Negative electrode for non-aqueous electrolyte energy storage element and non-aqueous electrolyte energy storage element

Abstract

The present invention provides a negative electrode for a non-aqueous electrolyte energy storage element containing a silicon-based active material and a solid electrolyte, which can enhance the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element, and a non-aqueous electrolyte energy storage element equipped with such a negative electrode. [Solution] A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material layer containing a silicon-based active material, a solid electrolyte, a binder, and a conductive agent, wherein the average particle size (D50) of the silicon-based active material is 1.0 μm or more and 10.0 μm or less, and the conductive agent includes a fibrous conductive agent and a particulate conductive agent.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a non-aqueous electrolyte energy storage element and a non-aqueous electrolyte 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, such as lithium 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 energy storage elements.

[0003] In recent years, non-aqueous electrolyte energy storage devices have been proposed that use solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes instead of non-aqueous electrolytes, which are liquid electrolytes in which electrolyte salts are dissolved in liquids such as non-aqueous solvents. Furthermore, silicon materials (silicon-based active materials) as negative electrode active materials are expected to be promising negative electrode active materials because they have a higher energy density compared to carbon materials such as graphite (carbon-based active materials). Patent Document 1 describes an all-solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, in which the negative electrode layer contains a silicon material as the negative electrode active material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-082514 [Overview of the project] [Problems that the invention aims to solve]

[0005] A non-aqueous electrolyte storage element using a negative electrode containing a silicon-based active material and a solid electrolyte has poor ionic conductivity and electronic conductivity in the silicon-based active material. Therefore, if the ionic conduction path and electronic conduction path in the negative electrode are not favorable, the discharge capacity and high-rate discharge characteristics will deteriorate. From the perspective of increasing the energy density and output performance of the non-aqueous electrolyte storage element, it is desirable to have high discharge capacity and high-rate discharge characteristics.

[0006] An object of the present invention is to provide a negative electrode for a non-aqueous electrolyte storage element containing a silicon-based active material and a solid electrolyte, which can improve the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element including such a negative electrode for a non-aqueous electrolyte storage element. [[Means for Solving the Problem]]

[0007] A negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode active material layer containing a silicon-based active material, a solid electrolyte, a binder, and a conductive agent, wherein an average particle diameter (D50) of the silicon-based active material is not less than 1.0 µm and not more than 10.0 µm, and the conductive agent includes a fibrous conductive agent and a particulate conductive agent.

[0008] A non-aqueous electrolyte storage element according to another aspect of the present invention includes the negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention. [[Effects of the Invention]]

[0009] According to any aspect of the present invention, there can be provided a negative electrode for a non-aqueous electrolyte storage element containing a silicon-based active material and a solid electrolyte, which can improve the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element including such a negative electrode for a non-aqueous electrolyte storage element. [[Brief Description of the Drawings]]

[0010] [Figure 1] Fig. 1 is a schematic cross-sectional view showing an all-solid-state battery which is an embodiment of the non-aqueous electrolyte storage element of the present invention. [Figure 2]Figure 2 is a schematic diagram showing an energy storage device comprising a non-aqueous electrolyte energy storage element according to multiple embodiments of the present invention. [Modes for carrying out the invention]

[0011] First, an overview of the negative electrode for a non-aqueous electrolyte energy storage element and the non-aqueous electrolyte energy storage element disclosed herein will be described.

[0012] (1) A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material layer containing a silicon-based active material, a solid electrolyte, a binder, and a conductive agent, wherein the average particle size (D50) of the silicon-based active material is 1.0 μm or more and 10.0 μm or less, and the conductive agent includes a fibrous conductive agent and a particulate conductive agent.

[0013] The negative electrode for a non-aqueous electrolyte energy storage element described in (1) above is a negative electrode for a non-aqueous electrolyte energy storage element containing a silicon-based active material and a solid electrolyte, and can improve the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element. The reason for this is not clear, but the following reasons are speculated. The silicon-based active material is a negative electrode active material that has poor ionic conductivity and electronic conductivity and undergoes large volume changes with charging and discharging. For this reason, in a conventional negative electrode for a non-aqueous electrolyte energy storage element that has a negative electrode active material layer containing a silicon-based active material and a solid electrolyte, the large volume change of the silicon-based active material during the first charge and discharge reduces the contactability of the interface between the silicon-based active material and the solid electrolyte, and between the silicon-based active material and the conductive agent. In particular, when the average particle size (D50) of the silicon-based active material is greater than 10.0 μm, the volume change of the silicon-based active material during charging and discharging becomes even larger, and the contactability of the interface between the silicon-based active material and the solid electrolyte, and between the silicon-based active material and the conductive agent, decreases even further. On the other hand, if the average particle size (D50) of the silicon-based active material is less than 1.0 μm, the curvature of the ion conduction path within the electrode increases, and the effective ion conductivity decreases. This disruption of the ion and electron conduction paths within the negative electrode active material layer, leading to isolation of the silicon-based active material and difficulty in maintaining sufficient ion conduction paths, is considered to be the reason for the low discharge capacity and high-rate discharge characteristics in conventional negative electrodes for non-aqueous electrolyte energy storage elements. In contrast, by setting the average particle size (D50) of the silicon-based active material to 1.0 μm or more and 10.0 μm or less, isolation of the silicon-based active material is suppressed even after the initial charge and discharge cycle. Furthermore, since particulate conductive agents disperse easily within the negative electrode active material layer, incorporating particulate conductive agents into the negative electrode active material layer allows for sufficient formation of electron conduction paths within the negative electrode active material layer, thus suppressing isolation of the silicon-based active material even after the initial charge and discharge cycle. However, because particulate conductive agents disperse easily within the negative electrode active material layer, they can potentially hinder ion conduction paths. In contrast, such adverse effects can be suppressed by incorporating a fibrous conductive agent into the negative electrode active material layer. For this reason, it is presumed that the negative electrode for non-aqueous electrolyte energy storage elements described in (1) above can improve the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0014] Furthermore, the negative electrode for a non-aqueous electrolyte energy storage element described in (1) above is a negative electrode for a non-aqueous electrolyte energy storage element containing a silicon-based active material and a solid electrolyte, and the problem of providing a negative electrode for a non-aqueous electrolyte energy storage element that can improve the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element is solved by setting the average particle size (D50) of the silicon-based active material to a predetermined range and including a fibrous conductive agent and a particulate conductive agent as the conductive agent. In this disclosure, the above problem is considered to have been solved if the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element are improved when compared under the same conditions except for differences in the average particle size (D50) of the silicon-based active material in the negative electrode active material layer and the type of conductive agent contained.

