Negative electrode composite material and solid-state battery

Abstract

Provided are: a negative electrode composite material for a negative electrode for a solid-state battery, the negative electrode composite material being capable of being used even when a high-capacity negative electrode active material having a large volume change rate and a sulfide-based solid electrolyte that is reactive with an ionic liquid are used in the negative electrode composite material; and a solid-state battery using the negative electrode composite material. As a result, it is possible to achieve a solid-state battery in which loss of an ion conduction path during charging and discharging of the solid-state battery is suppressed, and a decrease in capacity during a charging and discharging cycle is suppressed. The negative electrode composite material contains a specific ionic liquid. Specifically, in a negative electrode composite material containing a negative electrode active material, a solid electrolyte, and an ionic liquid, the negative electrode active material is a silicon-based negative electrode active material, the solid electrolyte is a sulfide-based solid electrolyte, and the ionic liquid contains an anion having a donor number of 9 or less as determined from the half-wave potential of a noble metal.

Description

Technical Field

[0001] The present invention relates to a negative electrode composite material and a solid-state battery using the negative electrode composite material. Background Art

[0002] In recent years, research and development of secondary batteries is underway to ensure that more people have access to economical, reliable, sustainable and advanced energy, thereby promoting energy efficiency.

[0003] Among secondary batteries, solid-state batteries are attracting widespread attention due to their high energy density and excellent thermal safety. Solid-state batteries have a laminated structure consisting of, for example, a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive and negative electrode layers (see Patent Document 1).

[0004] Solid-state batteries exchange ions and electrons at the solid-solid interface. Therefore, to achieve a long-lasting battery life, the ion conduction path at this interface must be maintained for a long time. On the other hand, high-capacity negative electrode active materials, such as silicon-based negative electrode active materials, experience a large volume change during charge and discharge. Consequently, negative electrode materials containing high-capacity negative electrode active materials experience repeated large volume changes due to repeated charge and discharge. Furthermore, the ion conduction path at the solid-solid interface can no longer keep up with these repeated volume changes and disappears, resulting in a decrease in battery capacity with each charge and discharge cycle.

[0005] In contrast, a method has been proposed to improve the bonding properties of the solid-solid interface by adding a binder, thereby improving the robustness of the electrode (see Patent Document 2). However, since binders do not have electronic and ionic conductivity, increasing the amount of binder added increases the resistance of the battery.

[0006] Furthermore, a method has been proposed to incorporate ionic liquids into electrode composite materials in order to maintain ion conduction paths at the solid-solid interface (Patent Document 3). However, in the case of batteries using sulfide-based solid electrolytes, the ionic liquids react with the sulfide-based solid electrolyte, leading to a decrease in battery performance. The realization of long-life solid-state batteries has not yet been achieved.

[0007] Background Art Literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-295446

[0010] Patent Document 2: Japanese Patent Application Publication No. 2019-169298

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-168435 Summary of the Invention

[0012] [Problems to be solved by the invention]

[0013] The present invention has been completed in view of the above-mentioned situation, and its purpose is to provide a negative electrode composite material for a negative electrode of a solid-state battery, and a solid-state battery using the negative electrode composite material. Even when a high-capacity negative electrode active material with a large volume change rate and a sulfide-based solid electrolyte reactive with an ionic liquid are used in the negative electrode composite material, the disappearance of the ion conduction path during the charge and discharge process of the solid-state battery can be suppressed, thereby realizing a solid-state battery in which the decrease in capacity during the charge and discharge cycle is suppressed.

[0014] [Technical means to solve the problem]

[0015] The present inventors conducted extensive research to achieve this objective. They discovered that incorporating a specific ionic liquid into a negative electrode composite material can suppress the disappearance of ion conduction paths during charge and discharge, even in negative electrode composite materials containing a high-capacity negative electrode active material with a large volume change rate and a sulfide-based solid electrolyte reactive with the ionic liquid. This resulted in a solid-state battery with suppressed capacity degradation during charge and discharge cycles, leading to the completion of the present invention.

[0016] That is, the present invention includes the following aspects.

