Solid electrolyte battery

Abstract

To provide a negative electrode for a solid electrolyte battery and a solid electrolyte battery that have excellent initial charge / discharge efficiency.SOLUTION: The negative electrode for a solid electrolyte battery includes a negative electrode active material, a first compound, and an organic material that is supported by the negative electrode active material and forms an SEI film on an interface with the negative electrode active material to protect the negative electrode active material during an initial charging process. The first compound is AaEbGcXd...(1). In formula (1), A is Li, or at least one of Na and Ca and Li, E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanides, G is a predetermined group, 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, and 0.1<c≤6, 0<d≤6.1 are satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention , solid Regarding body electrolyte batteries. [Background technology]

[0002] In recent years, advancements in electronics technology have been remarkable, leading to the miniaturization, weight reduction, thinning, and increased functionality of portable electronic devices. Consequently, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which power these devices. Solid-state electrolyte batteries, which use solid electrolytes, are attracting attention. Known solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and complex hydride-based solid electrolytes.

[0003] For example, Patent Document 1 describes a solid-state battery using an oxide-based solid electrolyte. Patent Document 2 describes an all-solid-state battery using a complex hydride solid electrolyte containing an alkali metal compound. Patent Document 3 describes an all-solid-state lithium battery using a sulfide-based solid electrolyte containing a lithium halide. Patent Documents 1 to 3 describe that adding lithium halides to electrodes may improve various properties. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-91583 [Patent Document 2] Japanese Patent Publication No. 2016-18679 [Patent Document 3] Japanese Patent Publication No. 2017-79126 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Oxide-based solid electrolytes, sulfide-based solid electrolytes, and complex hydride-based solid electrolytes have different characteristics because the materials that make them up are different. In recent years, halide-based solid electrolytes have been studied as solid electrolytes that may have higher ionic conductivity than these solid electrolytes.

[0006] Solid electrolyte batteries using halide-based solid electrolytes had a large irreversible capacity during the first charge-discharge cycle, and the initial charge-discharge efficiency was sometimes not sufficient.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a negative electrode for a solid electrolyte battery and a solid electrolyte battery having excellent initial charge-discharge efficiency.

Means for Solving the Problems

[0008] To solve the above problems, the following means are provided.

[0009] (1) The negative electrode for a solid electrolyte battery according to the first aspect includes a negative electrode active material, a first compound, and an organic substance carried on the negative electrode active material and forming a SEI film that protects the negative electrode active material at the interface with the negative electrode active material during the initial charging process. The first compound is A a E b G c X d …(1). In formula (1), A is Li, or at least one of Na and Ca and Li, E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanoids, and G is OH, BO2, BO3, BO4, B3O6, B4O7, CO3, NO3, AlO2, SiO3, SiO4, Si2O7, Si3O9, Si4O 11 、Si6O 18 、PO3、PO4、P2O7、P3O 10is 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, OOC-CH=CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, and O; X is at least one element selected from the group consisting of F, Cl, Br, and I. Also, 0.5≦a<6, 0<b<2, 0≦c≦6, and 0<d≦6.1 are satisfied.

[0010] (2) The negative electrode for a solid electrolyte battery according to the above aspect may further have a second compound. The second compound is different from the first compound and is Li a E b X d …(2). In formula (2), E is at least one element selected from the group consisting of Al, Sc, Y, Zr, Hf, and lanthanoids; 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, and 0<d≦6.1 are satisfied.

[0011] (3) In the negative electrode for a solid electrolyte battery according to the above aspect, the organic substance is any one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propane sultone, divinyl adipate, vinyl acetate, ethylene sulfide, chloroethylene carbonate, catechol carbonate, propynyl methanesulfonate, lithium bis[1,2-oxalato(2)-O,O’]borate, lithium difluoromon[1,2-dioxalato(2)-O,O’]borate, or a polymer thereof.

[0012] (4) The negative electrode for the solid electrolyte battery according to the above embodiment may further contain a lithium salt having a smaller molecular weight than the first compound.

[0013] (5) In the negative electrode for a solid electrolyte battery according to the above embodiment, the organic material may be solid at room temperature.

[0014] (6) The negative electrode for a solid electrolyte battery according to the above embodiment may further include the SEI coating that covers the negative electrode active material. The SEI coating comprises an organic SEI coating formed at the interface between the organic material and the negative electrode active material, and an inorganic SEI coating formed between the first compound and the negative electrode active material.

[0015] (7) A solid electrolyte battery according to a second embodiment comprises a negative electrode for a solid electrolyte battery according to the above embodiment, a positive electrode, and a solid electrolyte layer containing a solid electrolyte located between the negative electrode for a solid electrolyte battery and the positive electrode.

[0016] (8) In the solid electrolyte battery according to the above embodiment, the solid electrolyte may be the same as the first compound. [Effects of the Invention]

[0017] The negative electrode for a solid electrolyte battery and the solid electrolyte battery according to the above embodiment have excellent initial charge and discharge efficiency. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic cross-sectional view of the solid electrolyte battery according to this embodiment. [Figure 2] This is a schematic diagram of the negative electrode mixture according to this embodiment. [Figure 3] This is a schematic diagram of the characteristic features of the negative electrode mixture according to this embodiment. [Figure 4] This is an illustrative diagram of the organic material supported on the negative electrode active material in the negative electrode mixture according to this embodiment, when the negative electrode active material is graphite. [Figure 5] This is an illustrative diagram showing the state of the vicinity of the negative electrode active material after initial charging and discharging. [Figure 6] This is a schematic diagram of the characteristic features of the negative electrode mixture according to a modified example of this embodiment. [Modes for carrying out the invention]

[0019] The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without altering its essence.

