JP2000311708A - Manufacture of battery formed entirely of solid lithium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a surface resistance between a solid electrolyte and an electrode active material by improving wettability of the solid electrolyte against the electrode active material, and to improve a battery property by enhancing a filling rate of an electrode active material body or the solid electrolyte. SOLUTION: In this manufacturing method of a battery entirely formed of solid lithium, a solid electrolyte 4 is sandwiched between a positive electrode active material body 2 containing a lithium compound and a negative electrode active material body 3 and is sealed in a package 1. A metallic oxide constituting the positive electrode active material body 2 and/or the negative electrode active material body 3 is coated with a coupling agent or alkoxide, and then powder which is the same material as the solid electrolyte 4 is mixed and heated.

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 capable of obtaining high energy densities. Has been reached. 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 the battery case, and the organic electrolyte is injected into the container. It is a structure that is 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. LiCoO listed here
₂ and LiMn ₂ O _{4 have} a charge / discharge voltage of about 4V. On the other hand, the charge / discharge voltage 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, lightweight, and compact electronic application devices represented by portable information terminal devices such as video photographing devices, notebook personal computers, and mobile phones, the above-mentioned organic electrolyte solution has been required. Instead, a polymer electrolyte battery in which a polymer electrolyte and an organic electrolyte are mixed between a pair of positive and negative electrodes has attracted attention.

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. Also,
When an abnormality such as a short circuit occurs in the battery, there is a risk that the organic electrolyte solution reacts and the battery is ignited. Therefore, development of a lithium battery formed of a non-combustible solid is desired from the viewpoint of ensuring the safety of the battery.

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, 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.

In order to solve this problem, the solid electrolyte layer is formed under pressure at a temperature not lower than the softening point of the solid electrolyte and not higher than the glass transition point, or the solid electrolyte layer is formed by mixing a positive electrode active material powder and a solid electrolyte powder. After sandwiching the solid electrolyte layer obtained by press-molding the solid electrolyte powder with the anode made of the mixture of the negative electrode active material powder and the solid electrolyte powder, the softening point of the solid electrolyte is equal to or higher than the glass transition point. Pressing at a temperature or one of the positive electrode and the negative electrode is made of a mixture of the active material powder and the solid electrolyte powder, and the electrode and the solid electrolyte powder are pressed and obtained. In addition, a battery has been proposed in which these are pressurized at a temperature above the softening point of the solid electrolyte and below the glass transition point (JP-A-8-138724). Alternatively, an active material powder having an average particle size of 0.1 to 50 μm and an average particle size of 0.1
： 50 μm solid electrolyte powder in a weight ratio of 3.0: 7.
By mixing at 0 to 9.5: 0.5, both the ionic conduction path and the electron conduction path in the electrode are ensured, and the utilization rate in the electrode (theoretical capacity per unit weight of the active material in the electrode) Ratio of the measured discharge capacity to the
There has been proposed an electrode capable of increasing current collection efficiency and performing large current charging / discharging (Japanese Patent Application Laid-Open No. 8-195219).

[0008]

However, the solid electrolyte powder is compacted by pressing a positive electrode comprising a mixture of a positive electrode active material powder and a solid electrolyte powder and a negative electrode comprising a mixture of a negative electrode active material powder and a solid electrolyte powder. After sandwiching the obtained solid electrolyte layer, pressure is applied at a temperature not lower than the softening point of the solid electrolyte and not higher than the glass transition point, or one of the positive electrode and the negative electrode is a mixture of the active material powder and the solid electrolyte powder. When the electrode and the solid electrolyte powder are obtained by pressure molding, the solid electrolyte layer is overlaid, and these are pressed at a temperature higher than the softening point of the solid electrolyte and lower than the glass transition point. The solid electrolyte has poor wettability to the substance, resulting in uneven distribution of the solid electrolyte in the electrode active material body. Surface resistance is high, there is a problem that the impedance of the battery becomes high. In the heating step, the electrode active material may react with the solid electrolyte. 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 or crystal structure of the active material changes. 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, the void still remains,
Since this gap does not contribute to the battery reaction, 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.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and improves the wettability of a solid electrolyte to an electrode active material to suppress the interface resistance between the solid electrolyte and the electrode active material. It is another object of the present invention to improve the filling rate of the electrode active material or the solid electrolyte to improve the characteristics of the battery.

