Non-aqueous electrolyte power storage element negative electrode and non-aqueous electrolyte power storage element

Abstract

A non-aqueous electrolyte power storage element negative electrode according to one aspect of the present invention comprises a negative electrode active material layer that contains a negative electrode active material, a solid electrolyte, and a conductive agent. The negative electrode active material includes a substance that alloys with lithium. The conductive agent includes single-walled carbon nanotubes.

Description

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

[0001] The present invention relates to a negative electrode for a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element.

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. Non-aqueous electrolyte secondary batteries generally have a pair of electrically isolated electrodes and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions such as lithium ions between the electrodes. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] In recent years, non-aqueous electrolyte storage elements have been proposed that use solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes as the non-aqueous electrolyte, instead of non-aqueous electrolyte solutions in which an electrolyte salt is dissolved in a liquid such as a non-aqueous solvent. Furthermore, silicon materials (silicon-based active materials) as negative electrode active materials have a higher energy density than carbon materials (carbon-based active materials) such as graphite, and are therefore expected to be promising negative electrode 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. Materials other than silicon-based active materials that alloy with lithium are also known as negative electrode active materials.

[0004] Japanese Patent Application Laid-Open No. 2021-082514

[0005] Substances that alloy with lithium, such as silicon-based active materials, are negative electrode active materials that undergo large volume changes during charge and discharge. Meanwhile, in nonaqueous electrolyte storage elements, a high Coulombic efficiency, which is the ratio of discharge capacity to charge capacity, is desirable. However, nonaqueous electrolyte storage elements using negative electrodes containing a negative electrode active material that undergoes large volume changes during charge and discharge and a solid electrolyte, have the disadvantage of low Coulombic efficiency during the first charge and discharge (initial Coulombic efficiency). The inventors have found that, during the second and subsequent charge and discharge cycles, the difference in Coulombic efficiency between nonaqueous electrolyte storage elements using a material that alloys with lithium as the negative electrode active material and nonaqueous electrolyte storage elements using other negative electrode active materials (e.g., graphite) is small. A low initial Coulombic efficiency means that the first charge generates a large number of lithium ions, which are charge-transporting ions that do not contribute to the second and subsequent charge and discharge cycles. Therefore, a high initial Coulombic efficiency is desirable from the standpoint of increasing the capacity of the nonaqueous electrolyte storage element.

[0006] An object of the present invention is to provide a negative electrode for a nonaqueous electrolyte storage element that contains a substance that alloys with lithium and a solid electrolyte, and that can increase the initial coulombic efficiency of the nonaqueous electrolyte storage element, and a nonaqueous electrolyte storage element that includes such a negative electrode for a nonaqueous electrolyte storage element.

[0007] A negative electrode for a nonaqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode active material layer containing a negative electrode active material, a solid electrolyte, and a conductive agent, wherein the negative electrode active material contains a substance that alloys with lithium, and the conductive agent contains single-walled carbon nanotubes.

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the negative electrode for a nonaqueous electrolyte storage element according to the aspect of the present invention.

[0009] According to one aspect of the present invention, it is possible to provide a negative electrode for a nonaqueous electrolyte storage element that contains a substance that alloys with lithium and a solid electrolyte, and that can increase the initial coulombic efficiency of the nonaqueous electrolyte storage element, and a nonaqueous electrolyte storage element that includes such a negative electrode for a nonaqueous electrolyte storage element.

[0010] Fig. 1 is a schematic cross-sectional view showing one embodiment of a nonaqueous electrolyte energy storage element of the present invention. Fig. 2 is a schematic cross-sectional view showing a nonaqueous electrolyte energy storage element of an embodiment different from that shown in Fig. 1. Fig. 3 is a schematic view showing an energy storage device including a plurality of nonaqueous electrolyte energy storage elements according to one embodiment of the present invention.

[0011] First, an outline of the negative electrode for a nonaqueous electrolyte storage element and the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0012] (1) A negative electrode for a nonaqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode active material layer containing a negative electrode active material, a solid electrolyte, and a conductive agent, wherein the negative electrode active material contains a substance that alloys with lithium, and the conductive agent contains single-walled carbon nanotubes.

[0013] The negative electrode for a nonaqueous electrolyte storage element described in (1) above contains a substance that alloys with lithium and a solid electrolyte, and can improve the initial Coulombic efficiency of the nonaqueous electrolyte storage element. While the reason for this is unclear, the following reason is presumed. As described above, the substance that alloys with lithium is a negative electrode active material that undergoes large volume changes during charge and discharge. In a conventional negative electrode for a nonaqueous electrolyte storage element that includes a negative electrode active material layer containing a substance that alloys with lithium and a solid electrolyte, large volume changes in the negative electrode active material during the initial charge and discharge cause cracks in the negative electrode active material layer. The isolation of the negative electrode active material due to these cracks is thought to be the cause of the low initial Coulombic efficiency of conventional negative electrodes for nonaqueous electrolyte storage elements. In contrast, by incorporating single-walled carbon nanotubes into the negative electrode active material layer, the mechanical strength of the negative electrode active material layer is increased, making it less likely to crack even when the negative electrode active material undergoes large volume changes. For these reasons, it is presumed that the negative electrode for a nonaqueous electrolyte storage element described in (1) above can improve the initial Coulombic efficiency of the nonaqueous electrolyte storage element. The negative electrode for a nonaqueous electrolyte storage element described in (1) above is a negative electrode for a nonaqueous electrolyte storage element containing a substance that alloys with lithium and a solid electrolyte. The problem of providing a negative electrode for a nonaqueous electrolyte storage element that can improve the initial Coulombic efficiency of the nonaqueous electrolyte storage element is solved by using single-walled carbon nanotubes as a conductive agent. In the present disclosure, the problem is considered to be solved if the initial Coulombic efficiency of the nonaqueous electrolyte storage element is improved when compared under the same conditions except that the conductive agent in the negative electrode active material layer of the nonaqueous electrolyte storage element does not contain single-walled carbon nanotubes. Furthermore, the negative electrode for a nonaqueous electrolyte storage element described in (1) above can also suppress a decrease in discharge capacity after high-rate discharge (discharge at a high current density). That is, sufficient discharge capacity can be maintained even after discharge at a high current density. The reason for this effect is not clear, but it is speculated that the inclusion of single-walled carbon nanotubes in the negative electrode active material layer increases the mechanical strength of the negative electrode active material layer, thereby suppressing the occurrence of cracks in the negative electrode active material layer even if the negative electrode active material undergoes a sudden volume change during high-rate discharge.

[0014] (2) In the negative electrode for a nonaqueous electrolyte storage element according to (1) above, the content of the single-walled carbon nanotubes in the negative electrode active material layer may be 0.1% by mass or more and 3% by mass or less.

[0015] According to the negative electrode for a nonaqueous electrolyte storage element described in (2) above, the presence of a sufficient amount of single-walled carbon nanotubes in the negative electrode active material layer can further increase the initial coulombic efficiency of the nonaqueous electrolyte storage element.

[0016] (3) In the negative electrode for a nonaqueous electrolyte storage element according to (1) or (2) above, the content of the fibrous conductive agent in the conductive agent may be 90 mass % or more.

[0017] According to the negative electrode for a nonaqueous electrolyte storage element described in (3) above, a fibrous conductive agent is mainly used as the conductive agent, which further increases the mechanical strength of the negative electrode active material layer, thereby making it possible to further increase the initial coulombic efficiency of the nonaqueous electrolyte storage element.

[0018] "Fibrous conductive agent" refers to a conductive agent having a deformable, elongated shape. The ratio (aspect ratio) of the length to the diameter (fiber diameter) of the fibrous conductive agent 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 agent are determined based on images obtained by a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Single-walled carbon nanotubes are also included in the fibrous conductive agent.

[0019] (4) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (3) above, the content of the single-walled carbon nanotubes in the negative electrode active material layer may be 0.3 mass % or more.

[0020] According to the negative electrode for a nonaqueous electrolyte storage element described in (4) above, the presence of a particularly sufficient amount of single-walled carbon nanotubes in the negative electrode active material layer can further increase the initial coulombic efficiency of the nonaqueous electrolyte storage element.

[0021] (5) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (4) above, the substance that alloys with lithium element does not need to have a three-dimensional network structure.