[0020] [Solid electrolyte battery] Figure 1 is a schematic cross-sectional view of a solid electrolyte battery 100 according to this embodiment. The solid electrolyte battery 100 shown in Figure 1 comprises a power generation element 40 and an outer casing 50. The outer casing 50 covers the periphery of the power generation element 40. The power generation element 40 is connected to the outside by a pair of connected terminals 60 and 62. Although Figure 1 shows a stacked battery, a wound-type battery may also be used. The solid electrolyte battery 100 can be used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc.

[0021] <Power generation element> The power generation element 40 comprises a solid electrolyte layer 10, a positive electrode 20, and a negative electrode 30. The power generation element 40 charges or discharges through the exchange of ions between the positive electrode 20 and the negative electrode 30 via the solid electrolyte layer 10 and the exchange of electrons via an external circuit.

[0022] "Solid electrolyte layer" The solid electrolyte layer 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The solid electrolyte layer 10 contains a solid electrolyte that can move ions by an externally applied voltage. For example, the solid electrolyte conducts lithium ions and inhibits electron movement.

[0023] The solid electrolyte may include, for example, lithium. The solid electrolyte may also be, for example, an oxide-based material, a sulfide-based material, or a halide-based material.

[0024] Solid electrolytes are, for example, A a E b G c X d …(1) represents a halide-based solid electrolyte. The solid electrolyte may be in the form of a powder (particles) or a sintered body formed by sintering powder. The solid electrolyte may also be a molded body formed by compressing powder, a molded body formed by molding a mixture of powder and a binder, or a coating film formed by applying a paint containing powder, binder, and solvent, and then heating to remove the solvent.

[0025] A is Li, or at least one of Na and Ca and Li. When A contains Na or Ca, the ratio of Li to Na or Ca is preferably 1.00:0.03 to 1.00:0.20 in molar ratio (Li:Na or Ca), and more preferably 1.00:0.04 to 1.00:0.10. Within this range, the potential window on the reducing side of the solid electrolyte layer 10 is widened.

[0026] a satisfies 0.5 ≤ a < 6, 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 compound represented by formula (1), if a is 0.5 ≤ a < 6, the Li content in the compound becomes appropriate, and the ionic conductivity of the solid electrolyte layer 10 increases.

[0027] E is an essential component and 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). E preferably contains Al, Sc, Y, Zr, Hf, La, and more preferably contains Zr, Y. E improves the ionic conductivity of the solid electrolyte layer 10. 0 < b < 2. Since the effect by including E can be obtained more effectively, it is preferable that 0.6 ≤ b. Also, E is an element that forms the skeleton of the solid electrolyte layer 10. It is more preferable that b ≤ 1.

[0028] G is, for example, 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, OOC-CH=CH-COO, C(OH)(CH2COOH)2COO, AsO4, BiO4, CrO4, MnO4, PtF6, PtCl6, PtBr6, PtI6, SbO4, SeO4, TeO4, HCOO, and is at least one group selected from the group consisting of these. G is preferably at least one group selected from the group consisting of OH, SO4, CH3COO, CF3COO, HCOO, O, and particularly preferably SO4. When G is included, the potential window on the reduction side of the solid electrolyte layer 10 becomes wider and it becomes less likely to be reduced.

[0029] c satisfies 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 0.5 ≦ c. It is preferable that c ≦ 3 so that the decrease in the ionic conductivity of the solid electrolyte caused by too much content of G does not occur.

[0030] X is at least one or more selected from the group consisting of F, Cl, Br, and I. X is preferably at least one or more selected from the group consisting of Cl, Br, and I in order to increase the ionic conductivity of the solid electrolyte, preferably contains Br and / or I, and particularly preferably contains I. When X contains F, since X becomes a solid electrolyte with high ionic conductivity, it is preferable that X contains F and two or more selected from the group consisting of Cl, Br, and I.

[0031] When X is F, it becomes a solid electrolyte with sufficiently high ionic conductivity and excellent oxidation resistance. When X is Cl, it becomes a solid electrolyte with high ionic conductivity and a good balance between oxidation resistance and reduction resistance. When X is Br, it becomes a solid electrolyte with sufficiently high ionic conductivity and a good balance between oxidation resistance and reduction resistance. When X is I, it becomes a solid electrolyte with high ionic conductivity.

[0032] d satisfies 0 < d ≦ 6.1. It is preferable that 1 ≦ d. When 1 ≦ d, when the solid electrolyte is pressure-molded into a pellet shape, the strength of the pellet becomes high. Also, when 1 ≦ d, the ionic conductivity of the solid electrolyte becomes high. Also, it is preferable that d ≦ 5 so that G does not become insufficient due to too much content of X and the potential window of the solid electrolyte does not become narrow.

