Anode for all-solid-state lithium secondary batteries and all-solid-state lithium secondary batteries

Abstract

The present invention aims to provide a negative electrode for an all-solid-state lithium secondary battery in which the negative electrode active material layer does not contain an inorganic solid electrolyte and consists only of a negative electrode active material containing graphite particles (graphite negative electrode active material layer), and in which lithium ions move easily in the direction perpendicular to the plane of the layer. Furthermore, the invention aims to provide a high-capacity all-solid-state lithium secondary battery with high energy density and excellent charge / discharge characteristics at room temperature by using this negative electrode. [Solution] According to the present invention, a negative electrode for an all-solid-state lithium secondary battery is provided, comprising a graphite negative electrode active material layer, wherein the graphite negative electrode active material layer comprises graphite particles whose surface is coated with amorphous carbon (but does not contain an inorganic solid electrolyte), and the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for an all-solid-state lithium secondary battery, which includes a graphite negative electrode active material layer containing a predetermined amount of graphite particles whose surface is coated with amorphous carbon, but which does not contain an inorganic solid electrolyte, and to an all-solid-state lithium secondary battery containing said negative electrode. [Background technology]

[0002] High-capacity rechargeable batteries are used in a wide variety of applications, including electric vehicles (including hybrids), energy sources for electronic devices, and energy storage systems for renewable energy sources such as solar cells. However, to realize a low-carbon, smart society, there is a need for rechargeable batteries with even higher capacities and superior charge / discharge characteristics.

[0003] Lithium-ion batteries (also called lithium-ion secondary batteries), which began production in the 1990s and use organic non-aqueous electrolytes, can achieve a higher operating voltage than conventional secondary batteries using aqueous electrolytes, thereby improving energy density. For this reason, they are used in a wide range of fields, including small portable electronic devices. For example, lithium-ion batteries have been reported that use carbon materials such as highly graphitic carbonaceous or multilayer carbonaceous powder materials as the negative electrode material, and a liquid organic non-aqueous electrolyte as the electrolyte (Patent Documents 1 to 5). In these lithium-ion batteries, the organic electrolyte, simply by being poured into the battery system, permeates into the porous graphite negative electrode active material layer and bonds with the graphite particles, which are the negative electrode active material, over a wide reaction area, thereby imparting ionic conductivity to the entire negative electrode plate.

[0004] However, as the range of applications has expanded from small portable electronic devices to automobiles, the limitations of conventional lithium-ion batteries in terms of capacity and safety are beginning to become apparent. To address the need for even higher capacity, improved safety, and faster charging in the future, all-solid-state batteries, which use solid electrolytes that offer high capacity, superior safety, and ease of handling, are expected to be developed.

[0005] Among all-solid-state lithium secondary batteries using solid electrolytes, all-solid-state lithium secondary batteries using sulfide inorganic solid electrolytes (hereinafter also referred to as "sulfide-type all-solid-state lithium secondary batteries") and all-solid-state lithium secondary batteries using oxide inorganic solid electrolytes (hereinafter also referred to as "oxide-type all-solid-state lithium secondary batteries") have attracted particular attention (Patent Documents 6, 7, and Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3712288 [Patent Document 2] Patent No. 3193342 [Patent Document 3] Patent No. 3534391 [Patent Document 4] Patent No. 6229775 [Patent Document 5] Patent No. 6528826 [Patent Document 6] Japanese Patent Publication No. 2011-134617 [Patent Document 7] International Publication No. 2024 / 063014 [Non-patent literature]

[0007] [Non-Patent Document 1] ACS Energy Lett., 2020, 5, 2995-3004 [Overview of the project] [Problems that the invention aims to solve]

[0008] In all-solid-state lithium secondary batteries, particles made from graphite, a layered material (i.e., graphite particles), are generally used as the negative electrode active material, and the negative electrode active material layer is manufactured using these graphite particles. Therefore, because the negative electrode active material layer contains graphite particles as the negative electrode active material, it is sometimes simply referred to as the "graphite negative electrode active material layer." In this case, the movement of lithium ions is limited to the interlayers and intralayer defects of the graphite in the negative electrode active material layer, as well as the contact points between particles. Therefore, the utilization rate of the graphite particles, which are the negative electrode active material (hereinafter also referred to as "graphite negative electrode active material particles"), is limited to the extent of the lithium ion movement restrictions. In other words, the energy density of the all-solid-state lithium secondary battery is limited to the extent of the lithium ion movement restrictions. Therefore, in order to improve the energy density of the all-solid-state lithium secondary battery, it is necessary to increase the utilization rate of the graphite particles, which are the negative electrode active material, and to achieve reversible insertion and removal of lithium ions. Specifically, for all-solid-state lithium secondary batteries, it is necessary to introduce a configuration that can improve the restriction of lithium ion movement perpendicular to the plane of the graphite negative electrode active material layer even after the graphite negative electrode active material layer has been fabricated by compaction molding. Therefore, in typical all-solid-state lithium secondary batteries, a composite electrode is used as the negative electrode (negative electrode layer), which is a composite layer in which graphite particles, which are the negative electrode active material, and inorganic solid electrolyte particles that ensure the movement of lithium ions are mixed. Hereafter, this composite layer may also be referred to as the "negative electrode composite layer."

[0009] For example, in sulfide-type all-solid-state lithium secondary batteries, which are expected to be put into practical use in automobiles, a composite electrode is generally used, in which a mixture of inorganic solid electrolyte particles and graphite particles, which are the negative electrode active material, is used as the negative electrode. In this case, the composite electrode is generally manufactured by cold-pressing the mixture. By using this composite electrode, bonding between electrolyte particles and bonding between the electrolyte and the graphite negative electrode active material particles is facilitated.

[0010] However, in all-solid-state lithium secondary batteries, unlike lithium secondary batteries that use an electrolyte, it is not possible to impregnate the gaps in the active material, whose porosity has been controlled by pressing beforehand, with an electrolyte. Therefore, in order to obtain a charge / discharge capacity similar to that of lithium secondary batteries that use an electrolyte, a large amount of solid electrolyte must be mixed. Consequently, in all-solid-state lithium secondary batteries using sulfide inorganic solid electrolytes (sulfide-type all-solid-state lithium secondary batteries), even when using a composite electrode with a mixture of inorganic solid electrolyte particles and graphite negative electrode active material particles as the negative electrode, it is difficult to obtain an energy density similar to that of lithium secondary batteries that use an electrolyte. In this regard, there are reports that, as the negative electrode of sulfide-type all-solid-state lithium secondary batteries, a mixture of sulfide inorganic solid electrolyte particles and graphite negative electrode active material particles, which is commonly used as a composite electrode, is not used, but rather a negative electrode (diffusion-dependent electrode) using a mixture of graphite negative electrode active material particles consisting only of natural graphite particles and a binder is used (Non-Patent Literature 1).

[0011] Furthermore, in all-solid-state lithium secondary batteries using oxide inorganic solid electrolytes (oxide-type all-solid-state lithium secondary batteries), co-sintering of oxide inorganic solid electrolyte particles and graphite particles, which are the negative electrode active material, is generally carried out in an oxidizing atmosphere. However, because graphite is difficult to sinter, contact between the oxide inorganic solid electrolyte particles and the graphite particles, which are the negative electrode active material, is difficult, making it difficult to realize a low-resistance negative electrode. In this regard, an all-solid-state lithium secondary battery containing an inorganic solid electrolyte has been reported in which a highly conductive glass ceramic phase is generated in the raw glass by simultaneously firing a negative electrode precursor layer made from a mixture of raw glass powder of LISICON-type lithium-ion conductive glass ceramics and a carbon precursor that carbonizes by firing, such as phenolic resin, and graphite, thereby imparting ionic conductivity and electronic conductivity and enabling charging and discharging (Patent Document 6). Furthermore, as an oxide-type all-solid-state lithium secondary battery, an all-solid-state lithium secondary battery has also been reported in which a metal or semimetallic layer containing an element that alloys lithium is provided at the interface between the separator layer, which is made of an oxide solid electrolyte, and the negative electrode active material layer, which is made of graphite (specifically, ordinary graphite or a material mainly composed of such graphite), thereby creating a low-resistance junction between the oxide solid electrolyte of the separator layer and the graphite of the negative electrode active material layer at room temperature without firing (Patent Document 7).

[0012] However, regardless of whether the solid electrolyte used in an all-solid-state lithium secondary battery is a sulfide inorganic solid electrolyte or an oxide inorganic solid electrolyte, there is currently no negative electrode for all-solid-state lithium secondary batteries that improves the restriction of lithium ion movement in the direction perpendicular to the plane of the negative electrode active material layer, thereby facilitating such movement, resulting in a high utilization rate of the negative electrode active material and enabling reversible operation of the all-solid-state battery even at room temperature. Therefore, the development of such a negative electrode is highly desired. Furthermore, if the negative electrode active material layer constituting the negative electrode consists only of the negative electrode active material without mixing it with an inorganic solid electrolyte to ensure lithium ion movement, high-temperature sintering for joining the negative electrode active material and the inorganic solid electrolyte becomes unnecessary. Also, because the inorganic solid electrolyte is not mixed, the proportion of the negative electrode active material in the negative electrode increases, which can lead to a further improvement in the battery capacity of the all-solid-state lithium secondary battery.

[0013] Therefore, the object of the present invention is to provide a negative electrode for an all-solid-state lithium secondary battery in which the negative electrode active material layer does not contain an inorganic solid electrolyte and consists only of a negative electrode active material containing graphite particles (graphite negative electrode active material layer), and in which lithium ions move easily in the direction perpendicular to the plane of the layer, and to provide a high-capacity all-solid-state lithium secondary battery with high energy density and excellent charge / discharge characteristics at room temperature by using said negative electrode. [Means for solving the problem]

[0014] As a result of diligent research, the present inventors have found that the above problems can be solved by using a negative electrode for an all-solid-state lithium secondary battery that includes a graphite negative electrode active material layer, wherein the graphite negative electrode active material layer includes graphite particles whose surface is coated with amorphous carbon, and the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer, and have thus completed the present invention.

[0015] The present invention has, in particular, the following embodiments [1] to

[12] . [1] A negative electrode for an all-solid-state lithium secondary battery comprising a graphite negative electrode active material layer, The graphite negative electrode active material layer contains graphite particles whose surface is coated with amorphous carbon (however, it does not contain an inorganic solid electrolyte), The negative electrode for an all-solid-state lithium secondary battery, wherein the content of the graphite particles in the graphite negative electrode active material layer is 50% by weight or more. [2] The negative electrode for an all-solid-state lithium secondary battery according to [1], wherein the graphite particles whose surface is coated with amorphous carbon have the following physical properties: • The average particle size d50 is between 3 μm and 40 μm; • BET specific surface area is 0.5m² 2 / g or more 10m 2 It is less than or equal to / g; • Tap density is 0.7 g / cm³ 3 More than 1.20g / cm 3The following: 1580cm -1 The peak PA intensity IA and 1360cm -1 The Raman R value, expressed by the following formula 1 as the intensity ratio of the peak PB to the intensity IB, is between 0.01 and 1: Equation 1: Raman R-value = IB / IA; • The interlayer distance d002 of the lattice plane (002 plane) determined by X-ray diffraction is 0.334 nm or more and 0.340 nm or less; and • The degree of circularity is 0.8 or higher. [3] The negative electrode according to [1] or [2], wherein the DTA curve obtained by performing TG-DTA measurement on graphite particles whose surface is coated with amorphous carbon satisfies the following equation 2, with a first peak on the relatively low temperature side and a second peak on the relatively high temperature side occurring in the range of 500°C to 1000°C: Equation 2: (DTA [μV] at the first peak) / (DTA [μV] at the second peak) ≥ 0.15. [4] The negative electrode for an all-solid-state lithium secondary battery according to any one of [1] to [3], wherein the graphite negative electrode active material layer comprises graphite particles whose surface is coated with amorphous carbon alone, or graphite particles whose surface is coated with amorphous carbon and graphite particles different from the graphite particles whose surface is coated with amorphous carbon. [5] The negative electrode for an all-solid-state lithium secondary battery according to any one of [1] to [4], wherein the graphite negative electrode active material layer contains natural graphite. [6] The negative electrode for an all-solid-state lithium secondary battery according to any one of [1] to [5], further comprising a graphite negative electrode active material layer that can absorb less than 10% lithium ions. [7] Positive electrode and, A solid electrolyte separator layer, A negative electrode for an all-solid-state lithium secondary battery as described in any of [1] to [6], All-solid-state lithium secondary batteries, including... [8] The all-solid-state lithium secondary battery according to [7], wherein the solid electrolyte separator layer is an inorganic solid electrolyte separator layer. [9] The all-solid-state lithium secondary battery according to [8], wherein the inorganic solid electrolyte separator layer is a layer made of a sulfide inorganic solid electrolyte.

[10] The all-solid-state lithium secondary battery according to [8], wherein the inorganic solid electrolyte separator layer is a layer made of an oxide inorganic solid electrolyte.

[11] The graphite negative electrode active material layer is provided on the solid electrolyte separator layer, An all-solid-state lithium secondary battery according to any one of [7], [8], and

[10] , comprising a layer made of a metal or metalloid containing an element for alloying lithium at the interface between the solid electrolyte separator layer and the graphite negative electrode active material layer.

[12] The all-solid-state lithium secondary battery according to

[11] , wherein the metallic material or metalloid material contained in the layer made of a metal or metalloid containing an element for alloying lithium is a material made of at least one element selected from the group consisting of gold, silver, platinum, aluminum, tin, indium, germanium, lead, zinc, antimony, magnesium, silicon, cadmium, gallium, tellurium, and bismuth. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a negative electrode in which lithium ions can easily move in the direction perpendicular to the plane of the graphite negative electrode active material layer, regardless of whether it is a sulfide inorganic solid electrolyte or an oxide inorganic solid electrolyte. As a result, it is possible to provide a negative electrode with a high utilization rate of the negative electrode active material and that can reversibly operate the all-solid-state battery even at room temperature. Therefore, an all-solid-state lithium secondary battery using the negative electrode of the present invention can provide a high-capacity all-solid-state lithium secondary battery with high energy density and excellent charge / discharge characteristics at room temperature, regardless of whether it is a sulfide inorganic solid electrolyte or an oxide inorganic solid electrolyte.

[0017] According to the present invention, since the negative electrode active material layer does not contain an inorganic solid electrolyte, regardless of whether it is a sulfide inorganic solid electrolyte or an oxide inorganic solid electrolyte, it is possible to provide a negative electrode for an all-solid-state lithium secondary battery without requiring high-temperature sintering, as is done with conventional oxide inorganic solid electrolytes, to join the negative electrode active material and the inorganic solid electrolyte. Furthermore, because no inorganic solid electrolyte is mixed, regardless of whether it is a sulfide inorganic solid electrolyte or an oxide inorganic solid electrolyte, the proportion of the negative electrode active material in the negative electrode can be increased, thereby further improving the battery capacity of an all-solid-state lithium secondary battery using the negative electrode of the present invention.

[0018] As a result, the present invention can specifically achieve the following effects.

[0019] According to one aspect of the present invention, conventional sulfide-type all-solid-state lithium secondary batteries (Non-Patent Literature 1) that use a negative electrode (diffusion-dependent electrode) made of a mixture of graphite negative electrode active material particles consisting only of natural graphite particles and a binder, instead of using a mixture of sulfide inorganic solid electrolyte particles and graphite negative electrode active material particles, which are commonly used as composite electrodes, require heating to 60°C and constant current constant voltage (CCCV) charging. Furthermore, if the negative electrode (diffusion-dependent electrode) is made thicker to increase the packing density, the diffusion resistance of lithium ions in the direction perpendicular to the plane of the negative electrode (i.e., perpendicular to the plane of the negative electrode plate) becomes large, limiting the capacity and preventing the realization of a high-energy-density sulfide-type all-solid-state lithium secondary battery negative electrode that can be charged at room temperature by constant current (CC) charging alone.

[0020] According to another further aspect of the present invention, the problem that conventional oxide-type all-solid-state lithium secondary batteries (Patent Document 6) have a discharge capacity of 0.8 to 3.9 mAh / g, which is far from the theoretical capacity (372 mAh / g) when graphite is used as the negative electrode (also referred to in this application as "graphite negative electrode") can be solved.

[0021] According to another aspect of the present invention, in conventional oxide-type all-solid-state lithium secondary batteries (Patent Document 7) in which a metal or semimetallic layer containing an element that alloys lithium is provided at the interface between a separator layer made of an oxide solid electrolyte and a negative electrode active material layer made of graphite (specifically, ordinary graphite or a material mainly composed of said graphite), a low-resistance junction is created between the oxide solid electrolyte of the separator layer and the graphite of the negative electrode active material layer at room temperature without firing, but if the graphite negative electrode active material layer is made thicker to increase the packing density, the diffusion resistance of lithium ions in the direction perpendicular to the plane of the negative electrode active material layer (i.e., the direction perpendicular to the plane of the negative electrode plate) becomes large, making it difficult to further improve the utilization rate (specifically, the utilization rate of the graphite, which is the negative electrode active material) and battery capacity while achieving operation at room temperature, this problem can be solved. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram illustrating the configuration of a type A all-solid-state lithium secondary battery. [Figure 2] This is a schematic diagram illustrating the configuration of a Type B all-solid-state lithium secondary battery. [Figure 3] This is a schematic diagram illustrating the configuration of a half-cell of a type A all-solid-state lithium secondary battery. [Figure 4] This is a schematic diagram illustrating the configuration of a half-cell of a Type B all-solid-state lithium secondary battery. [Figure 5] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 1. [Figure 6] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 2. [Figure 7] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 3. [Figure 8] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 4. [Figure 9] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 5. [Figure 10] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 1. [Figure 11] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 2. [Figure 12] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 3. [Figure 13] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 4. [Figure 14] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 5. [Figure 15] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 6. [Figure 16] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 7. [Figure 17] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 8. [Figure 18] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 6. [Figure 19] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 7. [Figure 20] This figure shows the XRD pattern of the half-cell of the all-solid-state lithium secondary battery obtained in Example 7 after the first charge. [Figure 21] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 8. [Figure 22] This figure shows the XRD pattern of the half-cell of the all-solid-state lithium secondary battery obtained in Example 8 after the first charge. [Figure 23] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 9. [Figure 24] This figure shows the XRD pattern of the half-cell of the all-solid-state lithium secondary battery obtained in Example 9 after the first charge. [Figure 25] This figure shows the initial charge-discharge curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 9. [Figure 26] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 10. [Figure 27] This figure shows the XRD pattern of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 10 after the first charge. [Figure 28] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 11. [Figure 29] This figure shows the XRD pattern of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 11 after the first charge. [Figure 30] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Example 10. [Figure 31] This figure shows the initial charging curve of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 12. [Modes for carrying out the invention]

[0023] The present invention will be described in detail below, with reference to the drawings as appropriate. However, the present invention is not limited to the matters shown in the following description and drawings, and can be modified as appropriate without changing its essence. In particular, as long as the objective of the present invention can be achieved, the battery design can be carried out using materials and configurations appropriate to the objective of the present invention.