[0022] When a material that alloys with lithium has a three-dimensional network structure (typically porous), the voids formed by the three-dimensional network structure within the material that alloys with lithium are also utilized as spaces for volumetric changes, resulting in small volumetric changes during charging and discharging. Therefore, when such a negative electrode active material is used, cracks are less likely to occur in the negative electrode active material layer, and the initial coulombic efficiency may not be low. However, such a material that alloys with lithium and has a three-dimensional network structure must be manufactured using a special manufacturing method, resulting in low productivity and high costs. In contrast, the negative electrode for a nonaqueous electrolyte storage element described in (5) above can increase the initial coulombic efficiency of the nonaqueous electrolyte storage element, even though the material that alloys with lithium does not have a three-dimensional network structure. Therefore, the negative electrode for a nonaqueous electrolyte storage element described in (5) above can achieve both high productivity and increased initial coulombic efficiency of the nonaqueous electrolyte storage element. Furthermore, by applying the technology of the present invention to a negative electrode in which a substance that does not have a three-dimensional mesh structure and that undergoes a large volume change is used as a substance that alloys with lithium element, the occurrence of cracks in the negative electrode active material layer can be suppressed, and the advantages of increasing the initial coulombic efficiency of the nonaqueous electrolyte energy storage element can be particularly notable.

[0023] (6) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (5) above, the substance that alloys with lithium may have an average pore size of 30 nm or less.

[0024] When the average pore diameter of the material that alloys with lithium exceeds 30 nm (i.e., when the material is highly porous), the voids within the material that alloys with lithium, forming the pores, are also utilized as spaces for volumetric changes, resulting in small volumetric changes during charging and discharging. Therefore, when such a negative electrode active material is used, cracks are less likely to occur in the negative electrode active material layer, and the initial coulombic efficiency may not be low. Examples of materials with an average pore diameter of more than 30 nm include those having the three-dimensional network structure described above. However, as described above, such highly porous materials that alloy with lithium must be manufactured using special manufacturing methods, resulting in low productivity and high costs. In contrast, the negative electrode for a nonaqueous electrolyte storage element described in (6) above can increase the initial coulombic efficiency of the nonaqueous electrolyte storage element, even though the average pore diameter of the material that alloys with lithium is 30 nm or less. Therefore, the negative electrode for a nonaqueous electrolyte storage element described in (6) above can achieve both high productivity and increased initial coulombic efficiency of the nonaqueous electrolyte storage element. Furthermore, by applying the technology of the present invention to a negative electrode in which a substance that alloys with lithium and has an average pore diameter of 30 nm or less and undergoes a large volume change is used, the occurrence of cracks in the negative electrode active material layer can be suppressed, and the advantages of increasing the initial coulombic efficiency of the nonaqueous electrolyte energy storage element can be particularly notable.

[0025] The "average pore diameter" of a substance that alloys with lithium, as well as the "BET specific surface area," "total pore volume," and "average porosity" described below, are values ​​obtained by measuring the pore size distribution using the following method. The pore size distribution is measured on the substance that alloys with lithium before charge / discharge, or on the substance that alloys with lithium contained in the negative electrode of a nonaqueous electrolyte storage element after treatment using the following procedure. First, the nonaqueous electrolyte storage element is discharged at a constant current of 0.05 C to the lower limit voltage for normal use, resulting in a discharged state. Here, "normal use" refers to the use of the nonaqueous electrolyte storage element under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element. Next, the discharged nonaqueous electrolyte storage element is disassembled, the negative electrode is removed, and any adhering components (such as nonaqueous electrolyte) are thoroughly washed and dried, and the substance that alloys with lithium is removed. The substance that alloys with lithium is pretreated by vacuum drying at 150°C for 1 hour. The pore size distribution of the pretreated material alloyed with lithium is measured using a nitrogen adsorption method. This measurement is performed using a Shimadzu TriStar II. The measurement range is a pore diameter range of 0.1 nm to 300 nm. (BET specific surface area) Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the resulting adsorption isotherm, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the resulting line. (Total pore volume) From the total amount of adsorbed gas in the pore size distribution measurement, the cumulative volume of the pores in the adsorption side ranging from 0.1 nm to 300 nm in diameter is calculated as the total pore volume using the BJH method. (Average pore diameter) Assuming that the pores are cylindrical, the pore volume V and the pore surface area A are expressed as follows: V = π(d / 2) ２ H A = πdH d: pore diameter, H: pore depth (corresponding to the height of the cylinder) In calculating the surface area, the area of ​​the surface corresponding to the bottom of the cylinder can be ignored. From the above two equations, d = 4V / A is derived. Therefore, the average pore diameter d is calculated from the equation d = 4V / A using the values ​​of the BET specific surface area A and the total pore volume V. (Average porosity) The average porosity is calculated from the total pore volume (cm ３ / g) and true density (g / cm ３) expressed as a percentage.

[0026] (7) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (6) above, the substance that forms an alloy with lithium may have an average particle size of 0.6 μm or more.

[0027] In the negative electrode for a nonaqueous electrolyte storage element described in (7) above, the average particle size of the substance that alloys with lithium is 0.6 μm or more, which facilitates the production or handling of the substance that alloys with lithium. On the other hand, in conventional negative electrodes for nonaqueous electrolyte storage elements, if the average particle size of the substance that alloys with lithium is relatively large, cracks tend to occur in the negative electrode active material layer due to volume changes of the substance that alloys with lithium, resulting in a decrease in the initial Coulombic efficiency of the nonaqueous electrolyte storage element. Therefore, in the negative electrode for a nonaqueous electrolyte storage element described in (7) above, in which the technology of the present invention is applied to a negative electrode having a large average particle size of the substance that alloys with lithium, the advantages of suppressing the generation of cracks in the negative electrode active material layer and increasing the initial Coulombic efficiency of the nonaqueous electrolyte storage element are particularly significant. In other words, the negative electrode for a nonaqueous electrolyte storage element described in (7) above can achieve both easy production or handling of the substance that alloys with lithium and increased initial Coulombic efficiency of the nonaqueous electrolyte storage element.

[0028] "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013). The average particle size of a substance that alloys with lithium is the value measured before charge / discharge or after the nonaqueous electrolyte storage element is discharged at a constant current of 0.05 C to the lower limit voltage for normal use and then removed. The following conditions are used to measure the average particle size of a substance that alloys with lithium. Pretreatment: An ultrasonic generator, model UD-100, manufactured by Tomy Seiko Co., Ltd., is used, with a tip of 3 mm diameter, an output setting of 80%, and a treatment time of 2 min. Apparatus: SALD-2200 manufactured by Shimadzu Corporation Dispersion medium: water (refractive index: 1.333) Cell: flow cell type Measurement range: 0.03 to 1000 μm Particle refractive index: 3.85-0.01i However, if coloration of the dispersion is observed, it is preferable to take this into consideration and change the set value of the particle refractive index to "3.85-0.10i."

[0029] (8) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (7) above, the substance that forms an alloy with lithium may have an average particle size of 1.5 μm or more.

[0030] The negative electrode for a nonaqueous electrolyte storage element described in (8) above can facilitate the production or handling of a substance that alloys with lithium, while also improving the initial coulombic efficiency of the nonaqueous electrolyte storage element. Furthermore, the negative electrode for a nonaqueous electrolyte storage element described in (8) above can suppress a decrease in discharge capacity during high-rate discharge (discharge at a high current density). That is, sufficient discharge capacity can be ensured even when discharge is performed at a high current density.

[0031] (9) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (8), the BET specific surface area of ​​the substance that is alloyed with lithium element is 8.0 m ２ / g or less.

[0032] The negative electrode for a nonaqueous electrolyte storage element described in (9) above can also suppress a decrease in discharge capacity during high-rate discharge.

[0033] (10) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (9) above, the content of the substance that alloys with lithium in the negative electrode active material layer may be 45 mass % or less.

[0034] The negative electrode for a nonaqueous electrolyte storage element described in (10) above can also suppress a decrease in discharge capacity during high-rate discharge.

[0035] (11) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (10) above, the conductive agent may further include at least one selected from the group consisting of a fibrous conductive agent having an average diameter of 120 nm or more and a particulate conductive agent.

[0036] According to the negative electrode for a nonaqueous electrolyte storage element described in (11) above, it is possible to suppress a decrease in discharge capacity after high-rate discharge.

