All-solid-state battery

Abstract

This all-solid-state battery (10) is provided with: a positive electrode (1); a negative electrode (2); and a solid electrolyte layer (3) disposed between the positive electrode (1) and the negative electrode (2). The solid electrolyte layer (3) contains a solid electrolyte having a γ－Ｌｉ３ＰＯ４ structure. The solid electrolyte layer (3) has a cobalt-containing region containing cobalt. The cobalt-containing region does not have a cobalt-rich region (31) continuously connecting the positive electrode (1) and the negative electrode (2). The cobalt-rich region (31) has a cobalt content of 1 atm % or more.

Description

All solid state battery

[0001] The present invention relates to an all-solid-state battery. This application claims priority to Japanese Patent Application No. 2024-050671, filed on March 27, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, electronics technology has made remarkable progress, leading to efforts to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for batteries that serve as the power source for electronic devices to be smaller, lighter, thinner, and more reliable, and all-solid-state batteries that use solid electrolytes have attracted attention.

[0003] For example, Patent Document 1 discloses Li ３＋ｘ Si ｘ P １－ｘ O ４ and a solid electrolyte containing LiCoO ２ and a positive electrode active material comprising:

[0004] Japanese Patent Application Laid-Open No. 2023-125396

[0005] Battery capacity is the amount of electricity that a battery can output from start to finish of use, and a large capacity is desirable. Therefore, there is a demand for all-solid-state batteries with large capacities.

[0006] The present disclosure has been made in view of the above problems, and aims to provide an all-solid-state battery with a large capacity.

[0007] In order to solve the above problems, the following means are provided.

[0008] (1) A first aspect of the all-solid-state battery includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The solid electrolyte layer is made of γ-Li ３ P.O. ４ 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.

[0009] (2) In the all-solid-state battery according to the above aspect (1), the cobalt-containing region may not include the cobalt-rich region.

[0010] (3) In the all-solid-state battery according to the above aspect (1) or (2), the cobalt-containing region may account for 20% or more and 100% or less of the solid electrolyte layer.

[0011] (4) In the all-solid-state battery according to any one of the above aspects (1) to (3), the positive electrode may contain cobalt, and the solid electrolyte layer may have the cobalt-containing region in a portion in contact with the positive electrode.

[0012] (5) In the all-solid-state battery according to any one of the above aspects (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.

[0013] (6) In the all-solid-state battery according to the above aspect (5), the first region and the second region may have a uniform cobalt concentration in an in-plane direction perpendicular to the stacking direction.

[0014] (7) In the all-solid-state battery according to any one of the above aspects (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.

[0015] (8) In the all-solid-state battery according to the above aspect (7), the first region and the second region may have a uniform cobalt concentration in an in-plane direction perpendicular to the stacking direction.

[0016] (9) In the all-solid-state battery according to any one of the above aspects (1) to (8), the negative electrode may contain metallic lithium, a metal, semimetal, or compound capable of forming an alloy with lithium, or graphite.

[0017] (10) In the all-solid-state battery according to any one of the above aspects (1) to (9), the negative electrode may contain metallic lithium that is deposited by charging.

[0018] The all-solid-state battery according to the above embodiment has a large capacity.

[0019] Fig. 1 is a cross-sectional view of an all-solid-state battery according to a first embodiment; Fig. 2 is a cross-sectional view of an enlarged characteristic portion of the all-solid-state battery according to the first embodiment; Fig. 3 is a cross-sectional view of an enlarged characteristic portion of an all-solid-state battery according to a first modified example of the first embodiment; Fig. 4 is a cross-sectional view of an enlarged characteristic portion of an all-solid-state battery according to a second modified example of the first embodiment.

[0020] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0021] The directions are defined as follows. The stacking direction of the laminate 4 is the z direction, one direction in a plane perpendicular to the z direction is the x direction, and the direction perpendicular to the x direction and the z direction is the y direction. Hereinafter, one direction in the z direction may be expressed as "up" and the direction opposite to this direction as "down". Up and down do not necessarily coincide with the direction in which gravity is applied.