[0015] The "average particle size" of silicon-based active materials refers to the value (D50) at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) becomes 50%, based on the particle size distribution measured by laser diffraction / scattering on a diluted solution obtained by diluting particles with a solvent, in accordance with JIS-Z-8825 (2013). Furthermore, the "average particle size" of silicon-based active materials is the value before charging and discharging, or after the non-aqueous electrolyte energy storage element has been discharged at a constant current of 0.05C to the lower limit voltage for normal use and then extracted. Here, "normal use" refers to the case where the non-aqueous electrolyte energy storage element is used under the recommended or specified charging and discharging conditions for the said non-aqueous electrolyte energy storage element, or, if equipment for using the said non-aqueous electrolyte energy storage element is available, the case where that equipment is used.

[0016] A "fibrous conductive material" refers to a flexible, deformable, elongated conductive material. The ratio of the length to the diameter (fiber diameter) of the fibrous conductive material (aspect ratio) is, for example, 10 or more, preferably 100 or more, and more preferably 1,000 or more. The diameter and length of the fibrous conductive material are determined based on observation with a scanning electron microscope (SEM).

[0017] "Particulate conductive material" refers to a conductive material whose primary particles have an appearance close to spherical. Specifically, particulate conductive material is a conductive material in which the average aspect ratio of primary particles is 1 or greater and less than 10. The average aspect ratio is the average value of the aspect ratios of any 50 particulate conductive material particles (primary particles). The aspect ratio of particulate conductive material is the ratio of the major axis to the minor axis (major axis / minor axis). A primary particle is a particle in which no grain boundaries are observed on the surface when observed with a scanning electron microscope (SEM). This also includes cases where the primary particle has many voids. The shortest diameter passing through the center of the smallest circumscribed circle of a primary particle observed with an SEM is defined as the minor axis, and the diameter passing through the above center and perpendicular to the minor axis is defined as the major axis. The average value of the major axis and minor axis is defined as the particle size. If there are two or more shortest diameters, the longest perpendicular diameter is defined as the minor axis.

[0018] (2) In the negative electrode for a non-aqueous electrolyte energy storage element described in (1) above, the volume-based content of the conductive agent in the negative electrode active material layer may be 1.5 volume% or more and 4.0 volume% or less.

[0019] According to the negative electrode for non-aqueous electrolyte energy storage element described in (2) above, the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element can be further enhanced by the presence of a sufficient amount of conductive agent in the negative electrode active material layer.

[0020] The volume-based content (volume %) of each component in the negative electrode active material layer is the volume-based content relative to the total volume of each component constituting the negative electrode active material layer, excluding the volume of voids in the negative electrode active material layer. That is, the sum of the volume-based content (volume %) of each component constituting the negative electrode active material layer is 100 volume %. The same applies to the volume-based content of each component in the positive electrode active material layer and isolation layer, which will be described later. Furthermore, the volume-based content (volume %) of each component in the negative electrode active material layer is determined by the following procedure. If the negative electrode active material layer can be prepared before assembling the non-aqueous electrolyte energy storage element, it is used as is. First, the negative electrode active material layer is cut in the thickness direction by ion milling. Five arbitrary cross-sections of the obtained negative electrode active material layer are observed with a scanning electron microscope, and the content of each component in the negative electrode active material layer is determined from the area ratio of each component in each cross-section. If the negative electrode active material layer is prepared from an assembled non-aqueous electrolyte energy storage element, it is prepared by the following procedure. First, the non-aqueous electrolyte energy storage element is discharged at a constant current of 0.05C until it reaches the lower limit voltage for normal use. Next, the non-aqueous electrolyte energy storage element is disassembled and the electrode body is removed. The electrode body is cut in the thickness direction using ion milling. Five arbitrary cross-sections of the obtained electrode body are observed with a scanning microscope, and the content of each component in the negative electrode active material layer is determined from the area ratio of each component in the layer considered to be the negative electrode active material layer at each cross-section. The volume-based content of each component is the average value of the content of that component derived from the five arbitrary cross-sections.

[0021] (3) In the negative electrode for a non-aqueous electrolyte energy storage element described in (1) or (2) above, the conductive agent may be a carbon material.

[0022] According to the negative electrode for non-aqueous electrolyte energy storage element described in (3) above, the fact that the conductive agent is a carbon material improves the electronic conductivity of the negative electrode active material layer, thereby improving the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0023] "Carbon material" refers to 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.

[0024] (4) In the negative electrode for a non-aqueous electrolyte energy storage element described in any one of (1) to (3) above, the volume-based content of the fibrous conductive agent in the conductive agent may be greater than the volume-based content of the particulate conductive agent.

[0025] The negative electrode for non-aqueous electrolyte energy storage elements described in (4) above makes it possible to further improve the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0026] (5) A non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises a negative electrode for a non-aqueous electrolyte energy storage element as described in any one of (1) to (4) above.

[0027] The non-aqueous electrolyte energy storage element described in (5) above is a non-aqueous electrolyte energy storage element that uses a negative electrode for non-aqueous electrolyte energy storage elements containing a silicon-based active material and a solid electrolyte, and has improved discharge capacity and high-rate discharge characteristics.

[0028] (6) The non-aqueous electrolyte energy storage element described in (5) above may be an all-solid-state energy storage element.

[0029] The non-aqueous electrolyte energy storage element described in (6) above is a non-aqueous electrolyte energy storage element that uses a negative electrode for non-aqueous electrolyte energy storage elements containing a silicon-based active material and a solid electrolyte, and is particularly useful as an all-solid-state energy storage element because its discharge capacity and high-rate discharge characteristics are enhanced.

[0030] This paper describes in detail an embodiment of the negative electrode for a non-aqueous electrolyte energy storage element, a method for manufacturing the negative electrode for a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing the non-aqueous electrolyte energy storage element, and other embodiments related to one embodiment of the present invention.

[0031] Furthermore, the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0032] <Negative electrode for non-aqueous electrolyte energy storage elements> A negative electrode for a non-aqueous electrolyte energy storage element (hereinafter also referred to as "negative electrode") according to one embodiment of the present invention comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, the negative electrode has a portion in which the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is typically connected to a negative electrode lead, which will be described later. The negative electrode may have a shape such as a sheet, plate, or strip. The negative electrode may be a negative electrode for a non-aqueous electrolyte secondary battery, a negative electrode for an all-solid-state energy storage element, or a negative electrode for an all-solid-state secondary battery.

[0033] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the negative electrode 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 may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used. Furthermore, in this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0034] The negative electrode substrate is electronically conductive. In this specification, "having electronic conductivity" means that the volume resistivity is 10 -2 This means that it is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "having no electronic conductivity" or "having (electrical) insulating properties" means that the above volume resistivity is 10 7This means it is greater than or equal to Ω·cm.

[0035] Examples of materials for the negative electrode substrate 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.

[0036] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, copper foil or copper alloy foil.

[0037] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 50 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 40 μm, 30 μm, 25 μm, or 20 μm.

[0038] The intermediate layer is a layer placed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the negative electrode substrate and the negative electrode active material layer can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the negative electrode active material layer, which will be described later. However, the conductive agent used in the intermediate layer may be a particulate conductive agent, another conductive agent, or a fibrous conductive agent, etc.