[0017] [1] A negative electrode composite material comprising a negative electrode active material, a solid electrolyte and an ionic liquid,

[0018] The negative electrode active material is a silicon-based negative electrode active material,

[0019] The solid electrolyte is a sulfide-based solid electrolyte,

[0020] The ionic liquid contains anions having a donor number of 9 or less determined from the half-wave potential of the noble metal,

[0021] The noble metal is selected from Eu III / II 、Yb III / II and Sm III / II At least one of the groups.

[0022] [2] The negative electrode composite material according to aspect [1], wherein the content of the ionic liquid is 10% by mass or less relative to the total amount of the negative electrode composite material.

[0023] [3] According to the negative electrode composite material of embodiment [1] or [2], the ionic liquid is liquid at 25°C.

[0024] [4] According to any one of aspects [1] to [3], the negative electrode composite material, the anion is bis(trifluoromethanesulfonyl)imide (TFSI).

[0025] [5] According to the negative electrode composite material of any one of aspects [1] to [4], the ionic liquid is at least one selected from the group consisting of BMPTFSI, MPPTFSI, EMITFSI, BMITFSI, MOEMPTFSI, PP13TFSI, DEMETFSI, [Li(G2)]TFSI, [Li(G3)]TFSI, [Li(G4)]TFSI, [Li(G5)]TFSI, and [Li(SL)2]TFSI.

[0026] [6] According to the negative electrode composite material described in any one of aspects [1] to [5], the sulfide-based solid electrolyte is an LPS-based solid electrolyte.

[0027] [7] The negative electrode composite material according to any one of aspects [1] to [6] further comprises at least one binder selected from the group consisting of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyimide resin.

[0028] [8] A solid-state battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer,

[0029] The negative electrode active material layer is composed of the negative electrode composite material described in any one of aspects [1] to [7].

[0030] [Effects of the Invention]

[0031] The negative electrode composite material of the present invention can suppress the disappearance of the ion conduction path during charge and discharge even if it contains a silicon-based negative electrode active material with a large volume change rate and a sulfide-based solid electrolyte, thereby realizing a solid-state battery with suppressed capacity reduction during charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 1 and 2 are the initial charge and discharge curves of the solid-state batteries of Example 1 and Comparative Example 1.

[0033] Figure 2 This is a graph showing the initial discharge capacity of the solid-state batteries of Example 1 and Comparative Example 1.

[0034] Figure 3 This diagram explains how to determine various initial resistances based on the Nyquist plot.

[0035] Figure 4It is the Nyquist plot of the solid-state batteries of Example 1 and Comparative Example 1.

[0036] Figure 5 This is a graph showing various initial resistances of the solid-state batteries of Example 1 and Comparative Example 1.

[0037] Figure 6 This is a graph showing the capacities of the solid-state batteries of Example 1 and Comparative Example 1.

[0038] Figure 7 This is a graph showing the capacity retention rates of the solid-state batteries of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0039] <Negative Electrode Composite Material>

[0040] The negative electrode composite material of the present invention comprises a negative electrode active material, a solid electrolyte, and an ionic liquid.

[0041] [Negative electrode active material]

[0042] The negative electrode composite material of the present invention contains a silicon-based negative electrode active material as the negative electrode active material. Solid-state batteries prepared using silicon-based negative electrode active materials exhibit high-capacity battery properties. However, silicon-based negative electrode active materials are known to expand during charging and exhibit a high rate of volume change during charge and discharge. Consequently, with repeated charge and discharge, the ion conduction pathway disappears, preventing the desired battery properties from being fully exhibited, resulting in a reduction in cycle life.

[0043] However, the negative electrode composite material according to the present invention, by containing a specific ionic liquid, can suppress the disappearance of the ion conduction path during charge and discharge even if it contains a silicon-based negative electrode active material, thereby realizing a solid-state battery with suppressed capacity reduction during charge and discharge cycles.

[0044] The silicon-based negative electrode active material used in the negative electrode composite material of the present invention is not particularly limited as long as it contains silicon (Si) as a constituent element. As the silicon-based negative electrode active material, a known substance can be used as the negative electrode active material of the solid-state battery. As the silicon-based negative electrode active material, for example, Si, Si alloys and silicon oxides can be listed. In the present invention, not only one can be used, but also two or more can be used in combination.

