Solid-state battery and method for manufacturing a solid-state battery

Abstract

To provide a solid battery for suppressing lowering of cycle characteristics and a method for manufacturing the solid battery.SOLUTION: There are provided a solid battery including an electrode which includes a resin current collector containing a resin and a conductive material, an active substance layer containing an active substance, and an intermediate layer that is interposed between the active substance layer and the resin current collector, where at least one kind of component contained in the active substance layer and at least one kind of component contained in the resin current collector are mixed; and a method for manufacturing the solid battery.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a solid battery and a method for manufacturing the same.

Background Art

[0002] In recent years, secondary batteries such as lithium ion secondary batteries have been suitably used for portable power sources such as personal computers and mobile terminals, and power sources for vehicle drive such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV).

[0003] Since an electrolyte containing a flammable organic solvent is used in a secondary battery, it is necessary to attach a safety device for suppressing a temperature rise during a short circuit and to improve the structure and materials for preventing a short circuit. On the other hand, a solid battery in which the electrolyte is changed to a solid electrolyte layer and the material is solidified does not use a flammable organic solvent in the battery, so that the safety device can be simplified and it is considered to be excellent in manufacturing cost and productivity. For a current collector of a conventional solid battery, a single layer structure made of a ceramic foil or a metal foil, or a laminate including a ceramic foil and a metal foil is adopted (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a conventional solid battery including a current collector containing a ceramic foil or a metal foil, when the active material layer expands or contracts due to a rapid increase or release of the active material during the charge and discharge process, the active material layer may peel off from the current collector. As a result, the cycle characteristics (for example, the capacity retention rate after 50 cycles) may deteriorate. Therefore, in view of the above circumstances, this disclosure aims to provide a solid-state battery and a method for manufacturing a solid-state battery that suppresses the deterioration of cycle characteristics. [Means for solving the problem]

[0006] The means to solve the above problems include the following: <1> Resin current collector containing resin and conductive material, An active material layer containing an active material, and An intermediate layer interposed between the active material layer and the resin current collector, wherein at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed. A solid-state battery equipped with electrodes having the following properties. <2> The thickness of the intermediate layer (intermediate layer / resin current collector) relative to the thickness of the resin current collector is 1 / 30 or more and 1 / 6 or less, <1> Solid-state batteries as described above. <3> The active material includes a Si-based active material, <1> or <2> Solid-state batteries as described above. <4> The aforementioned resin current collector has a coefficient of linear expansion of 200 × 10 -6 ppm / K or more 350×10 -6 The above is less than or equal to ppm / K. <1> ~ <3> A solid battery as described in any one of the following. <5> It comprises a solid electrolyte layer containing a solid electrolyte, The softening temperature of the resin is less than or equal to the crystallization temperature of the solid electrolyte, <1> ~ <4> A solid battery as described in any one of the following. <6> The conductive material includes vapor-grown carbon fiber (VGCF), <1> ~ <5> A solid battery as described in any one of the following. <7> A method for manufacturing a solid battery, comprising the step of producing electrodes by pressing a laminate, in which a resin current collector containing a thermoplastic resin and a conductive material and an active material layer containing an active material are laminated, at a temperature above the softening temperature of the thermoplastic resin. [Effects of the Invention]

[0007] This disclosure provides a solid-state battery that suppresses the deterioration of cycle characteristics and a method for manufacturing a solid-state battery. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing one embodiment of the solid-state battery of the present disclosure. [Figure 2] Figure 2 is a graph showing the relationship between the confinement pressure fluctuation value and the amount of charge in Example 1 and Comparative Example 1. [Figure 3] Figure 3 is a graph showing the relationship between discharge capacity and the number of charge-discharge cycles in Example 1 and Comparative Example 1. [Figure 4] Figure 4 is a graph showing the relationship between the relative resistance value and the thickness of the intermediate layer in the solid-state batteries of Example 1, Example 2, and Comparative Example 1. [Modes for carrying out the invention]

[0009] The following describes an example embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of this disclosure.

[0010] In this disclosure, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this disclosure, the amount of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the notation of groups (atomic groups) in this disclosure, notations that do not specify substitution or unsubstituted include both those without substituents and those with substituents. In this disclosure, the term “layer” includes cases where, when observing the region in which the layer exists, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved.

[0011] -Solid battery- The solid-state battery according to this disclosure comprises a resin current collector containing a resin and a conductive material, an active material layer containing an active material, and an electrode interposed between the active material layer and the resin current collector, the electrode having an intermediate layer in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed. According to this disclosure, the decline in cycle characteristics (e.g., capacity retention rate after 50 cycles) is suppressed. The mechanism of action is not entirely clear, but it is presumed to be as follows. The electrodes of the solid-state battery according to this disclosure have an intermediate layer between the resin current collector and the active material layer. The intermediate layer contains a mixture of at least one component contained in the active material layer and at least one component contained in the resin current collector, so it is compatible with both the resin current collector and the active material layer, and the various components contained in the intermediate layer mix together to create an anchoring effect. As a result, it is thought that the peeling of the active material layer from the resin current collector due to the expansion and contraction of the active material layer during battery operation is suppressed, and the deterioration of cycle characteristics is suppressed.

[0012] Hereinafter, "a resin current collector containing resin and conductive material, an active material layer containing active material, and an electrode having an intermediate layer interposed between the active material layer and the resin current collector, in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed" will be referred to as a "specific electrode."