[0024] The negative electrode for an all-solid-state lithium secondary battery of the present invention is a negative electrode for an all-solid-state lithium secondary battery comprising a graphite negative electrode active material layer, wherein the graphite negative electrode active material layer comprises graphite particles whose surface is coated with amorphous carbon (but does not contain an inorganic solid electrolyte), and the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer.

[0025] <Structure of an all-solid-state lithium secondary battery> A all-solid-state lithium secondary battery uses a solid electrolyte as the electrolyte. In the all-solid-state lithium secondary battery of the present invention, a solid electrolyte is used in the separator layer having a separator function. As an exemplary schematic diagram of a typical all-solid-state lithium secondary battery, FIGS. 1 and 2 show the all-solid-state lithium secondary battery of the present invention respectively. FIG. 1 is an embodiment when an inorganic solid electrolyte that is easily plastically deformed and easily interface-bonded, such as a sulfide inorganic solid electrolyte, is used in the separator layer, and may also be referred to as "Type A all-solid-state lithium secondary battery" in this application. FIG. 2 is an embodiment when an inorganic solid electrolyte that is difficult to plastically deform, such as an oxide inorganic solid electrolyte, is used in the separator layer, and may also be referred to as "Type B all-solid-state lithium secondary battery" in this application.

[0026] <<Configuration of Type A All-Solid-State Lithium Secondary Battery>> As shown in FIG. 1, the Type A all-solid-state lithium secondary battery (101) includes a negative electrode current collector (11), a negative electrode active material layer (12), a solid electrolyte (specific example: sulfide inorganic solid electrolyte) separator layer (13), a positive electrode active material layer (15), and a positive electrode current collector (16). Here, the negative electrode (14), which is a negative electrode layer, is formed by the negative electrode current collector (11) and the negative electrode active material layer (12), and the positive electrode (17), which is a positive electrode layer, is formed by the positive electrode active material layer (15) and the positive electrode current collector (16). Note that the negative electrode active material layer (12) may also serve as the negative electrode (14) that combines the functions of the negative electrode current collector (11) without separating the negative electrode active material layer (12) from the negative electrode current collector (11). Similarly, the positive electrode active material layer (15) may also serve as the positive electrode (17) that combines the functions of the positive electrode current collector (16) without separating the positive electrode active material layer (15) from the positive electrode current collector (16). Note that since the negative electrode active material layer (12) contains graphite particles as the negative electrode active material as described later, it is also referred to as the graphite negative electrode active material layer (12).

[0027] The sulfide inorganic solid electrolyte, which is a specific example of the solid electrolyte in the solid electrolyte separator layer (13) of the Type A all-solid-state lithium secondary battery (101), can reduce the resistance of the contact interface between the negative electrode active material layer (12) and the solid electrolyte separator layer (13) by the strong restraint pressure caused by plastic deformation.

[0028] The negative electrode current collector (11) and the positive electrode current collector (16) (hereinafter, both are also collectively referred to as the "current collector") are electrodes for the purpose of mediating the movement of electrons from one surface in contact with the positive electrode active material layer (15) to the other surface in contact with the negative electrode active material layer (12). The current collector is not particularly limited as long as it is a material having conductivity, and a metal or a resin having conductivity can be used.

[0029] In the type A all-solid-state lithium secondary battery (101), in order to reduce the interfacial resistance, it is preferable to perform pressure molding at 300 MPa or more during electrode fabrication and to constrain the battery with a constraint pressure of 100 MPa or more.

[0030] <<Configuration of Type B All-Solid-State Lithium Secondary Battery>> As shown in FIG. 2, the type B all-solid-state lithium secondary battery (201) includes a negative electrode current collector (21), a negative electrode active material layer (22), a low-resistance layer (23), a solid electrolyte (specific example: oxide inorganic solid electrolyte) separator layer (25), a positive electrode active material layer (26), and a positive electrode current collector (27). Here, a negative electrode (24) which is a negative electrode layer is formed from the negative electrode current collector (21) and the negative electrode active material layer (22), and a positive electrode (28) which is a positive electrode layer is formed from the positive electrode active material layer (26) and the positive electrode current collector (27). Note that the negative electrode active material layer (22) may also serve as the negative electrode (24) that also has the function of the negative electrode current collector (21) without separating the negative electrode active material layer (22) from the negative electrode current collector (21). Further, the positive electrode active material layer (26) may also serve as the positive electrode (28) that also has the function of the positive electrode current collector (27) without separating the positive electrode active material layer (26) from the positive electrode current collector (27). Note that since the negative electrode active material layer (22) contains graphite particles as a negative electrode active material as described later, it is also referred to as a graphite negative electrode active material layer (22).

[0031] The oxide inorganic solid electrolyte which is a specific example of the solid electrolyte of the solid electrolyte separator layer (25) in the type B all-solid-state lithium secondary battery (201) is difficult to undergo plastic deformation, so it is preferable to provide an alloy layer as the low-resistance layer (23) between the negative electrode active material layer (22) and the solid electrolyte separator layer (25) to reduce the resistance.

[0032] The negative electrode current collector (21) and the positive electrode current collector (27) (hereinafter collectively referred to as the "collecting electrodes") are electrodes intended to mediate the movement of electrons from one surface in contact with the positive electrode active material layer (26) to the other surface in contact with the negative electrode active material layer (22). The collecting electrodes are not particularly limited as long as they are made of conductive material, and metals or conductive resins can be used.

[0033] In a Type B all-solid-state lithium secondary battery (201), if a solid electrolyte that is not easily plastically deformed, such as an oxide inorganic solid electrolyte, is used as the solid electrolyte separator layer (25), the resistance at the contact interface between the negative electrode active material layer (22) and the solid electrolyte separator layer (25) cannot be reduced by pressurization. Therefore, a layer made of a metal or semimetallic material containing an element that alloys lithium (Li) is provided as a low-resistance layer (23) between the negative electrode active material layer (22) and the solid electrolyte separator layer (25) to reduce the resistance at the contact interface. As a result, the confinement pressure of the battery can be reduced to 50 MPa or less.

[0034] <<Solid electrolyte separator layer>> In the present invention, the solid electrolyte separator layer is a layer that performs the role (function) of a separator layer constituting an all-solid-state lithium secondary battery. The solid electrolyte constituting the solid electrolyte separator layer is not particularly limited as long as it can achieve the objectives of the present invention, but it is preferably an inorganic solid electrolyte. Examples of inorganic solid electrolytes include sulfide-based solid electrolytes and oxide-based solid electrolytes that have high Li ion conductivity. The solid electrolyte (especially the inorganic solid electrolyte) used in the solid electrolyte separator layer in the present invention may be one type or a mixture of two or more types. Furthermore, the solid electrolyte (especially the inorganic solid electrolyte) used in the solid electrolyte separator layer in the present invention may be used by stacking two or more solid electrolytes as separate layers in a multilayer structure. The shape of the solid electrolyte is not particularly limited as long as it can achieve the objectives of the present invention, and may be granular or sheet-like. Furthermore, the solid electrolyte (especially the inorganic solid electrolyte) used in the solid electrolyte separator layer in the present invention may optionally include other components such as binders, plasticizers, and dispersants. The proportion of solid electrolyte (particularly inorganic solid electrolyte) in the solid electrolyte separator layer in the present invention is not particularly limited as long as the objective of the present invention can be achieved, but the lower limit is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. In the present invention, it is particularly preferable that the solid electrolyte separator layer consists only of solid electrolyte (particularly inorganic solid electrolyte) (i.e., 100% by mass of solid electrolyte (particularly inorganic solid electrolyte)). Furthermore, as will be described later, a small amount of liquid electrolyte may be added to the solid electrolyte interface as an auxiliary layer to reduce ion resistance.

[0035] Methods for forming a separator layer containing an inorganic solid electrolyte include spray coating, blade coating, slit die coating, and roll coating. Alternatively, the separator layer may be formed by compression molding of the inorganic solid electrolyte powder, followed by isotropic pressing (CIP, WIP, HIP) and then sintering, or by simultaneously molding and sintering using a discharge plasma sintering method (SPS).

[0036] As described above, since the solid electrolyte constituting the solid electrolyte separator layer in the all-solid-state lithium secondary battery may be appropriately designed according to the characteristics of the solid electrolyte, it is not limited to known sulfide-based solid electrolytes or oxide-based solid electrolytes, and even a novel inorganic solid electrolyte can be used.

[0037] Regarding the solid electrolyte separator layer in the present invention, the all-solid-state lithium secondary battery (101) of type A and the all-solid-state lithium secondary battery (201) of type B will be exemplarily described below.

[0038] As the solid electrolyte constituting the solid electrolyte separator layer (13) in the all-solid-state lithium secondary battery (101) of type A, a solid electrolyte containing a sulfide of an inorganic compound or consisting only of a sulfide of an inorganic compound (also referred to as "sulfide inorganic solid electrolyte" in the present application) is preferable. Sulfide inorganic solid electrolytes are characterized by having many materials with high ionic conductivity compared to the case of using an oxide of an inorganic compound as the solid electrolyte. Examples of materials for sulfide inorganic solid electrolytes include thiolsilicon type, LGPS type, argyrodite type, Li7P3S 11 type, glasses typified by Li2S-P2S5, glass-ceramic systems, α-Li3PS4 systems with high stability to metallic lithium, etc. Specifically, Li -2 Scm -1 showing an extremely high conductivity of 10 GeP2S 12 (LGPS), a superionic conductor Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 with a conductivity more than about twice that of LGPS, Li6PS5Cl (argyrodite) Li6PS5Cl, Li7P3S 11 , Li3PS4, Li8P2S9, Li 9.6 P3S 12 etc. can be mentioned. Among these, it is preferable to use a solid electrolyte having a high ionic conductivity argyrodite type or a crystal structure similar to the argyrodite type.

[0039] In a type B all-solid-state lithium secondary battery (201), the solid electrolyte constituting the solid electrolyte separator layer (25) is preferably a solid electrolyte containing an oxide of an inorganic compound or consisting solely of an oxide of an inorganic compound (also referred to in this application as an "oxide inorganic solid electrolyte"). As the oxide inorganic solid electrolyte, a solid electrolyte having a highly ionic conductive garnet-type or garnet-type similar crystal structure is preferred. A specific material for this is Li7La3Zr2O 12 Li 7-x La3Zr 2-x Ta x O 12 (Here, x is between 0 and 2), Li 7-3x La3Zr2Al x O 12 (Here, x is between 0 and 0.5), Li 7-x La3Zr 2-x Nb x O 12 (where x is between 0 and 2) and Li 7-x-3y La3Zr 2-x Ta x Al y O 12 (Here, we can give the cases where x is between 0 and 2 (inclusive), and y is between 0 and 0.5 (inclusive).

[0040] Furthermore, as the solid electrolyte contained in the solid electrolyte separator layer (25) of the B-type all-solid-state lithium secondary battery (201), examples include one or more inorganic compounds selected from the group consisting of a lithium (Li)-containing composite oxide and ceramics having a garnet-type structure, a perovskite-type structure, and a lisicon-type structure. Specific examples include lisicon, nasicon, peo, lipon, PVDF, Li3N, Li3P, LiI, LiBr, LiCl, LiF, and Li 0.5 TiO3; Li2S-SiS2-Li3PO4; Lithium nitride; Doped Li3N; Li2S-SiS2-Li3PO4; Li 14 Zn(GeO4)4; Li-β-alumina; Li 3.6 Si 0.6 P 0.4O4;PEO-LiClO4;LiN(CF3SO2)2 / (CH2CH2O)8;Li7La3Zr2O with one or more elements selected from the group consisting of Al, Ga, Nb, Ta, Ca, and Sr added. 12 One or more can be selected from the group consisting of ; and Li3BO3.

[0041] <<Low resistance layer>> The low-resistance layer in this invention is a layer made of a metal or metalloid containing an element that alloys lithium (Li), and it is a layer that can reduce the electrical resistance at the contact interface between the negative electrode active material layer and the solid electrolyte separator layer by being placed between the negative electrode active material layer and the solid electrolyte separator layer. The low-resistance layer in this invention will be explained below using a Type B all-solid-state lithium secondary battery (201).

[0042] In a Type B all-solid-state lithium secondary battery (201), the low-resistance layer (23) is a layer made of a material containing a metal capable of alloying lithium (Li). It is a layer made of a lithium alloy, or a layer that alloys lithium through secondary battery operation (charge / discharge operation). The presence of the low-resistance layer (23) can reduce the electrical resistance between the negative electrode active material layer (22) and the solid electrolyte separator layer (25) (specifically, the contact interface when both the negative electrode active material layer (22) and the solid electrolyte separator layer (25) are in contact). When the electrical resistance between the negative electrode active material layer (22) and the solid electrolyte separator layer (25) is reduced, the internal resistance of the secondary battery is also reduced, improving the charge / discharge characteristics and increasing the electrical capacity.

[0043] Specific metallic or metalloid materials to be included in the low-resistance layer (23) include materials containing one or more elements selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), aluminum (Al), tin (Sn), indium (In), germanium (Ge), lead (Pb), zinc (Zn), antimony (Sb), magnesium (Mg), silicon (Si), cadmium (Cd), gallium (Ga), tellurium (Te), and bismuth (Bi). In particular, using one or more elements selected from the group consisting of gold, silver, platinum, tin, indium, and silicon is preferable from the viewpoint of stability and ease of handling.

[0044] Furthermore, the low-resistance layer (23) is preferably layered. In the layered form, the contact area between the solid electrolyte separator layer (25) and the negative electrode active material layer (22) can be improved during charge and discharge operations, and the charge and discharge characteristics can be improved by reducing the resistance of these interfaces. The thickness of the low-resistance layer (23) is preferably 1 to 500 nm. More preferably 5 to 300 nm, and even more preferably 10 to 260 nm. It is preferable to keep the thickness within the above range because if it is too thin, it will not form a continuous layered film, and if it is too thick, it will not increase material costs and process costs.

[0045] The low-resistance layer (23) is preferably positioned in contact with the solid electrolyte separator layer (25), and more preferably in contact with the negative electrode layer (24) (particularly the negative electrode active material layer (22) that constitutes the negative electrode layer (24)). This is because when the low-resistance layer 23 is in contact with these layers, the resistance is more easily reduced, and the reliability and stability of the secondary battery operation are further enhanced by the contact.

[0046] The low-resistance layer (23) can be formed by one or more methods selected from the group consisting of sputtering, evaporation methods such as electron beam evaporation and thermal evaporation, coating methods, and foil application methods, but is not limited to these as long as the objective of the present invention can be achieved. Sputtering and evaporation are commonly used industrial methods, while coating and foil application methods do not require a vacuum environment and are therefore easy to handle. The low-resistance layer (23) can reduce resistance across the entire contact interface, thus providing high tolerance for defects such as localized pinholes. For this reason, low-cost methods such as foil application can be applied as the manufacturing method for the low-resistance layer (23).

[0047] <<Current collector>> In this invention, the negative electrode current collector and the positive electrode current collector are conductors whose purpose is to mediate the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. In this case, the conductor in contact with the positive electrode active material layer is the positive electrode current collector, and the conductor in contact with the negative electrode active material layer is the negative electrode current collector. As mentioned above, both are also referred to as "collecting electrodes". The negative electrode current collector and the positive electrode current collector in this invention will be explained below using a type A all-solid-state lithium secondary battery (101) and a type B all-solid-state lithium secondary battery (201).

[0048] In all-solid-state lithium secondary batteries (101, 201), the negative electrode current collectors (11, 21) and positive electrode current collectors (16, 27) are conductors (electrodes) whose purpose is to mediate the movement of electrons from one surface in contact with the positive electrode active material layer (15, 26) to the other surface in contact with the negative electrode active material layer (12, 22). The material of the negative electrode current collectors (11, 21) and positive electrode current collectors (16, 27) is not particularly limited as long as it is a conductive material; for example, metals or conductive resins can be used.

[0049] Specifically, the metal material for the negative electrode current collector (11, 21) and the positive electrode current collector (16, 27) can be one or more metals selected from the group consisting of copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), iron (Fe), stainless steel (also called stainless steel, e.g., SUS304, SUS316), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd). Therefore, individual metals selected from the above group, alloys containing one or more metals selected from the above group, or compounds of one or more metals selected from the above group with carbon (C) or nitrogen (N) can be used. Stainless steel or foil with aluminum coated on the metal surface may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoint of electronic conductivity, battery operating potential, and the application of the inexpensive and easy-to-handle sputtering method.

