All-solid-state batteries
By using a halide compound as the solid electrolyte and incorporating an intermediate layer with specific content and particle size ratios, the battery addresses delamination and cracking issues, enhancing the rate performance of all-solid-state batteries.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TDK CORP
- Filing Date
- 2022-02-09
- Publication Date
- 2026-06-01
AI Technical Summary
Conventional all-solid-state batteries face challenges in suppressing layer delamination and cracking, and achieving high rate performance due to the formation of point contacts and voids at the interfaces between the positive and negative electrode active material layers and the solid electrolyte layer.
Incorporating a halide compound as the solid electrolyte and providing an intermediate layer containing the active material and halide compound between the positive and negative electrode active material layers and the solid electrolyte layer, with specific content and particle size ratios to enhance interface stability.
The solution results in an all-solid-state battery that is less prone to delamination and cracking, and exhibits high rate performance.
Smart Images
Figure 0007867811000012 
Figure 0007867811000001 
Figure 0007867811000002
Abstract
Description
[Technical Field]
[0001] This invention relates to an all-solid-state battery. [Background technology]
[0002] In recent years, all-solid-state batteries have attracted attention from the perspective of improving safety and increasing power output. An all-solid-state battery includes a positive electrode, a solid electrolyte layer, and a negative electrode in that order. The positive electrode has a positive electrode active material layer containing positive electrode active material, and the negative electrode has a negative electrode active material layer containing negative electrode active material. In all-solid-state batteries, a challenge is to construct a good interface between the positive electrode active material layer or negative electrode active material layer and the solid electrolyte layer. In lithium-ion secondary batteries using an organic electrolyte, a good interface can be easily constructed between the positive electrode active material layer or negative electrode active material layer and the electrolyte by filling the porous positive electrode active material layer and negative electrode active material layer with the electrolyte. On the other hand, in the case of all-solid-state lithium-ion secondary batteries, because the constituent materials are solid, the interface between the positive electrode active material layer or negative electrode active material layer and the solid electrolyte layer tends to be a point contact, and voids are easily formed, making it difficult to form a good interface. This raises concerns about delamination between layers, electrode cracking due to volume changes of the active material during charging and discharging, and a decrease in rate performance and cycle performance due to insufficient interface formation.
[0003] As a countermeasure against delamination between the positive electrode active material layer or the negative electrode active material layer and the solid electrolyte layer, it has been considered to disperse fine particles substantially uniformly at at least one of the boundaries between the positive electrode active material layer and the solid electrolyte layer, and the boundary between the solid electrolyte layer and the negative electrode active material layer (Patent Document 1). Furthermore, in order to improve the rate performance of all-solid-state batteries, it has been considered to have a composition distribution in which at least one of the positive electrode active material layer and the negative electrode active material layer has a local content volume ratio, which is expressed as the volume of electrode active material contained in a part of the electrode active material layer to the volume of the solid electrolyte, that increases as the thickness direction of the electrode active material layer approaches the current collector interface from the solid electrolyte layer interface, and the porosity of the electrode active material layer increases as the thickness direction of the electrode active material layer approaches the current collector interface from the solid electrolyte layer interface (Patent Document 2). Furthermore, it has been considered that in the positive electrode active material layer, the concentration of positive electrode active material near the positive electrode current collector is higher than the concentration of positive electrode active material near the solid electrolyte layer, and in the negative electrode active material layer, the concentration of negative electrode active material near the negative electrode current collector is higher than the concentration of negative electrode active material near the solid electrolyte layer (Patent Document 3). [Prior art documents] [Patent Documents]
[0004] [Patent Document 1] Japanese Patent Publication No. 2014-191917 [Patent Document 2] Japanese Patent Publication No. 2012-104270 [Patent Document 3] Japanese Patent Publication No. 2015-225855 [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] However, conventional all-solid-state batteries sometimes struggled to adequately suppress layer delamination and cracking, or to achieve high rate performance. This invention has been made in view of the problems of the above-mentioned prior art, and aims to provide an all-solid-state battery that is less prone to delamination and cracking and has high rate performance. [Means for solving the problem]
[0006] The inventors of the present invention conducted extensive research to solve the above problems. As a result, they found that it is effective to use a halide compound as the solid electrolyte, and to provide an intermediate layer containing the active material and the halide compound between the positive electrode active material layer and the solid electrolyte layer, or between the negative electrode active material layer and the solid electrolyte layer, or both, in which the halide compound content is less than that of the positive electrode active material layer or the negative electrode active material layer. This led to the invention. In other words, the present invention provides the following means to solve the above problems.
[0007] [1] A positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer, The solid electrolyte layer contains a halide compound, An intermediate layer is provided between the positive electrode active material layer and the solid electrolyte layer, and between the negative electrode active material layer and the solid electrolyte layer, or in one or both cases. An all-solid-state battery, wherein an intermediate layer is provided on the positive electrode side between the positive electrode active material layer and the solid electrolyte layer, the positive electrode active material layer comprises a positive electrode active material and a halide compound, the intermediate layer on the positive electrode side comprises a positive electrode active material and a halide compound, and the content of the halide compound in the intermediate layer on the positive electrode side is greater than the content of the halide compound in the positive electrode active material layer; and an intermediate layer is provided on the negative electrode side between the negative electrode active material layer and the solid electrolyte layer, the negative electrode active material layer comprises a negative electrode active material and a halide compound, the intermediate layer on the negative electrode side comprises a negative electrode active material and a halide compound, and the content of the halide compound in the intermediate layer on the negative electrode side is greater than the content of the halide compound in the negative electrode active material layer.
[0008] [2] The difference between the content of the halide compound in the intermediate layer on the positive electrode side and the content of the halide compound in the positive electrode active material layer is within the range of 1% by mass or more and 80% by mass or less. The all-solid-state battery according to [1] above, wherein the difference between the content of the halide compound in the intermediate layer on the negative electrode side and the content of the halide compound in the negative electrode active material layer is within a range of 1% by mass or more and 70% by mass or less.
[0009] [3] The positive electrode active material contained in the intermediate layer on the positive electrode side has an average particle diameter smaller than that of the positive electrode active material contained in the positive electrode active material layer. The all-solid-state battery according to [1] or [2] above, wherein the negative electrode active material contained in the intermediate layer on the negative electrode side has an average particle diameter smaller than that of the negative electrode active material contained in the negative electrode active material layer.
[0010] [4] The ratio of the average particle diameter of the halide compound contained in the intermediate layer on the positive electrode side to the average particle diameter of the positive electrode active material contained in the intermediate layer on the positive electrode side is within a range of 0.2 or more and 0.4 or less. The all-solid-state battery according to any one of [1] to [3] above, wherein the ratio of the average particle diameter of the halide compound contained in the intermediate layer on the negative electrode side to the average particle diameter of the negative electrode active material contained in the intermediate layer on the negative electrode side is within a range of 0.2 or more and 0.4 or less.
[0011] [5] The intermediate layer on the positive electrode side has a layer thickness within a range of 1 μm or more and 50 μm or less. The all-solid-state battery according to any one of [1] to [4] above, wherein the intermediate layer on the negative electrode side has a layer thickness within a range of 1 μm or more and 50 μm or less.
[0012] [6] The positive electrode active material layer has a layer thickness within a range of 1 μm or more and 300 μm or less. The all-solid-state battery according to any one of [1] to [5] above, wherein the negative electrode active material layer has a layer thickness within a range of 1 μm or more and 300 μm or less.