[0010]

In order to achieve the above object, in a method for manufacturing an all solid lithium battery according to the present invention, a solid electrolyte is sandwiched between a positive electrode active material containing a lithium compound and a negative electrode active material. And enclosing the solid electrolyte in a package, the metal oxide constituting the positive electrode active material and / or the negative electrode active material is coated with a coupling agent or an alkoxide, and then the solid electrolyte and Powders of the same material are mixed and heated to form the positive electrode active material and / or the negative electrode active material.

The above-mentioned coupling agent is preferably a silane coupling agent.

The alkoxide is preferably a tetraalkoxysilane.

Preferably, the electrolyte is an oxide amorphous glass.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for manufacturing an all-solid lithium battery according to the present invention will be described. FIG. 1 is a cross-sectional view illustrating a configuration example of an all-solid lithium battery manufactured by the manufacturing method of the present invention. In FIG. 1, 1 is a package, 2 is a positive electrode active material, 3 is a negative electrode active material, 4 is a solid electrolyte, 5 is a positive electrode current collector, and 6 is a negative electrode current collector.

The material of the package 1 is not limited as long as it can maintain airtightness. For example, a laminate made of aluminum, a metal such as nickel or aluminum, or a shrink case can be used.

The positive electrode current collector 5 or the negative electrode current collector 6 is provided for current collection of the positive electrode active material body 2 or the negative electrode active material body 3. For example, aluminum (Al), nickel (Ni),
A metal foil such as copper (Cu) can be used.

The positive electrode active material member 2 is made of a mixture of a positive electrode active material powder coated with a coupling agent or an alkoxide and a solid electrolyte powder and heated. The negative electrode active material member 3 is made of a coupling agent or an alkoxide. It is composed of a mixture of a coated negative electrode active material powder and a solid electrolyte powder and heated. The negative electrode active material member 3 includes the positive electrode active material member 2
It is composed of a mixture of an oxide having a charge / discharge potential lower than the charge / discharge potential of the positive electrode active material therein and a solid electrolyte powder.

The positive electrode active material 2 or the negative electrode active material 3
As the electrode active material 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 derivatives thereof can be used. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material, and those showing a noble potential by comparing the charge and discharge potentials of the two compounds are shown as the positive electrode, and those showing the noble potential are shown as the negative electrode. It can be used to form a battery of any voltage.

As a method of coating the electrode active materials 2 and 3 with a coupling agent or an alkoxide, the coupling agent is dissolved in a solvent such as isopropyl alcohol, ethanol or methanol, and the electrode active material is added to the mixed solution. The powder is mixed and heat-treated at a temperature of 100 ° C. or lower to hydrolyze the coupling agent molecules, thereby forming a reaction layer of the coupling agent molecules on the surface of the electrode active material powder. After removing the solvent under the environment of heating under reduced pressure,
It is obtained by performing a heat treatment at 50 ° C. or lower to cause a dehydration reaction of the coupling agent molecule.

As the coupling agent, there are silane-based, titanium-based, aluminum-based, and chromium-based coupling agents. From the viewpoint of improving the stability to the oxidation-reduction reaction of the battery or the wettability of the amorphous glass. It is desirable to use a silane coupling agent.

Examples of the alkoxide include tetraalkoxysilane, triisopropoxyaluminum, triethoxyborate, triethoxyborane, tetraethoxytitanate and the like. From the viewpoint of improving the wettability of amorphous glass, tetraalkoxysilane is used. Is desirable.

The silane coupling agent or tetraalkoxysilane can form a Si—O bond on the surface of the electrode active material powder, thereby improving the wettability to the electrode active material.

The amount of the coupling agent or alkoxide added is (weight of electrode active material (g) × specific surface area of electrode active material (m ² / g))） (minimum covering area of coupling agent or alkoxide (m ² / G)).