[0050] The conductive resin material for the negative electrode current collector (11, 21) and positive electrode current collector (16, 27) is preferably a non-conductive polymer material to which a conductive filler has been added. Examples of non-conductive polymer materials include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Furthermore, examples of conductive filler materials include one or more metals selected from the group consisting of nickel (Ni), titanium (Ti), aluminum (Al), copper (Cu), platinum (Pt), chromium (Cr), iron (Fe), zinc (Zn), tin (Sn), indium (In), and antimony (Sb), alloys containing these metals, metal compounds, or carbon materials consisting of one or more selected from the group consisting of acetylene black, carbon nanofibers, carbon nanotubes, carbon nanohorns, carbon nanoballoons, and fullerenes.

[0051] <<Positive electrode active material layer>> The positive electrode active material layer in the present invention is a layer composed of a positive electrode active material containing lithium. The positive electrode active material layer in the present invention will be described below using the all-solid-state lithium secondary battery (101) of type A and the all-solid-state lithium secondary battery (201) of type B.

[0052] The positive electrode active material layers (16, 26) in the all-solid-state lithium secondary batteries (101, 201) are not particularly limited as long as they are positive electrode active materials containing lithium, and typically, lithium-containing composite metal oxides can be mentioned.

[0053] Specific materials for the positive electrode active material layers (16, 26) include LiM 1 x Mn 2-x O4 (where M 1 is at least one element selected from the group consisting of Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru, and Rh, and 0.01 ≦ x ≦ 0.5) spinel-type lithium manganese composite oxide; Li x Mn (1-y-x) Ni y M 2 z O (2-k) F l (where M 2 [[ID=�5]]is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, and 0.8 ≦ x ≦ 1.2, 0 < y < 0.5, 0 ≦ z ≦ 0.5, k + l < 1, -0.1 ≦ k ≦ 0.2, 0 ≦ l ≦ 0.1) layered compound; LiCo 1-x M 3 x O2 (where M 3 [ is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ≦ x ≦ 0.5) lithium cobalt composite oxide; LiNi1-x M 4 x O2 (however, M 4 LiM is a lithium nickel composite oxide (LiM) where LiM is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and is represented as 0 ≤ x ≤ 0.5. 5 1-x N 1 x PO4 (however, M 5 is at least one element selected from the group consisting of Fe, Mn, and Co, and N 1 This is an olivine-type composite oxide represented by (0 ≤ x ≤ 0.5), which is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba; and Li4Ti5O 12 One or more can be selected from the group consisting of lithium titanium composite oxides represented by . In addition, between the positive electrode active material layer and the solid electrolyte layer, for example, LiNbO3, Li4Ti5O 12 A coating layer such as Li3PO4 may be provided. Furthermore, the positive electrode active material layers (16, 26) may contain a conductive additive to improve conductivity. As the conductive additive, any known conductive additive usable in all-solid-state batteries can be used as appropriate. Specifically, carbon materials such as vapor-grown carbon fibers, acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF) can be used.

[0054] <<Negative electrode active material layer>> The negative electrode active material layer in the present invention is a layer containing graphite particles whose surface is coated with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer.

[0055] Here, "graphite particles" refers to particles made of graphite, which is a layered carbon material having a structure (graphene structure) in which six-membered rings of carbon atoms are linked together on the same plane. Its interlayer distance is in the range of 0.334 nm to 0.340 nm, and it has a structure in which layers are stacked while maintaining a uniform interlayer distance. Therefore, the graphite particles themselves used for coating with amorphous carbon are a highly crystalline carbon material.

[0056] The graphite particles are not particularly limited as long as they are graphitized carbon particles. Examples include graphite such as natural graphite and artificial graphite, coke powder, needle coke powder, and graphitized resin powder. Among these, graphite is preferred because it is readily available commercially and significantly improves charge-discharge characteristics at high current densities compared to using other known negative electrode active materials. Natural graphite is more preferred, and spheroidal graphite that has undergone spheroidization treatment is particularly preferred.

[0057] Apparatus used in the above-mentioned spheroidization process includes, for example, devices that repeatedly apply mechanical forces to particles, such as compression, friction, and shear forces, primarily through impact force and including particle interactions. In particular, devices that have a rotor with numerous blades installed inside a casing, and in which the rotor rotates at high speed, apply mechanical forces such as impact compression, friction, and shear forces to the carbon material introduced inside, thereby performing surface treatment, are preferred. Devices that have a mechanism to repeatedly apply mechanical forces by circulating the carbon material are also preferred. Examples of such preferred devices include hybridization systems (manufactured by Nara Machine Works Co., Ltd.), Cryptron (manufactured by Earth Technica Co., Ltd.), CF mills (manufactured by Ube Industries, Ltd.), mechanofusion systems (manufactured by Hosokawa Micron Corporation), and Theta Composers (manufactured by Tokuju Kogyo Co., Ltd.). Among these, the hybridization system manufactured by Nara Machine Works Co., Ltd. is preferred.

[0058] On the other hand, "amorphous carbon" refers to carbon materials in which the arrangement of atoms is not regular, also known as amorphous carbon or non-amorphous carbon. In such carbon materials, the graphene structure is not well developed, and the interlayer distance of graphite exceeds the above range (0.334 nm to 0.340 nm). Therefore, amorphous carbon is a carbon material with low crystallinity. In this application, in particular, carbon materials in which the interlayer distance of graphite is greater than 0.340 nm are referred to as amorphous carbon.

[0059] The material used to coat the graphite particles as "amorphous carbon" is not particularly limited as long as it can achieve the objectives of the present invention. However, a carbonaceous material that can amorphousize the surface of the graphite particles by firing is preferred, and generally, an organic compound is used. Examples include organic compounds that are condensed polycyclic aromatic compounds of petroleum and coal, ranging from tar to hard pitch. Specifically, examples include organic compounds such as impregnated pitch, coal tar pitch, coal-based heavy oils such as liquefied coal oil, straight-run heavy oils such as asphaltene, and decomposed heavy oils such as ethylene heavy end tar.

[0060] The organic compound used to coat the surface of graphite particles with amorphous carbon can be any carbonaceous compound that can amorphousize the surface of the graphite particles by firing, as described above, but it is preferable that it satisfies the following conditions (1) to (5).

[0061] (1) Surface functional group content of organic compounds (N / C, S / C, O / C) The surface functional group content (N / C, S / C, O / C) of the organic compound preferably satisfies the following conditions when the carbon powder obtained by calcining the organic compound at 1000°C and then grinding it in air for 30 seconds using a high-speed vibrating sample mill is analyzed.

[0062] (1-1) Surface functional group amount (N / C) The surface functional group content (N / C) of the organic compound, represented by the following formula 3, has a lower limit of 0.05% or more, preferably 0.1% or more, more preferably 0.27% or more, and even more preferably 0.40% or more, and an upper limit of 6% or less, preferably 4% or less, more preferably 2% or less, and even more preferably 1% or less. The above range is preferred to avoid the risk of reduced high-current charge / discharge characteristics if N / C is too low, and the risk of reduced charge / discharge efficiency if it is too high.

[0063] Furthermore, N / C is defined by the following equation 3.

[0064] Equation 3: N / C(%) = [N atom concentration determined based on the peak area of ​​the N1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / C atom concentration determined based on the peak area of ​​the C1s spectrum in XPS analysis] × 100

[0065] The surface functional group ratio (N / C) of organic compounds can be measured using X-ray photoelectron spectroscopy (XPS).

[0066] For X-ray photoelectron spectroscopy measurements, an X-ray photoelectron spectrometer is used. The sample is placed on a sample stage so that its surface is flat, and the Kα rays from aluminum are used as the X-ray source. Multiplex measurements are performed to measure the spectra of C1s (280-300 eV) and N1s (390-410 eV). The obtained C1s peak top is set to 284.3 eV and charge correction is applied to determine the peak areas of the C1s and N1s spectra. These areas are then multiplied by the instrument sensitivity coefficient to calculate the surface atomic concentrations of C and N, respectively. Using these obtained surface atomic concentrations of N and C, the N / C value is calculated using Equation 3.

[0067] (1-2) Surface functional group amount (S / C) The surface functional group ratio (S / C) of the organic compound, represented by the following formula 4, has a lower limit of 0.01% or more, preferably 0.02% or more, more preferably 0.05% or more, and even more preferably 0.07% or more, and an upper limit of 6% or less, preferably 4% or less, more preferably 2% or less, and even more preferably 1% or less. The above range is preferred in order to avoid the risk of reduced high-current charge / discharge characteristics if the S / C is too small, and the tendency for reduced charge / discharge efficiency if the S / C is too large.

[0068] Furthermore, S / C is defined by the following equation 4.

[0069] Equation 4: S / C(%) = [S atom concentration determined based on the peak area of ​​the S2s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / C atom concentration determined based on the peak area of ​​the C1s spectrum in XPS analysis] × 100

[0070] The surface functional group ratio (S / C) of organic compounds can be measured using X-ray photoelectron spectroscopy (XPS).

[0071] For X-ray photoelectron spectroscopy measurements, an X-ray photoelectron spectrometer is used. The sample is placed on a sample stage so that its surface is flat, and the Kα rays from aluminum are used as the X-ray source. Multiplex measurements are performed to measure the spectra of C1s (280-300 eV) and S2p (160-175 eV). The obtained C1s peak top is set to 284.3 eV and charge correction is applied to determine the peak areas of the C1s and S2p spectra. These areas are then multiplied by the instrument sensitivity coefficient to calculate the surface atomic concentrations of C and S, respectively. Using these obtained surface atomic concentrations of S and C, the S / C ratio is calculated using Equation 4.

[0072] (1-3) Surface functional group amount (O / C) The surface functional group content (O / C) of the organic compound has a lower limit of 0.1% or more, preferably 1% or more, and more preferably 4.1% or more. The upper limit is 10% or less, preferably 8% or less, and more preferably 5% or less. The above range is preferred to avoid the following: if the surface functional group content O / C is too low, the desolvation reactivity between Li ions and the electrolyte solvent on the negative electrode active material surface decreases, potentially reducing high-current charge-discharge characteristics; and if it is too high, it can lead to a decrease in charge-discharge efficiency.

[0073] O / C is defined by the following equation 5.

[0074] Equation 5: O / C(%) = [O atom concentration determined based on the peak area of ​​the O1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / C atom concentration determined based on the peak area of ​​the C1s spectrum in XPS analysis] × 100

[0075] The surface functional group content (O / C) in this invention can be measured using X-ray photoelectron spectroscopy (XPS).

[0076] For X-ray photoelectron spectroscopy measurements, an X-ray photoelectron spectrometer is used. The sample is placed on a sample stage so that its surface is flat, and the Kα rays from aluminum are used as the X-ray source. Multiplex measurements are performed to measure the spectra of C1s (280-300 eV) and O1s (525-545 eV). The obtained C1s peak top is set to 284.3 eV and charge correction is applied to determine the peak areas of the C1s and O1s spectra. These areas are then multiplied by the instrument sensitivity coefficient to calculate the surface atomic concentrations of C and O, respectively. Using these obtained surface atomic concentrations of O and C, the O / C ratio is calculated using Equation 5.

[0077] (1-4) Sum of S / C and N / C The sum of S / C and N / C in the organic compound has a lower limit of 0.3% or more, preferably 0.4% or more, and more preferably 0.5% or more, and an upper limit of 10% or less, preferably 8% or less, and more preferably 5% or less. The above range is preferred in order to avoid the risk of reduced high-current charge-discharge characteristics on the surface of the negative electrode active material if the sum of S / C and N / C is too small, and the tendency for charge-discharge efficiency to decrease if it is too large.

[0078] (2) X-ray parameters (d002 value) The interplanar spacing (d002) of the 002 plane of carbon powder obtained by amorphous carbonization treatment of an organic compound, as measured by X-ray wide-angle diffraction, is preferably 0.3357 nm or more, more preferably 0.3358 nm or more, and even more preferably 0.3359 nm or more, and preferably 0.340 nm or less, more preferably 0.338 nm or less, and even more preferably 0.337 nm or less, as measured by powder X-ray diffraction. The above range is preferred in order to avoid the following: if the interplanar spacing (d002) is too large, it indicates low crystallinity, and the "graphite particles coated with amorphous carbon on the surface" may become particles with low crystallinity, reducing the charge-discharge capacity. If the interplanar spacing (d002) is too small, the charge-discharge reactivity may decrease, potentially leading to a decrease in high-current charge-discharge characteristics. In this invention, "amorphous carbon" mainly refers to carbon whose interplanar spacing (d002) of the 002 plane, as measured by powder X-ray diffraction, is within the following range. In other words, amorphous carbon in this invention essentially refers to carbonaceous materials ranging from those with little development of crystalline structure to those with a structure close to that of graphite.

[0079] The interplanar spacing (d002) of the 002 plane of the carbon powder obtained by X-ray diffraction of the carbon powder obtained by calcining the above organic compound at 1000°C and then grinding it in air for 30 seconds using a high-speed vibrating sample mill is preferably 0.34 nm or more, more preferably 0.342 nm or more, even more preferably 0.345 nm or more, and particularly preferably 0.346 nm or more, with an upper limit preferably 0.360 nm or less, more preferably 0.355 nm or less, and even more preferably 0.350 nm or less. If the interplanar spacing (d002) is too large, it indicates low crystallinity, and the carbon material for all-solid-state lithium-ion secondary batteries may become particles with low crystallinity, resulting in a decrease in charge-discharge capacity. If the interplanar spacing (d002) is too small, the charge-discharge reactivity may decrease, which may lead to a decrease in high-current charge-discharge characteristics, so the above range is preferable.

[0080] (3) Crystallite size (Lc(004)) The crystallite size Lc(004) in the c-axis direction, determined from the 002 diffraction line by X-ray diffraction using the JSPS method for carbon powder obtained by amorphous carbonization treatment of organic compounds, is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more, and preferably 500 nm or less, and even more preferably 400 nm or less, and even more preferably 300 nm or less. The above range is preferred in order to avoid the following: if it exceeds this range, the carbon material for all-solid-state lithium-ion secondary batteries may become particles with low crystallinity, resulting in a decrease in charge-discharge capacity; and if it falls below this range, the charge-discharge reactivity may decrease, potentially leading to a decrease in high-current charge-discharge characteristics.

[0081] The above organic compound is calcined at 100°C, and then pulverized in air for 30 seconds using a high-speed vibrating sample mill. The resulting carbon powder, when measured by X-ray diffraction using the Japan Society for the Promotion of Science (JSPS) method, has a lower limit of preferably 0.1 nm or more, more preferably 1 nm or more, and even more preferably 3 nm or more, and an upper limit of 100 nm or less, preferably 50 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less. This range is preferred because exceeding this range may result in low crystallinity particles in the carbon material for all-solid-state lithium-ion secondary batteries, leading to a decrease in charge-discharge capacity, while falling below this range may reduce charge-discharge reactivity and potentially impair high-current charge-discharge characteristics.

[0082] (4) Softening point The softening point of the organic compound is 400°C or lower, preferably 200°C or lower, and more preferably 150°C or lower. Below this range, it becomes difficult to mix uniformly when mixing and kneading with graphite particles, and the process may be carried out at high temperatures, which can lead to low productivity. The above range is preferred to avoid this. There is no particular lower limit, but it is generally preferred to be 40°C or higher.

[0083] (5) Quinoline-insoluble content (QI), Toluene-insoluble content (TI) The quinoline-insoluble content in the organic compound has a lower limit of 0.6% by mass or more, preferably 1% by mass or more, and more preferably 5% by mass or more. The upper limit is 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0084] The toluene-insoluble content in the organic compound has a lower limit of 16% by mass or more, preferably 20% by mass or more, and more preferably 25% by mass or more. The upper limit is 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. The above ranges are preferred in order to avoid the following problems: if the quinoline-insoluble content (QI) and toluene-insoluble content (TI) exceed these ranges, the carbon material may become particles with low crystallinity, potentially reducing the charge-discharge capacity; and if they fall below these ranges, the charge-discharge reactivity may decrease, potentially leading to a decline in high-current charge-discharge characteristics.

[0085] The insertion reaction of lithium ions into graphite is an intercalation reaction, and 0.2V(vs.Li + This reaction occurs at or below 1V(Li), and the potential curve is flat. However, the insertion reaction of lithium ions into amorphous carbon lacks crystalline sites, and lithium is inserted into disordered or underdeveloped areas of the stacking structure where site energy is widely distributed. + The potential curve shows a gradual decrease in potential below the / Li potential.

[0086] In the present invention, "coating" in "graphite particles coated with amorphous carbon on their surface" means that amorphous carbon is present on the surface of the graphite particles constituting the graphite negative electrode active material layer such that the graphite negative electrode active material layer constituting the negative electrode has a network structure that generates the desired lithium ion conduction. To that extent, there are no particular restrictions on the form of "coating," but generally, it is preferable that amorphous carbon uniformly covers the entire surface of the graphite particles. In other words, it is preferable that the layer of amorphous carbon covering the surface of the graphite particles be as uniform as possible. The proportion (weight %) of amorphous carbon to be coated is not particularly limited as long as the objective of the present invention can be achieved, but the lower limit is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and the upper limit is preferably 30% by weight or less, more preferably 15% by weight or less.

[0087] The negative electrode active material layer in the present invention (specifically, the "graphite negative electrode active material layer") may contain graphite particles coated with amorphous carbon on their surface alone, or it may contain graphite particles coated with amorphous carbon on their surface and graphite particles different from those coated with amorphous carbon on their surface. In other words, the "negative electrode active material layer" in the present invention may contain one or more types of "graphite particles coated with amorphous carbon on their surface" as the negative electrode active material. An example of using two or more types of "graphite particles coated with amorphous carbon on their surface" is to use two or more types of graphite particles with different coating rates of amorphous carbon on the surface of the graphite particles as the negative electrode active material. The "negative electrode active material layer" in the present invention may be, for example, a layer consisting only of one or more types of "graphite particles whose surface is coated with amorphous carbon," or a layer consisting of a mixture of one or more types of "graphite particles whose surface is coated with amorphous carbon" and "other carbon materials" and / or "materials capable of adsorbing lithium ions," or a layer containing such a mixture. In the present invention, it is preferable that the "negative electrode active material layer" consists only of one or more types of "graphite particles whose surface is coated with amorphous carbon."