[0013] The solid-state batteries of this disclosure include so-called all-solid-state batteries that use a solid electrolyte as the electrolyte, and the solid electrolyte may contain less than 10% by mass of electrolyte relative to the total amount of electrolyte. The solid electrolyte may also be a composite solid electrolyte containing an inorganic solid electrolyte and a polymer electrolyte.

[0014] An example of a solid-state battery of this disclosure will be described with reference to the drawings. Figure 1 is a schematic cross-sectional view showing an example of a solid-state battery of this disclosure. The solid-state battery shown in Figure 1 comprises a negative electrode including a negative electrode current collector 113 and a negative electrode active material layer A, a solid electrolyte layer B, and a positive electrode including a positive electrode current collector 115 and a positive electrode active material layer C. The negative electrode active material layer A includes a negative electrode active material 101, a conductive additive 105, a binder 109, and a solid electrolyte 102. The positive electrode active material layer C includes a positive electrode active material 103, a conductive additive 107, a binder 111, and a solid electrolyte 102. The solid electrolyte layer B may be a single layer or a two-layer structure.

[0015] The solid-state battery shown in Figure 1 only needs to be equipped with a specific electrode as at least one of the negative and positive electrodes. When the negative electrode is the specific electrode, the negative electrode current collector 113 is a resin current collector containing resin and conductive material. When the positive electrode is the specific electrode, the positive electrode current collector 115 is a resin current collector containing resin and conductive material.

[0016] When a set consisting of a positive electrode, a solid electrolyte layer, and a negative electrode is considered a power generation unit, a solid-state battery may have only one power generation unit or two or more. If a solid-state battery has two or more power generation units, these units may be connected in series or in parallel.

[0017] When a solid-state battery has two or more power generation units (i.e., when it is a stacked battery), it is sufficient that at least one positive or negative electrode is a specific electrode. From the viewpoint of further suppressing the deterioration of cycle characteristics, it is preferable that the electrode located in the middle of the stacked structure (for example, in the case of a monopolar type, the portion of "positive electrode active material layer / current collector / positive electrode active material layer" and / or "negative electrode active material layer / current collector / negative electrode active material layer" in a stacked battery consisting of "negative electrode active material layer / current collector / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / current collector / positive electrode active material layer"; in the case of a bipolar type, the portion of "positive electrode active material layer / current collector" and / or "current collector / negative electrode active material layer") is a specific electrode, and it is preferable that the electrodes in all power generation units are specific electrodes.

[0018] The solid-state battery may have its stacked structure of positive electrode / solid electrolyte layer / negative electrode sealed with a sealing material such as resin at the stacked end faces (i.e., sides). The negative electrode current collector 113 and the positive electrode current collector 115 may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer arranged on their outer surfaces. The shape of the solid-state battery is not particularly limited and may be, for example, coin-shaped, cylindrical, prismatic, sheet-shaped, button-shaped, flat, or stacked.

[0019] <Specific electrode> The specific electrode is an electrode having a resin current collector containing resin and a conductive material, an active material layer containing an active material, and an intermediate layer interposed between the active material layer and the resin current collector, in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed.

[0020] The solid-state battery according to this disclosure only needs to be provided with a specific electrode as at least one of the negative electrode and the positive electrode. From the viewpoint of further suppressing the deterioration of cycle characteristics, for example, it is preferable that the specific electrode be provided as the negative electrode, and it is more preferable that the specific electrode be provided as both the negative electrode and the positive electrode.

[0021] [Resin current collector] The resin current collector includes resin and conductive material. Examples of resins include known thermoplastic resins such as poly(meth)acrylic acid, poly(meth)acrylate, polyethylene, polypropylene, polyethylene terephthalate, polyethernitrile, polyimide, polyamide, polytetrafluoroethylene, polyacrylonitrile, poly(meth)acrylate, and vinyl halogenated resins; thermosetting resins such as epoxy resins, vinyl ester resins, unsaturated polyester resins, phenolic resins, and melamine resins; and known conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, poly(para)phenylene, polyphenylenevinylene, polyacrylonitrile, and polyoxadiazole. The resin may be used alone or in combination of two or more types. Among the above, from the viewpoint of further suppressing the peeling of the active material layer from the resin current collector and the resulting decrease in cycle characteristics, the resin preferably contains at least one of a thermoplastic resin and a conductive polymer, more preferably contains a thermoplastic resin, and even more preferably contains one resin selected from the group consisting of methyl poly(meth)acrylate, poly(meth)acrylic acid, and polyacrylonitrile.

[0022] In this disclosure, "(meth)acrylic acid" is a concept that encompasses both acrylic acid and methacrylic acid, and "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate.

[0023] The resin may be a crystalline resin, an amorphous resin, or a mixture of both. From the viewpoint of increasing strength and further suppressing the peeling of the active material layer from the resin current collector and the resulting decrease in cycle characteristics, an amorphous resin is preferred. The "crystalline" nature of the resin refers to the presence of an endothermic peak with a full width at half maximum of 10°C or less when measured by differential scanning calorimetry (DSC measurement) at a heating rate of 10°C / min. On the other hand, the "amorphous" nature of the resin refers to the presence of a full width at half maximum exceeding 10°C, or the absence of a clear endothermic peak.

[0024] The softening temperature of the resin varies depending on the type of resin, but from the viewpoint of strength as a resin current collector and suppression of degradation of the active material, for example, it is preferable that the softening temperature of the resin is below the crystallization temperature of the solid electrolyte contained in the solid electrolyte layer described later. The softening temperature of the resin is determined from the DSC curve obtained by differential scanning calorimetry (DSC).