[0013] [7] The all-solid-state battery according to any one of [1] to [6] above, wherein the halide compound is a halide compound represented by the following formula (1). Li a E b G c X d ···(1) (In formula (1), E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanides, and G is OH, BO2, BO3, BO4, B3O6, B4O7, CO3, NO3, AlO2, SiO3, SiO4, Si2O7, Si3O9, Si4O 11 Si6O 18 PO3, PO4, P2O7, P3O 10 , SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, BF4, PF6, BOB, (COO)2, N, AlCl4, CF3SO3, CH3COO, CF3COO, OOC-(CH2)2-COO, OOC-CH2-COO, OOC-CH(OH)-CH(OH )-COO, OOC-CH(OH)-CH2-COO, C6H5SO3, OOC-CH=CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, CH3COO, O It is at least one group selected from the group consisting of, where X is at least one element selected from the group consisting of F, Cl, Br, I, and 0.5 ≤ a < 6, 0 <b<2、0≦c≦6、0<d≦6.1である。) [Effects of the Invention]
[0014] According to the present invention, it is possible to provide an all-solid-state battery that is less prone to layer delamination and cracking and has high rate performance. [Brief explanation of the drawing]
[0015] [Figure 1] This is a cross-sectional schematic diagram of an all-solid-state battery relating to one embodiment of the present invention. [Modes for carrying out the invention]
[0016] The following describes in detail an all-solid-state battery according to one embodiment of the present invention.
[0017] Figure 1 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention. The all-solid-state battery 10 shown in Figure 1 comprises a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The solid electrolyte layer 3 is sandwiched between the positive electrode 1 and the negative electrode 2. The all-solid-state battery 10 has a positive electrode-side intermediate layer 31 between the positive electrode 1 and the solid electrolyte layer 3, and a negative electrode-side intermediate layer 32 between the negative electrode 2 and the solid electrolyte layer 3. External terminals (not shown) are connected to the positive electrode 1 and the negative electrode 2, and the battery is electrically connected to the outside.
[0018] The all-solid-state battery 10 is charged or discharged by the exchange of ions through the solid electrolyte layer 3 between the positive electrode 1 and the negative electrode 2, and electrons through an external circuit. The all-solid-state battery 10 may be a laminate in which the positive electrode 1, the negative electrode 2, and the solid electrolyte layer 3 are stacked, or it may be a wound body in which the laminate is wound. The all-solid-state battery can be, for example, a laminated battery, a prismatic battery, a cylindrical battery, a coin cell battery, or a button cell battery.
[0019] (positive electrode) As shown in Figure 1, the positive electrode 1 has a positive electrode active material layer 1B provided on a plate-shaped (foil-shaped) positive electrode current collector 1A. The positive electrode 1 is arranged such that the positive electrode active material layer 1B is adjacent to the solid electrolyte layer 3.
[0020] (Positive electrode current collector) The positive electrode current collector 1A can be made of an electronically conductive material that is resistant to oxidation during charging and corrosion. For example, the positive electrode current collector 1A can be made of metals such as aluminum, stainless steel, nickel, or titanium, or a conductive resin. The positive electrode current collector 1A may be in the form of powder, foil, punched, or expanded material.
[0021] (Cathode active material layer) The positive electrode active material layer 1B contains a positive electrode active material and, if necessary, a solid electrolyte, a binder, and a conductive additive. The positive electrode active material layer 1B may have a thickness in the range of 1 μm to 300 μm.
[0022] (Cathode active material) The positive electrode active material is not particularly limited as long as it can reversibly proceed with the occlusion and release, insertion and desorption (intercalation and deintercalation) of lithium ions. As the positive electrode active material, the positive electrode active materials used in known lithium ion secondary batteries can be used. Examples of the positive electrode active material include lithium-containing metal oxides, lithium-containing metal phosphates, and the like.
[0023] Examples of the lithium-containing metal oxide include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), general formula: LiNi x Mn 2-x Composite metal oxide represented by O4 (x = 0.5), general formula: LiNi x Co y Mn z Composite metal oxide represented by O2 (x + y + z = 1), lithium vanadium compound (LiVOPO4, Li3V2(PO4)3), olivine-type LiMPO4 (where M represents at least one selected from Co, Ni, Mn, Fe), lithium titanate (Li4Ti5O 12 ) and the like.
[0024] In addition, positive electrode active materials that do not contain lithium can also be used. Examples of such positive electrode active materials include lithium-free metal oxides (MnO2, V2O5, etc.), lithium-free metal sulfides (MoS2, etc.), lithium-free fluorides (FeF3, VF3, etc.), sulfur-modified polyacrylonitrile, and the like. When using these positive electrode active materials that do not contain lithium, lithium ions may be doped into the negative electrode in advance, or a negative electrode containing lithium ions may be used.
[0025] The average particle size (r1) of the positive electrode active material may be larger than the average particle size (r3) of the solid electrolyte (halide compound). The ratio (r3 / r1) of the average particle size (r3) of the solid electrolyte (halide compound) to the average particle size (r1) of the positive electrode active material is preferably in the range of 0.01 to 0.4, and more preferably in the range of 0.01 to 0.04. The average particle size (r1) of the positive electrode active material is preferably in the range of 0.5 μm to 18 μm, and more preferably in the range of 5 μm to 16 μm.
[0026] The content of the positive electrode active material in the positive electrode active material layer 1B is not particularly limited, but is preferably in the range of 20% by mass or more and 85% by mass or less, and more preferably in the range of 50% by mass or more and 75% by mass or less, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive and binder.
[0027] (solid electrolyte) The solid electrolyte can be the same as the solid electrolyte (halide compound) contained in the solid electrolyte layer 3 described later. By using the same solid electrolyte in the positive electrode active material layer 1B and the solid electrolyte in the solid electrolyte layer 3, the ionic conductivity between the positive electrode active material layer 1B and the solid electrolyte layer 3 is improved.
[0028] The solid electrolyte content in the positive electrode active material layer 1B is not particularly limited, but is preferably in the range of 15% by mass or more and 80% by mass or less, and more preferably in the range of 15% by mass or more and 45% by mass or less, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive and binder.
[0029] (binder) The binder binds the positive electrode active material, solid electrolyte, and conductive additive that make up the positive electrode active material layer 1B together. The binder also adheres the positive electrode active material layer 1B to the positive electrode current collector 1A. Required properties for the binder include oxidation resistance and good adhesion.
[0030] Examples of binders used in the positive electrode active material layer 1B include polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid (PA) and its copolymers, metal ion crosslinked polymers of polyacrylic acid (PA) copolymers, polypropylene (PP) grafted with maleic anhydride, polyethylene (PE) grafted with maleic anhydride, or mixtures thereof. Among these, PVDF is particularly preferred as the binder.
[0031] The binder content in the positive electrode active material layer 1B is not particularly limited, but is preferably in the range of 0% to 10% by mass, and more preferably in the range of 2% to 6% by mass, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder. If the binder content is too low, it tends not to be possible to form a positive electrode 1 with sufficient adhesive strength. Also, general binders are electrochemically inert and do not contribute to the discharge capacity. For this reason, if the binder content is too high, it tends not to be possible to obtain a sufficient volumetric energy density or mass energy density.