[0045] The shape of the silicon-based negative electrode active material is not particularly limited, as long as it is a general shape, that is, a particle shape. Furthermore, the silicon-based negative electrode active material may be in the form of primary particles or secondary particles. The average particle size (D50) of the silicon-based negative electrode active material is not particularly limited, and may be, for example, 0.01 μm or more and 10 μm or less.

[0046] The content of the silicon-based negative electrode active material relative to the total negative electrode composite material is not particularly limited and can be appropriately determined based on the target battery performance. For example, the content of the silicon-based negative electrode active material relative to the total negative electrode composite material can be 30% by mass or more and 90% by mass or less, preferably 50% by mass or more and 80% by mass or less.

[0047] Furthermore, the negative electrode composite material of the present invention only needs to contain the silicon-based negative electrode active material as an essential active material. In addition to the silicon-based negative electrode active material, negative electrode active materials other than the silicon-based negative electrode active material may also be contained. Examples of negative electrode active materials other than the silicon-based negative electrode active material include carbon materials such as graphite and hard carbon, various oxides such as lithium titanate, and various metals such as metallic lithium and lithium alloys.

[0048] From the viewpoint of exerting a more significant effect, the content of the silicon-based negative electrode active material relative to the overall negative electrode active material contained in the negative electrode composite material is preferably 90% by mass or more, more preferably 95% by mass or more, and further preferably 99% by mass or more. In particular, it is preferred that the silicon-based active material be 100% by mass of the negative electrode active material contained in the negative electrode composite material of the present invention.

[0049] [Solid Electrolyte]

[0050] The negative electrode composite material of the present invention contains a sulfide-based solid electrolyte as a solid electrolyte. The sulfide-based solid electrolyte contains a metal element (M) and sulfur (S) as ion-conducting elements and is not particularly limited as long as it has ion conductivity of a metal belonging to Group 1 or Group 2 of the periodic table.

[0051] Examples of the metal element (M) of the sulfide-based solid electrolyte include Li, Na, K, Mg, and Ca, among which Li is preferred.

[0052] Furthermore, the sulfide-based solid electrolyte preferably contains Li, A (A is at least one selected from the group consisting of P, Si, Ge, Al, and B) and S. Among them, from the viewpoint of ion conductivity, the A is preferably P (phosphorus), that is, the sulfide-based solid electrolyte contained in the negative electrode composite material of the present invention is preferably an LPS-based solid electrolyte.

[0053] Furthermore, the sulfide-based solid electrolyte may contain halogens such as Cl, Br, and I. The inclusion of halogens in the sulfide-based solid electrolyte improves ion conductivity. Furthermore, the sulfide-based solid electrolyte may contain oxygen (O).

[0054] Examples of sulfide-based solid electrolytes having Li ion conductivity include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is any one of Ge, Zn, Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In), etc. In addition, the description of "Li2S-P2S5" refers to a sulfide-based solid electrolyte prepared using a raw material composition containing Li2S and P2S5, and the other descriptions are the same.

[0055] In the negative electrode composite material of the present invention, not only one type of sulfide-based solid electrolyte may be used, but two or more types may be used in combination.

[0056] The form of the solid electrolyte material is not particularly limited, and may be, for example, in the form of particles.

[0057] The content of the sulfide-based solid electrolyte relative to the total negative electrode composite material is not particularly limited and can be appropriately determined based on the target battery performance. For example, the content of the sulfide-based solid electrolyte relative to the total negative electrode composite material can be from 10% by mass to 70% by mass, and preferably from 20% by mass to 50% by mass.

[0058] Furthermore, the negative electrode composite material of the present invention only needs to contain the sulfide-based solid electrolyte as an essential solid electrolyte and may contain, in addition to the sulfide-based solid electrolyte, a solid electrolyte other than the sulfide-based solid electrolyte. Examples of solid electrolytes other than the sulfide-based solid electrolyte include oxide solid electrolyte materials, halide solid electrolytes, inorganic solid electrolytes such as those containing lithium salts, polymer-based solid electrolytes such as polyethylene oxide, and gel-based solid electrolytes containing lithium salts or lithium ion-conductive ionic liquids.