[0025] Examples of conductive materials include carbon materials, conductive polymers, and metal particles. The conductive material may be used alone or in combination of two or more types. Examples of carbon materials include particulate carbon materials and fibrous carbon materials. Examples of particulate carbon materials include acetylene black (AB) and Ketjenblack (KB). Examples of fibrous carbon materials include carbon nanotubes (CNT), carbon nanofibers (CNF), and vapor-grown carbon fibers (VGCF). Examples of conductive polymers include polythiophene, polyacetylene, poly(p-phenylene), and polyisothianaphthene. Examples of metal particles include nickel, copper, iron, and stainless steel. Among the above, from the viewpoint of enhancing the anchoring effect and further suppressing the peeling of the active material layer from the resin current collector and the resulting deterioration of cycle characteristics, the conductive material preferably contains a carbon material, more preferably contains at least one of acetylene black (AB) and vapor-grown carbon fiber (VGCF), and even more preferably contains vapor-grown carbon fiber (VGCF).

[0026] The conductive material content is preferably 10% to 50% by mass, more preferably 15% to 43% by mass, and even more preferably 15% to 35% by mass, relative to the total solid content of the resin current collector.

[0027] From the perspective of further suppressing the peeling of the active material layer from the resin current collector and the resulting decrease in cycle characteristics, the coefficient of thermal expansion of the resin current collector should be 100 × 10⁻⁶. -6 ppm / K or more 500×10-6 It is preferable that the concentration is ppm / K or less, and 200 × 10 -6 ppm / K or more 430×10 -6 It is more preferable that the concentration is 230 × 10⁻¹⁰ ppm / K or less. -6 ppm / K or more 350×10 -6 It is even more preferable that the coefficient of linear expansion is 1 / 2 ppm / K or less. The value of the coefficient of linear expansion is the value measured by the method in accordance with JIS H7404-1993.

[0028] The method for setting the coefficient of linear expansion of the resin current collector within the above range is not particularly limited, but examples include using the aforementioned preferred resin for the resin current collector.

[0029] The thickness of the resin current collector is not particularly limited, but from the viewpoint of further suppressing the peeling of the intermediate layer or active material layer from the resin current collector and the resulting decrease in cycle characteristics, it is preferably 5 μm to 80 μm, more preferably 10 μm to 50 μm, and even more preferably 10 μm to 30 μm.

[0030] The thickness of the resin current collector is the average of the thicknesses measured at 10 arbitrary points by observing the laminated cross-section cut in the thickness direction of the resin current collector using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX).

[0031] The method for forming the resin current collector is not particularly limited, but examples include, if the resin is thermoplastic, a method of forming it by coating and drying a coating liquid containing the resin and conductive material; and if the resin is thermosetting, a method of placing raw materials such as resin precursors and monomers and a conductive material in a mold and heating and solidifying them.

[0032] The resin current collector may further contain materials other than resin, spherical carbon material, and fibrous carbon. Examples of other materials include binders and metal powder materials.

[0033] [Active material layer] The active material layer contains the active material. The preferred form of the active material differs depending on whether it is the negative electrode or the positive electrode; therefore, this will be explained in the respective sections for the negative electrode and positive electrode described later.

[0034] The active material may include a Si-based active material. Si-based active materials are useful active materials with excellent charge-discharge characteristics. However, Si-based active materials tend to expand and contract significantly during charging and discharging, which can easily cause the active material layer to peel off from the current collector and degrade cycle performance. On the other hand, as mentioned above, the solid-state battery according to this disclosure has an intermediate layer interposed between the resin current collector and the active material layer in the electrode, thus suppressing the degradation of cycle performance caused by the peeling of the active material layer from the resin current collector. This is even more effective when a Si-based active material is included.

[0035] The Si-based active material is not particularly limited as long as it contains silicon and can act as an active material, but examples include elemental silicon particles, silicon alloy particles (e.g., alloys of Si with one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co, and Al), porous silicon, silicon clathrate compounds, silicon oxides, and mixtures thereof. The Si-based active material may be a single material or a combination of two or more materials.

[0036] The thickness of the active material layer is not particularly limited, but from the viewpoint of achieving superior charge-discharge characteristics and further suppressing the peeling of the active material layer from the resin current collector and the resulting decrease in cycle characteristics, it is preferably 0.1 μm to 100.0 μm, more preferably 1.0 μm to 100.0 μm, and more preferably 30.0 μm to 100.0 μm.

[0037] The thickness of the active material layer is the average of the thicknesses measured at 10 arbitrary points by observing the stacked cross-section cut in the thickness direction of the active material layer using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX).

[0038] [Middle class] The intermediate layer is a layer in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed. From the viewpoint of enhancing the anchoring effect and further reducing the peeling of the active material layer from the resin current collector, the intermediate layer is preferably a layer in which at least the active material contained in the active material layer and the resin contained in the resin current collector are mixed.

[0039] From the viewpoint of enhancing the anchoring effect and further reducing the peeling of the active material layer from the resin current collector, the thickness of the intermediate layer relative to the thickness of the resin current collector (intermediate layer / resin current collector) is preferably 1.0 / 30.0 or more and 1.0 / 4.0 or less, more preferably 1.0 / 20.0 or more and 1.0 / 5.0 or less, and even more preferably 1.0 / 10.0 or more and 1.0 / 6.0 or less.

[0040] The thickness of the intermediate layer is not particularly limited, but from the viewpoint of achieving superior charge-discharge characteristics and further suppressing the peeling of the active material layer from the resin current collector and the resulting decrease in cycle characteristics, it is preferably 0.1 μm to 15.0 μm, more preferably 0.4 μm to 10.0 μm, and even more preferably 0.6 μm to 8.0 μm.