[0032] (Conductive additive) The conductive additive is not particularly limited as long as it improves the electronic conductivity of the positive electrode active material layer 1B, and known conductive additives can be used. Examples include carbon materials such as carbon black, graphite, carbon nanotubes, and graphene; metals such as aluminum, copper, nickel, stainless steel, iron, and amorphous metals; conductive oxides such as ITO; or mixtures thereof. The conductive additive may be in the form of a powder or fibers.
[0033] The content of the conductive additive in the positive electrode active material layer 1B is not particularly limited. If the positive electrode active material layer 1B contains a conductive additive, it is preferably in the range of 0% by mass or more and 10% by mass or less, and more preferably in the range of 2% by mass or more and 6% by mass or less, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive and binder.
[0034] (Negative electrode) As shown in Figure 1, the negative electrode 2 has a negative electrode active material layer 2B provided on a negative electrode current collector 2A. The negative electrode 2 is arranged such that the negative electrode active material layer 2B is adjacent to the solid electrolyte layer 3.
[0035] (Negative electrode current collector) The negative electrode current collector 2A can be any material that is electrically conductive. For example, the negative electrode current collector 2A can be a metal such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin. The negative electrode current collector 2A may also be in the form of powder, foil, punched, or expanded material.
[0036] (Negative electrode active material layer) The negative electrode active material layer 2B contains a negative electrode active material and, if necessary, a solid electrolyte, a binder, and a conductive additive. The negative electrode active material layer 2B may have a thickness in the range of 1 μm to 300 μm.
[0037] (Negative electrode active material) The negative electrode active material is not particularly limited, as long as it can reversibly carry out the intercalation and release of lithium ions, and the insertion and deintercalation of lithium ions. As the negative electrode active material, any negative electrode active material used in known lithium-ion secondary batteries can be used. Examples of negative electrode active materials include carbon materials such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fibers (MCF), cokes, glassy carbon, and calcined organic compounds, as well as Si and SiO2. x Metals that can combine with lithium, such as Sn and aluminum, alloys of these metals, composite materials of these metals and carbon materials, lithium titanate (Li4Ti5O 12Examples include oxides such as SnO2, metallic lithium, and sulfur-modified polyacrylonitrile.
[0038] The average particle size (r2) of the negative electrode active material may be larger than the average particle size (r3) of the solid electrolyte (halide compound). The ratio (r3 / r2) of the average particle size (r3) of the solid electrolyte (halide compound) to the average particle size (r2) of the negative electrode active material is preferably in the range of 0.01 to 0.4, and more preferably in the range of 0.02 to 0.2. The average particle size (r2) of the negative electrode active material is preferably in the range of 0.5 μm to 15 μm, and more preferably in the range of 1 μm to 10 μm.
[0039] The content of the negative electrode active material in the negative electrode active material layer 2B is not particularly limited, but is preferably in the range of 20% by mass or more and 80% by mass or less, and more preferably in the range of 35% by mass or more and 75% by mass or less, based on the total mass of the negative electrode active material, solid electrolyte, conductive additive and binder.
[0040] (solid electrolyte) The solid electrolyte can be the same as the solid electrolyte (halide compound) contained in the solid electrolyte layer 3 described later. By using the same solid electrolyte in the negative electrode active material layer 2B and the solid electrolyte in the solid electrolyte layer 3, the ionic conductivity between the negative electrode active material layer 2B and the solid electrolyte layer 3 is improved.
[0041] The solid electrolyte content in the negative electrode active material layer 2B is not particularly limited, but is preferably in the range of 20% by mass or more and 80% by mass or less, and more preferably in the range of 25% by mass or more and 70% by mass or less, based on the total mass of the negative electrode active material, solid electrolyte, conductive additive and binder.
[0042] (binder) The binder binds the negative electrode active material, solid electrolyte, and conductive additive that make up the negative electrode active material layer 2B together. The binder also adheres the negative electrode active material layer 2B to the negative electrode current collector 2A. Required properties for the binder include resistance to reduction and good adhesion.
[0043] Examples of binders used in the negative electrode active material layer 2B include polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PA) and its copolymers, metal ion crosslinked polymers of polyacrylic acid (PA) copolymers, polypropylene (PP) grafted with maleic anhydride, polyethylene (PE) grafted with maleic anhydride, or mixtures thereof. Among these, it is preferable to use one or more selected from SBR, CMC, and PVDF as the binder.
[0044] The binder content in the negative electrode active material layer 2B is not particularly limited, but is preferably in the range of 0% to 10% by mass, and more preferably in the range of 2% to 6% by mass, based on the total mass of the negative electrode active material, conductive additive, and binder. If the binder content is too low, it tends not to be possible to form a negative electrode 2 with sufficient adhesive strength. Also, general binders are electrochemically inert and do not contribute to the discharge capacity. For this reason, if the binder content is too high, it tends not to be possible to obtain a sufficient volumetric energy density or mass energy density.
[0045] (Conductive additive) The conductive additives that may be included in the negative electrode active material layer 2B include carbon materials, metals, conductive oxides, or mixtures thereof. Examples of carbon materials, metals, and conductive oxides are the same as those for the conductive additives that may be included in the positive electrode active material layer 1B described above. The content of the conductive additive in the negative electrode active material layer 2B is not particularly limited. If the negative electrode active material layer 2B contains a conductive additive, it is preferably in the range of 0% by mass or more and 10% by mass or less, and more preferably in the range of 2% by mass or more and 8% by mass or less, based on the total mass of the negative electrode active material, solid electrolyte, conductive additive and binder.
[0046] (Solid electrolyte layer) The solid electrolyte layer 3 contains a halide compound as a solid electrolyte. The solid electrolyte layer 3 may also contain a binder. Preferably, the solid electrolyte layer 3 contains 80% by mass or more of the halide compound. The solid electrolyte layer 3 may also contain only the halide compound. The solid electrolyte layer 3 may have a thickness, for example, in the range of 1 μm to 300 μm.
[0047] Examples of halide compounds include LiX (where X is one or more of F, Cl, Br, or I), LiAlCl4, Li2TiCl4, and Li 1.25 Mn 1.24 Cl4, Li 1.9 CD 1.05 Cl4, Li2MnCl4, Li6FeCl8, Li4PbI6, Li3InBr3Cl3, LiInBr4, Li3InBr6, Li3InCl6, Li3YCl6, Li3M 1 Cl6(M 1 (One or more of Sc, Y, or Tb-Lu), Li3M 2 Br6(M 2 (One or more of Sc, Sm-Lu), Li3ErCl6, Li3YBr6, Li3In x Y 1-x Cl6 (where x is a number between 0 and 1, inclusive), Li x ScCl 3+x (x is 2.5, 3.0, 3.5 or 4.0), Li2Sc 2 / 3 Cl4 can be used.