[0022] 1 is a cross-sectional schematic diagram 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. The terminal electrodes 5 and 6 are formed on side surfaces of the laminate 4 that intersect (are perpendicular to) the laminate surface.

[0023] The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The positive electrode 1, the negative electrode 2, and the solid electrolyte layer 3 are stacked in the laminate 4. The number of positive electrode 1 and negative electrode 2 layers is not important. The solid electrolyte layer 3 is 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, for example, there is a solid electrolyte that is the same 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.

[0024] The all-solid-state battery 10 is charged or discharged by the exchange of ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. Although a stacked-type battery is shown in FIG. 1 , a wound-type battery may also be used. The all-solid-state battery 10 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc. The all-solid-state battery 10 may also be an injection-type battery in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0025] "Positive Electrode" The positive electrode 1 has, 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.

[0026] The positive electrode current collector layer 1A may be made of any conductive material that is resistant to oxidation during charging and corrosion. The positive electrode current collector layer 1A may be made of, for example, a metal such as aluminum, stainless steel, nickel, titanium, or gold, or a conductive resin. The positive electrode current collector layer 1A may be in the form of a powder, foil, punched, or expanded. The positive electrode current collector layer 1A may contain the positive electrode active material contained in the positive electrode active material layer 1B.

[0027] The positive electrode active material layer 1B contains a positive electrode active material, a solid electrolyte, and a conductive additive, and optionally a binder.

[0028] The positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions and insert and extract them (intercalate and deintercalate), and any positive electrode active material used in known all-solid-state batteries can be used. Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing metal phosphates.

[0029] The lithium-containing metal oxide is, for example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese spinel (LiMn ２ O ４ ), and the general formula: LiNi ｘ Co ｙ Mn ｚ O ２ A composite metal oxide represented by (x + y + z = 1), a lithium vanadium compound (LiVOPO ４ , Li３ V ２ (P.O. ４ ) ３ ), olivine-type LiMPO ４ (wherein M represents at least one selected from Co, Ni, Mn, and Fe), lithium titanate (Li ４ Ti ５ O １２ ) etc.

[0030] The positive electrode active material may not contain lithium. Examples of such a positive electrode active material include lithium-free metal oxides (MnO ２ , V ２ O ５ etc.), lithium-free metal sulfides (MoS ２ etc.), lithium-free fluorides (FeF ３ , V.F. ３ When a positive electrode active material that does not contain lithium is used, the negative electrode is doped with lithium ions in advance, or a negative electrode containing lithium ions is used.

[0031] The positive electrode active material may contain, for example, cobalt. ２ ) and cobalt composite oxides in which part of the cobalt in lithium cobalt oxide is replaced with other transition metals (for example, LiNi ｘ Co ｙ Mn ｚ O ｚ When the positive electrode active material contains cobalt, the electronic conductivity between the solid electrolyte layer 3 containing cobalt and the positive electrode active material layer 1B is improved, and the internal resistance of the all-solid-state battery 10 is reduced.

[0032] The conductive additive is not particularly limited as long as it improves the electronic conductivity in the positive electrode active material layer 1B, and known conductive additives can be used. Examples of the conductive additive include carbon powder, carbon nanotubes, carbon materials, metal fine powders, mixtures of carbon materials and metal fine powders, and conductive oxides. Examples of the carbon powder include carbon black, acetylene black, and ketjen black. Examples of the metal fine powder include powders of copper, nickel, stainless steel, and iron. The conductive additive improves the electronic conductivity of the positive electrode active material layer 1B. The conductive additive may be in the form of powder or fiber.

[0033] The binder bonds the positive electrode current collector layer 1A and the positive electrode active material layer 1B, the positive electrode active material layer 1B and the solid electrolyte layer 3, and the various materials constituting the positive electrode active material layer 1B together.

[0034] The binder can be used within a range that does not impair the function of the positive electrode active material layer 1B. If unnecessary, the binder need not be contained. The content of the binder in the positive electrode active material layer 1B is preferably, for example, 0.5 volume % or more and 30 volume % or less of the positive electrode active material layer 1B. Here, the volume % is, for example, approximately equal to the area % in a cross section measured with a scanning electron microscope. Therefore, the area ratio in a cross section measured with a scanning electron microscope can be regarded as the volume ratio as it is.

