JP7850872B2 - all solid state battery - Google Patents

Description

This invention relates to an all-solid-state battery.
This application claims priority based on Japanese Patent Application No. 2024-050671, filed in Japan on March 27, 2024, and the contents of that application are incorporated herein by reference.

In recent years, advancements in electronics technology have been remarkable, leading to the miniaturization, weight reduction, thinning, and increased functionality of portable electronic devices. Consequently, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which power these devices. All-solid-state batteries, which use solid electrolytes, are attracting attention as a result.

For example, Patent Document 1 discloses an all-solid-state battery having a solid electrolyte containing Li3 _{+ xSixP1 -xO4 and} a positive electrode active material containing _LiCoO2 .

Japanese Patent Publication No. 2023-125396

Battery capacity is the amount of electricity a battery can output from the start to the end of its use, and a large capacity is desirable. There is a demand for all-solid-state batteries with large capacities.

This disclosure has been made in view of the above-mentioned issues and aims to provide a large-capacity all-solid-state battery.

To solve the above problems, the following means are provided.

(1) The all-solid-state battery according to the first embodiment comprises a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The solid electrolyte layer contains a solid electrolyte having a γ- _Li3PO4 structure. The solid electrolyte layer has a cobalt _- containing region containing cobalt. The cobalt-containing region does not have a cobalt-rich region that continuously connects the positive electrode and the negative electrode. The cobalt-rich region has a cobalt content of 1 atm% or more.

(2) In the all-solid-state battery according to the above embodiment (1), the cobalt-containing region does not have to include the cobalt-rich region.

(3) In the all-solid-state battery according to the above embodiment (1) or (2), the proportion of the cobalt-containing region in the solid electrolyte layer may be 20% or more and 100% or less.

(4) In an all-solid-state battery according to any of the above embodiments (1) to (3), the positive electrode may contain cobalt, and the solid electrolyte layer may have the cobalt-containing region in the portion that is in contact with the positive electrode.

(5) In an all-solid-state battery according to any of the above embodiments (1) to (4), the solid electrolyte layer may have a first region and a second region. The first region is closer to the positive electrode than the second region in the stacking direction. The cobalt concentration in the first region is higher than the cobalt concentration in the second region.

(6) In the all-solid-state battery according to embodiment (5) above, the cobalt concentration in the first region and the second region may be uniform in an in-plane direction perpendicular to the stacking direction.

(7) In an all-solid-state battery according to any of the above embodiments (1) to (4), the solid electrolyte layer may have a first region and a second region. The first region is closer to the positive electrode than the second region in the stacking direction. The cobalt concentration in the second region is higher than the cobalt concentration in the first region.

(8) In the all-solid-state battery according to the above embodiment (7), the cobalt concentration in the first region and the second region may be uniform in an in-plane direction perpendicular to the stacking direction.

(9) In an all-solid-state battery according to any of the above embodiments (1) to (8), the negative electrode may contain metallic lithium, a metal alloyable with lithium, a metalloid or compound, or graphite.

(10) In an all-solid-state battery according to any of the above embodiments (1) to (9), the negative electrode may contain metallic lithium that is deposited by charging.

The all-solid-state battery according to the above embodiment has a large capacity.

This is a cross-sectional view of an all-solid-state battery according to the first embodiment. This is an enlarged cross-sectional view of a characteristic portion of the all-solid-state battery according to the first embodiment. This is an enlarged cross-sectional view of a characteristic portion of an all-solid-state battery according to a first modified example of the first embodiment. This is an enlarged cross-sectional view of a characteristic portion of an all-solid-state battery according to a second modified example of the first embodiment.

The following description of this embodiment will be made in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without changing its technical requirements.

The directions are defined as follows: The stacking direction of the laminate 4 is defined as the z-direction, one direction in the plane perpendicular to the z-direction is defined as the x-direction, and the direction perpendicular to both the x-direction and the z-direction is defined as the y-direction. Hereafter, one direction in the z-direction may be referred to as "up," and the opposite direction as "down." Up and down do not necessarily coincide with the direction in which gravity acts.

Figure 1 is a schematic cross-sectional view of an all-solid-state battery 10 according to this embodiment. The all-solid-state battery 10 has a laminate 4 and terminal electrodes 5 and 6. The terminal electrodes 5 and 6 are in contact with opposing surfaces of the laminate 4, respectively. The terminal electrodes 5 and 6 are formed on the side surfaces of the laminate 4 that intersect (are perpendicular to) the laminate surface.