[0033] The solid electrolyte is, for example, Li2ZrSO4Cl4, Li2ZrCO3Cl4, Li2Zr((COO)2) 0.5 Cl5, Li2Zr(CH3COO) 0.2 Cl 5.8 、Li2Zr(CF3COO) 0.2 Cl 5.8 、Li2Zr(HCOO) 0.4 Cl5.6 These are Li2ZrBO2Cl5, Li2ZrBF4Cl5, Li3YSO4Cl4, Li3YCO3Cl4, Li3YBO2Cl5, and Li3YBF4Cl5.

[0034] "Positive electrode" As shown in Figure 1, the positive electrode 20 has a plate-shaped (foil-shaped) positive electrode current collector 22 and a positive electrode mixture layer 24. The positive electrode mixture layer 24 is in contact with at least one surface of the positive electrode current collector 22.

[0035] (Positive electrode current collector) The positive electrode current collector 22 can be made of an electronically conductive material that is resistant to oxidation and corrosion during charging. Examples of materials for the positive electrode current collector 22 include metals such as aluminum, stainless steel, nickel, and titanium, and conductive resins. The positive electrode current collector 22 may also be in the form of powder, foil, punched, or expanded material.

[0036] (Positive electrode mixture layer) The positive electrode mixture layer 24 contains a positive electrode active material and, if necessary, a solid electrolyte, a binder, and a conductive additive.

[0037] (Cathode active material) The positive electrode active material is not particularly limited as long as it can reversibly carry out intercalation and deintercalation of lithium ions, and any positive electrode active material used in known solid electrolyte batteries can be used. Examples of positive electrode active materials include lithium-containing metal oxides and lithium-containing metal phosphorus oxides.

[0038] Lithium-containing metal oxides include, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), and LiNi x Co y Mn zComposite metal oxides represented by O2(x+y+z=1), lithium vanadium compounds (LiVOPO4, Li3V2(PO4)3), olivine-type LiMPO4 (where M represents at least one selected from Co, Ni, Mn, and Fe), lithium titanate (Li4Ti5O 12 ) etc.

[0039] Furthermore, the positive electrode active material may not contain lithium. Examples of such positive electrode active materials include lithium-free metal oxides (MnO2, V2O5, etc.), lithium-free metal sulfides (MoS2, etc.), and lithium-free fluorides (FeF3, VF3, etc.). When using a lithium-free positive electrode active material, the negative electrode is pre-doped with lithium ions, or a negative electrode containing lithium ions is used.

[0040] (binder) The binder binds the positive electrode active material, solid electrolyte, and conductive additive together within the positive electrode mixture layer 24, and firmly adheres the positive electrode mixture layer 24 to the positive electrode current collector 22. The positive electrode mixture layer 24 preferably contains the binder. The binder preferably has oxidation resistance and good adhesion.

[0041] Examples of binders used in the positive electrode mixture layer 24 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 polyacrylic acid (PA) and its 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.

[0042] The content of the solid electrolyte in the positive electrode mixture layer 24 is not particularly limited, but is preferably 1% to 50% by mass, and more preferably 5% to 30% by mass, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder.

[0043] The binder content in the positive electrode mixture layer 24 is not particularly limited, but is preferably 1% to 15% by mass, and more preferably 3% to 5% by mass, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder. If the amount of binder is too small, it tends not to be possible to form a positive electrode 20 with sufficient adhesive strength. Conversely, if the amount of binder is too large, since general binders are electrochemically inert, they do not contribute to the discharge capacity, and it tends not to be possible to obtain a sufficient volume or mass energy density.

[0044] (Conductive additive) The conductive additive improves the electronic conductivity of the positive electrode mixture layer 24. Known conductive additives can be used. Examples of conductive additives 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 powder or fiber form.

[0045] The content of the conductive additive in the positive electrode mixture layer 24 is not particularly limited. When a conductive additive is added, the mass ratio of the conductive additive is usually preferably 0.5% to 20% by mass, and more preferably 1% to 5% by mass, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder.

[0046] "Negative electrode" As shown in Figure 1, the negative electrode 30 has a negative electrode current collector 32 and a negative electrode mixture layer 34. The negative electrode mixture layer 34 is in contact with the negative electrode current collector 32.

[0047] (Negative electrode current collector) The negative electrode current collector 32 only needs to be electrically conductive. The negative electrode current collector 32 can be, for example, a metal such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin. The negative electrode current collector 32 may also be in the form of powder, foil, punched, or expanded material.

[0048] (Negative electrode mixture layer) The negative electrode mixture layer 34 contains a negative electrode active material 34A, a first compound 34B, and an organic substance 34C. Figure 2 is a schematic diagram of a magnified characteristic portion of the negative electrode mixture layer 34. The negative electrode mixture layer 34 may also contain a binder and a conductive additive 34D. Known materials can be used for the binder and conductive additive 34D. The conductive additive 34D is, for example, carbon black. Figure 3 is a schematic diagram of a magnified view of the vicinity of one negative electrode active material 34A in the negative electrode mixture layer 34.

[0049] The negative electrode active material 34A 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. Any negative electrode active material used in known solid electrolyte batteries can be used as the negative electrode active material 34A.