As the solid electrolyte 4, 30LiI-41 is used.
_{Li 2 O-29P 2 O 5} , 40Li 2 O-35B 2 O 5
-25LiNbO ₃ , 25Li ₂ O-25Al ₂ O ₃ −
_{50SiO 2, 40Li 2 O-6Y} 2 O 3 -54SiO
₂ or an oxide-based amorphous solid electrolyte such as 65LiNbO ₂ -35SiO ₂ .

Positive electrode active material 2 or negative electrode active material 3
Is to mix the active material powder and the powder of the same material as the solid electrolyte in a volume ratio of 50:50 to 97: 3,
(1) This is dispersed in water or a solvent in which a molding aid is dissolved, and a plasticizer and a dispersant are mixed as necessary to prepare a slurry, and this slurry is applied on a base film and dried. Or (2) a method in which a molding aid is added to a pre-mixed material in the same manner as described above, and granulated is charged into a mold, and pressure-molded by a press machine, or (3) a roll press For example, a method of forming a sheet by press molding with a machine is used.

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 usable here include one or a mixture of two or more of polyacrylic acid, carboxymethylcellulose, polyvinylidene fluoride, polyvinyl alcohol, diacetylcellulose, hydroxypropylcellulose, polyvinyl chloride, 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.

The all-solid-state lithium battery manufactured by the manufacturing method of the present invention may be any one in which the positive electrode active material body and / or the negative electrode active material body is composed of a mixture of a solid electrolyte and a powder of the same material. The battery may be a primary battery or a secondary battery. 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.

[0029]

EXAMPLES [Example] Lithium hydroxide and manganese dioxide were mixed at a molar ratio of Li: Mn of 1: 2, and this mixture was heated and baked at 900 ° C. in the air for 15 hours to obtain lithium manganese. 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, and this mixture is mixed with 85% of the air.
By heating and sintering 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.

Each of the LiMn ₂ O ₄ and Li ₄ Ti ₅ O ₁₂ was coated with trimethoxysilane (manufactured by Shin-Etsu Silicone), which is a silane coupling agent represented by the chemical formula 1.

[0031]

Embedded image

Each of LiMn ₂ O ₄ and Li ₄ Ti ₅ O ₁₂ was mixed with 30LiI-41Li ₂ O-29P ₂ O ₅ , and further, a molding aid and a solvent were added and mixed to prepare a slurry.

This slurry was applied on a polyethylene terephthalate (PET) film with a doctor blade and then dried to form a sheet. Further, 30LiI-41Li2O- ₂ is used as a powder of the same material as the solid electrolyte.
9P ₂ O ₅ was selected, a molding aid and a solvent were added thereto and mixed to prepare a slurry, which was formed into a sheet in the same manner as described above. The positive electrode active material was a sheet having a thickness of 0.8 mm, the negative electrode active material was a sheet having a thickness of 0.7 mm, and the solid electrolyte was a sheet having a thickness of 0.3 mm.

[0034] Each of the obtained sheet-like molded articles was molded into
After punching into a square having a size of 20 mm × 20 mm, the positive electrode active material body, the solid electrolyte, and the negative electrode active material
Debander at 0 ° C. for 5 hours. The delaminated laminate was further heated under the conditions of a temperature of 600 ° C. and a firing time of 1 hour.

The thickness of the obtained laminate was 1.0 mm. A positive electrode current collector 5 is applied to the heated positive electrode active material body 2 of the laminate.
The negative electrode side was bonded to the negative electrode active material body 3 in the same manner as the positive electrode side, and the negative electrode current collector 6 was mounted on the aluminum laminate of the package 1. The aluminum laminate was prepared by cutting two pieces having a size of 25 mm × 25 mm, and the outer periphery of the aluminum laminate was thermocompression-bonded across the laminate in which the current collectors were joined. A square lithium battery having a size of 25 mm and a thickness of 2.0 mm was assembled.

[Comparative Example] A method for preparing a positive electrode active material powder and a negative electrode active material powder, except that the silane coupling agent was not coated on the positive electrode active material powder and the negative electrode active material powder,
The selection of the solid electrolyte and the method of manufacturing the laminate were performed in the same manner as in Example 1. The obtained positive electrode active material body has a thickness of 0.8 m.
m, the negative electrode active material body was a sheet having a thickness of 0.7 mm, and 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 square of 20 mm × 20 mm with a mold, and then laminated so as to have a positive electrode active material body-solid electrolyte-negative electrode active material body and debanded at 300 ° C. for 5 hours. .