[0041] The thickness of the intermediate layer is the average of the thicknesses measured at 10 arbitrary points by observing the stacked cross-section cut in the thickness direction of the intermediate layer using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). The components contained in the intermediate layer can be confirmed by performing EDX analysis on the chemical composition of the laminated cross-section cut in the thickness direction of the intermediate layer using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX).

[0042] The method for forming the intermediate layer is not particularly limited, but examples include: 1) If the resin in the resin current collector is thermoplastic, a method in which a laminate is formed by laminating a resin current collector containing a thermoplastic resin (which may further contain a conductive material) and an active material layer containing an active material, heating the laminate to a temperature above the softening temperature of the thermoplastic resin, and pressing the laminate; 2) If the resin in the resin current collector is thermosetting, a method in which a precursor of a thermosetting resin and components such as the active material and binder in the active material layer are filled into a mold and heated to form the intermediate layer.

[0043] The following provides a detailed explanation of the components of a solid-state battery, including the negative electrode, positive electrode, and solid electrolyte layer.

[0044] <Negative electrode> The negative electrode is a layer comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector and containing negative electrode active material. When the negative electrode is a specific electrode, the negative electrode current collector refers to a resin current collector, and an intermediate layer is interposed between the active material layer and the resin current collector, in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed.

[0045] When the negative electrode is not a specific electrode, examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon. Examples of shapes for the negative electrode current collector include foil and mesh.

[0046] Examples of negative electrode active materials include carbon materials such as graphite, hard carbon, soft carbon, and carbon nanotubes; and Si-based active materials.

[0047] The negative electrode active material layer may, if necessary, further contain a solid electrolyte, a binder, and the like in addition to the negative electrode active material.

[0048] Examples of solid electrolytes include those similar to those exemplified as solid electrolytes that may be included in the solid electrolyte layer. Examples of the binder include rubber-based binders, fluoride-based binders, etc. Examples of the rubber-based binders include butadiene rubber, hydrogenated butadiene rubber, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, ethylene propylene rubber, etc. Examples of the fluoride-based binders include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, fluororubber, etc.

[0049] <Positive electrode> The positive electrode is, for example, a layer having a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector and containing a positive electrode active material. When the positive electrode is a specific electrode, the positive electrode current collector refers to a resin current collector, and an intermediate layer in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed is interposed between the active material layer and the resin current collector.

[0050] When the positive electrode is not a specific electrode, examples of the material of the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, carbon, etc. Examples of the shape of the positive electrode current collector include foil shape, mesh shape.

[0051] The positive electrode active material preferably contains a lithium composite oxide. The lithium composite oxide may contain at least one selected from the group consisting of F, Cl, N, S, Br, and I. Also, the lithium composite oxide may have a crystal structure belonging to at least one space group selected from the space groups R-3m, Immm, and P63-mmc (also referred to as P63mc, P6 / mmc). Further, the main arrangement of the transition metal, oxygen, and lithium in the lithium composite oxide may be an O2-type structure. Examples of the lithium composite oxide having a crystal structure belonging to R-3m include, for example, Li x Me y O α X β(Me represents at least one selected from the group consisting of Mn, Co, Ni, Fe, Al, Cu, V, Nb, Mo, Ti, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, W, B, Si and P, X represents at least one selected from the group consisting of F, Cl, N, S, Br and I, and satisfies 0.5≦x≦1.5, 0.5≦y≦1.0, 1≦α<2, 0<β≦1.) Compounds represented by are exemplified. Examples of the lithium composite oxide having a crystal structure belonging to Immm include, for example, Li x1 M 1 A 1 2 (satisfying 1.5≦x1≦2.3, M 1 includes at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe, A 1 includes at least oxygen, and the ratio of oxygen in A 1 is 85 atomic% or more.) Composite oxides represented by (specific examples include Li2NiO2), Li x1 M 1A 1-x2 M 1B x2 O 2-y A 2 y (0≦x2≦0.5, 0≦y≦0.3, at least one of x2 and y is not 0, M 1A represents at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe, M 1B represents at least one selected from the group consisting of Al, Mg, Sc, Ti, Cr, V, Zn, Ga, Zr, Mo, Nb, Ta and W, and A2 represents at least one selected from the group consisting of F, Cl, Br, S and P.) Composite oxides represented by are exemplified.

[0052] Examples of the lithium composite oxide having a crystal structure belonging to P63-mmc include, for example, M1 x M2 y O2 (M1 represents an alkali metal (at least one of Na and K is preferred), M2 represents a transition metal (at least one selected from the group consisting of Mn, Ni, Co and Fe is preferred), and x + y satisfies 0<x + y≦2.) Composite oxides represented by are exemplified.

[0053] Examples of the lithium composite oxide having an O2-type structure include, for example, Li x [Li α (Mn a Co b M c ) 1-α O2 (0.5 < x < 1.1, 0.1 < α < 0.33, 0.17 < a < 0.93, 0.03 < b < 0.50, 0.04 < c < 0.33, and M represents at least one selected from the group consisting of Ni, Mg, Ti, Fe, Sn, Zr, Nb, Mo, W, and Bi). Examples of the composite oxide represented thereby include Li 0.744 [Li 0.145 Mn 0.625 Co 0.115 Ni 0.115 O2 and the like.

[0054] In addition, the positive electrode preferably contains a solid electrolyte selected from the group of solid electrolytes consisting of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte in addition to the positive electrode active material, and a mode in which at least a part of the surface of the positive electrode active material is coated with a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte is more preferable. Examples of the halide solid electrolyte that coats at least a part of the surface of the positive electrode active material include Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) [LTAF electrolyte] is preferable.