[0035] Examples of the binder include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Furthermore, other binders such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin may also be used. Furthermore, a conductive polymer having electronic conductivity or an ionic conductive polymer having ionic conductivity may also be used as the binder. An example of an electrically conductive polymer having electronic conductivity is polyacetylene. In this case, the binder also functions as a conductive additive, so that no conductive additive needs to be added. Examples of ionic conductive polymers having ionic conductivity include those that conduct lithium ions, and include those that are obtained by mixing a monomer of a polymer compound (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) with LiClO. ４ , LiBF ４ , LiPF ６ Examples of the polymerization initiator used for the complex include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-mentioned monomers. The properties required for the binder include resistance to oxidation and reduction and good adhesiveness.

[0036] "Negative Electrode" The negative electrode 2 has, 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.

[0037] The negative electrode current collector layer 2A is electrically conductive. The negative electrode current collector layer 2A includes, for example, a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, Pt, and Cu. The negative electrode current collector is, for example, Ag, Cu, or an AgPd alloy. The negative electrode current collector layer 2A may include 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.

[0038] The negative electrode active material layer 2B contains a negative electrode active material and may also contain a conductive additive, a binder, and a solid electrolyte.

[0039] The negative electrode active material may be any compound capable of absorbing and releasing ions. Examples of the negative electrode active material include carbon materials, metals, alloys, semimetals, or compounds that can combine with lithium (can be alloyed with lithium), composite materials of these metals, alloys, or semimetals with carbon materials, oxides, sulfur-modified polyacrylonitrile, metallic lithium, etc. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, and organic compound sintered bodies. Examples of metals, alloys, semimetals, or compounds that can combine with lithium include Si, SiO ｘ , Sn, aluminum, etc. The oxides include lithium titanate (Li ４ Ti ５ O １２ ), SnO ２ Metallic lithium that deposits on the negative electrode upon charging may also be used as the negative electrode active material. In this case, part of the metallic lithium dissolves upon discharge.

[0040] The conductive additive improves the electronic conductivity of the negative electrode active material layer 2 B. As the conductive additive, the same materials as those used for the positive electrode active material layer 1 B can be used.

[0041] The binder bonds the negative electrode current collector layer 2A and the negative electrode active material layer 2B, the negative electrode active material layer 2B and the solid electrolyte layer 3, and the various materials constituting the negative electrode active material layer 2B together. The same material as that of the positive electrode active material layer 1B can be used as the binder. The binder content can also be the same as that of the positive electrode active material layer 1B. If a binder is not necessary, it need not be contained.

[0042] "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 includes a solid electrolyte. A solid electrolyte is a substance that can move ions by an externally applied electric field. For example, the solid electrolyte layer 3 conducts lithium ions and inhibits the movement of electrons. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering. The solid electrolyte layer 3 may also be a non-sintered body.

[0043] The solid electrolyte is γ-Li ３ P.O. ４ It has a γ-Li structure (lysicone-type crystal structure). ３ P.O.４ The solid electrolyte having the crystalline structure of this type has excellent ionic conductivity. ３＋ｘ Si ｘ P １－ｘ O ４ , Li ３＋ｘ Si ｘ V １－ｘ O ４ , Li ３＋ｘ Ge ｘ P １－ｘ O ４ , Li ３＋ｘ Ge ｘ V １－ｘ O ４ etc., preferably Li ３＋ｘ Si ｘ P １－ｘ O ４ The value of x satisfies the relationship 0.4≦x≦0.8. The solid electrolyte may be a ternary lithium oxide containing Si, V, Ge, and the like.

[0044] 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. The thickness of the solid electrolyte layer 3 is, for example, preferably 1 μm or more.

[0045] 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 as a simple substance in the solid electrolyte layer 3, or may exist in a state of being combined with other substances. The solid electrolyte layer 3 may consist of only the cobalt-containing region, or may have a cobalt-containing region and a cobalt-free region.