[0059] From the perspective of achieving a more significant effect, the content of the sulfide-based solid electrolyte relative to the total solid electrolyte contained in the negative electrode composite material is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. It is particularly preferred that the sulfide-based solid electrolyte constitute 100% by mass of the solid electrolyte contained in the negative electrode composite material of the present invention.

[0060] [Ionic Liquids]

[0061] The negative electrode composite material of the present invention contains an ionic liquid. Ionic liquids can be divided into 1) aprotic ionic liquids, 2) protic ionic liquids, 3) inorganic ionic liquids, and 4) solvated ionic liquids. 1) to 3) consist solely of cations and anions, while 4) contains neutral molecules such as ethylene glycol dimethyl ether or sulfolane. The ionic liquid contained in the negative electrode composite material of the present invention can be any of the ionic liquids in 1) to 4).

[0062] Because ionic liquids have high ionic conductivity, the inclusion of ionic liquids in the negative electrode composite material can suppress the resistance increase of the resulting solid-state battery. Moreover, because ionic liquids have high viscosity, they can follow the volume changes of the active material. As a result, even when the solid-solid interface has peeled off, the presence of the ionic liquid can maintain the ion conduction path.

[0063] Examples of 1) aprotic ionic liquids include EMITFSI. Examples of 2) protic ionic liquids include DEMATFSI. Examples of 3) inorganic ionic liquids include LiFSI. 0.45 -KFSI 0.55 4) As the solvating ionic liquid, for example, [Li(G4)]TFSI can be cited.

[0064] The ionic liquid contained in the negative electrode composite material of the present invention contains anions having a donor number of 9 or less determined from the half-wave potential of the noble metal. Here, the noble metal that is the object of the half-wave potential determining the donor number is Eu III / II 、Yb III / II and Sm III / II At least one of the groups.

[0065] As described above, the negative electrode composite material of the present invention contains a sulfide-based solid electrolyte. Ionic liquids containing anions with a donor number exceeding 9 are highly reactive with sulfide-based solid electrolytes. Therefore, when such ionic liquids are used together with sulfide-based solid electrolytes, the capacity decreases during charge-discharge cycles. The negative electrode composite material of the present invention, by including an ionic liquid containing anions with a donor number of 9 or less, as determined from the half-wave potential of the noble metal, i.e., by formulating an ionic liquid with high ionic conductivity and low electron donation, can achieve a solid-state battery that suppresses capacity decrease during charge-discharge cycles.

[0066] In this specification, the method for measuring the number of donors derived from the half-wave potential of a noble metal is to prepare an electrolyte by dissolving the noble metal salt in an ionic liquid. This electrolyte is then prepared into a cell together with a working electrode, a counter electrode, and a reference electrode. The half-wave potential is then determined from the peak potential of the differential pulse voltammogram. The donor number is then determined by extrapolating the obtained half-wave potential to an approximate straight line of a graph of the half-wave potential of the corresponding noble metal relative to the donor number of a known organic solvent. In this case, the working electrode and the counter electrode are materials inert to the redox reaction of the noble metal, such as platinum or glassy carbon. The working electrode is preferably disc-shaped, and the counter electrode has a larger surface area than the working electrode. The reference electrode preferably utilizes the equilibrium reaction of Ag|Ag(I), as long as the extrapolated potential can be converted to a ferrocene|ferrocenium ion reference. The approximate straight line of the half-wave potential of noble metals with respect to the number of donors is the Eu using benzonitrile, acetonitrile, propylene glycol-1,2-carbonate, trimethyl phosphate, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide as solvents. III / II 、Yb III / II and Sm III / II The half-wave potential is plotted as reference data.

[0067] The ionic liquid contained in the negative electrode composite material of the present invention is preferably liquid at 25° C. If the ionic liquid is liquid at 25° C. (room temperature), the negative electrode formed from the negative electrode composite material of the present invention has high ion conductivity at 25° C. (room temperature).

[0068] The anion of the ionic liquid containing an anion having a donor number of 9 or less as determined from the half-wave potential of the noble metal used in the negative electrode composite material of the present invention is preferably bis(trifluoromethanesulfonyl)imide (TFSI) represented by the following formula (1). Therefore, the ionic liquid containing an anion having a donor number of 9 or less as determined from the half-wave potential of the noble metal used in the negative electrode composite material of the present invention is preferably TFSI. - Ionic liquid or TFSI - It is a solvated ionic liquid.