[0048] Furthermore, as the halide compound, the halide compound represented by the following formula (1) can be used. Li a E b Gc X d ...(1) (In formula (1), E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanides, and G is OH, BO2, BO3, BO4, B3O6, B4O7, CO3, NO3, AlO2, SiO3, SiO4, Si2O7, Si3O9, Si4O 11 Si6O 18 PO3, PO4, P2O7, P3O 10 , SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, BF4, PF6, BOB, (COO)2, N, AlCl4, CF3SO3, CH3COO, CF 3COO, OOC-(CH2)2-COO, OOC-CH2-COO, OOC-CH(OH)-CH(OH)-COO, OOC-CH(OH)-CH2-COO, C6H5SO3, OOC-CH = at least one element or group selected from the group consisting of CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, CH3COO, O, where X is at least one element selected from the group consisting of F, Cl, Br, I, and 0.5 ≤ a < 6, 0 <b<2、0≦c≦6、0<d≦6.1である。)
[0049] In the halide compound represented by formula (1), when E is Al, Sc, Y, or a lanthanide, a is preferably 2.0 ≤ a ≤ 4.0, and more preferably 2.5 ≤ a ≤ 3.5. When E is Zr or Hf, a is preferably 1.0 ≤ a ≤ 3.0, and more preferably 1.5 ≤ a ≤ 2.5. In the halide compound represented by formula (1), since a is 0.5 ≤ a < 6, the Li content in the compound becomes appropriate, resulting in a solid electrolyte with high ionic conductivity.
[0050] In the halide compound represented by formula (1), E is an essential element and is an element that forms the skeleton of the halide compound represented by formula (1). E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). By including E, a solid electrolyte having a wide potential window and high ionic conductivity is obtained. As E, in order to obtain a solid electrolyte with higher ionic conductivity, it is preferable to include Al, Sc, Y, Zr, Hf, and La, and particularly preferable to include Zr and Y.
[0051] In the halide compound represented by formula (1), 0 < b < 2. Since the effect of including E can be obtained more effectively, it is preferable that 0.6 ≤ b. Further, E is an element that forms the skeleton of the halide compound represented by formula (1) and is an element with relatively high density. When b ≤ 1, it is preferable because it results in a solid electrolyte with a low density.
[0052] In the halide compound represented by formula (1), G is an optionally included group. G is OH, BO2, BO3, BO4, B3O6, B4O7, CO3, NO3, AlO2, SiO3, SiO4, Si2O7, Si3O9, Si4O 11 , Si6O 18 , PO3, PO4, P2O7, P3O 10It is at least one group selected from the group consisting of SO3, SO4, SO5, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, BF4, PF6, BOB, (COO)2, N, AlCl4, CF3SO3, CH3COO, CF3COO, OOC-(CH2)2-COO, OOC-CH2-COO, OOC-CH(OH)-CH(OH)-COO, OOC-CH(OH)-CH2-COO, C6H5SO3, OOC-CH=CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, CH3COO, and O. BOB is a bisoxalate borate. OOC-(CH2)2-COO is succinate. OOC-CH2-COO is malonate. OOC-CH(OH)-CH(OH)-COO is tartrate. OOC-CH(OH)-CH2-COO is malate. C6H5SO3 is benzenesulfonate. OOC-CH=CH-COO is fumarate (trans isomer) or maleate (cis isomer). C(OH)(CH2COOH)2COO is citrate.
[0053] The presence of G in the halide compound represented by formula (1) results in a wide potential window on the reduction side. G is preferably at least one group selected from the group consisting of SO4, BO2, CO3, BF4, and PF6, and particularly preferably SO4 or O, because its strong covalent bond with E makes the E ion less susceptible to reduction. Although the detailed reason is unclear, a strong covalent bond between E and G leads to a stronger ionic bond between E and X. Therefore, it is presumed that the E ion in the compound is less susceptible to reduction, resulting in a compound with a wide potential window on the reduction side.
[0054] In the halide compound represented by formula (1), 0 ≦ c ≦ 6. Since the effect of widening the potential window on the reduction side due to the inclusion of G becomes more prominent, it is preferable that 0.1 ≦ c, and more preferably that 0.5 ≦ c. It is preferable that c ≦ 3 so that the decrease in the ionic conductivity of the solid electrolyte due to an excessive content of G does not occur.
[0055] In the halide compound represented by formula (1), X is an essential component. X is at least one selected from the group consisting of F, Cl, Br, and I. X has a large ionic radius per valence. Therefore, when the halide compound represented by formula (1) contains X, the effect that lithium ions flow easily and the ionic conductivity increases can be obtained. As X, it is preferable to contain Cl because it becomes a solid electrolyte with high ionic conductivity.
[0056] In the halide compound represented by formula (1), 0 < d ≦ 6.1. In the halide compound represented by formula (1), it is preferable that 1 ≦ d. When 1 ≦ d, when the solid electrolyte is compression-molded into a pellet shape, a pellet having sufficient strength can be obtained, which is preferable. Also, when 1 ≦ d, the effect of increasing the ionic conductivity due to the inclusion of X can be sufficiently obtained. Further, it is preferable that d ≦ 5 so that G is not insufficient due to an excessive content of X and the potential window of the solid electrolyte does not become narrow.
[0057] Specific examples of the halide compound represented by formula (1) include Li2ZrCl6, Li2ZrSO4Cl4, Li2ZrCO3Cl4, Li2ZrBO2Cl5, Li2ZrBF4Cl5, Li3YSO4Cl4, Li3YCO3Cl4, Li3YBO2Cl5, Li3YBF4Cl5, and Li2ZrOCl4. These halide compounds may be used individually or in combination of two or more.
[0058] The average particle size (r3) of the halide compound is preferably in the range of 0.1 μm to 10 μm, and more preferably in the range of 0.2 μm to 0.5 μm.
[0059] Halide compounds can be produced, for example, by mixing raw material powders containing a predetermined element in a predetermined molar ratio and reacting them. More specifically, halide compounds can be produced, for example, by a mechanochemical method. To induce a mechanochemical reaction, a planetary ball mill can be used as a mixing apparatus for the raw material powders. A planetary ball mill is an apparatus that places media (balls for grinding or promoting a mechanochemical reaction) and raw material powders into a sealed container, rotates and revolves, and applies kinetic energy to the raw material powders to induce grinding or a mechanochemical reaction. The sealed container and balls of a planetary ball mill can be made of, for example, zirconia.
[0060] Halide compound powders can be produced, for example, by mixing raw materials containing a predetermined element in a predetermined molar ratio and reacting them. More specifically, they can be produced by a mechanochemical method. To induce a mechanochemical reaction, for example, a planetary ball mill is used. A planetary ball mill is a device that places media (balls to promote grinding or a mechanochemical reaction) and material into a sealed container, rotates and revolves, and applies kinetic energy to the material to induce grinding or a mechanochemical reaction. Generally, planetary ball mills do not have a cooling device or heating mechanism. However, kinetic energy can be converted into thermal energy, causing the sealed container (and consequently the material inside the sealed container) to heat up. Therefore, some planetary ball mills are equipped with a cooling device to prevent the material from heating up. There are also planetary ball mills that have a heating mechanism to heat the sealed container (and consequently the material inside the sealed container) to promote the mechanochemical reaction.
[0061] In a planetary ball mill, the reaction takes place within a sealed container, so the material essentially has nowhere to escape (although if gas is produced during the reaction, that gas may escape outside the sealed container). Also, when reacting materials using a planetary ball mill, the materials do not easily reach high temperatures during the reaction, so phase separation is less likely to occur (this is not the case if heating is involved). In contrast, for example, when reacting materials using a calcination process, phase separation can occur when the material returns to room temperature after a chemical reaction at high temperatures, and the desired compound may not be obtained.