[0046] The cobalt-containing region is defined as a region in the solid electrolyte layer 3 where the cobalt content is 0.01 atom % or more. The cobalt content in the cobalt-containing region is preferably 10 atom % or less. Hereinafter, atomic percentage will be referred to as atom %, atomic %, or at %.

[0047] The cobalt content in the entire solid electrolyte layer 3 is, for example, 0.01 atom % or more and 1 atom % or less, and preferably 0.01 atom % or more and 0.1 atom % or less. 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 points in the z direction and averaging the results. The measurement points are positioned at equal intervals in the z direction.

[0048] The cobalt-containing region is divided into a cobalt-rich region 31 and a cobalt-poor region 32. The cobalt-rich region 31 is a region where the cobalt content is 1 atm % or more. The cobalt-poor region 32 is a region where the cobalt content is more than 0 atm % and less than 1 atm %. The cobalt-containing region may not include the cobalt-rich region 31 and may consist of only the cobalt-poor region 32.

[0049] The cobalt-rich region 31 is not formed so as 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 that communicates between the positive electrode 1 and the negative electrode 2. If the solid electrolyte layer 3 contains a cobalt-rich region 31 that communicates between the positive electrode 1 and the negative electrode 2, a small amount of leakage will occur through this cobalt-rich region 31, reducing the capacity of the all-solid-state battery 10.

[0050] Unlike the cobalt-rich region 31, the cobalt-poor region 32 may be present in any manner within the solid electrolyte layer 3. For example, the cobalt-poor region 32 may be present throughout the entire solid electrolyte layer 3, or may be present so as to continuously connect the positive electrode 1 and the negative electrode 2, or the cobalt-poor region 32 may be scattered within the solid electrolyte layer 3.

[0051] The proportion of the cobalt-containing region in the solid electrolyte layer 3 is, for example, 20% or more and 100% or less, and preferably 30% or more and 90% or less. When the solid electrolyte layer 3 includes the cobalt-containing region, the ionic conductivity of the solid electrolyte layer 3 is improved.

[0052] At least a part of the cobalt-containing region is preferably in a portion in contact with the positive electrode 1. When the positive electrode 1 contains cobalt, the internal resistance of the all-solid-state battery 10 can be reduced if the cobalt-containing region is in contact with the positive electrode.

[0053] The proportion of the cobalt-rich region 31 in the solid electrolyte layer 3 is, for example, 0% to 50%, and preferably 10% to 50%. The proportion of the cobalt-poor region 32 in the solid electrolyte layer 3 is, for example, 5% to 100%, and preferably 10% to 50%. The proportion of the cobalt-rich region 31 in the solid electrolyte layer 3 may be higher or lower than the proportion of the cobalt-poor region 32 in the solid electrolyte layer 3.

[0054] The solid electrolyte layer 3 may have a cobalt concentration distribution in the z direction. For example, the first region A1 of the solid electrolyte layer 3 may have a higher cobalt concentration than the second region A2. Conversely, the second region A2 of the solid electrolyte layer 3 may have a higher cobalt concentration than the first region A1. The first region A1 is a region that is closer to the positive electrode 1 in the z direction than the second region A2. The first region A1 and the second region A2 are regions that extend in the xy plane. The cobalt concentration in the first region A1 is preferably uniform in the xy plane. The cobalt concentration in the second region A2 is preferably uniform in the xy plane. Here, "uniform in the xy plane" refers to a case where, when the cobalt content is measured at five different points in 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 the cobalt concentration is distributed in the z direction of the solid electrolyte layer 3, a potential difference is generated along the distribution of the cobalt concentration, and the ionic conductivity in the solid electrolyte layer 3 is improved.

[0055] For example, when the cobalt content is measured at five different equally spaced locations in the z direction in the solid electrolyte layer 3, the cobalt concentration at each measurement point may be higher the closer to the positive electrode 1, or conversely, lower the closer to the positive electrode 1. Furthermore, the cobalt concentration in the solid electrolyte layer 3 may be gradually lower in the z direction as it approaches the positive electrode 1, as shown in Fig. 3, or may be gradually higher in the z direction as it approaches the positive electrode 1, as shown in Fig. 4.