[0088] As for the "other carbon materials" mentioned above, for example, natural graphite, artificial graphite, amorphous coated graphite, or amorphous carbon can be used. These materials may be used individually or in any combination and composition of two or more. From the viewpoint of versatility, natural graphite is preferred.

[0089] Examples of natural graphite include highly purified flaky graphite and spherical graphite.

[0090] Examples of artificial graphite include particles made by graphitizing carbon materials. For instance, single graphite precursor particles can be calcined in powder form to produce graphitized particles.

[0091] As amorphous coated graphite, for example, particles obtained by coating natural graphite or artificial graphite with an amorphous precursor and calcining, or particles obtained by coating natural graphite or artificial graphite with amorphous material by CVD can be used.

[0092] As amorphous carbon, you can use coke, bulk mesophase, or soft carbon (easily graphitizable carbon) obtained by heat-treating polyvinyl chloride, which readily form a graphite structure with three-dimensional stacking regularity by passing through a liquid phase at a temperature of 350-500°C during heat treatment, and hard carbon (difficult to graphitize carbon) which does not readily form a graphite structure by carbonizing consistently in a solid phase, such as organic materials like phenolic resins, furan resins, and sugar, or organic compounds that have undergone infusibility treatment. Amorphous carbon may be used alone, or two or more types of amorphous carbon may be mixed in any combination.

[0093] Furthermore, the "other carbon materials" mentioned above may also be artificial carbonaceous materials or carbonaceous materials obtained by heat-treating artificial graphite materials at a temperature of 400 to 3200°C once or more. Specific examples of these materials include natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or oxidized products of these pitches; needle coke, pitch coke, or carbon materials obtained by graphitizing a portion of these; thermal decomposition products of organic materials such as furnace black, acetylene black, or pitch-based carbon fibers; carbonizable organic materials and their carbonized products; or solutions obtained by dissolving carbonizable organic materials in low-molecular-weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and their carbonized products.

[0094] There are no particular limitations on the apparatus used when mixing the above-mentioned "other carbon materials" with the "graphite particles coated with amorphous carbon on their surface" in the present invention. For example, in the case of rotary mixers: cylindrical mixers, twin cylindrical mixers, double cone mixers, cubic mixers, hoe-shaped mixers, and in the case of stationary mixers: helical mixers, ribbon mixers, Muller mixers, Helical Flight mixers, Pugmill mixers, fluidizing mixers, etc., can be used.

[0095] As described above, the "negative electrode active material layer" in the present invention may contain a "material capable of intercepting lithium ions." Preferably, the "material capable of intercepting lithium ions" is a material capable of intercepting less than 10% lithium ions within the negative electrode active material layer. Examples of the "material capable of intercepting lithium ions" include silicon and tin, and may also be a material containing silicon or tin.

[0096] The content (specifically, total content) of "graphite particles coated with amorphous carbon on the surface" in the negative electrode active material layer must be 50% by weight or more. Here, if the negative electrode active material layer consists of one or more types of "graphite particles coated with amorphous carbon on the surface" and "other carbon materials and / or materials capable of absorbing lithium ions," the ratio of the weight of "other carbon materials and / or materials capable of absorbing lithium ions" to the total weight of "graphite particles coated with amorphous carbon on the surface" and "other carbon materials and / or materials capable of absorbing lithium ions" contained in the negative electrode active material layer must have a lower limit of 1% by weight or more, preferably 5% by weight or more, and an upper limit of less than 50% by weight, preferably 25% by weight or less. The above lower limit is preferred to avoid the tendency for the added effect to be difficult to observe if the mixing ratio of "other carbon materials and / or materials capable of absorbing lithium ions" is too small. Furthermore, the above upper limit is preferable in order to avoid the tendency for the characteristics of all-solid-state lithium secondary batteries to be difficult to exhibit if the mixing ratio of "other carbon materials and / or materials capable of adsorbing lithium ions" is too high.

[0097] The weight of "graphite particles coated with amorphous carbon" constituting the negative electrode active material layer in the present invention (i.e., the content of "graphite particles coated with amorphous carbon" in the negative electrode active material layer in the present invention) is 50% by weight or more of the weight of the graphite negative electrode active material layer, preferably 60% by weight or more, and more preferably 70% by weight or more. When the negative electrode active material layer in the present invention consists of "graphite particles coated with amorphous carbon" and "other carbon materials" that make up 50% by weight or more of the weight of the graphite negative electrode active material layer, it is preferable to use amorphous carbon as the "other carbon material".

[0098] In this invention, "graphite particles coated with amorphous carbon on the surface" are obtained by coating the surface of highly crystalline graphite particles, which are the raw material, with low-crystalline amorphous carbon. Therefore, "graphite particles coated with amorphous carbon on the surface" obtained by actually coating the surface of the raw material graphite particles with amorphous carbon can be said to be a carbonaceous material having two different crystallinity properties but no interface between the graphite particles and amorphous carbon, or a carbonaceous material having two different crystallinity properties and an interface between the graphite particles and amorphous carbon, or a carbonaceous material consisting of both. From the viewpoint of orientation, it can also be said to be a carbonaceous material having two different orientations but no interface between the graphite particles and amorphous carbon, or a carbonaceous material having two different orientations and an interface between the graphite particles and amorphous carbon, or a carbonaceous material consisting of both.

[0099] <<Physical properties of graphite particles coated with amorphous carbon>> In the present invention, the "graphite particles whose surface is coated with amorphous carbon" preferably satisfy one or more of the following conditions (1) to (7) simultaneously.

[0100] (1) Volume-based average particle size (average particle size (median diameter): d50) The volume-based average particle size (d50) of "graphite particles coated with amorphous carbon on the surface" is not particularly limited, but the lower limit is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and especially preferably 7 μm or more. The upper limit is 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and especially preferably 25 μm or less. The average particle size (d50) can be determined by methods such as laser diffraction / scattering particle size distribution measurement.

[0101] The volume-based average particle size is measured by dispersing carbon powder (specifically, "graphite particles coated with amorphous carbon") in a 0.2% by mass aqueous solution (approximately 10 mL) of polyoxyethylene (20) sorbitan monolaurate, a surfactant, and using a laser diffraction / scattering particle size analyzer (for example, LA-700 manufactured by Horiba, Ltd.). The median diameter, or average particle size (d50), obtained by this measurement is defined as the volume-based average particle size of the "graphite particles coated with amorphous carbon" in this invention.

[0102] (2) Raman R value, Raman half-width The Raman R value of "graphite particles coated with amorphous carbon on the surface," as measured using argon ion laser Raman spectroscopy, has a lower limit of 0.01 or higher, preferably 0.03 or higher, more preferably 0.1 or higher, and an upper limit of 1.5 or lower, preferably 1.2 or lower, more preferably 1 or lower, and particularly preferably 0.5 or lower.

[0103] If the Raman R value falls below the lower limit, the crystallinity of the particle surface may become too high, resulting in fewer sites for Li to enter the interlayers of graphite during charging and discharging (i.e., the charge acceptance may decrease). Also, when the negative electrode is made denser by pressing after coating the current collector, the crystals tend to orient in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds the upper limit, the crystallinity of the particle surface decreases, increasing reactivity with the electrolyte and potentially leading to a decrease in efficiency. To avoid these problems, the upper and lower limits of the Raman R value are preferably within the above range.

[0104] Furthermore, 1580 cm² of "graphite particles with an amorphous carbon coating on the surface" -1 There are no particular restrictions on the Raman width at half maximum in this vicinity, but the lower limit is 10 cm. -1 That's all. 15cm -1 The above is preferable, and the upper limit is 100 cm. -1 The following is 80cm -1 The following is preferable: 60cm -1 The following is even more preferable: 40 cm -1 The following are particularly preferable.

[0105] If the Raman full width at half maximum (FWHM) falls below the lower limit, the crystallinity of the particle surface may become too high, reducing the number of sites where Li can enter the interlayers of graphite during charging and discharging. In other words, the charge acceptance may decrease. Also, when the negative electrode is made denser by pressing after coating the current collector, the crystals tend to orient parallel to the electrode plate, which can lead to a decrease in load characteristics. On the other hand, if it exceeds the upper limit, the crystallinity of the particle surface decreases, increasing reactivity with the electrolyte and potentially leading to a decrease in efficiency. To avoid these problems, the upper and lower limits of the Raman FWHM are preferably within the ranges described above.

[0106] Raman spectra are measured using a Raman spectrometer (e.g., a Raman spectrometer manufactured by JASCO Corporation). The sample is allowed to fall naturally into the measurement cell, and while irradiating the sample surface within the cell with argon ion laser light, the cell is rotated in a plane perpendicular to the laser beam. The resulting Raman spectrum is measured at 1580 cm⁻¹. -1 The intensity IA of the nearby peak PA and 1360cm -1 The intensity of the nearby peak PB and IB are measured, and their intensity ratio R (R = IB / IA) is calculated. The R value calculated in this measurement is defined as the Raman R value and is defined as the Raman R value of "graphite particles coated with amorphous carbon on the surface" in this invention. Furthermore, the 1580 cm⁻¹ of the obtained Raman spectrum is also measured. -1 The full width at half maximum (FWHM) of the nearby peak PA is measured and defined as the Raman FWHM of the "graphite particles coated with amorphous carbon on the surface" in this invention.

[0107] Also, the Raman measurement conditions are as follows. · Argon ion laser wavelength: 514.5 nm · Laser power on the sample: 15 - 25 mW · Resolution: 10 - 20 cm -1 · Measurement range: 1100 cm -1 ~1730 cm -1 · Raman R value, Raman half-width analysis: Background processing · Smoothing processing: Simple average, convolution 5 points

[0108] (3) BET specific surface area Regarding the BET specific surface area of "graphite particles coated with amorphous carbon on the surface", the lower limit value of the measured specific surface area value using the BET method is 0.1 m <…> / g or more, preferably 0.7 m <…> / g or more, more preferably 1.0 m <…> / g or more, particularly preferably 1.5 m <…> / g or more, and the upper limit value is 100 m <…> / g or less, preferably 25 m <…> / g or less, more preferably 15 m <…> / g or less, particularly preferably 10 m <…> / g or less.

[0109] When the value of the BET specific surface area is below the above lower limit value, the lithium acceptance during charging when used as a negative electrode material tends to deteriorate, lithium tends to precipitate on the electrode surface, and the stability may decrease. On the other hand, when it exceeds the above upper limit value, the reactivity with the electrolyte increases when used as a negative electrode material, and it may be difficult to obtain a preferable battery. To avoid such problems, the upper and lower limit values of the BET specific surface area are preferably in the above range.

[0110] The specific surface area is measured using the BET method by first pre-drying the sample at 350°C for 15 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken). Then, the nitrogen adsorption BET single-point method is performed using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3. The specific surface area obtained by this measurement is defined as the BET specific surface area of ​​"graphite particles coated with amorphous carbon" in this invention.

[0111] (4) Circularity When measuring the circularity of "graphite particles coated with amorphous carbon on the surface," it is preferable that it falls within the following range. Note that circularity is defined as "circularity = (perimeter of an equivalent circle with the same area as the particle projection shape) / (actual perimeter of the particle projection shape)," and a circularity of 1 represents a theoretically perfect sphere.

[0112] For "graphite particles coated with amorphous carbon on the surface," the circularity of particles with a particle diameter in the range of 3 to 40 μm is preferably as close to 1 as possible, preferably 0.1 or higher, more preferably 0.5 or higher, even more preferably 0.8 or higher, particularly preferably 0.85 or higher, and most preferably 0.9 or higher.

[0113] High-current-density charge-discharge characteristics improve with increasing circularity. Therefore, if the circularity falls below the above range, the packing efficiency of the negative electrode active material decreases, interparticle resistance increases, and the short-time high-current-density charge-discharge characteristics may deteriorate. To avoid this, the above range is preferable.

[0114] The circularity is measured using a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Corporation). Approximately 0.2 g of the sample is dispersed in a 0.2 mass% aqueous solution (approximately 50 mL) of polyoxyethylene (20) sorbitan monolaurate, a surfactant. After irradiating with 28 kHz ultrasound at an output of 60 W for 1 minute, the detection range is set to 0.6 to 400 μm, and measurements are taken for particles with a particle diameter in the range of 3 to 40 μm. The circularity obtained by this measurement is defined as the circularity of "graphite particles coated with amorphous carbon on the surface" in this invention.

[0115] The method for improving the circularity is not particularly limited. However, it is preferable to perform a spheroidization treatment to make it spherical because the shape of the inter-particle voids when made into an electrode body becomes regular. Examples of the spheroidization treatment include a method of mechanically approaching a spherical shape by applying a shearing force and a compressive force, a mechanical and physical treatment method of granulating a plurality of fine particles by a binder or the adhesive force possessed by the particles themselves, and the like.

[0116] (5) Tap density The tap density of "graphite particles coated with amorphous carbon on the surface" has a lower limit value of 0.1 g / cm 3 or more, preferably 0.5 g / cm 3 or more, more preferably 0.7 g / cm 3 or more, particularly preferably 1 g / cm 3 or more. Also, the upper limit value is preferably 2 g / cm 3 or less, more preferably 1.8 g / cm 3 or less, particularly preferably 1.6 g / cm 3 or less.

[0117] When the tap density is below the above lower limit value, it may be difficult to increase the packing density when used as a negative electrode, and it may not be possible to obtain a high-capacity battery. Also, when the above upper limit value is exceeded, the voids between the particles in the electrode become too few, it becomes difficult to ensure the conductivity between the particles, and it may be difficult to obtain favorable battery characteristics. To avoid such problems, the upper and lower limit values of the tap density are preferably within the above range.

[0118] For the measurement of the tap density, after passing through a sieve with a mesh size of 300 μm and dropping the sample into a tapping cell of 20 cm 3 to fill the sample up to the upper end face of the cell, using a powder density measuring instrument (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.), perform tapping with a stroke length of 10 mm 1000 times, and calculate the tap density from the volume and the mass of the sample at that time. The tap density calculated by this measurement is defined as the tap density of "graphite particles coated with amorphous carbon on the surface" in the present invention.

[0119] (6) X-ray parameters The d-value (interlayer distance of graphite) of the lattice plane (002 plane) determined by X-ray diffraction using the JSPS method for "graphite particles coated with amorphous carbon on the surface" is sometimes denoted as d002 in this application, and is 0.335 to 0.340 nm, with a preference for 0.335 to 0.338 nm, and especially 0.335 to 0.337 nm. Furthermore, the crystallite size (Lc) determined by X-ray diffraction using the JSPS method has a lower limit of 1.0 nm or more, preferably 1.5 nm or more, and particularly preferably 2 nm or more.

[0120] (7) Orientation ratio The orientation ratio of "graphite particles coated with amorphous carbon" has a lower limit of 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher, and an upper limit of 0.67 or lower. If the orientation ratio falls below the lower limit, the high-density charge-discharge characteristics may decrease. The upper limit (0.67) is the theoretical upper limit for the orientation ratio of "graphite particles coated with amorphous carbon".

[0121] The orientation ratio is measured by X-ray diffraction after the sample is pressure-molded. 0.47 g of the sample was packed into a 17 mm diameter molding machine and measured 58.8 MN / m². 2 The molded body obtained by compression is set using clay so that it is flush with the surface of the sample holder for measurement, and X-ray diffraction is measured. From the peak intensities of the (110) diffraction and (004) diffraction of carbon obtained, the ratio expressed as (110) diffraction peak intensity / (004) diffraction peak intensity is calculated. The orientation ratio calculated by this measurement is defined as the orientation ratio of "graphite particles coated with amorphous carbon on the surface" in this invention.

[0122] The X-ray diffraction measurement conditions are as follows. Note that "2θ" indicates the diffraction angle. • Target: Cu (Kα-ray) graphite monochromator ·slit: Divergence slit = 0.5 degrees Light-receiving slit = 0.15 mm Scattering slit = 0.5 degrees • Measurement range and step angle / measurement time: (110) plane: 75 degrees ≦2θ≦80 degrees 1 degree / 60 seconds (004) plane: 52 degrees ≦2θ≦57 degrees 1 degree / 60 seconds

[0123] <<Method for producing graphite particles coated with amorphous carbon on the surface>> The method for producing "graphite particles coated with amorphous carbon" in the present invention is not particularly limited, as long as it is a method in which the graphite particles of the raw material described above become particles of a carbon material having a multilayer structure (also referred to as a multilayer structure carbon material) coated with amorphous carbon. For example, methods include a method of mixing graphite particles and an organic compound in any proportion and then heat-treating it at a high temperature, a method of fixing amorphous carbon powder to graphite particles using static electricity or a binder, chemical vapor deposition (CVD), vacuum deposition and sputtering methods and methods derived therefrom (PVD). Of these, the method of mixing graphite particles and an organic compound in any proportion and then heat-treating it at a high temperature is preferred from the viewpoint that the amount of amorphous carbon coating can be easily adjusted.

[0124] When producing "graphite particles coated with amorphous carbon" by mixing graphite particles with an organic compound and performing a carbonization treatment on the organic compound in the mixture, for example, the following method can be used: (i) A method for producing "graphite particles with an amorphous carbon coating on the surface" by heat-treating a mixture of an organic compound and graphite particles to obtain an amorphous carbon coating; (ii) A method for producing "graphite particles coated with amorphous carbon" by first preparing amorphous carbon powder in which an organic compound is partially carbonized, mixing graphite particles with the amorphous carbon powder, and then heat-treating the mixture to form a composite; (iii) A method for producing "graphite particles coated with amorphous carbon" by first preparing amorphous carbon powder, mixing the amorphous carbon powder with graphite particles and an organic compound, and then heat-treating the mixture to form a composite; The following can be used. In the methods of (ii) and (iii) in which amorphous carbon powder is prepared in advance, it is preferable to use amorphous carbon in which the average particle size is one-tenth or less of the average particle size of the graphite particles. In addition, it is also possible to use a method in which the amorphous carbon powder and graphite particles are prepared in advance and subjected to mechanical energy such as pulverization to create a structure in which one is incorporated into the other, or a structure in which they are electrostatically attached.