[0062] In a planetary ball mill apparatus, a sealed container, such as one made of zirconia, is used. Raw materials containing predetermined proportions and zirconia balls are placed in this sealed container. If there is a risk of hydrolysis of the raw materials due to moisture, the raw materials may be handled in a glove box with circulating argon gas at a dew point of -99°C and an oxygen concentration of 1 ppm. The raw materials may be in powder or liquid form. For example, titanium chloride (TiCl4) and tin chloride (SnCl4) are liquids at room temperature. After the raw materials are placed in the sealed container, the zirconia lid is screwed shut to seal it. Then, the apparatus is operated at predetermined rotation and revolution speeds for predetermined times. This method generates a mechanochemical reaction, yielding a powdery halide compound consisting of compounds with predetermined compositions.
[0063] (Intermediate layer on the positive electrode side) The positive electrode intermediate layer 31 is located between the positive electrode active material layer 1B and the solid electrolyte layer 3 of the positive electrode 1. The positive electrode side intermediate layer 31 contains a positive electrode active material and a halide compound. The positive electrode side intermediate layer 31 may also contain a binder and a conductive additive. Preferably, the total content of the positive electrode active material and the halide compound in the positive electrode side intermediate layer 31 is 80% by mass or more. The positive electrode side intermediate layer 31 may contain only the positive electrode active material and the halide compound. The positive electrode side intermediate layer 31 may have a layer thickness in the range of 1 μm to 50 μm, for example.
[0064] The halide compound content in the positive electrode intermediate layer 31 is set to be greater than the halide compound content in the positive electrode active material layer 1B. The difference between the halide compound content in the positive electrode intermediate layer 31 and the halide compound content in the positive electrode active material layer 1B is, for example, in the range of 1% by mass or more and 80% by mass or less, and preferably in the range of 5% by mass or more and 60% by mass or less. The halide compound content in the positive electrode intermediate layer 31 is preferably in the range of 30% by mass or more and 98% by mass or less, and more preferably in the range of 30% by mass or more and 90% by mass or less.
[0065] The positive electrode active material, halide compound, binder, and conductive additive can be the same as those used in the positive electrode active material layer 1B. The average particle size of the positive electrode active material contained in the positive electrode side intermediate layer 31 may be smaller than that of the positive electrode active material contained in the positive electrode active material layer 1B. The average particle size (r1') of the positive electrode active material contained in the positive electrode side intermediate layer 31 may be larger than the average particle size (r3) of the halide compound. The ratio (r3 / r1') of the average particle size (r1') of the halide compound to the average particle size (r1') of the positive electrode active material is preferably in the range of 0.2 to 0.4, and more preferably in the range of 0.25 to 0.4. The average particle size (r1') of the positive electrode active material is preferably in the range of 0.5 μm to 1 μm, and preferably in the range of 0.5 μm to 0.7 μm.
[0066] (Negative electrode intermediate layer) The negative electrode intermediate layer 32 is located between the negative electrode active material layer 2B and the solid electrolyte layer 3 of the negative electrode 2. The negative electrode side intermediate layer 32 contains a negative electrode active material and a halide compound. The negative electrode side intermediate layer 32 may also contain a binder and a conductive additive. Preferably, the total content of the negative electrode active material and the halide compound in the negative electrode side intermediate layer 32 is 80% by mass or more. The negative electrode side intermediate layer 32 may contain only the negative electrode active material and the halide compound. The negative electrode side intermediate layer 32 may have a layer thickness in the range of 1 μm to 50 μm.
[0067] The halide compound content in the negative electrode intermediate layer 32 is set to be greater than the halide compound content in the negative electrode active material layer 2B. The difference between the halide compound content in the negative electrode intermediate layer 32 and the halide compound content in the negative electrode active material layer 2B is, for example, in the range of 1% by mass or more and 70% by mass or less, and preferably in the range of 5% by mass or more and 60% by mass or less. The halide compound content in the negative electrode intermediate layer 32 is preferably in the range of 30% by mass or more and 98% by mass or less, and more preferably in the range of 30% by mass or more and 90% by mass or less.
[0068] The negative electrode active material, halide compound, binder, and conductive additive can be the same as those used in the negative electrode active material layer 2B. The average particle size of the negative electrode active material contained in the negative electrode side intermediate layer 32 may be smaller than that of the negative electrode active material contained in the negative electrode active material layer 2B. The average particle size (r2') of the negative electrode active material contained in the negative electrode side intermediate layer 32 may be larger than the average particle size (r3) of the halide compound. The ratio (r3 / r2') of the average particle size (r3) of the halide compound to the average particle size (r2') of the negative electrode active material is preferably in the range of 0.2 to 0.4, and more preferably in the range of 0.25 to 0.4. The average particle size (r2') of the negative electrode active material is preferably in the range of 0.5 μm to 1 μm, and preferably in the range of 0.5 μm to 0.7 μm.
[0069] (Exterior) In this embodiment of the all-solid-state battery, the battery elements, consisting of a positive electrode 1, a positive electrode-side intermediate layer 31, a solid electrolyte layer 3, a negative electrode-side intermediate layer 32, and a negative electrode 2, are housed and sealed in an outer casing. The battery elements may be a laminate or a wound laminate. The outer casing is not particularly limited and can be any material that can prevent moisture and other elements from entering from the outside. For example, as an outer casing, a metal laminate film, formed by coating both sides of a metal foil with a polymer film, can be used, which is then shaped into a bag. Such an outer casing is sealed by heat sealing the opening. Alternatively, a metal container can be used as an outer casing. The all-solid-state battery may be, for example, a prismatic battery, a cylindrical battery, a coin cell battery, or a button cell battery.
[0070] As the metal foil forming the metal laminate film, for example, aluminum foil or stainless steel foil can be used. As the polymer film placed on the outside of the outer casing, it is preferable to use a polymer with a high melting point, for example, polyethylene terephthalate (PET) or polyamide. As the polymer film placed on the inside of the outer casing, it is preferable to use, for example, polyethylene (PE) or polypropylene (PP).
[0071] (External terminals) The positive electrode 1 of the battery element is electrically connected to a positive terminal. The negative electrode 2 is electrically connected to a negative terminal. In this embodiment, the positive terminal is electrically connected to the positive electrode current collector 1A. The negative terminal is electrically connected to the negative electrode current collector 2A. The connection portion between the positive electrode current collector 1A or the negative electrode current collector 2A and the external terminals (positive terminal and negative terminal) is located inside the outer casing. External terminals can be made of conductive materials such as aluminum or nickel.
[0072] Preferably, a film made of PE grafted with maleic anhydride (hereinafter sometimes referred to as "acid-modified PE") or PP grafted with maleic anhydride (hereinafter sometimes referred to as "acid-modified PP") is placed between the outer casing and the external terminals. By heat-sealing the portion where the acid-modified PE or acid-modified PP film is placed, an all-solid-state battery with good adhesion between the outer casing and the external terminals is obtained.
[0073] Next, a method for manufacturing an all-solid-state battery according to this embodiment will be described.
[0074] First, prepare the raw materials: solid electrolyte, positive electrode active material, and negative electrode active material. The positive electrode active material is prepared in two parts: one with a relatively large average particle size for the positive electrode active material layer and one with a relatively small average particle size for the positive electrode intermediate layer. The negative electrode active material is prepared in two parts: one with a relatively large average particle size for the negative electrode active material layer and one with a relatively small average particle size for the negative electrode intermediate layer.