[0055] The positive electrode may further contain a solid electrolyte, a binder, etc. in addition to the positive electrode active material, if necessary.

[0056] The solid electrolyte preferably contains at least one solid electrolyte selected from the group of solid electrolytes consisting of a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte. The positive electrode preferably has a mode in which at least a part of the surface of the positive electrode active material is coated with a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte. As the halide solid electrolyte that coats at least a part of the surface of the positive electrode active material, Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) [LTAF electrolyte] is preferred.

[0057] Examples of the binder include the same ones as those exemplified as the binder that can be included in the negative electrode.

[0058] <Solid electrolyte layer> The solid electrolyte layer contains a solid electrolyte. From the viewpoint of battery performance, the solid electrolyte preferably contains at least one solid electrolyte species selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes, and more preferably contains a sulfide solid electrolyte. As the sulfide solid electrolyte, it is preferable to contain sulfur (S) as the main component of the anion element, and it is also preferable to further contain, for example, Li element and A element in addition to S. The A element is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen element (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). The sulfide solid electrolyte may have a composition represented by the following general formula (1). Li 4-x Ge 1-x P x S4 (0 < x < 1) ··· Formula (1) In formula (1), at least a part of Ge may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. Also, at least a part of P may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. A part of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A part of S may be substituted with a halogen. The halogen is at least one of F, Cl, Br, and I. As the oxide solid electrolyte, it is preferable to contain oxygen (O) as the main component of the anion element. For example, it may contain Li, Q element (Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of the oxide solid electrolyte include garnet-type solid electrolyte, perovskite-type solid electrolyte, NASICON-type solid electrolyte, Li-P-O-based solid electrolyte, Li-B-O-based solid electrolyte, etc. Examples of the garnet-type solid electrolyte include, for example, Li7La3Zr2O 12 、Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 etc. Examples of the perovskite-type solid electrolyte include, for example, (Li, La)TiO3, (Li, La)NbO3, (Li, Sr)(Ta, Zr)O3, etc. Examples of the NASICON-type solid electrolyte include, for example, Li(Al, Ti)(PO4)3, Li(Al, Ga)(PO4)3, etc. Examples of the Li-P-O-based solid electrolyte include Li3PO4, LIPON (a compound in which a part of O in Li3PO4 is substituted with N), and examples of the Li-B-O-based solid electrolyte include Li3BO3, a compound in which a part of O in Li3BO3 is substituted with C, etc. As the halide solid electrolyte, a solid electrolyte containing Li, M, and X (M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br) is suitable. Specifically, Li 6-3z Y z X6 (X represents Cl or Br, and z satisfies 0 < z < 2), Li6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferred. Li 6-3z Y z Among LiX6, Li3YX6 (where X represents Cl or Br) is more preferred and Li3YCl6 is even more preferred in terms of excellent lithium ion conductivity. Also, Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferably included together with a solid electrolyte such as a sulfide solid electrolyte, from the viewpoint of suppressing, for example, the oxidative decomposition of the sulfide solid electrolyte.

[0059] The crystallization temperature of the solid electrolyte varies depending on the type of solid electrolyte employed. For example, it is preferably 0% or more and 90% or less, more preferably 20% or more and 85% or less, and even more preferably 50% or more and 85% or less. The crystallinity of the solid electrolyte is a value measured by the X-ray diffraction method.

[0060] The ratio of the negative electrode active material layer to the solid electrolyte layer (negative electrode active material layer / solid electrolyte) is not particularly limited. For example, it is preferably 85 / 15 or more and 30 / 70 or less, and more preferably 80 / 20 or more and 40 / 60 or less.

[0061] The ratio of the positive electrode active material layer to the solid electrolyte layer (positive electrode active material layer / solid active material layer) is not particularly limited. For example, it is preferably 85 / 15 or more and 30 / 70 or less, and more preferably 80 / 20 or more and 50 / 50 or less.

[0062] <Outer package> The solid battery may further include an outer package. The outer package houses at least the above-described power generation unit. Examples of the outer package include a laminate type outer package and a case type outer package.

[0063] <Restraining member> The solid-state battery may further include a restraining member. The restraining member applies restraining pressure in the thickness direction to the positive electrode, solid electrolyte layer, and negative electrode. The restraining pressure is preferably 0.1 MPa or more, more preferably 1 MPa or more, and even more preferably 5 MPa or more. The restraining pressure is preferably 100 MPa or less, more preferably 50 MPa or less, and even more preferably 20 MPa or less. The restraining pressure is preferably 0.1 MPa to 100 MPa.

[0064] <Application> The solid-state battery of this disclosure is a typical solid-state secondary battery (more preferably a solid-state lithium-ion secondary battery). Examples of applications for solid-state batteries include power sources for vehicles, electronic devices, and electrical storage. Examples of vehicles include electric four-wheeled vehicles, electric two-wheeled vehicles, gasoline automobiles, diesel automobiles, etc. Examples of electric four-wheeled vehicles include electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid automobiles (HEVs). Examples of electric two-wheeled vehicles include electric motorcycles and electric-assist bicycles. Examples of electronic devices include handheld devices (e.g., smartphones, tablet computers, audio players, etc.), portable devices (e.g., notebook computers, CD (Compact Disc) players), and mobile devices (e.g., power tools, professional video cameras, etc.). In particular, the solid-state battery of this disclosure is preferably used as a power source for hybrid automobiles, plug-in hybrid automobiles, or electric automobiles.