[0037] (12) In the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (11) above, the content of the single-walled carbon nanotubes in the conductive agent may be 50% by mass or more.

[0038] The negative electrode for a nonaqueous electrolyte electricity storage element described in (12) above can also suppress a decrease in discharge capacity after high-rate discharge.

[0039] (13) A nonaqueous electrolyte storage element according to another aspect of the present invention includes the negative electrode for a nonaqueous electrolyte storage element according to any one of (1) to (12) above.

[0040] The nonaqueous electrolyte storage element described in (13) above is a nonaqueous electrolyte storage element using a negative electrode for a nonaqueous electrolyte storage element containing a substance that alloys with lithium and a solid electrolyte, and has an improved initial coulombic efficiency.

[0041] (14) The nonaqueous electrolyte electricity storage element described in (13) above may be an all-solid-state electricity storage element.

[0042] The nonaqueous electrolyte storage element described in (14) above is a nonaqueous electrolyte storage element using a negative electrode for a nonaqueous electrolyte storage element containing a substance that alloys with lithium and a solid electrolyte, and has an enhanced initial coulombic efficiency, and is therefore particularly useful as an all-solid-state storage element.

[0043] A negative electrode for a nonaqueous electrolyte storage element, a nonaqueous electrolyte storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte storage element, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the names of the components (elements) used in each embodiment may differ from the names of the components (elements) used in the background art. Furthermore, the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any desired manner.

[0044] <Negative electrode for non-aqueous electrolyte storage element> A negative electrode for a non-aqueous electrolyte storage element (hereinafter also referred to as "negative electrode") according to one embodiment of the present invention includes a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer.

[0045] (Negative electrode substrate) The negative electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by measuring the volume resistivity of the negative electrode substrate in accordance with JIS-H-0505 (1975) at 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof, carbon materials, and the like are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0046] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per volume of the nonaqueous electrolyte storage element. Here, the "average thickness" refers to the average value of thicknesses measured at any five positions.

[0047] (Intermediate layer) The intermediate layer is a layer disposed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0048] (Negative electrode active material layer) The negative electrode active material layer contains a negative electrode active material, a solid electrolyte, and a conductive agent. The negative electrode active material layer can be formed from a so-called negative electrode mixture containing a negative electrode active material, a solid electrolyte, and a conductive agent. The negative electrode active material layer contains optional components such as a binder, a thickener, and a filler, as needed. One or more of these optional components may not be substantially contained in the negative electrode active material layer.

[0049] The negative electrode active material includes a substance that can be alloyed with lithium. Examples of substances that can be alloyed with lithium include silicon-based active materials, tin-based active materials, aluminum-based active materials, magnesium-based active materials, zinc-based active materials, and germanium-based active materials. Among these, silicon-based active materials are preferred as substances that can be alloyed with lithium. One or more types of substances that can be alloyed with lithium can be used.

[0050] The silicon-based active material refers to a substance that contains silicon element and is alloyed with lithium element. Examples of the silicon-based active material include silicon element and compounds containing silicon element. Examples of compounds containing silicon element include silicon oxide (SiO ｘ (x: 0<x<2, preferably 0.8≦x≦1.2), silicon nitride, silicon carbide, metal silicon compounds, etc. Examples of metal silicon compounds include compounds containing silicon element and elements such as aluminum, tin, zinc, nickel, copper, titanium, vanadium, magnesium, etc. Other silicon-based active materials include SiO / Si / SiO ２ The silicon-based active material may be a composite material such as a composite material. The silicon-based active material may be pre-doped. That is, the silicon-based active material may further contain lithium element. The silicon-based active material may be used alone or in combination of two or more. As the silicon-based active material, silicon element or silicon oxide is preferred, and silicon element is more preferred.

[0051] Substances that alloy with lithium other than silicon-based active materials are also defined in the same way as silicon-based active materials. That is, for example, a tin-based active material refers to a substance that contains tin and alloys with lithium. Substances that alloy with lithium include simple substances of each element (tin, aluminum, etc.) and compounds containing each element. Examples of compounds containing each element include oxides, nitrides, carbides, and compounds with metal elements of each element.

[0052] The surface of the substance that can be alloyed with lithium may be coated with a conductive material such as a carbon material. By using such a substance that can be alloyed with lithium, the electronic conductivity of the negative electrode active material layer can be increased. When the substance that can be alloyed with lithium is in the form of particles coated with a conductive material, the mass ratio of the conductive material to the total amount of the substance that can be alloyed with lithium and the conductive material that coats it is, for example, preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 5% by mass or less.

[0053] The shape of the substance alloyed with lithium is not particularly limited, but particulate is preferred. The lower limit of the average particle size of the substance alloyed with lithium is, for example, preferably 0.1 μm, more preferably 0.5 μm, even more preferably 0.6 μm, even more preferably 1.5 μm, and may be 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, or 8.0 μm. By setting the average particle size of the substance alloyed with lithium to be equal to or greater than the above lower limit, the production or handling of the substance alloyed with lithium becomes easier. Furthermore, if the average particle size of the substance alloyed with lithium is relatively large, cracks are likely to occur in the negative electrode active material layer due to volume changes of the substance alloyed with lithium, and this, in turn, reduces the initial Coulombic efficiency of the non-aqueous electrolyte storage element. Therefore, by applying the technology of the present invention to a negative electrode having a large average particle size of the substance alloyed with lithium, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial Coulombic efficiency of the non-aqueous electrolyte storage element are particularly significant. Furthermore, by setting the average particle size of the substance that can be alloyed with lithium to be equal to or greater than the above-mentioned lower limit, it is possible to suppress a decrease in discharge capacity during high-rate discharge. The upper limit of the average particle size of the substance that can be alloyed with lithium is, for example, preferably 20 μm, more preferably 10 μm, and may be 5.0 μm, 4.0 μm, 3.0 μm, or 2.0 μm. By setting the average particle size of the substance that can be alloyed with lithium to be equal to or less than the above-mentioned upper limit, volume change of the negative electrode active material layer is suppressed, and the initial coulombic efficiency of the nonaqueous electrolyte storage element can be further improved. Furthermore, by setting the average particle size of the substance that can be alloyed with lithium to be equal to or less than the above-mentioned upper limit, it is possible to increase the capacity retention rate after charge-discharge cycles.

[0054] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0055] The material that alloys with lithium may not have a three-dimensional network structure. The material that alloys with lithium may not be porous. Such a material that alloys with lithium can be produced relatively easily, thereby increasing productivity and reducing production costs. Furthermore, when a material that alloys with lithium does not have a three-dimensional network structure and is not porous, it generally undergoes a large volume change during charge and discharge. Therefore, when the technology of the present invention is applied to a negative electrode for a nonaqueous electrolyte storage element that uses such a material that alloys with lithium, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial Coulombic efficiency of the nonaqueous electrolyte storage element are particularly significant.

[0056] The upper limit of the average pore diameter of the material that alloys with lithium is preferably 30 nm, more preferably 20 nm, even more preferably 15 nm, and even more preferably 12 nm. A material that alloys with lithium and has a small average pore diameter, in other words, a material that alloys with lithium and has low porosity, can be produced relatively easily, thereby increasing productivity and reducing production costs. Furthermore, a material that alloys with lithium and has a small average pore diameter generally has low porosity and tends to have a large volume change during charge and discharge. Therefore, when the technology of the present invention is applied to a negative electrode for a nonaqueous electrolyte storage element that uses such a material that alloys with lithium, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial Coulombic efficiency of the nonaqueous electrolyte storage element are particularly significant. The lower limit of the average pore diameter of the material that alloys with lithium is preferably 1 nm, and may be 3 nm or 5 nm.