[0039] The negative electrode active material layer comprises a silicon-based active material, a solid electrolyte, a binder, a fibrous conductive agent, and a particulate conductive agent. The negative electrode active material layer may optionally include other negative electrode active materials other than the silicon-based active material, other conductive agents other than the fibrous conductive agent and the particulate conductive agent, a thickener, a filler, and other optional components. The negative electrode active material layer may be formed from a negative electrode mixture containing the silicon-based active material, etc. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet. In another embodiment, the negative electrode active material layer may be provided on both sides of the negative electrode substrate.

[0040] A silicon-based active material is a material that functions as a negative electrode active material and contains elemental silicon. Examples of the silicon-based active material include a simple substance of elemental silicon or a compound containing elemental silicon. Examples of the compound containing elemental silicon include silicon oxide (SiO x x, 0<x<2, preferably 0.8≦x≦1.2), silicon nitride, silicon carbide, metal silicon compounds, and the like. Examples of the metal silicon compound include compounds containing elemental silicon and elements such as aluminum, tin, zinc, nickel, copper, titanium, vanadium, and magnesium. In addition, the silicon-based active material may be a composite material such as an SiO / Si / SiO2 composite material. A silicon-based active material that has been pre-doped with lithium can also be used. That is, for example, the silicon-based active material may further contain elemental lithium. One type or a mixture of two or more types of silicon-based active materials can be used. As the silicon-based active material, elemental silicon or silicon oxide is preferable, and elemental silicon is more preferable. The silicon-based active material used as elemental silicon may contain a trace amount (e.g., 1% by mass or less) of elements other than elemental silicon. One or two or more types of silicon-based active materials can be used.

[0041] The lower limit of the content of elemental silicon in the silicon-based active material is preferably 30% by mass, more preferably 40% by mass, still more preferably 50% by mass, and may be 60% by mass, 70% by mass, 80% by mass, 90% by mass, 95% by mass, 97% by mass, or 99% by mass. The upper limit of the content of elemental silicon in the silicon-based active material may be 100% by mass or 99% by mass.

[0042] The surface of the silicon-based active material may be coated with another substance having electronic conductivity such as a carbon material. The use of such a silicon-based active material can improve electronic conductivity, among other effects.

[0043] The silicon-based active material is particulate. The average particle size of the silicon-based active material is between 1.0 μm and 10.0 μm. The lower limit of the average particle size of the silicon-based active material is 1.0 μm, but may be 1.5 μm, 2.0 μm, or 2.5 μm. Setting the average particle size of the silicon-based active material to be above the lower limit makes it easier to manufacture or handle the silicon-based active material. Furthermore, when the average particle size of the silicon-based active material is relatively large, the electron conduction path is easily interrupted due to volume changes in the silicon-based active material, and this leads to a decrease in the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element. For this reason, by applying the technology of the present invention to a negative electrode with such a large average particle size of silicon-based active material, the advantages of the present invention, such as sufficiently forming electron conduction paths and improving the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element, are particularly pronounced. The upper limit of the average particle size of the silicon-based active material is 10.0 μm, but may be 8.0 μm, 6.0 μm, or 4.0 μm. By keeping the average particle size of the silicon-based active material below the above upper limit, the ionic conductivity and electronic conductivity within the negative electrode active material layer are improved, which can further enhance the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element and increase its discharge capacity. For obtaining particles of the silicon-based active material and the positive electrode active material (described later) with predetermined particle sizes, known methods using, for example, pulverizers and classifiers can be employed.

[0044] The lower limit of the volume-based content of silicon-based active material in the negative electrode active material layer is preferably 10 vol%, more preferably 20 vol%, and even more preferably 30 vol% or 40 vol%. By setting the volume-based content of silicon-based active material to above the above lower limit, it is possible to increase the energy density per unit volume of the non-aqueous electrolyte energy storage element. Furthermore, when the volume-based content of silicon-based active material is relatively high, the electron conduction path is easily interrupted due to volume changes in the silicon-based active material, and the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element are likely to decrease as a result. For this reason, by applying the technology of the present invention to a negative electrode with such a high volume-based content of silicon-based active material, the advantages of the present invention, such as sufficiently forming electron conduction paths and improving the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element, are particularly pronounced. The upper limit of the volume-based content of silicon-based active material in the negative electrode active material layer is preferably 70 vol%, more preferably 60 vol%, and even more preferably 50 vol%. By keeping the volume-based content of silicon-based active material below the above upper limit, other components such as solid electrolytes, binders, and conductive agents can be sufficiently incorporated into the negative electrode active material layer, thereby further improving the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0045] The negative electrode active material layer may contain negative electrode active materials other than silicon-based active materials. Examples of other negative electrode active materials include metallic lithium; Li4Ti5O 12 LiTiO 2、 Examples include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon).

[0046] The lower limit of the volume-based content of silicon-based active material in the total negative electrode active material contained in the negative electrode active material layer is preferably 50 vol%, more preferably 70 vol%, even more preferably 90 vol%, and even more preferably 95 vol%, 98 vol%, or 99 vol%. By applying the technology of the present invention to a negative electrode with a high volume-based content of silicon-based active material, which has low electronic conductivity and is prone to isolation during charging and discharging, the advantages of the present invention, such as sufficiently forming electron conduction paths and improving the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element, are particularly pronounced. The negative electrode active material contained in the negative electrode active material layer may consist only of silicon-based active material.

[0047] The lower limit of the volume-based content of all negative electrode active materials in the negative electrode active material layer is preferably 10 vol%, more preferably 20 vol%, and even more preferably 30 vol% or 40 vol%. By setting the volume-based content of all negative electrode active materials to be above the above lower limit, it is possible to increase the energy density per unit volume of the non-aqueous electrolyte energy storage element. The upper limit of the volume-based content of all negative electrode active materials in the negative electrode active material layer is preferably 70 vol%, more preferably 60 vol%, and even more preferably 50 vol%. By setting the volume-based content of all negative electrode active materials to be below the above upper limit, other components such as solid electrolytes, binders, and conductive agents can be sufficiently included in the negative electrode active material layer, and the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element can be further improved.

[0048] A solid electrolyte refers to an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes, with sulfide solid electrolytes being preferred. The solid electrolyte may also be a solid electrolyte other than an oxide solid electrolyte. The upper limit of the oxygen content in the solid electrolyte may be 10 mol%, 1 mol%, or 0.1 mol%. The solid electrolyte may be crystalline or amorphous. A crystalline solid electrolyte is a solid electrolyte in which peaks originating from the solid electrolyte are observed in the X-ray diffraction pattern. An amorphous solid electrolyte is a solid electrolyte in which a halo pattern is observed in the X-ray diffraction pattern, where substantially no peaks other than those originating from the raw materials are observed. One or more types of solid electrolytes can be used.