The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The positive electrode 1, negative electrode 2, and solid electrolyte layer 3 are laminated in the laminate 4. The number of layers for the positive electrode 1 and negative electrode 2 is not limited. The solid electrolyte layer 3 is located at least between the positive electrode 1 and the negative electrode 2. Between the positive electrode 1 and the terminal electrode 6, and between the negative electrode 2 and the terminal electrode 5, there is, for example, the same solid electrolyte as the solid electrolyte layer 3. One end of the positive electrode 1 is connected to the terminal electrode 5. One end of the negative electrode 2 is connected to the terminal electrode 6.

The all-solid-state battery 10 charges or discharges by the exchange of ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. Figure 1 shows a stacked battery, but a wound-type battery may also be used. The all-solid-state battery 10 is used in, for example, laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc. Furthermore, the all-solid-state battery 10 may be a liquid-injection type in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

"Positive electrode"
The positive electrode 1 includes, for example, a positive electrode current collector layer 1A and a positive electrode active material layer 1B. The positive electrode active material layer 1B is in contact with at least one surface of the positive electrode current collector layer 1A.

The positive electrode current collector layer 1A can be any conductive material that is resistant to oxidation during charging and corrosion. Examples of materials for the positive electrode current collector layer 1A include metals such as aluminum, stainless steel, nickel, titanium, and gold, and conductive resins. The positive electrode current collector layer 1A may also be in the form of powder, foil, punched, or expanded material. The positive electrode current collector layer 1A may also contain the positive electrode active material included in the positive electrode active material layer 1B.

The positive electrode active material layer 1B comprises a positive electrode active material, a solid electrolyte, and a conductive additive, and optionally includes a binder.

The positive electrode active material is not particularly limited as long as it can reversibly carry out intercalation and deintercalation of lithium ions, and any positive electrode active material used in known all-solid-state batteries can be used. Examples of positive electrode active materials include lithium-containing metal oxides and lithium-containing metal phosphorus oxides.

Lithium-containing metal oxides include, for example, lithium cobalt oxide ( _LiCoO₂ ), lithium nickelate ( _LiNiO₂ ), lithium manganese spinel ( _{LiMn₂O₄ )} , and composite metal oxides represented by the general formula: LiNi _x Co _y Mn _{z O₂} (x + y + z = 1), lithium vanadium compounds _{( LiVOPO₄} , _Li₃V₂ ( _PO₄ ) _₃ ), olivine-type _LiMPO₄ (where M represents at least one selected from Co, Ni, Mn, _{and Fe), lithium titanate (Li₄Ti₅O₁₂ )} , _etc.

Furthermore, the positive electrode active material may not contain lithium. Examples of such positive electrode active materials include lithium-free metal oxides ( _MnO₂ , _V₂O₅ , _etc. ), lithium-free metal sulfides ( _MoS₂, etc.), and lithium-free fluorides ( _FeF₃ , _VF₃ , etc.). When using a lithium-free positive electrode active material, the negative electrode is pre-doped with lithium ions, or a negative electrode containing lithium ions is used.

The positive electrode active material may contain, for example, cobalt. More preferably, the positive electrode active material contains lithium cobalt oxide ( _LiCoO₂ ) or a cobalt composite oxide (e.g., LiNi _x Co _y Mn _z O _z ) in which some of the cobalt in lithium cobalt oxide is replaced with other transition metals. When the positive electrode active material contains cobalt, the electronic conductivity between the cobalt-containing solid electrolyte layer 3 and the positive electrode active material layer 1B is improved, and the internal resistance of the all-solid-state battery 10 is reduced.

The conductive additive is not particularly limited as long as it improves the electronic conductivity within the positive electrode active material layer 1B, and known conductive additives can be used. Examples of conductive additives include carbon powder, carbon nanotubes, carbon materials, metal powders, mixtures of carbon materials and metal powders, and conductive oxides. Examples of carbon powders include carbon black, acetylene black, and Ketjen black. Examples of metal powders include copper, nickel, stainless steel, and iron powders. The conductive additive improves the electronic conductivity of the positive electrode active material layer 1B. The conductive additive may be in the form of a powder or fibers.

The binder bonds the positive electrode current collector layer 1A to the positive electrode active material layer 1B, the positive electrode active material layer 1B to the solid electrolyte layer 3, and the various materials that make up the positive electrode active material layer 1B to each other.

The binder can be used within a range that does not impair the function of the positive electrode active material layer 1B. The binder may be omitted if it is not needed. The binder content in the positive electrode active material layer 1B is preferably, for example, 0.5% to 30% by volume. Here, the volume percentage is approximately equal to the area percentage in a cross-section measured by a scanning electron microscope. Therefore, the area ratio in a cross-section measured by a scanning electron microscope can be directly considered as the volume ratio.

