All-solid-state secondary battery and charging method thereof

Abstract

To enhance the output characteristic more than before by suppressing short-circuiting while suppressing the manufacturing cost of an all-solid secondary battery.SOLUTION: A negative electrode active material layer material contains amorphous carbon, a first element forming alloy or a compound with lithium by electrochemical reaction, and a second element not forming alloy or a compound with lithium by electrochemical reaction. The second element is an element belonging to the fourth period in the periodic table of elements and an element belonging to any of Group 3 to Group 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state secondary battery and a method for charging the same. [Background technology]

[0002] One example of an all-solid-state secondary battery that uses lithium as the negative electrode active material is one that uses lithium deposited in the negative electrode layer during charging as the active material. In such an all-solid-state secondary battery, if the lithium deposited on the negative electrode side grows in a branch-like manner, weaving through the gaps in the solid electrolyte layer, it can not only cause a short circuit in the battery but also lead to a decrease in battery capacity.

[0003] Therefore, as an all-solid-state secondary battery that can suppress the generation and growth of lithium dendrites in the solid electrolyte layer, such as the one described in Patent Document 1, is being considered. In the all-solid-state secondary battery described in Patent Document 1, by using an element that forms an alloy or compound with lithium as the negative electrode active material, lithium is absorbed into the negative electrode active material layer in the initial stages of charging, and after the charging capacity of the negative electrode active material layer is exceeded, lithium can be deposited inside the negative electrode active material layer or on the back side (current collector side) of the negative electrode active material layer. As a result, the generation and growth of lithium dendrites in the solid electrolyte layer can be suppressed, thereby suppressing short circuits and a decrease in battery capacity. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-096610 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in the process of researching the all-solid-state secondary battery described in Patent Document 1 mentioned above, it became clear that precious metal elements such as silver are particularly effective as elements that form alloys or compounds with lithium contained in the negative electrode active material layer. However, using precious metal elements in the negative electrode active material layer increases the manufacturing cost of the all-solid-state secondary battery. Therefore, the present invention aims to provide an all-solid-state secondary battery that uses lithium deposited in the negative electrode layer by charging as an active material, thereby minimizing the amount of precious metal elements used in the manufacture of the negative electrode and thus reducing costs, while also suppressing the generation and growth of lithium dendrites in the solid electrolyte layer. [Means for solving the problem]

[0006] This invention was completed for the first time when the inventors discovered, through diligent research to solve the aforementioned problems, that by further adding a second element that does not form an alloy with lithium to the negative electrode active material layer, it is possible not only to suppress the generation and growth of lithium dendrites in the solid electrolyte layer, but also to manufacture an all-solid-state secondary battery with superior performance compared to the case where only an element that forms an alloy or compound with lithium (also called the first element), such as silver, is added.

[0007] In other words, the negative electrode active material layer material for an all-solid-state secondary battery according to the present invention comprises amorphous carbon, a first element that forms an alloy with lithium by electrochemical reaction, and a second element that does not form an alloy with lithium by electrochemical reaction. The second element is an element belonging to the fourth period of the periodic table and belonging to groups 3 to 11. The second element is at least one selected from the group consisting of iron, copper, titanium, and nickel. Whether a certain element forms an alloy or a compound with lithium through an electrochemical reaction can be determined, for example, by conducting the following experiments. First, using a Li metal foil as the counter electrode and 10 mg of a powder obtained by mixing the powder of the target element and the powder of the solid electrolyte at a weight ratio of 1:1 as the working electrode, CC-CV charging is performed from the OCV (open circuit voltage) to 0.01 V. When the target element forms an alloy or a compound with lithium, a capacity of several hundred to several thousand mAh / g per unit weight of the target element is observed. On the other hand, when no alloy or compound is formed, almost no capacity is observed.

[0008] According to the material for the negative electrode active material layer of the all-solid-state secondary battery configured as described above, while suppressing the manufacturing cost of the all-solid-state secondary battery including the negative electrode active material layer formed using this material for the negative electrode active material layer, short circuits can be suppressed, and the output characteristics can be further improved compared to the prior art.

[0009] As a specific embodiment of the present invention, an example can be given where the amorphous carbon is carbon black.

[0010] As a specific embodiment of the present invention, an example can be given where the first element is at least one selected from the group consisting of silver, platinum, and gold.

[0011] In order to significantly improve the output characteristics of the battery compared to the prior art, it is preferable that when the content of the amorphous carbon in the negative electrode active material layer material is 100 parts by mass, the content of the second element is 8 parts by mass or more and 50 parts by mass or less.

[0012] As a specific embodiment of the present invention, an all-solid-state secondary battery including a negative electrode active material layer formed using the negative electrode active material as described above can be given, where the initial charging capacity of the positive electrode active material layer and the initial charging capacity of the negative electrode active material layer satisfy the following formula (1). 0.01 < b / a < 0.5 (1) In formula (1), a represents the charging capacity (mAh) of the positive electrode active material layer 12, and b represents the charging capacity (mAh) of the negative electrode active material layer 22, respectively.