[0049] The sulfide solid electrolyte preferably contains at least a sulfur element and more preferably a lithium element. The sulfide solid electrolyte preferably has lithium ion conductivity. The sulfide solid electrolyte may also preferably contain a phosphorus element and more preferably a halogen element. The sulfide solid electrolyte preferably contains at least one of a bromine element and an iodine element as the halogen element.

[0050] When a sulfide solid electrolyte is a crystalline solid electrolyte, its crystal structure can be an argyrodite crystal structure, a Li3PS4 crystal structure, a Li4P2S6 crystal structure, or a Li7P3S crystal structure. 11 Crystal structure, Li 10 GeP2S 12A sulfide solid electrolyte having a crystal structure such as a Thio-LISICON crystal structure, an antifluorite crystal structure, a crystal structure having diffraction peaks at diffraction angles 2θ in the ranges of 19.9°±0.5° and 29.3°±0.5° in an X-ray diffraction pattern obtained by using CuKα radiation, a crystal structure having diffraction peaks at diffraction angles 2θ in the ranges of 21.0°±0.5° and 28.0°±0.5° in an X-ray diffraction diagram obtained by using CuKα radiation, and a crystal structure having different diffraction peaks at a diffraction angle 2θ in the range of 17.9°±0.5° or 19.1°±0.5°, at a diffraction angle 2θ in the range of 29.1°±0.5°, and at a diffraction angle 2θ in the range of 29.8°±0.5° respectively, in an X-ray diffraction pattern obtained by using CuKα radiation, wherein any one of these diffraction peaks is the strongest diffraction peak, can be mentioned.

[0051] Examples of the sulfide solid electrolyte 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, Li2S-P2S5-Z m S 2n (wherein m and n are positive numbers, and Z is any one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga and In), Li 10 GeP2S 12 and the like can be mentioned.

[0052] In the negative electrode active material layer, the solid electrolyte may be in a particulate form. The average particle diameter of the solid electrolyte is preferably from 0.1 µm to 10 µm, more preferably from 0.2 µm to 6 µm, and still more preferably from 0.5 µm to 4 µm.

[0053] In the negative electrode active material layer, the solid electrolyte may form a complex with the silicon-based active material. Such a complex may further contain other components (e.g., conductive agents) in addition to the solid electrolyte and the silicon-based active material.

[0054] The lower limit of the volume-based content of the solid electrolyte in the negative electrode active material layer is preferably 20 vol%, more preferably 30 vol%, even more preferably 40 vol%, and even more preferably 45 vol%. The upper limit of the volume-based content of the solid electrolyte is preferably 80 vol%, more preferably 70 vol%, even more preferably 60 vol%, and even more preferably 55 vol%. By setting the volume-based content of the solid electrolyte within the above ranges, it is possible to optimize the high-rate discharge characteristics, discharge capacity, and other charge-discharge performance in a well-balanced manner.

[0055] Examples of binders include water-based binders and organic solvent-based binders.

[0056] 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 of water at 20°C. When forming a negative electrode active material layer using a negative 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. 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, and cellulose. However, when using a sulfide solid electrolyte, it is preferable not to use a water-based binder because it reacts easily with water.

[0057] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An 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 a negative electrode active material layer using a negative 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.

[0058] 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. Elastomers are preferred as the binder, and styrene butadiene rubber is more preferred. One or more types of binders can be used.

[0059] The lower limit of the binder content by volume in the negative electrode active material layer is preferably 0.1% by volume, more preferably 1% by volume, even more preferably 2% by volume, and still more preferably 2.5% by volume. The upper limit of the binder content by volume is preferably 10% by volume, more preferably 7% by volume, even more preferably 5% by volume, and still more preferably 3.5% by volume. By setting the binder content by volume within the above range, it is possible to stably retain silicon-based active materials, etc.

[0060] A conductive agent is a component that has electronic conductivity. Even if the volume resistivity of the conductive agent cannot be directly measured, if the volume resistivity is 10 -2 Materials that are known to have a conductivity of Ω·cm or less are classified as conductive agents.

[0061] Fibrous conductive agents are fibrous components that have electronic conductivity. Examples of fibrous conductive agents include fibrous carbon materials such as carbon fibers and carbon nanotubes, and fibrous metal materials. Carbon fibers are preferred as fibrous conductive agents, and vapor-processed carbon fibers (VGCF®) are particularly preferred. The upper limit of the volume-based content of fibrous conductive agents in the negative electrode active material layer is preferably 3.5 vol%, more preferably 3.0 vol%, even more preferably 2.5 vol%, and still more preferably 2.0 vol%. By keeping the volume-based content of fibrous conductive agents in the negative electrode active material layer below the above upper limit, the viscosity of the negative electrode mixture paste for forming the negative electrode active material layer can be suppressed, thereby increasing productivity. The lower limit of the volume-based content of fibrous conductive agents in the negative electrode active material layer is preferably 0.5 vol%, more preferably 1.0 vol%, even more preferably 1.5 vol%, and still more preferably 1.8 vol%, 2.0 vol%, 2.3 vol%, or 2.5 vol%. By setting the volume-based content of particulate conductive agent above the above lower limit, the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element can be further improved.

[0062] Particulate conductive agents are particulate components that possess electrical conductivity.

[0063] The lower limit of the specific surface area of ​​particulate conductive material is 60 m². 2 / g is preferred, 100m 2 / g is more preferable, 300m 2 / g, 600m 2 / g or 1,000m 2 In some cases, a value of / g is even more preferable. When the specific surface area of ​​the particulate conductive agent is above the above lower limit, sufficient electron conduction pathways are formed in the negative electrode active material layer, thereby improving the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element and increasing its discharge capacity. The upper limit of the specific surface area of ​​the particulate conductive agent is 1,500 m².2 It is / g, and 1,400m 2 It may also be / g, 1,200m 2 / g, 1,000m 2 / g, 900m 2 / g, 500m 2 / g or 300m 2 It may also be / g. By keeping the specific surface area of ​​the particulate conductive agent below the above upper limit, it is possible to suppress the increase in viscosity of the negative electrode mixture paste and manufacture the negative electrode with high productivity.

[0064] As particulate conductive agents, for example, particulate conductive agents such as carbon materials, metals, and electronically conductive ceramics can be used. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjenblack (registered trademark). Examples of graphene-based carbon include graphene and fullerene. One or more types of particulate conductive agents can be used.

[0065] As particulate conductive agents, carbon materials are preferred, carbon black is more preferred, and Ketjenblack or acetylene black is even more preferred. By using such particulate conductive agents, it is possible to further improve the high-rate discharge characteristics of non-aqueous electrolyte energy storage elements and increase their discharge capacity.

[0066] The average aspect ratio of the particulate conductive agent is 1 or more and less than 10, may be 1 or more and less than 5, or 1 or more and less than 2.