Examples of binders include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In addition to the above, other binders such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin may also be used. Furthermore, conductive polymers having electronic conductivity or ionic conductive polymers having ionic conductivity may be used as binders. Examples of conductive polymers having electronic conductivity include polyacetylene. In this case, since the binder also functions as a conductive additive, it is not necessary to add a conductive additive. Examples of ionic conductive polymers having ionic conductivity include those that conduct lithium ions, and include composites of monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphozenes, etc.) and lithium salts such as _LiClO₄ , _LiBF₄ , _LiPF₆, etc., or alkali metal salts mainly composed of lithium. Polymerization initiators used in compounding include, for example, photopolymerization initiators or thermal polymerization initiators compatible with the above-mentioned monomers. Required properties for the binder include oxidation/reduction resistance and good adhesion.

"Negative electrode"
The negative electrode 2 includes, for example, a negative electrode current collector layer 2A and a negative electrode active material layer 2B. The negative electrode active material layer 2B is in contact with at least one surface of the negative electrode current collector layer 2A.

The negative electrode current collector layer 2A is conductive. The negative electrode current collector layer 2A comprises a metal or alloy containing, for example, one selected from the group consisting of Ag, Pd, Au, Pt, and Cu. The negative electrode current collector is, for example, an Ag, Cu, AgPd alloy. The negative electrode current collector layer 2A may also contain the negative electrode active material contained in the negative electrode active material layer 2B and the solid electrolyte contained in the solid electrolyte layer 3.

The negative electrode active material layer 2B contains a negative electrode active material. The negative electrode active material layer 2B may also contain a conductive additive, a binder, and a solid electrolyte.

The negative electrode active material can be any compound capable of intercalating and releasing ions. Examples of negative electrode active materials include carbon materials, metals, alloys, metalloids, or compounds that can combine with lithium (or alloy with lithium), composite materials of these metals, alloys, or metalloids with carbon materials, oxides, sulfur-modified polyacrylonitrile, and metallic lithium. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fibers (MCF), coke, glassy carbon, and calcined organic compounds. Examples of metals, alloys, metalloids, or compounds that can combine with lithium include Si, _SiO₂x , Sn, and aluminum. Examples of oxides include lithium titanate ( _{Li₄Ti₅O₁₂} ) _{and SnO₂} . Alternatively, metallic lithium deposited on the negative electrode during charging may be _used as the negative electrode active material. In this case, some of the metallic lithium dissolves during discharge.

The conductive additive improves the electronic conductivity of the negative electrode active material layer 2B. The conductive additive can be made from the same material as that used for the positive electrode active material layer 1B.

The binder bonds the negative electrode current collector layer 2A to the negative electrode active material layer 2B, the negative electrode active material layer 2B to the solid electrolyte layer 3, and the various materials constituting the negative electrode active material layer 2B to each other. The binder can be made of the same material as the positive electrode active material layer 1B. The binder content ratio can also be the same as that of the positive electrode active material layer 1B. If the binder is not needed, it does not need to be included.

"Solid electrolyte layer"
The solid electrolyte layer 3 is located between the positive electrode 1 and the negative electrode 2. The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is a material that can move ions by an externally applied electric field. For example, the solid electrolyte layer 3 conducts lithium ions and inhibits electron movement. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering. The solid electrolyte layer 3 may also be an unsintered body.

The solid electrolyte has _a γ- _Li₃PO₄ structure (Lithicon-type crystal structure). Solid electrolytes having a γ- _Li₃PO₄ type crystal structure have excellent ionic conductivity. Examples of solid electrolytes include Li₃ _{+ xSi₂xP₁ - xO₄} , Li₃ _{+ xSi₂xV₁ - xO₄} , Li₃+xGe₂xP₁ _{- xO₄} , Li₃ _{+ xGe₂xV₁ - xO₄} , and preferably Li₃ _{+ xSi₂xP₁ - xO₄} , where x satisfies 0.4 ≤ x ≤ _0.8 . The solid electrolyte may also be a ternary lithium oxide containing Si, V _{, Ge} , etc.

The thickness of the solid electrolyte layer 3 is, for example, 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. Furthermore, the thickness of the solid electrolyte layer 3 is preferably, for example, 1 μm or more.