Effect of the Invention

[0013] As described above, according to the present invention, while suppressing the manufacturing cost of the all-solid-state secondary battery, it is possible to suppress short circuits and further improve the output characteristics compared to the prior art.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view showing a schematic configuration of an all-solid-state secondary battery according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view showing a schematic configuration of an all-solid-state secondary battery according to another embodiment of the present invention. [Figure 3] It is a cross-sectional view showing a schematic configuration showing the case where a lithium metal layer is deposited in the all-solid-state secondary battery according to the present embodiment. [Figure 4] It is a cross-sectional view showing a schematic configuration showing the case where a lithium metal layer is deposited in the all-solid-state secondary battery according to the present embodiment. [Figure 5] It is a cross-sectional view showing a schematic configuration of an all-solid-state secondary battery according to another embodiment of the present invention.

Mode for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0016] <1. Basic Configuration of All-Solid-State Secondary Battery According to the Present Embodiment> As shown in FIG. 1, the all-solid-state secondary battery 1 according to the present embodiment includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30.

[0017] (1-1. Positive Electrode Layer) The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. Examples of the positive electrode current collector 11 include a plate-shaped or foil-shaped body made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. The positive electrode current collector 11 may be omitted.

[0018] The positive electrode active material layer 12 contains a positive electrode active material and a solid electrolyte. The solid electrolyte contained in the positive electrode layer 10 may or may not be the same type as the solid electrolyte contained in the solid electrolyte layer 30. Details of the solid electrolyte will be explained in detail in the section on the solid electrolyte layer 30.

[0019] The positive electrode active material can be any positive electrode active material capable of reversibly intercepting and releasing lithium ions.

[0020] For example, the positive electrode active material can be formed using lithium salts such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminate (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganese oxide, and lithium iron phosphate, as well as nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide. These positive electrode active materials may be used individually or in combination of two or more.

[0021] Further, the positive electrode active material preferably contains a lithium salt of a transition metal oxide having a layered rock salt structure among the lithium salts described above. Here, the "layered rock salt structure" refers to a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged in the <111> direction of the cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. The "cubic rock salt structure" represents a sodium chloride type structure which is a type of crystal structure. Specifically, it represents a structure in which the face-centered cubic lattices formed by each of the cations and anions are displaced from each other by 1 / 2 of the edge of the unit lattice.

[0022] Examples of the lithium salt of a transition metal oxide having such a layered rock salt structure include, for example, LiNi x Co y Al z O2 (NCA), or LiNi x Co y Mn z O2 (NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1), and lithium salts of ternary transition metal oxides such as these.

[0023] When the positive electrode active material contains a lithium salt of a ternary transition metal oxide having the above-described layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery 1 can be improved.

[0024] The positive electrode active material may be covered with a coating layer. Here, the coating layer of the present embodiment may be any known coating layer for the positive electrode active material of an all-solid-state secondary battery. Examples of the coating layer include, for example, Li2O-ZrO2 and the like.

[0025] Furthermore, if the positive electrode active material is formed from a lithium salt of a ternary transition metal oxide such as NCA or NCM, and contains nickel (Ni) as the positive electrode active material, the coating layer can increase the capacity density of the all-solid-state secondary battery 1 and reduce metal leaching from the positive electrode active material in the charged state. As a result, the all-solid-state secondary battery 1 according to this embodiment can improve long-term reliability and cycle characteristics in the charged state.

[0026] Here, the shape of the positive electrode active material can be, for example, a perfect sphere or an ellipsoid. Furthermore, the particle size of the positive electrode active material is not particularly limited and should be within a range applicable to the positive electrode active material of conventional all-solid-state secondary batteries. In addition, the content of the positive electrode active material in the positive electrode layer 10 is not particularly limited and should be within a range applicable to the positive electrode layer 10 of conventional all-solid-state secondary batteries.

[0027] Furthermore, in addition to the positive electrode active material and solid electrolyte described above, the positive electrode layer 10 may appropriately contain additives such as conductive additives, binders, fillers, dispersants, and ionic conductive additives.

[0028] Examples of conductive additives that can be incorporated into the positive electrode layer 10 include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Examples of binders that can be incorporated into the positive electrode layer 10 include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Furthermore, known materials generally used in electrodes of all-solid-state secondary batteries can be used as fillers, dispersants, and ionic conductive additives that can be incorporated into the positive electrode layer 10.

[0029] (1-2. Negative electrode layer) The negative electrode layer 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 is preferably composed of a material that does not react with lithium, i.e., does not form any alloys or compounds. Examples of materials constituting the negative electrode current collector 21 include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The negative electrode current collector 21 may be composed of one of these metals, or of an alloy or clad material of two or more metals. The negative electrode current collector 21 may be, for example, in the form of a plate or foil.

[0030] Here, as shown in Figure 2, a thin film 24 may be formed on the surface of the negative electrode current collector 21. The thin film 24 contains elements capable of forming an alloy with lithium. Examples of such elements include gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth. The thin film 24 may be composed of one of these metals or of an alloy of multiple metals. The presence of the thin film 24 makes the deposition morphology of the metal layer 23 flatter, further improving the characteristics of the all-solid-state secondary battery 1.

[0031] Here, the thickness of the thin film 24 is not particularly limited, but it is preferably between 1 nm and 500 nm. If the thickness of the thin film 24 is less than 1 nm, it may not be able to fully perform its function. If the thickness of the thin film 24 exceeds 500 nm, the amount of lithium deposited on the negative electrode may decrease due to lithium absorption by the thin film 24 itself, which may actually degrade the characteristics of the all-solid-state secondary battery 1. The thin film 24 is formed on the negative electrode current collector 21 by, for example, vacuum deposition, sputtering, or plating.