[0067] The average primary particle diameter of the particulate conductive agent may be, for example, between 10 nm and 100 nm, or between 20 nm and 60 nm. The average primary particle diameter is the average value of the particle size of each primary particle in any 50 primary particles observed by SEM. The particle size of a primary particle is the average value of its major axis and minor axis.

[0068] The lower limit of the volume-based content of particulate conductive agent in the negative electrode active material layer is preferably 0.5 volume%, more preferably 1.0 volume%, even more preferably 1.5 volume%, and even more preferably 1.8 volume%, 2.0 volume%, 2.3 volume%, or 2.5 volume%. By setting the volume-based content of particulate conductive agent to above the above lower limit, the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element can be improved. The upper limit of the volume-based content of particulate conductive agent is preferably 3.5 volume%, and may be 3.1 volume%, 2.8 volume%, or 2.5 volume%. By setting the volume-based content of particulate conductive agent to below the above upper limit, the volume-based content of other components can be optimized, thereby improving the discharge capacity and high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0069] The negative electrode active material layer may further contain conductive agents other than fibrous conductive agents and particulate conductive agents.

[0070] The volume-based content of fibrous conductive agent in the conductive agent contained in the negative electrode active material layer is preferably greater than the volume-based content of particulate conductive agent. The lower limit of the volume-based content of fibrous conductive agent in the total conductive agent (fibrous conductive agent, particulate conductive agent, and other conductive agents) in the negative electrode active material layer is preferably 50 vol%, more preferably 70 vol%, even more preferably 90 vol%, and even more preferably 95 vol%, 98 vol%, or 99 vol%.

[0071] The lower limit of the volume-based content of all conductive agents (fibrous conductive agents, particulate conductive agents, and other conductive agents) in the negative electrode active material layer is preferably 1.5 volume%, more preferably 1.8 volume%, 2.3 volume%, or 2.5 volume%. The upper limit of the volume-based content of all the above conductive agents is preferably 4.0 volume%, and may be 3.5 volume%, 3.1 volume%, 2.8 volume%, or 2.5 volume%.

[0072] Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickener has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like. The thickener may also function as a binder. One or more types of thickeners can be used. When the negative electrode active material layer contains a thickener, the volume-based content of the thickener in the negative electrode active material layer is preferably 0.1% by volume or more and 8% by volume or less, more preferably 5% by volume or less, even more preferably 2% by volume or less, and may be 1% by volume or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickener.

[0073] The filler is not particularly limited. The filler may be a component other than the negative electrode active material, solid electrolyte, binder, conductive agent, 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, 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 negative electrode active material layer contains a filler, the volume-based content of the filler in the negative electrode active material layer can be 0.1% by volume or more and 8% by volume or less, usually preferably 5% by volume or less, more preferably 2% by volume or less, and even more preferably 1% by volume or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0074] The negative electrode active material layer may further contain other components besides the negative electrode active material, solid electrolyte, binder, conductive agent, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the volume-based content of these other components in the negative electrode active material layer may be 10 volume%, 5 volume%, 2 volume%, 1 volume%, 0.1 volume%, or 0.01 volume%. The upper limit of the volume-based content of unintentionally present components in the negative electrode active material layer may be 10 volume%, 5 volume%, 2 volume%, 1 volume%, 0.1 volume%, or 0.01 volume%. The upper limit of the volume-based content of unintentionally included impurities in the negative electrode active material layer may be 10 volume%, 5 volume%, 2 volume%, 1 volume%, 0.1 volume%, or 0.01 volume%.

[0075] The lower limit of the total volume-based content of silicon-based active material, solid electrolyte, binder, and conductive agent in the negative electrode active material layer may be 90 vol%, 95 vol%, 96 vol%, 97 vol%, 98 vol%, 99 vol%, or 99.5 vol%. The upper limit of the total volume-based content of silicon-based active material, solid electrolyte, binder, and particulate conductive agent in the negative electrode active material layer may be 100 vol%, or 99.99 vol%.

[0076] The thickness of the negative electrode active material layer is set appropriately according to the type of negative electrode active material, the application of the non-aqueous electrolyte energy storage element, etc. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer 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 negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer may be, for example, 2 mg / cm². 2 More than 50mg / cm 2The following is also acceptable: The lower limit of the mass per unit area of ​​one negative electrode active material layer 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 negative electrode active material layer 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.

[0077] <Method for manufacturing a negative electrode for a non-aqueous electrolyte energy storage element> The method for manufacturing the negative electrode according to one embodiment of the present invention is not particularly limited and can be manufactured in accordance with conventionally known methods. For example, the method for manufacturing the negative electrode includes coating a negative electrode mixture paste (paste-like negative electrode mixture) directly onto a negative electrode substrate or via an intermediate layer, and forming a negative electrode active material layer by drying the coated negative electrode mixture paste. After drying, the negative electrode active material layer may be pressed or otherwise subjected to the process.

[0078] A method for manufacturing a negative electrode according to one embodiment of the present invention preferably comprises mixing a fibrous conductive agent, a particulate conductive agent, a silicon-based active material having an average particle size (D50) of 1.0 μm or more and 10.0 μm or less, a solid electrolyte, and a binder in a dispersion medium. In this method for manufacturing a negative electrode, by preparing a negative electrode mixture paste in which such components are mixed, a negative electrode active material layer in which the particulate conductive agent is well dispersed can be formed. As a result, a negative electrode for a non-aqueous electrolyte energy storage element containing a silicon-based active material and a solid electrolyte can be efficiently obtained, which can improve the high-rate discharge characteristics of the non-aqueous electrolyte energy storage element.

[0079] The specific forms and preferred forms of each component (components other than the dispersion medium), such as the silicon-based active material, solid electrolyte, binder, and conductive agent, used in the method for manufacturing the negative electrode are the same as the specific forms and preferred forms of each component in the negative electrode according to one embodiment of the present invention. As the dispersion medium for the negative electrode mixture paste used in the method for manufacturing the negative electrode, organic solvents such as esters, ethers, alcohols, ketones, and alkanes are preferred, polar organic solvents are more preferred, and esters (such as carboxylic acid esters such as butyl butyrate and ethyl propionate) are even more preferred.

[0080] A negative electrode according to one embodiment of the present invention may be manufactured by a method other than the one described above. For example, the negative electrode active material layer may be formed by pressure molding a powdered negative electrode mixture containing a mixture of the components forming the negative electrode active material layer. The powdered negative electrode mixture can be prepared, for example, by mixing a silicon-based active material, a solid electrolyte, a fibrous conductive agent, a particulate conductive agent, etc., using a mechanical milling method. However, by forming the negative electrode active material layer from a negative electrode mixture paste, it is possible to form a negative electrode active material layer with high dispersibility of the fibrous conductive agent and the particulate conductive agent.