[0065] -Method of manufacturing solid-state batteries- The method for manufacturing a solid battery according to this disclosure includes a step of producing electrodes by pressing a laminate, in which a resin current collector containing a thermoplastic resin and a conductive material and an active material layer containing an active material are laminated, at a temperature above the softening temperature of the thermoplastic resin.

[0066] The method for manufacturing a solid-state battery according to this disclosure involves, for example, pressing the laminate at a temperature above the softening temperature of the thermoplastic resin. This causes the active material layer to penetrate into the softened region of the thermoplastic resin in the resin current collector, forming an intermediate layer between the active material layer and the resin current collector in which at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed. This intermediate layer is compatible with both the resin current collector and the active material layer, and the various components contained in the intermediate layer have an anchoring effect. As a result, it is believed that the peeling of the active material layer from the resin current collector due to the expansion and contraction of the active material layer during battery operation is suppressed, and the deterioration of cycle characteristics is suppressed.

[0067] The method for manufacturing a solid-state battery according to this disclosure may include, for example, a step of manufacturing an electrode by pressing a laminate in which a resin current collector containing a thermoplastic resin and a conductive material and an active material layer containing an active material are laminated at a temperature above the softening temperature of the thermoplastic resin (hereinafter also referred to as the "electrode manufacturing step"), and a step of laminating the electrode, which is at least one of the positive electrode and the negative electrode, with a solid electrolyte layer to obtain a solid-state battery (hereinafter also referred to as the "lamination step").

[0068] <Electrode fabrication process> In the electrode fabrication process, a laminate comprising a resin current collector containing a thermoplastic resin and a conductive material, and an active material layer containing an active material, is pressed at a temperature above the softening temperature of the thermoplastic resin to produce the electrode. A preferred embodiment of the resin current collector containing a thermoplastic resin and a conductive material is the same as the preferred embodiment described above in the section on solid-state batteries. A preferred embodiment of the active material layer containing the active material is the same as the preferred embodiment described above in the section on solid-state batteries.

[0069] The softening temperature of the thermoplastic resin varies depending on the thermoplastic resin used, but for example, it may be between 100°C and 200°C, between 110°C and 190°C, or between 130°C and 180°C.

[0070] The heating temperature of the laminate should be above the softening temperature of the thermoplastic resin. From the viewpoint of battery performance and more efficiently creating the intermediate layer, it is preferable that the temperature is above the softening temperature of the thermoplastic resin and below the softening temperature + 100°C, preferably above the softening temperature and below the softening temperature + 90°C, more preferably above the softening temperature and below the softening temperature + 80°C, and even more preferably above the softening temperature and below the softening temperature + 75°C.

[0071] The method for pressing the laminate is not particularly limited. The laminate may be pressed after being heated to a temperature above the softening temperature of the thermoplastic resin (i.e., heating and pressing may be separate processes), or the laminate may be pressed while being heated to a temperature above the softening temperature of the thermoplastic resin (i.e., heating and pressing may be simultaneous processes). From the viewpoint of manufacturing efficiency, it is preferable to press the laminate while heating it to a temperature above the softening temperature of the thermoplastic resin.

[0072] Examples of pressing methods include roll pressing and cold isostatic pressing (CIP). The pressing pressure is not particularly limited as long as it is sufficient for the active material layer to bite into the resin current collector and form an intermediate layer, and may be between 1 kN / cm and 100 kN / cm, between 5 kN / cm and 80 kN / cm, or between 10 kN / cm and 70 kN / cm.

[0073] <Lamination process> In the lamination process, a solid-state battery is obtained by laminating the electrode, which is at least one of the positive electrode and the negative electrode, with a solid electrolyte layer. The electrode manufactured in the above-described electrode manufacturing process may be used as either the positive or negative electrode. However, from the viewpoint of further suppressing the deterioration of cycle characteristics, for example, it is preferable to use the electrode manufactured in the above-described electrode manufacturing process as the negative electrode, and it is even more preferable to use the electrode as both the negative and positive electrode.

[0074] The preferred embodiment of the solid electrolyte layer is the same as the preferred embodiment described in the section on solid-state batteries above. Known methods can be applied to stack the electrodes and the solid electrolyte layer.

[0075] <Other processes> The method for manufacturing a solid-state battery according to this disclosure may further include other steps besides the electrode manufacturing step and the stacking step. Examples of other steps include a step of initial charging the solid-state battery; a step of converting the solid-state battery into a bipolar solid-state battery; a step of processing it to a predetermined size by cutting, punching, etc.; and a step of stacking the solid-state batteries. [Examples]

[0076] <Example 1> [Fabrication of the positive electrode] As a raw material, NCA-based cathode active material (LiNi 0.8 Co 0.15 Al 0.05 A cathode slurry was prepared by stirring a cathode composite material containing O2, a sulfide-based solid electrolyte (Li2S-P2S5), a conductive material (VGCF), a PVdF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of NCA-based cathode active material: sulfide-based solid electrolyte: vapor-deposited carbon fiber: PVdF-based binder in the cathode slurry was adjusted to 88.2:9.8:1.3:0.7. This cathode slurry was coated onto Al foil and SUS foil, respectively, using the blade method, and these were dried on a hot plate at 100°C for 30 minutes to obtain two cathodes having a cathode active material layer.