[0057] The upper limit of the BET specific surface area of ​​the substance alloyed with lithium is, for example, 50 m ２ / g is preferred, and 30m ２ / g is more preferred, and 20m ２ / g, 10m ２ / g, 8.0 m ２ / g, 7.0 m ２ / g, 6.0 m ２ / g, 5.0 m ２ / g, 4.0 m ２ / g or 3.0m ２ / g. In a substance that can be alloyed with lithium, even if the BET specific surface area is small, the porosity is low and the volume change during charge and discharge generally tends to be large. Therefore, when the technology of the present invention is applied to a negative electrode for a non-aqueous electrolyte storage element using such a substance that can be alloyed with lithium, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial coulomb efficiency of the non-aqueous electrolyte storage element are particularly remarkable. Furthermore, by making the BET specific surface area of ​​the substance that can be alloyed with lithium equal to or less than the above upper limit, it is possible to suppress a decrease in discharge capacity during high-rate discharge. The lower limit of the BET specific surface area of ​​the substance that can be alloyed with lithium is 0.5 m ２ / g is preferred, and 1.0m ２ / g, 2.0 m ２ / g, 3.0 m ２ / g, 4.0 m ２ / g, 5.0 m ２ / g or 6.0m ２ When the BET specific surface area of ​​the substance that can be alloyed with lithium is equal to or greater than the lower limit, the capacity retention rate after charge-discharge cycles can be increased.

[0058] The upper limit of the total pore volume of the material alloyed with lithium element is, for example, 0.2 cm ３ / g is preferred, and 0.1 cm ３ / g is more preferred, and 0.05 cm ３ / g. In a material that can be alloyed with lithium element, even if the total pore volume is small, the porosity is low and the volume change during charge and discharge generally tends to be large. Therefore, when the technology of the present invention is applied to a negative electrode for a non-aqueous electrolyte storage element that uses such a material that can be alloyed with lithium element, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial coulomb efficiency of the non-aqueous electrolyte storage element are particularly remarkable. The lower limit of the total pore volume of the material that can be alloyed with lithium element is 0.005 cm ３ / g is preferred, and 0.01 cm ３ / g.

[0059] The upper limit of the average porosity of the material that alloys with lithium is, for example, preferably 30% or less, more preferably less than 20%. Even when the average porosity of a material that alloys with lithium is low, the material tends to have low porosity and generally has a large volume change during charge and discharge. Therefore, when the technology of the present invention is applied to a negative electrode for a nonaqueous electrolyte storage element that uses such a material that alloys with lithium, the advantages of suppressing the occurrence of cracks in the negative electrode active material layer and increasing the initial Coulomb efficiency of the nonaqueous electrolyte storage element are particularly pronounced. The lower limit of the average porosity of the material that alloys with lithium is preferably 1%, and may be 2%.

[0060] The lower limit of the content of the substance that alloys with lithium relative to all negative electrode active materials in the negative electrode active material layer is preferably 50% by mass, more preferably 70% by mass, even more preferably 90% by mass, and even more preferably 95% by mass, 99% by mass, or 100% by mass. By adjusting the content of the substance that alloys with lithium to above the lower limit, it is possible to increase the energy density, etc. On the other hand, if the content of the substance that alloys with lithium is above the lower limit, cracks are likely to occur in the negative electrode active material layer due to volume changes of the substance that alloys with lithium, and the initial coulombic efficiency is therefore likely to decrease. Therefore, by applying the technology of the present invention to a negative electrode having a high content of the substance that alloys with lithium, the advantages of suppressing cracks in the negative electrode active material layer and increasing the initial coulombic efficiency are particularly significant. The upper limit of the content of the substance that alloys with lithium relative to all negative electrode active materials in the negative electrode active material layer may be 100% by mass.

[0061] The content of the substance that alloys with lithium in the negative electrode active material layer is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, even more preferably 30% by mass or more and 60% by mass or less, and even more preferably 40% by mass or more and 50% by mass or less. By setting the content of the substance that alloys with lithium in the above range, the initial coulombic efficiency and other charge / discharge performance can be balanced and optimized. For example, by setting the content of the substance that alloys with lithium in the negative electrode active material layer to the above upper limit or less, the decrease in discharge capacity during high-rate discharge can be suppressed. From the viewpoint of suppressing the decrease in discharge capacity during high-rate discharge, the upper limit of the content of the substance that alloys with lithium in the negative electrode active material layer may be 45% by mass, 40% by mass, 35% by mass, or 30% by mass.

[0062] The negative electrode active material may further contain other negative electrode active materials other than the material that alloys with lithium element. Examples of other negative electrode active materials include metallic lithium; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７ polyphosphate compounds; carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon); and the like.

[0063] The content of the negative electrode active material in the negative electrode active material layer is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, even more preferably 30% by mass or more and 60% by mass or less, and even more preferably 40% by mass or more and 50% by mass or less. By setting the content of the negative electrode active material within the above range, the initial coulombic efficiency and other charge / discharge performance can be balanced and optimized. For example, by setting the content of the negative electrode active material in the negative electrode active material layer to the above upper limit or less, the decrease in discharge capacity during high-rate discharge can be suppressed. From the viewpoint of suppressing the decrease in discharge capacity during high-rate discharge, the upper limit of the content of the negative electrode active material in the negative electrode active material layer may be 45% by mass, 40% by mass, 35% by mass, or 30% by mass.

[0064] The negative electrode active material and the solid electrolyte may form a complex, which may further contain other components such as a conductive agent.

[0065] The solid electrolyte is not particularly limited, and a conventionally known solid electrolyte can be used. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes, with sulfide solid electrolytes being preferred. One or more types of solid electrolytes can be used.

[0066] The sulfide solid electrolyte may be, for example, Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-P ２ S ５ -Li ３ N., Li. ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li２ S-P ２ S ５ -Z ｍ S ２ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.), Li １０ GeP ２ S １２ The following can be mentioned:

[0067] The solid electrolyte may have a crystalline structure or may be amorphous. In one embodiment, the solid electrolyte may be a sulfide solid electrolyte having an argyrodite-type crystalline structure.

[0068] The content of the solid electrolyte in the negative electrode active material layer is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 70% by mass or less, even more preferably 40% by mass or more and 60% by mass or less, and even more preferably 45% by mass or more and 55% by mass or less. By setting the content of the solid electrolyte within the above range, the initial coulomb efficiency and other charge / discharge performance can be optimized in a balanced manner. The lower limit of the content of the solid electrolyte in the negative electrode active material layer may be 50% by mass, 60% by mass, or 70% by mass.

[0069] The conductive agent has electrical conductivity. The conductive agent includes a single-wall carbon nanotube (SWCNT). The SWCNT is a carbon nanotube formed of a single layer of graphene. It is believed that the SWCNT not only functions as a conductive agent in the negative electrode active material layer but also functions to enhance the mechanical strength. The SWCNT is more flexible than, for example, a multi-wall carbon nanotube (MWCNT) formed of multiple layers of graphene. Therefore, it is believed that the SWCNT can exist in a shape that conforms to the shape of the negative electrode active material, etc., in the negative electrode active material layer, and can effectively enhance the mechanical strength of the negative electrode active material layer.

[0070] The structure of the SWCNT is not particularly limited, and may be any type such as chiral (spiral), zigzag, armchair, etc. The SWCNT may contain catalytic metal elements (e.g., Fe, Co, and platinum group elements (Ru, Rh, Pd, Os, Ir, Pt)) used in the synthesis of the SWCNT.

[0071] The average diameter of the SWCNTs may be, for example, 0.3 nm to 5 nm, 0.5 nm to 4 nm, or 1 nm to 3 nm. The average length of the SWCNTs may be, for example, 0.1 μm to 500 μm, 1 μm to 200 μm, or 3 μm to 100 μm.

[0072] The average aspect ratio of the SWCNTs (ratio of average length to average diameter) is, for example, 10 or more. The lower limit of the average aspect ratio of the SWCNTs is preferably 20, 50, 100, 500, or 1,000. The upper limit of the average aspect ratio of the SWCNTs may be, for example, 100,000, 50,000, 20,000, or 10,000. Use of SWCNTs with a relatively high average aspect ratio tends to further increase the mechanical strength of the negative electrode active material layer.

[0073] The average diameter, average length, and average aspect ratio of SWCNTs are the average values ​​measured for 10 randomly selected SWCNTs observed by SEM or TEM. When calculating the average aspect ratio, it is preferable that the 10 SWCNTs used to determine the average diameter and the 10 SWCNTs used to determine the average length are the same SWCNTs. However, the average diameter and average length may be determined for 10 different SWCNTs, and the ratio of these values ​​may be used as the average aspect ratio. In other words, the average aspect ratio is the average value of the aspect ratios of 10 randomly selected SWCNTs observed by SEM or TEM, or the ratio of the average length of 10 randomly selected SWCNTs observed by SEM or TEM to the average diameter of 10 randomly selected SWCNTs observed by SEM or TEM.