Further, the laminate was heated in an electric furnace at a temperature of 60.degree.
Heating was performed at 0 ° C. for a firing time of 1 hr. The thickness of the obtained laminate was 1.1 mm. A prismatic lithium battery was assembled from this laminate in the same manner as in the example.

(Evaluation) A charge / discharge cycle test was performed using a charge / discharge device using the thus obtained rectangular lithium battery for evaluation. The charging / discharging conditions were as follows: the evaluation cell was charged to a voltage of 2.5 V with a current of 300 μA, and after the voltage reached 2.5 V, charging was stopped and held for 5 minutes.
Discharge with a current of 300 μA to a voltage of V, then 2.5 V
After reaching this voltage, charging was stopped and maintained for 5 minutes. The amount of discharge electricity was determined for each fixed cycle, and the performance as a battery was evaluated.

As a result, the discharge capacity of the sample of the above example was 27 mAh, and the discharge capacity of the comparative example was 15 mAh.
Thus, the sample in which the electrode active material was coated with the coupling agent had a large discharge capacity. When the cross sections of the positive electrode active material and the negative electrode active material of the laminate were observed with an electron microscope, the electrode active material using the electrode active material coated with the coupling agent showed the same material as the mixed solid electrolyte. It was confirmed that the active material was present at the triple point of the active material, but the same material as the solid electrolyte was scattered in the electrode active material using the electrode active material that was not coated with the coupling agent. It was confirmed that. This is presumably because the coating treatment of the electrode active material with the coupling agent improved the wettability of the same material as the solid electrolyte and facilitated the flow of the same material as the solid electrolyte during heating. It is also assumed that the improved wettability reduced the interfacial resistance between the same material of the solid electrolyte and the electrode active material, thereby reducing the battery impedance and increasing the discharge capacity.

[0040]

As described above, the method for producing an all-solid lithium battery according to the present invention provides a method for coating a positive electrode active material and / or a negative electrode active material with a silane coupling agent or an alkoxide. The wettability of the same material as the solid electrolyte made of the oxide amorphous glass mixed with the negative electrode active material body is improved, the interface resistance in the electrode is reduced, and the impedance of the battery can be reduced.
The discharge current increases, and as a result, a high energy density is obtained, and 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 ... Package, 2 ... Positive electrode active material,
3... Negative electrode active material body, 4... Solid electrolyte, 5... Positive electrode current collector, 6... Negative electrode current collector

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yoko Mishima 3-5-chome, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratory, Kyocera Corporation (72) Inventor Shinji Magome 3-chome, Seika-cho, Soraku-gun, Kyoto 5 Kyocera Corporation Central Research Laboratory (72) Inventor Nobuyuki Kitahara 3-chome, Seika-cho, Soraku-gun, Kyoto Prefecture 5-5-2 Kyocera Corporation Central Research Laboratory (72) Inventor, Ei Higuchi Seika-cho, Kyoto 3-5-5 Kyocera Corporation Central Research Laboratory F-term (reference) 5H029 AJ06 AK02 AK03 AL06 AM12 BJ02 BJ03 BJ04 BJ12 CJ02 CJ03 CJ08 CJ22 DJ08 DJ16 DJ18 EJ11

Claims (4)

[Claims] 1. A method for manufacturing an all-solid lithium battery in which a solid electrolyte is sandwiched between a positive electrode active material body containing a lithium compound and a negative electrode active material body and sealed in a package, the positive electrode active material body and / or After the electrode active material constituting the negative electrode active material body is coated with a coupling agent or an alkoxide, a powder made of the same material as the solid electrolyte is mixed and heated to heat the positive electrode active material body and / or the negative electrode active material body Forming an all-solid lithium battery. 2. The method according to claim 1, wherein the coupling agent is a silane coupling agent. 3. The method according to claim 1, wherein the alkoxide is tetraalkoxysilane. 4. The method for producing an all-solid lithium battery according to claim 1, wherein the electrolyte is an amorphous glass of an oxide.