[0032] The negative electrode active material layer 22 contains a negative electrode active material that forms an alloy or compound with lithium. The ratio of the charging capacity of the positive electrode active material layer 12 to the charging capacity of the negative electrode active material layer 22, i.e., the capacity ratio, satisfies the requirements of the following formula (1). 0.01 a: Charging capacity of the positive electrode active material layer 12 (mAh) b: Charging capacity of the negative electrode active material layer 22 (mAh)​

[0033] Here, the charging capacity of the positive electrode active material layer 12 is obtained by multiplying the charging capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode active material layer 12. If multiple types of positive electrode active materials are used, the value of charging capacity density × mass should be calculated for each positive electrode active material, and the sum of these values ​​should be taken as the charging capacity of the positive electrode active material layer 12. The charging capacity of the negative electrode active material layer 22 is calculated in the same way. That is, the charging capacity of the negative electrode active material layer 22 is obtained by multiplying the charging capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the negative electrode active material layer 22. If multiple types of negative electrode active materials are used, the value of charging capacity density × mass should be calculated for each negative electrode active material, and the sum of these values ​​should be taken as the capacity of the negative electrode active material layer 22. Here, the charging capacity densities of the positive and negative electrode active materials are capacities estimated using an all-solid-state half-cell with lithium metal as the counter electrode. In practice, the charging capacity of the positive electrode active material layer 12 and the negative electrode active material layer 22 is directly measured using an all-solid-state half-cell.

[0034] The following methods can be used to directly measure the charging capacity. First, the charging capacity of the positive electrode active material layer 12 is measured by creating a test cell using the positive electrode active material layer 12 as the working electrode and Li as the counter electrode, and performing CC-CV charging from the OCV (open circuit voltage) to the upper limit charging voltage. This upper limit charging voltage is defined in the JIS C 8712:2015 standard, and is 4.25V for lithium cobalt oxide-based positive electrodes, and for other positive electrodes, it refers to the voltage obtained by applying the provisions of A.3.2.3 (safety requirements when applying different upper limit charging voltages) of JIS C 8712:2015. The charging capacity of the negative electrode active material layer 22 is measured by creating a test cell using the negative electrode active material layer 22 as the working electrode and Li as the counter electrode, and performing CC-CV charging from the OCV (open circuit voltage) to 0.01V.

[0035] The aforementioned test cell can be manufactured, for example, by the following method: The positive electrode active material layer 12 or negative electrode active material layer 22 whose charging capacity is to be measured is punched out in the shape of a 13 mm diameter disc. 200 g of the same solid electrolyte powder used in the all-solid-state secondary battery 1 is compacted at 40 MPa to form a pellet with a diameter of 13 mm and a thickness of approximately 1 mm. This pellet is placed inside a cylinder with an inner diameter of 13 mm, and the positive electrode active material layer 12 or negative electrode active material layer 22 punched out in the shape of a disc is inserted from one side, and a lithium foil with a diameter of 13 mm and a thickness of 0.03 mm is inserted from the other side. Furthermore, one stainless steel disc is inserted from each side, and the entire assembly is pressurized at 300 MPa in the axial direction of the cylinder for one minute to integrate the contents. The integrated contents are removed from the cylinder and sealed in a case under a constant pressure of 22 MPa to form a test cell. The charging capacity of the positive electrode active material layer 12 can be measured by, for example, CC charging the test cell prepared as described above at a current density of 0.1 mA, followed by CV charging to 0.02 mA.

[0036] The charge capacity density is calculated by dividing this charge capacity by the mass of each active material. The initial charge capacity of the positive electrode active material layer 12 and the negative electrode active material layer 22 may be the initial charge capacity measured during the first charging cycle. In the embodiment described later, this value was used.

[0037] Thus, the charging capacity of the positive electrode active material layer 12 becomes excessive compared to the charging capacity of the negative electrode active material layer 22. As will be described later, in this embodiment, the all-solid-state secondary battery 1 is charged beyond the charging capacity of the negative electrode active material layer 22. That is, the negative electrode active material layer 22 is overcharged. In the initial stages of charging, lithium is absorbed into the negative electrode active material layer 22. That is, the negative electrode active material forms an alloy or compound with lithium ions that have moved from the positive electrode layer 10. If charging continues beyond the capacity of the negative electrode active material layer 22, as shown in Figure 3, lithium is deposited on the back side of the negative electrode active material layer 22, i.e., between the negative electrode current collector 21 and the negative electrode active material layer 22, and a metal layer 23 is formed by this lithium. The metal layer 23 may be formed inside the negative electrode active material layer 22, for example, as shown in Figure 4. In other words, the metal layer 23 may be formed sandwiched between two halves of the negative electrode active material layer 22. The metal layer 23 is mainly composed of lithium (i.e., metallic lithium). This phenomenon occurs when a specific substance, namely an element that forms an alloy or compound with lithium, is used as the negative electrode active material. During discharge, lithium in the negative electrode active material layer 22 and the metal layer 23 is ionized and moves to the positive electrode layer 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. Furthermore, since the negative electrode active material layer 22 covers the metal layer 23, it functions as a protective layer for the metal layer 23 and can suppress the deposition and growth of dendrites. As a result, short circuits and capacity degradation of the all-solid-state secondary battery 1 are suppressed, and consequently, the characteristics of the all-solid-state secondary battery 1 are improved.