[0125] The method for confirming that amorphous carbon has been coated is not particularly limited, but for example, the following method can be used for confirmation. When amorphous carbon is coated, the DTA (Differential Thermal Analysis) curve obtained when TG-DTA measurement is performed will have a first peak on the relatively lower temperature side and a second peak on the relatively higher temperature side in the range of 500°C to 1000°C, and the first and second peaks will satisfy the following equation 6 (the same as equation 2 above), so it can be confirmed by this method.

[0126] (Equation 6): (DTA [μV] at the first peak) / (DTA [μV] at the second peak) ≥ 0.15

[0127] The TG-DTA measurement method in this case is not particularly limited, but for example, a Rigaku TG8120 differential thermal balance can be used as the measuring device, and the measurement conditions can be set to flow air at a flow rate of 100 ml / min, with a heating rate of 10°C / min, and using a platinum pan with a diameter (φ) of 5 mm and a height of 2.5 mm as the measuring container, with a sample mass of 5 mg. The value of "(DTA [μV] at the first peak) / (DTA [μV] at the second peak)" in (Equation 6) above is preferably 0.2 or higher.

[0128] The mass of amorphous carbon depends on the size and shape of the graphite particles coated with amorphous carbon, but generally, if the mass of the raw material graphite particles is set to 1, the mass of amorphous carbon should be 0.02 or more, and more preferably 0.04 or more. The larger the ratio of the mass of amorphous carbon to the mass of the raw material graphite particles, the larger the value of "(DTA [μV] at the first peak) / (DTA [μV] at the second peak)" in (Equation 6) tends to be. It is preferable to set the value of "(DTA [μV] at the first peak) / (DTA [μV] at the second peak)" in (Equation 6) to 2.5 or less in order to avoid a decrease in battery capacity due to an excessive amount of amorphous carbon relative to the raw material graphite particles. On the other hand, it is preferable to set this value to 0.15 or more in order to avoid the amount of amorphous carbon coating being too small and not providing a substantially effective coating.

[0129] The detailed manufacturing process for producing "graphite particles coated with amorphous carbon" involves heating a mixture of graphite particles and an organic compound to obtain an intermediate material, followed by carbonization, calcination, and pulverization to ultimately create "graphite particles coated with amorphous carbon" with amorphous carbon composites on the surface of the graphite particles. This process can be divided into the following three steps.

[0130] Step 1: Graphite particles, an organic compound, and, if necessary, a solvent are mixed using various commercially available mixers and kneaders to obtain a mixture. The amount of organic compound added is adjusted so that the ratio of residual carbon components derived from the organic compound to the final "graphite particles coated with amorphous carbon on the surface" is 0.3% by mass or more, preferably 0.5% by mass or more, and more preferably 1% by mass or more. The upper limit of this amount is such that the ratio of residual carbon components is 60% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. If the amount of organic compound added is too high, the charge and discharge capacity will decrease, the press load required when rolling the active material layer coated on the current collector to high density will increase, and as a result, it may become difficult to increase the capacity of the all-solid-state lithium secondary battery. On the other hand, if the amount of organic compound added is too low, the particles may break or deform when the active material layer coated on the current collector is rolled to high density, and good high-current charge and discharge characteristics may not be obtained. To avoid such problems, it is preferable to adjust the upper and lower limits of the amount of organic compound to be added so that the ratio of the residual carbon components falls within the above range.

[0131] The amount of carbon components derived from organic compounds in "graphite particles coated with amorphous carbon" is controlled by the amount of organic compound added in a step prior to obtaining the above mixture. For example, if the residual carbon content of the organic compound determined by the method described in JIS K2270 is p%, then the desired amount of 100 / p times the amount of organic compound will be added.

[0132] The raw materials, including graphite particles, organic compounds, solvents as needed, and catalysts added as desired, are first kneaded under heating as necessary. This results in a state where the liquid organic compound is attached to the carbonaceous particles and raw materials that do not melt at the kneading temperature. In this case, all raw materials may be charged into the kneader and kneading and heating may be performed simultaneously, or the components other than the organic compound may be charged into the kneader, heated while stirring, and then the organic compound may be charged at room temperature or in a vulcanized molten state after the temperature has risen to the kneading temperature.

[0133] The lower limit of the heating temperature is above the softening point of the organic compound, preferably at least 10°C higher than the softening point, and more preferably at least 20°C higher than the softening point. The upper limit is preferably 450°C or lower, and more preferably 250°C or lower. If the heating temperature is too low, the viscosity of the organic compound may increase, making mixing difficult. If the heating temperature is too high, the viscosity of the mixed system may become too high due to the volatilization and polycondensation of the organic compound. To avoid these problems, the lower and upper limits of the heating temperature are preferably within the above ranges.

[0134] A mixer equipped with stirring blades is preferred, and general-purpose stirring blades such as Z-type or matiscalator-type blades can be used. The amount of raw materials to be put into the mixer is 10% or more by volume of the mixer's volume, preferably 15% or more by volume, and 50% or less by volume, preferably 30% or less by volume. The mixing time is required to be 5 minutes or more, and at most until a significant change in viscosity occurs due to the volatilization of volatile components, which is usually 30 to 120 minutes. It is preferable to preheat the mixer to the mixing temperature prior to mixing.

[0135] The resulting mixture may be subjected to a de-VM calcination process for the purpose of removing volatile components (hereinafter abbreviated as "VM") and carbonization, or it may be molded as needed for easier handling before being subjected to the de-VM calcination process. There are no particular restrictions on the molding method as long as it is possible to maintain the shape, and extrusion molding, die molding, hydrostatic molding, etc. can be used. Of these, die molding and hydrostatic molding, which maintain random particle orientation, are preferred over extrusion molding, in which particles tend to be oriented within the molded body.

[0136] The molding temperature can be either room temperature (cold) or heated (hot, above the binder's softening point). When molding cold, it is preferable to pre-crush the mixture, after kneading and cooling, to a maximum size of 1 mm or less in order to improve moldability and obtain uniformity of the molded body. There are no particular restrictions on the shape or size of the molded body, but in hot molding, if the molded body is too large, it takes time to perform uniform preheating before molding. To avoid this problem, it is preferable to keep the size to a maximum of about 150 cm or less.

[0137] The molding pressure should be set to 3 tf / cm² because excessively high pressure makes it difficult to remove volatile components (VM) through the pores of the molded body, and can cause non-circular carbonaceous particles to be oriented, making subsequent grinding difficult. 2 (294 MPa) or less, preferably 1500 kgf / cm² 2 (49 MPa) or less, more preferably 600 kgf / cm² 2 The pressure should be 0.98 MPa or less. There are no particular restrictions on the lower limit of pressure, but it is preferable to set it to a level that allows the molded body to maintain its shape during the de-VM process.

[0138] Step 2: The molded body obtained in Step 1 is heated and de-VM calcination is performed to remove volatile components (VM) generated from graphite particles, solvent, and organic compounds to obtain an intermediate material. De-VM calcination is performed for 0.1 to 10 hours at a calcination temperature with a lower limit of 600°C or higher, preferably 650°C or higher, and an upper limit of 1300°C or lower, preferably 1100°C or lower. To prevent oxidation, heating is performed under the flow of an inert gas such as nitrogen or argon, or in a non-oxidizing atmosphere with granular carbon material such as breeze or packing coke filling the gaps.

[0139] The equipment used for de-VM calcination is not particularly limited as long as it can calcine in a non-oxidizing atmosphere, such as reaction vessels like shuttle furnaces, tunnel furnaces, reed hammer furnaces, rotary kilns, and autoclaves, cokers (heat treatment tanks for coke production), electric furnaces, and gas furnaces. The heating rate is preferably low to remove volatile components, and the temperature is raised at a rate of 3 to 100°C / hr from around 200°C, where volatilization of low-boiling components begins, to around 700°C, where only hydrogen is generated. Stirring may be performed during the process as needed.

[0140] The carbon material intermediate obtained by de-VM calcination is subjected to high-temperature heating (calcination) treatment. When calcining organic compounds at low temperatures, the lower limit of the heating temperature is 600°C or higher, preferably 800°C or higher, more preferably 900°C or higher, and even more preferably 1000°C or higher, and the upper limit is 2600°C or lower, preferably 2200°C or lower, more preferably 1800°C or lower, and even more preferably 1500°C or lower.

[0141] To prevent oxidation, the heat treatment is carried out under the flow of an inert gas such as nitrogen or argon, or under a non-oxidizing atmosphere with granular carbon material such as breeze or packing coke filling the gaps. The equipment used for the heat treatment is not particularly limited as long as it is suitable for the above purpose, such as a shuttle furnace, tunnel furnace, reed hammer furnace, rotary kiln, autoclave or other reaction vessel, coker (heat treatment tank for coke production), electric furnace or gas furnace, Acheson furnace for electrode materials, etc., and the heating rate, cooling rate, heat treatment time, etc. can be arbitrarily set within the allowable range of the equipment used.

[0142] Step 3: The carbon material finally obtained in Step 2 is processed into powder by crushing, pulverizing, grinding, classifying, etc., as needed. This yields a powder of graphite particles coated on the surface with amorphous carbon (also referred to in this application as "amorphous carbon-coated spherical graphite powder"). There are no particular restrictions on the equipment used for crushing, but examples of coarse crushers include shear mills, jaw crushers, impact crushers, and cone crushers; examples of intermediate crushers include roll crushers and hammer mills; and examples of fine crushers include ball mills, vibratory mills, pin mills, agitator mills, and jet mills.

[0143] There are no particular restrictions on the equipment used for classification, but for example, in the case of dry sieving, rotary sieves, orbital sieves, vibrating sieves, etc. can be used, and in the case of dry airflow classification, gravity classifiers, inertial force classifiers, centrifugal classifiers (classifiers, cyclones, etc.) can be used, and wet sieving, mechanical wet classifiers, hydraulic classifiers, sedimentation classifiers, centrifugal wet classifiers, etc. can also be used.

[0144] <<Negative electrode>> In this invention, the term "negative electrode" refers to the negative electrode layer, which consists of a negative electrode current collector and a negative electrode active material layer, as described above. The method for forming the negative electrode will be explained below using a type A all-solid-state lithium secondary battery (101) and a type B all-solid-state lithium secondary battery (201).

[0145] The graphite anode active material layers (12, 22) were formed primarily of graphite particles coated with amorphous carbon on their surface (specifically, 50% by weight or more in the graphite anode active material layers (12, 22) constituting the anodes (14, 17)) and did not contain inorganic solid electrolytes, using the following coating and filling methods.

[0146] Coating methods include spray coating, blade coating, slit die coating, roll coating, and dry coating. Taking spray coating as an example, a dispersion containing graphite particles coated with amorphous carbon is applied to the surface of the negative electrode current collector (11, 21) by spray coating. This forms a graphite negative electrode active material layer (12, 22) mainly composed of graphite particles coated with amorphous carbon, and does not contain an inorganic solid electrolyte within the negative electrode layer, thereby obtaining the negative electrode (14, 17). The spray coating method has the advantage of maximizing the energy density of the negative electrode (14, 24) because it can form the negative electrode layer (14, 24) without using a binder. On the other hand, the spray coating method has a limit to the thickness of the negative electrode that can be formed. If it is desired to address this problem, blade coating, slit die coating, or roll coating methods using a slurry mixed with a small amount of binder solution, similar to current lithium-ion batteries that use an electrolyte, should be used. Dry coating, a method for forming electrodes without using solvents, has the advantage of being environmentally friendly, although the manufacturing conditions for the negative electrode layer (14, 24) are limited.

[0147] Furthermore, the following methods are possible, but are not limited to, the filling method. For example, a solid electrolyte material powder and, if necessary, other components (e.g., binders) are placed in a compression cylinder for powder compression molding, and a solid electrolyte powder layer deposited to a uniform thickness is formed as a solid electrolyte separator layer (13, 25) by compression molding with a press. Then, on top of the solid electrolyte separator layer (13, 25), a graphite particle powder coated with amorphous carbon on its surface, which will be the raw material for the graphite anode active material layer (12, 22), is placed (filled), and a graphite anode active material layer (12, 22) deposited to a uniform thickness is formed by compression molding with a press. In this case, if the function of the anode current collector (11, 21) is also incorporated, an anode layer (14, 17) is obtained. The graphite anode (12, 22) and the solid electrolyte separator layer (13, 25) may be compressed and molded at the same time, or they may be compressed and molded separately.

[0148] A small amount of liquid electrolyte may be added as an auxiliary layer to the negative electrode and the solid electrolyte interface, and to the positive electrode and the solid electrolyte interface, as a layer to reduce ion resistance. The amount of electrolyte added is preferably 1% to 10% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the graphite negative electrode active material layer, the positive electrode active material layer, and the solid electrolyte layer.

[0149] Liquid electrolytes include non-aqueous electrolytes prepared by dissolving a lithium salt in a non-aqueous solvent, and non-aqueous electrolytes prepared in the form of gels, rubbers, or solid sheets using organic polymer compounds. The non-aqueous solvent used in the non-aqueous electrolyte is not particularly limited and can be appropriately selected from known non-aqueous solvents that have been conventionally proposed as solvents for non-aqueous electrolytes. These non-aqueous solvents may be used individually or in mixtures of two or more. The lithium salt used in the non-aqueous electrolyte is also not particularly limited and can be appropriately selected from known lithium salts that are known to be usable for this purpose. The lithium salt may be used individually or in mixtures of two or more.

[0150] Furthermore, the above-mentioned non-aqueous electrolyte can be used in the form of a gel, rubber, or solid sheet by adding an organic polymer compound. The above-mentioned non-aqueous electrolyte may also contain a film-forming agent. In addition, an overcharge prevention agent may be added.

[0151] Furthermore, polymers that are conductors of alkali metal cations such as lithium ions are used as electrolytes. Solid electrolytes can also be used.

[0152] With regard to conditions not specified in this application, there are no particular restrictions as long as the objectives of the present invention are achieved. [Examples]

[0153] The embodiments for carrying out the present invention will be described in detail below. It should be noted that the present invention is not limited to the following embodiments, and can be carried out with various modifications within the scope of its gist. First, the method for preparing the samples will be summarized, and then the characteristics will be described. Table 1 summarizes the types of graphite constituting each negative electrode active material layer and the measurement results for the predetermined physical properties of each graphite in each example and comparative example.

[0154] (Solid electrolyte A) In a glove box under an argon atmosphere, Li2S and P2S5 were mixed in a molar ratio of 4:1 to obtain the raw material composition. Next, 1 g of the raw material composition was placed in a zirconia pot (45 mL) together with 80 zirconia balls (diameter (φ): 5 mm), and the pot was completely sealed. These operations were performed under an argon atmosphere. This pot was mounted on a planetary ball mill (P7, manufactured by Fritsch Japan), and mechanical milling was performed for 20 hours at a plate rotation speed of 500 rpm. This yielded a powder of the sulfide inorganic solid electrolyte Li8P2S9, which was designated as solid electrolyte A.

[0155] (Solid electrolyte B) As solid electrolyte B, Li has a diameter (φ) of 10 mm and a thickness of 2 mm. 6.6 La3Zr1.6 Ta 0.4 O 12 A sintered oxide inorganic solid electrolyte (manufactured by Toyoshima Seisakusho) was used.

[0156] (Low coverage amorphous carbon-coated spherical graphite powder) Spherical graphite obtained by spheroidizing natural graphite was mixed with an organic compound, and the mixture was heat-treated in an inert gas at a constant temperature of 1100°C or higher. The resulting calcined material was then crushed and classified to obtain graphite particle powder (i.e., low-coverage amorphous carbon-coated spherical graphite powder), which is a spherical multilayer structure carbon material with a low coverage of amorphous carbon on its surface. The coverage of the low-coverage amorphous carbon-coated spherical graphite powder (specifically, the proportion of amorphous carbon covering the surface of each low-coverage amorphous carbon-coated spherical graphite particle constituting the low-coverage amorphous carbon-coated spherical graphite powder) was confirmed to be due to the amorphous carbon coating by measuring the weight change rate of the graphite powder before and after coating. Table 1 shows the measurement results for the obtained "low-coverage amorphous carbon-coated spherical graphite powder," including average particle size (d50), specific surface area, tap density, circularity, Raman R value, d002 value, and Lc value. As shown in Table 1, the obtained low-coverage amorphous carbon-coated spherical graphite powder was used in Examples 1 to 7, Examples 9 to 10, and Comparative Example 5, which will be described later.

[0157] (High coverage amorphous carbon-coated spherical graphite powder) Except for changing the mixing ratio of spherical graphite obtained by spheroidizing natural graphite and an organic compound, the procedure was carried out in the same manner as in Example 1, and a powder of graphite particles, which is a spherical multilayer structure carbon material with a high coverage of amorphous carbon on its surface (i.e., high coverage amorphous carbon coated spherical graphite powder), was obtained. In this example, of the two amorphous carbon coated spherical graphite powders whose coating with amorphous carbon was confirmed by measuring the weight change rate of the graphite powder before and after coating, the one with the lower coverage rate was designated as "low coverage amorphous carbon coated spherical graphite powder," and the one with the higher coverage rate was designated as "high coverage amorphous carbon coated spherical graphite powder." In fact, as shown in Table 1, the specific surface area of ​​the "low coverage amorphous carbon coated spherical graphite powder" was 4.4 m². 2 The Raman R value is 0.41, and the specific surface area of ​​the "high coverage amorphous carbon-coated spherical graphite powder" is 3.7 m². 2 The particle size per g and Raman R value of 0.46 indicate that the "high-coverage amorphous carbon-coated spherical graphite powder" has a higher amorphous carbon coverage than the "low-coverage amorphous carbon-coated spherical graphite powder." The physical properties of the obtained "high-coverage amorphous carbon-coated spherical graphite powder," such as average particle size (d50), specific surface area, tap density, circularity, Raman R value, d002 value, and Lc value, were measured using the same method as in Example 1. The results are shown in Table 1. As shown in Table 1, the obtained high-coverage amorphous carbon-coated spherical graphite powder was used in Example 8, which will be described later.