[0050] The negative electrode active material 34A can be, for example, carbon materials such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), coke, 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 12 These include oxides such as SnO2 and metallic lithium. Natural graphite is preferred for the negative electrode active material 34A.

[0051] The first compound 34B is A a E b G c X d …(1) The first compound 34B is the same material as the halide-based solid electrolyte described above. The first compound 34B and the solid electrolyte used in the solid electrolyte layer 10 may be different or the same.

[0052] The organic material 34C is supported on the negative electrode active material 34A. Figure 4 is an illustrative diagram of the organic material 34C supported on the negative electrode active material when the negative electrode active material 34A is graphite. The organic material 34C is supported, for example, in scattered locations on the negative electrode active material 34A. Figure 4 shows the state of the vicinity of the negative electrode active material 34A before repeated initial charge and discharge cycles.

[0053] Organic material 34C is an organic material that forms a protective SEI (Solid Electrolyte Interphase) film at the interface with the negative electrode active material 34A during the initial charging process. The SEI film is a layer formed on the surface of the negative electrode active material of the battery during the charging and discharging process. Lithium ions can pass through the SEI film, while larger molecules that move with the lithium ions cannot. Therefore, the formation of the SEI film protects the negative electrode active material from side reactions. The SEI film is a protective layer that protects the negative electrode active material.

[0054] A portion of the organic material 34C decomposes during the initial charge-discharge process, forming an SEI film. A portion of the organic material 34C remains unreacted within the negative electrode mixture layer 34. An example of the initial charge-discharge process is observed in a half-cell measurement of the negative electrode, where a current of 0.01C yields 5mV (vs. Li / Li). + After charging to 3.0V (vs.Li / Li) with a current of 0.01C + This is the process of discharge to 0.01C. In other words, organic material 34C discharges to 5mV (vs. Li / Li) with a current of 0.01C. + After charging to 3.0V (vs.Li / Li) with a current of 0.01C + It is an organic substance that partially decomposes during the discharge process to form the SEI film.

[0055] Specifically, organic compound 34C is any of the following selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), propanesultone, divinyl adipate, vinyl acetate, ethylene sulfide, chloroethylene carbonate, catechol carbonate, propynyl methanesulfonate, lithium bis[1,2-oxalato(2)-O,O']borate (LiBOB), and lithium difluoromono[1,2-dioxalato(2)-O,O']borate (LiDFOB), or polymers thereof.

[0056] The organic substance 34C is preferably solid at room temperature. Room temperature is, for example, 25°C. Ethylene carbonate, propane sultone, and divinyl adipate are solid at room temperature.

[0057] Figure 5 is an illustrative diagram of the state of the vicinity of the negative electrode active material 34A after initial charging and discharging. An SEI film 35 is formed around the negative electrode active material 34A. Lithium ions can pass through the SEI film 35. A mixed salt 37 of organic matter 34C and the first compound 34B may also be present around the SEI film 35. Although not shown in the figure, unreacted organic matter 34C may remain supported on the negative electrode active material 34A.

[0058] The SEI coating 35 has both an organic SEI coating and an inorganic SEI coating. For example, the SEI coating 35 has a portion dominated by the organic SEI coating and a portion dominated by the inorganic SEI coating. Dominant portion means that 50% or more of a particular region is dominated by a particular structure.

[0059] The organic SEI film is formed by the decomposition of the organic substance 34C. At the interface between the first compound 34B contained in the negative electrode mixture layer 34 and the organic substance 34C, lithium ions coordinate to the organic substance, forming a coordination structure. At the interface between this coordinate structure and the negative electrode active material 34A, a stable SEI film is formed at room temperature during the first charge. This reaction is presumed to occur because the first compound 34A readily releases lithium ions. The organic SEI film is formed at the interface between the organic substance 34C and the negative electrode active material 34A. As shown in Figure 4, since the organic substance 34C is scattered and supported at multiple locations on the negative electrode active material 34A, a portion of the SEI film 35 is dominated by the organic SEI film.

[0060] The inorganic SEI coating is formed by the decomposition of the first compound 34B. The inorganic SEI coating is formed between the first compound 34B and the negative electrode active material 34A.

[0061] Organic SEI coatings are thinner than inorganic SEI coatings. For example, organic SEI coatings are a few nanometers to tens of nanometers thick, while inorganic SEI coatings are tens of nanometers to hundreds of nanometers thick.

[0062] The mixed salt 37 of organic matter 34C and first compound 34B is formed when lithium ions from the first compound 34B are released and coordinate to the organic matter.

[0063] Furthermore, the negative electrode mixture layer 34 may also contain a second compound 34E. Figure 6 is an enlarged view of a characteristic portion of the negative electrode mixture layer according to a modified example. The second compound 34E is different from the first compound 34B. The second compound 34E is Li a E b X d …This is expressed by equation (2). In equation (2), the definitions of X, E, a, b, and d are the same as in equation (1) above.

[0064] The compound represented by formula (2) is, for example, E is at least one element selected from the group consisting of Al, Zr, and Hf, 0.5 ≦ a < 3, 0 < b < 0.05, and 0 < d ≦ 3. The compound represented by formula (2) preferably contains Zr as E and at least one of Cl and I as X.