Figure 2 is an enlarged cross-sectional view of the vicinity of the solid electrolyte layer 3 of the all-solid-state battery according to the first embodiment. The solid electrolyte layer 3 includes a cobalt-containing region. The cobalt-containing region is a region containing cobalt. Cobalt may exist in the solid electrolyte layer 3 as a single element or in a compounded state with other substances. The solid electrolyte layer 3 may consist only of the cobalt-containing region, or it may have both a cobalt-containing region and a cobalt-free region.

The cobalt-containing region is defined as the region in the solid electrolyte layer 3 where the cobalt content is 0.01 atom% or more. Preferably, the cobalt content in the cobalt-containing region is 10 atom% or less.
Hereafter, atomic percentages will be denoted as atom%, atm%, and at%, respectively.

The cobalt content in the entire solid electrolyte layer 3 is, for example, 0.01 atom% to 1 atom%, and preferably 0.01 atom% to 0.1 atom%. The cobalt content in the solid electrolyte layer 3 can be measured by energy-dispersive X-ray spectroscopy (EDS) or electron probe microanalyzer (EPMA). The cobalt content in the entire solid electrolyte layer 3 is determined by measuring the cobalt content at five different locations in the z direction and taking the average value. The measurement points are positioned at equal intervals in the z direction.

The cobalt-containing region is divided into a cobalt-rich region 31 and a cobalt-poor region 32. The cobalt-rich region 31 is the region with a cobalt content of 1 atm% or more. The cobalt-poor region 32 is the region with a cobalt content greater than 0 atm% and less than 1 atm%. The cobalt-containing region may not include the cobalt-rich region 31 and may consist only of the cobalt-poor region 32.

The cobalt-rich region 31 is not formed to continuously connect the positive electrode 1 and the negative electrode 2. That is, the solid electrolyte layer 3 does not have a cobalt-rich region 31 connecting the positive electrode 1 and the negative electrode 2. If there were a cobalt-rich region 31 connecting the positive electrode 1 and the negative electrode 2 within the solid electrolyte layer 3, a slight leak would occur through this cobalt-rich region 31, reducing the capacity of the all-solid-state battery 10.

Unlike the cobalt-rich regions 31, the cobalt-poor regions 32 may be located in any way within the solid electrolyte layer 3. For example, the cobalt-poor regions 32 may be present throughout the entire solid electrolyte layer 3, or they may be located to continuously connect the positive electrode 1 and the negative electrode 2, or the cobalt-poor regions 32 may be scattered throughout the solid electrolyte layer 3.

The proportion of the cobalt-containing region in the solid electrolyte layer 3 is, for example, 20% to 100%, preferably 30% to 90%. Including a cobalt-containing region in the solid electrolyte layer 3 improves the ionic conductivity of the solid electrolyte layer 3.

Preferably, at least a portion of the cobalt-containing region is located in the area in contact with the positive electrode 1. If the positive electrode 1 contains cobalt, having a cobalt-containing region in the area in contact with the positive electrode can reduce the internal resistance of the all-solid-state battery 10.

The proportion of cobalt-rich regions 31 in the solid electrolyte layer 3 is, for example, 0% to 50%, preferably 10% to 50%. The proportion of cobalt-poor regions 32 in the solid electrolyte layer 3 is, for example, 5% to 100%, preferably 10% to 50%. The proportion of cobalt-rich regions 31 in the solid electrolyte layer 3 may be higher or lower than the proportion of cobalt-poor regions 32 in the solid electrolyte layer 3.

The solid electrolyte layer 3 may have a distribution of cobalt concentration in the z direction. For example, the cobalt concentration in the first region A1 of the solid electrolyte layer 3 may be higher than that in the second region A2. Conversely, the cobalt concentration in the second region A2 of the solid electrolyte layer 3 may be higher than that in the first region A1. The first region A1 is a region that is closer to the positive electrode 1 than the second region A2 in the z direction. The first region A1 and the second region A2 are regions that extend within the xy plane. It is preferable that the cobalt concentration in the first region A1 is uniform in the xy plane direction. It is also preferable that the cobalt concentration in the second region A2 is uniform in the xy plane direction. Here, uniformity within the xy plane means that when the cobalt content is measured at five different locations within the xy plane, the cobalt content at each measurement point is in the range of 90% to 110% of the average value of the cobalt content at each measurement point. If there is a cobalt concentration distribution in the z direction of the solid electrolyte layer 3, a potential difference is generated along the cobalt concentration distribution, improving the ionic conductivity within the solid electrolyte layer 3.

For example, when measuring the cobalt content at five different locations in the z-direction that are spaced at equal intervals in the solid electrolyte layer 3, the cobalt concentration at each measurement point may be higher closer to the positive electrode 1, or conversely, lower closer to the positive electrode 1. Furthermore, the cobalt concentration in the solid electrolyte layer 3 may decrease in a gradient in the z-direction as it approaches the positive electrode 1, as shown in Figure 3, or it may increase in a gradient in the z-direction as it approaches the positive electrode 1, as shown in Figure 4.