[0158] (Graphite powder before amorphous carbon coating) The average particle size (d50) of the spherical graphite particle powder obtained by spheroidizing natural graphite (i.e., graphite powder before amorphous carbon coating) was 8 μm, the circularity was 0.92, and the Raman R value was 0.31. This amorphous graphite powder before amorphous carbon coating was used in Comparative Examples 1 to 4, 6, 8 to 11, and 12, as described later, as shown in Table 1.

[0159] (Amorphous carbon powder) Table 1 shows the physical properties of the amorphous carbon particle powder (i.e., amorphous carbon powder) used in Example 5, Comparative Example 7, and Comparative Example 8, described later, including the average particle size (d50). Although not shown in Table 1, the presence of amorphous carbon coating was measured using the TG-DTA measurement method with the Rigaku TG8120 differential thermal balance described above. For the "low-coverage amorphous carbon-coated spherical graphite powder" and the "high-coverage amorphous carbon-coated spherical graphite powder," it was confirmed that "(DTA at the first peak [μV]) / (DTA at the second peak [μV])" was 0.1 or greater, while for the "graphite powder before amorphous carbon coating," it was confirmed that "(DTA at the first peak [μV]) / (DTA at the second peak [μV])" was far below 0.1.

[0160] [Table 1]

[0161] (Graphite dispersion A) As graphite dispersion A, a dispersion was used in which 4.5 g of low-coverage amorphous carbon-coated spherical graphite powder (manufactured by Mitsubishi Chemical Corporation, average particle size (d50): 8 μm) shown in Table 1 was dispersed in a mixed solvent of 15 g of 99.5% ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 1.5 g of propylene glycol 1-monomethyl ether 2-acetate (manufactured by Tokyo Chemical Industries, Ltd.).

[0162] (Graphite dispersion B) For graphite dispersion B, the same dispersion as graphite dispersion A was used, except that the type of dispersed phase was changed from the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 to the high-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 (manufactured by Mitsubishi Chemical Corporation, average particle size (d50): 8 μm).

[0163] (Graphite dispersion C) For graphite dispersion C, the same dispersion as graphite dispersion A was used, except that the mixed solvent was changed to 30 g of 99.5% ethanol, 150 mg of propylene glycol 1-monomethyl ether 2-acetate, and 15 mg of deionized water.

[0164] (Graphite dispersion D) For graphite dispersion D, the same dispersion as graphite dispersion A was used, except that the type of dispersed phase was changed from the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 to the graphite powder before amorphous carbon coating (manufactured by Mitsubishi Chemical Corporation, average particle size (d50): 8 μm) shown in Table 1.

[0165] Table 2 summarizes the graphite dispersions A to D described above.

[0166] [Table 2]

[0167] (Graphite and silicon mixed dispersion A) For the mixed dispersion A of graphite and silicon, the same dispersion as graphite dispersion A was used, except that the weight of the low-coverage amorphous carbon-coated spherical graphite powder (manufactured by Mitsubishi Chemical Corporation, average particle size (d50): 8 μm) shown in Table 1 was set to 0.9 g, and 90 mg of silicon powder (manufactured by Alfa Aesar, average particle size: 50 nm) was added to make the dispersed phase a mixture of graphite and silicon.

[0168] (Graphite and silicon mixed dispersion B) For mixed dispersion B of graphite and silicon, the same dispersion as mixed dispersion A of graphite and silicon was used, except that the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 was changed to graphite powder before amorphous carbon coating (manufactured by Mitsubishi Chemical Corporation, average particle size (d50): 8 μm).

[0169] Table 3 summarizes the above graphite and silicon mixed dispersions A and B.

[0170] [Table 3]

[0171] (Evaluation half-battery) In the examples, to eliminate the influence of the positive electrode used and investigate the interfacial bonding with a layer that uses pure graphite as the negative electrode active material (i.e., a graphite negative electrode active material layer), half-cells (102, 202) of an all-solid-state lithium secondary battery were fabricated (see Figures 3 and 4). Figure 3 is a schematic diagram showing the configuration of half-cell (102) of a so-called sulfide-type all-solid-state lithium secondary battery, in which a layer made of an inorganic solid electrolyte, a sulfide inorganic solid electrolyte, is used as the separator layer (33), and a foil with lithium and indium attached (also referred to in this application as "lithium-indium foil") was used as the counter electrode (34). Figure 4 is a schematic diagram showing the configuration of half-cell (202) of a so-called oxide-type all-solid-state lithium secondary battery, in which a layer made of an inorganic solid electrolyte, an oxide inorganic solid electrolyte, is used as the separator layer (44), and a lithium foil was used as the counter electrode (45). The characteristics of each half-cell (102, 202) of the fabricated all-solid-state lithium secondary battery were evaluated. In addition, in the half-cells (102, 202) of an all-solid-state lithium secondary battery, the graphite electrode, which has a higher electrochemical potential, becomes the positive electrode, and the lithium metal, which has a lower potential, becomes the negative electrode. Therefore, to avoid confusion with the configuration of an all-solid-state lithium secondary battery (101, 201), for convenience, in Figures 3 and 4, the positive electrode current collectors represented by reference numerals 31 and 41 and the negative electrode current collectors represented by reference numerals 35 and 46 are simply referred to as "current collectors," and the negative electrode active material layer (32, 42) is simply referred to as the "test negative electrode active material layer."

[0172] <Example 1> (Preparation process (spray coating method) and manufacturing process of the half-cell (102) of a type A all-solid-state lithium secondary battery by pressure molding) 1. First, using a small spray coating device (AV-8 model, manufactured by A-Sing Technologies), graphite dispersion A was spray-coated onto an unpolished SUS304 disc with a diameter (φ) of 10 mm and a thickness of 0.5 mm. The amount of graphite dispersion A applied (specifically, the amount of low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1) was 2.19 mg / cm². 2 A test negative electrode active material layer (32) was obtained on a stainless steel current collector (31). 2. 150 mg of solid electrolyte A (Li8P2S9) powder was added to a PET (polyethylene terephthalate) cylinder with an inner diameter of 10 mm and pressed at 357 MPa to form a solid electrolyte material portion (i.e., a solid electrolyte separator layer (33)) consisting of the solid electrolyte A. 3. In this embodiment, a lithium-indium foil was used as the counter electrode (34), which consisted of an indium foil (manufactured by Rare Metallic Co., Ltd., diameter (φ): 10 mm, thickness: 0.1 mm) with a lithium foil (manufactured by Honjo Chemical Co., Ltd., diameter (φ): 10 mm, thickness: 0.05 mm) attached to it. The lithium foil side of the lithium-indium foil was placed on one surface of a solid electrolyte separator layer (33) made of solid electrolyte A, and then the test negative electrode active material layer (32) was placed on the other surface of the separator layer (33). Subsequently, the test negative electrode active material layer (32) on the stainless steel current collector (31), the separator layer (33) of solid electrolyte A, the lithium-indium foil counter electrode (34), and the stainless steel current collector (35) were joined together to obtain a primary assembly.

[0173] The obtained primary assembly was screwed together with a torque of 6.0 Nm, thereby applying a constraining pressure of 120 MPa in the stacking direction to obtain a half-cell (102) of a type A all-solid-state lithium secondary battery.

[0174] <Example 2> Table 1 shows the coating amount of low-coverage amorphous carbon-coated spherical graphite powder: 3.48 mg / cm² 2 Except for the change made, the half-cell (102) of the all-solid-state lithium secondary battery of Example 2 was obtained in the same manner as in Example 1.

[0175] <Example 3> The coating amount of the low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 was changed to 4.59 mg / cm 2 A half-cell (102) of an all-solid-state lithium secondary battery of Example 3 was obtained in the same manner as in Example 1, except that the coating amount was changed as described above.

[0176] <Example 4> (Preparation process (filling method) and pressing process of a half-cell (102) of a type A all-solid-state lithium secondary battery) 1. In the same manner as in Example 1, 150 mg of the powder of solid electrolyte A (Li8P2S9) was added into a PET cylinder with an inner diameter of 10 mm and pressed at 357 MPa to form a solid electrolyte material part made of solid electrolyte A. 2. On one surface of the separator layer (33) which is the above solid electrolyte material part, the low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material constituting the test negative electrode active material layer (32) was added (filled) so as to be 12.74 mg / cm 2 Subsequently, after arranging the indium foil side of the lithium-indium foil in which a lithium foil (manufactured by Honjo Chemical Co., Ltd., diameter (φ): 10 mm, thickness: 0.05 mm) was attached to an indium foil (manufactured by Rare Metallic Co., Ltd., diameter (φ): 10 mm, thickness: 0.1 mm) as the counter electrode (34) on the other surface of the solid electrolyte material part, it was pressed at 535 MPa, and a graphite negative electrode layer (that is, a negative electrode composed of a stainless steel current collector (31) and a test negative electrode active material layer (32) using the low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material), a separator layer (33) of solid electrolyte A, a counter electrode (34) of lithium-indium foil, and a stainless steel current collector (35) were obtained to form a primary assembly.

[0177] In the same manner as in Example 1, the obtained primary assembly was screwed with a torque of 6.0 Nm to apply a constraint pressure of 120 MPa in the stacking direction to obtain a half-cell (102) of an all-solid-state lithium secondary battery.

[0178] <Example 5> In Example 4, a test negative electrode active material layer (32) (i.e., a layer using the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material) was obtained using only the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1. The low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 and the amorphous carbon powder shown in Table 1 were each measured at 6.37 mg / cm³. 2 and 0.64 mg / cm³ 2 Except for mixing and adding (filling) the materials in such a manner to obtain the test negative electrode active material layer (32), which is the negative electrode mixture layer, the half-cell (102) of the all-solid-state lithium secondary battery of Example 5 was obtained in the same manner as in Example 4.

[0179] <Example 6> (Preparation process (spray coating method) and pressurization process for half-cell (202) of a Type B all-solid-state lithium secondary battery) 1. The amount of graphite dispersion A applied in Example 1 (specifically, the amount of low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1) was 1.96 mg / cm². 2 Except for the change made, the test negative electrode active material layer (42) of Example 6 was obtained on the stainless steel current collector (41) in the same manner as in Example 1. 2. Using a compact sputtering apparatus (Sanyu Electronics Co., Ltd., SC-701MkII ADVANCE), a sintered body of solid electrolyte B (10 mm (diameter (φ)) × 2 mm (thickness), Li 6.6 La3Zr 1.6 Ta 0.4 O 12 (manufactured by Toyoshima Seisakusho) sintered body) has 0.34 mg / cm² of material applied to both surfaces. 2 A gold layer was obtained. A sintered body of solid electrolyte B, with both sides coated with the gold layer, was used as the solid electrolyte separator layer (44). 3. A lithium foil (manufactured by Honjo Chemical Co., Ltd.) was used as the counter electrode (45). The lithium foil was placed on one surface of the solid electrolyte B, which is a separator layer (44) coated with a gold layer. Subsequently, the test negative electrode active material layer (42) was placed on the other surface of the solid electrolyte B, which is a separator layer (44) coated with a gold layer. Here, of the two gold layers coating the surface of the solid electrolyte B, which is the separator layer (44), the gold layer in contact with the surface of the test negative electrode active material layer (42) was designated as the low-resistance layer (43). Then, the test negative electrode active material layer (42) on the stainless steel current collector (41), the solid electrolyte B (44) which is coated on both sides with gold layers and in which the gold layer in contact with the surface of the test negative electrode active material layer (42) is designated as the low-resistance layer (43), the Li foil counter electrode (45), and the stainless steel current collector (46) were joined together to obtain a primary assembly. The gold layer on the surface of the solid electrolyte B (= solid electrolyte separator layer (44)) in contact with the counter electrode (45) of the lithium foil is merely a layer provided to improve the physical contact with the polished surface of the commercially available lithium foil used to remove impurities. If the surface of the lithium foil is purified, such as by a vapor-deposited film, this layer is unnecessary and does not directly affect the configuration of the all-solid-state lithium secondary battery (201) or the half-cell (202) of the all-solid-state lithium secondary battery in this embodiment. For this reason, it is not shown in Figures 2 and 4.

[0180] The obtained primary assembly was screwed together with a torque of 2.0 Nm, thereby applying a constraining pressure of 40 MPa in the stacking direction to obtain a half-cell (202) of the all-solid-state lithium secondary battery.

[0181] <Example 7> Graphite dispersion A was spray-coated onto a copper disc with a diameter (φ) of 10 mm and a thickness of 2 μm. The amount of low-coverage amorphous carbon-coated spherical graphite powder contained in graphite dispersion A, as shown in Table 1, was applied at a rate of 2.17 mg / cm². 2 Except for the difference made, the half-cell (202) of the all-solid-state lithium secondary battery of Example 7 was obtained in the same manner as in Example 6.

[0182] <Example 8> Using graphite dispersion B, a layer was obtained as the test negative electrode active material layer (42) using the high-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material, and the coating amount of the high-coverage amorphous carbon-coated spherical graphite powder was 2.11 mg / cm². 2 Except for the difference, the half-cell (202) of the all-solid-state lithium secondary battery of Example 8 was obtained in the same manner as in Example 7.

[0183] <Example 9> In Example 7, graphite dispersion A was replaced with a mixed dispersion A of graphite and silicon to obtain a negative electrode mixture layer consisting of low-coverage amorphous carbon-coated spherical graphite powder and silicon powder as shown in Table 1, which was used as the test negative electrode active material layer (42). The coating amounts of low-coverage amorphous carbon-coated spherical graphite powder and silicon powder in the negative electrode mixture layer were set to 1.45 mg / cm², respectively. 2 and 0.15 mg / cm³ 2 Except for the difference made, the half-cell (202) of the all-solid-state lithium secondary battery of Example 9 was obtained in the same manner as in Example 7.

[0184] <Example 10> In Example 6, graphite dispersion A was replaced with graphite dispersion C to obtain a layer using the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material, which was used as the test negative electrode active material layer (42). The amount of the low-coverage amorphous carbon-coated spherical graphite powder applied was 3.83 mg / cm². 2 Except for the difference made, a half-cell (202) of the all-solid-state lithium secondary battery of Example 10 was obtained in the same manner as in Example 6.

[0185] <Comparative Example 1> (Preparation process (spray coating method) and pressurization process for half-cell (102) of a Type A all-solid-state lithium secondary battery) In Example 1, graphite dispersion A was replaced with graphite dispersion D, and a layer using graphite powder before amorphous carbon coating as the negative electrode active material, as shown in Table 1, was obtained as the test negative electrode active material layer (32). The amount of the graphite powder before amorphous carbon coating was applied was 1.83 mg / cm². 2Except for the difference, a half-cell (102) of the all-solid-state lithium secondary battery of Comparative Example 1 was obtained in the same manner as in Example 1.

[0186] <Comparative Example 2> Table 1 shows the amount of graphite powder applied before amorphous carbon coating: 3.49 mg / cm² 2 Except for the difference mentioned above, a half-cell (102) of the all-solid-state lithium secondary battery for Comparative Example 2 was obtained in the same manner as for Comparative Example 1.

[0187] <Comparative Example 3> Table 1 shows the amount of graphite powder applied before amorphous carbon coating: 4.04 mg / cm² 2 Except for the difference mentioned above, a half-cell (102) of the all-solid-state lithium secondary battery of Comparative Example 3 was obtained in the same manner as in Comparative Example 1.

[0188] <Comparative Example 4> Instead of the low coverage amorphous carbon-coated spherical graphite powder shown in Table 1, use the graphite powder before amorphous carbon coating shown in Table 1 (12.74 mg / cm³). 2 A half-cell (102) of the all-solid-state lithium secondary battery of Comparative Example 4 was obtained in the same manner as in Example 4, except that the mixture was added (filled).

[0189] <Comparative Example 5> In Example 4, when a test negative electrode active material layer (32) (i.e., a layer using the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1 as the negative electrode active material) was obtained using only the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1, the low-coverage amorphous carbon-coated spherical graphite powder and the solid electrolyte A (Li8P2S9) powder were both added at a concentration of 6.40 mg / cm³. 2 Except for mixing and adding (filling) the materials in such a manner to obtain the test negative electrode active material layer (32), which is the negative electrode mixture layer, a half-cell (102) of the all-solid-state lithium secondary battery of Comparative Example 5 was obtained in the same manner as in Example 4.

[0190] <Comparative Example 6> The low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 was changed to the graphite powder before amorphous carbon coating shown in Table 1, and a test negative electrode active material layer (32) which is a negative electrode binder layer composed of the graphite powder before amorphous carbon coating and the powder of solid electrolyte A (Li8P2S9) was obtained. A half-cell (102) of an all-solid-state lithium secondary battery of Comparative Example 6 was obtained in the same manner as in Comparative Example 5, except for this.

[0191] <Comparative Example 7> The low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 was changed to amorphous carbon powder 12.74 mg / cm shown in Table 1 2 A half-cell (102) of an all-solid-state lithium secondary battery of Comparative Example 7 was obtained in the same manner as in Example 4, except that it was changed.

[0192] <Comparative Example 8> The low coating rate amorphous carbon-coated spherical graphite powder shown in Table 1 was changed to the graphite powder before amorphous carbon coating shown in Table 1, and a test negative electrode active material layer (32) which is a negative electrode binder layer composed of the graphite powder before amorphous carbon coating and the amorphous carbon powder shown in Table 1 was obtained. A half-cell (102) of an all-solid-state lithium secondary battery of Comparative Example 8 was obtained in the same manner as in Example 5, except for this.

