixing positive electrode active material powder and solid electrolyte powder and heating with microwaves, and a negative electrode active material body 6 is prepared by mixing negative electrode active material powder and solid electrolyte powder and heating with microwaves. The negative electrode active material body 6 is a mixture of an oxide having charging-discharging potential lower than that of a positive electrode active material in the positive electrode active material body 3 and the solid electrolyte powder. A solid electrolyte 5 is prepared by also heating with microwaves. As an oxide used in the positive electrode active material body 3 and the negative electrode active material body 6, lithium manganese composite oxide, for example, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing an all-solid lithium battery.

[0002]

2. Description of the Related Art With the recent remarkable development of portable devices typified by portable telephones and personal computers, demand for batteries as power sources has been rapidly increasing. In particular, lithium ion batteries are batteries that use lithium, which has a low atomic weight and a large ionization energy, and are therefore being actively studied as batteries that can obtain high energy densities. It has been used. These lithium-ion batteries are roughly classified into cylindrical type and square type.In both cases, the positive electrode and the negative electrode are inserted through a separator into a battery case. The structure has been injected and sealed.

In the above-mentioned lithium ion battery, lithium cobalt oxide (LiCoO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) are generally used as a positive electrode active material. Further, a carbon material such as coke and carbon fiber is used for the negative electrode active material. LiCo listed here
The charge and discharge voltage of O ₂ and LiMn ₂ O ₄ is about 4V. On the other hand, the charge / discharge potential of the carbon material is around 0V. Therefore, a lithium ion battery achieves a high voltage of about 3.5 V by combining these positive electrode active materials and negative electrode active materials.

[0004] In recent years, with the demand for thin, light and small electronic devices such as video photographing devices, notebook personal computers, and portable information terminals such as portable telephones, the above-mentioned organic electrolytic solution has been required. Instead, a polymer electrolyte and an organic electrolyte were mixed between a pair of positive and negative electrodes. Attention has been focused on polymer electrolyte batteries. However, since these lithium ion batteries or polymer electrolyte batteries use a liquid as an electrolyte, the problem of liquid leakage cannot be eliminated at all. Further, when an abnormality such as a short circuit occurs in the battery, there is a risk that the organic electrolyte reacts and the battery is ignited. Therefore, in order to ensure the safety of the battery, development of a lithium battery formed of a nonflammable solid is desired.

As an electrolyte used in such a battery, lithium halide, lithium nitride, lithium ion conductive sulfide amorphous, or Li ₂ O—B ₂ O ₃ —
A solid electrolyte such as a lithium ion conductive oxide glass such as SiO ₂ is being researched and developed. Since these electrolytes are inorganic solid powders, the powders are used under pressure when applied to batteries. However, in pressure molding of powder, the bonding between particles is basically in a state close to point contact, and the impedance of the electrode is high, making it difficult to charge and discharge with a large current. to solve this problem,
The solid electrolyte layer may be formed under pressure at a temperature between the softening point of the solid electrolyte and the glass transition point or less, or a mixture of the cathode active material powder and the solid electrolyte powder, and the mixture of the anode active material powder and the solid electrolyte powder. After sandwiching the solid electrolyte layer obtained by press-molding the solid electrolyte powder with the negative electrode, or pressing the solid electrolyte at a temperature equal to or higher than the softening point and lower than the glass transition point of the solid electrolyte, one of the positive and negative electrodes Consists of a mixture of the active material powder and the solid electrolyte powder, after obtaining the electrode and the solid electrolyte powder by pressure molding, the solid electrolyte layer is superimposed, and these are softened point or more and glass transition point or less of the solid electrolyte. A battery which is pressurized at a temperature has been proposed (JP-A-8-138724). Or, the average particle size is 0.1 to
A 50 μm active material powder and a solid electrolyte powder having an average particle diameter of 0.1 to 50 μm were mixed at a weight ratio of 3.0: 7.0 to 9.5:
By mixing at 0.5, both the ion conduction path and the electron conduction path in the electrode are ensured, the utilization rate in the electrode is improved, the current collection efficiency is increased, and the electrode capable of large current charging and discharging is possible. (Japanese Patent Laid-Open No. 8-195219)
issue).

[0006]

However, when pressure molding is performed at a temperature between the softening point and the glass transition point of the solid electrolyte, the electrode active material and the solid electrolyte may react in the heating step. In particular, many electrode active materials contain a transition metal element, which easily diffuses into the solid electrolyte during the heating step, and has a problem that the original composition and crystal structure of the active material change. Therefore, it is very difficult to suppress this reaction in the heating step, and it is difficult to obtain reproducible battery characteristics. Alternatively, even when two kinds of powders having different average particle diameters are mixed, a void still remains, and the void does not contribute to the battery reaction, so that there is a problem that the battery capacity is reduced. Further, in the powder molding method, the bonding between particles is basically in a state close to a point contact, and there is a problem that the contact area between the particles increases as the number of voids increases.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and suppresses the interfacial reaction between a solid electrolyte and an electrode active material, and reduces the filling rate of the electrode active material or the solid electrolyte. It is intended to improve the characteristics of the battery.