[0069] [Chemistry 1]

[0070]

[0071] Furthermore, the ionic liquid used in the negative electrode composite material of the present invention is preferably at least one of the group consisting of BMPTFSI, MPPTFSI, EMITFSI, BMITFSI, MOEMPTFSI, PP13TFSI, DEMETFSI, [Li(G2)]TFSI, [Li(G3)]TFSI, [Li(G4)]TFSI, [Li(G5)]TFSI, and [Li(SL)2]TFSI.

[0072] More preferably, the ionic liquid used in the negative electrode composite material of the present invention is an aprotic ionic liquid, and more preferably, a pyrrolidinium cation and TFSI - The ionic liquid constituting the present invention is particularly preferably BMPTFSI.

[0073] In the negative electrode composite material of the present invention, the content of the ionic liquid is preferably 10% by mass or less relative to the total amount of the negative electrode composite material.

[0074] In the negative electrode composite material of the present invention, the content of the ionic liquid may be 1% by mass or more relative to the total amount of the negative electrode composite material. Alternatively, the content of the ionic liquid may be 10% by mass or less, or 5% by mass or less relative to the total amount of the negative electrode composite material.

[0075] [Other ingredients]

[0076] The negative electrode composite material of the present invention may optionally contain other components in addition to the essential components of the negative electrode active material, solid electrolyte, and ionic liquid. Such other components may be any known substances that can be incorporated into the negative electrode composite material of a solid-state battery. Examples of such other components include binders and conductive materials.

[0077] (Adhesive)

[0078] The binder that can be incorporated into the negative electrode composite material of the present invention can be any known binder for solid-state batteries. Due to the presence of the binder, the negative electrode obtained from the negative electrode material of the present invention has improved solid-solid interface bonding, thereby enhancing electrode robustness, thereby enabling a higher level of benefit from the present invention.

[0079] Preferably, the binder that can be formulated into the negative electrode composite material of the present invention is at least one selected from the group consisting of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyimide resin.

[0080] <Solid-state battery>

[0081] The solid-state battery of the present invention comprises a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material layer is composed of the negative electrode composite material of the present invention.

[0082] The solid-state battery of the present invention may contain other layers as long as it contains a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer as essential constituent layers. Examples of other layers include a positive electrode current collector and a negative electrode current collector.

[0083] Hereinafter, the solid-state battery of the present invention will be described according to its structure.

[0084] [Positive Electrode Active Material Layer]

[0085] The positive electrode active material layer is a layer containing at least a positive electrode active material. The positive electrode active material contained in the positive electrode active material layer is not particularly limited as long as it is a material used in the positive electrode active material layer of a general solid-state battery. As the positive electrode active material, for example, if it is a lithium-ion battery, layered active materials containing lithium, spinel-type active materials, olivine-type active materials, etc. can be listed. Specific examples of positive electrode active materials include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), LiNiO2, etc. p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganese oxide (LiMn2O4), heterogeneous element substituted Li-Mn spinel represented by Li1 + xMn2-x-yMyO4 (x + y = 2, M = at least one selected from Al, Mg, Co, Fe, Ni and Zn), lithium titanate (oxide containing Li and Ti), lithium metal phosphate (LiMPO4, M = at least one selected from Fe, Mn, Co and Ni), etc.

[0086] The content of the positive electrode active material in the positive electrode active material layer may be, for example, in the range of 50% to 99% by mass. The surface of the positive electrode active material may be covered with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer.

[0087] In order to improve lithium ion conductivity, the positive electrode active material layer may optionally contain the following solid electrolyte. In addition, the positive electrode active material layer may also optionally contain a binder or a conductive additive. As these substances, substances used in general solid-state batteries can be used.

[0088] The method for producing the positive electrode active material layer is not particularly limited and can be produced using a known method. The positive electrode active material layer can be produced, for example, by mixing the material constituting the positive electrode active material layer with a solvent to form a slurry, applying the slurry to the positive electrode collector, and drying.