[0065] The second compound 34E is, for example, between the negative electrode active material 34A and the first compound 34B. The second compound 34E prevents the reaction between the negative electrode active material 34A and the first compound 34B and suppresses the decomposition of the first compound 34B.

[0066] The second compound 34E, for example, covers at least a part of the periphery of the negative electrode active material 34A. The second compound 34E preferably covers 30% or more of the peripheral length of the negative electrode active material 34A in a cross section obtained by cutting the negative electrode binder layer 34 along the lamination direction. The cross-sectional image can be confirmed, for example, by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0067] The compound represented by formula (2) is easily deformed by physical forces and is easily chemically compatible. Therefore, the second compound 34E coats the surface of the negative electrode active material 34A under the action of physical forces. In addition, due to the high compatibility of the second compound 34E with the first compound 34B, it binds between the negative electrode active material 34A and the first compound 34B at the molecular level.

[0068] The mass percentage of the first compound 34B contained in the negative electrode binder layer 34 is, for example, greater than the mass percentage of the organic substance 34C. Also, the mass percentage of the first compound 34B contained in the negative electrode binder layer 34 is, for example, greater than the mass percentage of the second compound 34E. The mass percentage of the organic substance 34C contained in the negative electrode binder layer 34 is, for example, greater than the mass percentage of the second compound 34E.

[0069] The mass percentage of the negative electrode active material 34A contained in the negative electrode mixture layer 34 is, for example, 50% by mass or more, preferably 60% by mass or more. The mass percentage of the first compound 34B contained in the negative electrode mixture layer 34 is, for example, 20% by mass or more and 30% by mass or less. The mass percentage of the organic substance 34C contained in the negative electrode mixture layer 34 is, for example, 10% by mass or less. The mass percentage of the second compound 34E is, for example, 10% by mass or less.

[0070] The average particle size of the negative electrode active material 34A is larger than, for example, the average particle size of the organic substance 34C or the second compound 34E. When this condition is met, the organic substance 34C or the second compound 34E is more likely to form between the negative electrode active material 34A and the first compound 34B.

[0071] The average particle size is determined from a cross-sectional image obtained by cutting the negative electrode mixture layer 34 along the stacking direction. The cross-sectional image can be obtained, for example, using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Ten samples each of the negative electrode active material 34A, the first compound 34B, the organic substance 34C, and the second compound 34E, which can be seen in the cross-sectional image, are extracted, and the average of these samples is calculated to obtain the average particle size. Each substance can be separated and extracted based on the contrast of the image. If the negative electrode active material 34A, the first compound 34B, the organic substance 34C, and the second compound 34E are amorphous, their diameter along their long axis is used as the particle size.

[0072] Furthermore, the negative electrode mixture layer 34 may further contain a lithium salt having a smaller molecular weight than the first compound 34B. By mixing lithium salts with different molecular weights, the formation of a coordination structure of lithium ions at the interface between the first compound 34B and the organic material 34C is promoted, and the irreversible capacity of the solid electrolyte battery 100 is reduced. Examples of lithium salts include LiF, LiCl, LiBr, LiI, LiPF6, lithium borofluoride (LiBF4), LiClO4, LiCF3SO3, LiCF3CF2SO3, LiC(CF3SO2)3, LiN(SO2F)2, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(CF3CF2CO)2, LiBOB, LiN(FSO2)2, etc.

[0073] <Exterior> The outer casing 50 houses the power generation element 40 inside. The outer casing 50 prevents moisture and other elements from entering the interior from the outside. The outer casing 50 has, for example, a metal foil 52 and resin layers 54 laminated on each surface of the metal foil 52, as shown in Figure 1. The outer casing 50 is a metal laminate film in which the metal foil 52 is coated on both sides with resin layers 54.

[0074] The metal foil 52 is, for example, aluminum foil or stainless steel foil. The resin layer 54 can be, for example, a resin film such as polypropylene. The materials constituting the resin layer 54 may be different on the inside and outside. For example, a polymer with a high melting point, such as polyethylene terephthalate (PET) or polyamide (PA), can be used as the outer material, while polyethylene (PE) or polypropylene (PP) can be used as the inner material.

[0075] <Terminal> Terminals 60 and 62 are connected to the positive electrode 20 and the negative electrode 30, respectively. Terminal 60, connected to the positive electrode 20, is the positive terminal, and terminal 62, connected to the negative electrode 30, is the negative terminal. Terminals 60 and 62 are responsible for electrical connections to the outside. Terminals 60 and 62 are made of conductive materials such as aluminum, nickel, and copper. The connection method may be welding or screw fastening. It is preferable to protect terminals 60 and 62 with insulating tape to prevent short circuits.

[0076] [Manufacturing method for solid electrolyte batteries] Next, a method for manufacturing a solid electrolyte battery according to this embodiment will be described. First, the solid electrolyte is prepared. The solid electrolyte can be manufactured, for example, by mixing raw material powders containing a predetermined element in a predetermined molar ratio and causing a mechanochemical reaction. Alternatively, a sintered solid electrolyte may be formed by mixing and molding raw material powders containing a predetermined element in a predetermined molar ratio and sintering them in a vacuum or inert gas atmosphere.