[0056] "Method for manufacturing all-solid-state battery" Next, a method for manufacturing the all-solid-state battery 10 will be described. First, the laminate 4 is manufactured. The laminate 4 is manufactured by, for example, a co-firing method or a sequential firing method.

[0057] The co-firing method is a method of laminating materials for forming each layer and then firing them all at once to produce a laminate 4. The sequential firing method is a method of firing each layer as it is formed. The co-firing method can produce a laminate 4 with fewer steps than the sequential firing method. Furthermore, the laminate 4 produced by the co-firing method is denser than the laminate 4 produced by the sequential firing method. Below, an example of using the co-firing method will be explained.

[0058] First, the materials for 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 that constitute the laminate 4 are made into a paste.

[0059] The method for forming each material into a paste is not particularly limited, and for example, a method of mixing powders of each material with a vehicle to obtain a paste is used. Here, the vehicle is a general term for a medium in a liquid phase. The vehicle includes a solvent and a binder.

[0060] 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 necessary, and then peeling off the substrate. The method for applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0061] Next, the green sheets prepared for each material are stacked in the desired order and number of layers to produce a laminated sheet. For example, the solid electrolyte layer 3 is obtained by stacking multiple solid electrolyte sheets using a paste for the solid electrolyte layer. 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 containing 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 cobalt distribution within the solid electrolyte layer 3 can be freely designed.

[0062] However, if all of the plurality of solid electrolyte sheets are cobalt-rich sheets, a cobalt-rich region 31 connecting the positive electrode 1 and the negative electrode 2 is formed in the solid electrolyte layer 3. Therefore, not all of the plurality of solid electrolyte sheets are cobalt-rich sheets.

[0063] When stacking the green sheets, alignment, cutting, etc. are performed as necessary. For example, when fabricating a parallel or series-parallel battery, alignment is performed 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 with each other, and then the respective green sheets are stacked.

[0064] The laminate sheet may be produced by preparing a positive electrode unit and a negative electrode unit and then laminating these units. The positive electrode unit is a laminate 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 laminate 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 positive electrode unit and the negative electrode unit are laminated so that the solid electrolyte layer 3 of the positive electrode unit faces the negative electrode active material layer 2B of the negative electrode unit, or so that the positive electrode active material layer 1B of the positive electrode unit faces the solid electrolyte layer 3 of the negative electrode unit.

[0065] Next, the produced laminated sheet is pressed together to enhance the adhesion of each layer. Pressurization can be performed, for example, by a mold press, hot isostatic pressing (WIP), cold isostatic pressing (CIP), isostatic pressing, or the like. Pressurization is preferably performed while heating. The heating temperature during pressure bonding is, for example, 40°C or higher and 95°C or lower. Next, 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 binder removal treatment and sintering.

[0066] The binder removal process can be performed as a separate process from the firing process. By performing the binder removal process, the binder components contained in the chips are thermally decomposed before the firing process, thereby preventing the binder components from rapidly decomposing during the firing process. In the binder removal process, for example, heating is performed in an air atmosphere at a temperature of 300°C to 800°C for 0.1 to 10 hours. The atmosphere in the binder removal process is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte are not or are difficult to oxidize and reduce, and the type of gas can be selected arbitrarily so as not to react with the materials constituting the positive electrode, negative electrode, and solid electrolyte. For example, the binder removal process may be performed in a nitrogen atmosphere, an argon atmosphere, a nitrogen-hydrogen mixed atmosphere, a water vapor atmosphere, or a mixture thereof.

[0067] The firing step is performed, for example, by placing the chip on a ceramic base. The firing is performed, for example, by heating to 600°C or higher and 1000°C or lower in a nitrogen atmosphere. The firing time is, for example, 0.1 hour or higher and 3 hours or lower. The atmosphere for the sintering step is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte do not or do not easily undergo oxidation-reduction, and the type of gas can be selected arbitrarily so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, the sintering step may be performed in a nitrogen atmosphere, an argon atmosphere, a nitrogen-hydrogen mixed atmosphere, a water vapor atmosphere, or a mixture thereof.