[0038] Here, the capacity ratio is greater than 0.01. If the capacity ratio is 0.01 or less, the characteristics of the all-solid-state secondary battery 1 deteriorate. This is because the negative electrode active material layer 22 no longer functions adequately as a protective layer. For example, if the thickness of the negative electrode active material layer 22 is very thin, the capacity ratio may be 0.01 or less. In this case, repeated charging and discharging may cause the negative electrode active material layer 22 to disintegrate, leading to the deposition and growth of dendrites. As a result, the characteristics of the all-solid-state secondary battery 1 deteriorate. It is presumed that in Patent Document 1 and Non-Patent Document 1, the characteristics of the all-solid-state secondary battery were not sufficiently improved because the interface layer or carbon layer was too thin. Furthermore, it is preferable that the capacity ratio is less than 0.5. This is because if the capacity ratio is 0.5 or more, the amount of lithium deposited on the negative electrode decreases, which may reduce the battery capacity. For similar reasons, it is considered more preferable that the capacity ratio be less than 0.25. In addition, by having a capacity ratio of less than 0.25, the output characteristics of the battery can also be further improved.

[0039] As an example of a negative electrode active material layer 22 for realizing the above-mentioned functions, the negative electrode active material may include amorphous carbon and a first element. Examples of amorphous carbon include carbon black and graphene. Examples of carbon black include acetylene black, furnace black, and Ketjen black. The first element is an element that forms an alloy or compound with lithium, and specifically, it can be one or more selected from the group consisting of gold, platinum, palladium, and silver.

[0040] When one or more of gold, platinum, palladium, and silver are used as the first element, these negative electrode active materials are, for example, granular, and their particle size is preferably 4 μm or less, more preferably 300 nm or less. In this case, the characteristics of the all-solid-state secondary battery 1 are further improved. Here, the particle size of the negative electrode active material is, for example, the median diameter (so-called D) measured using a laser particle size distribution system. 50 ) can be used. In the following examples and comparative examples, the particle size was measured by this method. The lower limit of the particle size is not particularly limited, but it may be 10 nm.

[0041] Furthermore, the negative electrode active material layer 22 may contain a binder. Examples of such binders include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder may consist of one of these materials or two or more.

[0042] By including a binder in the negative electrode active material layer 22, the negative electrode active material layer 22 can be stabilized on the negative electrode current collector 21. For example, if the negative electrode active material layer 22 does not include a binder, the negative electrode active material layer 22 may easily detach from the negative electrode current collector 21. At the points where the negative electrode active material layer 22 detaches from the negative electrode current collector 21, the negative electrode current collector 21 becomes exposed, which may cause a short circuit. Furthermore, as will be described in detail later, the negative electrode active material layer 22 is manufactured by coating a slurry in which the materials constituting the negative electrode active material layer 22 are dispersed onto the negative electrode current collector 21 and drying it. By including a binder in the negative electrode active material layer 22, the negative electrode active material can be stably dispersed in the aforementioned slurry. As a result, for example, when coating the slurry onto the negative electrode current collector 21 by screen printing, clogging of the screen (for example, clogging by aggregates of the negative electrode active material) can be suppressed.

[0043] Here, when a binder is included in the negative electrode active material layer 22, the binder content is preferably 0.3% by mass or more and 15% by mass or less relative to the total mass of the negative electrode active material. If the binder content is less than 0.3% by mass, the strength of the film may not be sufficient, the properties may deteriorate, and it may become impossible to handle. If the binder content exceeds 20% by mass, the properties of the all-solid-state secondary battery 1 may deteriorate. The preferred lower limit for the binder content is 3% by mass.

[0044] The thickness of the negative electrode active material layer 22 is not particularly limited as long as it satisfies the requirements of formula (1) above, but it is preferably 1 μm or more and 20 μm or less. If the thickness of the negative electrode active material layer 22 is less than 1 μm, the characteristics of the all-solid-state secondary battery 1 may not be sufficiently improved. If the thickness of the negative electrode active material layer 22 exceeds 20 μm, the resistance value of the negative electrode active material layer 22 will be high, and as a result, the characteristics of the all-solid-state secondary battery 1 may not be sufficiently improved. The thickness of the negative electrode active material layer 22 can be estimated, for example, by observing the cross-section of the all-solid-state secondary battery after assembly and pressure molding using a scanning electron microscope (SEM).

[0045] The negative electrode active material layer 22 may contain additives used in conventional all-solid-state secondary batteries, such as fillers, dispersants, and ion conductive agents, as appropriate.

[0046] (1-3.Solid electrolyte layer) The solid electrolyte layer 30 is formed between the positive electrode layer 10 and the negative electrode layer 20 and contains a solid electrolyte.