"Manufacturing method for all-solid-state batteries"
Next, a method for manufacturing the all-solid-state battery 10 will be described. First, a laminate 4 is manufactured. The laminate 4 is manufactured, for example, by a co-firing method or a sequential firing method.

The simultaneous firing method involves stacking the materials that form each layer and then firing them all at once to create the laminate 4. The sequential firing method involves firing each layer as it is formed. The simultaneous firing method allows for the creation of the laminate 4 with fewer steps than the sequential firing method. Furthermore, the laminate 4 produced by the simultaneous firing method is denser than the laminate 4 produced using the sequential firing method. The following explanation will use the simultaneous firing method as an example.

First, the materials constituting the laminate 4—the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, and the negative electrode current collector layer 2A—are made into a paste.

The method for forming the paste from each material is not particularly limited; for example, a method of mixing the powders of each material with a vehicle to obtain a paste can be used. Here, "vehicle" is a general term for the medium in the liquid phase. The vehicle includes solvents and binders.

Next, a green sheet is prepared. The green sheet is obtained by applying a paste prepared for each material onto a substrate such as a PET (polyethylene terephthalate) film, drying it as needed, and then peeling off the substrate. The method of applying the paste is not particularly limited; for example, known methods such as screen printing, coating, transfer, and doctor blade application can be used.

Next, the green sheets prepared for each material are stacked in a desired order and number of layers to create a laminated sheet. For example, the solid electrolyte layer 3 is obtained by stacking multiple solid electrolyte sheets using a paste for solid electrolyte layers. Cobalt is added to at least one of the multiple solid electrolyte sheets. The multiple solid electrolyte sheets may include, for example, a cobalt-rich sheet containing 1 atm% or more of cobalt, a cobalt-poor sheet containing less than 1 atm%, or a cobalt-free sheet with no added cobalt. By changing the stacking order and number of layers of the cobalt-rich sheet, cobalt-poor sheet, and cobalt-free sheet, the distribution of cobalt within the solid electrolyte layer 3 can be freely designed.

However, if all of the multiple solid electrolyte sheets are made of cobalt-rich sheets, a cobalt-rich region 31 connecting the positive electrode 1 and the negative electrode 2 will be formed within the solid electrolyte layer 3. Therefore, not all of the multiple solid electrolyte sheets are made of cobalt-rich sheets.

Furthermore, when stacking the green sheets, alignment and cutting are performed as needed. For example, when manufacturing parallel or series-parallel batteries, the green sheets are aligned so that the end face of the positive electrode current collector layer 1A and the end face of the negative electrode current collector layer 2A do not coincide, and then stacked.

The laminated sheet may be manufactured by creating a positive electrode unit and a negative electrode unit and then laminating these units. The positive electrode unit is a laminated sheet in which a solid electrolyte layer 3, a positive electrode active material layer 1B, a positive electrode current collector layer 1A, and a positive electrode active material layer 1B are laminated in this order. The negative electrode unit is a laminated sheet in which a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector layer 2A, and a negative electrode active material layer 2B are laminated in this order. The solid electrolyte layer 3 of the positive electrode unit and the negative electrode active material layer 2B of the negative electrode unit are laminated facing each other, or the positive electrode active material layer 1B of the positive electrode unit and the solid electrolyte layer 3 of the negative electrode unit are laminated facing each other.

Next, the fabricated laminated sheets are pressed together to improve the adhesion of each layer. Pressurization can be performed using, for example, a die press, a hot water isostatic press (WIP), a cold water isostatic press (CIP), or a hydrostatic press. It is preferable to perform the pressurization while heating. The heating temperature during pressing should be, for example, 40°C to 95°C. Then, the pressed laminate is cut into chips using a dicing device. If the laminate 4 is to be a sintered body, the chips are subjected to a debinder treatment and firing.

The debinding process can be carried out as a separate step from the firing process. Performing the debinding process allows for the thermal decomposition of binder components within the chip before the firing process, thereby suppressing the rapid decomposition of binder components during the firing process. In the debinding process, for example, heating is performed in an atmospheric environment at a temperature of 300°C to 800°C for a period of 0.1 hours to 10 hours. The atmosphere in the debinding process is an oxygen partial pressure environment where the materials constituting the positive electrode, negative electrode, and solid electrolyte do not undergo oxidation-reduction, or are difficult to oxidize. The type of gas can be arbitrarily selected to prevent reaction between the materials constituting the positive electrode, negative electrode, and solid electrolyte and the atmospheric gas. For example, it may be carried out in a nitrogen atmosphere, argon atmosphere, nitrogen-hydrogen mixed atmosphere, water vapor atmosphere, or a mixture thereof.