[0068] Alternatively, the laminate 4 may be placed in a cylindrical container together with an abrasive such as alumina and barrel polished. This allows the corners of the laminate to be chamfered. Polishing may also be performed using sandblasting. Sandblasting is preferred because it allows only specific portions to be polished.

[0069] Terminal electrodes 5 and 6 are formed on the opposing side surfaces of the fabricated laminate 4. The terminal electrodes 5 and 6 can be formed by means of sputtering, dipping, screen printing, spray coating, or the like. Through the above-described steps, the all-solid-state battery 10 can be fabricated. When the terminal electrodes 5 and 6 are formed only on predetermined portions, the portions are masked with tape or the like and the above-described process is carried out.

[0070] 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, because the solid electrolyte does not have a cobalt-rich region 31 that continuously connects the positive electrode 1 and the negative electrode 2, a decrease in Coulomb efficiency due to slight leakage through the cobalt-rich region 31 can be suppressed.

[0071] The above describes the embodiments of the present invention in detail with reference to the drawings. However, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope of the technical requirements of the present invention.

[0072] Example 1 A paste for a positive electrode active material layer, a paste for a solid electrolyte layer, and a paste for a negative electrode active material layer were prepared.

[0073] The paste for the positive electrode active material layer is LiCoO ２ The ethyl cellulose was used as a binder, and dihydroterpineol was used as a solvent.

[0074] Three types of pastes for the solid electrolyte layer were prepared: a paste containing no cobalt, a paste containing less than 1 atm % of cobalt, and a paste containing 1 atm % or more of cobalt.

[0075] First, Li ２ CO ３ and SiO ２ and Li ３ P.O. ４ These were used as starting materials and mixed in a molar ratio of 2:1:1. The mixture was wet mixed for 16 hours using a ball mill with water as a dispersion medium. The mixture was calcined at 950°C for 2 hours to obtain Li ３．５ Si ０．５ P ０．５ O ４ 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 a ball mill and wet mixed. 16 parts by mass of a polyvinyl butyral binder and 4.8 parts by mass of benzyl butyl phthalate were further added and mixed to prepare a cobalt-free paste for a solid electrolyte layer.

[0076] Next, cobalt was added to a portion of the cobalt-free paste for the solid electrolyte layer to prepare a paste containing cobalt in an amount less than 1 atm % and a paste containing cobalt in an amount of 1 atm % or more.

[0077] The paste for the negative electrode active material layer was prepared by adding ethyl cellulose and dihydroterpineol to AgPd powder.

[0078] Next, a solid electrolyte layer sheet was fabricated on a PET film using the three types of solid electrolyte layer pastes. The solid electrolyte layer sheet was fabricated by laminating sheets of each of the three types of solid electrolyte layer pastes. The state of the cobalt-containing region in the solid electrolyte sheet was controlled by changing the lamination order and abundance ratio.

[0079] Next, a positive electrode unit and a negative electrode unit were fabricated by the following procedure. First, a positive electrode active material layer paste was printed to a thickness of 5 μm on the above-mentioned solid electrolyte layer sheet using screen printing. Next, the printed positive electrode active material layer paste was dried at 80° C. for 5 minutes. Then, a positive electrode current collector paste was printed on the dried positive electrode active material layer paste and dried to form a positive electrode current collector layer. Then, a positive electrode active material paste was printed again to a thickness of 5 μm on the positive electrode current collector layer using screen printing and dried. Then, the PET film was peeled off. In this way, a positive electrode unit was obtained in which a positive electrode active material layer / positive electrode current collector layer / positive electrode active material layer were stacked in this order on the main surface of the solid electrolyte layer.

[0080] A negative electrode unit was obtained in which a negative electrode active material layer, a negative electrode current collector layer, and a negative electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer by the same procedure, except that the paste for the positive electrode active material layer was changed to a paste for the negative electrode active material layer. The thickness of the negative electrode active material paste was 15 μm.