[0047] Solid electrolytes are composed of, for example, sulfide-based solid electrolyte materials or oxide-based solid electrolytes. Examples of sulfide-based solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element, e.g., I, Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, and Li2 S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is any one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga or In), etc. Here, the sulfide-based solid electrolyte material is produced by treating starting materials (such as Li2S, P2S5, etc.) by methods such as melt quenching or mechanical milling. Further heat treatment may be performed after these treatments. The solid electrolyte may be amorphous, crystalline, or in a state where both are mixed.

[0048] Also, as the solid electrolyte, among the above sulfide solid electrolyte materials, those containing at least sulfur (S), phosphorus (P) and lithium (Li) as constituent elements are preferably used, and those containing Li2S-P2S5 are more preferably used.

[0049] Here, when using a material containing Li2S-P2S5 as the sulfide-based solid electrolyte material forming the solid electrolyte, the mixing molar ratio of Li2S and P2S5 may be selected, for example, in the range of Li2S:P2S5 = 50:50 to 90:10. The solid electrolyte layer 30 may further contain a binder. Examples of the binder contained in the solid electrolyte layer 30 include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. The binder in the solid electrolyte layer 30 may be the same type as or different from the binders in the positive electrode active material layer 12 and the negative electrode active material layer 22.

[0050] Examples of oxide-based solid electrolytes include garnet-type composite oxides, perovskite-type oxides, LISICON-type composite oxides, NASICON-type composite oxides, Li-alumina-type composite oxides, LiPON, and oxide glasses. Among these oxide-based solid electrolytes, it is preferable to select one that can be used stably with lithium metal. For example, La 0.51 Li 0.34 TiO 2.94 Li 1.3 Al 10.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 10.5 Ge 1.5 (PO4)3 is preferred.

[0051] <2. Characteristic Configuration of the All-Solid-State Secondary Battery According to This Embodiment> However, the negative electrode active material layer 22 further contains a second element that does not form an alloy or compound with lithium. The second element is an element belonging to the fourth period of the periodic table, and is limited to elements belonging to groups 3 through 11. More specifically, the second element is one or more elements selected from the group consisting of iron, copper, nickel, and titanium, and may be just one of these elements, or a combination of several of these elements. These second elements are preferably in granular form, and the preferred average primary particle size varies depending on the element, but for example, it is preferably between 65 nm and 800 nm.

[0052] The amount of amorphous carbon contained in the negative electrode active material layer 22 is preferably in the range of 33 parts by mass or more and 95 parts by mass or less, when the amount of negative electrode active material (in this embodiment, the total amount of amorphous carbon and the first element) is 100 parts by mass. The first element is preferably present in an amount of 10 parts by mass or more and 25 parts by mass or less, and more preferably in an amount of 15 parts by mass or more and 20 parts by mass or less, when the amount of amorphous carbon contained in the negative electrode active material layer 22 is 100 parts by mass. The content of the second element is preferably 8 parts by mass or more and 50 parts by mass or less, and more preferably 16 parts by mass or more and 50 parts by mass or less, when the content of amorphous carbon in the negative electrode active material layer 22 is 100 parts by mass.

[0053] <3. Method for manufacturing an all-solid-state secondary battery according to this embodiment> Next, a method for manufacturing the all-solid-state secondary battery 1 according to this embodiment will be described. The all-solid-state secondary battery 1 according to this embodiment can be manufactured by first manufacturing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, and then stacking each of the above layers.

[0054] (3-1. Cathode layer fabrication process) First, a slurry (the slurry may be a paste; the same applies to other slurries) is prepared by adding the materials constituting the positive electrode active material layer 12 (positive electrode active material, binder, etc.) to a nonpolar solvent. Next, the obtained slurry is applied to the positive electrode current collector 11 and dried. Then, the positive electrode layer 10 is prepared by pressurizing the resulting laminate (for example, by applying hydrostatic pressure). The pressurizing step may be omitted. The positive electrode layer 10 may also be prepared by compacting the mixture of materials constituting the positive electrode active material layer 12 into a pellet or by stretching it into a sheet. When the positive electrode layer 10 is prepared by these methods, the positive electrode current collector 11 may be pressed onto the prepared pellet or sheet.

[0055] (3-2. Negative electrode layer fabrication process) First, a slurry is prepared by adding the negative electrode active material (negative electrode active material, second element, binder, etc.) constituting the negative electrode active material layer 22 to a polar or nonpolar solvent. Next, the obtained slurry is applied onto the negative electrode current collector 21 and dried. Then, the negative electrode layer 20 is prepared by pressurizing the resulting laminate (for example, by applying hydrostatic pressure). The pressurization step may be omitted.

[0056] (3-3. Solid Electrolyte Layer Fabrication Process) The solid electrolyte layer 30 can be made from a solid electrolyte formed from a sulfide-based solid electrolyte material.

[0057] First, the starting material is processed using methods such as melt-and-quench method or mechanical milling.

[0058] For example, when using the melt-and-cool method, a sulfide-based solid electrolyte material can be produced by mixing a predetermined amount of starting materials (e.g., Li2S, P2S5, etc.), forming them into pellets, reacting them in a vacuum at a predetermined reaction temperature, and then rapidly cooling them. The reaction temperature of the Li2S and P2S5 mixture is preferably 400°C to 1000°C, more preferably 800°C to 900°C. The reaction time is preferably 0.1 hours to 12 hours, more preferably 1 hour to 12 hours. Furthermore, the rapid cooling temperature of the reactants is usually 10°C or lower, preferably 0°C or lower, and the rapid cooling rate is usually about 1°C / sec to 10000°C / sec, more preferably about 1°C / sec to 1000°C / sec.

