Energy storage element

Abstract

To provide an energy storage element that has high energy density and can suppress fracture of the positive electrode substrate. [Solution] An energy storage element according to one aspect of the present invention comprises an electrode body having a positive electrode having a positive electrode substrate consisting of a single layer and positive electrode active material layers laminated on both sides of the positive electrode substrate, a solid electrolyte layer laminated on each of the positive electrode active material layers, and a negative electrode laminated on each of the solid electrolyte layers, wherein the negative electrode has a negative electrode active material layer containing silicon, and the tensile strength of the positive electrode substrate is 350 MPa or more.

Description

[Technical Field]

[0001] This invention relates to an energy storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrically isolated electrodes and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. Besides non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] In recent years, in order to improve the safety of non-aqueous electrolyte energy storage devices, energy storage devices that use solid electrolytes such as sulfide solid electrolytes instead of liquid electrolytes containing organic solvents have been proposed. Such energy storage devices are manufactured by laminating a positive electrode and a negative electrode with an isolation layer (solid electrolyte) in between. The positive electrode and the negative electrode are usually manufactured by laminating active material layers on a substrate.

[0004] To increase the energy density of energy storage elements, the use of a negative electrode containing silicon-based active material has been investigated (Patent Document 1). Furthermore, a configuration in which positive electrode active material layers are laminated on both sides of a positive electrode substrate can also be adopted. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-190537 [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors have found that when a positive electrode active material layer is laminated on both sides of a positive electrode base material composed of a single layer, and a negative electrode containing a silicon-based active material is further laminated on the positive electrode active material layer, the positive electrode base material is likely to break. The breakage of the positive electrode base material can be a factor causing a short circuit in the power storage element.

[0007] The present invention has been made based on the above circumstances, and an object thereof is to provide a power storage element having a high energy density and capable of suppressing breakage of a positive electrode base material.

Means for Solving the Problems

[0008] The power storage element according to one aspect of the present invention includes an electrode body having a positive electrode base material composed of a single layer, a positive electrode having a positive electrode active material layer laminated on both sides of the positive electrode base material, a solid electrolyte layer laminated on each of the positive electrode active material layers, and a negative electrode laminated on each of the solid electrolyte layers. The negative electrode has a negative electrode active material layer containing a silicon element, and the tensile strength of the positive electrode base material is 350 MPa or more.

Effects of the Invention

[0009] The power storage element according to one aspect of the present invention has a high energy density and can suppress breakage of the positive electrode base material.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic plan view of an electrode body of a power storage element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II of the electrode body of FIG. 1. [Figure 3] FIG. 3 is a schematic view showing a power storage device configured by assembling a plurality of power storage elements according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0011] First, an overview of the power storage element disclosed by this specification will be described.

[0012] (1) An energy storage element according to one aspect of the present invention comprises an electrode body having a positive electrode having a positive electrode substrate consisting of a single layer and positive electrode active material layers laminated on both sides of the positive electrode substrate, a solid electrolyte layer laminated on each of the positive electrode active material layers, and a negative electrode laminated on each of the solid electrolyte layers, wherein the negative electrode has a negative electrode active material layer containing silicon, and the tensile strength of the positive electrode substrate is 350 MPa or more.

[0013] The energy storage element described in (1) above has a high energy density and can suppress the fracture of the positive electrode substrate. The reason for this is not clear, but the following reasons are speculated. In the energy storage element described in (1) above, by using a single-layer positive electrode substrate and laminating positive electrode active material layers on both sides of the positive electrode substrate, the thickness and mass of the positive electrode substrate within the energy storage element can be reduced, thereby increasing the energy density. Furthermore, in the negative electrode, by using a negative electrode active material layer containing silicon, which has a high capacity density per unit mass (hereinafter also referred to as "negative electrode active material layer containing silicon-based active material"), the energy density can be increased. For this reason, the energy storage element described in (1) above has a high energy density. According to the inventors' findings, when a positive electrode substrate consisting of a single layer is laminated with positive electrode active material layers on both sides, and a negative electrode having a negative electrode active material layer containing silicon-based active material is laminated between each positive electrode active material layer with a solid electrolyte layer in between, the positive electrode substrate is prone to fracture. The reasons why the positive electrode substrate is prone to fracture include the large volume change of silicon-based active material during charging and discharging, causing the negative electrode active material layer to expand in the lamination direction and in a direction perpendicular to the lamination direction during charging, the solid electrolyte layer and positive electrode active material layer to stretch in a direction perpendicular to the lamination direction in response to this expansion, and the tensile force applied to the positive electrode substrate due to the expansion of the positive electrode active material layers laminated on both sides of the positive electrode substrate. In contrast, in the energy storage element described in (1) above, the tensile strength of the positive electrode substrate is 350 MPa or more. Therefore, even when a tensile force is applied to the positive electrode substrate due to the expansion of the silicon-based active material, the positive electrode substrate is less likely to fracture. Therefore, the energy storage element described in (1) above has a high energy density and can suppress the fracture of the positive electrode substrate.

[0014] A "single-layer positive electrode substrate" refers to a positive electrode substrate in which one component constitutes a single layer. Therefore, a positive electrode substrate made by layering two or more metal foils, for example, is not included in the definition of a "single-layer positive electrode substrate."

[0015] "Tensile strength" refers to the tensile strength measured in accordance with JIS-Z-2241 (2011). The measurement temperature is 25°C.

[0016] (2) In the energy storage element described in (1) above, the electrode body may be pressed in the stacking direction.

[0017] In the energy storage element described in (2) above, the electrode body is pressed in the stacking direction, which improves the charge-discharge cycle performance. Furthermore, while the expansion of the silicon-based active material in the stacking direction is suppressed, expansion in the direction perpendicular to the stacking direction is promoted. As a result, the tensile force applied to the positive electrode substrate in the direction perpendicular to the stacking direction increases. Therefore, in the energy storage element described in (2) above, the effect of the present invention, which suppresses the fracture of the positive electrode substrate, is significantly obtained.

[0018] (3) In the energy storage element described in (1) or (2) above, the positive electrode substrate may include stainless steel.