[0074] The BET specific surface area of ​​SWCNT is 400 m ２ / g or more 3000m ２ / g or less is preferable, and 600m ２ / g or more 2000m ２ / g or less is more preferable, and 800m ２ / g or more 1500m ２ / g or less is more preferable.

[0075] SWCNTs can be obtained by known methods such as plasma arc discharge, laser ablation, vapor phase growth, etc. Commercially available SWCNTs can be used.

[0076] In the spectrum (Raman spectrum) obtained by Raman spectroscopy using an excitation laser with a wavelength of 532 nm, SWCNT has a peak at 200 cm , which is called RBM (Radial Breathing Mode). －１ or in the vicinity (for example, 200 cm －１ ±100cm －１ ) in the negative electrode active material layer. This peak corresponds to the expansion and contraction of the SWCNT in the diameter direction, and the position of the peak is known to depend on the diameter of the SWCNT. This peak is not observed in carbon materials other than SWCNT, such as MWCNT. In other words, the negative electrode according to one embodiment of the present invention has a peak in the negative electrode active material layer at 200 cm in the Raman spectrum using an excitation laser with a wavelength of 532 nm.－１ ±100cm －１ The carbon material includes a carbon material in which a peak is observed at 1000 nm. The carbon content in the carbon material is, for example, 70 mass % or more, preferably 90 mass % or more, and more preferably 95 mass % or more.

[0077] The lower limit of the SWCNT content in the negative electrode active material layer is preferably 0.1 mass%, more preferably 0.3 mass%, and even more preferably 0.5 mass%, and may be 0.7 mass% or 1.0 mass%. By setting the SWCNT content to be equal to or greater than the above lower limit, the mechanical strength of the negative electrode active material layer is further increased, and the initial coulombic efficiency of the nonaqueous electrolyte storage element can be further increased. The upper limit of the SWCNT content in the negative electrode active material layer is preferably 3 mass%, more preferably 2 mass%, and may be 1.5 mass%, 1.0 mass%, or 0.7 mass%. By setting the SWCNT content to be equal to or less than the above upper limit, the content of the negative electrode active material can be relatively increased, and as a result, the energy density can be increased, etc.

[0078] The conductive agent may contain another conductive agent other than SWCNT. Examples of the other conductive agent include carbon materials other than SWCNT, metals, conductive ceramics, etc. Examples of carbon materials other than SWCNT include graphite, non-graphitic carbon, and graphene-based carbon other than SWCNT. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon other than SWCNT include graphene, MWCNT, and fullerene. Examples of the conductive agent other than SWCNT include powder and fibrous forms. Preferred examples of the other conductive agent include fibrous conductive agents other than SWCNT, and more preferred are fibrous carbon materials other than SWCNT (fibrous carbon). Examples of fibrous carbon other than SWCNT include carbon nanofibers, pitch-based carbon fibers, and MWCNT.

[0079] In one embodiment of the present invention, the lower limit of the content of the fibrous conductive agent in the conductive agent (the total content of SWCNT and fibrous conductive agent other than SWCNT) is preferably 90 mass %, more preferably 95 mass %, and even more preferably 99 mass %. By mainly using a fibrous conductive agent as the conductive agent in this way, the mechanical strength of the negative electrode active material layer can be further increased, thereby increasing the initial coulombic efficiency of the nonaqueous electrolyte storage element. The upper limit of the content of the fibrous conductive agent in the conductive agent may be 100 mass %.

[0080] In one embodiment of the present invention, the conductive agent may be made of a fibrous conductive agent containing SWCNT, or may be made of fibrous carbon containing SWCNT.

[0081] In one embodiment of the present invention, the conductive agent preferably further contains, together with the SWCNTs, at least one selected from the group consisting of a fibrous conductive agent having an average diameter of 120 nm or more and a particulate conductive agent. In such a case, it is possible to suppress a decrease in discharge capacity after high-rate discharge. The upper limit of the average diameter of the fibrous conductive agent is preferably 400 nm, more preferably 300 nm. Furthermore, the fibrous conductive agent is preferably fibrous carbon. The BET specific surface area of ​​the fibrous conductive agent is preferably 5 m ２ / g or more 40m ２ / g or less is preferable, and 10m ２ / g or more 20m ２ / g or less is more preferable.

[0082] The particulate conductive agent is preferably carbon black, more preferably acetylene black. The particulate conductive agent has an average particle size of preferably 10 nm or more and 100 nm or less, more preferably 20 nm or more and 50 nm or less. The particulate conductive agent has a BET specific surface area of ​​10 m ２ / g or more 150m ２ / g or less is preferable, and 30m ２ / g or more 100m ２ / g or less is more preferable.

[0083] When the negative electrode active material layer further contains at least one selected from the group consisting of a fibrous conductive agent having an average diameter of 120 nm or more and a particulate conductive agent, the total content of the fibrous conductive agent and the particulate conductive agent having an average diameter of 120 nm or more in the negative electrode active material layer is preferably 0.5% by mass to 5% by mass, more preferably 1% by mass to 3% by mass. Furthermore, the mass ratio of the total content of the fibrous conductive agent and the particulate conductive agent having an average diameter of 120 nm or more to the content of SWCNTs is preferably 2 to 10 times, more preferably 3 to 8 times, and even more preferably 4 to 6 times. By including at least one selected from the group consisting of a fibrous conductive agent having an average diameter of 120 nm or more and a particulate conductive agent in such a content, the decrease in discharge capacity after high-rate discharge can be further suppressed.

[0084] In one embodiment of the present invention, the lower limit of the SWCNT content in the conductive agent is preferably 50% by mass, more preferably 70% by mass, and even more preferably 90% by mass, and may be 95%, 98%, or 99% by mass. SWCNT alone may be used as the conductive agent. In such a case, the decrease in discharge capacity after high-rate discharge can also be suppressed.

[0085] The lower limit of the content of the conductive agent in the negative electrode active material layer is preferably 0.1 mass%, more preferably 0.3 mass%, and even more preferably 0.5 mass%, and may be 0.7 mass% or 1.0 mass%. The upper limit of the content of the conductive agent in the negative electrode active material layer is preferably 6 mass%, more preferably 4 mass%, and may be 3 mass%, 2.5 mass%, or 2.0 mass%. By setting the content of the conductive agent within the above range, the initial coulombic efficiency and other charge / discharge performance of the nonaqueous electrolyte storage element can be optimized in a balanced manner.

[0086] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers. Among these, elastomers are preferred, and SBR is more preferred.

[0087] The content of the binder in the negative electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, and even more preferably 2% by mass to 4% by mass. By setting the binder content within the above range, the negative electrode active material can be stably maintained.

[0088] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. In one embodiment of the present invention, the content of the thickener in the negative electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, or the negative electrode active material layer may be substantially free of thickener.

[0089] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. In one embodiment of the present invention, the content of the filler in the negative electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, or may be substantially filler-free.

[0090] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0091] The average thickness of the negative electrode active material layer is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the negative electrode active material layer to the above lower limit or more, a nonaqueous electrolyte storage element having a high energy density can be obtained. By setting the average thickness of the negative electrode active material layer to the above upper limit or less, it is possible to achieve miniaturization of the nonaqueous electrolyte storage element.

[0092] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, and a separator layer interposed between the positive electrode and the negative electrode. In a non-aqueous electrolyte storage element, a laminate of the positive electrode, the negative electrode, and the separator layer is usually housed in a container. The non-aqueous electrolyte storage element may be a non-aqueous electrolyte secondary battery, an all-solid-state storage element, or an all-solid-state secondary battery. As an example of a non-aqueous electrolyte storage element, an all-solid-state secondary battery will be specifically described.

[0093] The positive electrode includes a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the negative electrode.

[0094] The positive electrode substrate is conductive. Examples of the material for the positive electrode substrate include metals such as aluminum, titanium, tantalum, and stainless steel, as well as alloys thereof. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0095] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0096] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer includes optional components such as a solid electrolyte, a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the solid electrolyte, the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the negative electrode active material layer. The conductive agent in the positive electrode active material layer may or may not include SWNCT.

