All-solid-state secondary battery, sheet for the battery, and manufacturing method for both

Abstract

This invention provides a method for manufacturing a sheet for an all-solid-state secondary battery, a method for manufacturing an all-solid-state secondary battery manufactured by the method, and the sheet for an all-solid-state secondary battery and the all-solid-state secondary battery. In the method for manufacturing the sheet for the all-solid-state secondary battery, an inorganic solid electrolyte composition containing an inorganic solid electrolyte and a dispersion medium is coated onto a substrate to form a film. Either or both of the preparation temperature of the inorganic solid electrolyte composition and the temperature before coating are set to 35-90°C.

Description

Technical Field

[0001] This invention relates to a sheet for all-solid-state secondary batteries and a method for manufacturing all-solid-state secondary batteries, as well as the sheet for all-solid-state secondary batteries and all-solid-state secondary batteries. Background Technology

[0002] In all-solid-state secondary batteries, all the negative electrode, electrolyte, and positive electrode are made of solids, which can significantly improve the safety and reliability of batteries using organic electrolytes. It also extends battery life. Furthermore, all-solid-state secondary batteries can be configured with electrodes and electrolytes directly arranged and connected in series. Therefore, compared to secondary batteries using organic electrolytes, they can achieve higher energy density and are expected to be used in electric vehicles or large-capacity batteries.

[0003] In this type of all-solid-state secondary battery, inorganic solid electrolytes and active materials can be used as the materials forming the constituent layers (solid electrolyte layer, negative electrode active material layer, positive electrode active material layer, etc.). In recent years, inorganic solid electrolytes, especially oxide-based and sulfide-based inorganic solid electrolytes, have been anticipated as electrolyte materials with high ionic conductivity approaching that of organic electrolytes.

[0004] As a material for forming the constituent layer of an all-solid-state secondary battery (constituent layer forming material), the above-mentioned composition containing inorganic solid electrolyte and dispersion medium has been proposed, and a method for forming the constituent layer using the composition has also been proposed. For example, Patent Document 1 describes a method for manufacturing a solid electrolyte layer. Specifically, this manufacturing method includes: a solid electrolyte layer forming slurry preparation step, in which a solid electrolyte layer forming slurry is obtained by mixing a sulfide-based solid electrolyte material and a binder polymer having double bonds capable of bonding with sulfur components in a solvent; and a bonding treatment step, in which the sulfur components in the sulfide-based solid electrolyte material are bonded to the double bonds of the binder polymer by bonding the solid electrolyte layer forming slurry.

[0005] Previous technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-186682 Summary of the Invention

[0008] The technical problem to be solved by the invention

[0009] When the constituent layer is formed by solid particle materials (inorganic solid electrolyte, active material, conductive additive, etc.), from the viewpoint of improving the battery performance (e.g., cycle characteristics) of all-solid-state secondary batteries, it is preferable to have excellent properties such as dispersibility and ease of handling of the constituent layer forming material.

[0010] In recent years, from the perspective of reducing environmental impact and thus manufacturing costs, high-concentration compositions (slurries) with increased solids content have been studied as constituent layer forming materials. However, as the solids content of the composition increases, the properties of the composition usually deteriorate significantly. Therefore, it is difficult to achieve the properties required for constituent layer forming materials in high-concentration compositions, and further research is warranted.

[0011] Furthermore, the research and development of high-performance and practical electric vehicles is progressing rapidly, leading to increasingly higher requirements for the battery performance of all-solid-state rechargeable batteries. To meet these requirements, it is important to enable the constituent layer forming materials to exhibit superior properties in forming the constituent layers.

[0012] However, the manufacturing method described in Patent Document 1 is a method of manufacturing a solid electrolyte layer by chemically bonding the sulfide-based solid electrolyte material with the binder polymer after heating the slurry. From the viewpoint of improving the properties of the slurry to form a solid electrolyte layer, no research has been conducted.

[0013] The objective of this invention is to provide a method for manufacturing an all-solid-state secondary battery sheet that improves the cycle characteristics of an all-solid-state secondary battery even when using an inorganic solid electrolyte composition with increased solid component concentration, and a method for manufacturing an all-solid-state secondary battery that achieves excellent cycle characteristics. Furthermore, the objective of this invention is to provide an all-solid-state secondary battery sheet and an all-solid-state secondary battery manufactured by the above-described manufacturing method.

[0014] means for solving technical problems

[0015] The inventors, through various studies on inorganic solid electrolyte compositions for manufacturing sheets of all-solid-state secondary batteries, discovered that the temperature during the preparation of the inorganic solid electrolyte composition (slurry) (preparation temperature) is highly relevant to dispersion characteristics such as inhibiting the aggregation of solid particle materials (also called solid particles). Furthermore, the temperature of the slurry-like inorganic solid electrolyte composition used for coating (pre-coating temperature) is highly relevant to imparting appropriate viscosity to the slurry and exhibiting high fluidity, thus ensuring the solid particles in the constituent layers are tightly bonded to the substrate (stable coating suitability). This results in improved cycle characteristics of all-solid-state secondary batteries. Further research based on this insight revealed that for inorganic solid electrolyte compositions containing both inorganic solid electrolyte and dispersion medium, setting either or both of the preparation temperature and pre-coating temperature to 35–90°C allows for excellent dispersion characteristics and coating suitability even with increased solid component concentration. Based on these insights, the present invention was completed through repeated research.

[0016] That is, the above-mentioned problems are solved through the following solutions.

[0017] <1> A method for manufacturing a sheet for an all-solid-state secondary battery, comprising coating a composition containing an inorganic solid electrolyte having conductive ions of metals belonging to Group 1 or Group 2 of the periodic table and a dispersion medium onto a substrate to form a film, wherein,

[0018] The preparation temperature of the inorganic solid electrolyte composition and the temperature before coating are set to 35–90°C.

[0019] <2> The manufacturing method of the sheet for all-solid-state secondary batteries described in <1>, wherein,

[0020] The preparation temperature and the temperature before coating and film formation were both set to 35–90°C.

[0021] <3> The method for manufacturing the sheet for all-solid-state secondary batteries according to <1> or <2>, wherein,

[0022] The viscosity of the inorganic solid electrolyte composition at 25°C is 500–10,000 cP.

[0023] <4> A method for manufacturing a sheet for an all-solid-state secondary battery according to any one of <1> to <3>, wherein,

[0024] The difference (absolute value) between the viscosity at 25°C and the viscosity of the inorganic solid electrolyte composition at the higher of the above preparation temperature and the above coating film-forming temperature is 1,000 cP or more.

[0025] <5> A method for manufacturing a sheet for an all-solid-state secondary battery according to any one of <1> to <4>, wherein,

[0026] The boiling point of the dispersion medium is 100–250℃.

[0027] <6> A method for manufacturing a sheet for an all-solid-state secondary battery according to any one of <1> to <5>, wherein the inorganic solid electrolyte composition contains an adhesive.

[0028] <7> A method for manufacturing a sheet for an all-solid-state secondary battery according to any one of <1> to <6>, wherein the inorganic solid electrolyte composition contains an active substance.

[0029] <8> A method for manufacturing an all-solid-state secondary battery, wherein the all-solid-state secondary battery sequentially comprises a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, and the method for manufacturing the all-solid-state secondary battery includes the following steps:

[0030] At least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is manufactured by the manufacturing method of the sheet for all-solid-state secondary batteries as described in any one of <1> to <7>.

[0031] <9> The manufacturing method of the all-solid-state secondary battery according to <8> includes a current collector stacked on the opposite side of the positive electrode active material layer and the negative electrode active material layer, respectively, opposite to the solid electrolyte layer. The manufacturing method of the all-solid-state secondary battery includes the following steps:

[0032] The method for manufacturing sheet material for all-solid-state secondary batteries as described in any one of <1> to <7> is used to manufacture at least one of a positive electrode having a current collector and a positive electrode active material layer stacked on top of it, a solid electrolyte layer, and a negative electrode having a current collector and a negative electrode active material layer stacked on top of it.

[0033] <10> A sheet for an all-solid-state secondary battery, which is manufactured by any one of the manufacturing methods for the all-solid-state secondary battery sheet described in <1> to <7> above.

[0034] <11> An all-solid-state secondary battery, which sequentially comprises a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, wherein,

[0035] At least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is composed of the all-solid-state secondary battery sheet described in <10>.

[0036] <12> According to the all-solid-state secondary battery described in <11>, it comprises a current collector stacked on the side opposite to the solid electrolyte layer of both the positive electrode active material layer and the negative electrode active material layer, wherein,

[0037] At least one of the positive electrode having a current collector and a positive electrode active material layer stacked on top of the solid electrolyte layer and the negative electrode having a current collector and a negative electrode active material layer stacked on top of the negative electrode is made of the all-solid-state secondary battery sheet described in <10>.

[0038] Invention Effects

[0039] The method for manufacturing all-solid-state secondary battery sheets of the present invention can produce all-solid-state secondary battery sheets that improve the cycle characteristics of all-solid-state secondary batteries even when using an inorganic solid electrolyte composition with increased solid component concentration. Furthermore, the method for manufacturing all-solid-state secondary batteries of the present invention can produce excellent all-solid-state secondary batteries even when using an inorganic solid electrolyte composition with increased solid component concentration.

[0040] Furthermore, the all-solid-state secondary battery sheet of the present invention is assembled into the all-solid-state secondary battery as a constituent layer, thereby improving the cycle characteristics of the all-solid-state secondary battery. Moreover, the all-solid-state secondary battery of the present invention achieves excellent cycle characteristics.

[0041] The above-described features and other features and advantages of the present invention will become more apparent from the accompanying drawings and from the following description. Attached Figure Description

[0042] Figure 1 This is a longitudinal sectional view illustrating a preferred embodiment of the all-solid-state secondary battery of the present invention. Detailed Implementation

[0043] In this invention, the numerical range represented by “~” refers to the range encompassed by the values ​​recorded before and after “~” as the lower limit and upper limit values.

[0044] In this invention, the designation of a compound (e.g., when referred to as a compound by appending a compound at the end) means that in addition to the compound itself, it also includes its salt and its ions. Furthermore, it refers to derivatives that include modifications to the introduced substituents or other components without impairing the effects of this invention.

[0045] In this invention, (meth)acrylic acid refers to one or both of acrylic acid and methacrylic acid. The same applies to (meth)acrylates.

[0046] First, the all-solid-state secondary battery sheet and the all-solid-state secondary battery manufactured using the manufacturing method of the all-solid-state secondary battery of the present invention (sometimes collectively referred to as the manufacturing method of the present invention) will be described.

[0047] [Sheets for all-solid-state rechargeable batteries]

[0048] The sheet material for all-solid-state secondary batteries of the present invention is a sheet-shaped molded body capable of forming the constituent layers of an all-solid-state secondary battery, and includes various forms depending on its application. For example, sheets preferably used for solid electrolyte layers (also called solid electrolyte sheets for all-solid-state secondary batteries) and sheets preferably used for electrodes or laminates of electrodes and solid electrolyte layers (electrode sheets for all-solid-state secondary batteries) are examples. In the present invention, these various sheets are collectively referred to as sheets for all-solid-state secondary batteries.

[0049] In this invention, each layer constituting the sheet for all-solid-state secondary batteries can be a single-layer structure or a multi-layer structure.

[0050] In the all-solid-state secondary battery sheet of the present invention, the solid electrolyte layer or the active material layer on the substrate is formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention. Therefore, the all-solid-state secondary battery sheet of the present invention, by appropriately peeling off the substrate, serves as the solid electrolyte layer, active material layer, or electrode of the all-solid-state secondary battery, thereby improving the cycle characteristics of the all-solid-state secondary battery. In particular, when the all-solid-state secondary battery electrode sheet is assembled as an electrode into the all-solid-state secondary battery, since the active material layer is firmly bonded to the current collector, further improvement in cycle characteristics can be achieved.

[0051] The detailed reasons why the all-solid-state secondary battery sheet of the present invention can improve the cycle characteristics of all-solid-state secondary batteries are not yet clear. However, it can be considered that the inorganic solid electrolyte composition used in the manufacturing method of the all-solid-state secondary battery sheet of the present invention can achieve excellent dispersion characteristics and coating suitability.

[0052] It is believed that in the manufacturing method of the all-solid-state secondary battery sheet of the present invention, if the inorganic solid electrolyte composition is prepared by mixing (dispersing) the components at a preparation temperature of 30 to 95°C, the interaction between solid particles can be weakened, and the aggregation or precipitation of solid particles can be suppressed. As a result, the dispersibility of solid particles in the composition can be improved, and a highly dispersed state can be stably maintained over time. When the inorganic solid electrolyte composition exhibiting such excellent dispersion characteristics is used to form a constituent layer, a constituent layer with fewer agglomerates of solid particles and uniformly bonded solid particles can be formed. Therefore, the generation or amplification of voids caused by charging and discharging can be suppressed, and the cycle characteristics of the all-solid-state secondary battery can be improved.

[0053] On the other hand, it is believed that if the inorganic solid electrolyte composition is preheated to 30–95°C before coating and film formation (also referred to as film formation), the interaction between solid particles is effectively weakened. For the inorganic solid electrolyte composition just before film formation, in addition to improving dispersion characteristics, it can also exhibit suitable viscosity (flowability) for film formation. As a result, the coated inorganic solid electrolyte composition flows moderately (leveling), which can suppress the generation of severe unevenness caused by insufficient or excessive flow (excellent surface properties of the coated surface), and the interfacial contact state of the solid particles is good and firmly adhered.

[0054] In particular, in this invention, even if the concentration of the solid component in the inorganic solid electrolyte composition is set to be higher than before, the aforementioned effects can be achieved without impairing the effects produced by setting either or both of the preparation temperature and the pre-coating temperature to the aforementioned temperature, and the aforementioned excellent dispersion characteristics and coating suitability can be realized.