The firing process is carried out, for example, by placing the chip on a ceramic base. Firing is performed, for example, by heating to a temperature of 600°C to 1000°C under a nitrogen atmosphere. The firing time is, for example, 0.1 hours to 3 hours. The atmosphere during the sintering process is an oxygen partial pressure environment where the materials constituting the positive electrode, negative electrode, and solid electrolyte do not undergo oxidation-reduction, or are difficult to oxidize. The type of gas can be arbitrarily selected so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, it may be carried out in a nitrogen atmosphere, argon atmosphere, nitrogen-hydrogen mixed atmosphere, water vapor atmosphere, or a mixture thereof.

Alternatively, the laminate 4 may be placed in a cylindrical container with an abrasive such as alumina and barrel polished. This allows for chamfering of the corners of the laminate. Polishing may also be performed using sandblasting. Sandblasting is preferred because it allows for the removal of only specific parts.

Terminal electrodes 5 and 6 are formed on the opposing sides of the fabricated laminate 4. The terminal electrodes 5 and 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating. By following these steps, an all-solid-state battery 10 can be manufactured. If the terminal electrodes 5 and 6 are to be formed only in specific areas, the area is masked with tape or the like before the above process is performed.

The all-solid-state battery 10 according to this embodiment has a large capacity. This is thought to be because the solid electrolyte layer 3 contains cobalt but does not contain a cobalt-rich region 31 that continuously connects the positive electrode 1 and the negative electrode 2. When the solid electrolyte layer 3 contains cobalt, the internal resistance of the all-solid-state battery 10 decreases, and the capacity increases. Furthermore, by not having a cobalt-rich region 31 that continuously connects the positive electrode 1 and the negative electrode 2 in the solid electrolyte, the decrease in Coulomb efficiency due to slight leakage through the cobalt-rich region 31 can be suppressed.

Although embodiments of the present invention have been described in detail above with reference to the drawings, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications to the configurations are possible without departing from the technical requirements of the present invention.

"Example 1"
Pastes for the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer were prepared.

The paste for the positive electrode active material layer was prepared by adding ethylcellulose and dihydroterpineol to _LiCoO2 . Ethylcellulose acts as a binder, and dihydroterpineol acts as a solvent.

Three types of pastes were prepared for the solid electrolyte layer: a cobalt-free paste, a paste containing less than 1 atm% cobalt, and a paste containing 1 atm% or more cobalt.

First, _Li₂CO₃ , _SiO₂ , _{and Li₃PO₄} were _used as starting materials and mixed in a molar ratio of 2:1:1. The mixing was performed wet for 16 hours using a ball mill with water as the dispersion medium. The mixture was calcined at 950°C for 2 _hours to produce _{Li₃.5Si₀.5P₀.5O₄} . Then, 100 parts by mass of this calcined powder, ₁₀₀ parts by mass of ethanol, and 200 parts by mass _of toluene were added to the ball mill and wet mixed. Finally, 16 parts by mass of polyvinyl butyral binder and 4.8 parts by mass of benzyl butyl phthalate were added and mixed to produce a cobalt-free paste for a solid electrolyte layer.

Next, cobalt was added to a portion of the cobalt-free solid electrolyte layer paste to prepare two pastes: one containing less than 1 atm% cobalt and another containing 1 atm% or more cobalt.

The paste for the negative electrode active material layer was prepared by adding ethylcellulose and dihydroterpineol to AgPd powder.

Next, solid electrolyte layer sheets were fabricated on a PET film using the three types of solid electrolyte layer pastes described above. The solid electrolyte layer sheets were created by laminating sheets of each of the three types of solid electrolyte layer pastes. The state of the cobalt-containing regions within the solid electrolyte sheet was controlled by changing the lamination order and their relative proportions.

Next, the positive electrode unit and negative electrode unit were manufactured using the following procedure. First, a paste for the positive electrode active material layer was printed onto the solid electrolyte layer sheet using screen printing to a thickness of 5 μm. Next, the printed paste for the positive electrode active material layer was dried at 80°C for 5 minutes. Then, a positive electrode current collector paste was printed onto the dried paste for the positive electrode active material layer and dried to form a positive electrode current collector layer. Then, the paste for the positive electrode active material was printed again onto the positive electrode current collector layer using screen printing to a thickness of 5 μm and dried. After that, the PET film was peeled off. In this way, a positive electrode unit was obtained in which the positive electrode active material layer/positive electrode current collector layer/positive electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer.