[0059] Furthermore, when using the mechanical milling method, sulfide-based solid electrolyte materials can be produced by stirring and reacting the starting materials (e.g., Li2S, P2S5, etc.) using a ball mill or the like. While the stirring speed and time in the mechanical milling method are not particularly limited, a faster stirring speed can increase the rate of sulfide-based solid electrolyte material production, and a longer stirring time can increase the conversion rate of the raw materials to sulfide-based solid electrolyte material.

[0060] Subsequently, the mixed raw materials obtained by the melt-quenching method or the mechanical milling method can be heat-treated at a predetermined temperature and then pulverized to produce particulate solid electrolytes. If the solid electrolyte has a glass transition temperature, it may change from amorphous to crystalline upon heat treatment.

[0061] Next, the solid electrolyte obtained by the above method can be used to create a solid electrolyte layer 30 by forming a film using a known film formation method such as aerosol deposition, cold spray, or sputtering. Alternatively, the solid electrolyte layer 30 may be prepared by pressurizing individual solid electrolyte particles. Furthermore, the solid electrolyte layer 30 may also be prepared by mixing the solid electrolyte with a solvent and a binder, coating and drying the mixture, and then pressurizing it.

[0062] (3-4. Assembly process of all-solid-state secondary batteries) The positive electrode layer 10, negative electrode layer 20, and solid electrolyte layer 30 prepared by the above method can be stacked so that the solid electrolyte layer 30 is sandwiched between the positive electrode layer 10 and the negative electrode layer 20, and then pressurized (for example, by applying hydrostatic pressure) to produce the all-solid-state secondary battery 1 according to this embodiment.

[0063] When operating the all-solid-state battery prepared using the method described above, it is also possible to do so while applying pressure to the all-solid-state battery.

[0064] The above pressure may be between 0.5 MPa and 10 MPa. The pressure may also be applied by sandwiching the all-solid-state battery between two hard plates made of stainless steel, brass, aluminum, glass, etc., and tightening screws between the two plates.

[0065] <4. Charging Method for All-Solid-State Rechargeable Batteries> Next, the charging method for the all-solid-state secondary battery 1 will be described. In this embodiment, as described above, the all-solid-state secondary battery 1 is charged beyond the charging capacity of the negative electrode active material layer 22. That is, the negative electrode active material layer 22 is overcharged. In the initial stages of charging, lithium is absorbed into the negative electrode active material layer 22. When charging is performed beyond the charging capacity of the negative electrode active material layer 22, for example, as shown in Figure 3, lithium is deposited on the back side of the negative electrode active material layer 22, that is, between the negative electrode current collector 21 and the negative electrode active material layer 22, and this lithium forms a metal layer 23 that was not present at the time of manufacture. During discharge, the lithium in the negative electrode active material layer 22 and the metal layer 23 is ionized and moves to the positive electrode layer 10 side. Furthermore, the amount of charge is preferably a value between 2 times and 100 times the charging capacity of the negative electrode active material layer 22, more preferably in the range of 4 times and 100 times.

[0066] <5. Effects of this embodiment> In the all-solid-state secondary battery 1 configured as described above, the negative electrode active material layer 22 contains amorphous carbon and a first element as the negative electrode active material. Therefore, lithium can be used as the negative electrode active material, and when the battery is charged beyond the charging capacity of the negative electrode active material, the deposition of lithium on the surface of the negative electrode active material layer 22 on the solid electrolyte layer 30 side can be suppressed.

[0067] Furthermore, by overcharging the negative electrode active material layer 22, lithium can be deposited in layers, for example, as shown as the metal layer 23 in Figure 3 or Figure 4. As a result, the pressure rise inside the all-solid-state secondary battery 1 due to charging and discharging can be suppressed compared to the case where lithium is not deposited in layers. In addition, the generation of voids inside the all-solid-state secondary battery 1 due to charging and discharging can be suppressed compared to the case where lithium is not deposited in layers.

[0068] For the reasons explained above, the all-solid-state secondary battery 1 according to this embodiment can suppress the deposition and growth of dendrites. This suppresses short circuits and capacity degradation in the all-solid-state secondary battery, and consequently improves the characteristics of the all-solid-state secondary battery.

[0069] In the all-solid-state secondary battery 1 according to this embodiment, the negative electrode active material layer 22 further contains the second element described above. Therefore, while suppressing the deposition and growth of dendrites as described above, it is possible to reduce the amount of precious metal used as the first element in the negative electrode active material layer 22. As a result, the manufacturing cost of the all-solid-state secondary battery 1 can be kept as low as possible.

[0070] Furthermore, in the all-solid-state secondary battery 1 according to this embodiment, the metal layer 23 is not formed in advance before the first charge. Therefore, compared to the all-solid-state secondary battery 1 according to the second embodiment of the present invention, in which the metal layer 23 is formed in advance as described later, the manufacturing cost can be further reduced.