[0077] [Fabrication of the negative electrode] A negative electrode slurry was prepared by stirring a negative electrode mixture containing powdered Si particles, a sulfide-based solid electrolyte (Li2S-P2S5), a conductive material (VGCF), a PVDF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of powdered Si particles:sulfide-based solid electrolyte:carbon material:PVDF-based binder in the negative electrode slurry was adjusted to 100:77.6:2:15. This negative electrode slurry was coated onto Ni foil and SUS foil, respectively, using the blade method, and these were dried on a hot plate at 100°C for 30 minutes to obtain two negative electrodes with a negative electrode active material layer.

[0078] [Preparation of the solid electrolyte layer] A solid electrolyte slurry was prepared by stirring a solid electrolyte mixture containing a sulfide-based solid electrolyte (Li2S-P2S5), a PVDF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of the sulfide-based solid electrolyte to the PVDF-based binder in the solid electrolyte slurry was adjusted to 99.4:0.4. This solid electrolyte slurry was coated onto the positive electrode active material layers of the two positive electrodes prepared above using the blade method to obtain a laminate of solid electrolyte layer / positive electrode active material layer / Al foil (solid electrolyte layer / positive electrode) and a laminate of solid electrolyte layer / positive electrode active material layer / SUS foil (solid electrolyte layer / positive electrode).

[0079] [Manufacturing of resin current collectors] A conductive paste was prepared by mixing the types and quantities of conductive material shown in Table 1, polymethyl methacrylate (amorphous resin), and butyl butyrate as resins. This paste was coated onto a PET film using the blade method, dried at 150°C for 30 minutes, and then peeled off to obtain a resin current collector. The glass transition temperature (i.e., softening temperature) of the resin was below the crystallization temperature of the solid electrolyte.

[0080] [Fabrication of laminates] The two types of positive electrode / solid electrolyte layers and the two types of negative electrodes prepared above were stacked in the following combinations to obtain two quasi-laminated structures. ·Ni foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / SUS foil ·SUS foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / Al foil Next, the two semi-laminated materials were pressed in a roll press at a pressure of 50 kN / cm and a temperature of 160°C. Then, the SUS foil was peeled off each of the semi-laminated materials, and a resin current collector was placed between the laminates from which the SUS foil had been peeled, and the layers were laminated to obtain a laminate with the laminated structure of "Ni foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / resin current collector / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / Al foil". After that, this laminate was pressed in a roll press at a pressure of 20 kN / cm and a temperature of 160°C. Next, 1 cm 2 By punching out the material to the specified size, a solid-state battery having a laminated structure of "Ni foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / intermediate layer / resin current collector / intermediate layer / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / Al foil" was obtained.

[0081] <Examples 2 to 6> In the fabrication of the resin current collector, a resin current collector was obtained using the same specifications as in Example 1, except that the amount of resin and the type and amount of conductive material were as shown in Table 1. A solid battery was obtained using the same specifications as in Example 1, except that the obtained resin current collector was used.

[0082] <Comparative Example 1> [Fabrication of the positive electrode] As a raw material, NCA-based cathode active material (LiNi 0.8 Co 0.15 Al 0.05 A cathode slurry was prepared by stirring a cathode composite material containing O2, a sulfide-based solid electrolyte (Li2S-P2S5), a conductive material (VGCF), a PVdF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of NCA-based cathode active material: sulfide-based solid electrolyte: vapor-deposited carbon fiber: PVdF-based binder in the cathode slurry was adjusted to 88.2:9.8:1.3:0.7. This cathode slurry was coated onto an Al foil using the blade method, and these were dried on a hot plate at 100°C for 30 minutes to obtain one cathode with a cathode active material layer.

[0083] [Fabrication of the negative electrode] A negative electrode slurry was prepared by stirring a negative electrode mixture containing powdered Si particles, a sulfide-based solid electrolyte (Li2S-P2S5), a conductive material (VGCF), a PVDF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of powdered Si particles:sulfide-based solid electrolyte:carbon material:PVDF-based binder in the negative electrode slurry was adjusted to 100:77.6:2:15. This negative electrode slurry was coated onto Ni foil using the blade method, and these were dried on a hot plate at 100°C for 30 minutes to obtain one negative electrode with a negative electrode active material layer.

[0084] [Preparation of the solid electrolyte layer] A solid electrolyte slurry was prepared by stirring a solid electrolyte mixture containing a sulfide-based solid electrolyte (Li2S-P2S5), a PVDF-based binder, and butyl butyrate using an ultrasonic dispersion device. The mass ratio of the sulfide-based solid electrolyte to the PVDF-based binder in the solid electrolyte slurry was adjusted to 99.4:0.4. This solid electrolyte slurry was coated onto the positive electrode active material layer of the positive electrode prepared above using the blade method to obtain a laminate of solid electrolyte layer / positive electrode active material layer / Al foil (solid electrolyte layer / positive electrode).

[0085] [Fabrication of laminates] One type of positive electrode / solid electrolyte layer and one type of negative electrode, prepared as described above, were stacked in the following combinations to obtain a single laminate. ·Ni foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / Al foil Next, the laminate was pressed in a roll press machine at a press pressure of 50 kN / cm and a temperature of 160°C. Then, 1 cm 2 By punching out the material to the specified size, a solid-state battery having a laminated structure of "Ni foil / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer / Al foil" was obtained.

[0086] <Comparative Example 2> In the fabrication of the laminate, a solid-state battery was obtained with the same specifications as in Example 1, except that the laminate was pressed at 25°C without heating using a roll press machine at a press pressure of 20 kN / cm.

[0087] <Comparative Example 3> In the fabrication of the laminate, a solid-state battery was obtained using the same specifications as in Example 1, except that the temperature at which the laminate was heated and pressed (indicated as "press temperature" in the table) was set to the specifications shown in Table 1 (i.e., a temperature lower than the softening temperature of polymethyl methacrylate).