[0019] In the energy storage element described in (3) above, the tensile strength of the positive electrode substrate is easily increased by including stainless steel in the positive electrode substrate. Therefore, the energy storage element described in (3) above can further suppress the fracture of the positive electrode substrate.

[0020] (4) In the energy storage element described in any of (1) to (3) above, the Young's modulus of the positive electrode substrate may be 150 GPa or more.

[0021] In the energy storage element described in (4) above, the durability of the positive electrode substrate against tensile force is increased. Therefore, the energy storage element described in (4) above can further suppress the fracture of the positive electrode substrate.

[0022] "Young's modulus" refers to the "elastic modulus" measured in accordance with JIS-Z-2241 (2011). The measurement temperature is 25°C.

[0023] (5) In the energy storage element described in any of (1) to (4) above, the solid electrolyte layer may be arranged so as to cover the side surface of the positive electrode active material layer.

[0024] In the energy storage element described in (5) above, the extension of the positive electrode active material layer in a direction perpendicular to the lamination direction can be further suppressed. Therefore, the energy storage element described in (5) above can further suppress the fracture of the positive electrode substrate.

[0025] (6) In the energy storage element described in any of (1) to (5) above, the positive electrode active material layer may contain a binder, and the binder content in the positive electrode active material layer may be more than 1% by mass.

[0026] In the energy storage element described in (6) above, the positive electrode active material layer tends to stretch in a direction perpendicular to the lamination direction. Therefore, in the energy storage element described in (6) above, the effect of the present invention, which suppresses fracture of the positive electrode substrate, can be significantly obtained.

[0027] A power storage element, a method for manufacturing a power storage element, a power storage device, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0028] <Energy storage element> As one embodiment of the energy storage element of the present invention, an all-solid-state secondary battery will be described below as a specific example.

[0029] The energy storage element 1 shown in Figures 1 and 2 comprises an electrode body having a positive electrode 10 having a single-layer positive electrode substrate 11 and positive electrode active material layers 12 laminated on both sides of the positive electrode substrate 11, a solid electrolyte layer 20 laminated on each positive electrode active material layer 12, and a negative electrode 30 laminated on each solid electrolyte layer 20. In other words, the electrode body of the energy storage element 1 has a laminated structure on both sides of the positive electrode substrate 11, with the positive electrode active material layer 12, solid electrolyte layer 20, and negative electrode 30 in that order. To put it another way, the electrode body of the energy storage element 1 has one positive electrode 10 and two negative electrodes 30 facing it. The negative electrode 30 has a negative electrode active material layer 32 containing the element silicon. More specifically, the negative electrode active material layer 32 contains a silicon-based active material containing the element silicon. The silicon-based active material will be described later. The tensile strength of the positive electrode substrate 11 is 350 MPa or more.

[0030] The energy storage element 1 has a high energy density because it uses a single-layer positive electrode substrate 11, has positive electrode active material layers 12 laminated on both sides of the positive electrode substrate 11, and uses a high-capacity silicon-based active material in the negative electrode 30. Furthermore, because the volume change of the silicon-based active material contained in the negative electrode active material layer 32 is large during charging and discharging, a tensile force is applied to the positive electrode substrate 11 in a direction perpendicular to the lamination direction (the XZ plane direction in Figures 1 and 2). However, since the tensile strength of the positive electrode substrate 11 is 350 MPa or more, the positive electrode substrate 11 is less likely to break. Therefore, the energy storage element 1 has a high energy density and can suppress the breakage of the positive electrode substrate 11.

[0031] As described above, the lower limit of the tensile strength of the positive electrode substrate 11 is 350 MPa, preferably 400 MPa, more preferably 450 MPa, and even more preferably 500 MPa. By ensuring that the tensile strength of the positive electrode substrate 11 is above the above lower limit, fracture of the positive electrode substrate 11 can be suppressed. The upper limit of the tensile strength of the positive electrode substrate 11 is not particularly limited, but may be 700 MPa or 600 MPa.

[0032] The lower limit of the Young's modulus of the positive electrode substrate 11 may be 100 GPa, but 150 GPa is preferred, 170 GPa is more preferred, and 190 GPa is even more preferred. Having a Young's modulus of the positive electrode substrate 11 above this lower limit further suppresses fracture of the positive electrode substrate 11. The upper limit of the Young's modulus of the positive electrode substrate 11 is not particularly limited, but may be 300 GPa or 250 GPa.

[0033] The positive electrode substrate 11 and the positive electrode active material layer 12 may each be plate-shaped, such as rectangular or circular in plan view. In the energy storage element 1 shown in Figures 1 and 2, the positive electrode substrate 11 and the positive electrode active material layer 12 are square in plan view.

[0034] In the stacking direction (Y-axis direction in Figures 1 and 2), the area of ​​the positive electrode substrate 11, excluding the positive electrode leads described later, may be the same as the area of ​​the positive electrode active material layer 12, or it may be larger than the area of ​​the positive electrode active material layer 12. In this embodiment, in the stacking direction, the positive electrode active material layer 12 is stacked in the central part of the positive electrode substrate 11. In other words, in the stacking direction, the outer edge of the positive electrode active material layer 12 is located inside the outer edge of the positive electrode substrate 11. That is, the positive electrode substrate 11 has a central part where the positive electrode active material layer 12 is stacked, and a peripheral part where the positive electrode active material layer 12 is not stacked. The peripheral part of the positive electrode substrate 11 is a region that includes the outer edge of the positive electrode substrate 11. In this embodiment, the peripheral part is an annular region that occupies a uniform width from the outer edge of the central part outward in the stacking direction. The positive electrode substrate 11 has a peripheral portion that is not laminated with the positive electrode active material layer 12, making it easier to arrange the solid electrolyte layer 20, etc., so as to cover the side surface of the positive electrode active material layer 12. This suppresses the positive electrode active material layer 12 from extending in a direction perpendicular to the lamination direction. The positive electrode substrate 11 may further have positive electrode leads, which will be described later.