[0055] When an inorganic solid electrolyte composition with excellent dispersion and coating properties is used to form the constituent layer, voids caused by improved dispersion properties can be suppressed, while the adhesion between solid particles and even between solid particles and the substrate (current collector) is strengthened, and current concentration (deterioration of solid particles) on the steep protrusions of the constituent layer surface can be suppressed. Therefore, the cycle characteristics of all-solid-state secondary batteries can be improved.

[0056] Solid electrolyte sheets for all-solid-state secondary batteries

[0057] The solid electrolyte sheet for all-solid-state secondary batteries of the present invention can be any sheet having a solid electrolyte layer. Examples include sheets without a substrate but formed from the solid electrolyte layer (sheets with the substrate peeled off), laminated sheets with the solid electrolyte layer formed on a substrate, and laminated sheets having a solid electrolyte layer and a protective layer sequentially on a substrate. The solid electrolyte sheet for all-solid-state secondary batteries may also have other layers besides the solid electrolyte layer. Examples of other layers include a protective layer (release sheet), a current collector, and a coating.

[0058] The solid electrolyte layer of the solid electrolyte sheet for all-solid-state secondary batteries is formed by the manufacturing method of the sheet for all-solid-state secondary batteries of the present invention.

[0059] The surface condition of the solid electrolyte layer is appropriately determined considering factors such as ionic conductivity and adhesion to layers disposed on the surface. However, if the surface roughness is too large, current will concentrate on the steep protrusions, causing solid particle degradation and resulting in a decrease in the cycle characteristics of the all-solid-state secondary battery. Therefore, in terms of cycle characteristics, the surface of the solid electrolyte layer is preferably flat (smooth) (with few steep protrusions). For example, its maximum height roughness Rz is preferably less than 10 μm, more preferably less than 8.0 μm, and even more preferably less than 6.0 μm. There is no particular limitation on the lower limit of the maximum height roughness Rz, for example, it is practically set to 0.5 μm or more. The maximum height roughness Rz of the solid electrolyte layer is set to a value calculated by the method described in the examples.

[0060] Furthermore, in the solid electrolyte layer, the solid particles are tightly bonded to each other, and the layer itself has high strength.

[0061] The content of each component in the solid electrolyte layer is not particularly limited, and the preferred meaning is the same as that of the content of each component in the solid component of the inorganic solid electrolyte composition described later. The layer thickness of each layer constituting the solid electrolyte sheet for all-solid-state secondary batteries is the same as the layer thickness described later in the all-solid-state secondary battery section.

[0062] As for the substrate, there are no particular limitations as long as it is a substrate capable of supporting the solid electrolyte layer. Examples include sheet-like materials (plate-like bodies) such as those described in the current collector section (described later), organic materials, and inorganic materials. Examples of organic materials include various polymers, specifically polyethylene terephthalate, polypropylene, polyethylene, and cellulose. Examples of inorganic materials include, for example, glass and ceramics.

[0063] <Electrode sheets for all-solid-state secondary batteries>

[0064] The electrode sheet for all-solid-state secondary batteries of the present invention (also simply referred to as "electrode sheet") can be any sheet having an active material layer, typically a sheet having a current collector and an active material layer. Examples include a sheet without a substrate and formed of an active material layer (a sheet with the substrate removed), a laminated sheet with an active material layer formed on a substrate (current collector), a laminated sheet with an active material layer and a solid electrolyte layer sequentially formed on a substrate, and a laminated sheet with an active material layer, a solid electrolyte layer, and an active material layer sequentially formed on a substrate. Furthermore, the electrode sheet may have other layers as described above.

[0065] Preferably, the active material layer formed on the substrate is formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention, and the solid electrolyte layer formed on the active material layer is formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention.

[0066] The surface state and solid particle adhesion of the active material layer and solid electrolyte layer formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention are the same as those of the solid electrolyte layer described above. Furthermore, in addition to the solid particle adhesion, the active material layer formed on the substrate also exhibits strong adhesion to the current collector. This is believed to be because the interfacial contact state between the solid particles and the current collector surface is improved.

[0067] The content of each component in the solid electrolyte layer or active material layer of the electrode sheet is not particularly limited, and the preferred meaning is the same as that of the content of each component in the solid component of the inorganic solid electrolyte composition (electrode composition) described later. The layer thickness of each layer constituting the electrode sheet of the present invention is the same as the layer thickness described later in the description of all-solid-state secondary batteries.

[0068] Furthermore, when the all-solid-state secondary battery sheet has a layer other than the active material layer or the solid electrolyte layer formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention, this layer can be made of a material manufactured by conventional methods using known materials.

[0069] [All-solid-state rechargeable battery]

[0070] The all-solid-state secondary battery of the present invention comprises a positive electrode active material layer, a negative electrode active material layer opposite to the positive electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. The all-solid-state secondary battery of the present invention is only required to have a structure with a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer; other structures are not particularly limited, for example, known structures related to all-solid-state secondary batteries can be used. In a preferred all-solid-state secondary battery, a positive electrode current collector is stacked on the surface of the positive electrode active material layer opposite to the solid electrolyte layer to form a positive electrode, and a negative electrode current collector is stacked on the surface of the negative electrode active material layer opposite to the solid electrolyte layer to form a negative electrode. In the present invention, each constituent layer (including the current collector, etc.) constituting the all-solid-state secondary battery can be a single-layer structure or a multi-layer structure.

[0071] In the all-solid-state secondary battery of the present invention, at least one of the negative electrode active material layer (negative electrode), the positive electrode active material layer (positive electrode), and the solid electrolyte layer is composed of an all-solid-state secondary battery sheet formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention. One preferred embodiment of the all-solid-state secondary battery is that all three layers—the negative electrode active material layer (negative electrode), the positive electrode active material layer (positive electrode), and the solid electrolyte layer—are composed of an all-solid-state secondary battery sheet formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention.

[0072] The all-solid-state secondary battery of the present invention is assembled with an all-solid-state secondary battery sheet formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention as at least one constituent layer. Therefore, the all-solid-state secondary battery of the present invention exhibits excellent cycle characteristics.

[0073] <Active Material Layer and Solid Electrolyte Layer>

[0074] The details of the active material layer and the solid electrolyte layer formed by the all-solid secondary battery sheet manufactured by the method of manufacturing the all-solid secondary battery sheet of the present invention will be described later.

[0075] There are no particular limitations on the thickness of the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer. Considering the size of a typical all-solid-state secondary battery, the thickness of each layer is preferably 10 to 1,000 μm, more preferably 20 μm or more and less than 500 μm. In the all-solid-state secondary battery of the present invention, the thickness of at least one of the positive electrode active material layer and the negative electrode active material layer is further preferably 50 μm or more and less than 500 μm.

[0076] Furthermore, when the active material layer or the solid electrolyte layer is composed of an all-solid-state secondary battery sheet formed by the manufacturing method of the all-solid-state secondary battery sheet of the present invention, the layer can be made of a material manufactured by conventional methods using known materials.

[0077] <Current Collector>

[0078] The positive and negative current collectors are preferably electron conductors.

[0079] In this invention, either the positive current collector or the negative current collector, or both of them together, are sometimes referred to simply as a current collector.

[0080] In addition to aluminum, aluminum alloys, stainless steel, nickel, and titanium, materials in which carbon, nickel, titanium, or silver (materials forming thin films) are treated on the surface of aluminum or stainless steel are preferred as the material forming the positive current collector. Among these, aluminum and aluminum alloys are more preferred.

[0081] In addition to aluminum, copper, copper alloys, stainless steel, nickel, and titanium, materials that have been treated with carbon, nickel, titanium, or silver on the surface of aluminum, copper, copper alloys, or stainless steel are preferred as materials for forming the negative current collector. More preferably, aluminum, copper, copper alloys, and stainless steel are preferred.

[0082] Current collectors are typically in the form of a membrane, but can also be made of mesh, perforated material, lath, porous material, foam, or fiber assembly.

[0083] There is no particular limitation on the thickness of the current collector, but it is preferably 1 to 500 μm. Furthermore, it is also preferable to have irregularities on the surface of the current collector through surface treatment.

[0084] <Other Structures>

[0085] In this invention, functional layers or components may be appropriately inserted or disposed between or on the outside of the layers of the negative electrode current collector, the negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector.

[0086] <Shell>

[0087] The all-solid-state secondary battery of the present invention can be used as an all-solid-state secondary battery in the above-described structural state depending on the application, but in order to make it into a dry cell form, it is preferable to further enclose it in a suitable casing. The casing can be a metallic casing or a resin (plastic) casing. When using a metallic casing, for example, a casing made of aluminum alloy or stainless steel can be cited. Preferably, the metallic casing is divided into a positive electrode side casing and a negative electrode side casing, which are electrically connected to the positive electrode current collector and the negative electrode current collector, respectively. Preferably, the positive electrode side casing and the negative electrode side casing are joined together as one piece with a short-circuit prevention gasket.

[0088] The following is for reference. Figure 1 The preferred embodiments of the present invention will be described, but the present invention is not limited thereto.

[0089] Figure 1 This is a schematic cross-sectional view illustrating a preferred embodiment of the all-solid-state secondary battery (lithium-ion secondary battery) of the present invention. Viewed from the negative electrode side, the all-solid-state secondary battery 10 of this embodiment sequentially comprises a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5. Each layer is in contact with the others and has an adjacent structure. By employing such a structure, electrons (electrons) are supplied to the negative electrode side during charging. - ), and accumulate lithium ions (Li) here. + On the other hand, during discharge, lithium ions (Li) accumulated at the negative electrode... + The electrons return to the positive side and supply electrons to the working part 6. In the illustrated example, a light bulb is used as a model in the working part 6, and the bulb is lit by discharging.

[0090] In having Figure 1 When the layered solid-state secondary battery shown is placed in a 2032-type button cell, it is sometimes referred to as a laminate for solid-state secondary batteries. A battery made by placing the laminate for solid-state secondary batteries in a 2032-type button cell is called a solid-state secondary battery.

[0091] (Positive electrode active material layer, solid electrolyte layer, negative electrode active material layer)

[0092] In the all-solid-state secondary battery 10, the positive electrode, formed by stacking a positive current collector and a positive active material layer, the solid electrolyte layer, and the negative electrode, formed by stacking a negative current collector and a negative active material layer, are all composed of an all-solid-state secondary battery sheet manufactured by the method for manufacturing all-solid-state secondary battery sheets of the present invention. Furthermore, the solid electrolyte sheet constituting the solid electrolyte layer is used after peeling off the substrate.

[0093] The solid electrolyte layer contains an inorganic solid electrolyte having conductivity ions belonging to Group I or Group II of the periodic table, and the components described later within the scope that does not impair the effects of the present invention. It typically does not contain positive electrode active materials and / or negative electrode active materials. The content of the inorganic solid electrolyte, etc., in the solid electrolyte layer is the same as the content of the solid components in the inorganic solid electrolyte composition described later (100% by mass).

[0094] The positive electrode active material layer contains an inorganic solid electrolyte having conductivity of ions belonging to Group I or Group II of the periodic table, a positive electrode active material, and the components described later within the scope that do not impair the effects of the present invention. The content of the positive electrode active material, inorganic solid electrolyte, etc. in the positive electrode active material layer is the same as the content of the solid components in the positive electrode composition described later in 100% by mass.

[0095] The negative electrode active material layer contains an inorganic solid electrolyte having conductivity of ions belonging to Group I or Group II of the periodic table, a negative electrode active material, and the components described later within the scope that do not impair the effects of the present invention. The content of the negative electrode active material, inorganic solid electrolyte, etc. in the negative electrode active material layer is the same as the content of the solid components in the negative electrode composition described later in 100% by mass.

[0096] In the all-solid-state secondary battery 10, the negative electrode active material layer can be a lithium metal layer. Examples of lithium metal layers include layers formed by stacking or molding lithium metal powder, lithium foil, and lithium vapor-deposited films. The thickness of the lithium metal layer is independent of the thickness of the negative electrode active material layer, and for example, can be set to 1 to 500 μm.

[0097] The positive electrode active material layer 4, the solid electrolyte layer 3, and the negative electrode active material layer 2 can be composed of the same type or different types.

[0098] In this invention, either or both of the positive electrode active material layer and the negative electrode active material layer are simply referred to as the active material layer or the electrode active material layer. Furthermore, either or both of the positive electrode active material and the negative electrode active material are collectively referred to as the active material or the electrode active material.

[0099] (Current collector)

[0100] The positive current collector 5 and the negative current collector 1 are as described above.

[0101] <Applications of all-solid-state secondary batteries>

[0102] The all-solid-state secondary battery of this invention is applicable to a wide variety of uses. There are no particular limitations on its application; for example, when incorporated into electronic devices, it can be used in laptops, pen-and-paper computers, mobile computers, e-book readers, mobile phones, cordless phones, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, stereo headphones, camcorders, LCD TVs, portable vacuum cleaners, portable CD players, mini disk drives, electric shavers, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, etc. As other civilian products, it can be used in automobiles (electric vehicles), electric vehicles, motors, lighting fixtures, toys, game consoles, load conditioners, clocks, flashlights, cameras, and medical equipment (pacemakers, hearing aids, and shoulder massagers, etc.). Furthermore, it can be used in various military and aerospace applications. It can also be combined with solar cells.

[0103] [Manufacturing Method of Sheets for All-Solid-State Secondary Batteries]

[0104] The method for manufacturing a sheet for an all-solid-state secondary battery according to the present invention (sometimes referred to as the sheet manufacturing method of the present invention) is as follows: In the method for manufacturing a sheet by coating (coating and drying) an inorganic solid electrolyte composition containing conductive inorganic solid electrolyte having ions belonging to Group 1 or Group 2 of the periodic table and a dispersion medium on a substrate, either the preparation temperature of the inorganic solid electrolyte composition or the temperature before coating (also simply referred to as the pre-coating temperature) is set to 35 to 90°C, preferably both, thereby performing the preparation or coating film formation.