[0081] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, an isolation layer, and a container housing these. The isolation layer is interposed between the positive electrode and the negative electrode and electrically insulates the positive electrode and the negative electrode, and contains a solid electrolyte which is a non-aqueous electrolyte. The solid electrolyte may also be contained in the positive electrode and the negative electrode. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may be a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery may be an all-solid-state battery.

[0082] The non-aqueous electrolyte energy storage element 1 shown in Figure 1, which is one embodiment of the present invention, is an all-solid-state battery and a secondary battery in which a positive electrode 2 and a negative electrode 3 are arranged with an isolation layer 4 in between. The positive electrode 2 has a positive electrode substrate 5 and a positive electrode active material layer 6, with the positive electrode substrate 5 being the outermost layer of the positive electrode 2. The negative electrode 3 has a negative electrode substrate 7 and a negative electrode active material layer 8, with the negative electrode substrate 7 being the outermost layer of the negative electrode 2. In the non-aqueous electrolyte energy storage element 1 shown in Figure 1, the negative electrode active material layer 8, isolation layer 4, positive electrode active material layer 6, and positive electrode substrate 5 are stacked in this order on the negative electrode substrate 7. An intermediate layer may be provided between the positive electrode substrate 5 and the positive electrode active material layer 6. Similarly, an intermediate layer may be provided between the negative electrode substrate 7 and the negative electrode active material layer 8. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other members such as a container. In the non-aqueous electrolyte energy storage element 1 shown in Figure 1, other members such as a container are omitted.

[0083] A non-aqueous electrolyte energy storage element according to one embodiment of the present invention 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 inside a container. The positive electrode external terminal and the negative electrode external terminal are provided outside the container. The positive electrode is electrically connected to the positive electrode external terminal via the positive electrode lead. The negative electrode is electrically connected to the negative electrode external terminal via the negative electrode lead.

[0084] The following will provide a detailed explanation of the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, focusing primarily on the case where the non-aqueous electrolyte energy storage element is an all-solid-state battery, but this is not intended to limit the scope of application of the present invention.

[0085] (positive electrode) As described above, the positive electrode comprises a positive electrode substrate and a positive electrode active material layer laminated directly to the positive electrode substrate or via an intermediate layer. Typically, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the positive electrode lead described above. The positive electrode may have a shape such as a sheet, plate, or strip.

[0086] The thickness of the positive electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the positive electrode 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 may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion in which the positive electrode active material layer is laminated directly onto the positive electrode substrate or via an intermediate layer. If both portions exist in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions in which the positive electrode active material layer is laminated on only one side of the positive electrode substrate, then the average thickness of the portion in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used.

[0087] The positive electrode substrate has electronic conductivity. Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (stainless steel, etc.). Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0088] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0089] The average thickness of the positive electrode substrate 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 may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0090] The configuration of the intermediate layer of the positive electrode is not particularly limited; for example, it can be selected from the configurations exemplified for the intermediate layer of the negative electrode.

[0091] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer optionally contains components such as a solid electrolyte, binder, conductive agent, thickener, and filler. The optional components such as the solid electrolyte, binder, conductive agent, thickener, and filler can be selected from the materials exemplified in the negative electrode active material layer described above. The conductive agent in the positive electrode active material layer may be a fibrous conductive agent, a particulate conductive agent, or another conductive agent. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet. In another embodiment, the positive electrode active material layer may be provided on both sides of the positive electrode substrate.

[0092] 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.

[0093] 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.

[0094] Li 1+α Ma 1-αO₂ (Ma is a metal element other than lithium element, containing one or more transition metal elements, where 0≦α<1). It is preferable that Ma contains one or more selected from Ni, Co and Mn. The total content of Ni, Co and Mn relative to Ma ((Ni+Co+Mn) / Ma) is preferably 90 mol% or more, more preferably 98 mol% or more.

[0095] Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li β Mb₂O₄ (Mb is a metal element other than lithium element, containing one or more transition metal elements, where 0<β≦1.2). It is preferable that Mb contains Mn. The content of Mn relative to Mb (Mn / Mb) is preferably 50 mol% or more, more preferably 80 mol% or more.

[0096] A polyanion compound is a compound composed of polyanions (that is, polyvalent oxoacid anions) and cations. The polyanion compound preferably contains lithium cations and transition metal cations as cations. 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 particles of the polyanion compound may be coated with another material (for example, a carbon material described later).

[0097] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0098] Examples of the sulfur-based material include elemental sulfur, metal sulfides such as lithium sulfide, organic disulfide compounds, organic sulfur compounds such as carbon sulfide compounds, etc.

[0099] 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.

[0100] 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 manufacturing 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. When using a composite material of the positive electrode active material and other materials, the average particle size of the composite material is used as the average particle size of the positive electrode active material.

[0101] The volume-based content of the positive electrode active material in the positive electrode active material layer is preferably 30% to 99% by volume, more preferably 40% to 95% by volume, and may also be 50% to 90% by volume. By setting the volume-based content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0102] When the positive electrode active material layer contains a solid electrolyte, the volume-based content of the solid electrolyte in the positive electrode active material layer is preferably 10% to 50% by volume, but may also be 15% to 45% by volume, or 20% to 40% by volume.

[0103] The binder content in the positive electrode active material layer, on a volume basis, is preferably 0.1% to 10% by volume, preferably 0.5% to 9% by volume, and more preferably 1% to 8% by volume. By setting the binder content on a volume basis within the above range, the positive electrode active material can be stably maintained. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a binder.

[0104] The volume-based content of the conductive agent in the positive electrode active material layer is preferably 0% to 10% by volume, more preferably 0.1% to 9% by volume, and even more preferably 0.2% to 8% by volume. By setting the volume-based content of the conductive agent within the above range, it is possible to increase the energy density of the non-aqueous electrolyte energy storage element.

[0105] The volume-based content of the thickener in the positive electrode active material layer is preferably 0% to 8% by volume, more preferably 5% or less by volume, and even more preferably 2% or less by volume. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a thickener.

[0106] The filler in the positive electrode active material layer is a component other than the positive electrode active material, solid electrolyte, binder, conductive agent, 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, or it may be included for other purposes. The volume-based content of the filler in the positive electrode active material layer can be 0% by volume or more and 8% by volume or less, usually preferably 5% by volume or less, and more preferably 2% by volume or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain filler.

[0107] The positive electrode active material layer may further contain other components besides the positive electrode active material, solid electrolyte, binder, conductive agent, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. The positive electrode active material layer may also contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the volume-based content of these other components in the positive electrode active material layer may be 10 vol%, 5 vol%, 2 vol%, 1 vol%, 0.1 vol%, or 0.01 vol%. The upper limit of the volume-based content of unintentionally present components in the positive electrode active material layer may be 10 vol%, 5 vol%, 2 vol%, 1 vol%, 0.1 vol%, or 0.01 vol%. The upper limit of the volume-based content of unintentionally included impurities in the positive electrode active material layer may be 10 volume%, 5 volume%, 2 volume%, 1 volume%, 0.1 volume%, or 0.01 volume%.