[0193] <Comparative Example 9> The graphite dispersion liquid A in Example 6 was changed to graphite dispersion liquid D, and a layer using the graphite powder before amorphous carbon coating shown in Table 1 as a negative electrode active material was obtained as a test negative electrode active material layer (42), and the coating amount of the graphite powder before amorphous carbon coating was 2.01 mg / cm 2 A half-cell (202) of an all-solid-state lithium secondary battery of Comparative Example 9 was obtained in the same manner as in Example 6, except that it was changed to this.

[0194] <Comparative Example 10> The graphite dispersion liquid D was spray-coated onto a copper disk having a diameter (φ) of 10 mm and a thickness of 2 μm, and the coating amount of the graphite powder before amorphous carbon coating contained in the graphite dispersion liquid D was 2.10 mg / cm 2Except for the above, a half-cell (202) of the all-solid-state lithium secondary battery of Comparative Example 10 was obtained in the same manner as in Comparative Example 9.

[0195] <Comparative Example 11> In Example 9, the mixed dispersion A of graphite and silicon was changed to the mixed dispersion B of graphite and silicon, and the negative electrode mixture layer consisting of graphite powder and silicon powder before amorphous carbon coating, as shown in Table 1, was obtained as the test negative electrode active material layer (42). The coating amounts of the graphite powder and silicon powder before amorphous carbon coating were each 1.44 mg / cm². 2 and 0.14 mg / cm³ 2 Except for the difference made, a half-cell (202) of the all-solid-state lithium secondary battery of Comparative Example 11 was obtained in the same manner as in Example 9.

[0196] <Comparative Example 12> Table 1 shows the amount of graphite powder applied before amorphous carbon coating: 5.90 mg / cm². 2 Except for the above, a half-cell (202) of the all-solid-state lithium secondary battery of Comparative Example 12 was obtained in the same manner as in Comparative Example 10.

[0197] Table 4 summarizes the types of graphite listed in Table 1 and the amounts of graphite applied or filled to prepare each negative electrode active material layer in Examples 1-4, 6-8, and 10, and Comparative Examples 1-4, 7, 9-10, and 12. Table 5 summarizes the types of graphite and other materials listed in Table 1 and applied or filled to prepare each negative electrode mixture layer in Examples 5 and 9, and Comparative Examples 5-6, 8, and 11, as well as the amounts of graphite applied or filled. As shown in Table 5, the content of "low coverage amorphous carbon-coated spherical graphite powder" in each negative electrode active material layer of Examples 5, 9, and Comparative Example 5 is 91% by weight.

[0198] [Table 4]

[0199] [Table 5]

[0200] <Characteristic evaluation of half-cells of all-solid-state lithium secondary batteries obtained in each example and comparative example> (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Examples 1-4 and Comparative Examples 1-4) Using the half-cells of all-solid-state lithium secondary batteries employing the negative electrodes described in Examples 1-4 and Comparative Examples 1-4, initial charge-discharge tests were performed in a voltage range of 0.01V-1.2V relative to lithium metal. As the solid electrolyte for the solid electrolyte separator layer (33), an inorganic solid electrolyte, a sulfide inorganic solid electrolyte (Li8P2S9), was used.

[0201] As described above, the negative electrodes described in Examples 1 to 4 have a negative electrode active material layer (32) which does not contain a solid electrolyte and consists only of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1, while the negative electrodes described in Comparative Examples 1 to 4 have a negative electrode active material layer (32) which does not contain a solid electrolyte and consists only of graphite particles before amorphous carbon coating as shown in Table 1.

[0202] The half-cells of the all-solid-state lithium secondary batteries obtained in Examples 1-4 and Comparative Examples 1-4 had a current value of 100 μA / cm². 2 Charge-discharge tests were conducted (Table 6). The initial charge-discharge curves obtained from the test results are shown in Figures 5-8 and 10-13. The initial discharge capacity and initial irreversible capacity obtained from the test results are summarized in Table 7. In Table 7, the active material weight and electrode weight refer to the weight of the negative electrode active material in the negative electrode active material layer and the weight of the negative electrode, respectively. The test atmosphere was an argon atmosphere.

[0203] As shown in Table 7, the initial charge / discharge capacity per unit weight of active material of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Examples 1 to 4 was confirmed to be approximately 40% to 60% of the initial charge / discharge capacity per unit weight of active material of the half-cell of the all-solid-state lithium secondary battery obtained in Examples 1 to 4. In other words, it was confirmed that using the negative electrode according to the embodiment of the present invention (i.e., a negative electrode including a graphite negative electrode layer containing graphite particles coated on its surface with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer) in the half-cell of an all-solid-state lithium secondary battery can significantly improve the initial charge / discharge capacity per unit weight of active material. Therefore, it was found that the negative electrode according to the embodiment of the present invention facilitates the movement of lithium ions in the direction perpendicular to the surface of the graphite negative electrode active material layer, resulting in a high utilization rate of the negative electrode active material. Furthermore, it was found that the negative electrode according to the embodiment of the present invention can improve the battery capacity of an all-solid-state lithium secondary battery without including an inorganic solid electrolyte in the negative electrode active material layer.

[0204] (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Example 3, Comparative Example 3, and Comparative Examples 5-6) The initial charge-discharge tests of the half-cells of each all-solid-state lithium secondary battery obtained using the negative electrodes described in Example 3 and Comparative Example 3 are as described above.

[0205] The initial charge-discharge tests of the half-cells of each all-solid-state lithium secondary battery obtained using the negative electrodes described in Comparative Examples 5 and 6 are as follows:

[0206] Using half-cells of all-solid-state lithium secondary batteries employing the negative electrodes described in Comparative Examples 5 and 6, initial charge-discharge tests were performed in a voltage range of 0.01V-1.2V relative to lithium metal.

[0207] As described above, the negative electrode described in Example 3 has a negative electrode active material layer (32) which is the negative electrode active material layer, and does not contain a solid electrolyte, but consists only of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1. The negative electrode described in Comparative Example 3 has a negative electrode active material layer (32) which is the negative electrode active material layer, and does not contain a solid electrolyte, but consists only of graphite particles before amorphous carbon coating as shown in Table 1. The negative electrodes described in Comparative Examples 5 and 6 have a composite layer (i.e., a negative electrode composite layer) which is the negative electrode active material layer (32) which is the negative electrode active material layer, and consists of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1 and powder of solid electrolyte A (Li8P2S9).

[0208] The half-cells of the all-solid-state lithium secondary batteries obtained in Comparative Examples 5 and 6 had a current value of 100 μA / cm². 2 Charge and discharge tests were conducted (Table 6). The initial charge and discharge curves obtained as test results are shown in Figure 14 (Comparative Example 5) and Figure 15 (Comparative Example 6). The initial discharge capacity and initial irreversible capacity obtained as test results are shown in Table 7. The test atmosphere was an argon atmosphere.

[0209] As shown in Table 7, the initial charge / discharge capacity per unit weight of active material, as shown by the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 5, was confirmed to be equivalent to the initial charge / discharge capacity per unit weight of active material, as shown by the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 6.

[0210] Furthermore, when comparing the negative electrodes described in Example 3 and Comparative Example 3, which have the same amount of graphite used to fabricate the negative electrode active material layer and whose negative electrode active material layer consists of only one type of graphite, the following was confirmed.

[0211] As shown in Table 7, the initial charge / discharge capacity per unit weight of active material for a half-cell of the all-solid-state lithium secondary battery obtained using the negative electrode described in Example 3 was 231 mAh / g. The initial charge / discharge capacities per unit weight of active material for a half-cell of the all-solid-state lithium secondary batteries obtained in Comparative Examples 5 and 6 were 270 mAh / g and 271 mAh / g, respectively, confirming that all of them exhibited high initial charge / discharge capacities per unit weight of active material.

[0212] On the other hand, the initial charge / discharge capacity per unit weight of active material obtained by the half-cell of the all-solid-state lithium secondary battery in Comparative Example 3 was 99 mAh / g, as shown in Table 7, which was found to be less than 40% of the initial discharge capacity per unit weight of active material obtained in Comparative Examples 5 and 6.

[0213] Therefore, from the above results of Example 3 and Comparative Example 3, it was found that when the negative electrode of the embodiment of the present invention is used as a negative electrode for an all-solid-state lithium secondary battery, the movement of lithium ions in the direction perpendicular to the plane of the graphite negative electrode active material layer constituting the negative electrode becomes easier, thereby enabling a high utilization rate of the graphite negative electrode active material (i.e., a high energy density).

[0214] Furthermore, as shown in Table 7, in both Comparative Examples 5 and 6, 50% by weight of the negative electrode active material layer is an inorganic solid electrolyte. Although the initial discharge capacity per unit weight of active material is 270 mAh / g and 271 mAh / g, respectively, when converted to the initial discharge capacity per unit weight of electrode, it is 135 mAh / g and 136 mAh / g, respectively. On the other hand, in Example 3, where the negative electrode active material layer consists only of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1, and does not contain a solid electrolyte, the discharge capacity per unit weight of electrode is 231 mAh / g, the same as the initial discharge capacity per unit weight of active material, which is significantly higher than the results of Comparative Examples 5 and 6. Therefore, it was found that when the negative electrode of the embodiment of the present invention is used as the negative electrode of an all-solid-state lithium secondary battery, it is not necessary to include an inorganic solid electrolyte in the negative electrode, and thus the battery capacity of the all-solid-state lithium secondary battery can be further improved compared to when an inorganic solid electrolyte is included.

[0215] (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Example 5, Comparative Example 7, and Comparative Example 8) Using the all-solid-state lithium-ion half-cells obtained in Example 5, Comparative Example 7, and Comparative Example 8, initial charge-discharge tests were performed in a voltage range of 0.01V-1.2V relative to lithium metal.

[0216] As described above, the negative electrode described in Example 5 has a test negative electrode active material layer (32) which is the negative electrode active material layer, and is a composite layer (negative electrode composite layer) consisting of low-coverage amorphous carbon coated spherical graphite powder shown in Table 1 and amorphous carbon powder shown in Table 1. In other words, the negative electrode described in Example 5 has a composite layer (negative electrode composite layer) which is a composite layer (negative electrode composite layer) in which amorphous carbon is mixed with graphite powder whose particle surface is coated with amorphous carbon as another carbon material. The negative electrode described in Comparative Example 7 has a negative electrode active material layer (32) which is the negative electrode active material layer, and is a negative electrode active material layer consisting only of amorphous carbon powder shown in Table 1. The negative electrode described in Comparative Example 8 has a composite layer (negative electrode composite layer) which is a composite layer (negative electrode composite layer) consisting of graphite particles before amorphous carbon coating shown in Table 1 and amorphous carbon powder shown in Table 1, and is a composite layer (negative electrode composite layer) as the test negative electrode active material layer (32) which is the negative electrode active material layer.

[0217] The all-solid-state batteries obtained in Example 5, Comparative Example 7, and Comparative Example 8 had a current value of 100 μA / cm². 2 Charge and discharge tests were conducted (Table 6). The initial charge and discharge curves obtained from the test results are shown in Figures 9, 16, and 17. The initial discharge capacity and initial irreversible capacity obtained from the test results are shown in Table 7. The test atmosphere was an argon atmosphere.

[0218] As shown in Figures 16, 17, and Table 7, it was confirmed that the half-cells of the all-solid-state lithium secondary batteries obtained in Comparative Examples 7 and 8 exhibited poor initial charge-discharge efficiency and only yielded small discharge amounts. From this, it was found that when an all-solid-state lithium secondary battery is used with a negative electrode whose negative electrode active material layer consists only of amorphous carbon powder, as in Comparative Example 7, or when an all-solid-state lithium secondary battery is used with a negative electrode whose negative electrode active material layer is a composite layer (negative electrode composite layer) consisting of graphite particles and amorphous carbon powder before amorphous carbon coating, as in Comparative Example 8, the initial charge-discharge efficiency is poor and only small discharge amounts can be obtained. On the other hand, as shown in Figure 9 and Table 7, it was confirmed that the half-cell of the all-solid-state lithium secondary battery obtained in Example 5 maintained high initial charge-discharge efficiency and high discharge capacity. From this, it was found that when the negative electrode, which is a composite layer (negative electrode composite layer) in which amorphous carbon is mixed with graphite powder whose particle surface is coated with amorphous carbon, is used as an all-solid-state lithium secondary battery, as in Example 5, high initial charge-discharge efficiency and high discharge capacity are maintained.

[0219] Furthermore, from the above results of Example 5, Comparative Example 7, and Comparative Example 8, it was determined that 1V(vs.Li / Li) is the material for the negative electrode active material layer. + It was confirmed that simply using amorphous carbon alone, which can undergo lithium ion insertion reactions from a high potential of 1V (vs.Li / Li), does not yield the high charge-discharge characteristics shown when amorphous carbon-coated graphite particles are used as the material for the negative electrode active material layer. These high charge-discharge characteristics can only be obtained by using a carbon material in which graphite particles are coated with amorphous carbon as the material for the negative electrode active material layer. This indicates that it is difficult for lithium ions to move from amorphous carbon containing lithium to the graphite phase within the negative electrode active material layer but not within the same particle. When amorphous carbon-coated graphite particles are used, the amorphous carbon phase formed on the graphite surface is 1V (vs.Li / Li + It is understood that a large charge / discharge capacity is achieved because, after an insertion reaction of lithium ions occurs at a high potential, the lithium ions easily move into the graphite phase within the same particle.

[0220] (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Example 6 and Comparative Example 9) Using the all-solid-state lithium-ion half-cells obtained in Example 6 and Comparative Example 9, initial charge-discharge tests were performed in a voltage range of 0.01V-1.2V relative to lithium metal. As the solid electrolyte of the solid electrolyte separator layer (44), an inorganic solid electrolyte, an oxide inorganic solid electrolyte (Li 6.6 La3Zr 1.6 Ta 0.4 O 12 ) was used.

[0221] As described above, the negative electrode described in Example 6 has a negative electrode active material layer consisting only of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1, as the negative electrode active material layer, which is the test negative electrode active material layer (42). The negative electrode described in Comparative Example 9 has a negative electrode active material layer consisting only of graphite particles before amorphous carbon coating as shown in Table 1, as the test negative electrode active material layer (42).

[0222] The all-solid-state lithium-ion half-cells obtained in Example 6 and Comparative Example 9 were subjected to charge-discharge tests at a current value of 0.05C, calculated using the amount of graphite anode applied and the theoretical gravimetric capacity density of the graphite anode (372 mAh / g) (Table 6). The initial charge-discharge curves obtained as test results are shown in Figures 18 and 25. The initial discharge capacity and initial irreversible capacity obtained as test results are shown in Table 7. The test atmosphere was an argon atmosphere.

[0223] As shown in Table 7, the initial charge / discharge capacity per unit weight of active material of the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 9 was confirmed to be approximately 55% of the initial charge / discharge capacity per unit weight of active material of the half-cell of the all-solid-state lithium secondary battery obtained in Example 6. In other words, it was confirmed that using the negative electrode of the embodiment of the present invention (i.e., a negative electrode including a graphite negative electrode layer containing graphite particles coated on its surface with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer) in the half-cell of an all-solid-state lithium secondary battery can significantly improve the initial charge / discharge capacity per unit weight of active material. Therefore, it was found that with an all-solid-state lithium secondary battery using the negative electrode of the embodiment of the present invention, even if an inorganic solid electrolyte of oxide is used as the solid electrolyte separator layer instead of an inorganic solid electrolyte of sulfide, the movement of lithium ions in the direction perpendicular to the surface of the graphite negative electrode layer becomes easier, resulting in a high utilization rate. Furthermore, it has been found that, according to the negative electrode embodiment of the present invention, the battery capacity of an all-solid-state lithium secondary battery can be improved without including a solid electrolyte in the negative electrode active material layer.

[0224] (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Examples 7 and 8 and Comparative Example 10) Using the half-cells of the all-solid-state lithium secondary batteries obtained in Examples 7 and 8 and Comparative Example 10, an initial charge test was performed to 0.01V based on lithium metal. As the solid electrolyte of the solid electrolyte separator layer (44), an inorganic solid electrolyte oxide inorganic solid electrolyte (Li 6.6 La3Zr 1.6 Ta 0.4 O 12 ) was used.

[0225] As described above, the negative electrode described in Example 7 has a negative electrode active material layer (42) which does not contain a solid electrolyte and consists only of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1. The negative electrode described in Example 8 has a negative electrode active material layer (42) which does not contain a solid electrolyte and consists only of high-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1. The negative electrode described in Comparative Example 10 has a negative electrode active material layer (42) which does not contain a solid electrolyte and consists only of graphite particles before amorphous carbon coating as shown in Table 1. As described above, the amount of each negative electrode active material applied to prepare the negative electrode active material layer in Examples 7, 8, and Comparative Example 7 was 2.17 mg / cm². 2 , 2.11 mg / cm³ 2 , and 2.10 mg / cm³ 2 As can be seen from this, the amounts were made to be almost the same. In other words, when comparing the negative electrodes described in Examples 7 and 8 and Comparative Example 7, the only substantially different difference is the coverage rate of the amorphous carbon coating that covers the graphite powder, which is the negative electrode active material applied to produce the negative electrode active material layer.

[0226] The half-cells of the all-solid-state lithium secondary batteries obtained in Examples 7 and 8 and Comparative Example 10 were subjected to charging tests at a current value of 0.05C, calculated using the amount of graphite applied to fabricate the negative electrode active material layer in each negative electrode and the theoretical gravimetric capacity density of the graphite negative electrode (372 mAh / g) (Table 6). The initial charging curves obtained as test results are shown in Figures 19, 21, and 26, respectively. Furthermore, the initial charging capacity per unit weight of active material (i.e., gravimetric capacity density) for each half-cell of the all-solid-state lithium secondary battery obtained as test results is shown in Table 8, along with the type of negative electrode active material used in the calculation of its gravimetric capacity density. In Table 8, the active material weight refers to the weight of the negative electrode active material in the negative electrode active material layer. The test atmosphere was an argon atmosphere.