[0105] By setting the preparation temperature and the pre-filming temperature to the aforementioned temperature range, as described above, excellent dispersion characteristics and coating suitability can be imparted to the inorganic solid electrolyte composition. Therefore, by assembling the all-solid-state secondary battery sheet manufactured using this inorganic solid electrolyte composition as a constituent layer into an all-solid-state secondary battery, as described above, an all-solid-state secondary battery exhibiting superior cycle characteristics compared to conventional batteries can be achieved.

[0106] In the sheet manufacturing method of the present invention, the above-mentioned effects are achieved by setting either or both of the preparation temperature and the pre-film forming temperature to the above-mentioned temperature range. From the viewpoint that coating suitability can be further optimized in addition to the dispersion characteristics of the inorganic solid electrolyte composition before film forming (before coating), it is preferable to set the pre-film forming temperature to the above-mentioned temperature range. From the viewpoint that dispersion characteristics and coating suitability can be balanced at a higher level, it is more preferable to set both the preparation temperature and the pre-film forming temperature to the above-mentioned temperature range.

[0107] In the sheet manufacturing method of the present invention, if the preparation temperature and the pre-film forming temperature of the inorganic solid electrolyte composition are set within the above-mentioned range, and an inorganic solid electrolyte composition with a high solid component concentration is used, then, apart from this, a sheet for all-solid-state secondary batteries can be manufactured in substantially the same manner as the conventional method of film forming using an inorganic solid electrolyte composition.

[0108] First, the preparation method and film-forming method of the inorganic solid electrolyte composition are described.

[0109] <Preparation Method of Inorganic Solid Electrolyte Composition>

[0110] The inorganic solid electrolyte composition can be prepared, for example, by mixing the inorganic solid electrolyte and dispersion medium, preferably a binder, a suitable conductive agent, a lithium salt, and any other components as a mixture, preferably as a slurry, using various commonly used mixers. When manufacturing electrode sheets for all-solid-state secondary batteries, the inorganic solid electrolyte composition (electrode composition) is further mixed with an active material.

[0111] There are no particular restrictions on the mixing method; any known mixer, such as a ball mill, bead mill, planetary mixer, scraper mixer, roller mill, kneader, disc pulverizer, rotation-revolution mixer, or narrow-gap disperser, can be used.

[0112] There are no particular limitations on the mixing conditions. For example, the rotation speed of a rotary-revolutionary mixer can be set to 200 to 3,000 rpm. The mixing atmosphere can be any atmosphere, including atmospheric pressure, dry air (dew point below -20°C), and inert gases (e.g., argon, helium, nitrogen). Since inorganic solid electrolytes readily react with moisture, mixing under dry air or an inert gas is preferred.

[0113] The mixing temperature (also known as the preparation temperature or dispersion temperature) and mixing time are not particularly limited, and appropriate temperatures can be applied. For example, it can be set to 15°C or higher. In this invention, the mixing temperature is preferably set to 35°C or higher, more preferably 40°C or higher. The upper limit of the mixing temperature is preferably set to 90°C or lower, more preferably 80°C or lower, further preferably 70°C or lower, particularly preferably 65°C or lower, and most preferably 60°C or lower. The method of heating the inorganic solid electrolyte composition to the above-mentioned temperature is not particularly limited. For example, it is preferable to preheat the dispersion medium and other components, and it is also preferable to use the heating function of a mixer. By preparing the inorganic solid electrolyte composition at the temperature within the above-mentioned range, even if the concentration of solid components is high, an inorganic solid electrolyte composition with particularly excellent dispersion characteristics can be obtained. The mixing time is not particularly limited at this time. For example, it can be set to 1 to 60 minutes, and when using a rotation-revolution mixer or the like, the lower limit can be set to 10 seconds.

[0114] In this invention, the components can be mixed simultaneously, sequentially, or in multiple stages. When mixing in multiple stages, it is preferable to set the mixing temperature within the aforementioned range in the final mixing step where at least all components are mixed into the dispersion medium, or the mixing temperature within the aforementioned range can be set in each mixing step. Furthermore, the mixing conditions in each stage are generally set to the aforementioned mixing conditions.

[0115] <Method for forming a film containing an inorganic solid electrolyte composition>

[0116] In the sheet manufacturing method of the present invention, the prepared inorganic solid electrolyte composition is then coated on a substrate, i.e., coated and dried on the surface of the substrate.

[0117] In this invention, the prepared inorganic solid electrolyte composition (without heating or below 35°C) can be directly film-formed, but it is preferable to heat it to the pre-film-forming temperature before film-forming. Therefore, even with a high solid component concentration, excellent coating suitability, which cannot be achieved solely by preparing the inorganic solid electrolyte composition, can be maintained while preserving dispersion characteristics. In this invention, heating the inorganic solid electrolyte composition to the pre-film-forming temperature includes methods such as heating the inorganic solid electrolyte composition (compositions prepared at preparation temperatures outside the aforementioned range, compositions whose temperature has decreased after preparation, etc.) before reaching the pre-film-forming temperature, and also methods such as maintaining (holding) the temperature of the inorganic solid electrolyte composition prepared at a preparation temperature of 35–90°C until coating is performed.

[0118] The pre-film-forming temperature refers to the temperature of the inorganic solid electrolyte composition at the point (before) coating, and is set within the same range as the preparation temperature described above, but does not need to be the same temperature. There are no particular limitations on the method of heating the inorganic solid electrolyte composition to the above temperature before film formation; for example, methods such as preheating the inorganic solid electrolyte composition in a mixer, thermostatic bath, etc., or heating the inorganic solid electrolyte composition while transferring it in a preheated piping system are examples. There are no particular limitations on the method of maintaining the temperature; heat preservation methods based on the above heating methods can be cited. When heating the inorganic solid electrolyte composition, it is preferable to stir or flow the inorganic solid electrolyte composition. Temperature stability is preferable during heating or heat preservation of the inorganic solid electrolyte composition. The heating time is not particularly limited as long as it is the time required to reach the specified temperature; for example, it can be set to 1 to 60 minutes. Furthermore, the heating and heat preservation conditions can be appropriately set.

[0119] (Coating)

[0120] In the sheet manufacturing method of the present invention, the coating method containing the inorganic solid electrolyte composition is not particularly limited and can be appropriately selected. For example, wet coating methods such as spraying, spin coating, dip coating, slot coating, strip coating, and bar coating can be cited.

[0121] The inorganic solid electrolyte composition is prepared and then coated. However, the time from preparation to coating is appropriately determined considering factors such as the dispersion characteristics of the inorganic solid electrolyte composition. For example, when the inorganic solid electrolyte composition is not heated or kept warm before coating, it is preferable to coat the film within 48 hours after preparation. On the other hand, when the inorganic solid electrolyte composition is heated or kept warm before coating, the time can exceed 48 hours, and there is no particular limitation. Furthermore, the time from heating or keeping warm to coating is appropriately determined considering factors such as the dispersion characteristics and coating suitability of the inorganic solid electrolyte composition. For example, it is preferable to coat the film within 48 hours after heating or keeping warm, and more preferably within 12 hours.

[0122] When coating compositions containing inorganic solid electrolytes, the substrate is typically used without heating or cooling, but heating is also possible. There are no particular limitations on the heating temperature of the substrate, for example, it can be set within the range of the temperature before film formation.

[0123] (dry)

[0124] The drying temperature of the coated inorganic solid electrolyte composition is not particularly limited as long as the dispersion medium can be removed, and can be appropriately set according to the boiling point of the dispersion medium, etc. For example, the lower limit of the drying temperature is preferably 60°C or higher, more preferably 90°C or higher, further preferably 100°C or higher, and especially preferably 120°C or higher. The upper limit is preferably 300°C or lower, more preferably 250°C or lower, further preferably 230°C or lower, and especially preferably 200°C or lower. The drying method of the inorganic solid electrolyte composition is not particularly limited, and various known drying methods can be used. The drying time is not particularly limited, and can be set to 1 minute or more and 5 hours or less.

[0125] In addition, coated inorganic solid electrolyte compositions are usually dried rapidly, but drying can also be carried out at intervals without impairing the effects of the present invention (dispersion characteristics, coating suitability).

[0126] In this way, a layer (coated and dried layer) consisting of an inorganic solid electrolyte composition can be formed. Here, the coated and dried layer refers to a layer formed by coating an inorganic solid electrolyte composition and drying to remove the dispersion medium. As long as it does not impair the effects of the present invention, the dispersion medium may remain, and the residual amount can be, for example, 3% by mass or less in each layer.

[0127] (Pressure)

[0128] The coating drying layer is preferably applied under pressure. Methods for applying pressure include using a hydraulic cylinder press, etc. There are no particular limitations on the applied pressure, but a range of 5 to 1500 MPa is generally preferred.

[0129] Furthermore, the coated inorganic solid electrolyte composition can be heated while under pressure. The heating temperature is the same as the aforementioned drying temperature, allowing stamping to be performed at a temperature higher than the glass transition temperature of the inorganic solid electrolyte. Alternatively, stamping can also be performed at a temperature higher than the glass transition temperature of the polymer contained in the binder. However, this temperature is typically no higher than the melting point of the polymer.

[0130] Pressurization can be performed either with the solvent or dispersion medium pre-dried or with residual solvent or dispersion medium remaining.

[0131] The stamping time can be either a short period of high pressure (e.g., within a few hours) or a long period of medium pressure (more than one day). The stamping pressure can be uniform or varied relative to the pressure-bearing areas such as the sheet surface. The stamping pressure can be varied according to the area or film thickness of the pressure-bearing area. Furthermore, different pressures can be applied to the same area in stages. The stamped surface can be smooth or rough.

[0132] There are no particular limitations on the atmosphere used in film-forming methods (coating, drying, pressurization (under heating)). For example, the above-mentioned mixed atmosphere in the preparation method containing the inorganic solid electrolyte composition can be appropriately used without particular limitations.

[0133] As described above, a sheet for an all-solid-state secondary battery is manufactured by coating a substrate with an inorganic solid electrolyte composition to form a film.

[0134] <Inorganic solid electrolyte composition>

[0135] Next, the inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention will be described.

[0136] The inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention contains an inorganic solid electrolyte having conductive ions of metals belonging to Group 1 or Group 2 of the periodic table and a dispersion medium. The inorganic solid electrolyte composition is preferably a slurry formed by dispersing the inorganic solid electrolyte in a dispersion medium.

[0137] There is no particular limitation on the concentration of the solid component in the inorganic solid electrolyte composition, and it can be set appropriately, for example, it can be set to 20-80% by mass, preferably 30-70% by mass, and more preferably 40-60% by mass.

[0138] In this invention, by setting the preparation temperature and pre-filming temperature of the inorganic solid electrolyte composition within the aforementioned ranges, dispersion characteristics and coating suitability can be effectively improved. Therefore, high-concentration compositions with higher solid component concentrations than previously possible can be used as inorganic solid electrolyte compositions. For example, the lower limit of the solid component concentration of the high-concentration composition can be set to more than 50% by mass, preferably more than 60% by mass, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit is less than 100% by mass, for example, it can be set to 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less.

[0139] The viscosity of the inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention at 25°C (room temperature) is not particularly limited. From the viewpoint of improving dispersion characteristics and coating suitability, and setting the viscosity variation range Δ, the viscosity at 25°C is preferably 200 to 15,000 cP, more preferably 500 to 10,000 cP, even more preferably 200 to 8,000 cP, and particularly preferably 400 to 6,000 cP.

[0140] Furthermore, in the sheet manufacturing method of the present invention, it is preferable to use an inorganic solid electrolyte composition in which the absolute value (difference) between the viscosity at 25°C of the inorganic solid electrolyte composition and the viscosity at the higher of the preparation temperature and the pre-film forming temperature is 1,000 cP or more. This viscosity difference (viscosity change amplitude Δ) of 1,000 cP or more allows for more active molecular motion of solid particles in the inorganic solid electrolyte composition during preparation or before film forming, leading to further improvements in dispersion characteristics and coating suitability. The viscosity change amplitude Δ is more preferably 1,200 cP or more, and even more preferably 1,500 cP or more. There is no particular upper limit to the viscosity change amplitude Δ, but it is practically 10,000 cP or less, and preferably 5,000 cP or less.

[0141] There are no particular limitations on the preparation temperature and the viscosity at the pre-filming temperature. Generally, the viscosity is lower than that at 25°C. From the viewpoint of improving dispersion characteristics and coating suitability, as well as setting the viscosity change range Δ, it is preferably 50 to 3,500 cP, more preferably 100 to 3,000 cP, and even more preferably 200 to 2,500 cP.

[0142] The viscosity of the inorganic solid electrolyte composition at each temperature is set as the value calculated by the method described in the examples.

[0143] The viscosity of the inorganic solid electrolyte composition can be appropriately set, for example, by changing or adjusting the concentration of the solid components in the inorganic solid electrolyte composition, the type or content of solid particles or binders, the type of dispersion medium, and thus the dispersion conditions. In particular, the viscosity variation range Δ can be set within the above-mentioned range by changing or adjusting the concentration of the solid components in the inorganic solid electrolyte composition, the type of dispersion medium, the preparation temperature, or the temperature before film formation.

[0144] The inorganic solid electrolyte composition is preferably a non-aqueous composition. In this invention, the non-aqueous composition includes not only being free of water but also having a water content (also referred to as moisture content) preferably of 500 ppm or less. In the non-aqueous composition, the water content is more preferably 200 ppm or less, further preferably 100 ppm or less, and particularly preferably 50 ppm or less. If the inorganic solid electrolyte composition is a non-aqueous composition, the degradation of the inorganic solid electrolyte can be suppressed. The water content refers to the amount of water contained in the inorganic solid electrolyte composition (mass ratio of the inorganic solid electrolyte composition), specifically, it is defined as the value obtained by filtration using a 0.02 μm membrane filter and determination using Karl Fischer titration.