[0035] The negative electrode 30 comprises a negative electrode substrate 31 and a negative electrode active material layer 32 laminated on the negative electrode substrate 31. The negative electrode active material layer 32 faces the positive electrode active material layer 12 with a solid electrolyte layer 20 in between. That is, the electrode body of the energy storage element 1 has a laminated structure on both sides of the positive electrode substrate 11, comprising the positive electrode active material layer 12, the solid electrolyte layer 20, the negative electrode active material layer 32, and the negative electrode substrate 31 in this order. The negative electrode substrate 31 may have a laminated portion on which the negative electrode active material layer 32 is laminated and a negative electrode lead, which will be described later.

[0036] The positive electrode active material layer 12 and the solid electrolyte layer 20 are usually bonded together. The solid electrolyte layer 20 and the negative electrode active material layer 32 are also usually bonded together. The negative electrode active material layer 32 and the negative electrode substrate 31 may be bonded together, or they may be laminated without being bonded together.

[0037] In the stacking direction view, the area of ​​the negative electrode substrate 31, excluding the negative electrode leads described later, may be the same as the area of ​​the negative electrode active material layer 32, or it may be larger than the area of ​​the negative electrode active material layer 32. Also, in the stacking direction view, the outer edge of the negative electrode active material layer 32 may coincide with the outer edge of the negative electrode substrate 31, excluding the negative electrode leads described later, or it may be located inside the outer edge of the negative electrode substrate 31.

[0038] The area of ​​the negative electrode active material layer 32 in the stacking direction may be the same as the area of ​​the positive electrode active material layer 12, or it may be larger than the area of ​​the positive electrode active material layer 12. Also, in the stacking direction, the outer edge of the negative electrode active material layer 32 may coincide with the outer edge of the positive electrode active material layer 12, or it may be located outside the outer edge of the positive electrode active material layer 12. By having the outer edge of the negative electrode active material layer 32 located outside the outer edge of the positive electrode active material layer 12, it may be easier to suppress the deposition of metals and other materials originating from charge transport ions in the negative electrode active material layer 32.

[0039] The area of ​​the solid electrolyte layer 20 in the stacking direction may be the same as the area of ​​the positive electrode active material layer 12, or it may be larger than the area of ​​the positive electrode active material layer 12. The area of ​​the solid electrolyte layer 20 in the stacking direction may be the same as the area of ​​the negative electrode active material layer 32, or it may be larger than the area of ​​the negative electrode active material layer 32. Preferably, the solid electrolyte layer 20 is arranged such that a part of it covers at least a part of the side surface of the positive electrode active material layer 12, and more preferably, it is arranged so as to cover the entire side surface of the positive electrode active material layer 12. By the solid electrolyte layer 20 covering the side surface of the positive electrode active material layer 12, it is possible to suppress the stretching of the positive electrode active material layer 12 in a direction perpendicular to the stacking direction, and consequently, the fracture of the positive electrode substrate 11 can be further suppressed.

[0040] In a view of the stacking direction, it is preferable that the solid electrolyte layer 20 covers the side of the positive electrode active material layer 12 opposite to the positive electrode substrate 11, the side of the positive electrode active material layer 12, and the peripheral edge of the positive electrode substrate 11. By covering the peripheral edge of the positive electrode substrate 11 with the solid electrolyte layer 20, fracture of the positive electrode substrate 11 can be further suppressed.

[0041] In the energy storage element 1, the solid electrolyte layer 20 extends continuously along the side of the positive electrode active material layer 12 opposite to the positive electrode substrate 11, the side of the positive electrode active material layer 12, and the peripheral edge of the positive electrode substrate 11. By extending the solid electrolyte layer 20 continuously in this manner, the solid electrolyte layer 20 can be easily and suitably positioned.

[0042] The energy storage element 1 may further include other components such as a container. In the energy storage element 1 shown in Figures 1 and 2, other components such as a container are omitted. The energy storage element 1 may further include, for example, a positive electrode lead, a positive electrode external terminal, a negative electrode lead, and a negative electrode external terminal. The positive electrode lead and the negative electrode lead are housed in the container. The positive electrode lead is usually connected to the positive electrode substrate 11. In this embodiment, the positive electrode lead is a part of the positive electrode substrate 11 in which the positive electrode active material layer 12 and the solid electrolyte layer 20 are not laminated, and is a part that protrudes outward from the outer edge of the periphery of the solid electrolyte layer 20 and the positive electrode substrate 11 when viewed in the lamination direction (see Figure 1). The negative electrode lead is usually connected to the negative electrode substrate 31. In this embodiment, the negative electrode lead is a part of the negative electrode substrate 31 in which the negative electrode active material layer 32 is not laminated, and is a part that protrudes outward from the outer edge of the laminated portion of the negative electrode active material layer 32 and the negative electrode substrate 31 when viewed in the lamination direction (see Figure 1). The positive and negative external terminals are located outside the container. The positive electrode 10 is electrically connected to the positive external terminal via a positive lead. The negative electrode 20 is electrically connected to the negative external terminal via a negative lead.

[0043] The following provides a detailed explanation of the main components of the energy storage element 1.

[0044] (positive electrode) As described above, the positive electrode 10 has a positive electrode substrate 11 consisting of a single layer and a positive electrode active material layer 12 that is laminated on both sides of the positive electrode substrate 11 either directly or via an intermediate layer.

[0045] The thickness of the positive electrode 10 is set appropriately according to the application of the energy storage element 1. The average thickness of the positive electrode 10 may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode 10 may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode 10 may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode 10 is the average thickness of the portion in which the positive electrode active material layer 12 is laminated directly onto the positive electrode substrate 11 or via an intermediate layer. If both a portion in which the positive electrode active material layer 12 is laminated on both sides of the positive electrode substrate 11 and a portion in which the positive electrode active material layer 12 is laminated on only one side of the positive electrode substrate 11 exist, then the average thickness of the portion in which the positive electrode active material layer 12 is laminated on both sides of the positive electrode substrate 11 is used.