[0077] When a halogenated raw material is present in the raw material powder, the halogenated raw material tends to evaporate when the temperature is raised. For this reason, halogen gas may be present in the atmosphere during sintering to supplement the halogen. Alternatively, when a halogenated raw material is present in the raw material powder, sintering may be performed by hot pressing using a highly airtight mold. In this case, because the mold is highly airtight, evaporation of the halogenated raw material due to sintering can be suppressed. By sintering in this manner, a solid electrolyte in the form of a sintered body made of a compound having a predetermined composition can be obtained.

[0078] Furthermore, heat treatment may be performed as needed during the production of the solid electrolyte. By performing heat treatment, the crystallite size of the solid electrolyte can be adjusted. For example, the heat treatment is preferably carried out in an argon gas atmosphere at 130°C to 650°C for 0.5 to 60 hours, and more preferably at 140°C to 600°C for 1 to 30 hours. By carrying out the heat treatment in an argon gas atmosphere at 150 to 550°C for 5 to 24 hours, a solid electrolyte with a crystallite size of 5 nm to 500 nm can be obtained.

[0079] Next, the positive electrode 20 is prepared. The positive electrode is manufactured by applying a paste containing the positive electrode active material onto the positive electrode current collector 22 and drying it to form a positive electrode mixture layer 24.

[0080] Next, the negative electrode 30 is prepared. First, the organic substance 34C is supported on the negative electrode active material 34A. The organic substance 34C is supported on the surface of the negative electrode active material 34A by, for example, dry mixing the negative electrode active material 34A and the organic substance 34C. Alternatively, the organic substance 34C may be supported on the surface of the negative electrode active material 34A by a wet mixing method in which the organic substance 34C is added to a solvent and then mixed with the negative electrode active material 34A. A lithium salt may also be added during dry or wet mixing. Next, a paste made by mixing the negative electrode active material 34 with the supported organic substance 34C and the first compound 34B is applied to the negative electrode current collector 32. The coating film is then dried to form the negative electrode mixture layer 34. The second compound 34E may be added to the paste as needed.

[0081] The power generation element 40 can be manufactured, for example, using a powder molding method. A guide with holes is placed on the positive electrode 20, and a solid electrolyte is filled into the guide. Then, the surface of the solid electrolyte is smoothed, and the negative electrode 30 is placed on top of the solid electrolyte. This sandwiches the solid electrolyte between the positive electrode 20 and the negative electrode 30. Then, pressure is applied to the positive electrode 20 and the negative electrode 30 to pressure-molde the solid electrolyte. By pressure molding, a laminate is obtained in which the positive electrode 20, the solid electrolyte layer 10, and the negative electrode 30 are stacked in that order.

[0082] Next, external terminals are welded to the positive electrode current collector 22 of the positive electrode 20 and the negative electrode current collector 32 of the negative electrode 30, respectively, using a known method, thereby electrically connecting the positive electrode current collector 22 or the negative electrode current collector 32 to the external terminals. After that, the laminate connected to the external terminals is housed in the outer casing 50, and the opening of the outer casing 50 is sealed by heat sealing. Through these steps, the solid electrolyte battery 100 of this embodiment is obtained.

[0083] In this embodiment, the solid electrolyte battery 100 has an organic substance 34C in the negative electrode mixture layer 34, which allows for the formation of a stable SEI film on the surface of the negative electrode active material 34A. The SEI film formed by the decomposition of the organic substance 34C is thinner than the SEI film formed by the decomposition of the first compound 34B. That is, the SEI film formed by the decomposition of the organic substance 34C consumes less chemical capacity than the SEI film formed by the decomposition of the first compound 34B. By decomposing the organic substance 34C instead of the first compound 34B and suppressing the decomposition of the first compound 34B, the irreversible capacity of the solid electrolyte battery 100 is reduced, and the initial charge-discharge efficiency is improved.

[0084] 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. [Examples]

[0085] "Example 1" (Preparation of solid electrolytes) In a glove box with a dew point of approximately -70°C, the raw material powders of zirconium chloride (ZrCl4) and lithium sulfate (Li2SO4) were weighed in a molar ratio of 1:1. The raw material powders were placed into a sealed zirconia container for a planetary ball mill, which already contained zirconia balls. Next, the container was covered with a lid, screwed to the container body, and the gap between the lid and the container was sealed with polyimide tape. The polyimide tape has the effect of blocking moisture. Then, the sealed zirconia container was set in a planetary ball mill. The rotation speed was set to 500 rpm and the revolution speed to 500 rpm, with the rotation direction and revolution direction being opposite, and a mechanochemical reaction was carried out for 24 hours to produce a solid electrolyte (Li2ZrSO4Cl4).

[0086] The obtained solid electrolyte had an average primary particle size of 0.1 μm. The planetary ball mill is normally installed in an ambient atmosphere (air). The zirconia sealed container for the planetary ball mill is screw-fastened and further sealed with polyimide tape. When the zirconia sealed container is set in the planetary ball mill, it is firmly pressed and fixed in place. Therefore, even in a normal atmosphere, it is considered that there is almost no contamination of the zirconia sealed container from the atmosphere.