[0145] In addition to containing inorganic solid electrolytes, inorganic solid electrolyte compositions may also include active substances and conductive additives (compositions of this type are referred to as electrode compositions).

[0146] The following describes the components contained in the inorganic solid electrolyte composition and the components that may be contained therein.

[0147] <Inorganic Solid Electrolytes>

[0148] The composition containing inorganic solid electrolytes contains inorganic solid electrolytes (in the case of particulate form, also referred to as inorganic solid electrolyte particles).

[0149] In this invention, inorganic solid electrolyte refers to an inorganic solid electrolyte, which is a solid electrolyte capable of allowing ions to move within it. It is clearly distinguished from organic solid electrolytes (such as polymeric electrolytes represented by polyethylene oxide (PEO) and organic electrolyte salts represented by lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)) from the perspective of not containing organic materials as the primary ion-conducting material. Furthermore, since inorganic solid electrolytes are solid in their stable state, they generally do not dissociate or ionize into cations and anions. In this respect, they are clearly distinguished from inorganic electrolyte salts (such as LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), and LiCl) that dissociate or ionize into cations and anions in electrolytes or polymers. There are no particular limitations as long as the inorganic solid electrolyte possesses the ion conductivity of metals belonging to Group 1 or Group 2 of the periodic table; it generally does not possess electronic conductivity. In the case of the all-solid-state secondary battery of the present invention being a lithium-ion battery, it is preferable that the inorganic solid electrolyte has the ionic conductivity of lithium ions.

[0150] The aforementioned inorganic solid electrolyte can be appropriately selected from solid electrolyte materials commonly used in all-solid-state secondary batteries. For example, as inorganic solid electrolytes, (i) sulfide-based inorganic solid electrolytes, (ii) oxide-based inorganic solid electrolytes, (iii) halide-based inorganic solid electrolytes, and (iv) hydride-based inorganic solid electrolytes can be mentioned. From the viewpoint of forming a better interface between the active material and the inorganic solid electrolyte, sulfide-based inorganic solid electrolytes are preferred.

[0151] (i) Sulfide-based inorganic solid electrolytes

[0152] The preferred form is a sulfide-based inorganic solid electrolyte containing sulfur atoms, possessing ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and exhibiting electronic insulation properties. The preferred form is a sulfide-based inorganic solid electrolyte containing at least Li, S, and P as elements, and exhibiting lithium-ion conductivity; however, it may contain other elements besides Li, S, and P, depending on the purpose or circumstances.

[0153] As a sulfide-based inorganic solid electrolyte, for example, a lithium-ion conductive inorganic solid electrolyte that satisfies the composition represented by the following formula (S1) can be cited.

[0154] L a1 M b1 P c1 S d1 A e1 (S1)

[0155] In the formula, L represents an element selected from Li, Na, and K, preferably Li. M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. A represents an element selected from I, Br, Cl, and F. a1 to e1 represent the composition ratio of each element, where a1:b1:c1:d1:e1 satisfies 1–12:0–5:1:2–12:0–10. a1 is preferably 1–9, more preferably 1.5–7.5. b1 is preferably 0–3, more preferably 0–1. d1 is preferably 2.5–10, more preferably 3.0–8.5. e1 is preferably 0–5, more preferably 0–3.

[0156] As described below, the composition ratio of each element can be controlled by adjusting the amount of raw material compounds used in the manufacture of sulfide-based inorganic solid electrolytes.

[0157] Sulfide-based inorganic solid electrolytes can be amorphous (glass), crystallized (glass-ceramic), or partially crystallized. For example, Li-PS-based glasses or Li-PS-based glass-ceramics containing Li, P, and S can be used.

[0158] Sulfide-based inorganic solid electrolytes can be manufactured by reacting at least two of the following raw materials: lithium sulfide (Li2S), phosphorus sulfide (e.g., phosphorus pentasulfide (P2S5)), monomeric phosphorus, monomeric sulfur, sodium sulfide, hydrogen sulfide, lithium halides (e.g., LiI, LiBr, LiCl), and sulfides of the element represented by M above (e.g., SiS2, SnS, GeS2).

[0159] The ratio of Li₂S to P₂S₅ in Li-PS-based glasses and Li-PS-based glass ceramics is preferably 60:40 to 90:10, more preferably 68:32 to 78:22, in terms of the molar ratio of Li₂S:P₂S₅. Setting the Li₂S to P₂S₅ ratio within this range improves lithium-ion conductivity. Specifically, the lithium-ion conductivity is preferably set to 1 × 10⁻⁶. -4 S / cm or higher, more preferably 1×10 -3 S / cm or higher. Although no specific upper limit is set, it is actually 1×10⁻⁶. -1 Below S / cm.

[0160] As specific examples of sulfide-based inorganic solid electrolytes, combinations of raw materials are illustrated below. For example, Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-H₂S, Li₂S-P₂S₅-H₂S-LiCl, Li₂S-LiI-P₂S₅, Li₂S-LiI-Li₂O-P₂S₅, Li₂S-LiBr-P₂S₅, Li₂S-Li₂O-P₂S₅, Li₂S-Li₃PO₄-P₂S₅, Li₂S-P₂S₅-P₂O₅, Li₂S-P₂S₅-SiS₂, Li₂S-P₂S₅-SiS₂-LiCl, Li₂S-P₂S₅-SnS, and Li₂S-P₂S₅-Al₂ can be cited. S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 And so on. The mixing ratio of each raw material is not limited. As a method for synthesizing sulfide-based inorganic solid electrolyte materials using this raw material composition, for example, an amorphization method can be mentioned. As an amorphization method, examples include mechanical polishing, solution processing, and melt quenching. Processing at room temperature is possible, thereby simplifying the manufacturing process.

[0161] (ii) Oxide-based inorganic solid electrolytes

[0162] Oxide-based inorganic solid electrolytes are preferably compounds containing oxygen atoms, possessing ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and having electronic insulation properties.

[0163] For oxide-based inorganic solid electrolytes, the preferred ionic conductivity is 1×10⁻⁶. -6 S / cm or higher, preferably 5×10 -6 S / cm or higher, especially preferably 1×10 -5 S / cm or higher. Although there is no specific upper limit, it is actually 1×10 -1 Below S / cm.

[0164] As a specific example of a compound, Li can be cited. xa La ya TiO3 [xa satisfies 0.3≤xa≤0.7, ya satisfies 0.3≤ya≤0.7.] (LLT); Li xb La yb Zr zb M bb mb O nb (M bb It consists of one or more elements selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn. xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20. Li xc B yc M cc zc O nc (M cc It is an element selected from C, S, Al, Si, Ga, Ge, In, and Sn. xc satisfies 0 < xc ≤ 5, yc satisfies 0 < yc ≤ 1, zc satisfies 0 < zc ≤ 1, and nc satisfies 0 < nc ≤ 6. ); Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd (xd satisfies 1≤xd≤3, yd satisfies 0≤yd≤1, zd satisfies 0≤zd≤2, ad satisfies 0≤ad≤1, md satisfies 1≤md≤7, nd satisfies 3≤nd≤13.) ; Li (3-2xe) M ee xe D ee O(xe) represents a number greater than 0 and less than 0.1, M ee This represents a divalent metal atom. (D) eeThis represents a halogen atom or a combination of two or more halogen atoms. (Li) xf Si yf O zf (xf satisfies 1 ≤ xf ≤ 5, yf satisfies 0 < yf ≤ 3, zf satisfies 1 ≤ zf ≤ 10.) ; Li xg S yg O zg (xg satisfies 1≤xg≤3, yg satisfies 0<yg≤2, zg satisfies 1≤zg≤10.) ; Li3BO3; Li3BO3-Li2SO4; Li2O-B2O3-P2O5; Li2O-SiO2; Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w (w satisfies w < 1); Li has a LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4; La with a perovskite-type crystal structure 0.55 Li 0.35 TiO3; LiTi2P3O with a NASICON (Natrium super ionic conductor) crystal structure 12 Li 1+xh+yh (Al, Ga) xh (Ti, Ge) 2-xh Si yh P 3-yh O 12 (xh satisfies 0≤xh≤1, yh satisfies 0≤yh≤1); Li7La3Zr2O has a garnet-type crystal structure. 12 (LLZ) etc.

[0165] Furthermore, phosphorus compounds containing Li, P, and O are preferred. Examples include lithium phosphate (Li3PO4); LiPON, in which nitrogen element replaces a portion of the oxygen element in lithium phosphate; and LiPOD. 1 (D 1 Preferably, it contains one or more elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au.

[0166] Furthermore, LiA can be preferably used. 1 ON(A 1 It consists of one or more elements selected from Si, B, Ge, Al, C, and Ga.

[0167] (iii) Halogen-based inorganic solid electrolytes

[0168] Halogen-based inorganic solid electrolytes are preferably compounds containing halogen atoms, possessing conductivity of ions belonging to Group 1 or Group 2 of the periodic table, and having electronic insulation properties.

[0169] There are no particular limitations on the type of inorganic solid electrolyte, such as LiCl, LiBr, LiI, and compounds like Li3YBr6 and Li3YCl6 described in ADVANCED MATERIALS, 2018, 30, 1803075. Among these, Li3YBr6 and Li3YCl6 are preferred.

[0170] (iv) Hydride-based inorganic solid electrolytes

[0171] Hydride-based inorganic solid electrolytes are preferably compounds containing hydrogen atoms, possessing ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and having electronic insulation properties.

[0172] There are no particular limitations as hydride-based inorganic solid electrolytes; examples include LiBH4, Li4(BH4)3I, and 3LiBH4-LiCl.

[0173] The inorganic solid electrolyte is preferably a particle. There is no particular limitation on the average particle size (volume average particle size) of the inorganic solid electrolyte, but it is preferably 0.01 μm or more, more preferably 0.1 μm or more. As an upper limit, it is preferably 100 μm or less, more preferably 50 μm or less.

[0174] The determination of the average particle size of the inorganic solid electrolyte is performed using the following steps. A 1% (w / w) dispersion of the inorganic solid electrolyte particles is prepared by diluting the particles with water (or heptane in the case of substances unstable in water) in a 20 mL sample vial. The diluted dispersion sample is irradiated with ultrasound at 1 kHz for 10 minutes and then immediately used in the test. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution measuring device LA-920 (trade name, manufactured by HORIBA, Ltd.) at 25°C using a measuring quartz cell, thereby obtaining the volume average particle size. Other detailed conditions are as needed, refer to the description in Japanese Industrial Standard (JIS) Z8828:2013 "Particle Size Analysis - Dynamic Light Scattering Method". Five samples are prepared for each grade, and their average value is used.

[0175] The inorganic solid electrolyte composition may contain one or more types of inorganic solid electrolytes.

[0176] There is no particular limitation on the content of inorganic solid electrolyte in the inorganic solid electrolyte composition. In terms of dispersion characteristics and binding properties, it is preferable that the solid content is 50% by mass or more out of 100% by mass, more preferably 70% by mass or more, and especially preferably 90% by mass or more. As an upper limit, from the same point of view, it is preferable that it is 99.9% by mass or less, more preferably 99.5% by mass or less, and especially preferably 99% by mass or less.

[0177] However, when the inorganic solid electrolyte composition contains the active substance described later, the total content of the active substance and the inorganic solid electrolyte in the inorganic solid electrolyte composition is preferably within the range described above.

[0178] In this invention, solid components refer to those components that, when dried at 150°C for 6 hours under a nitrogen atmosphere and at a pressure of 1 mmHg, volatilize or evaporate without disappearing. Typically, this refers to components other than the dispersion medium described later.

[0179] <Dispersion Medium>

[0180] As a dispersion medium contained in an inorganic solid electrolyte composition, any organic compound that appears liquid in the environment of use can be used. Examples include various organic solvents, specifically alcohols, ethers, amides, amines, ketones, aromatics, aliphatic compounds, nitriles, and esters.

[0181] The dispersion medium can be a nonpolar dispersion medium (hydrophobic dispersion medium) or a polar dispersion medium (hydrophilic dispersion medium). From the viewpoint of exhibiting excellent dispersibility, a nonpolar dispersion medium is preferred. A nonpolar dispersion medium generally refers to a medium with low affinity for water; however, in this invention, examples include ester compounds, ketone compounds, ether compounds, aromatic compounds, and aliphatic compounds.

[0182] Examples of alcohol compounds include, for example, methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, ethylene glycol, propylene glycol, glycerol, 1,6-hexanediol, cyclohexanediol, sorbitol, xylitol, 2-methyl-2,4-pentanediol, 1,3-butanediol, and 1,4-butanediol.

[0183] Examples of ether compounds include alkylene glycols (diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, etc.), alkylene glycol monoalkyl ethers (ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether, etc.), alkylene glycol dialkyl ethers (ethylene glycol dimethyl ether, etc.), dialkyl ethers (dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, etc.), and cyclic ethers (tetrahydrofuran, dioxanes (including 1,2-, 1,3- and 1,4- isomers, etc.)).

[0184] Examples of amide compounds include, for example, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolinone, ε-caprolactam, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, N-methylpropaneamide, hexamethylphosphoric triamide, etc.

[0185] Examples of amine compounds include triethylamine, diisopropylethylamine, and tri-n-butylamine.

[0186] Examples of ketone compounds include acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, cycloheptanone, dipropyl ketone, dibutyl ketone, diisopropyl ketone, diisobutyl ketone (DIBK), isobutylpropyl ketone, sec-butylpropyl ketone, pentylpropyl ketone, butylpropyl ketone, etc.