[0108] The thickness of the positive electrode active material layer is set appropriately according to the type of positive electrode active material, the application of the non-aqueous electrolyte energy storage element, etc. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer 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 positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer 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 positive electrode active material layer 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 positive electrode active material layer 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.

[0109] (Negative electrode) In a non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the negative electrode is the negative electrode for the non-aqueous electrolyte energy storage element according to the above embodiment of the present invention.

[0110] (isolation layer) The isolation layer typically contains a solid electrolyte. The solid electrolyte used in the isolation layer can be selected from the materials exemplified in the negative electrode active material layer described above. The volume-based content of the solid electrolyte in the isolation layer is preferably 70% to 100%. The volume-based content of the solid electrolyte in the isolation layer may be 90% or more, 99% or more, or 100%.

[0111] The isolation layer may contain optional components such as additives (e.g., phosphoric acid compounds such as Li3PO4, oxides, halogen compounds), binders, thickeners, and fillers. These optional components can be selected from the materials exemplified in the positive electrode active material layer.

[0112] The average thickness of the isolation layer 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 isolation layer to above the lower limit, it becomes possible to reliably insulate the positive electrode and the negative electrode. By setting the average thickness of the isolation layer to below the upper limit, it becomes possible to increase the energy density of the non-aqueous electrolyte energy storage element.

[0113] (container) The container houses the positive electrode, negative electrode, etc., within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material; metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0114] 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.

[0115] (Shape, application, etc. of non-aqueous electrolyte energy storage elements) The shape of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0116] The applications of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention are not particularly limited. The non-aqueous electrolyte energy storage element 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.

[0117] The non-aqueous electrolyte energy storage element of the present invention can be used individually or in combination. The non-aqueous electrolyte energy storage element may be used individually when the required output and voltage are small. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage element may be used as part of an energy storage device combined with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0118] In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the container may be restrained to maintain a certain thickness, or it may not be restrained in such a way. Alternatively, the container may be restrained to have a certain load applied to it. When the container is restrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is restrained, the positive and negative electrodes inside the container may or may not have a load applied to them. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a restraining member that performs such restraint.

[0119] <Method for manufacturing a non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention can be manufactured by known methods. The method for manufacturing the non-aqueous electrolyte energy storage element comprises, for example, preparing a positive electrode mixture, preparing a material for the isolation layer, preparing a negative electrode mixture, and laminating the positive electrode, isolation layer, and negative electrode.

[0120] Preparing a positive electrode mixture may also mean preparing a positive electrode mixture. There are no particular restrictions on the method of preparing the positive electrode mixture, and it can be appropriately selected according to the purpose. For example, a positive electrode mixture can be prepared by mixing a positive electrode active material with a solid electrolyte, etc., using a mechanical milling method or the like. The positive electrode mixture may also be in the form of a paste containing a dispersion medium (positive electrode mixture paste).

[0121] Preparing materials for the isolation layer may also mean fabricating the materials for the isolation layer. Solid electrolytes used as isolation layer materials can be fabricated by conventionally known methods. For example, they can be obtained by processing a predetermined material by mechanical milling. Alternatively, the materials for the isolation layer may be fabricated by heating a predetermined material above its melting temperature using a melt-and-cooling method, melting and mixing the two in a predetermined ratio, and then rapidly cooling. Other methods for fabricating isolation layer materials include, for example, a solid-phase method involving encapsulation under reduced pressure and firing, a liquid-phase method such as dissolution extraction, a gas-phase method (PLD), and firing under an argon atmosphere after processing by mechanical milling. The isolation layer material may also be in the form of a paste containing a dispersion medium.

[0122] Preparing a negative electrode mixture may also mean preparing a negative electrode mixture. There are no particular restrictions on the method of preparing the negative electrode mixture, and it can be appropriately selected according to the purpose. The negative electrode mixture may be in powder form or in paste form containing a dispersion medium (negative electrode mixture paste). As mentioned above, it is preferable to use a negative electrode mixture paste containing a dispersion medium from the viewpoint of improving the dispersibility of particulate conductive agents. The preferred procedure for preparing the negative electrode mixture paste is as described above.

[0123] By laminating a positive electrode, an isolation layer, and a negative electrode, for example, a positive electrode having a positive electrode substrate and a positive electrode active material layer, an isolation layer, and a negative electrode having a negative electrode substrate and a negative electrode active material layer are laminated.

[0124] The positive electrode active material layer, the negative electrode active material layer, and the isolation layer can be provided by coating. For example, the positive electrode active material layer can be provided by coating the surface of the positive electrode substrate with a paste-like positive electrode mixture (positive electrode mixture paste) and drying it. Similarly, as described above, the negative electrode active material layer can be provided by coating the surface of the negative electrode substrate with a paste-like negative electrode mixture (negative electrode mixture paste) and drying it. The isolation layer can be provided by coating the surface of the positive electrode active material layer or the negative electrode active material layer with a paste-like isolation layer material and drying it. Subsequently, for example, a laminate of the positive electrode substrate and the positive electrode active material layer (positive electrode) and a laminate of the negative electrode substrate, the negative electrode active material layer and the isolation layer (laminate of negative electrode and isolation layer) are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other with the isolation layer in between, and a non-aqueous electrolyte energy storage element can be obtained by heating and pressing or the like. A non-aqueous electrolyte energy storage element may be obtained by arranging a laminate of a positive electrode substrate, a positive electrode active material layer, and an isolation layer (a laminate of the positive electrode and an isolation layer) and a laminate of a negative electrode and an isolation layer, such that the positive electrode active material layer and the negative electrode active material layer face each other with the isolation layer in between.

[0125] The positive electrode active material layer, the negative electrode active material layer, and the isolation layer may be formed by pressure molding. The positive electrode, isolation layer, and negative electrode may be laminated by pressure molding the positive electrode substrate, positive electrode mixture, isolation layer material, negative electrode mixture, and negative electrode substrate at the same time. Alternatively, the positive electrode and negative electrode may be pre-formed and then laminated by pressure molding with the isolation layer.

[0126] The lamination of each layer may be carried out by a combination of coating and pressure molding. The lamination of each layer may also be carried out, for example, by creating a layer on another substrate by coating, and then transferring this layer.

[0127] <Energy storage device> The energy storage device 30 in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may also include busbars (not shown) for electrically connecting the plurality of non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0128] <Other Embodiments> The negative electrode for a non-aqueous electrolyte energy storage element, the method for manufacturing the negative electrode for a non-aqueous electrolyte energy storage element, and the non-aqueous electrolyte energy storage element of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present 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.

[0129] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte 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.