[0046] The positive electrode substrate 11 is conductive. In this specification, "having conductivity" means that the volume resistivity is 10 -2 This means it is less than or equal to Ω·cm.

[0047] As mentioned above, the material of the positive electrode base material 11 is not particularly limited as long as its tensile strength is 350 MPa or more, but from the viewpoint of achieving both tensile strength and potential resistance, it may be stainless steel, titanium, titanium alloy, etc. Furthermore, from the viewpoint of sufficiently increasing the tensile strength, the positive electrode base material 11 preferably contains stainless steel, and more preferably is made of stainless steel.

[0048] The positive electrode substrate 11 has a shape such as a sheet, plate, or strip. Examples of the positive electrode substrate 11's form include foil. The positive electrode substrate 11 may be, for example, stainless steel foil.

[0049] The average thickness of the positive electrode substrate 11 may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate 11 may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate 11 may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0050] The intermediate layer is a layer disposed between the positive electrode substrate 11 and the positive electrode active material layer 12. The intermediate layer is not included in the positive electrode substrate 11. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer includes a conductive agent, the contact resistance between the positive electrode substrate 11 and the positive electrode active material layer 12 can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer 12, which will be described later.

[0051] The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material layer 12 may optionally contain components such as a solid electrolyte, a conductive agent, a binder, a thickener, or a filler. The positive electrode active material layer 12 may also be formed from a positive electrode mixture containing the positive electrode active material and other optional components.

[0052] For the positive electrode active material, known positive electrode active materials can be used. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used. Examples of positive electrode active materials include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, sulfur-based materials, and lithium oxide. One or more positive electrode active materials can be used.

[0053] Examples of transition metal elements included in lithium transition metal composite oxides include nickel, cobalt, and manganese. Lithium transition metal composite oxides may also contain typical metal elements such as aluminum. Examples of lithium transition metal composite oxides include those having an α-NaFeO2 crystal structure and those having a spinel crystal structure.

[0054] Li 1+α Ma 1-αThose represented by O2(Ma is a metal element other than lithium element, containing one or more transition metal elements. 0 ≦ α < 1). Ma preferably contains one or more of Ni, Co and Mn. The total content of Ni, Co and Mn with respect to Ma ((Ni + Co + Mn) / Ma) is preferably 90 mol% or more, more preferably 98 mol% or more.

[0055] As the lithium transition metal composite oxide having a spinel-type crystal structure, Li β Those represented by Mb2O4 (Mb is a metal element other than lithium element, containing one or more transition metal elements. 0 < β ≦ 1.2). Mb preferably contains Mn. The content of Mn with respect to Mb (Mn / Mb) is preferably 50 mol% or more, more preferably 80 mol% or more.

[0056] The polyanion compound is a compound composed of a polyanion (that is, a polyvalent oxoacid anion) and a cation. The polyanion compound preferably contains a lithium cation and a transition metal cation as the cation. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The surface of the particles of the polyanion compound may be coated with another material (such as a carbon material described later).

[0057] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0058] Examples of the sulfur-based material include elemental sulfur, metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds.

[0059] The atoms or polyanions in these materials, which are the positive electrode active materials, may be partially substituted with atoms or anions of other elements. These materials may also be coated on the surface with other materials.

[0060] The positive electrode active material is usually in particulate form. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit facilitates the manufacture and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer 12. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value (D50) where the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%. For obtaining particles of the positive electrode active material and the negative electrode active material described later with predetermined particle sizes, known methods using, for example, pulverizers and classifiers can be employed.

[0061] The content of the positive electrode active material in the positive electrode active material layer 12 is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and may also be 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer 12.

[0062] A solid electrolyte means an electrolyte that maintains a solid state at 1 atm and 25 °C in a nitrogen atmosphere. Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, pseudo solid electrolytes, etc., and sulfide solid electrolytes are preferred. The solid electrolyte may be a solid electrolyte other than an oxide solid electrolyte. The upper limit of the content of oxygen element in the solid electrolyte may be 10 mol%, 1 mol%, or 0.1 mol%. The solid electrolyte may be a crystalline solid electrolyte or an amorphous solid electrolyte. A crystalline solid electrolyte refers to a solid electrolyte in which peaks derived from the solid electrolyte are observed in an X-ray diffraction pattern. An amorphous solid electrolyte refers to a solid electrolyte in which a halo pattern is observed and substantially no peaks other than peaks derived from the raw materials are observed in an X-ray diffraction pattern. One kind or two or more kinds of solid electrolytes can be used.

[0063] The sulfide solid electrolyte preferably contains at least a sulfur element and further contains a lithium element. The sulfide solid electrolyte preferably has lithium ion conductivity. The sulfide solid electrolyte preferably contains a phosphorus element and further preferably contains a halogen element. The sulfide solid electrolyte preferably contains at least one of bromine element and iodine element as the halogen element.

[0064] When the sulfide solid electrolyte is a crystalline solid electrolyte, its crystal structure includes an argyrodite-type crystal structure, a Li3PS4 crystal structure, a Li4P2S6 crystal structure, a Li7P3S 11 crystal structure, Li 10 GeP2S 12Examples of sulfide solid electrolytes include crystal structures such as crystalline structures, thio-LISICON type crystal structures, inverse fluorite type crystal structures, crystal structures (High Ion Conduction Phase: HICP) having diffraction peaks in the ranges of 19.9°±0.5° and 29.3°±0.5° in X-ray diffraction patterns using CuKα rays, crystal structures (Low Ion Conduction Phase: LICP) having diffraction peaks in the ranges of 21.0±0.5° and 28.0±0.5° in X-ray diffraction patterns using CuKα rays, and crystal structures having different diffraction peaks in the ranges of 17.9°±0.5° or 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5°, with one of these diffraction peaks being the largest diffraction peak.

[0065] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S 2n (However, m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (However, x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In.) Li 10 GeP2S 12 These are some examples.

[0066] In the positive electrode active material layer 12, the solid electrolyte may form a composite with the positive electrode active material. Such a composite may further contain other components (e.g., conductive agents) in addition to the solid electrolyte and the positive electrode active material.