[0087] (Preparation of negative electrode mixture) The negative electrode mixture was also prepared in a glove box with a dew point of approximately -70°C. Graphite (Gr) with an average particle size of 11.0 μm was used as the negative electrode active material 34A. The nominal capacity of this graphite was 342 mAhg. -1 The same solid electrolyte as described above was used as the first compound 34B. Ethylene carbonate (EC) was used as the organic substance 34C. The negative electrode active material 34A, the first compound 34B, and the insulator 34C were weighed in a mass ratio of 70:29.25:0.75 (=Gr:Li2ZrSO4Cl4:EC), and mixed for 15 minutes using an agate mortar and pestle to obtain the negative electrode mixture. This method of preparing the negative electrode mixture by mixing is called dry mixing.

[0088] (Half-cell creation) The half-cells were also fabricated in a glove box with a dew point of approximately -70°C. The half-cells were fabricated using a pellet fabrication jig. The pellet fabrication jig consists of a PEEK (polyetheretherketone) holder with an inner diameter of 10 mm, and an upper punch and a lower punch with a diameter of 9.99 mm. The upper and lower punches are made of die steel (SKD11 material).

[0089] A lower punch was inserted into the PEEK holder of the pellet manufacturing jig, and 110 mg of solid electrolyte was placed on top of the lower punch. Next, 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 and pressed with a load of approximately 4 kN using a press machine.

[0090] Next, the upper punch was removed, and 10 mg of negative electrode mixture was placed on top of the solid electrolyte. Then, the PEEK holder was vibrated to level the surface of the negative electrode mixture, and the upper punch was inserted on top of the negative electrode mixture and pressed with a load of 3 kN using a press machine. Next, the lower punch was removed, a 10 mm diameter Li foil was placed on top of the solid electrolyte layer, and the lower punch was inserted. In this way, a half-cell was fabricated in which the negative electrode mixture layer, solid electrolyte layer, and Li foil were stacked in order.

[0091] In addition, two stainless steel plates with a diameter of 50 mm and a thickness of 5 mm, and two Bakelite® plates with a diameter of 50 mm and a thickness of 2 mm were prepared. Next, four holes for screws were made in each of the two stainless steel plates and the two Bakelite® plates. The holes for the screws were positioned so that when the electrochemical cell and the two stainless steel plates and the two Bakelite® plates are stacked, the two stainless steel plates and the two Bakelite® plates overlap in a plan view, but do not overlap with the electrochemical cell in a plan view.

[0092] Subsequently, stainless steel plates, bakelite® plates, half cells, bakelite® plates, and stainless steel plates were stacked in this order, and screws were inserted into the screw holes and tightened with a torque of 1 N·m. In this way, a half cell was obtained in which the upper and lower punches of the electrochemical cell were insulated by bakelite® plates. Next, the half cell was left to stand in a constant temperature bath at 25°C for 48 hours to stabilize the open-circuit voltage.

[0093] The electrochemical properties of the negative electrode were evaluated using the fabricated half-cell. Measurements were performed by placing the half-cell in a constant temperature bath at 25°C. The charge-discharge current was expressed using the C (c) rate. nC (mA) is the current that can charge and discharge the nominal capacity (mAh) at 1 / n (h). The nominal discharge capacity of the graphite mentioned above was 342 mAhg -1 Therefore, the nominal capacity of the above half cell is calculated as: "Negative electrode mixture mass (mg)" / 1000 × "Percentage of graphite in negative electrode mixture" × "Nominal capacity of graphite (mAhg)" -1 )」 = 10 / 1000 × 0.67 × 342 = 2.29 mAh. Therefore, the current at 0.01 C is 2.29 mA × 0.01 × 1000 = 22.9 μA. At a current of 0.01 C, 5 mV (vs. Li / Li + Charge to 3.0V (vs.Li / Li) with a current of 0.01C. + The battery was discharged to ). The initial charge-discharge efficiency of the cell in Example 1 was 65%.

[0094] The initial charge-discharge efficiency was calculated using the following formula. Initial charge / discharge efficiency (%) = Discharge capacity (mAh) / Charge capacity (mAh) × 100

[0095] Next, the half-cell after charging and discharging was disassembled inside the glove box, the negative electrode mixture was removed and cut, and the cross-section was measured using a scanning electron microscope. It was confirmed that the insulator was located between the negative electrode active material and the first compound. The particle sizes of the negative electrode active material and the insulator were also measured.

[0096] "Examples 2 to 12" Examples 2 to 12 differ from Example 1 in that the material used as the organic substance is changed. In addition, some of Examples 2 to 12 apply a wet mixing method as the method for supporting the organic substance on the negative electrode active material 34A (see Table 1). Half cells were prepared with the same configuration as in Example 1, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 1. In Example 2, fluoroethylene carbonate (FEC) was used as the organic material. In Example 3, vinylene carbonate (VC) was used as the organic material. In Example 4, the organic substance was propanesultone. In Example 5, the organic substance was divinyl adipate. In Example 6, vinyl acetate was used as the organic material. In Example 7, the organic substance was ethylene sulfide. In Example 8, chloroethylene carbonate (CLEC) was used as the organic substance. In Example 9, the organic material was catechol carbonate. In Example 10, the organic substance was propynyl methanesulfonate. In Example 11, the organic material was lithium bis[1,2-oxalato(2)-O,O']borate (LiBOB). In Example 12, the organic material was lithium difluoromono[1,2-dioxalato(2)-O,O']borate (LiDFOB).