[0075] Next, a positive electrode mixture for manufacturing the positive electrode active material layer, a positive electrode-side intermediate layer mixture for manufacturing the positive electrode-side intermediate layer, a negative electrode mixture for manufacturing the negative electrode active material layer, and a negative electrode-side intermediate layer mixture for manufacturing the negative electrode-side intermediate layer are prepared. The positive electrode mixture can be prepared by mixing a positive electrode active material for the positive electrode active material layer, a solid electrolyte, and, if necessary, a conductive additive and a binder. The positive electrode intermediate layer mixture can be prepared by mixing a positive electrode active material for the positive electrode intermediate layer, a solid electrolyte, and, if necessary, a conductive additive and a binder. The negative electrode mixture can be prepared by mixing a negative electrode active material for the negative electrode active material layer, a solid electrolyte, and, if necessary, a conductive additive and a binder. The negative electrode intermediate layer mixture can be prepared by mixing a negative electrode active material for the negative electrode intermediate layer, a solid electrolyte, and, if necessary, a conductive additive and a binder.
[0076] Next, a pellet manufacturing jig is used to create a laminate in which positive electrode 1 (positive electrode current collector 1A, positive electrode active material layer 1B), positive electrode side intermediate layer 31, solid electrolyte layer 3, negative electrode side intermediate layer 32, and negative electrode 2 (negative electrode active material layer 2B, negative electrode current collector 2A) are stacked in this order. The pellet manufacturing jig has a cylindrical holder (die) and an upper punch and a lower punch that can be inserted into this cylindrical holder. The lower punch is inserted into the cylindrical holder, and the negative electrode mixture, the mixture for the negative electrode side intermediate layer, the solid electrolyte, the mixture for the positive electrode side intermediate layer, and the positive electrode mixture are put on top of the lower punch in this order. After putting in the positive electrode mixture, the upper punch is inserted on top of the positive electrode mixture. Then, the pellet manufacturing jig is placed on a press machine and the lower punch and upper punch are pressed. Next, the positive electrode current collector 1A is pressed onto the surface of the positive electrode active material layer 1B of the obtained laminate, and the negative electrode current collector 2A is pressed onto the surface of the negative electrode active material layer 2B.
[0077] Next, external terminals are welded to the positive electrode current collector 1A of the positive electrode 1 and the negative electrode current collector 2A of the negative electrode 2, respectively, using a known method, thereby electrically connecting the positive electrode current collector 1A or the negative electrode current collector 2A to the external terminals. After that, the laminate connected to the external terminals is housed in an outer casing, and the opening of the outer casing is sealed by heat sealing. Through the above steps, the all-solid-state battery 10 of this embodiment is obtained.
[0078] In this embodiment, the all-solid-state battery 10, configured as described above, has a positive electrode-side intermediate layer 31 between the positive electrode active material layer 1B and the solid electrolyte layer 3, and a negative electrode-side intermediate layer 32 between the negative electrode active material layer 2B and the solid electrolyte layer 3. The positive electrode-side intermediate layer 31 has a higher halide compound content than the positive electrode active material layer 1B. Since the halide compound, which is the solid electrolyte, has higher ionic conductivity than the positive electrode active material, by providing the positive electrode-side intermediate layer 31 and gradually increasing the ratio of halide compounds from the positive electrode active material layer 1B to the solid electrolyte layer 3, the ionic conductivity is gradually improved, and the adhesion from the positive electrode active material layer 1B to the solid electrolyte layer 3 is also improved. Similarly, by providing the negative electrode-side intermediate layer 32 and gradually increasing the ratio of halide compounds from the negative electrode active material layer 2B to the solid electrolyte layer 3, the ionic conductivity is gradually improved, and the adhesion from the negative electrode active material layer 2B to the solid electrolyte layer 3 is also improved. The ionic conductivity between the positive electrode active material layer 1B and the solid electrolyte layer 3, and between the negative electrode active material layer 2B and the solid electrolyte layer 3, is gradually improved, reducing resistance and thus increasing rate performance. Furthermore, the improved adhesion between the positive electrode active material layer 1B and the solid electrolyte layer 3, and between the negative electrode active material layer 2B and the solid electrolyte layer 3, suppresses the occurrence of layer delamination and cracking.
[0079] In the all-solid-state battery 10 of this embodiment, if the difference between the halide compound content of the positive electrode intermediate layer 31 and the halide compound content of the positive electrode active material layer 1B is within the range of 1% by mass to 80% by mass, preferably within the range of 5% by mass to 60% by mass, and the difference between the halide compound content of the negative electrode intermediate layer 32 and the halide compound content of the negative electrode active material layer 2B is within the range of 1% by mass to 70% by mass, preferably within the range of 5% by mass to 60% by mass, then rate performance can be further improved and the occurrence of layer delamination and cracking can be further suppressed.
[0080] Furthermore, in the all-solid-state battery 10 of this embodiment, if the average particle size of the positive electrode active material contained in the positive electrode intermediate layer 31 is smaller than that of the positive electrode active material contained in the positive electrode active material layer 1B, the relatively smaller average particle size of the positive electrode active material contained in the positive electrode intermediate layer 31 can penetrate the fine irregularities at the interface between the positive electrode intermediate layer 31 and the positive electrode active material layer 1B (anchor effect), thereby further suppressing delamination and cracking between the positive electrode intermediate layer 31 and the positive electrode active material layer 1B. Similarly, if the average particle size of the negative electrode active material contained in the negative electrode intermediate layer 32 is smaller than that of the positive electrode active material contained in the negative electrode active material layer 2B, the anchor effect can further suppress delamination and cracking between the negative electrode intermediate layer 32 and the negative electrode active material layer 2B.
[0081] In the all-solid-state battery 10 of this embodiment, if the ratio (r3 / r1') of the average particle diameter (r3) of the halide compound to the average particle diameter (r1') of the positive electrode active material contained in the positive electrode intermediate layer 31 is within the range of 0.2 to 0.4, an anchoring effect is obtained at the interface between the positive electrode active material layer 1B and the positive electrode intermediate layer 31, and at the interface between the positive electrode intermediate layer 31 and the solid electrolyte layer 3. Similarly, if the ratio (r3 / r2') of the average particle diameter (r3) of the halide compound to the average particle diameter (r2') of the negative electrode active material contained in the negative electrode intermediate layer 32 is within the range of 0.2 to 0.4, an anchoring effect is obtained at the interface between the negative electrode active material layer 2B and the negative electrode intermediate layer 32, and at the interface between the negative electrode intermediate layer 32 and the solid electrolyte layer 3. Therefore, the occurrence of delamination and cracking from the positive electrode active material layer 1B to the negative electrode active material layer 2B can be further suppressed.
[0082] 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 spirit of the present invention. For example, in the all-solid-state battery 10 of this embodiment, intermediate layers are provided both between the positive electrode active material layer 1B and the solid electrolyte layer 3, and between the negative electrode active material layer 2B and the solid electrolyte layer 3. However, the intermediate layer may be provided only in one of the two locations. Also, in the all-solid-state battery 10 of this embodiment, the positive electrode side intermediate layer 31 is one layer, but it may be two or more layers. In this case, it is preferable to gradually increase the content of the halide compound from the solid electrolyte layer 3 towards the positive electrode active material layer 1B. Similarly, the negative electrode side intermediate layer 32 may be two or more layers. [Examples]
[0083] [Example 1] (1) Preparation of solid electrolytes A raw material powder mixture was obtained by mixing zirconium chloride (ZrCl4) and lithium sulfate (Li2SO4) in a molar ratio of 1:1. This raw material powder mixture was reacted using a planetary ball mill with a rotation speed of 500 rpm and an orbital rotation speed of 500 rpm, with the rotation and orbital rotation directions reversed, for 24 hours to produce a solid electrolyte (Li2ZrSO4Cl4). The obtained solid electrolyte had an average particle size of 0.2 μm. The sealed container and balls used for the planetary ball mill were made of zirconia.