By replacing the paste for the positive electrode active material layer with the paste for the negative electrode active material layer and following the same procedure, a negative electrode unit was obtained in which the negative electrode active material layer/negative electrode current collector layer/negative electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer. The thickness of the negative electrode active material paste was 15 μm.

Furthermore, a solid electrolyte unit was fabricated by stacking five solid electrolyte layer sheets. Fifty electrode units (25 positive electrode units and 25 negative electrode units) were stacked alternately, sandwiching the solid electrolyte unit, to create a laminate. At this time, the units were stacked with a staggered arrangement such that the current collector layer of the odd-numbered electrode units extended only to one end face, and the current collector layer of the even-numbered electrode units extended only to the opposite end face. Six solid electrolyte layer sheets were then stacked on top of this stacked unit. Subsequently, this was formed by thermocompression bonding, and then cut to produce laminated chips. After that, the laminated chips were co-fired to obtain a laminate. Co-fired firing was performed in a nitrogen atmosphere, raising the temperature to 800°C at a heating rate of 200°C/hour, holding it at that temperature for 2 hours, and then allowing it to cool naturally.

A solid-state battery was fabricated by attaching terminal electrodes 5 and 6 to a sintered laminate (sintered body) using a known method.

The cross-section of the fabricated all-solid-state battery was measured using the EDS method to determine the distribution of cobalt in the solid electrolyte layer. In the solid electrolyte layer of Example 1, the proportion of cobalt-rich regions was 30%, the proportion of cobalt-poor regions was 40%, and the proportion of cobalt-free regions was 30%. Furthermore, no cobalt-rich regions were observed continuously connecting the positive and negative electrodes within the solid electrolyte layer. Nor were any cobalt-rich regions in contact with the positive electrode. In addition, no continuous change in cobalt concentration was observed at five measurement points equally spaced in the z direction within the solid electrolyte layer. Furthermore, for the first region A1 and the second region A2, which are located at different positions in the z direction, the cobalt concentration at five measurement points equally spaced in the x direction was measured to confirm the uniformity of cobalt concentration in the x and y directions, and the average value of the cobalt concentration in each region was calculated.

Furthermore, 100 similar samples were prepared, and the discharge capacity of the all-solid-state batteries was determined. The discharge capacity was calculated as the average of these samples. The discharge capacity was measured using a charge/discharge device BCS805 (product name: Biologic Corporation). For the discharge capacity, constant current charging (CC charging) was performed at a constant current of 0.2C rate until the battery voltage reached 4.0V in an environment of 25°C, then paused for 1 minute, and then discharged at a constant current of 0.2C rate until the battery voltage reached 0V (CC discharge). The capacity was measured during this process.

"Example 2"
Example 2 differs from Example 1 in that the type of solid electrolyte was changed. In Example 2, when preparing the solid electrolyte, _GeO2 was used instead of _SiO2 , and _{Li3.5Ge0.5P0.5O4} was prepared as the _{solid electrolyte} . Other conditions were the same as in Example 1, and the EDS and discharge capacity of _the cross-section were measured.

Examples 3-11
Examples 3 to 11 differ from Example 1 in the relative proportions of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer. These relative proportions were adjusted by changing the cobalt concentration in the sheet used to fabricate the solid electrolyte layer and by changing the stacking order of the sheets. Other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross-section were measured. In Examples 4, 9, and 10, a cobalt-rich region was confirmed at the position in contact with the positive electrode. In Example 10, a continuous change in cobalt concentration was confirmed at five measurement points arranged at equal intervals in the z direction. In Example 11, uniformity of cobalt concentration was confirmed in the first region A1 and the second region A2 in the xy plane.

"Comparative Example 1"
Comparative Example 1 differs from Example 1 in the ratio of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer. In Comparative Example 1, the solid electrolyte layer was prepared using only a cobalt-free paste for solid electrolyte layers. The solid electrolyte layer of Comparative Example 1 does not have cobalt-containing regions. In Comparative Example 1, as in Example 1, the EDS and discharge capacity of the cross-section were measured.

Comparative Examples 2 and 3
Comparative Examples 2 and 3 differ from Example 1 in the ratio of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer. In Comparative Examples 2 and 3, a cobalt-rich region continuously connecting the positive electrode 1 and the negative electrode 2 was confirmed. In Comparative Examples 2 and 3, the EDS and discharge capacity of the cross-section were measured in the same manner as in Example 1.