[0089] The thickness of the positive electrode active material layer is not particularly limited and can be appropriately set according to the required battery performance. For example, the thickness of the positive electrode active material layer can be in the range of 0.1 μm to 1 mm.

[0090] [Negative Electrode Active Material Layer]

[0091] The negative electrode active material layer in the solid-state battery of the present invention is obtained from the negative electrode composite material of the present invention.

[0092] (Method for Manufacturing Negative Electrode Active Material Layer)

[0093] The method for producing the negative electrode active material layer in the solid-state battery of the present invention from the negative electrode composite material of the present invention is not particularly limited. A known method for forming a negative electrode active material layer using the negative electrode composite material can be applied.

[0094] For example, a slurry in which the negative electrode composite material of the present invention is dispersed and / or dissolved in a solvent is prepared, the slurry is applied to at least one surface of the negative electrode current collector, dried, and then optionally pressed to form a negative electrode active material layer on at least one surface of the negative electrode current collector. Moreover, the thickness of the negative electrode active material layer can be easily adjusted by adjusting the amount of the slurry applied, etc.

[0095] The thickness of the negative electrode active material layer is not particularly limited and can be appropriately set according to the required battery performance. For example, the thickness of the negative electrode active material layer can be in the range of 0.1 μm to 1 mm.

[0096] [Solid electrolyte layer]

[0097] The solid electrolyte layer is a layer containing a solid electrolyte and is disposed between the positive electrode active material layer and the negative electrode active material layer.

[0098] The material of the solid electrolyte is not particularly limited as long as it is a material having ion conductivity and insulating properties, such as lithium. As the material of the solid electrolyte, known substances used in solid-state batteries can be used.

[0099] Examples of solid electrolyte materials include sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, inorganic solid electrolytes containing lithium salts, polymer solid electrolytes such as polyethylene oxide, and gel-based solid electrolytes containing ionic liquids containing lithium salts or lithium ion conductivity. Among these, sulfide solid electrolyte materials are preferred from the perspectives of high electrical conductivity, structural formability by pressing, and good interfacial bonding.

[0100] The form of the solid electrolyte material is not particularly limited and may be, for example, in the form of particles. Furthermore, the content of the solid electrolyte in the solid electrolyte layer of the solid-state battery of the present invention is not particularly limited. For example, the solid electrolyte content may be in the range of 50% to 99% by mass.

[0101] The solid electrolyte layer may optionally contain a binder. Furthermore, an adhesive may be optionally included to impart mechanical strength or flexibility. As these substances, substances commonly used in solid-state batteries can be used.

[0102] The method for producing the solid electrolyte layer is not particularly limited and can be produced using a known method. The solid electrolyte layer can be produced, for example, by mixing the materials constituting the solid electrolyte layer with a solvent to form a slurry, applying the slurry on a substrate, and drying it.

[0103] [Positive electrode current collector]

[0104] The positive electrode current collector, which is an arbitrary component of the solid-state battery of the present invention, is arranged in contact with the positive electrode active material layer and has the function of collecting the positive electrode active material layer. The material of the positive electrode current collector is not particularly limited as long as it can collect the positive electrode active material layer. Examples of materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, iron, and titanium, among which at least one selected from the group consisting of aluminum, aluminum alloys, and stainless steel is preferred.

[0105] The shape of the positive electrode current collector is not particularly limited, and examples thereof include foil and plate. Furthermore, the thickness of the positive electrode current collector is not particularly limited and can be the same as that used in the positive electrode of a typical solid-state battery. For example, the thickness of the positive electrode current collector can be in the range of 0.1 μm to 1 mm.

[0106] [Negative electrode current collector]

[0107] The negative electrode current collector used in the solid-state battery of the present invention is arranged in contact with the negative electrode active material layer and has the function of collecting the negative electrode active material layer. The material of the negative electrode current collector is not particularly limited as long as it can collect the negative electrode active material layer, and is preferably composed of a material with high electrical conductivity. Examples of materials with high electrical conductivity include metals containing at least one metal element selected from the group consisting of silver, palladium, gold, platinum, aluminum, copper and nickel, alloys such as stainless steel materials, or non-metals such as carbon (C).