[0067] When the positive electrode active material layer 12 contains a solid electrolyte, the content of the solid electrolyte in the positive electrode active material layer 12 is preferably 5% by mass or more and 50% by mass or less, but may also be 10% by mass or more and 40% by mass or less, or 15% by mass or more and 30% by mass or less.

[0068] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, if the volume resistivity is 10 -2 Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element that is present in the largest quantity by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. Conductive agents can take the form of powder or fibers. One or more types of conductive agents can be used. These materials may also be used as a composite of conductive agents. For example, a composite material of carbon black and CNTs may be used.

[0069] The conductive agent content in the positive electrode active material layer 12 is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the conductive agent content may be 5% by mass, 4% by mass, or 3% by mass. By setting the conductive agent content within the above range, it is possible to increase the energy density of the energy storage element 1.

[0070] The positive electrode active material layer preferably contains a binder. Examples of binders include aqueous binders and organic solvent-based binders.

[0071] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one that dissolves or disperses in 100 parts by mass or more per 100 parts by mass of water at 20°C. When forming the positive electrode active material layer 12 using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (water-soluble or water-dispersible polymer material) can be used. Here, "main component" means the component that accounts for the largest proportion by mass (for example, a component accounting for 50% or more by mass), and the same applies to subsequent descriptions in this specification. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, cellulose, and the like.

[0072] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming the positive electrode active material layer 12 using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, and derivatives of chitosan.

[0073] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0074] The lower limit of the binder content in the positive electrode active material layer 12 is preferably more than 1% by mass, more preferably 1.5% by mass, and even more preferably 2% by mass. A binder content above the above lower limit suppresses cracking in the positive electrode active material layer 12 due to expansion of the silicon-based active material. Furthermore, a binder content above the above lower limit makes the positive electrode active material layer 12 more stretchable due to expansion of the silicon-based active material, making it easier for tensile force to be applied to the positive electrode substrate 11, thus significantly suppressing the fracture of the positive electrode substrate 11—an effect of the present invention. The upper limit of the binder content in the positive electrode active material layer 12 is preferably 8% by mass, more preferably 6% by mass, and even more preferably 5% by mass. A binder content below the above upper limit makes it easy to increase the energy density of the energy storage element 1. Furthermore, a binder content below the above upper limit makes it easier for tensile force to be applied to the positive electrode substrate 11, thus significantly suppressing the fracture of the positive electrode substrate 11—an effect of the present invention.

[0075] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like. The thickening agent may also function as a binder. One or more types of thickening agents can be used. When the positive electrode active material layer 12 contains a thickening agent, the content of the thickening agent in the positive electrode active material layer 12 is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer 12 does not contain a thickening agent.

[0076] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, solid electrolyte, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer 12, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers may be used. When the positive electrode active material layer 12 contains a filler, the filler content in the positive electrode active material layer 12 can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer 12 does not contain a filler.

[0077] The positive electrode active material layer 12 may further contain other components besides the positive electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer 12. Furthermore, the positive electrode active material layer 12 may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the positive electrode active material layer 12 may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the positive electrode active material layer 12 may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit for the amount of impurities unintentionally contained in the positive electrode active material layer 12 may be 10% by mass, or it may be 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0078] The thickness of the positive electrode active material layer 12 is set appropriately according to the type of positive electrode active material, the application of the energy storage element 1, etc. The average thickness of one layer of the positive electrode active material layer 12 may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one layer of the positive electrode active material layer 12 may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one layer of the positive electrode active material layer 12 may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one layer of the positive electrode active material layer 12 may be, for example, 4 mg / cm². 2 More than 100mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one layer of the positive electrode active material layer 12 is 6 mg / cm². 2 , 8 mg / cm³ 2 or 10 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one layer of the positive electrode active material layer 12 is 50 mg / cm². 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0079] (Negative electrode) As described above, the negative electrode 30 comprises a negative electrode substrate 31 and a negative electrode active material layer 32 which is laminated directly or via an intermediate layer on both sides or one side of the negative electrode substrate 31.

[0080] The thickness of the negative electrode 30 is set appropriately according to the application of the energy storage element 1. The average thickness of the negative electrode 30 may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode 30 may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode 30 may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode 30 is the average thickness of the portion in which the negative electrode active material layer 32 is laminated directly or via an intermediate layer on the negative electrode substrate 31. If both a portion in which the negative electrode active material layer 32 is laminated on both sides of the negative electrode substrate 31 and a portion in which the negative electrode active material layer 32 is laminated on only one side of the negative electrode substrate 31 exist, then the average thickness of the portion in which the negative electrode active material layer 32 is laminated on both sides of the negative electrode substrate 31 is used.

[0081] The negative electrode substrate 31 is electrically conductive. Examples of materials for the negative electrode substrate 31 include metals such as copper, nickel, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, copper or copper alloys are preferred.

[0082] The negative electrode substrate 31 has a shape such as a sheet, plate, or strip. Examples of the negative electrode substrate 31 include foil, vapor-deposited film, mesh, porous material, etc., with foil being preferred. The negative electrode substrate 31 may be, for example, copper foil or copper alloy foil.

[0083] The average thickness of the negative electrode substrate 31 may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate 31 may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate 31 may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0084] The configuration of the intermediate layer of the negative electrode 30 is not particularly limited and can be selected from, for example, the configurations exemplified for the intermediate layer of the positive electrode 10.

[0085] The negative electrode active material layer 32 contains a negative electrode active material. The negative electrode active material layer 32 may contain optional components such as a solid electrolyte, a conductive agent, a binder, a thickening agent, a filler, etc. as needed. The optional components such as a solid electrolyte, a conductive agent, a binder, a thickening agent, a filler, etc. can be selected from the materials exemplified in the above positive electrode 10. The negative electrode active material layer 32 may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. In the power storage element 1 of FIG. 1, the negative electrode active material layer 32 is provided only on one side with respect to the sheet-shaped negative electrode substrate 31. As another embodiment, the negative electrode active material layer 32 may be provided on both sides of the negative electrode substrate 31, respectively.