[0187] Examples of aromatic compounds include, for example, benzene, toluene, and xylene.

[0188] Examples of aliphatic compounds include hexane, heptane, octane, nonane, decane, dodecane, cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, cyclooctane, decahydronaphthalene, paraffin wax, gasoline, naphtha, kerosine, kerosene, and light oil.

[0189] Examples of nitrile compounds include acetonitrile, propionitrile, and isobutyronitrile.

[0190] Examples of ester compounds include, for example, ethyl acetate, propyl acetate, butyl acetate, ethyl butyrate, propyl butyrate, isopropyl butyrate, butyl butyrate, isobutyl butyrate, butyl valerate, pentyl valerate, ethyl isobutyrate, propyl isobutyrate, isopropyl isobutyrate, isobutyl isobutyrate, propyl neovalerate, isopropyl neovalerate, butyl neovalerate, isobutyl neovalerate, etc.

[0191] In this invention, ether compounds, ketone compounds, aromatic compounds, aliphatic compounds, and ester compounds are preferred, and ester compounds, ketone compounds, or ether compounds are more preferred.

[0192] There is no particular limitation on the number of carbon atoms in the compound constituting the dispersion medium, but it is preferably 2 to 30, more preferably 4 to 20, even more preferably 6 to 15, and especially preferably 7 to 12.

[0193] There is no particular limitation on the boiling point of the dispersion medium at atmospheric pressure (1 atmosphere). However, considering the preparation temperature, the temperature before film formation, and the heating temperature during film formation, it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. The upper limit is preferably 250°C or lower, more preferably 230°C or lower, even more preferably 200°C or lower, and most preferably 180°C or lower.

[0194] The dispersion medium contained in the inorganic solid electrolyte composition may be one type or two or more types.

[0195] In this invention, the content of the dispersion medium in the inorganic solid electrolyte composition is not particularly limited, but is set within the range that satisfies the above-mentioned concentration of solid components.

[0196] <Adhesive>

[0197] From the viewpoint of further enhancing the adhesion of solid particles and improving their dispersion properties, the inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention preferably contains a binder.

[0198] As a binder contained in the inorganic solid electrolyte composition, a binder formed from one or more polymers is preferred. The polymer can be any known polymer used in the manufacture of all-solid-state secondary batteries without particular limitation. Examples of such polymers include step-growth polymers (condensation, addition, or addition condensation) such as polyurethane, polyurea, polyamide, polyimide, polyester, polycarbonate resin, and polyether resin; fluoropolymers; hydrocarbon polymers; vinyl polymers; (meth)acrylic acid polymers; and chain polymers or copolymers thereof. Cellulose polymers can also be used. The mass-average molecular weight (based on the method described in International Publication No. 2019 / 065066A1, obtained by gel permeation chromatography (GPC) of these polymers is not particularly limited and can be set to 50,000 to 1,500,000. In this invention, "polymer" refers to a polymer, but has the same meaning as "high molecular weight compound." The polymer forming the adhesive is preferably a polymer that does not react with solid electrolyte particles when heated. For example, it may have unsaturated bonds such as carbon-carbon double bonds within the molecule, and preferably no unsaturated bonds, to a extent that does not impair the effectiveness of the invention. There are no particular limitations on the bonding mode of the polymer, and it may be any of block copolymers, alternating copolymers, or random copolymers.

[0199] The binder contained in the inorganic solid electrolyte composition can be soluble in the dispersion medium (solubilized binder) or insoluble in the dispersion medium (particulate binder). The shape of the particulate binder is not particularly limited and can be flat, amorphous, etc., but is preferably spherical or granular. The average particle size of the particulate binder is preferably 1–1000 nm, more preferably 10–800 nm, further preferably 20–500 nm, and particularly preferably 40–300 nm. The average particle size can be measured in the same manner as the particle size of the inorganic solid electrolyte described above.

[0200] The binder contained in the inorganic solid electrolyte composition may be one type or two or more types.

[0201] There is no particular limitation on the content of the binder in the inorganic solid electrolyte composition, but from the viewpoint of dispersion characteristics and coating suitability, it is preferably 0.1 to 10.0% by mass of the solid component in 100% by mass, more preferably 0.2 to 5.0% by mass, and even more preferably 0.3 to 4.0% by mass.

[0202] In this invention, the mass ratio of the total mass (total amount) of the inorganic solid electrolyte and the active material to the total mass of the binder [(mass of inorganic solid electrolyte + mass of active material) / (total mass of binder)] in 100% by mass of the solid component is preferably in the range of 1,000 to 1. Furthermore, this ratio is more preferably 500 to 2, and even more preferably 100 to 10.

[0203] <Active Substances>

[0204] The inorganic solid electrolyte composition may also contain an active material capable of intercalating or deintercalating ions belonging to Group 1 or Group 2 of the periodic table. Examples of active materials, including positive electrode active materials and negative electrode active materials, will be described below.

[0205] In this invention, an inorganic solid electrolyte composition containing an active material (positive electrode active material or negative electrode active material) is sometimes referred to as an electrode composition (positive electrode composition or negative electrode composition).

[0206] (Positive electrode active material)

[0207] The positive electrode active material is an active material capable of intercalating and deintercalating ions of metals belonging to Group 1 or Group 2 of the periodic table, preferably an active material capable of reversibly intercalating and deintercalating lithium ions. There are no particular limitations as long as the material has the above-mentioned characteristics, and it can be a transition metal oxide from a decomposition battery or an element that can recombine with Li, such as sulfur.

[0208] Among them, transition metal oxides are preferred as positive electrode active materials, and more preferably materials containing the transition metal element M.a A transition metal oxide (selected from one or more elements including Co, Ni, Fe, Mn, Cu, and V). Furthermore, element M may also be mixed into this transition metal oxide. b (Elements of Group 1(Ia) and Group 2(IIa) of the periodic table, excluding lithium, and elements such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, and B). As a mixing amount, it is preferable to be relative to the transition metal element M. a The amount (100 mol%) is 0-30 mol%. More preferably, it is Li / M a They are synthesized by mixing in a molar ratio of 0.3 to 2.2.

[0209] Specific examples of transition metal oxides include (MA) transition metal oxides with a layered rock salt structure, (MB) transition metal oxides with a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD) lithium-containing transition metal halophosphate compounds, and (ME) lithium-containing transition metal silicate compounds.

[0210] Specific examples of transition metal oxides (MA) with layered rock salt-type structures include LiCoO2 (lithium cobalt oxide [LCO]), LiNi2O2 (lithium nickel oxide), and LiNi 0.85 Co 0.10 Al 0.05 O2 (lithium nickel cobalt aluminum oxide [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (lithium nickel manganese cobalt oxide [NMC]) and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide).

[0211] Specific examples of transition metal oxides (MB) with spinel-type structures include LiMn2O4 (LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8.

[0212] Examples of lithium-containing transition metal phosphates (MC) include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic NASICON-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate).

[0213] Examples of lithium-containing transition metal halophosphates (MD) include, for example, iron fluorophosphates such as Li2FePO4F, manganese fluorophosphates such as Li2MnPO4F, and cobalt fluorophosphates such as Li2CoPO4F.

[0214] Examples of lithium-containing transition metal silicate compounds include, for example, Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4.

[0215] In this invention, (MA) is preferably a transition metal oxide having a layered rock salt structure, and more preferably LCO or NMC.

[0216] The shape of the positive electrode active material is not particularly limited, but particulate form is preferred. The average particle size (volume average particle size) of the positive electrode active material is not particularly limited. For example, it can be set to 0.1–50 μm. The average particle size of the positive electrode active material particles can be measured in the same manner as the average particle size of the inorganic solid electrolytes described above. To achieve the desired particle size of the positive electrode active material, a conventional pulverizer or classifier is used. For example, a mortar, ball mill, sand mill, vibratory ball mill, satellite ball mill, planetary ball mill, and rotary airflow jet mill or sieve can be suitably used. During pulverization, wet pulverization with a dispersion medium such as water or methanol can also be appropriately performed. To achieve the desired particle size, classification is preferred. Classification is not particularly limited, and sieves, air classifiers, etc., can be used. Both dry and wet classification can be used.

[0217] Positive active materials obtained by sintering can also be used after being cleaned with water, acidic aqueous solutions, alkaline aqueous solutions, and organic solvents.

[0218] The positive electrode active material contained in the inorganic solid electrolyte composition can be one type or two or more types.

[0219] The content of the positive electrode active material in the inorganic solid electrolyte composition is not particularly limited, but it is preferably 10-97% by mass, more preferably 30-95% by mass, further preferably 40-93% by mass, and especially preferably 50-90% by mass in 100% by mass of the solid component.

[0220] (Negative electrode active material)

[0221] The negative electrode active material is an active material capable of intercalating and deintercalating ions of metals belonging to Group 1 or Group 2 of the periodic table, preferably an active material capable of reversibly intercalating and deintercalating lithium ions. There are no particular limitations on the material as long as it possesses the aforementioned properties; examples include carbonaceous materials, metal oxides, metal composite oxides, lithium monomers, lithium alloys, and negative electrode active materials capable of forming alloys with lithium. From a reliability perspective, carbonaceous materials, metal composite oxides, or lithium monomers are preferred.

[0222] Carbonaceous materials used as negative electrode active materials refer to materials that are essentially composed of carbon. Examples include carbonaceous materials produced by sintering petroleum asphalt, carbon black such as acetylene black (AB), graphite (natural graphite, vapor-grown graphite, and other artificial graphite), and various synthetic resins such as PAN (polyacrylonitrile) resins or furfuryl alcohol resins. Furthermore, examples include various types of carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, as well as mesophase microspheres, graphite whiskers, and planar graphite.

[0223] These carbonaceous materials are classified into non-graphitized carbonaceous materials (also known as hard carbon) and graphite-based carbonaceous materials based on the degree of graphitization. Furthermore, the carbonaceous materials preferably possess the facet spacing or density and crystallite size described in Japanese Patent Application Publication Nos. 62-22066, 2-6856, and 3-45473. The carbonaceous material need not be a single material; mixtures of natural and artificial graphite as described in Japanese Patent Application Publication No. 5-90844, or coated graphite as described in Japanese Patent Application Publication No. 6-4516, etc., can also be used.

[0224] As a carbonaceous material, hard carbon or graphite is preferred, with graphite being more preferred.

[0225] As oxides of metals or half-metals suitable as negative electrode active materials, there are no particular limitations as long as they are oxides capable of absorbing and releasing lithium. Examples include oxides of metal elements (metal oxides), composite oxides of metal elements, or composite oxides of metal elements and half-metal elements (collectively referred to as metal composite oxides), and oxides of half-metal elements (half-metal oxides). Among these oxides, amorphous oxides are preferred, and further preferred are chalcogenides, products of the reaction between metal elements and elements of Group 16 of the periodic table. In this invention, a half-metal element refers to an element exhibiting intermediate properties between a metal element and a non-half-metal element, typically including six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and further including three elements: selenium, polonium, and astatine. Furthermore, amorphous refers to a material having a broad scattering band with vertices in the region of 20° to 40° at 2θ values ​​using CuKα X-ray diffraction, and may also have crystalline diffraction lines. The strongest intensity of the crystalline diffraction lines appearing in the region of 40° to 70° at a 2θ value is preferably 100 times or less than the intensity of the diffraction line at the apex of the broad scattering band appearing in the region of 20° to 40° at a 2θ value, more preferably 5 times or less, and especially preferably a non-crystalline diffraction line.

[0226] Among the compounds comprising the aforementioned amorphous oxides and chalcogenides, amorphous oxides of half-metallic elements or the aforementioned chalcogenides are more preferred, and (composite) oxides or chalcogenides comprising one or more elements selected from groups 13(IIIB) to 15(VB) of the periodic table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) are particularly preferred. Specific examples of preferred amorphous oxides and chalcogenides include, for example, Ga₂O₃, GeO, PbO, PbO₂, Pb₂O₃, Pb₂O₄, Pb₃O₄, Sb₂O₄, Sb₂O₈Bi₂O₃, Sb₂O₈Si₂O₃, Sb₂O₅, Bi₂O₃, Bi₂O₄, GeS, PbS, PbS₂, Sb₂S₃, or Sb₂S₅.

[0227] As a negative electrode active material that can be used with amorphous oxides centered on Sn, Si, and Ge, carbonaceous materials, lithium monomers, lithium alloys, and negative electrode active materials that can be alloyed with lithium are preferred examples.

[0228] From the viewpoint of high current density charge and discharge characteristics, oxides of metal or half-metal elements, especially metal (composite) oxides and the aforementioned chalcogenides, preferably contain at least one of titanium and lithium as constituent components. Examples of lithium-containing metal composite oxides (lithium composite metal oxides) include composite oxides of lithium oxide with the aforementioned metal (composite) oxides or chalcogenides; more specifically, Li₂SnO₂ can be cited.

[0229] Negative electrode active materials, such as metal oxides, are preferably those containing titanium (titanium oxide). Specifically, due to Li4Ti5O 12 Lithium titanate (LTO) exhibits minimal volume change during lithium ion adsorption and deintercalation, resulting in excellent rapid charge and discharge characteristics. It is preferred in terms of both suppressing electrode degradation and improving the lifespan of lithium-ion secondary batteries.

[0230] There are no particular restrictions on the lithium alloy used as the negative electrode active material, as long as it is an alloy commonly used as the negative electrode active material in secondary batteries. For example, lithium-aluminum alloy, which is made by adding 10% by mass of aluminum to lithium as the base metal, can be cited.