[0108] Among these highly conductive materials, considering both high conductivity and manufacturing cost, it is preferred to use at least one selected from the group consisting of copper, SUS, and nickel. Stainless steel, in particular, is less likely to react with the negative electrode active material, positive electrode active material, and solid electrolyte. Therefore, using stainless steel as the negative electrode current collector material can reduce the internal resistance of solid-state batteries.

[0109] The shape of the negative electrode current collector is not particularly limited, and examples thereof include foil, plate, mesh, nonwoven fabric, foam, etc. Furthermore, in order to improve adhesion to the negative electrode active material layer, a carbon layer may be configured on the surface of the negative electrode current collector, and the surface may be roughened.

[0110] The thickness of the negative electrode current collector is not particularly limited and can be the same as that used in negative electrodes of general solid-state batteries. For example, the thickness of the negative electrode current collector can be in the range of 0.1 μm to 1 mm.

[0111] <Method for manufacturing solid-state batteries>

[0112] The method for manufacturing the solid-state battery of the present invention is not particularly limited, and a known method can be used. For example, an electrode body can be prepared by stacking a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. Then, a plurality of electrode bodies are stacked and optionally pressed to form an integrated electrode stack, thereby preparing an electrode stack, which can be used as the solid-state battery of the present invention.

[0113] While preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and modifications and improvements within the scope of achieving the object of the present invention are also included in the present invention.

[0114] [Example]

[0115] Hereinafter, the present invention will be described in more detail based on Examples and the like, but the present invention is not limited to the following Examples and the like.

[0116] <Example 1>

[0117] [Material]

[0118] The following materials were prepared as materials for the laminated battery cell for evaluation.

[0119] (positive electrode)

[0120] Positive electrode active material: NMC622 (LiNi 0.6 Mn 0.2 CO 0.2 O2)

[0121] Positive electrode collector: aluminum foil

[0122] (negative electrode)

[0123] Negative electrode active material: Si / C composite active material (Si: 55% by mass)

[0124] Solid electrolyte: LPS system - halogen (Cl): Li 7-x PS 6-x C1 x

[0125] Ionic liquid: BMPTFSI (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide)

[0126] Binder: Styrene-butadiene rubber (SBR)

[0127] Negative electrode collector: copper foil

[0128] (Solid Electrolyte)

[0129] Solid electrolyte: LPS system - halogen (Cl): Li 7-x PS 6-x C1 x

[0130] [Preparation of negative electrode composite material slurry]

[0131] A negative electrode composite material slurry was prepared by mixing a negative electrode active material, a solid electrolyte, an ionic liquid, and a binder. The negative electrode active material content was 70% by mass, the solid electrolyte content was 28% by mass, the ionic liquid content was 1% by mass, and the binder content was 1% by mass.

[0132] [Preparation of solid-state batteries for evaluation]

[0133] The positive electrode current collector, positive electrode active material layer, solid electrolyte layer, negative electrode active material layer, and negative electrode current collector were stacked in this order and pressed at 25°C (room temperature) and a molding pressure of 980 MPa for 5 minutes to produce an electrode assembly. The resulting electrode assembly was laminated and packaged, and restrained at 1.5 MPa to produce a solid-state battery for evaluation.

[0134] <Comparative Example 1>

[0135] [Preparation of solid-state batteries for evaluation]

[0136] A laminated battery cell was prepared in the same manner as in Example 1 except that no ionic liquid was used in the negative electrode composite material.

[0137] <Assessment>

[0138] (Initial discharge capacity)

[0139] The resulting evaluation battery was aged at 60°C under the following conditions: charging at a 1 / 100C rate with an upper limit charge capacity of 175 mAh / g, and discharging at a 1 / 10C rate with a voltage of 2.65 V at the end of discharge.

[0140] The aged solid-state battery was then subjected to initial charge and discharge to obtain the initial charge and discharge curve. The initial charge and discharge conditions were 25°C and a 1 / 10C rate, with a voltage of 2.65V at the end of discharge and 3.72V at the end of charge. Subsequently, charge and discharge were repeated at 25°C and a 1 / 3C rate, with a voltage of 2.65V at the end of discharge and 3.72V at the end of charge.