[0008]

In order to achieve the above object, a method for manufacturing an all solid lithium battery according to the present invention comprises a positive electrode active material body in which a positive electrode active material powder and a solid electrolyte powder are mixed; The solid electrolyte powder is sandwiched between the material powder and the negative electrode active material body in which the solid electrolyte powder is mixed, and microwave heating is performed.

Further, the positive electrode active material obtained by mixing the positive electrode active material powder and the solid electrolyte powder, and the negative electrode active material obtained by mixing the negative electrode active material powder and the solid electrolyte powder are each microwave-heated. Microwave heating is performed by sandwiching the solid electrolyte powder between the active material body and the negative electrode active material body.

Further, the positive electrode active material body in which the positive electrode active material powder and the solid electrolyte powder are mixed, the negative electrode active material body in which the negative electrode active material powder and the solid electrolyte powder are mixed, and the solid electrolyte powder are each microwave-heated. Then, the solid electrolyte layer is sandwiched between the positive electrode active material body and the negative electrode active material body, and microwave heating is performed.

[0011] Further, the active material obtained by mixing one of the positive electrode active material powder and the negative electrode active material powder with the solid electrolyte powder is microwave-heated to form the positive electrode active material and the negative electrode active material. Then, the solid electrolyte powder is sandwiched between the positive electrode active material body and the negative electrode active material body, and microwave heating is performed.

In this manner, the interfacial reaction between the solid electrolyte and the electrode active material can be suppressed, the filling rate of the electrode active material or the solid electrolyte can be improved, and the characteristics of the battery can be improved. That is, the microwave heating is a method in which microwaves are absorbed by a material and self-heat is generated from the inside of the material, and rapid heating is possible as compared with a conventional method of heating from the outside by thermal conductivity or radiation. Therefore,
Baking can be performed in a short time, and mass transfer between different materials can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for producing an all solid lithium battery according to the present invention will be described below. FIG. 1 is a cross-sectional view illustrating a configuration example of a coin-type lithium battery manufactured by the manufacturing method of the present invention. In FIG. 1, 1 is a positive electrode can, 2 is a positive electrode current collecting layer, 3 is a positive electrode active material, 5 is a solid electrolyte, 6 is a negative electrode active material, 7 is a negative electrode current collecting layer, and 8 is a negative electrode can.

The positive electrode current collecting layer 2 is disposed between the positive electrode can 1 and the positive electrode active material member 3 for adhesion and current collection, and is made of, for example, a polyimide adhesive containing a carbon material.

The positive electrode active material body 3 is made of a mixture of the positive electrode active material powder and the solid electrolyte powder, which is heated by microwave,
The negative electrode active material body 6 is formed by mixing the negative electrode active material powder and the solid electrolyte powder and heating them by microwave. The negative electrode active material member 6 is composed of a mixture of an oxide having a charge / discharge potential lower than that of the positive electrode active material in the positive electrode active material member 3 and a solid electrolyte powder. In addition, the solid electrolyte 5 is also formed by microwave heating.

The positive electrode active material 3 and the negative electrode active material 6
The following compounds may be mentioned as oxides to be used for: For example, lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide, lithium titanium composite oxide, titanium oxide, niobium oxide, vanadium oxide , Tungsten oxide and the like and their inducers. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material.
By comparing the charge / discharge potentials of the various compounds, a battery having a noble potential is used as a positive electrode, and a compound showing a noble potential is used as a negative electrode, whereby a battery having an arbitrary voltage can be formed.

Such electrode active material members 3 and 6 are (1)
The active material powder and the solid electrolyte powder are mixed and dispersed in water or a solvent in which a molding aid is dissolved.If necessary, a plasticizer and a dispersant are mixed to prepare a slurry. A method of heating the film which has been coated, dried and debindered on a film by microwave heating, or (2)
As before, a molding aid was added to the pre-mixed one, and the mixture was granulated and poured into a mold.
A method of microwave heating after removing the binder, or (3) a method of press-molding with a roll press machine to form a sheet, and then cutting the sheet as appropriate to apply microwaves is used.

As a heating furnace for performing microwave heating, a multi-mode resonator and a single-mode resonator can be used, and a microwave resonator generally has a frequency of 2.45 GHz.
Alternatively, a frequency of 6 GHz is used. The heating rate and the heating temperature are controlled by the microwave output, and the temperature of the object to be heated is read using an infrared thermometer or the like.