[0231] There are no particular limitations on the negative electrode active material that can form an alloy with lithium, as long as it is a negative electrode active material commonly used in secondary batteries. Because such an active material undergoes significant expansion and contraction during the charging and discharging of an all-solid-state secondary battery, which accelerates the decline in cycle characteristics, the sheet for an all-solid-state secondary battery of the present invention, manufactured using the sheet manufacturing method of the present invention as a constituent layer assembly, can suppress the decline in cycle characteristics. Examples of such active materials include (negative electrode) active materials (alloys, etc.) containing silicon or tin, and various metals such as Al and In. Preferably, a negative electrode active material containing silicon (a silicon-containing active material) is preferred, as it can achieve higher battery capacity. More preferably, a silicon-containing active material has a silicon content of 50 mol% or more of all constituent elements.

[0232] Generally, negative electrodes containing these active materials (e.g., Si negative electrodes containing silicon-containing active materials, Sn negative electrodes containing tin-containing active materials, etc.) can absorb more Li ions compared to carbon negative electrodes (graphite and acetylene black, etc.). That is, the amount of Li ions retained per unit mass increases. Therefore, the battery capacity (energy density) can be increased. Consequently, it has the advantage of extending battery operating time.

[0233] Examples of silicon-containing active materials include silicon materials such as Si and SiOx (0 < x ≤ 1), as well as silicon-containing alloys (e.g., LaSi2, VSi2, La-Si, Gd-Si, Ni-Si) or structured active materials (e.g., LaSi2 / Si) containing elements such as titanium, vanadium, chromium, manganese, nickel, copper, and lanthanum. Additionally, active materials containing silicon elements such as SnSiO3 and SnSiS3, and tin elements, are also included. Furthermore, SiOx can be used as a negative electrode active material (a half-metal oxide) itself, and since Si is generated through the operation of an all-solid-state secondary battery, it can be used as a negative electrode active material (its precursor material) that can be alloyed with lithium.

[0234] Examples of anode active materials containing tin include those containing Sn, SnO, SnO2, SnS, SnS2, and the aforementioned silicon and tin elements. Furthermore, composite oxides with lithium oxide, such as Li2SnO2, can also be cited.

[0235] In this invention, the above-mentioned negative electrode active material can be used without particular limitation. However, from the viewpoint of battery capacity, it is preferable to use a negative electrode active material that can be alloyed with lithium. More preferably, it is the above-mentioned silicon material or silicon-containing alloy (an alloy containing silicon element). It is even more preferably to contain silicon (Si) or a silicon-containing alloy.

[0236] As a determination method, inductively coupled plasma (ICP) emission spectroscopy can be used. As a simple method, the chemical formula of the compound obtained by the above-mentioned firing method can be calculated from the mass difference of the powder before and after firing.

[0237] The shape of the negative electrode active material is not particularly limited, but particulate form is preferred. The average particle size (volume average particle size) of the negative electrode active material is not particularly limited, but is preferably 0.1–60 μm. The volume average particle size of the negative electrode active material particles can be measured in the same manner as the average particle size of the inorganic solid electrolytes described above. To achieve the specified particle size, a conventional pulverizer or classifier is used, similar to that used for the positive electrode active material.

[0238] The negative electrode active material contained in the inorganic solid electrolyte composition can be one type or two or more types.

[0239] The content of the negative electrode active material in the inorganic solid electrolyte composition is not particularly limited, but is preferably 10-90% by mass, more preferably 20-85% by mass, more preferably 30-80% by mass, and even more preferably 40-75% by mass in 100% by mass of solid components.

[0240] (Coating of active substances)

[0241] The surfaces of both the positive and negative electrode active materials can be coated with different metal oxides. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, examples include spinel titanate, tantalum oxides, niobium oxides, and lithium niobate compounds; for instance, Li₄Ti₅O₅ can be used. 12 , Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, etc.

[0242] Furthermore, the electrode surface containing positive or negative active materials can be surface-treated with sulfur or phosphorus.

[0243] Furthermore, the particle surfaces of the positive or negative active materials can be surface-treated by photochemical rays or active gases (such as plasma) before and after the aforementioned surface coating.

[0244] <Conductive additives>

[0245] The inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention preferably contains a conductive additive.

[0246] There are no particular restrictions on the conductive additives used; any conductive additives known to be used as conductive additives can be used. For example, they can be graphite materials such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, and furnace black, amorphous carbon such as needle coke, carbon fiber materials such as vapor-grown carbon fibers or carbon nanotubes, carbonaceous materials such as graphene or fullerene, metal powders such as copper and nickel, metal fibers, or conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives.

[0247] In this invention, when active materials and conductive additives are used in combination, the conductive additives that do not produce the insertion and extraction of metal ions (preferably Li ions) belonging to Group I or Group II of the periodic table during battery charging and discharging, and do not function as active materials, are classified as conductive additives. Therefore, among conductive additives, those that can function as active materials in the active material layer during battery charging and discharging are classified as active materials rather than conductive additives. Whether an additive functions as an active material during battery charging and discharging is determined by its combination with active materials, rather than by a general rule.

[0248] There are no particular restrictions on the shape of the conductive additive, but it is preferably in particulate form.

[0249] The conductive additive contained in the inorganic solid electrolyte composition may be one type or two or more types.

[0250] When the inorganic solid electrolyte composition contains a conductive additive, the content of the conductive additive in the inorganic solid electrolyte composition is preferably 0 to 10% by mass of 100% by mass of the solid component.

[0251] <Lithium Salts>

[0252] The inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention preferably contains a lithium salt (supporting electrolyte).

[0253] As a lithium salt, the lithium salt commonly used in this product is preferred, and there are no particular limitations. For example, the lithium salt described in paragraphs 0082 to 0085 of Japanese Patent Application Publication No. 2015-088486 is preferred.

[0254] When the inorganic solid electrolyte composition contains a lithium salt, the lithium salt content is preferably 0.1 parts by mass or more, more preferably 5 parts by mass or more, relative to 100 parts by mass of the solid electrolyte. As an upper limit, it is preferably 50 parts by mass or less, more preferably 20 parts by mass or less.

[0255] <Dispersant>

[0256] The inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention may contain a dispersant. As a dispersant, a dispersant commonly used in all-solid-state secondary batteries can be suitably selected. Typically, compounds suitable for particle adsorption, steric reflux, and / or electrostatic repulsion are used.

[0257] <Other Additives>

[0258] The inorganic solid electrolyte composition used in the sheet manufacturing method of the present invention can appropriately contain ionic liquids, thickeners, crosslinking agents (substances that undergo crosslinking reactions via free radical polymerization, condensation polymerization, or ring-opening polymerization, etc.), polymerization initiators (substances that generate acids or free radicals through heat or light, etc.), defoamers, homogenizing agents, dehydrating agents, antioxidants, etc., as other components besides those mentioned above. The ionic liquid is a liquid contained to further improve ionic conductivity, and known liquids can be used without particular restriction. Furthermore, polymers other than the polymers forming the aforementioned adhesives can contain commonly used binders, etc.

[0259] [Manufacturing method of all-solid-state secondary batteries]

[0260] The method for manufacturing an all-solid-state secondary battery of the present invention (also referred to as the battery manufacturing method of the present invention) is a manufacturing method including the step of manufacturing at least one of the constituent layers by the sheet manufacturing method of the present invention. Specifically, in a conventional all-solid-state secondary battery manufacturing method, at least one of a solid electrolyte layer and an active material layer is manufactured by the sheet manufacturing method of the present invention described above. In other words, in a conventional all-solid-state secondary battery manufacturing method, the sheet for an all-solid-state secondary battery of the present invention, which is manufactured by the sheet manufacturing method of the present invention to produce at least one of a solid electrolyte layer and an active material layer, is used.

[0261] A method for manufacturing an all-solid-state secondary battery having a current collector on the side of the active material opposite to the solid electrolyte layer includes the following steps: manufacturing at least one of a positive electrode having a positive current collector and a positive active material layer stacked together, a solid electrolyte layer, and a negative electrode having a negative current collector and a negative active material layer stacked together using the sheet manufacturing method of the present invention. In other words, at least one of the electrode of the stack of current collector and active material layer and the solid electrolyte layer is an electrode sheet or a solid electrolyte sheet for all-solid-state secondary batteries manufactured by the sheet manufacturing method of the present invention.

[0262] By manufacturing at least one of the constituent layers using the sheet manufacturing method of the present invention, and especially by manufacturing electrodes using the sheet manufacturing method of the present invention, it is possible to manufacture all-solid-state secondary batteries with excellent cycle characteristics.

[0263] The sheets used in the following manufacturing methods can be appropriately made from sheets manufactured by the sheet manufacturing method of the present invention or sheets manufactured by conventional methods. Furthermore, when another layer is directly coated (dried) onto the surface of the first layer, an inorganic solid electrolyte composition prepared with the preparation temperature set within the aforementioned range, an inorganic solid electrolyte composition heated to the pre-coating temperature within the aforementioned range, or an inorganic solid electrolyte composition prepared by conventional methods can be appropriately used. Drying of the inorganic solid electrolyte composition can be performed after coating or simultaneously after multilayer coating.

[0264] When using the solid electrolyte sheet for all-solid-state secondary batteries of the present invention, the substrate is usually peeled off and used. When using the electrode sheet for all-solid-state secondary batteries of the present invention, it is preferable to use a laminate of the substrate and the active material layer as the electrode.

[0265] As a method for manufacturing an all-solid-state secondary battery, for example, a positive electrode active material layer is formed by coating and drying an inorganic solid electrolyte composition containing positive electrode active material as a positive electrode material (positive electrode composition) onto a positive electrode current collector as a substrate to form a positive electrode sheet for an all-solid-state secondary battery. Next, an inorganic solid electrolyte composition for forming a solid electrolyte layer is coated and dried onto this positive electrode active material layer to form a solid electrolyte layer. Furthermore, a negative electrode active material layer is formed by coating and drying an inorganic solid electrolyte composition containing negative electrode active material as a negative electrode material (negative electrode composition) onto the solid electrolyte layer. By overlapping a negative electrode current collector (metal foil) onto the negative electrode active material layer, an all-solid-state secondary battery with a structure in which a solid electrolyte layer is sandwiched between the positive electrode active material layer and the negative electrode active material layer can be obtained.

[0266] Furthermore, in contrast to the methods for forming each layer, it is also possible to manufacture an all-solid-state secondary battery by forming a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer on a negative electrode current collector as a substrate and then overlapping a positive electrode current collector.

[0267] As another method, the following approach can be used: The positive electrode sheet for an all-solid-state secondary battery is fabricated as described above. Similarly, a negative electrode sheet for an all-solid-state secondary battery with a negative active material layer is fabricated on the negative current collector. Next, a solid electrolyte layer is formed on the active material layer of any one of these sheets, as described above. Furthermore, the positive electrode sheet for an all-solid-state secondary battery and another negative electrode sheet for an all-solid-state secondary battery are stacked on the solid electrolyte layer in such a manner that the solid electrolyte layer and the active material layer are in contact. In this way, an all-solid-state secondary battery can be manufactured.

[0268] Furthermore, as another method, the following method can be cited. That is, to manufacture the positive electrode sheet and the negative electrode sheet for all-solid-state secondary batteries as described above. In addition, a solid electrolyte sheet for all-solid-state secondary batteries composed of a solid electrolyte layer is manufactured by coating an inorganic solid electrolyte composition onto a substrate. Moreover, the solid electrolyte layer peeled off from the substrate is stacked in a manner where the positive electrode sheet and the negative electrode sheet for all-solid-state secondary batteries are sandwiched between them. In this way, an all-solid-state secondary battery can be manufactured. This method is preferred because it allows the use of electrode sheets and solid electrolyte sheets for all-solid-state secondary batteries manufactured by the sheet manufacturing method of the present invention in the negative electrode, the solid electrolyte layer, and the positive electrode, and it can simultaneously produce an all-solid-state secondary battery with higher cycle characteristics.

[0269] Furthermore, as described above, a positive electrode sheet, a negative electrode sheet, and a solid electrolyte sheet for an all-solid-state secondary battery are manufactured. Next, the positive or negative electrode active material layer and the solid electrolyte sheet are overlapped and pressurized. This transfers the solid electrolyte layer onto the positive or negative electrode sheet. Then, the solid electrolyte layer obtained by peeling off the substrate of the solid electrolyte sheet is overlapped with the negative or positive electrode sheet (while the negative or positive electrode active material layer is in contact with the solid electrolyte layer) and pressurized. In this way, an all-solid-state secondary battery can be manufactured. The pressing method and conditions in this method are not particularly limited, and the methods and conditions described in the pressing process described later can be used.

[0270] Solid electrolyte layers, for example, can also be formed by pressure molding on a substrate or active material layer under the conditions described in the pressure molding process described later, to form an inorganic solid electrolyte composition, or a sheet molded body using solid electrolytes or active materials.

[0271] (Pressure application process)

[0272] After coating with an inorganic solid electrolyte composition, the layers are stacked or the all-solid-state secondary battery is fabricated, and then each layer or the all-solid-state secondary battery is pressurized. Furthermore, pressurization is preferably performed while the layers are stacked. The pressurization method and conditions for coating the dried layer can be applied without particular limitation. Additionally, when pressurizing the all-solid-state secondary battery, a moderate level of pressure can be continuously applied using a constraint tool for the all-solid-state secondary battery (such as screw tightening pressure). The heating temperature during simultaneous heating with pressurization is not particularly limited and is typically set in the range of 30–300°C.

[0273] (initialization)

[0274] All-solid-state secondary batteries manufactured in the manner described above are preferably initialized after manufacturing or before use. There are no particular limitations on initialization; for example, initial charging and discharging can be performed under increased stamping pressure, followed by releasing the pressure until the normal operating pressure of the all-solid-state secondary battery is reached.

[0275] Example

[0276] The present invention will now be described in further detail with reference to embodiments, but the invention is not limited thereto. In the following embodiments, unless otherwise specified, "parts" and "%" of composition refer to mass. In the present invention, "room temperature" refers to 25°C.