[0071] <6. Other Embodiments of the Invention> <6-1. Configuration of an all-solid-state secondary battery according to the second embodiment of the present invention> Next, the configuration of the all-solid-state secondary battery 1a according to the second embodiment will be described with reference to Figure 6. As shown in Figure 1, the all-solid-state secondary battery 1a comprises a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30. The configuration of the positive electrode layer 10 and the solid electrolyte layer 30 is the same as in the first embodiment.

[0072] (6-1-1. Composition of the negative electrode layer) The negative electrode layer 20 comprises a negative electrode current collector 21, a negative electrode active material layer 22, and a metal layer 23. In other words, in the first embodiment, overcharging of the negative electrode active material layer 22 forms a metal layer 23 between the negative electrode current collector 21 and the negative electrode active material layer 22 that does not exist before the initial charge. In contrast, in the second embodiment, as shown in Figure 5, this metal layer 23' is formed in advance (i.e., before the initial charge) between the negative electrode current collector 21 and the negative electrode active material layer 22. Even in this case, similar to the first embodiment described above, a metal layer 23 may be further formed inside the negative electrode active material layer 22 by the deposited lithium.

[0073] The configuration of the negative electrode current collector 21 and the negative electrode active material layer 22 is the same as in the first embodiment. The metal layers 23 and 23' contain lithium or a lithium alloy. That is, the metal layers 23 and 23' function as a lithium reservoir. Examples of lithium alloys include Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, and Li-Si alloy. The metal layers 23 and 23' may be composed of one of these alloys or lithium, or of multiple types of alloys. In the second embodiment, the characteristics of the all-solid-state secondary battery 1 are further improved because the metal layers 23 and 23' act as a lithium reservoir.

[0074] Here, the thickness of the metal layer 23' is not particularly limited, but it is preferably between 1 μm and 200 μm. If the thickness of the metal layer 23' is less than 1 μm, the reservoir function of the metal layer 23' may not be fully realized. If the thickness of the metal layer 23' exceeds 200 μm, the mass and volume of the all-solid-state secondary battery 1 will increase, and its characteristics may actually deteriorate. For these reasons, the metal layer 23' is composed of, for example, a metal foil having the above thickness.

[0075] <6-2. Method for manufacturing an all-solid-state secondary battery according to the second embodiment of the present invention> Next, a method for manufacturing the all-solid-state secondary battery 1 according to the second embodiment will be described. The positive electrode layer 10 and the solid electrolyte layer 30 are manufactured in the same manner as in the first embodiment.

[0076] (6-2-1. Negative electrode layer fabrication process) In the second embodiment, the negative electrode active material layer 22 is placed on the metal layer 23'. The metal layer 23' is often substantially a metal foil. Since it is difficult to form the negative electrode active material layer 22 on lithium foil or lithium alloy foil, the negative electrode layer 20 may be fabricated by the following method.

[0077] First, a negative electrode active material layer 22 is formed on some substrate (e.g., a Ni plate) in the same manner as in the first embodiment. Specifically, a slurry is prepared by adding the materials constituting the negative electrode active material layer 22 to a solvent. Next, the obtained slurry is applied to the substrate and dried. Then, the resulting laminate is pressurized (for example, by applying hydrostatic pressure) to form the negative electrode active material layer 22 on the substrate. The pressurization step may be omitted.

[0078] Next, a solid electrolyte layer 30 is laminated onto the negative electrode active material layer 22, and the resulting laminate is pressurized (for example, by applying hydrostatic pressure). Then, the substrate is removed. This creates a laminate of the negative electrode active material layer 22 and the solid electrolyte layer 30.

[0079] Next, the metal foil constituting the metal layer 23', the laminate of the negative electrode active material layer 22 and the solid electrolyte layer 30, and the positive electrode layer 10 are sequentially laminated on the negative electrode current collector 21. Then, the resulting laminate is pressurized (for example, by pressurizing using hydrostatic pressure) to produce an all-solid-state secondary battery 1a.

[0080] When operating the all-solid-state battery prepared using the method described above, it is also possible to do so while applying pressure to the all-solid-state battery.

[0081] The above pressure may be between 0.5 MPa and 10 MPa. The pressure may also be applied by sandwiching the all-solid-state battery between two hard plates made of stainless steel, brass, aluminum, glass, etc., and tightening screws between the two plates.

[0082] <6-3. Charging method for an all-solid-state secondary battery according to the second embodiment of the present invention> The charging method for the all-solid-state secondary battery 1a is the same as in the first embodiment. That is, the all-solid-state secondary battery 1a is charged beyond the charging capacity of the negative electrode active material layer 22. In other words, the negative electrode active material layer 22 is overcharged. In the initial stages of charging, lithium is absorbed into the negative electrode active material layer 22. When charging exceeds the capacity of the negative electrode active material layer 22, lithium is deposited in (or on) the metal layer 23'. During discharge, the lithium in the negative electrode active material layer 22 and the metal layer 23' (or on the metal layer 23) is ionized and moves to the positive electrode layer 10 side.

[0083] <7. Effects of the Second Embodiment of the Present Invention> In the all-solid-state secondary battery 1a configured in this way, lithium can be used as the negative electrode active material, similar to the embodiment described above. Furthermore, since the negative electrode active material layer 22 covers the metal layer 23, it functions as a protective layer for the metal layer 23 and can suppress the deposition and growth of dendrites. As a result, short circuits and capacity degradation of the all-solid-state secondary battery 1a are suppressed, and consequently, the characteristics of the all-solid-state secondary battery 1a are improved.