The granulation of (2) and (3) may be wet granulation from the slurry described in the method of (1) or dry granulation without using a solvent. In the method (2), a molding aid may not be used. Examples of the molding aid that can be used here include one or a mixture of two or more of polyacrylic acid, carboxymethylcellulose, polyvinylidene fluoride, polyvinyl alcohol, diacetylcellulose, hydroxypropylcellulose, polyvinylchlorite, and polyvinylpyrrolidone. No.

As the base film, for example, resin films such as polyethylene terephthalate, polypropylene, polyethylene and tetrafluoroethylene, and metal foils such as aluminum, stainless steel and copper can be used.

As the solid electrolyte, for example, Li _1.3 Al
_{0.3 Ti 1.7 (PO 4) 3} , Li 3. 6 Ge 0.6 V 0.4 O
_{4, Li 1 + x + y} Al x Ti 2-x Si y P 3-y O 12 crystalline solid electrolyte such as, 30LiI-41Li ₂ O-29P
₂ O ₅ and _{40Li 2 O-35B 2 O 5} -25LiNbO
Oxidized amorphous solid electrolyte such as ₃ , 45LiI-37
Li ₂ S-18P ₂ O ₅ and 1Li ₃ PO ₄ -63Li ₂
A sulfide-based amorphous solid electrolyte such as S-36SiS ₂ can be used.

The negative electrode current collecting layer 7 is disposed for bonding and collecting current between the negative electrode active material 6 and the negative electrode can 8 made of, for example, stainless steel, and is made of, for example, a conductive adhesive containing silver. The positive electrode can 1 containing the above-mentioned positive electrode active material 3 and the negative electrode active material 6
The negative electrode can 8 in which is stored and attached is caulked via the insulating packing 4 and sealed. The lithium battery to which the present invention is applied is a primary battery or a secondary battery as long as the positive electrode active material body and / or the negative electrode active material body is composed of a mixture with a solid electrolyte powder. Is also good. The battery shape is not limited to a cylindrical type, a square type, a button type, a coin type, a flat type and the like.

[0023]

EXAMPLES [Example] Lithium manganese was mixed by mixing lithium hydroxide and manganese dioxide so that the molar ratio of Li and Mn was 1: 2, and then firing the mixture at 900 ° C. for 15 hours in the air. Complex oxide (LiMn
₂ O ₄ ) was prepared and used as a positive electrode active material powder. Next, lithium hydroxide and titanium dioxide are mixed so that the molar ratio of Li and Ti is 4: 5.
By heating and baking at 0 ° C. for 15 hours, a lithium-titanium composite oxide (Li ₄ Ti ₅ O ₁₂ ) was prepared to obtain a negative electrode active material powder. To each of LiMn ₂ O ₄ and Li ₄ Ti ₅ O ₁₂ , 30LiI-41Li ₂ O-29P ₂ O ₅ was mixed, and a molding aid and a solvent were added and mixed to adjust the slurry.

This slurry was applied on a polyethylene terephthalate (PET) film with a doctor blade and then dried to form a sheet. Further select _{30LiI-41Li 2 O-29P 2} O 5 to the solid electrolyte powder, after a molding aid and a solvent was added and mixed to prepare a slurry into which was molded into the same sheetlike. The positive electrode active material body is 1.2 mm in thickness, and the negative electrode active material body is 1.0 m in thickness.
m, the solid electrolyte was a sheet having a thickness of 0.3 mm.

Each of the obtained sheet-like molded bodies was punched into a mold with a diameter of 16.5 mm, and then laminated so as to have a positive electrode active material body-a solid electrolyte-anode active material body. Bander. The delaminated laminate was further heated at a rate of 120 ° C./min and a firing temperature of 720 to 75.
Microwave heating was performed under the conditions of 0 ° C. and a baking time of 3 minutes.

The thickness of the obtained laminate was 2.0 mm. The microwave-heated laminated positive electrode active material body 3 was housed and mounted in the positive electrode can 1 via the positive electrode current collecting layer 2. on the other hand,
On the negative electrode side, similarly to the positive electrode side, the negative electrode active material body 6 was housed and mounted in the negative electrode can 8 via the negative electrode current collecting layer 7 made of a conductive adhesive. Next, the positive electrode can 1 and the negative electrode can 8 were caulked via the insulating packing 4 to assemble the coin-type lithium battery having an outer diameter of 20 mm and a thickness of 2.5 mm shown in FIG.

COMPARATIVE EXAMPLE The method for preparing the positive electrode active material powder and the negative electrode active material powder, the selection of the solid electrolyte, and the method for producing the laminate were performed in the same manner as in Example 1. The obtained positive electrode active material was a 1.3 mm thick sheet, the negative electrode active material was a 1.2 mm thick sheet, and the solid electrolyte was a 0.3 mm thick sheet. Each of the obtained sheet-shaped molded bodies was punched into a mold with a diameter of 16.5 mm, and then laminated so as to have a positive electrode active material body-solid electrolyte-negative electrode active material body, and was subjected to debanding at 200 ° C. for 5 hours.