[0130] For example, the non-aqueous electrolyte energy storage element according to the present invention may include layers other than the positive electrode, isolation layer, and negative electrode. The present invention can also be applied to a non-aqueous electrolyte energy storage element equipped with bipolar electrodes. Furthermore, the non-aqueous electrolyte energy storage element according to the present invention may contain a liquid. Examples of such non-aqueous electrolyte energy storage elements include a non-aqueous electrolyte energy storage element in which a non-aqueous electrolyte containing an ionic liquid or the like is filled into the voids of the positive electrode active material layer 6, isolation layer 4, and negative electrode active material layer 8 of the non-aqueous electrolyte energy storage element 1 described above.

[0131] <Examples> The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0132] [Example 1] The silicon-based active material is elemental silicon (average particle size 3 μm), the solid electrolyte is an argyrodite-type sulfide solid electrolyte (average particle size 3 μm), the binder is styrene-butadiene rubber, and the fibrous conductive agent is vapor-processed carbon fiber (VGCF: specific surface area 15 m²). 2 / g) and particulate conductive agent Ketjenblack (KB: specific surface area 775m²). 2 The materials ( / g) were weighed in a volume ratio of 39.9:50.2:6.9:2.0:1.0, and butyl butyrate was added as a dispersion medium and mixed in a hybrid mixer. The negative electrode mixture paste was applied to the carbon coat layer of carbon-coated copper foil, which was the negative electrode substrate with an intermediate layer laminated on top. The applied negative electrode mixture paste was dried to form a negative electrode active material layer, and the negative electrode was obtained. After loading an argyrodite-type sulfide solid electrolyte into a powder molding machine, an isolation layer was formed by uniaxial pressure molding at 50 MPa or less using a hydraulic press. After the pressure was released, the fabricated negative electrode was placed on one side of the isolation layer so that the negative electrode active material layer faced each other, and uniaxial pressure molding was performed again using a hydraulic press at 400 MPa and 160°C. After the pressure was released, a metal foil, consisting of a metallic lithium foil bonded to a metallic indium foil, was placed on the side of the isolation layer opposite to the side where the negative electrode was placed, and joined by uniaxial pressure molding at 80 MPa. A non-aqueous electrolyte energy storage element was obtained by removing this from the powder molding machine. The following measurements were performed on this non-aqueous electrolyte energy storage element while it was compressed in the stacking direction at a pressure of approximately 40 MPa using a compression jig. The non-aqueous electrolyte energy storage element was fabricated in an argon atmosphere with a dew point of -70°C or lower.

[0133] [Example 2, Comparative Examples 1 and 2] Non-aqueous electrolyte energy storage elements for Example 2 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the type and volume-based content of the conductive agent used in the preparation of the negative electrode were as shown in Table 1.

[0134] [Comparative Examples 3 to 6] The non-aqueous electrolyte energy storage elements of Comparative Examples 3 to 6 were obtained in the same manner as in Example 1, except that the silicon-based active material used in the preparation of the negative electrode was changed to elemental silicon with an average particle size of 0.7 μm, and the type and volume-based content of the conductive agent were as shown in Table 2.

[0135] In addition, for the conductive agents listed in Tables 1 and 2, "KB" represents Ketjenblack, a particulate conductive agent, and "VGCF" represents vapor-processed carbon fiber, a fibrous conductive agent.

[0136] [Initial charge / discharge] Initial charging and discharging were performed on each obtained non-aqueous electrolyte energy storage element at 25°C according to the following procedure. Constant current and constant voltage charging was performed with a current of 0.1C and a charging termination voltage of -0.6V. The charging termination condition was when the current reached 0.025C. A 10-minute rest period was then observed. Subsequently, constant current discharge was performed with a current of 0.1C and a discharge termination voltage of 0.9V. The discharge capacities measured in this manner are shown in Tables 1 and 2. Note that the reduction reaction in which lithium ions are intercalated in the silicon-based active material, which is the negative electrode active material, is called "charging," and the oxidation reaction in which lithium ions are released is called "discharging."

[0137] [High-rate discharge characteristics] The high-rate discharge characteristics of each non-aqueous electrolyte energy storage element after initial charging and discharging were evaluated at 25°C in the following manner. Constant current and constant voltage charging was performed with a current of 0.1C and a charging termination voltage of -0.6V. The charging termination condition was defined as the current reaching 0.025C. A 10-minute rest period was then observed. Subsequently, constant current discharge was performed with a current of 0.1C and a discharge termination voltage of 0.9V, and the 0.1C discharge capacity was measured. A 10-minute rest period was then observed. Next, charging was performed in the same manner, followed by a 10-minute rest period, and then constant current discharge was performed with a current of 1C and a discharge termination voltage of 0.9V, and the 1C discharge capacity was measured. As a measure of high-rate discharge characteristics, the percentage of the 1C discharge capacity relative to the 0.1C discharge capacity of each non-aqueous electrolyte energy storage element was calculated and defined as the 1C / 0.1C discharge capacity maintenance rate. The 1C / 0.1C discharge capacity maintenance rates are shown in Tables 1 and 2.

[0138] [Table 1]

[0139] [Table 2]

[0140] As shown in Table 1, the non-aqueous electrolyte energy storage elements of Examples 1 and 2, which contained a silicon-based active material with an average particle size of 3 μm along with fibrous and particulate conductive agents, exhibited higher discharge capacity and high-rate discharge characteristics than the non-aqueous electrolyte energy storage elements of Comparative Examples 1 and 2. Among the non-aqueous electrolyte energy storage elements of Examples 1 and 2, the non-aqueous electrolyte energy storage element of Example 1, in which the volume-based content of fibrous conductive agent in the conductive agent was greater than the volume-based content of particulate conductive agent, showed even higher high-rate discharge characteristics. Furthermore, as shown in Table 2, when a silicon-based active material with an average particle size of 0.7 μm was used, the high-rate discharge characteristics were low regardless of the type of conductive agent and the volume-based content.

[0141] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles and the like. [Explanation of Symbols]

[0142] 1. Non-aqueous electrolyte energy storage element 2 Positive electrode 3 negative electrode 4 isolation layer 5. Positive electrode substrate 6 Cathode active material layer 7. Negative electrode substrate 8 Negative electrode active material layer 20 Energy storage units 30 Energy storage devices

Claims

1. The negative electrode active material layer comprises a silicon-based active material, a solid electrolyte, a binder, and a conductive agent. The average particle size (D50) of the above silicon-based active material is 1.0 μm or more and 10.0 μm or less. The above conductive agent is a negative electrode for a non-aqueous electrolyte energy storage element, comprising a fibrous conductive agent and a particulate conductive agent.

2. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1, wherein the volume-based content of the conductive agent in the negative electrode active material layer is 1.5 volume% or more and 4.0 volume% or less.

3. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the conductive agent is a carbon material.

4. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the volume-based content of the fibrous conductive agent in the conductive agent is greater than the volume-based content of the particulate conductive agent.

5. A non-aqueous electrolyte energy storage element comprising a negative electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2.

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