[0097] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material, a material capable of absorbing and releasing lithium ions is usually used. For example, α-NaFeO ２ Examples of suitable lithium transition metal composite oxides include those having a α-type crystal structure, those having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. ２ As the lithium transition metal composite oxide having a crystalline structure, for example, Li[Li ｘ Ni （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘNi γ Co （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Co （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Mn （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), Li[Li ｘ Ni γ Co β Al （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li ｘ Mn ２ O ４ , Li ｘ Ni γ Mn （２－γ） O ４ Examples of polyanion compounds include LiFePO ４ , LiMnPO ４ , LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２ CoPO ４ Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0098] The positive electrode active material is preferably a lithium transition metal composite oxide, more preferably a lithium transition metal composite oxide containing at least one of nickel, cobalt, and manganese, even more preferably a lithium transition metal composite oxide containing at least two of nickel, cobalt, and manganese, and even more preferably a lithium transition metal composite oxide containing nickel, cobalt, and manganese. This lithium transition metal composite oxide is α-NaFeO ２ It is preferable that the lithium transition metal composite oxide has a crystalline structure of the type 1. By using such a lithium transition metal composite oxide, it is possible to increase the energy density, etc.

[0099] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easy to manufacture or handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material.

[0100] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 95% by mass, more preferably 60% by mass to 90% by mass, and even more preferably 70% by mass to 85% by mass. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0101] The content of the solid electrolyte in the positive electrode active material layer is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 15% by mass to 30% by mass. By setting the content of the solid electrolyte within this range, it is possible to increase the energy density of the nonaqueous electrolyte storage element.

[0102] The positive electrode active material and the solid electrolyte may form a complex, which may further contain other components such as a conductive agent.

[0103] The content of the conductive agent in the positive electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, and may be 1.5% by mass to 4% by mass. By setting the content of the conductive agent in this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0104] The content of the binder in the positive electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, and may be 1.5% by mass to 4% by mass. By setting the binder content within this range, the positive electrode active material can be stably maintained.

[0105] The content of the thickener in the positive electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, or the positive electrode active material layer may be substantially free of thickener.

[0106] The content of the filler in the positive electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, or the positive electrode active material layer may be substantially free of filler.

[0107] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0108] The average thickness of the positive electrode active material layer is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the positive electrode active material layer to the above lower limit or more, a nonaqueous electrolyte storage element having a high energy density can be obtained. By setting the average thickness of the positive electrode active material layer to the above upper limit or less, it is possible to achieve miniaturization of the nonaqueous electrolyte storage element.

[0109] (Negative Electrode) In the nonaqueous electrolyte storage element according to one embodiment of the present invention, the above-described negative electrode for a nonaqueous electrolyte storage element according to one embodiment of the present invention is used as the negative electrode.

[0110] (Isolation Layer) The isolation layer usually contains a solid electrolyte. The content of the solid electrolyte in the isolation layer is preferably 70% by mass or more, more preferably 80% by mass or more, and may be 90% by mass or more.

[0111] The isolation layer may contain an additive (e.g., Li ３ P.O. ４ The negative electrode active material layer may contain optional components such as phosphate compounds, oxides, and halogen compounds (such as phosphate compounds, oxides, and halogen compounds), binders, thickeners, and fillers. The optional components such as binders, thickeners, and fillers can be selected from the materials exemplified for the negative electrode active material layer.

[0112] The average thickness of the separator is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 50 μm or less, and even more preferably 3 μm or more and 20 μm or less. By setting the average thickness of the separator to be equal to or greater than the lower limit, it is possible to insulate the positive electrode and the negative electrode with high reliability. By setting the average thickness of the separator to be equal to or less than the upper limit, it is possible to increase the energy density of the nonaqueous electrolyte storage element.

[0113] (Container) The container accommodates the positive electrode, negative electrode, etc. in its internal space. Materials for the container include metal materials such as aluminum and stainless steel, and resin materials, with metal materials being preferred from the viewpoint of strength, etc. Composite materials of metal materials and resin materials can also be used.

[0114] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the form of a sheet, etc.

[0115] A nonaqueous electrolyte storage element 1 shown in FIG. 1 , which is one embodiment of the present invention, is an all-solid-state secondary battery, and includes a positive electrode 2 and a negative electrode 3 disposed with a separator 4 interposed therebetween. The positive electrode 2 includes a positive electrode substrate 5 and a positive electrode active material layer 6, with the positive electrode substrate 5 forming the outermost layer of the positive electrode 2. The negative electrode 3 includes a negative electrode substrate 7 and a negative electrode active material layer 8, with the negative electrode substrate 7 forming the outermost layer of the negative electrode 2. In the nonaqueous electrolyte storage element 1 shown in FIG. 1 , the negative electrode active material layer 8, the separator 4, the positive electrode active material layer 6, and the 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 nonaqueous electrolyte storage element according to one embodiment of the present invention may further include other components, such as a container. Other components, such as a container, are omitted from the nonaqueous electrolyte storage element 1 shown in FIG. 1 .

[0116] The nonaqueous electrolyte 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 in 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.

[0117] FIG. 2 shows a nonaqueous electrolyte storage element 1A, which has a different configuration from the nonaqueous electrolyte storage element 1 shown in FIG. 1 . Like the nonaqueous electrolyte storage element 1, the nonaqueous electrolyte storage element 1A is an all-solid-state secondary battery in which a positive electrode 2A and a negative electrode 3A are arranged with an isolating layer 4A interposed therebetween. The positive electrode 2A has a positive electrode substrate 5A and a positive electrode active material layer 6A, with the positive electrode substrate 5A forming the outermost layer of the positive electrode 2A. The negative electrode 3A has a negative electrode substrate 7A and a negative electrode active material layer 8A, with the negative electrode substrate 7A forming the outermost layer of the negative electrode 2A. In the nonaqueous electrolyte storage element 1A, an isolating layer 4A is also disposed on the side surface of the negative electrode active material layer 8A. In this embodiment, the isolating layer 4A is laminated so as to be in contact with the negative electrode substrate 7A and the negative electrode active material layer 8A. The negative electrode active material layer 8A has a structure in which the entire outer surface is covered with other members (the negative electrode substrate 7A and the isolating layer 4A). The side surfaces of the negative electrode active material layer may be covered with an electrically insulating member separate from the separator layer. In the nonaqueous electrolyte storage element 1A having such a structure, the mechanical strength of the negative electrode active material layer 8A is further increased, which further suppresses the occurrence of cracks in the negative electrode active material layer and further increases the initial coulombic efficiency of the nonaqueous electrolyte storage element.

[0118] <Electricity Storage Device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0119] 3 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0120] <Method for manufacturing nonaqueous electrolyte storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode mixture, preparing a separator material, preparing a negative electrode mixture, and laminating the positive electrode, the separator, and the negative electrode.

[0121] Preparing a positive electrode mixture may mean producing a positive electrode mixture. The method for preparing the positive electrode mixture is not particularly limited and can be appropriately selected depending on the purpose. For example, the positive electrode mixture can be prepared by mixing a positive electrode active material and a solid electrolyte using a mechanical milling method or the like. The positive electrode mixture may be in the form of a paste containing a dispersion medium.

[0122] Preparing an isolation layer material may mean producing an isolation layer material. A solid electrolyte as an isolation layer material can be produced by a conventionally known method. For example, it can be obtained by treating a predetermined material by mechanical milling. The isolation layer material may be produced by heating a predetermined material to a melting temperature or higher by melt-quenching, melt-mixing the two at a predetermined ratio, and then quenching. Other methods for producing an isolation layer material include, for example, a solid-phase method in which the material is sintered under reduced pressure, a liquid-phase method such as solution deposition, a gas-phase method (PLD), or a method in which the material is sintered under an argon atmosphere after treatment by mechanical milling. The isolation layer material may be in the form of a paste containing a dispersion medium.

[0123] Preparing the negative electrode mixture may mean producing a negative electrode mixture. The method for preparing the negative electrode mixture is not particularly limited and can be appropriately selected depending on the purpose. For example, the negative electrode mixture can be prepared by mixing a negative electrode active material, a solid electrolyte, a conductive agent, etc. using a mechanical milling method or the like. The negative electrode mixture may be in a paste form containing a dispersion medium. Note that, from the viewpoint of improving the dispersibility of SWCNTs, it is preferable to use a paste negative electrode mixture containing a dispersion medium.