[0097] "Example 13" Example 13 differs from Example 2 in that LiCl was added as a lithium salt to the negative electrode mixture. The mass ratio of the negative electrode active material 34A, the first compound 34B, the insulator 34C, and the lithium salt was 70:29.25:0.68:0.07 (=Gr:Li2ZrSO4Cl4:FEC:LiCl). Half cells were prepared with the same configuration as in Example 2, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 2.

[0098] "Example 14" Example 14 involves adding Li as the second compound to the negative electrode mixture. 1.96 Zr 0.01The difference from Example 2 is the addition of Cl2. The mass ratio of the negative electrode active material 34A, the first compound 34B, the organic substance 34C, and the second compound 34E is 70:29:0.75:0.25 (=Gr:Li2ZrSO4Cl4:FEC:Li2Zr 0.01 Cl2) was used. Half cells were fabricated with the same configuration as in Example 2, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 2.

[0099] Examples 15-17 Examples 15-17 differ from Example 2 in that the first compound and the solid electrolyte were changed. Half cells were prepared using the same configuration as in Example 2, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 2. In Example 15, the first compound was Li2Zr(HCOO)Cl5. Example 16 involves using Li2Zr((COO)2) as the first compound. 0.5 I set it to Cl5. In Example 17, the first compound was Li2Zr(CH3COO)Cl5.

[0100] Example 18 Example 18 differs from Example 2 in that the negative electrode active material is changed to silicon, and carbon black is added as a conductive additive and LiPF6 as a lithium salt. The mass ratio of the negative electrode active material 34A, conductive additive 34D, first compound 34B, organic material 34C, and lithium salt was 67:3:29.25:0.7:0.05 (=Gr:CB:Li2ZrSO4Cl4:FEC:LiPF6). Half cells were fabricated with the same configuration as in Example 2, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 2.

[0101] "Comparative Example 1" Comparative Example 1 differs from Example 1 in that organic substance 34C was not added when preparing the negative electrode mixture. The mass ratio of negative electrode active material 34A to the first compound 34B in the negative electrode mixture was set to 70:30. Half cells were prepared using the same configuration as in Example 1, and the initial charge-discharge efficiency was determined under the same charge-discharge conditions as in Example 1.

[0102] Table 1 below summarizes the results for Examples 1-20 and Comparative Example 1. In Table 1, Gr represents graphite and CB represents carbon black.

[0103] [Table 1]

[0104] The cells using the negative electrodes shown in Examples 1 to 20 all had higher initial charge-discharge efficiencies than the cells using the negative electrode shown in Comparative Example 1. In other words, adding organic matter to the negative electrode mixture improved the initial charge-discharge efficiency. [Explanation of Symbols]

[0105] 10...Solid electrolyte layer, 20...Positive electrode, 22...Positive electrode current collector, 24...Positive electrode mixture layer, 30...Negative electrode, 32...Negative electrode current collector, 34...Negative electrode mixture layer, 34A...Negative electrode active material, 34B...First compound, 34C...Organic material, 34D...Conductive additive, 34E...Second compound, 40...Power generation element, 50...Outsole, 52...Metal foil, 54...Resin layer, 60, 62...Terminals, 100...Solid electrolyte battery

Claims

1. The battery comprises a negative electrode for a solid electrolyte battery, a positive electrode, and a solid electrolyte layer containing a solid electrolyte located between the negative electrode and the positive electrode. The negative electrode for the solid electrolyte battery comprises a negative electrode active material, a first compound, a second compound, and an organic substance supported on the negative electrode active material and forming a protective SEI film at the interface with the negative electrode active material during the initial charging process. The first compound is A ａ E ｂ G ｃ X ｄ ... (1) In equation (1), A is Li, E is Zr, G is at least one group selected from the group consisting of SO₄, CH₃COO, (COO)₂, and HCOO. X is Cl, Satisfying 0.5 ≤ a < 6, 0 < b < 2, 0 < c ≤ 6, 0 < d ≤ 6.1, Unlike the first compound, the second compound contains Li ａ E ｂ X ｄ ...(2) In equation (2), E is Zr, X is Cl, Satisfying 0.5 ≤ a < 6, 0 < b < 2, 0 < d ≤ 6.1, A solid electrolyte battery in which the solid electrolyte is the same as the first compound.

2. The solid electrolyte battery according to claim 1, wherein the organic substance is any of the following selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propanesultone, divinyl adipate, vinyl acetate, ethylene sulfide, chloroethylene carbonate, catechol carbonate, propynyl methanesulfonate, lithium bis[1,2-oxalato(2)-O,O']borate, and lithium difluoromono[1,2-dioxalato(2)-O,O']borate, or polymers thereof.

3. The solid electrolyte battery according to claim 1 or 2, further comprising a lithium salt having a smaller molecular weight than the first compound.

4. The solid electrolyte battery according to any one of claims 1 to 3, wherein the organic material is solid at room temperature.

5. The SEI coating that covers the negative electrode active material further comprises The solid electrolyte battery according to any one of claims 1 to 4, wherein the SEI coating comprises an organic SEI coating formed at the interface between the organic material and the negative electrode active material, and an inorganic SEI coating formed between the first compound and the negative electrode active material.

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