[0084] (2) Preparation of the positive electrode mixture Lithium cobalt oxide (LCO) with an average particle size of 7.5 μm was used as the positive electrode active material for the positive electrode active material layer. This LCO, the solid electrolyte obtained in the preparation of the solid electrolyte described in (1) above, and acetylene black (AB) were weighed in a mass ratio of 62:35:3 (=LCO:solid electrolyte:AB), and mixed for 15 minutes using an agate mortar and pestle to obtain the positive electrode mixture.
[0085] (3) Preparation of the mixture for the positive electrode intermediate layer Lithium cobalt oxide (LCO) with an average particle size of 1.0 μm was used as the positive electrode active material for the positive electrode intermediate layer. This LCO, the solid electrolyte obtained in (1) preparation of the solid electrolyte, and acetylene black (AB) were weighed in a mass ratio of 46:51:3 (=LCO:solid electrolyte:AB), and mixed for 15 minutes using an agate mortar and pestle to obtain the mixture for the positive electrode intermediate layer.
[0086] (4) Preparation of the negative electrode mixture Graphite (Gr) with an average particle size of 3.0 μm was used as the negative electrode active material for the negative electrode active material layer. This graphite, the solid electrolyte obtained in the preparation of the solid electrolyte described in (1) above, and acetylene black (AB) were weighed in a mass ratio of 58:40:2 (=Gr:solid electrolyte:AB), and mixed for 15 minutes using an agate mortar and pestle to obtain the negative electrode mixture.
[0087] (5) Preparation of the mixture for the negative electrode intermediate layer As the negative electrode active material for the negative electrode intermediate layer, graphite (Gr) with an average particle size of 1.0 μm was used. This graphite, the solid electrolyte obtained in the preparation of the solid electrolyte described in (1) above, and acetylene black (AB) were weighed in a mass ratio of 33:65:2 (=Gr:solid electrolyte:AB), and mixed for 15 minutes using an agate mortar and pestle to obtain the mixture for the negative electrode intermediate layer.
[0088] (6) Fabrication of all-solid-state batteries The solid-state batteries were fabricated using a pellet fabrication jig as follows: The pellet fabrication jig consists of a 10 mm diameter resin holder and an upper and lower punch with diameters of 9.99 mm. The upper and lower punches are made of die steel (SKD material). The solid-state batteries were fabricated inside a glove box.
[0089] A lower punch was inserted into the resin holder of the pellet manufacturing jig, and 2 mg of the negative electrode mixture obtained in (4) preparation of the negative electrode mixture was placed on top of the lower punch. Then, the resin holder was vibrated to level the surface of the negative electrode mixture, and then an upper punch was inserted on top of the negative electrode mixture to smooth the surface. Next, the upper punch was removed, and 1 mg of the negative electrode side intermediate layer mixture obtained in (5) preparation of the negative electrode side intermediate layer mixture was placed on top of the negative electrode mixture. Then, the resin holder was vibrated to level the surface of the negative electrode side intermediate layer mixture, and then an upper punch was inserted on top of the negative electrode side intermediate layer mixture to smooth the surface. Next, the upper punch was removed, and 50 mg of the solid electrolyte obtained in (1) preparation of the solid electrolyte was placed on top of the negative electrode side intermediate layer mixture. Then, the resin holder was vibrated to level the surface of the solid electrolyte, and then an upper punch was inserted on top of the solid electrolyte to smooth the surface. Next, the upper punch was removed, and 1 mg of the positive electrode intermediate layer mixture obtained in (3) preparation of the positive electrode intermediate layer mixture was added on top of the solid electrolyte. Then, the resin holder was vibrated to level the surface of the positive electrode intermediate layer mixture, and then the upper punch was inserted on top of the positive electrode intermediate layer mixture to smooth the surface of the positive electrode intermediate layer mixture. Next, the upper punch was removed, and 2 mg of the positive electrode mixture obtained in (2) preparation of the positive electrode mixture was added on top of the positive electrode intermediate layer mixture. Then, the resin holder was vibrated to level the surface of the positive electrode mixture, and then the upper punch was inserted on top of the positive electrode mixture to smooth the surface of the positive electrode mixture.
[0090] A pellet-making jig with the upper punch inserted was placed on a press machine and pressurized with a molding pressure of 2.4 tons to obtain a laminate in which the negative electrode active material layer, the negative electrode intermediate layer, the solid electrolyte layer, the positive electrode intermediate layer, and the positive electrode active material layer were stacked in this order from the lower punch side. Next, the upper punch was removed, a 10 mm diameter aluminum foil (positive electrode current collector) was placed on the positive electrode active material layer, and the upper punch was inserted on top of the aluminum foil. Similarly, the lower punch was removed, a 10 mm diameter copper foil (negative electrode current collector) was placed on the negative electrode active material layer, and the lower punch was inserted on top of the copper foil. In this way, a cell was obtained in which the copper foil (negative electrode current collector), the negative electrode active material layer, the negative electrode intermediate layer, the solid electrolyte layer, the positive electrode intermediate layer, the positive electrode active material layer, and the aluminum foil (positive electrode current collector) were stacked in this order from the lower punch side.
[0091] A pellet-making jig, in which cells were sandwiched between a lower punch and an upper punch, was restrained using a restraining jig that had square-shaped plates positioned above and below, and adjustable-length columns at the four corners of the upper and lower plates. Specifically, the pellet-making jig was placed in the center of the lower plate of the restraining jig, and the length of the columns was adjusted to restrain the lower and upper punches of the pellet-making jig between the lower and upper plates. With the pellet-making jig still restrained by the restraining jig, it was placed inside an aluminum laminate bag equipped with negative and positive terminals. After connecting the negative terminal of the aluminum laminate bag to the lower punch and the positive terminal to the upper punch with alligator clip cords, the aluminum laminate bag was sealed to obtain an all-solid-state battery. The obtained all-solid-state battery was removed from the glove box, and the AC impedance was measured to confirm that the alligator clip cords had not come loose inside the aluminum laminate bag.
[0092] The resulting all-solid-state battery had a positive electrode active material layer thickness of 10 μm, a positive electrode intermediate layer thickness of 5 μm, a solid electrolyte layer thickness of 300 μm, a negative electrode intermediate layer thickness of 5 μm, and a negative electrode active material layer thickness of 10 μm.
[0093] [Examples 2-165, Comparative Examples 1-6] In Example 1, the solid electrolyte was prepared in the same manner as in Example 1, except that the type and amount of raw materials for the solid electrolyte were changed as shown in Table 1 below. The composition and average particle size of the obtained solid electrolyte are shown in Table 1.