[0081] A solid electrolyte unit was also fabricated by stacking five solid electrolyte layer sheets. 50 electrode units (25 positive electrode units, 25 negative electrode units) were alternately stacked with the solid electrolyte unit sandwiched between them to fabricate a laminate. At this time, each unit was stacked with a shift so that the current collector layer of the odd-numbered electrode units extended only to one end surface, and the current collector layer of the even-numbered electrode units extended only to the opposite end surface. Six solid electrolyte layer sheets were stacked on top of this stacked unit. This was then molded by thermocompression bonding and then cut to fabricate a laminated chip. The laminated chips were then co-fired to obtain a laminate. The co-firing was performed in a nitrogen atmosphere, with the temperature rising at a rate of 200°C / hour to a firing temperature of 800°C, and the temperature was maintained for 2 hours. After firing, the unit was allowed to cool naturally.

[0082] Terminal electrodes 5 and 6 were attached to the sintered laminate (sintered body) by a known method to fabricate an all-solid-state battery.

[0083] The cross section of the fabricated all-solid-state battery was then measured using EDS to determine the cobalt distribution 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 continuously connecting the positive electrode and negative electrode were observed in the solid electrolyte layer. Also, no cobalt-rich regions in contact with the positive electrode were observed. Furthermore, no continuous changes in cobalt concentration were observed at five measurement points equally spaced in the z direction in 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 concentrations were measured at five measurement points equally spaced in the x direction to confirm the uniformity of the cobalt concentrations in the x and y directions, and the average cobalt concentrations in each region were calculated.

[0084] In addition, 100 similar samples were prepared, and the discharge capacity of the all-solid-state battery was determined. The discharge capacity was calculated as the average of these samples. The discharge capacity was measured using a charge / discharge device BCS805 (trade name: manufactured by Biologic). Regarding the discharge capacity, in an environment of 25°C, constant current charging (CC charging) was performed at a constant current of 0.2 C rate until the battery voltage reached 4.0 V, followed by a 1-minute pause, and then discharge (CC discharging) at a constant current of 0.2 C rate until the battery voltage reached 0 V, and the capacity was measured.

[0085] Example 2 Example 2 differs from Example 1 in that the type of solid electrolyte was changed. In Example 2, when the solid electrolyte was prepared, SiO ２ Instead of GeO ２ As a solid electrolyte, Li ３．５ Ge ０．５ P ０．５ O ４ The other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross section were measured.

[0086] Examples 3 to 11: Examples 3 to 11 differ from Example 1 in the abundance ratios of the cobalt-rich region, cobalt-poor region, and cobalt-free region in the solid electrolyte layer. These abundance ratios were adjusted by changing the cobalt concentration contained in the sheets and the stacking order of the sheets when fabricating the solid electrolyte layer. Other conditions were the same as in Example 1, and EDS and discharge capacity were measured for the cross section. In Examples 4, 9, and 10, a cobalt-rich region was observed in the position in contact with the positive electrode. In Example 10, a continuous change in cobalt concentration was confirmed at five measurement points equally spaced in the z direction. In Example 11, uniformity of the cobalt concentration was confirmed in the first region A1 and the second region A2 in the xy plane.

[0087] Comparative Example 1 Comparative Example 1 differs from Example 1 in the abundance ratio of the cobalt-rich region, cobalt-poor region, and cobalt-free region in the solid electrolyte layer. In Comparative Example 1, a solid electrolyte layer was produced using only a cobalt-free paste for a solid electrolyte layer. The solid electrolyte layer of Comparative Example 1 does not have a cobalt-containing region. In Comparative Example 1, the EDS and discharge capacity of the cross section were measured in the same manner as in Example 1.

[0088] Comparative Examples 2 and 3 Comparative Examples 2 and 3 differ from Example 1 in the abundance ratio of the cobalt-rich region, cobalt-poor region, and cobalt-free region in 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, EDS and discharge capacity of the cross section were measured in the same manner as in Example 1.