[0124] By stacking a positive electrode, a separator, and a negative electrode, for example, a positive electrode having a positive electrode substrate and a positive electrode active material layer, a separator, and a negative electrode having a negative electrode substrate and a negative electrode active material layer are stacked. In this process, the positive electrode, the separator, and the negative electrode may be formed sequentially in this order, or vice versa, and the order of forming each layer is not particularly important. For example, the positive electrode is formed by pressure molding a positive electrode substrate and a positive electrode mixture, the separator is formed by pressure molding an separator material, and the negative electrode is formed by pressure molding a negative electrode substrate and a negative electrode mixture. The positive electrode, the separator, and the negative electrode may be stacked by pressure molding the positive electrode substrate, the positive electrode mixture, the separator material, the negative electrode mixture, and the negative electrode substrate all at once. The positive electrode and the negative electrode may be formed in advance, and then pressure molded and stacked with the separator.

[0125] The positive electrode active material layer, the negative electrode active material layer, and the separator layer may be formed by coating. For example, a positive electrode active material layer can be formed by coating a paste-like positive electrode mixture on the surface of a positive electrode substrate and drying the mixture. Similarly, a negative electrode active material layer can be formed by coating a paste-like negative electrode mixture on the surface of a negative electrode substrate and drying the mixture. A separator layer can be formed by coating a paste-like separator material on the surface of a positive electrode active material layer or a negative electrode active material layer and drying the material. Thereafter, for example, a laminate (positive electrode) of a positive electrode substrate and a positive electrode active material layer and a laminate (a laminate (negative electrode and separator)) of a negative electrode substrate, a negative electrode active material layer, and a separator layer are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator layer, and then subjected to hot pressing or the like to obtain a nonaqueous electrolyte storage element. A laminate of a positive electrode substrate, a positive electrode active material layer, and a separator layer (a laminate of a positive electrode and a separator layer) and a laminate of a negative electrode and a separator layer may be arranged so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator layer interposed therebetween to obtain a nonaqueous electrolyte storage element.

[0126] The lamination of each layer may be performed by combining coating and pressure molding. The lamination of each layer may be performed, for example, by providing a layer on another substrate by coating or the like and then transferring this layer.

[0127] <Other Embodiments> The negative electrode for a nonaqueous electrolyte storage element and the nonaqueous electrolyte storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0128] For example, the nonaqueous electrolyte storage element according to the present invention may include layers other than the positive electrode, separator, and negative electrode. The nonaqueous electrolyte storage element according to the present invention may contain a liquid. Examples of such nonaqueous electrolyte storage elements include a nonaqueous electrolyte storage element in which voids in the positive electrode active material layer 6, separator 4, negative electrode active material layer 8, etc. in the nonaqueous electrolyte storage element 1 described above are filled with a nonaqueous electrolyte solution. The nonaqueous electrolyte storage element according to the present invention may be a secondary battery or a capacitor.

[0129] 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.

[0130] [Example 1] A positive electrode was obtained by laminating a positive electrode active material layer having a square shape in plan view of 2.0 cm x 2.0 cm on the surface of an aluminum foil having a size of 2.5 cm x 2.5 cm. ３／５ Co １／５ Mn １／５ O ２The cathode mixture was formed from a paste of an argyrodite-type sulfide solid electrolyte, fibrous carbon (VGCF (registered trademark) manufactured by Showa Denko Materials) as a conductive agent, styrene butadiene rubber (SBR) as a binder, and butyl butyrate as a dispersion medium. The mass ratio of the positive electrode active material, solid electrolyte, conductive agent, and binder was 76:20:2:2 in terms of solid content. Next, an argyrodite-type sulfide solid electrolyte was laminated as an isolation layer on the surface of the positive electrode active material layer to obtain a first laminate (a laminate of a positive electrode and an isolation layer). A negative electrode active material with an average particle size of 3.0 μm and a BET specific surface area of ​​3.5 m was used. ２ / g, total pore volume 0.015 cm ３ A non-porous silicon element (Si) having a pore size of 9.7 nm and an average porosity of 3.5% was prepared. The silicon element (Si) as the negative electrode active material, an argyrodite-type sulfide solid electrolyte (SE), SWCNT (average diameter 1.6 nm, average length greater than 5 μm) as a conductive agent, and fibrous carbon other than SWCNT ("VGCF" (registered trademark) manufactured by Showa Denko Materials Co., Ltd.), and SBR as a binder were mixed, and butyl butyrate was added as a dispersion medium to prepare a paste-like negative electrode mixture. The mass ratio of the negative electrode active material (Si), the solid electrolyte (SE), the SWCNT, the VGCF, and the binder (SBR) was 44.0:50.0:0.5:2.5:3.0 in terms of solid content. The paste-like negative electrode mixture was applied to a 2.1 cm × 2.1 cm copper foil negative electrode substrate so as to completely cover the surface, and then dried to form a negative electrode active material layer, thereby obtaining a second laminate (negative electrode). The first laminate and the second laminate were overlapped with each other so that the positive electrode active material layer and the negative electrode active material layer faced each other via the separator layer, and then hot-pressed to obtain the nonaqueous electrolyte storage element of Example 1. The nonaqueous electrolyte storage element was fabricated in an argon atmosphere with a dew point of −50° C. or lower.

[0131] [Examples 2 to 5, Comparative Examples 1 to 5] The nonaqueous electrolyte storage elements of Examples 2 to 5 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the composition of the negative electrode active material layer (negative electrode mixture) was changed as shown in Table 1.

[0132] In Table 1, Gr denotes graphite, MWCNT(a) denotes MWCNT with an average diameter of about 7 to 15 nm and an average length of about 5 to 15 μm, and MWCNT(b) denotes MWCNT with an average diameter of about 60 to 100 nm and an average length of more than 5 μm. In Example 5 and Comparative Examples 2 and 3, a graphite having an average particle diameter of 0.8 μm and a BET specific surface area of ​​26.6 m was used as the negative electrode active material. ２ / g, total pore volume 0.079 cm ３ Non-porous elemental silicon (Si) having a pore size of 6.2 nm and an average porosity of 18.5% was used.

[0133] [Initial Charge / Discharge] Each of the obtained nonaqueous electrolyte storage elements was initially charged and discharged at 25°C as follows. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed at a current of 0.1 C with a discharge cut-off voltage of 2.50 V. 1 C was defined as 24 mA. The percentage of the discharge capacity relative to the initial charge capacity was calculated as the initial coulombic efficiency. The results are shown in Table 1.

[0134]

[0135] As shown in Table 1, the nonaqueous electrolyte storage elements of Comparative Examples 1 to 5, each of which had a negative electrode whose negative electrode active material layer did not contain SWCNT, had an initial Coulombic efficiency of 80% or less. In contrast, the nonaqueous electrolyte storage elements of Examples 1 to 5, each of which had a negative electrode whose negative electrode active material layer contained SWCNT, had an initial Coulombic efficiency of greater than 80%, indicating high initial Coulombic efficiency. Comparisons between Example 1 and Comparative Example 1, in which elemental silicon (Si) having an average particle size of 3.0 μm was used as the negative electrode active material, and Example 5 and Comparative Example 2, in which Si having an average particle size of 0.8 μm was used as the negative electrode active material, confirm that the effect of SWCNT on improving the initial Coulombic efficiency is significant when elemental silicon (Si), which has a relatively large average particle size and is alloyed with lithium, is used as the negative electrode active material.

[0136] [Examples 6 to 16] LiNi as a positive electrode active material ０．８０ Co ０．１５ Al ０．０５ O２ The nonaqueous electrolyte storage elements of Examples 6 to 16 were obtained in the same manner as in Example 1, except that the composition of the negative electrode active material layer (negative electrode mixture) was changed as shown in Tables 2 to 4.

[0137] [Initial Charge / Discharge] The obtained nonaqueous electrolyte storage elements of Examples 6 to 16 were initially charged and discharged at 25°C as follows. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed at a current of 0.1 C with a discharge cut-off voltage of 2.50 V. Note that 1 C was 24 mA.

[0138] [High-Rate Discharge Test (Discharge Capacity Ratio (1.0 C / 0.1 C))] After the "initial charge / discharge" test, a high-rate discharge test was conducted at 25°C for each of the nonaqueous electrolyte storage elements of Examples 6 to 16 in the following manner. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed at a current of 1.0 C with a discharge cut-off voltage of 2.50 V. The percentage of the discharge capacity at a current of 1.0 C in the "high-rate discharge test" relative to the discharge capacity at a current of 0.1 C in the "initial charge / discharge" test was calculated as the discharge capacity ratio (1.0 C / 0.1 C). The results are shown in Tables 2 to 4.