[0088] The thicknesses of the active material layer, intermediate layer, and resin current collector in the 'positive electrode active material layer / intermediate layer / resin current collector / intermediate layer / negative electrode active material layer' of each example solid-state battery were measured using the method described above. The results are shown in Table 1. It was found that the solid-state batteries of Comparative Examples 2 and 3 did not have an intermediate layer, as measured using the method described above. In Table 1, the item "Thickness Ratio (Intermediate Layer / Resin Current Collector)" refers to the ratio of the thickness of the intermediate layer to the thickness of the resin current collector (intermediate layer / resin current collector).

[0089] <Evaluation of charging constraint pressure> The solid batteries of Example 1 and Comparative Example 1 were sandwiched between two restraining plates, and these two restraining plates were fastened together with a fastener to fix the distance between them with a restraining pressure of 5 MPa. Next, constant current charging was performed on this restrained laminate up to 8.10V at 1 / 10C, ​​and then constant voltage charging was performed up to 8.10V with a termination current of 1 / 100C. The restraining pressure before the start of charging and at the end of charging was recorded. Restraining pressure P before the start of charging BEFORE and the restraining pressure P at the end of charging AFTER The difference (P BEFORE -P AFTER The absolute value of ) divided by the discharge capacity was defined as the confinement pressure fluctuation value. A larger confinement pressure fluctuation value indicates greater expansion of the solid-state battery during charging.

[0090] Figure 2 is a graph showing the relationship between the confinement pressure fluctuation value and the amount of charge in Example 1 and Comparative Example 1. As shown in Figure 2, the solid-state battery of Example 1 showed suppressed fluctuations in confinement pressure during charging compared to the solid-state battery of Comparative Example 1.

[0091] <Evaluation of discharge capacity> A galvanostat was used to perform 50 charge-discharge cycles under the conditions of a current of 0.1C, a charge termination voltage of 8.10V, and a discharge termination voltage of 5.0V. Starting with charging, the current required to discharge to 5.0V after the first charge cycle was calculated and divided by the weight of the active material used to determine the discharge capacity for each cycle. The capacity retention rate (%) after 50 cycles was then obtained by dividing the discharge capacity of the 50th cycle by the discharge capacity of the first cycle. The results are shown in Table 1.

[0092] Figure 3 is a graph showing the relationship between discharge capacity and the number of charge-discharge cycles in Example 1 and Comparative Example 1. As shown in Figure 3, the solid-state battery of Example 1 showed superior capacity retention compared to the solid-state battery of Comparative Example 1, meaning that the deterioration of cycle characteristics was suppressed.

[0093] <Evaluation of resistance> The solid-state batteries of Example 1, Example 2, and Comparative Example 1 were sandwiched between two restraining plates, and these two restraining plates were fastened together with a restraining pressure of 5 MPa to fix the distance between them. Next, constant current charging was performed on this restrained laminate up to 1 / 10C and 8.10V, followed by constant voltage charging up to 8.10V and a cutoff current of 1 / 100C. Furthermore, constant current discharge was performed up to 1 / 10C and 5.0V, followed by constant voltage discharge up to 5.0V and a cutoff current of 1 / 100C. The resistance value was then calculated by dividing the absolute value of the difference between the voltage before charging and the voltage after 0.1 seconds of discharge by the current equivalent to 1 / 100C. Figure 4 shows the obtained resistance value relative to the resistance value of the solid-state battery of Comparative Example 1. Figure 4 is a graph showing the relationship between the relative resistance value and the thickness of the intermediate layer in the solid-state batteries of Example 1, Example 2, and Comparative Example 1. As shown in Figure 4, it was found that the solid-state batteries of the Examples suppressed the increase in resistance value caused by the peeling of the active material layer from the current collector compared to the solid-state battery of Comparative Example 1.

[0094] [Table 1]

[0095] As shown in Table 1, the solid-state battery of the example demonstrated superior capacity retention compared to the solid-state battery of the comparative example, meaning that the degradation of cycle characteristics was suppressed. [Explanation of symbols]

[0096] A negative electrode active material layer B Solid electrolyte layer C positive electrode active material layer 101 Negative electrode active material 102 Solid electrolyte 103 Cathode active material 105, 107 Conductive additives 109, 111 Binders 113 Negative electrode current collector 115 Positive electrode current collector

Claims

1. Resin current collector containing resin and conductive material, An active material layer containing an active material, and An intermediate layer interposed between the active material layer and the resin current collector, wherein at least one component contained in the active material layer and at least one component contained in the resin current collector are mixed. It comprises electrodes having, A solid-state battery in which the thickness of the intermediate layer (intermediate layer / resin current collector) is 1 / 30 or more and 1 / 6 or less of the thickness of the resin current collector.

2. The solid battery according to claim 1, wherein the thickness of the intermediate layer is 1.0 μm or more and 5.0 μm or less.

3. The solid battery according to claim 1 or claim 2, wherein the active material includes a Si-based active material.

4. The aforementioned resin current collector has a coefficient of linear expansion of 200 × 10 －６ ppm / K or more 350×10 －６ A solid-state battery according to claim 1 or claim 2, wherein the concentration is ppm / K or less.

5. It comprises a solid electrolyte layer containing a solid electrolyte, The solid battery according to claim 1 or claim 2, wherein the softening temperature of the resin is less than or equal to the crystallization temperature of the solid electrolyte.

6. The solid battery according to claim 1 or claim 2, wherein the conductive material includes vapor-grown carbon fibers.

Images