Comparative Example 4, Examples 12 and 13
Comparative Examples 4 and Examples 12 and 13 differ from Example 1 in that the positive electrode material was changed to LiNi _0.8 Co _0.1 Mn _0.1 O _2. The relative abundance of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer also differs from Example 1. Other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross-section were measured.

"Comparative Example 5, Examples 14, 15"
Comparative Examples 5 and Examples 14 and 15 differ from Example ₁ in that the positive electrode material is changed to _Li₂MnO₃ . Furthermore, the relative proportions of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer also differ from those of Example 1. Other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross-section were measured.

Examples 16 and 17
Example 16 differs from Example 1 in that the negative electrode material was changed. Example 17 differs from Example 1 in that the thickness of the paste for the negative electrode active material layer was set to 1 μm. Furthermore, Examples 16 and 17 differ from Example 1 in the relative proportions of cobalt-rich regions, cobalt-poor regions, and cobalt-free regions within the solid electrolyte layer. Other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross-section were measured. In Example 16, graphite was used as the negative electrode. In Example 17, by reducing the thickness of the paste for the negative electrode active material layer, the portion of silver exceeding the allowable limit during charging and discharging is deposited as metallic lithium and functions as the negative electrode. The negative electrode thickness in Table 1 is the thickness of the negative electrode at the time the all-solid-state battery was manufactured, before charging and discharging.

The results of Examples 1 to 17 and Comparative Examples 1 to 5 are summarized in Tables 1 to 3 below.

Examples 1 to 14 had a larger discharge capacity than Comparative Examples 1 to 5. In Comparative Examples 1, 4, and 5, the internal resistance of the all-solid-state battery was high because the solid electrolyte layer did not contain cobalt, and it is thought that the discharge capacity of the all-solid-state battery was not obtained sufficiently. In Comparative Examples 2 and 3, it is thought that the cobalt-rich region continuously connecting the positive electrode 1 and the negative electrode 2 caused leakage, and it is thought that the discharge capacity of the all-solid-state battery was not obtained sufficiently.

The all-solid-state battery of this embodiment is suitably applied as a power source for electronic devices.

1...Positive electrode, 1A...Positive electrode current collector layer, 1B...Positive electrode active material layer, 2...Negative electrode, 2A...Negative electrode current collector layer, 2B...Negative electrode active material layer, 3...Solid electrolyte layer, 4...Laminate, 5,6...Terminal electrodes, 10...All-solid-state battery, 31...Cobalt-rich region, 32...Cobalt-poor region, A1...First region, A2...Second region.

Claims (9)

It comprises a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode,
The solid electrolyte layer comprises a solid electrolyte having _a γ- _Li3PO4 structure.
The solid electrolyte layer has a cobalt-containing region containing cobalt,
The cobalt-containing region does not have a cobalt-rich region that continuously connects the positive electrode and the negative electrode.
The aforementioned cobalt-containing region has a cobalt content of 0.01 atom% or more and 10 atom% or less.
The cobalt-rich region is defined as having a cobalt content of 1 atm% or more.
An all-solid-state battery in which the proportion of the cobalt-containing region in the solid electrolyte layer is 20% or more and 100% or less . The all-solid-state battery according to claim 1, wherein the cobalt-containing region does not include the cobalt-rich region. The aforementioned positive electrode contains cobalt,
The all-solid-state battery according to claim 1, wherein the solid electrolyte layer has the cobalt-containing region in the portion that is in contact with the positive electrode. The solid electrolyte layer has a first region and a second region,
The first region is located closer to the positive electrode than the second region in the stacking direction.
The all-solid-state battery according to claim 1, wherein the cobalt concentration in the first region is higher than the cobalt concentration in the second region. The all-solid-state battery according to claim 4 , wherein the cobalt concentration is uniform in the in-plane direction perpendicular to the stacking direction in the first region and the second region. The solid electrolyte layer has a first region and a second region,
The first region is located closer to the positive electrode than the second region in the stacking direction.
The all-solid-state battery according to claim 1, wherein the cobalt concentration in the second region is higher than the cobalt concentration in the first region. The all-solid-state battery according to claim 6 , wherein the cobalt concentration is uniform in the in-plane direction perpendicular to the stacking direction in the first region and the second region. The all-solid-state battery according to claim 1, wherein the negative electrode comprises metallic lithium, silicon, silicon oxide, tin, aluminum , or graphite. The all-solid-state battery according to claim 1, wherein the negative electrode contains metallic lithium deposited by charging.