[0094] Lithium cobalt oxide (LCO) with an average particle size shown in Tables 2A to E was used as the positive electrode active material for the positive electrode active material layer, and the composition and thickness of the positive electrode active material layer were changed to the values shown in Tables 2A to E. Lithium cobalt oxide (LCO) with an average particle size shown in Tables 2A to E was used as the positive electrode active material for the positive electrode intermediate layer, and the composition and thickness of the positive electrode intermediate layer were changed to the values shown in Tables 2A to E. Graphite (Gr) with an average particle size shown in Tables 3A to E was used as the negative electrode active material for the negative electrode intermediate layer, and the composition and thickness of the negative electrode intermediate layer were changed to the values shown in Tables 3A to E. The composition and thickness of the negative electrode active material layer were changed to the values shown in Tables 3A to E. Except for the above, an all-solid-state battery was fabricated in the same manner as in Example 1.
[0095] [evaluation] (1)Discharge capacity / design capacity First, the all-solid-state battery was charged to 4.2V using a constant current of 0.1C, and after reaching a constant voltage, it was charged until the current was equivalent to 0.05C. After charging, it was discharged to 2.8V using a constant current of 0.1C. The ratio of this discharge capacity (discharge capacity after one cycle) to the design capacity (discharge capacity / design capacity) was calculated. These values are shown in Tables 3A to 3E. The design capacity is a value calculated based on the capacities of the positive electrode active material and negative electrode active material measured by fabricating half-cells, and the content of the positive electrode active material and negative electrode active material in the all-solid-state batteries fabricated in each example and comparative example.
[0096] (2) Cycle characteristics The charge and discharge cycles were repeated 100 times under the conditions described in (1) above. The discharge capacity after 100 cycles was measured, and the ratio of the discharge capacity at 100 cycles to the discharge capacity after 1 cycle measured in (1) above (capacity at 100 cycles / capacity at 1 cycle) was calculated. The results are shown in Tables 3A to 3E.
[0097] [Table 1]
[0098] [Table 2A]
[0099] Table 2B
[0100] Table 2C
[0101]
Table 2D
[0102] Table 2E
[0103] Table 3A
[0104] Table 3B
[0105]
Table 3C
[0106]
Table 3D
[0107] Table 3E
[0108] From the results in Tables 2A-E and 3A-E, the all-solid-state batteries of Examples 1-165, in which the solid electrolyte (halide compound) content in the positive electrode intermediate layer was greater than that in the positive electrode active material layer, and the solid electrolyte content in the negative electrode intermediate layer was greater than that in the negative electrode active material layer, showed improved discharge capacity / design capacity. This is because the resistance was reduced due to a stepwise improvement in ionic conductivity between the positive electrode active material layer and the solid electrolyte layer, and between the negative electrode active material layer and the solid electrolyte layer. In addition, the all-solid-state batteries of Examples 1-165 also showed improved cycle characteristics. This is because the adhesion between the positive electrode active material layer and the solid electrolyte layer, and between the negative electrode active material layer and the solid electrolyte layer was improved, suppressing the occurrence of layer delamination and cracking. [Explanation of Symbols]
[0109] 1...Positive electrode, 1A...Positive electrode current collector, 1B...Positive electrode active material layer, 2...Negative electrode, 2A...Negative electrode current collector, 2B...Negative electrode active material layer, 3...Solid electrolyte layer, 31...Positive electrode side intermediate layer, 32...Negative electrode side intermediate layer, 10...All solid-state battery
Claims
1. The device comprises a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer. The solid electrolyte layer contains a halide compound, An intermediate layer is provided between the positive electrode active material layer and the solid electrolyte layer, and between the negative electrode active material layer and the solid electrolyte layer, or in one or both cases. When an intermediate layer is provided on the positive electrode side between the positive electrode active material layer and the solid electrolyte layer, the positive electrode active material layer comprises a positive electrode active material and a halide compound, the intermediate layer on the positive electrode side comprises a positive electrode active material and a halide compound, and the content of the halide compound in the intermediate layer on the positive electrode side is greater than the content of the halide compound in the positive electrode active material layer. When an intermediate layer is provided on the negative electrode side between the negative electrode active material layer and the solid electrolyte layer, the negative electrode active material layer comprises a negative electrode active material and a halide compound, the intermediate layer on the negative electrode side comprises a negative electrode active material and a halide compound, and the content of the halide compound in the intermediate layer on the negative electrode side is greater than the content of the halide compound in the negative electrode active material layer. The positive electrode active material contained in the intermediate layer on the positive electrode side has an average particle diameter smaller than that of the positive electrode active material contained in the positive electrode active material layer. An all-solid-state battery in which the negative electrode active material contained in the intermediate layer on the negative electrode side has an average particle diameter smaller than that of the negative electrode active material contained in the negative electrode active material layer.
2. The difference between the halide compound content in the intermediate layer on the positive electrode side and the halide compound content in the positive electrode active material layer is within the range of 1% by mass or more and 80% by mass or less. The all-solid-state battery according to claim 1, wherein the difference between the content of the halide compound in the intermediate layer on the negative electrode side and the content of the halide compound in the negative electrode active material layer is within the range of 1% by mass or more and 70% by mass or less.
3. The ratio of the average particle diameter of the halide compound contained in the intermediate layer on the positive electrode side to the average particle diameter of the positive electrode active material contained in the intermediate layer on the positive electrode side is within the range of 0.2 or more and 0.4 or less. The all-solid-state battery according to claim 1 or 2, wherein the ratio of the average particle diameter of the halide compound contained in the intermediate layer on the negative electrode side to the average particle diameter of the negative electrode active material contained in the intermediate layer on the negative electrode side is within the range of 0.2 or more and 0.4 or less.
4. The intermediate layer on the positive electrode side has a layer thickness within the range of 1 μm to 50 μm. The all-solid-state battery according to any one of claims 1 to 3, wherein the intermediate layer on the negative electrode side has a layer thickness in the range of 1 μm or more and 50 μm or less.
5. The positive electrode active material layer has a thickness in the range of 1 μm to 300 μm. The all-solid-state battery according to any one of claims 1 to 4, wherein the negative electrode active material layer has a thickness in the range of 1 μm to 300 μm.
6. The all-solid-state battery according to any one of claims 1 to 5, wherein the halide compound is a halide compound represented by the following formula (1). Li ａ E ｂ G ｃ X ｄ ・・・(1) (In formula (1), E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanoids, and G is OH, BO ２ BO ３ BO ４ B ３ O ６ B ４ O ７ CO ３ NO ３ AlO ２ SiO ３ SiO ４ Si ２ O ７ Si ３ O ９ Si ４ O １１ Si ６ O １８ PO ３ PO ４ P ２ O ７ P ３ O １０ SO ３ SO ４ SO ５ S ２ O ３ S ２ O ４ S ２ O ５ S ２ O ６ S ２ O ７ S ２ O ８ BF ４ PF ６ BOB, (COO) ２ N, AlCl ４ CF ３ SO ３ CH ３ COO, CF ３ COO, OOC-(CH ２ ) ２ -COO, OOC-CH ２ -COO, OOC-CH(OH)-CH(OH)-COO, OOC-CH(OH)-CH ２ -COO, C ６ H ５ SO ３ , OOC-CH=CH-COO, C(OH)(CH ２ COOH) ２ COO, AsO ４ Bio ４ ,CrO ４ MnO ４ , PtF ６ , PtCl ６ , PtBr ６ , PtI ６ SbO ４ SeO ４ TeO ４ , HCOO, CH ３ COO is at least one group selected from the group consisting of O, and X is at least one element selected from the group consisting of F, Cl, Br, and I, and 0.5 ≤ a < 6, 0 < b < 2, 0 ≤ c ≤ 6, 0 < d ≤ 6.1.