[0086] The negative electrode active material contains a silicon-based active material. Examples of the silicon-based active material include a simple substance of silicon element or a compound containing silicon element. Examples of the compound containing silicon element include silicon oxide (SiO x : 0 <x <2, preferably 0.8 ≦ x ≦ 1.2), silicon nitride, silicon carbide, metal silicon compound, etc. Examples of the metal silicon compound include compounds containing silicon element and aluminum element, tin element, zinc element, nickel element, copper element, titanium element, vanadium element, magnesium element, etc. In addition, the silicon-based active material may be a composite material such as a SiO / Si / SiO2 composite material. A pre-doped silicon-based active material can also be used. That is, for example, the silicon-based active material may further contain an element that becomes a charge transport ion such as lithium element. The silicon-based active material can be used by mixing one kind or two or more kinds. Among the silicon-based active materials, silicon oxide, silicon carbide or a simple substance of silicon element is preferable, and a simple substance of silicon element is more preferable.

[0087] The shape of the silicon-based active material is usually particulate. The average particle diameter of the silicon-based active material may be 0.1 μm or more and 20 μm or less, preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0088] The silicon-based active material may have its surface coated with a conductive material such as a carbonaceous material. By using a silicon-based active material in this form, the electronic conductivity of the negative electrode active material layer 32 can be increased. When the silicon-based active material is in the form of particles or the like coated with a conductive material, the mass ratio of the conductive material to the total amount of the silicon-based active material and the conductive material coating it is preferably, for example, 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less.

[0089] The lower limit of the silicon-based active material content in the negative electrode active material (the proportion of silicon-based active material in the total negative electrode active material) is preferably 10% by mass, more preferably 30% by mass, even more preferably 50% by mass, and even more preferably 70% by mass. By setting the silicon-based active material content to above the above lower limit, the energy density of the energy storage element 1 can be increased. On the other hand, the upper limit of this content may be, for example, 100% by mass.

[0090] The negative electrode active material may further contain a carbon-based active material. Examples of carbon-based active materials include graphite and non-graphitic carbon.

[0091] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 This refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite.

[0092] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. 002 ) refers to carbon materials with a nautical index of 0.34 nm to 0.42 nm. Non-graphitic carbons include poorly graphitizable carbons and easily graphitizable carbons. "Potentially graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.36 nm or more and 0.42 nm or less. "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0093] Here, the "discharge state" of the carbon material refers to a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode, this is a state in which the open-circuit voltage is 0.7V or higher.

[0094] The content of the negative electrode active material in the negative electrode active material layer 32 is preferably, for example, 30% by mass or more and 90% by mass or less, and more preferably 40% by mass or more and 90% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer 32.

[0095] When the negative electrode active material layer 32 contains a conductive agent, the content of the conductive agent in the negative electrode active material layer 32 is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer 32 may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer 32 does not contain a conductive agent.

[0096] If the negative electrode active material layer 32 contains a solid electrolyte, the solid electrolyte content is preferably 5% by mass or more and 90% by mass or less, but may also be 10% by mass or more and 70% by mass or less, or 20% by mass or more and 50% by mass or less.

[0097] When the negative electrode active material layer 32 contains a binder, the binder content in the negative electrode active material layer 32 is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The binder content in the negative electrode active material layer 32 may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer 32 does not contain a binder.

[0098] When the negative electrode active material layer 32 contains a thickening agent, the content of the thickening agent in the negative electrode active material layer 32 is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickening agent in the negative electrode active material layer 32 may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer 32 does not contain a thickening agent.

[0099] The filler in the negative electrode active material layer 32 is a component other than the negative electrode active material, solid electrolyte, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer 32, or it may be included for other purposes. When the negative electrode active material layer 32 contains a filler, the filler content in the negative electrode active material layer 32 can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer 32 does not contain a filler.

[0100] The negative electrode active material layer 32 may further contain other components besides the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer 32. Furthermore, the negative electrode active material layer 32 may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer 32 may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer 32 may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit for the amount of impurities unintentionally contained in the negative electrode active material layer 32 may be 10% by mass, or it may be 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0101] The thickness of the negative electrode active material layer 32 is set appropriately according to the type of negative electrode active material, the application of the energy storage element 1, etc. The average thickness of one layer of the negative electrode active material layer 32 may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one layer of the negative electrode active material layer 32 may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one layer of the negative electrode active material layer 32 may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one layer of the negative electrode active material layer 32 may be, for example, 2 mg / cm². 2 More than 50mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one layer of the negative electrode active material layer 32 is 3 mg / cm². 2 , 4 mg / cm³ 2 , 5 mg / cm³ 2 or 6 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one layer of the negative electrode active material layer 32 is 30 mg / cm². 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0102] (solid electrolyte layer) The solid electrolyte layer 20 typically contains a solid electrolyte. The solid electrolyte can be selected from the materials exemplified in the positive electrode active material layer 12. The solid electrolyte content in the solid electrolyte layer 20 is preferably 70% by mass or more and 100% by mass or less. The solid electrolyte content in the solid electrolyte layer 20 may be 90% by mass or more, 99% by mass or more, or 100% by mass.

[0103] The solid electrolyte layer 20 may contain optional components such as additives (e.g., phosphoric acid compounds such as Li3PO4, oxides, halogen compounds), binders, thickeners, and fillers. The optional components such as binders, thickeners, and fillers can be selected from the materials exemplified in the positive electrode active material layer 12.

[0104] The average thickness of the solid electrolyte layer 20 is preferably 1 μm to 100 μm, more preferably 2 μm to 50 μm, and even more preferably 3 μm to 20 μm. By setting the average thickness of the solid electrolyte layer 20 to above the lower limit, it becomes possible to reliably insulate the positive electrode 10 and the negative electrode 30. By setting the average thickness of the solid electrolyte layer 20 to below the upper limit, it becomes possible to increase the energy density of the energy storage element 1.

[0105] (container) The container houses the positive electrode 10 and the negative electrode 30, etc., within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material, with metal materials being preferred from the viewpoint of strength, etc. A composite material of metal and resin materials can also be used.