[0089] "Comparative Example 4, Examples 12 and 13" In Comparative Example 4 and Examples 12 and 13, the positive electrode material was LiNi ０．８ Co ０．１ Mn ０．１ O ２ The difference from Example 1 is that the ratio of the cobalt-rich region, the cobalt-poor region, and the cobalt-free region in the solid electrolyte layer was also different from Example 1. The other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross section were measured.

[0090] "Comparative Example 5, Examples 14 and 15" In Comparative Example 5 and Examples 14 and 15, the positive electrode material was Li ２ MnO ３ The difference from Example 1 is that the ratio of the cobalt-rich region, the cobalt-poor region, and the cobalt-free region in the solid electrolyte layer was also different from Example 1. The other conditions were the same as in Example 1, and the EDS and discharge capacity of the cross section were measured.

[0091] "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 negative electrode active material layer paste was set to 1 μm. Examples 16 and 17 also differ from Example 1 in the abundance ratio of the cobalt-rich region, cobalt-poor region, and cobalt-free region in the solid electrolyte layer. Other conditions were the same as Example 1, and EDS and discharge capacity of the cross section were measured. Example 16 used graphite for the negative electrode. Example 17 reduces the thickness of the negative electrode active material layer paste, so that the portion outside the allowable silver amount precipitates as metallic lithium during charge and discharge, functioning as the negative electrode. The negative electrode thickness in Table 1 is the thickness of the negative electrode at the time of fabrication of the all-solid-state battery before charge and discharge.

[0092] The results of Examples 1 to 17 and Comparative Examples 1 to 5 are summarized in Tables 1 to 3 below.

[0093]

[0094]

[0095]

[0096] Examples 1 to 14 had larger discharge capacities than Comparative Examples 1 to 5. In Comparative Examples 1, 4, and 5, the solid electrolyte layer did not contain cobalt, which is thought to have increased the internal resistance of the all-solid-state battery, preventing a sufficient discharge capacity from being obtained. In Comparative Examples 2 and 3, the cobalt-rich region continuously connecting the positive electrode 1 and the negative electrode 2 was thought to have caused leakage, preventing a sufficient discharge capacity from being obtained.

[0097] The all-solid-state battery of this embodiment is suitably used as a power source for electronic devices.

[0098] 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

1. A battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode, wherein the solid electrolyte layer is made of γ-Li ３ P.O. ４ the solid electrolyte layer has a cobalt-containing region that contains cobalt, the cobalt-containing region does not have a cobalt-rich region that continuously connects the positive electrode and the negative electrode, and the cobalt-rich region has a cobalt content of 1 atm % or more.

2. The all-solid-state battery of claim 1, wherein the cobalt-containing region does not include the cobalt-rich region.

3. The all-solid-state battery according to claim 1, wherein the proportion of the cobalt-containing region in the solid electrolyte layer is 20% or more and 100% or less.

4. The all-solid-state battery according to claim 1, wherein the positive electrode contains cobalt, and the solid electrolyte layer has the cobalt-containing region in a portion in contact with the positive electrode.

5. The all-solid-state battery according to claim 1, wherein the solid electrolyte layer has a first region and a second region, the first region is closer to the positive electrode in the stacking direction than the second region, and the cobalt concentration of the first region is higher than the cobalt concentration of the second region.

6. The all-solid-state battery according to claim 5, wherein the first region and the second region have a uniform cobalt concentration in an in-plane direction perpendicular to the stacking direction.

7. The all-solid-state battery according to claim 1, wherein the solid electrolyte layer has a first region and a second region, the first region is closer to the positive electrode than the second region in the stacking direction, and the cobalt concentration of the second region is higher than the cobalt concentration of the first region.

8. The all-solid-state battery according to claim 7, wherein the first region and the second region have a uniform cobalt concentration in an in-plane direction perpendicular to the stacking direction.

9. The all-solid-state battery of claim 1, wherein the negative electrode comprises metallic lithium, a metal, semimetal, or compound capable of alloying with lithium, or graphite.

10. The all-solid-state battery according to claim 1, wherein the negative electrode contains metallic lithium that is deposited upon charging.

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