[0141] The initial charge and discharge curves at 1 / 10C rate and 1 / 3C rate are shown in Figure 1 Furthermore, the initial discharge capacity at 1 / 10C rate and 1 / 3C rate is shown in Figure 2 middle.

[0142] (Initial resistance)

[0143] Then, the solid-state battery that has undergone the initial discharge capacity test is subjected to an initial resistance test. The initial resistance test is performed by the AC impedance method. The impedance at multiple frequencies measured by the AC impedance method is plotted into a graph, and the following is obtained: Figure 3 The Nyquist plot is shown in Figure 1. Figure 3 As shown, the 0.1 Hz resistance, conduction resistance, reaction resistance and diffusion resistance can be defined based on the parts presented in the Nyquist plot.

[0144] AC impedance measurement was performed using SI1287 (Solartron Analytical Co., Ltd.) as a measuring instrument. The measurement conditions were a temperature of 25° C., an applied AC voltage of 10 mV, and a frequency of 0.1 Hz to 1 MHz.

[0145] The resulting Nyquist diagram is plotted in Figure 4 Moreover, according to Figure 4 The Nyquist plots of 0.1Hz resistance, conduction resistance, reaction resistance, and diffusion resistance are calculated. The results are shown in Figure 5 .

[0146] (Capacity maintenance rate)

[0147] Then, the solid-state battery that has undergone the initial resistance test was subjected to a charge-discharge cycle test at a temperature of 60°C. In the charge-discharge cycle test, the current density was 2.0 mA / cm 2 At a constant current of , the battery was charged to a charge upper limit voltage of 4.00 V, and then the current density was set at 20 mA / cm 2 The battery was discharged at a constant current of 1.5 V to a lower discharge voltage of 2.65 V. Each charge and discharge cycle was considered a cycle, and 50 cycles were performed in total. The discharge capacity of each cycle was then measured.

[0148] The curve obtained by plotting the cycle and discharge capacity is shown in Figure 6 Furthermore, the discharge capacity of the solid-state battery before the cycle test (at 0 cycle) is set to 100%, and the capacity retention rate in each cycle is calculated. The curve obtained by plotting the cycle and capacity retention rate is shown in Figure 7 middle.

[0149] <Inspection>

[0150] Compared with the solid-state battery prepared in Comparative Example 1, the solid-state battery prepared in Example 1 has an improved C / 3 discharge capacity, and its 0.1 Hz resistance, reaction resistance, and diffusion resistance are all reduced. Moreover, compared with the solid-state battery prepared in Comparative Example 1, the solid-state battery prepared in Example 1 also has a higher discharge capacity retention rate after 50 cycles.

Claims

1. A negative electrode composite material comprising a negative electrode active material, a solid electrolyte and an ionic liquid, characterized in that: The negative electrode active material is a silicon-based negative electrode active material, The solid electrolyte is a sulfide-based solid electrolyte, The ionic liquid contains anions having a donor number of 9 or less as determined from the half-wave potential of the noble metal. The noble metal is selected from Eu III / II 、Yb III / II and Sm III / II At least one of the groups.

2. The negative electrode composite material according to claim 1, wherein The content of the ionic liquid is 10% by mass or less relative to the total amount of the negative electrode composite material.

3. The negative electrode composite material according to claim 1 or 2, wherein The ionic liquid is liquid at 25°C.

4. The negative electrode composite material according to claim 1 or 2, wherein The anion is bis(trifluoromethanesulfonyl)imide (TFSI).

5. The negative electrode composite material according to claim 1 or 2, wherein The ionic liquid is at least one selected from the group consisting of BMPTFSI, MPPTFSI, EMITFSI, BMITFSI, MOEMPTFSI, PP13TFSI, DEMETFSI, [Li(G2)]TFSI, [Li(G3)]TFSI, [Li(G4)]TFSI, [Li(G5)]TFSI, and [Li(SL)2]TFSI.

6. The negative electrode composite material according to claim 1 or 2, wherein The sulfide-based solid electrolyte is an LPS-based solid electrolyte.

7. The negative electrode composite material according to claim 1 or 2, wherein: The invention further comprises at least one adhesive selected from the group consisting of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyimide resin.

8. A solid-state battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, characterized in that: The negative electrode active material layer is composed of the negative electrode composite material according to claim 1 or 2.

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