[0106] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0107] (Shape and application of energy storage elements, etc.) The shape of the energy storage element 1 is not particularly limited. The energy storage element 1 may be, for example, a rectangular battery, a flat battery, or the like.

[0108] The applications of the energy storage element 1 are not particularly limited. The energy storage element 1 can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0109] The energy storage element 1 can be used individually or in combination with other energy storage elements. When the required output and voltage are small, the energy storage element 1 may be used individually. On the other hand, when at least one of the required output and voltage is large, the energy storage element 1 may be used as part of an energy storage device combined with other energy storage elements. In an energy storage device composed of multiple energy storage elements, at least one of the energy storage elements included in the energy storage device may be the energy storage element 1 in this embodiment. The energy storage device will be described in detail later.

[0110] It is preferable that the electrode body of the energy storage element 1 is pressed in the stacking direction. Pressing the electrode body in the stacking direction can improve the charge-discharge cycle performance. Furthermore, while the expansion of the silicon-based active material in the stacking direction is suppressed, expansion in the direction perpendicular to the stacking direction is promoted. As a result, the tensile force applied to the positive electrode substrate 11 in the direction perpendicular to the stacking direction increases. Therefore, the effect of the present invention, which suppresses the fracture of the positive electrode substrate 11, is significantly obtained.

[0111] Methods for pressing the electrode bodies of the energy storage element 1 in the stacking direction include restraining the container or electrode bodies so that they maintain a constant thickness, and restraining the container or electrode bodies so that a constant load is applied to them. Furthermore, the energy storage element 1 or the energy storage device may be provided with a restraining member to perform such restraint.

[0112] The pressure applied in the stacking direction of the electrode bodies of the energy storage element 1 may be between 1 MPa and 20 MPa, preferably between 5 MPa and 15 MPa, and more preferably between 8 MPa and 12 MPa. By having the pressure applied in the stacking direction of the electrode bodies of the energy storage element 1 within the above range, the effect of the present invention, which suppresses the fracture of the positive electrode substrate 11, is significantly obtained.

[0113] The pressure applied in the stacking direction of the electrode body shall be the value measured by the following method. First, the energy storage element is discharged with a constant current of 0.2C to the lower limit voltage for normal use, and then placed in the X-ray CT scanner. The maximum thickness of the electrode body in the stacking direction is measured by scanning along a direction parallel to the stacking direction of the electrode body (Y direction in Figure 1) and acquiring an X-ray transmission image of the electrode body. The energy storage element is disassembled to remove the electrode body and placed in the autograph so that the probe is in contact with the surface perpendicular to the stacking direction of the electrode body. Using the autograph, a load is gradually applied to the surface perpendicular to the stacking direction of the electrode body, compressing the electrode body to the maximum thickness in the stacking direction measured from the X-ray transmission image. At this time, the load measured by the autograph is taken as the load applied to the electrode body in the stacking direction. The value obtained by dividing this load by the planar area of ​​the electrode body (the planar area where the positive electrode active material layer and the negative electrode active material layer face each other) is taken as the pressure applied to the electrode body in the stacking direction.

[0114] <Manufacturing method for energy storage elements> The method for manufacturing the energy storage element 1 according to one embodiment of the present invention is not particularly limited, but an example is described below. Since the components of the energy storage element 1 manufactured by this method are the same as those of the energy storage element 1 described above, they are denoted by the same reference numerals and their descriptions are omitted.

[0115] A positive electrode 10 is prepared by laminating positive electrode active material layers 12 on both sides of a positive electrode substrate 11. The lamination of the positive electrode active material layers 12 can be performed, for example, by coating a paste-like positive electrode mixture onto the positive electrode substrate 11, drying it, and then pressing it. The pressing may be done by hot pressing, for example, and the same applies in the following description. When coating a paste-like positive electrode mixture, for example, the coating is performed on the positive electrode substrate 11 with a mask applied, and the mask is removed after coating to laminate a positive electrode active material layer 12 of a predetermined shape. The lamination of the positive electrode active material layers 12 can also be performed by transferring a positive electrode active material layer 12 that has been pre-formed into a predetermined shape.

[0116] Next, a solid electrolyte layer 20 is laminated onto each positive electrode active material layer 12. At this time, the layer may be laminated so as to cover the sides of the positive electrode active material layer 12 and the periphery of the positive electrode substrate 11, as shown in Figures 1 and 2. The solid electrolyte layer 20 can be laminated by transfer, coating, pressing, etc. Pressing the solid electrolyte layer 20 may be performed simultaneously with pressing the negative electrode active material layer 32, which will be described later.

[0117] Furthermore, a negative electrode active material layer 32 is laminated onto each solid electrolyte layer 20. The lamination of the negative electrode active material layer 32 may be done, for example, by coating the solid electrolyte layer 20 with a paste-like negative electrode mixture, drying it, and then pressing it, or by transferring a negative electrode active material layer 32 that has been pre-formed into a predetermined shape.

[0118] Subsequently, by placing the negative electrode substrate 31 on the negative electrode active material layer 32, an electrode body of the energy storage element 1 is obtained in which the positive electrode 10, solid electrolyte 20, and negative electrode 30 are stacked.

[0119] The electrode body of the energy storage element 1 may be manufactured by first preparing a negative electrode 30 in which a negative electrode active material layer 32 is laminated on a negative electrode substrate 31, and then laminating the negative electrode 30 onto the solid electrolyte layer 20.

[0120] After obtaining the electrode body, the energy storage element 1 can be completed by conventionally known methods, such as housing the electrode body in a container.

[0121] <Energy storage device> The energy storage device 50 in Figure 3 comprises a plurality of energy storage units 40. Each energy storage unit 40 comprises a plurality of electrically connected energy storage elements 1. The energy storage device 50 may also include busbars (not shown) for electrically connecting the plurality of energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 40, etc. The energy storage unit 40 or the energy storage device 50 may also include a condition monitoring device (not shown) for monitoring the state of one or more energy storage elements 1.