[0277] 1. Synthesis of fluoropolymer SP-1 and preparation of adhesive solution SP-1

[0278] [Preparation Example 1]

[0279] A fluoropolymer SP-1 was synthesized, and an adhesive solution SP-1 (concentration 10% by mass) composed of this fluoropolymer was prepared.

[0280] Specifically, 200 parts by mass of ion-exchanged water, 120 parts by mass of vinylidene fluoride (VDF), 80 parts by mass of hexafluoropropylene (HFP), and 1 part by mass of diisopropyl peroxide dicarbonate were added to an autoclave, and the mixture was stirred at 30°C for 24 hours. After the polymerization reaction was complete, the precipitate was filtered and dried at 100°C for 10 hours to obtain the fluoropolymer (adhesive) SP-1. The obtained polymer (VDF:HFP (molar ratio) = 78:22) is a random copolymer with a mass-average molecular weight of 1,100,000. The fluoropolymer SP-1 was dissolved in butyl butyrate to obtain the adhesive solution SP-1.

[0281] 2. Synthesis of sulfide-based inorganic solid electrolytes

[0282] [Synthesis Example A]

[0283] The sulfide-based inorganic solid electrolyte was synthesized with reference to non-patent literature, T. Ohtomo, A. Hayashi, M. Tatsumisago, Y. Tsuchida, S. Hama, K. Kawamoto, Journal of Power Sources, 233, (2013), pp231-235 and A. Hayashi, S. Hama, H. Morimoto, M. Tatsumisago, T. Minami, Chem. Lett., (2001), pp872-873.

[0284] Specifically, 2.42 g of lithium sulfide (Li₂S, manufactured by Aldrich, Inc., purity > 99.98%) and 3.90 g of phosphorus pentasulfide (P₂S₅, manufactured by Aldrich, Inc., purity > 99%) were weighed out in a glove box under an argon atmosphere (dew point -70°C) and placed into an agate mortar. The mixture was then mixed for 5 minutes using an agate pestle. The molar ratio of Li₂S to P₂S₅ was set as Li₂S:P₂S₅ = 75:25.

[0285] Next, 66g of 5mm diameter zirconia beads were added to a 45mL zirconia container (manufactured by Fritsch Co., Ltd.), along with the total amount of the aforementioned mixture of lithium sulfide and phosphorus pentasulfide. The container was then completely sealed under argon atmosphere. The container was placed in a planetary ball mill P-7 (trade name, manufactured by Fritsch Co., Ltd.), and mechanically ground at 25°C and 510 rpm for 36 hours, yielding 6.20g of a yellow powder sulfide-based inorganic solid electrolyte (Li-PS glass, hereinafter, sometimes labeled LPS). The Li-PS glass had a particle size of 4μm.

[0286] [Example 1]

[0287] <Preparation of inorganic solid electrolyte compositions S-1 to S-5>

[0288] In a container of a rotation-revolution mixer ARE-310 (trade name, manufactured by THINKY CORPORATION), 2.8 g of LPS synthesized in Synthesis Example A, 0.08 g (solid component mass) of the binder solution SP-1 prepared in Preparation Example 1, and butyl butyrate as a dispersion medium were added to achieve the solid component concentration shown in Table 1. The container was then placed in the rotation-revolution mixer ARE-310 and mixed for 5 minutes at the preparation temperature shown in Table 1 and a rotation speed of 2,000 rpm to prepare inorganic solid electrolyte compositions (slurries) S-1 to S-5. Alternatively, at a preparation temperature of 45°C or 100°C, under an argon atmosphere, the mixture was stirred at a specified temperature using a hot plate stirrer PC-420D (trade name, manufactured by TIETECH Co., Ltd.) while being heated (for 20 minutes), and then placed in a rotation-revolution mixer for mixing (the same applies below).

[0289] The content of each component in the composition is 97.2% by mass of LPS and 2.8% by mass of binder per 100% by mass of solid components.

[0290] <Preparation of positive electrode compositions P-1 to P-5>

[0291] 2.8 g of LPS synthesized in Synthesis Example A and butyl butyrate as a dispersion medium were added to a container in a rotation-revolution mixer ARE-310 to achieve the "solid component concentration" shown in Table 1. The container was then placed in the ARE-310 mixer and mixed for 2 minutes at the "preparation temperature" and 2,000 rpm shown in Table 1. LiNi, as the positive electrode active material, was then added to the container. 1 / 3 Co 1 / 3 Mn1 / 3 13.2 g of O2 (NMC, manufactured by Aldrich, CO.LTD.), 0.32 g of acetylene black (AB) as a conductive additive, and 0.16 g (solid mass) of the binder solution SP-1 prepared in Preparation Example 1 were mixed in a rotation-revolution mixer ARE-310 for 2 minutes at the “Preparation Temperature” and 2,000 rpm as shown in Table 1, respectively, to prepare positive electrode compositions (slurries) P-1 to P-5.

[0292] The content of each component in the composition is as follows (in 100% by mass of solids): LPS 17.0% by mass, NMC 80.1% by mass, binder 1.0% by mass, and AB 1.9% by mass.

[0293] <Preparation of negative electrode compositions N-1 to N-12>

[0294] In a container of a rotation-revolution mixer ARE-310, 2.8 g of LPS synthesized in Synthesis Example A, 0.08 g of binder solution SP-1 prepared in Preparation Example 1 (solid component mass), and the "dispersion medium" shown in Table 1 were added to make the solid component concentration in the composition reach the "solid component concentration" shown in Table 1. Then, the container was placed in the rotation-revolution mixer ARE-310 and mixed for 2 minutes at the "preparation temperature" and a rotation speed of 2,000 rpm shown in Table 1. Then, 3.53 g of silicon (Si, manufactured by Aldrich) as the negative electrode active material and 0.27 g of carbon nanotubes VGCF (trade name, manufactured by SHOWA DENKO KK) as the conductive additive were added and placed in the rotation-revolution mixer ARE-310. The mixture was further mixed for 2 minutes at the "preparation temperature" and a rotation speed of 2,000 rpm shown in Table 1 to prepare negative electrode compositions (slurries) N-1 to N-12.

[0295] The content of each component in the composition is as follows, per 100% by mass of solids: LPS 42.0% by mass, Si 52.8% by mass, binder 1.2% by mass, and VGCF 4.0% by mass. Specifically, the content of each component in composition N-2 is as follows, per 100% by mass of solids: LPS 42.4% by mass, Si 53.5% by mass, and VGCF 4.1% by mass.

[0296] For each of the prepared compositions, the viscosity at 25°C, the preparation temperature, and the coating temperature during the manufacture of each sheet (described below) was determined using the following method. Furthermore, for each composition, the difference between the viscosity at 25°C and the viscosity at the higher of the preparation and coating temperatures (viscosity change Δ (absolute value)) was calculated. These results are shown in Table 1.

[0297] [Viscosity determination of the composition]

[0298] Using an E-type viscometer (TV-35 type, manufactured by Toki Sangyo Co., Ltd.) and a standard conical rotor (1°34'×R24), 1.1 mL of the sample (composition) was added to a sample cup adjusted to the specified measurement temperature and placed in the main body. After maintaining the temperature for 5 minutes until it became constant, the measurement range was set to "U". The value obtained after 1 minute of rotation at a shear rate of 10 / s (rotation speed of 2.5 rpm) was taken as the viscosity.

[0299]

[0300] <Manufacturing of Solid Electrolyte Sheets S-1 to S-5 for All-Solid-State Secondary Batteries>

[0301] The temperatures of the inorganic solid electrolyte compositions S-1 to S-5 obtained above were set to the "coating temperatures" (temperatures before film formation) shown in Table 1. Specifically, for S-1 and S-2, whose "coating temperatures" were higher than room temperature, each composition was heated (for 20 minutes) while being stirred using a hot plate stirrer PC-420D (trade name, manufactured by TIETECH Co., Ltd.) under an argon atmosphere, and the coating temperature was set to the specified temperature.

[0302] Using a Becker applicator (trade name: SA-201, manufactured by TESTER SANGYO CO,.LTD.), each inorganic solid electrolyte composition, with the coating temperature set, was coated onto a 20 μm thick aluminum foil (non-heated: 25°C) (approximately 1 hour from preparation to the start of coating, and approximately 20 minutes from setting the coating temperature to the start of coating). The coated inorganic solid electrolyte composition was heated at 110°C for 2 hours and then dried (to remove the dispersion medium). Then, using a hot press, the dried inorganic solid electrolyte composition was pressurized at 25°C (10 MPa, 10 seconds) to form a film (50 μm thick solid electrolyte layer). In this way, solid electrolyte sheets S-1 to S-5 for all-solid-state secondary batteries were manufactured.

[0303] <Manufacturing of Positive Electrode Plates P-1 to P-5 for All-Solid-State Secondary Batteries>

[0304] The temperatures of the aforementioned positive electrode compositions P-1 to P-5 were set to the same "coating temperatures" shown in Table 1 as those of the aforementioned compositions containing inorganic solid electrolytes. Using a Becker applicator (trade name: SA-201), the positive electrode compositions P-1 to P-5, with the coating temperatures set as described above, were coated onto a 20 μm thick aluminum foil (non-heated: 25°C) (approximately 1 hour from preparation to the start of coating, and approximately 20 minutes from the start of coating after setting the coating temperature). The coated positive electrode compositions were heated at 110°C for 1 hour and then dried (to remove the dispersion medium). Then, using a hot press, the dried positive electrode compositions were pressurized at 25°C (10 MPa, 1 minute) to form a film (the film thickness of the positive electrode active material layer was 100 μm). In this way, positive electrode sheets P-1 to P-5 for all-solid-state secondary batteries were manufactured.

[0305] <Manufacturing of negative electrode sheets N-1 to N-12 for all-solid-state secondary batteries>

[0306] The temperatures of the aforementioned negative electrode compositions N-1 to N-12 were set to the same "coating temperatures" shown in Table 1 as those of the aforementioned compositions containing inorganic solid electrolytes. Using a Becker applicator (trade name: SA-201), each negative electrode composition with the coating temperature set as described above was coated onto a 20 μm thick copper foil (non-heated: 25°C) (approximately 1 hour from preparation to the start of coating, and approximately 20 minutes from the start of coating after setting the coating temperature). The coated negative electrode compositions were heated at 110°C for 1 hour, and then further dried at 110°C for 2 hours in a vacuum dryer AVO-200NS (trade name, manufactured by AS ONE Corporation) to remove the dispersion medium. Then, using a hot press, the dried negative electrode compositions were pressurized at 25°C (10 MPa, 1 minute) to form a film (the film thickness of the negative electrode active material layer was 70 μm). In this way, negative electrode sheets N-1 to N-12 for all-solid-state secondary batteries were manufactured.

[0307] The various compositions and sheets manufactured were evaluated as follows, and the results are shown in Table 2.

[0308] <Evaluation 1: Dispersion Characteristics (Dispersion)>

[0309] In the following dispersibility test, samples were taken from the compositions (set to the coating temperatures shown in Table 1) that were coated onto the substrate in the above-described sheet manufacturing methods.

[0310] Each sampled composition (slurry) was suspended in the tank of a particle size analyzer (grinding tester) type 232 / III (trade name, manufactured by AS ONE Corporation), and the value read from the position of the line appearing after scraping with a scraper was taken as the agglomeration size X. On the other hand, the agglomeration size X0 of the composition with the viscosity adjusted to 300 cP was measured in the same way as the agglomeration size X. The agglomeration size ratio [X / X0] was calculated using the obtained agglomeration sizes X and X0.

[0311] The aggregation size ratio [X / X0] is included in any of the following evaluation criteria, which evaluate the ease with which solid particles aggregate as a measure of the dispersibility of the composition.

[0312] In this experiment, the smaller the agglomeration size ratio [X / X0], the more difficult it is for solid particles to agglomerate or precipitate, indicating excellent dispersibility. Evaluation standard "F" and above are considered qualified.

[0313] In addition, the inorganic solid electrolyte composition N-10 is included in the evaluation criterion “G”, with a condensation size ratio [X / X0] of 2.0.

[0314] -Evaluation Criteria-

[0315] A: X / X0 < 1.1

[0316] B: 1.1 ≤ X / X0 < 1.2

[0317] C: 1.2 ≤ X / X0 < 1.3

[0318] D: 1.3 ≤ X / X0 < 1.4

[0319] E: 1.4 ≤ X / X0 < 1.5

[0320] F: 1.5 ≤ X / X0 < 1.6

[0321] G: 1.6 ≤ X / X0

[0322] <Evaluation 2: Dispersion Characteristics (Stability)>

[0323] In the following dispersion stability test, samples were taken from the compositions coated on the substrate in the above-mentioned sheet manufacturing methods (compositions after setting the coating temperature shown in Table 1).

[0324] Each sampled composition (slurry) was placed into a glass test tube with a diameter of 10 mm and a height of 4 cm until the height reached 4 cm, and allowed to stand at 25°C for 24 hours. The reduction rate of solids in the top 30% (height) of the composition before and after standing was calculated using the following formula. Based on whether this reduction rate of solids was included in any of the following evaluation criteria, the ease with which solid particles precipitated over time was evaluated as the dispersion stability (storage stability) of the composition. In this test, the smaller the reduction rate of solids, the better the dispersion stability; an evaluation criterion of "F" or higher is considered acceptable.