[0139] [Charge-Discharge Cycle Test] After the "high-rate discharge test," each of the nonaqueous electrolyte storage elements of Examples 6 to 13 was subjected to a charge-discharge cycle test at 25°C as follows. Constant-current, constant-voltage charging was performed at a current of 0.3 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.1 C. Thereafter, constant-current discharging was performed at a current of 0.3 C with a discharge cut-off voltage of 2.50 V. A 10-minute pause was provided after discharge and after charge. The above charge and discharge cycles were repeated 300 times. The percentage of the discharge capacity at the 300th cycle relative to the discharge capacity at the first cycle in the charge-discharge cycle test was calculated as the post-cycle capacity retention rate. The results are shown in Tables 2 and 3.

[0140]

[0141]

[0142]

[0143] As shown in Table 2, the larger the average particle size of silicon (Si), a substance that alloys with lithium, the higher the discharge capacity ratio (1.0 C / 0.1 C), and the more effectively the discharge capacity was suppressed during high-rate discharge. The larger the average particle size of silicon (Si), the more effectively the negative electrode active material layer was suppressed from cracking after the high-rate discharge test. It is believed that the use of silicon (Si) with a larger average particle size suppresses the occurrence of cracks in the negative electrode active material layer even during high-rate discharge, thereby suppressing the decrease in discharge capacity. On the other hand, as shown in Table 2, the smaller the average particle size of silicon (Si), the higher the post-cycle capacity retention rate. The initial coulombic efficiency of each nonaqueous electrolyte storage element in Table 2 was in the range of 87% to 88%, and the initial coulombic efficiency was also high. Furthermore, as shown in Tables 3 and 4, the discharge capacity ratio (1.0 C / 0.1 C) increased as the content of elemental silicon (Si) in the negative electrode active material layer decreased, and the decrease in discharge capacity during high-rate discharge was suppressed.

[0144] [Examples 17 to 22, Comparative Example 6] LiNi as the positive electrode active material ０．８０ Co ０．１５ Al ０．０５ O ２ The nonaqueous electrolyte storage elements of Examples 17 to 22 and Comparative Example 6 were obtained in the same manner as in Example 1, except that the composition of the negative electrode active material layer (negative electrode mixture) was changed as shown in Table 5. The conductive agents used in these Examples and Comparative Examples and listed in Table 5 are as follows: SWCNT: average diameter 1.6 nm, average length greater than 5 μm, BET specific surface area 1040 m ２ / g VGCF: average diameter 150 nm, average length 10 to 20 μm, BET specific surface area 13 m ２ / g MWCNT (A): average diameter 7 to 15 nm, average length 5 to 15 μm, BET specific surface area 200 to 250 m ２ / g MWCNT (B): average diameter 20 to 40 nm, average length less than 2 μm, BET specific surface area 70 to 150 m ２ / g MWCNT (C): average diameter 60 to 100 nm, average length more than 5 μm, BET specific surface area 40 to 70 m ２ / g MWCNT (D): average diameter 20 to 60 nm, average length 7 μm AB (acetylene black): average particle size 35 nm, BET specific surface area 68 m ２ / g

[0145] [Initial Charge / Discharge] The obtained nonaqueous electrolyte storage elements of Examples 17 to 22 and Comparative Example 6 were initially charged and discharged at 25°C in the following manner. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed at a current of 0.1 C with a discharge cut-off voltage of 2.50 V. 1 C was defined as 24 mA. The discharge capacity at this time was defined as the initial discharge capacity.

[0146] [Measurement of Discharge Capacity Retention Rate After High-Rate Discharge Test] A high-rate discharge test was performed at 25°C on each of the nonaqueous electrolyte storage elements of Examples 17 to 22 and Comparative Example 6 after the "initial charge / discharge" described above, as follows. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 4.25 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed at a current of 0.1 C with a discharge cut-off voltage of 2.50 V. Next, constant-current, constant-voltage charging was performed under the same conditions as above, and after a 10-minute rest period, constant-current discharging was performed at a current of 1.0 C with a discharge cut-off voltage of 2.50 V as a high-rate discharge, followed by constant-current discharging at a current of 0.1 C with a discharge cut-off voltage of 2.50 V as a residual discharge. Next, a high-rate discharge test was performed using the same constant-current / constant-voltage charging conditions, resting conditions, and residual discharge conditions as above, with the high-rate discharge current sequentially changed to 2.0 C, 3.0 C, and 5.0 C. Charge and discharge were then performed under the same conditions as in the "initial charge / discharge" test, and the discharge capacity after the high-rate discharge test was measured. The percentage of the discharge capacity after the high-rate discharge test relative to the initial discharge capacity was calculated as the discharge capacity retention rate after the high-rate discharge test. The results are shown in Table 5.

[0147]

[0148] As shown in Table 5, the nonaqueous electrolyte storage elements of Examples 17 to 22, in which the conductive agent contained SWCNT, had a discharge capacity retention rate of 90% or more after the high-rate discharge test, and the decrease in discharge capacity after high-rate discharge was suppressed. In particular, the nonaqueous electrolyte storage elements of Example 17, which used VGCF, a fibrous conductive agent having an average diameter of 120 nm or more, together with SWCNT as the conductive agent; Example 18, which used AB, a particulate conductive agent, together with SWCNT as the conductive agent; and Example 19, which used SWCNT alone as the conductive agent, had a discharge capacity retention rate of 99% or more after the high-rate discharge test, and the decrease in discharge capacity after high-rate discharge was particularly suppressed. The initial coulombic efficiency of each of the nonaqueous electrolyte storage elements in Table 5 was also high, with an initial coulombic efficiency ranging from 87% to 89%.

[0149] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0150] 1, 1A Non-aqueous electrolyte electricity storage element 2, 2A Positive electrode 3, 3A Negative electrode 4, 4A Separation layer 5, 5A Positive electrode base material 6, 6A Positive electrode active material layer 7, 7A Negative electrode base material 8, 8A Negative electrode active material layer 20 Energy storage unit 30 Energy storage device

Claims

1. A negative electrode for a non-aqueous electrolyte storage element, comprising a negative electrode active material layer containing a negative electrode active material, a solid electrolyte, and a conductive agent, the negative electrode active material containing a substance that alloys with lithium element, and the conductive agent containing single-walled carbon nanotubes.

2. The negative electrode for a non-aqueous electrolyte storage element according to claim 1, wherein the content of the single-walled carbon nanotubes in the negative electrode active material layer is from 0.1% by mass to 3% by mass.

3. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the content of the fibrous conductive agent in the conductive agent is 90 mass % or more.

4. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the content of the single-walled carbon nanotubes in the negative electrode active material layer is 0.3 mass % or more.

5. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the substance that is alloyed with the lithium element does not have a three-dimensional network structure.

6. The negative electrode for a nonaqueous electrolyte storage element according to claim 1 or 2, wherein the substance that forms an alloy with lithium has an average pore size of 30 nm or less.

7. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the substance which forms an alloy with lithium has an average particle size of 0.6 μm or more.

8. The negative electrode for a nonaqueous electrolyte storage element according to claim 1 or 2, wherein the substance that forms an alloy with lithium has an average particle size of 1.5 μm or more.

9. The BET specific surface area of ​​the material alloyed with the lithium element is 8.0 m ２ The negative electrode for a nonaqueous electrolyte storage element according to claim 1 or 2, wherein the molecular weight of the negative electrode is 1 / g or less.

10. A negative electrode for a non-aqueous electrolyte storage element as set forth in claim 1 or 2, wherein the content of the substance that can be alloyed with the lithium element in the negative electrode active material layer is 45 mass % or less.

11. The negative electrode for a nonaqueous electrolyte storage element according to claim 1 or 2, wherein the conductive agent further comprises at least one type selected from the group consisting of fibrous conductive agents having an average diameter of 120 nm or more and particulate conductive agents.

12. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the content of the single-walled carbon nanotubes in the conductive agent is 50 mass % or more.

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

14. The nonaqueous electrolyte electricity storage element according to claim 13, which is an all-solid-state electricity storage element.