[0227] As shown in Table 8, it was confirmed that the initial charge capacity per unit weight of active material shown by the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 10 was approximately 65 to 68% of the initial charge capacity per unit weight of active material shown by the half-cell of the all-solid-state lithium secondary battery obtained in Examples 7 and 8. Furthermore, it was confirmed that the initial charge capacity per unit weight of active material shown by the half-cell of the all-solid-state lithium secondary battery obtained in Example 7 was approximately 95% of the initial charge capacity per unit weight of active material shown by the half-cell of the all-solid-state lithium secondary battery obtained in Example 8. Therefore, it was found that using a negative electrode according to an embodiment of the present invention (i.e., a negative electrode comprising a graphite negative electrode layer containing graphite particles coated on its surface with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer) in the half-cell of an all-solid-state lithium secondary battery significantly improves the initial charge / discharge capacity per unit weight of active material. Furthermore, it was found that using graphite particles coated with amorphous carbon to a high degree of coverage (i.e., spherical graphite powder coated with highly coverage amorphous carbon) further improves the initial charge / discharge capacity per unit weight of active material.

[0228] (XRD pattern measurements of each negative electrode after the initial charging test of the half-cells of each all-solid-state lithium secondary battery obtained in Examples 7 and 8 and Comparative Example 10, and the measurement results.) After performing the initial charge test using the half-cells of the all-solid-state lithium secondary batteries obtained in Examples 7 and 8 and Comparative Example 10, the all-solid-state batteries were disassembled in a glove box under an argon atmosphere. The primary assembly was sealed in an argon atmosphere using an X-ray diffraction atmosphere separator (manufactured by Rigaku Corporation), and X-rays were irradiated onto the graphite layer of the negative electrode active material through a copper disc, which is the current collector, to perform X-ray diffraction measurements. For the X-ray diffraction measurements, an X-ray diffractometer (Miniflex600, manufactured by Rigaku Corporation) was used, and measurements were performed in the diffraction angle range of 20°-30° (2θ). The X-ray diffraction patterns obtained from the test results are shown in Figure 20 (Example 7), Figure 22 (Example 8), and Figure 27 (Comparative Example 10).

[0229] From the X-ray diffraction patterns shown in Figure 20 (Example 7), Figure 22 (Example 8), and Figure 27 (Comparative Example 10), it was confirmed that in each negative electrode of the half-cell of the all-solid-state lithium secondary battery obtained in Examples 7, 8, and Comparative Example 10, after the initial charging test, the gold layer (gold film) constituting the negative electrode active material layer reacted with lithium and changed into a Li3Au alloy. On the other hand, when CC charging was performed using a current value of 0.05C at room temperature, lithium was only inserted up to the stage 2 charging state (stages will be described later) in the graphite layer, which is the negative electrode active material layer in the half-cell of the all-solid-state lithium secondary battery obtained in Comparative Example 8, before the amorphous carbon coating. On the other hand, it was found that lithium was inserted to a charge state close to Stage 1 in the graphite layer of the half-cell of the all-solid-state lithium secondary battery obtained in Example 7, and lithium was inserted to a charge state of Stage 1 in the graphite layer of the negative electrode active material layer of the half-cell of the all-solid-state lithium secondary battery obtained in Example 8. Let's explain what Stages 1 and 2 mean here. The reaction in which lithium ions are inserted into graphite is mainly a two-phase coexistence reaction, and when lithium ions enter graphite, a lithium-graphite intercalation compound is formed. A unique structure called a stage is known for the graphite intercalation compound. For example, if there are four graphite layers between the insertion species, it is Stage 4; if there are three, it is Stage 3; if there are two, it is Stage 2; and if there is one, it is Stage 1.

[0230] From the above, it was found that when a negative electrode according to an embodiment of the present invention (i.e., a negative electrode comprising a graphite negative electrode layer containing graphite particles whose surface is coated with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer) is used as a negative electrode for an all-solid-state lithium secondary battery, the movement of lithium ions in the direction perpendicular to the surface of the graphite negative electrode active material layer constituting the negative electrode becomes easier, thereby enabling a high utilization rate (i.e., high energy density) of the graphite particles, which are the negative electrode active material. Furthermore, it was found that by using a negative electrode according to an embodiment of the present invention, the all-solid-state battery can be operated reversibly even at room temperature, and a high-capacity all-solid-state lithium secondary battery with excellent charge-discharge characteristics at room temperature can be provided.

[0231] (Initial charge-discharge tests and results of half-cells of each all-solid-state lithium secondary battery obtained in Example 9 and Comparative Example 11) An initial charge test was performed using the all-solid-state lithium-ion half-cells obtained in Example 9 and Comparative Example 11, down to 0.01V based on lithium metal. The solid electrolyte separator layer (44) was an inorganic solid electrolyte, an oxide inorganic solid electrolyte (Li 6.6 La3Zr 1.6 Ta 0.4 O 12 ) was used.

[0232] As described above, the negative electrode described in Example 9 has a test negative electrode active material layer (42) which does not contain a solid electrolyte and is composed of a composite layer (negative electrode composite layer) consisting of low-coverage amorphous carbon-coated spherical graphite powder and silicon powder (manufactured by Alfa Aesar, average particle size 50 nm) as shown in Table 1. The negative electrode described in Comparative Example 11 has a test negative electrode active material layer (42) which does not contain a solid electrolyte and is composed of a composite layer (negative electrode composite layer) consisting of graphite powder before amorphous carbon coating and silicon powder (manufactured by Alfa Aesar, average particle size 50 nm) as shown in Table 1.

[0233] The half-cells of the all-solid-state lithium secondary batteries obtained in Example 9 and Comparative Example 11 were subjected to charging tests at a current value of 0.05C, calculated using the amount of graphite coated in the composite layer (negative electrode composite layer) made of graphite and silicon used to fabricate the negative electrode active material layer in each negative electrode, and the theoretical gravimetric capacity density (372 mAh / g) of the graphite negative electrode. The initial charging curves obtained as test results are shown in Figure 23 (Example 9) and Figure 28 (Comparative Example 11). The initial charging capacities obtained as test results are shown in Table 8. The test atmosphere was an argon atmosphere.

[0234] (XRD pattern measurement of each negative electrode after the initial charging test of the half-cells of each all-solid-state lithium secondary battery obtained in Example 9 and Comparative Example 11, and the measurement results) After performing the initial charging test using the half-cells of the all-solid-state lithium secondary batteries obtained in Example 9 and Comparative Example 11, the all-solid-state batteries were disassembled in a glove box under an argon atmosphere, the primary assembly was sealed in an X-ray diffraction atmosphere separator (manufactured by Rigaku Corporation) (argon atmosphere), and X-rays were irradiated onto the graphite layer through a copper disc, which is the current collector. X-ray diffraction measurements were performed using an X-ray diffractometer (Rigaku Corporation, Miniflex600) in the diffraction angle range of 20°-30° (2θ). The X-ray diffraction patterns obtained from the test results are shown in Figure 24 (Example 9) and Figure 29 (Comparative Example 11).

[0235] From the X-ray diffraction patterns shown in Figure 24 (Example 9) and Figure 29 (Comparative Example 11), it was confirmed that in each negative electrode after the initial charging test of the half-cells of the all-solid-state lithium secondary batteries obtained in Example 9 and Comparative Example 11, the gold layer (gold film) constituting the negative electrode active material layer of the negative electrode reacted with lithium and changed into a Li3Au alloy. On the other hand, in CC charging using a current value of 0.05C at room temperature, lithium was inserted to a charging state close to Stage 1 in both the graphite with low coverage amorphous carbon coating and the graphite before amorphous carbon coating contained in the composite layer (negative electrode composite layer), which is the negative electrode active material layer of the half-cells of the all-solid-state lithium secondary batteries obtained in Example 9 and Comparative Example 11, and it was found that lithium was inserted to a charging state equivalent to that of the graphite with low coverage amorphous carbon coating contained in the graphite layer of the half-cell of the all-solid-state lithium secondary battery obtained in Example 7. In other words, it was found that when a negative electrode according to an embodiment of the present invention (i.e., a negative electrode comprising a graphite negative electrode layer containing graphite particles whose surface is coated with amorphous carbon, wherein the content of the graphite particles is 50% by weight or more in the graphite negative electrode active material layer) is used as a negative electrode for an all-solid-state lithium secondary battery, the movement of lithium ions in the direction perpendicular to the surface of the graphite negative electrode active material layer constituting the negative electrode becomes easier, thereby enabling a high utilization rate (i.e., high energy density) of the graphite particles, which are the negative electrode active material. Furthermore, it was found that using a negative electrode according to an embodiment of the present invention allows for reversible operation of the all-solid-state battery even at room temperature, and that a high-capacity all-solid-state lithium secondary battery with excellent charge-discharge characteristics at room temperature can be provided.

[0236] (Cycle characteristics of half-cells of each all-solid-state lithium secondary battery obtained in Example 10 and Comparative Example 12) Using the half-cells of each all-solid-state lithium secondary battery obtained in Example 10 and Comparative Example 12, a discharge capacity cycle test was performed at room temperature for five cycles up to 0.01V relative to lithium metal, using a constant current of 0.05C. The results are shown in Table 9 as the discharge ratio capacity (i.e., the value expressed as discharge capacity of each cycle / (discharge capacity of the first cycle) × 100 (%)).

[0237] As shown in Table 9, in Example 10, which has a low-resistance layer (43) between a test negative electrode active material layer (42), which is a negative electrode active material layer made of low-coverage amorphous carbon-coated spherical graphite powder as shown in Table 1, and a separator (44) using an oxide inorganic solid electrolyte as an inorganic solid electrolyte (also referred to in this application as an oxide inorganic solid electrolyte separator), it was confirmed that the test negative electrode active material layer (42) exhibits an extremely high discharge ratio capacity compared to Comparative Example 12, which uses a negative electrode active material layer made only of graphite powder before amorphous carbon coating as shown in Table 1. Therefore, it was found that even if a low-resistance layer (43) is present between the negative electrode active material layer (42), which is the negative electrode active material layer, and the oxide inorganic solid electrolyte separator (44), if the negative electrode active material layer (42), which is the negative electrode active material layer, does not contain graphite particles coated with amorphous carbon, lithium ions cannot move perpendicular to the plane of the graphite negative electrode active material layer (42), and a half-cell of a high-capacity, long-life all-solid-state lithium secondary battery cannot be obtained. Therefore, it was found that with the all-solid-state lithium secondary battery using the negative electrode of the embodiment of the present invention, even if an oxide inorganic solid electrolyte is used as the solid electrolyte separator layer instead of a sulfide inorganic solid electrolyte, lithium ions can move perpendicular to the plane of the graphite negative electrode layer more easily, resulting in a high utilization rate. Furthermore, it was found that with the negative electrode of the embodiment of the present invention, the battery capacity of the all-solid-state lithium secondary battery can be improved without including a solid electrolyte in the negative electrode active material layer. Furthermore, it was found that by using the negative electrode according to the embodiment of the present invention, the all-solid-state battery can be operated reversibly even at room temperature, and a high-capacity all-solid-state lithium secondary battery with excellent charge-discharge characteristics at room temperature can be provided.

[0238] Incidentally, a half-cell of an all-solid-state lithium secondary battery was fabricated in which there was no low-resistance layer (43) between the test negative electrode active material layer (42), which is the negative electrode active material layer, and the oxide inorganic solid electrolyte separator (44), and the test negative electrode active material layer (42) consisted only of the low-coverage amorphous carbon-coated spherical graphite powder shown in Table 1. This discharge capacity cycle test was also performed (not shown). Comparing these results with those of Example 10, it was confirmed that in order to obtain an extremely high discharge ratio capacity like that of Example 10, it is preferable to provide a low-resistance layer (43) between the test negative electrode active material layer (42), which is the negative electrode active material layer, and the oxide inorganic solid electrolyte separator (44).

[0239] The first charge-discharge tests were performed on the half-cells of the all-solid-state lithium secondary batteries obtained in Examples 1-10 and Comparative Examples 1-13, as described above. The current values ​​used in the first charge-discharge tests for each example are summarized in Table 6.

[0240] [Table 6]

[0241] Table 7 summarizes the results of the initial charge-discharge tests on the half-cells of the all-solid-state lithium secondary batteries obtained in Examples 1-6 and Comparative Examples 1-10 and 12, including the initial discharge capacity per unit weight of active material, the initial irreversible capacity per unit weight of active material, the substance used to calculate the specific capacity per unit weight of active material, the initial discharge capacity per unit weight of electrode, the initial irreversible capacity per unit weight of electrode, the substance used to calculate the specific capacity per unit weight of electrode, and the initial charge-discharge efficiency.

[0242] [Table 7]

[0243] Table 8 summarizes the initial charge capacity per unit weight of active material and the active materials used in calculating the charge capacity density, obtained from the initial charge-discharge test results of the half-cells of the all-solid-state lithium secondary batteries obtained in Examples 7-9 and Comparative Examples 10 and 11.

[0244] [Table 8]

[0245] Table 9 shows a comparison of the discharge ratio capacities (mAh / g) of the half-cells of the all-solid-state lithium secondary batteries obtained in Example 10 and Comparative Example 12 up to 5 cycles.

[0246] [Table 9] [Industrial applicability]

[0247] According to the present invention, it is expected to be used in various fields where the use of secondary batteries is expanding, such as as a power source for electric vehicles and drones, or for use in portable electronic devices. [Explanation of symbols]

[0248] 11: Negative electrode current collector 12: Negative electrode active material layer 13: Solid electrolyte separator layer 14: Negative electrode (negative electrode layer) 15: Positive electrode active material layer 16: Positive electrode current collector 17: Positive electrode (positive electrode layer) 21: Negative electrode current collector 22: Negative electrode active material layer 23: Low resistance layer 24: Negative electrode (negative electrode layer) 25: Solid electrolyte separator layer 26: Positive electrode active material layer 27: Positive electrode current collector 28: Positive electrode (positive electrode layer) 31: Current collector 32: Test negative electrode active material layer 33: Solid electrolyte separator layer 34: Counter electrode (lithium-indium foil) 35: Current collector 41: Current collector 42: Test negative electrode active material layer 43: Low resistance layer 44: Solid electrolyte separator layer 45: Counter electrode (lithium foil) 46: Current collector 101: Type A all-solid-state lithium secondary battery 102: Half-cell of a Type A all-solid-state lithium secondary battery 201: Type B all-solid-state lithium secondary battery 202: Half-cell of a Type B all-solid-state lithium secondary battery

Claims

1. A negative electrode for an all-solid-state lithium secondary battery, comprising a graphite negative electrode active material layer, The graphite negative electrode active material layer contains graphite particles whose surface is coated with amorphous carbon (however, it does not contain an inorganic solid electrolyte), The negative electrode for an all-solid-state lithium secondary battery, wherein the content of the graphite particles in the graphite negative electrode active material layer is 50% by weight or more.

2. The negative electrode for an all-solid-state lithium secondary battery according to claim 1, wherein the graphite particles whose surface is coated with amorphous carbon have the following physical properties: - The average particle size d50 is between 3 μm and 40 μm; - BET specific surface area is 0.5 m² ２ / g or more 10m ２ / g or less; • Tap density is 0.7 g / cm³ ３ 1.20g / cm or more ３ The following: 1580cm －１ The peak PA intensity IA and 1360 cm －１ The Raman R value, expressed by the following formula 1 as the intensity ratio of the peak PB to the intensity IB, is between 0.01 and 1: Equation 1: Raman R value = IB / IA; - The interlayer distance d002 of the lattice plane (002 plane) determined by X-ray diffraction is 0.334 nm or more and 0.340 nm or less; and - The degree of circularity is 0.8 or higher.

3. The negative electrode according to claim 1 or 2, wherein the DTA curve obtained by performing TG-DTA measurement on graphite particles whose surface is coated with amorphous carbon satisfies the following formula 2, and the first peak on the relatively low temperature side and the second peak on the relatively high temperature side, which occur in the range of 500°C to 1000°C, are satisfied in the range of 500°C to 1000°C: Equation 2: (DTA [μV] at the first peak) / (DTA [μV] at the second peak) ≥ 0.

15.

4. The negative electrode for an all-solid-state lithium secondary battery according to any one of claims 1 to 3, wherein the graphite negative electrode active material layer comprises graphite particles whose surface is coated with amorphous carbon, or comprises graphite particles whose surface is coated with amorphous carbon and graphite particles different from those whose surface is coated with amorphous carbon.

5. The negative electrode for an all-solid-state lithium secondary battery according to any one of claims 1 to 4, wherein the graphite negative electrode active material layer contains natural graphite.

6. The anode for an all-solid-state lithium secondary battery according to any one of claims 1 to 5, wherein the graphite anode active material layer further comprises a material capable of absorbing less than 10% lithium ions.

7. Positive electrode and, A solid electrolyte separator layer, A negative electrode for an all-solid-state lithium secondary battery according to any one of claims 1 to 6, All-solid-state lithium secondary batteries, including...

8. The all-solid-state lithium secondary battery according to claim 7, wherein the solid electrolyte separator layer is an inorganic solid electrolyte separator layer.

9. The all-solid-state lithium secondary battery according to claim 8, wherein the inorganic solid electrolyte separator layer is a layer made of a sulfide inorganic solid electrolyte.

10. The all-solid-state lithium secondary battery according to claim 8, wherein the inorganic solid electrolyte separator layer is a layer made of an oxide inorganic solid electrolyte.

11. The graphite negative electrode active material layer is provided on the solid electrolyte separator layer, The all-solid-state lithium secondary battery according to any one of claims 7, 8, and 10, wherein the interface between the solid electrolyte separator layer and the graphite negative electrode active material layer includes a layer made of a metal or metalloid containing an element that alloys lithium.

12. The all-solid-state lithium secondary battery according to claim 11, wherein the metallic material or metalloid material contained in the layer made of a metal or metalloid containing an element for alloying lithium is a material made of at least one element selected from the group consisting of gold, silver, platinum, aluminum, tin, indium, germanium, lead, zinc, antimony, magnesium, silicon, cadmium, gallium, tellurium, and bismuth.

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