[0122] <Other Embodiments> The energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0123] In the above embodiment, the case in which the energy storage element is used as a non-aqueous electrolyte secondary battery that can be charged and discharged was described, but the type, shape, dimensions, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors. [Examples]

[0124] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0125] [Example 1] A single-layer stainless steel foil (SUS304, tensile strength: 520 MPa, Young's modulus: 193 GPa) was prepared as the positive electrode substrate. Intermediate layers (carbon coating layers) were provided on both sides of the positive electrode substrate, and then a positive electrode material layer, in a square shape in plan view, was laminated on the center of both sides of the positive electrode substrate in a plan view, with the intermediate layer in between. The positive electrode active material layer was made of positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05A positive electrode mixture consisting of 76.0 parts by mass of O2, 19.0 parts by mass of argyrodite-type sulfide solid electrolyte, 2.0 parts by mass of conductive agent, and 3.0 parts by mass of binder was used. Next, a solid electrolyte layer consisting of the argyrodite-type sulfide solid electrolyte and binder was laminated on the positive electrode active material layer as shown in Figure 1. Subsequently, a negative electrode active material layer was laminated on the solid electrolyte layer and hot-pressed to form the negative electrode active material layer. For the negative electrode active material layer, a mixture consisting of 44.0 parts by mass of negative electrode active material (particulate Si element, average particle size 3 μm), 47.0 parts by mass of sulfide solid electrolyte, 6.0 parts by mass of conductive agent, and 3.0 parts by mass of binder was used. Furthermore, a copper negative electrode substrate was placed on the negative electrode active material layer, and an electrode body was obtained in which the negative electrode was laminated with solid electrolyte layers sandwiched between both sides of the positive electrode, as shown in Figure 1. The electrode assembly was placed in a container made of a metal-resin composite film such that the tips of the positive electrode lead and the negative electrode lead were exposed to the outside of the container, thereby completing the energy storage element of Example 1.

[0126] [Comparative Example 1] The energy storage element of Comparative Example 1 was completed using the same procedure as in Example 1, except that aluminum foil (A1085-H18, tensile strength: 180 MPa, Young's modulus: 70 GPa) was used as the positive electrode substrate.

[0127] [evaluation] Each of the obtained energy storage elements in the examples and comparative examples was fitted with a restraining member that pressed the outer surface of the container in the direction of electrode stacking, and subjected to the following initial charge-discharge test and charge-discharge cycle test while being pressed in the direction of electrode stacking at a pressure of 10 MPa.

[0128] (Initial charge / discharge test) Each energy storage element in the examples and comparative examples was subjected to constant current constant voltage (CCCV) charging under the conditions of a charging current of 0.1C and a charging termination voltage of 4.25V. The charging termination condition was defined as the charging current becoming 0.025C. After a 10-minute rest period, constant current (CC) discharge was performed under the conditions of a discharge current of 0.1C and a discharge termination voltage of 2.50V, followed by a 10-minute rest period. Note that 1C was defined as 46mA. The above charging and discharging process was considered one cycle, and three cycles were performed. The percentage of discharged electricity relative to charged electricity in each cycle was calculated as the Coulomb efficiency.

[0129] The energy storage element in Comparative Example 1 experienced a short circuit during the first charging cycle. Upon disassembly of the energy storage element in Comparative Example 1 after the short circuit, it was confirmed that the positive electrode substrate was fractured. In contrast, the energy storage element in Example 1 was able to charge and discharge up to the third cycle without a short circuit. The Coulomb efficiency at this time was 85.0% for the first cycle, 98.0% for the second cycle, and 98.7% for the third cycle.

[0130] (Charge-discharge cycle test) The energy storage element of Example 1, after the initial charge-discharge test, underwent a charge-discharge cycle test at a temperature of 50°C in the following manner. Constant current and constant voltage charging was performed with a charging current of 0.1C and a charging termination voltage of 4.25V. The charging termination condition was when the charging current became 0.025C. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.50V. A 10-minute rest period was provided after both charging and discharging. This charge-discharge cycle was performed. Next, constant current and constant voltage charging was performed with a charging current of 0.3C and a charging termination voltage of 4.25V. The charging termination condition was set to when the charging current became 0.1C. After that, constant current discharge was performed with a discharge current of 0.3C and a discharge termination voltage of 2.50V. A 10-minute rest period was provided after both charging and discharging. This charge-discharge cycle was performed 50 times.

[0131] During the charge-discharge cycle test, no short circuit occurred in the energy storage element of Example 1, and even after disassembling the energy storage element of Example 1 after the charge-discharge cycle test, no fracture of the positive electrode substrate was observed. [Industrial applicability]

[0132] This invention can be applied to all-solid-state energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, and for automobiles, etc. [Explanation of Symbols]

[0133] 1. Energy storage element 10 positive electrode 11 Positive electrode substrate 12 Cathode active material layer 20 Solid electrolyte layer 30 negative electrode 31 Negative electrode substrate 32 Negative electrode active material layer 40 Energy storage units 50 Energy storage devices

Claims

1. A positive electrode comprising a single-layer positive electrode substrate and positive electrode active material layers laminated on both sides of the positive electrode substrate, Each of the above positive electrode active material layers is laminated with a solid electrolyte layer, The negative electrode stacked on each of the above solid electrolyte layers and The electrode body comprises having The above-mentioned negative electrode has a negative electrode active material layer containing silicon element, An energy storage element in which the tensile strength of the positive electrode substrate is 350 MPa or more.

2. The energy storage element according to claim 1, wherein the electrode body is pressed in the stacking direction.

3. The energy storage element according to claim 1 or claim 2, wherein the positive electrode substrate includes stainless steel.

4. The energy storage element according to claim 1 or claim 2, wherein the Young's modulus of the positive electrode substrate is 150 GPa or more.

5. The energy storage element according to claim 1 or claim 2, wherein the solid electrolyte layer is arranged so as to cover the side surface of the positive electrode active material layer.

6. The energy storage element according to claim 1 or claim 2, wherein the positive electrode active material layer contains a binder, and the content of the binder in the positive electrode active material layer is more than 1% by mass.

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