[0325] Solid content reduction rate (%) = [(Solid content concentration of the top 30% before settling - Solid content concentration of the top 30% after settling) / Solid content concentration of the top 30% before settling] × 100

[0326] -Evaluation Criteria-

[0327] A: Solid content reduction rate <1%

[0328] B: 1% ≤ reduction rate of solid content < 3%

[0329] C: 3% ≤ Solid content reduction rate < 5%

[0330] D: 5% ≤ Solid content reduction rate < 7%

[0331] E: 7% ≤ Solid content reduction rate < 9%

[0332] F: 9% ≤ Solid content reduction rate < 11%

[0333] G: 11% ≤ reduction rate of solid content

[0334] <Evaluation 3: Coating suitability (flatness)>

[0335] To assess the coating suitability of each composition, the maximum height roughness Rz of the solid electrolyte layer surface or active material layer surface of each obtained sheet was measured and evaluated.

[0336] Specifically, the maximum height roughness Rz of the solid electrolyte layer surface or active material layer surface of each sheet was measured under the following measuring apparatus and conditions according to Japanese Industrial Standard (JIS) B 0601:2013.

[0337] The maximum height roughness Rz is included in any of the following evaluation criteria, and is used to evaluate the ease of forming a flat and well-surfaced constituent layer as a measure of the coating suitability of the composition (flatness). In this test, a smaller maximum height roughness Rz indicates better coating suitability (flatness), and an evaluation criterion of "F" or above is considered acceptable.

[0338] In addition, the inorganic solid electrolyte composition N-10 is included in the evaluation criterion “G”, with a maximum height roughness Rz of 15 μm.

[0339] -Measuring Apparatus and Conditions-

[0340] Measurement Apparatus: Three-Dimensional Micro-Shape Measuring Instrument (Model ET-4000A: Trade Name, Manufactured by Kosaka Laboratory Ltd.)

[0341] Analysis equipment: Three-dimensional surface roughness analysis system (model TDA-31)

[0342] Stylus: Tip radius 0.5μmR, diameter 2μm, made of diamond

[0343] Needle pressure: 1μN

[0344] Measurement length: 5.0 mm

[0345] Measurement speed: 0.02 mm / s

[0346] Measurement interval: 0.62 μm

[0347] Cutoff value: None

[0348] Filtering method: Gaussian space type

[0349] Leveling: (with quadratic curve)

[0350] -Evaluation Criteria-

[0351] A: Rz < 1.0 μm

[0352] B: 1.0μm≤Rz<2.0μm

[0353] C: 2.0μm≤Rz<4.0μm

[0354] D: 4.0μm ≤ Rz < 6.0μm

[0355] E: 6.0μm≤Rz<8.0μm

[0356] F: 8.0μm≤Rz<10μm

[0357] G: 10μm≤Rz

[0358] <Evaluation 4: Coating Suitability (Adhesion)>

[0359] As for the coating suitability of each composition, the adhesion of solid particles in the solid electrolyte layer or active material layer of each obtained sheet and the adhesion between the active material layer and the current collector were evaluated.

[0360] Each sheet was cut into a rectangle 3cm wide x 14cm long. Using a cylindrical mandrel testing machine (product code 056, mandrel diameter 10mm, manufactured by Allgood), one end of the cut sheet was fixed in the machine along its length, and the central portion of the sheet was positioned to abut against the cylindrical mandrel. While stretching the other portion of the sheet along its length with a force of 5N, it was bent 180° along the circumference of the mandrel (with the mandrel as the axis). Furthermore, the solid electrolyte layer or active material layer of the sheet was placed on the side opposite to the mandrel (the substrate or current collector was placed on the mandrel side), and the width direction was set parallel to the axis of the mandrel. The test was conducted by gradually reducing the diameter of the mandrel from 32mm.

[0361] The evaluation is conducted under the following conditions: in the state of being wound on a mandrel and in the state of being unwound and restored to a sheet shape, the generation of defects (cracks, fissures, gaps, etc.) caused by the bonding collapse of solid particles on the solid electrolyte layer or active material layer is measured. For the active material layer, the minimum diameter at which the peeling between the active material layer and the current collector cannot be confirmed is further measured. This minimum diameter corresponds to any of the following evaluation criteria.

[0362] In this test, the smaller the minimum diameter, the stronger the adhesion of the solid particles constituting the solid electrolyte layer or active material layer, and the stronger the adhesion between the active material layer and the current collector. Evaluation standard "F" and above is considered qualified.

[0363] In addition, the inorganic solid electrolyte composition N-10 is included in the evaluation criterion "G" and has a minimum diameter of 32 mm.

[0364] -Evaluation Criteria-

[0365] A: Minimum diameter < 5mm

[0366] B: 5mm ≤ minimum diameter < 6mm

[0367] C: 6mm ≤ minimum diameter < 8mm

[0368] D: 8mm ≤ minimum diameter < 10mm

[0369] E: 10mm ≤ minimum diameter < 14mm

[0370] F: 14mm ≤ minimum diameter < 25mm

[0371] G: 25mm ≤ minimum diameter

[0372] [Table 2]

[0373]

[0374] <Manufacturing of all-solid-state secondary batteries C-1 to C-5>

[0375] An all-solid-state secondary battery was manufactured by using the positive electrode sheet, the solid electrolyte sheet, and the negative electrode sheet for an all-solid-state secondary battery in the combination of the constituent layers shown in Table 3.

[0376] The positive electrode sheet P-1 or P-4 for the all-solid-state secondary battery is punched into a disc shape with a diameter of 10 mm and placed inside a PET cylinder with an inner diameter of 10 mm. Inside the cylinder, the solid electrolyte sheet S-1 or S-4 for the all-solid-state secondary battery is punched into a disc shape with a diameter of 10 mm and placed inside the cylinder. A 10 mm stainless steel (SUS) rod is inserted through openings at both ends of the cylinder. A pressure of 350 MPa is applied to the current collector side of the positive electrode sheet and the aluminum foil side of the solid electrolyte sheet through the SUS rod. Then, the SUS rod is temporarily removed from the solid electrolyte sheet side, and the aluminum foil of the solid electrolyte sheet is gently peeled off. Next, the negative electrode sheet N-1 or N-10 for the all-solid-state secondary battery is punched into a disc shape with a diameter of 10 mm and inserted onto the solid electrolyte layer of the solid electrolyte sheet inside the cylinder. The removed SUS rod was reinserted into the cylinder and fixed under a pressure of 50 MPa. This yielded all-solid-state secondary batteries No. C-1 to C-5 with a structure of aluminum foil (20 μm thick), positive electrode active material layer (90 μm thick), solid electrolyte layer (45 μm thick), negative electrode active material layer (65 μm thick), and copper foil (20 μm thick).

[0377] <Evaluation 5: Cyclic Characteristics>

[0378] For each of the manufactured all-solid-state secondary batteries, the discharge capacity retention was measured using the TOSCAT-3000 charge-discharge evaluation device (trade name, manufactured by TOYO SYSTEM Co., Ltd.).

[0379] Specifically, each all-solid-state secondary battery was charged at 25°C until the current density reached 0.1 mA / cm². 2 And continue discharging until the battery voltage reaches 3.6V. Then, discharge until the current density reaches 0.1mA / cm². 2The battery voltage was maintained until it reached 2.5V. One charge and one discharge cycle was considered one initial charge-discharge cycle, and this was repeated for three cycles under the same conditions to initialize the battery. Then, under the same conditions as the initial charge-discharge cycle, the charge-discharge cycle was repeated 1000 times. The discharge capacity of the first and 1000th cycles was measured using a TOSCAT-3000 (trade name) charge-discharge evaluation device. The discharge capacity retention rate was calculated using the following formula, and this rate was applied to the following evaluation criteria to evaluate the cycle characteristics of the all-solid-state secondary battery. In this test, the higher the evaluation criterion, the better the battery performance (cycle characteristics), and the better the battery performance maintained even after repeated charge-discharge cycles (even with long-term use). In this test, an evaluation criterion of "F" or higher was considered acceptable.

[0380] Furthermore, the initial discharge capacity of the all-solid-state secondary batteries of the present invention all show values ​​sufficient for functioning as all-solid-state secondary batteries.

[0381] Discharge capacity retention (%) = (Discharge capacity in the 1000th cycle / Discharge capacity in the 1st cycle) × 100

[0382] -Evaluation Criteria-

[0383] A: 90% ≤ Discharge Capacity Maintenance Rate

[0384] B: 85% ≤ Discharge Capacity Retention < 90%

[0385] C: 80% ≤ Discharge capacity retention < 85%

[0386] D: 75% ≤ Discharge Capacity Retention < 80%

[0387] E: 70% ≤ Discharge capacity retention < 75%

[0388] F: 60% ≤ Discharge capacity retention < 70%

[0389] G: Discharge capacity retention rate < 60%

[0390] [Table 3]

[0391]

[0392] The following information can be obtained from the results shown in Tables 2 and 3.

[0393] In the manufacture of sheets for all-solid-state secondary batteries, inorganic solid electrolyte compositions with room temperature (without adjusting the preparation and coating temperatures) and with both the preparation and coating temperatures set to 100°C exhibit poor dispersibility, stability, and coating suitability. Therefore, even when using sheets for all-solid-state secondary batteries manufactured using such inorganic solid electrolyte compositions, it is impossible to manufacture (achieve) an all-solid-state secondary battery exhibiting sufficient cycle characteristics.

[0394] In contrast, in the manufacture of sheets for all-solid-state secondary batteries, the dispersion characteristics (dispersion and stability) and coating suitability (flatness and adhesion) of inorganic solid electrolyte compositions are improved when either or both of the preparation temperature and coating temperature are set to 45°C. In particular, inorganic solid electrolyte compositions with both the preparation temperature and coating temperature set to 45°C exhibit excellent dispersion characteristics and coating suitability in a balanced manner. Furthermore, a comparison of the inorganic solid electrolyte compositions used with comparative examples (e.g., N-10 and N-11) where the coating temperature was not set to the specified temperature and the drying temperature after coating on the substrate was heated to a range of 35–90°C, shows that setting the coating temperature to the specified temperature significantly improves not only the dispersion characteristics of the composition but also the coating suitability. In this invention, even when the concentration of the solid component in the inorganic solid electrolyte composition is set to a high concentration of 65% by mass or more, such excellent dispersion characteristics and coating suitability can be achieved. Therefore, if an all-solid-state secondary battery sheet is manufactured using an inorganic solid electrolyte composition containing either or both of the set preparation temperature and coating temperature, an all-solid-state secondary battery exhibiting excellent cycle characteristics can be manufactured (achieved).

[0395] The invention has been described together with its embodiments, but unless otherwise specified, the invention is not limited in any detail of the description and should be interpreted broadly without departing from the spirit and scope of the invention as shown in the appended claims.

[0396] This application claims priority based on Japanese Patent Application 2020-114680, filed on July 2, 2020, the contents of which are incorporated herein by reference and are part of the description herein.

[0397] Symbol Explanation

[0398] 1-Negative electrode current collector, 2-Negative electrode active material layer, 3-Solid electrolyte layer, 4-Positive electrode active material layer, 5-Positive electrode current collector, 6-Working part, 10-All-solid-state secondary battery.

Claims

1. A method for manufacturing a sheet for an all-solid-state secondary battery, wherein the method involves coating a substrate with an inorganic solid electrolyte composition to form a film. This inorganic solid electrolyte composition contains: Inorganic solid electrolytes with conductivity of ions of metals belonging to Group 1 or Group 2 of the periodic table, and Dispersion medium, in, The preparation temperature and the temperature before coating and film formation of the inorganic solid electrolyte composition were set to 35–90°C, respectively. The concentration of the solid component in the inorganic solid electrolyte composition is 65% by mass or more.

2. The method for manufacturing the sheet for all-solid-state secondary batteries according to claim 1, wherein, The viscosity of the inorganic solid electrolyte composition at 25°C is 500–10,000 cP.

3. The method for manufacturing the sheet for all-solid-state secondary batteries according to claim 2, wherein, The difference (absolute value) between the viscosity at 25°C and the viscosity at the higher of the preparation temperature and the temperature before coating film formation is 1,000 cP or more.

4. The method for manufacturing the sheet for all-solid-state secondary batteries according to claim 1, wherein, The boiling point of the dispersion medium is 100–250°C.

5. The method for manufacturing the sheet for all-solid-state secondary batteries according to claim 1, wherein, The inorganic solid electrolyte composition contains a binder.

6. The method for manufacturing the sheet for all-solid-state secondary batteries according to claim 1, wherein, The inorganic solid electrolyte composition contains active substances.

7. A method for manufacturing an all-solid-state secondary battery, wherein the all-solid-state secondary battery sequentially comprises a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer. The manufacturing method of the all-solid-state secondary battery includes the following steps: At least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is manufactured by the method for manufacturing sheet for all-solid-state secondary batteries according to claim 1.

8. The method for manufacturing an all-solid-state secondary battery according to claim 7, wherein the all-solid-state secondary battery comprises: a current collector stacked on the side opposite to the solid electrolyte layer of each of the positive electrode active material layer and the negative electrode active material layer. The manufacturing method of the all-solid-state secondary battery includes the following steps: At least one of the following is manufactured by the method for manufacturing sheet for all-solid-state secondary batteries according to any one of claims 1 to 6: a positive electrode having the current collector and the positive electrode active material layer stacked together, a solid electrolyte layer, and a negative electrode having the current collector and the negative electrode active material layer stacked together.

9. A sheet for an all-solid-state secondary battery, manufactured by the manufacturing method of the all-solid-state secondary battery sheet according to any one of claims 1 to 6.

10. An all-solid-state secondary battery, comprising sequentially a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, wherein, At least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is composed of the sheet material for all-solid-state secondary batteries as described in claim 9.

11. The all-solid-state secondary battery according to claim 10, comprising: a current collector stacked on the side opposite to the solid electrolyte layer of each of the positive electrode active material layer and the negative electrode active material layer. in, At least one of the positive electrode having the current collector and the positive electrode active material layer stacked thereon, the solid electrolyte layer, and the negative electrode having the current collector and the negative electrode active material layer stacked thereon is made of the sheet for an all-solid-state secondary battery as described in claim 9.

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