Further, this laminate was heated in an electric furnace at a heating rate of 20 ° C./min, a firing temperature of 740 ° C., and a firing time of 10 m.
Heated in conditions. The thickness of the obtained laminate is 2.
1 mm. A coin-type lithium battery was assembled from this laminate in the same manner as in Example 1.

(Evaluation) Using the thus obtained coin type lithium battery for evaluation, the charging / discharging device was used to charge and discharge 2.5 V to the cell for evaluation at a current of 300 μA.
After the voltage reaches 2.5 V, the charging is stopped and held for 5 minutes.
The battery was discharged with a current of A, then charged again to 2.5 V, and after reaching this voltage, a charge / discharge cycle test was performed in which charging was stopped and held for 5 minutes, and the amount of discharged electricity was determined every fixed cycle. The performance as was evaluated.

As a result, in the sample of the above example, the electric discharge amount was 35 mAh, and in the comparative example, the electric discharge amount was 20 mAh.
Ah, which resulted in a large amount of discharge electricity of the sample subjected to microwave heating. Further, when the laminate was observed visually or with a binocular microscope, no change in the solid electrolyte layer was confirmed in the sample of the example, but the sample of the comparative example was the interface between the positive electrode active material and the solid electrolyte, particularly the solid electrolyte. Discoloration on the side was remarkable. This is presumed that the transition metal element contained in the positive electrode active material diffused or reacted in the solid electrolyte. This is presumed to be due to the fact that the step of microwave heating can suppress the reaction between the electrode active material and the solid electrolyte.

[0031]

As described above, the method for producing an all-solid lithium battery of the present invention performs microwave heating in the heating step of the positive electrode active material, the negative electrode active material, or the solid electrolyte. The interfacial reaction of the electrode active material can be suppressed, and the filling rate of the electrode active material or the solid electrolyte can be improved, so that the characteristics of the battery can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an all-solid lithium battery manufactured by a manufacturing method according to the present invention.

[Explanation of symbols]

1 ... Positive electrode can, 2 ... Positive current collecting layer, 3 ...
... Positive electrode active material, 4 ... Insulating packing, 5
..... Solid electrolyte, 6 ... Negative electrode active material, 7
.... Negative electrode current collecting layer, 8 ... Negative electrode can

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ei Higuchi 3-5 Koikodai, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratory, Kyocera Corporation (72) Inventor Makoto Osaki 3-chome Koikodai, Seika-cho, Kyoto Prefecture 5 Kyocera Corporation Central Research Center (72) Inventor Shinji Magome 3-5 Koikadai, Seika-cho, Soraku-gun, Kyoto F-term in Kyocera Corporation Central Research Center 5H014 AA01 BB01 BB06 EE10 5H015 AA01 BB00 BB01 BB07 BB17 BB18 CC01 CC11 DD01 EE01 EE18 5H024 AA02 BB01 BB07 BB18 CC03 FF23 FF31 5H029 AJ01 AK02 AK03 AL02 AL03 AM12 BJ12 CJ02 CJ08 CJ28 DJ09 DJ16 DJ17 DJ18

Claims (4)

[Claims] A solid electrolyte powder is sandwiched between a positive electrode active material body obtained by mixing a positive electrode active material powder and a solid electrolyte powder, and a negative electrode active material body obtained by mixing a negative electrode active material powder and a solid electrolyte powder. A method for producing an all-solid lithium battery which is sealed in a can after microwave heating. 2. The positive electrode active material body obtained by mixing a positive electrode active material powder and a solid electrolyte powder, and the negative electrode active material body obtained by mixing a negative electrode active material powder and a solid electrolyte powder are each subjected to microwave heating. A method for producing an all-solid lithium battery in which a solid electrolyte powder is sandwiched between an active material body and a negative electrode active material body, microwave-heated, and then sealed in a can. 3. The positive electrode active material body obtained by mixing the positive electrode active material powder and the solid electrolyte powder, the negative electrode active material body obtained by mixing the negative electrode active material powder and the solid electrolyte powder, and the solid electrolyte powder are each microwave-heated. And a method for producing an all-solid lithium battery in which a solid electrolyte layer is sandwiched between the positive electrode active material body and the negative electrode active material body, microwave-heated, and then sealed in a can. 4. A method of heating an active material obtained by mixing one of a positive electrode active material powder and a negative electrode active material powder with a solid electrolyte powder to form a positive electrode active material and a negative electrode active material. And a method for producing an all-solid lithium battery in which a solid electrolyte powder is sandwiched between the positive electrode active material body and the negative electrode active material body, microwave heated, and then sealed in a can.