[0084] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention. [Examples]

[0085] The negative electrode active material layer material, the negative electrode active material layer prepared using this negative electrode active material layer material, and the all-solid-state secondary battery equipped with this negative electrode active material layer will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0086] (1. Description of each example and comparative example) <Example 1> In this embodiment, a negative electrode active material layer was formed using a negative electrode active material layer material in which carbon black was used as amorphous carbon, silver as an alloying element, and iron as an alloying non-alloying element. The charge and discharge characteristics of an all-solid-state secondary battery equipped with this negative electrode active material layer were then investigated.

[0087] (1-1. Fabrication of the negative electrode layer) Twelve g of amorphous carbon black, two g of silver particles as the primary element, and six g of iron particles as the secondary element were placed in a container. An NMP solution containing 8 wt% binder (Kureha #9300) was added, and the mixture was stirred while gradually adding more NMP to obtain a slurry-like negative electrode active material. The carbon black had a nitrogen adsorption specific surface area of ​​54 m². 2 A material with a DBP oil absorption capacity of 182 ml / 100 g was used, with silver particles of approximately 60 nm and iron particles of 65-75 nm. This slurry-like negative electrode active material layer was coated onto a 10-micron thick stainless steel foil using a blade coater, dried in air at 80°C for approximately 20 minutes, and then vacuum-dried at 100°C for approximately 12 hours. In this way, a negative electrode layer was fabricated on a stainless steel foil negative electrode current collector, comprising a negative electrode active material layer consisting of a mixed particle thin film containing silver, iron, and carbon black. The initial charge capacity of this negative electrode layer was approximately 2 mAh.

[0088] (1-2) Fabrication of all-solid-state secondary batteries An all-solid-state battery using this negative electrode layer was fabricated by the following method. Li6PS5Cl, an argyrodite-type crystal, was used as the solid electrolyte. LiNi was used as the positive electrode active material. 0.8 Co 0.15 Mn 0.05Using O2(NCM), the Li6PS5Cl solid electrolyte, carbon nanofiber (CNF) as a conductive agent, and Teflon binder were mixed in the ratio of positive electrode active material:solid electrolyte:CNF:Teflon binder = 83:13.5:2:1.5 (mass), and stretched into a sheet to form the positive electrode active material layer. This positive electrode active material layer sheet was then molded into approximately 2 cm squares to form the positive electrode active material layer, and the positive electrode layer was fabricated by pressing it onto an 18 μm thick aluminum foil positive electrode current collector. The initial charge capacity of the positive electrode layer (charge capacity in the first cycle) was approximately 18 mAh for a 4.25 V charge. Therefore, the negative electrode capacity / positive electrode capacity was approximately 0.11, confirming that the requirements of equation (1) described above were met.

[0089] Next, a solid electrolyte sheet was prepared by the following method. A 1% by weight binder was added to the Li6PS5Cl solid electrolyte, and the mixture was stirred while adding xylene and diethylbenzene to prepare a slurry-like solid electrolyte material. This slurry was applied onto a nonwoven fabric using a blade coater, dried in air at 40°C, and then vacuum-dried at 40°C for 12 hours to obtain a solid electrolyte sheet.

[0090] The positive electrode layer, solid electrolyte sheet, and negative electrode layer, thus fabricated, were stacked in this order and sealed in a laminate film in a vacuum to create an all-solid-state battery. A portion of each of the positive and negative electrode layers was left outside the laminate film to avoid breaking the vacuum, and these protruding portions served as terminals for electrically connecting the positive or negative electrode layer to external wiring. The all-solid-state secondary battery manufactured in this manner was further subjected to hydrostatic pressure treatment at 490 MPa. Furthermore, this all-solid-state battery was sandwiched between two stainless steel plates approximately 1 cm thick on both sides in the stacking direction. Each of the two stainless steel plates had four holes in the same location, and the all-solid-state battery was positioned within the square formed by these four holes. In this state, one bolt was passed through each of the four holes from the outside of the two stainless steel plates. Then, a pressure of approximately 4 MPa was applied to the all-solid-state battery by tightening the four bolts with nuts to press down on the two stainless steel plates from the outside. Afterward, its charge and discharge characteristics were investigated under the following conditions.

[0091] (1-3. Evaluation of charge and discharge characteristics) Measurements were performed by placing the all-solid-state battery in a constant temperature bath at 25°C. Charging was performed at 0.6mA / cm² until the battery voltage reached 4.25V. 2 The battery was charged with a constant current, and then charged at a constant voltage of 4.25V until the current reached 0.3mA. The discharge rate was 0.6 mA / cm² in the first, second, and third cycles. 2 , 2mA / cm 2 , 6mA / cm 2 The battery was discharged at a constant current until the battery voltage reached 2.5V. The discharge capacity per unit weight of active material (discharge ratio capacity) for the first and third cycles was 185.7 mAh / g and 127.7 mAh / g, respectively. The results are shown in Table 1.

[0092] <Examples 2 and 3> All-solid-state secondary batteries were fabricated in the same manner as in Example 1, except that the weight of iron particles, the second element of the negative electrode active material, was set to 2g and 1g, respectively. The charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0093] <Examples 4 and 5> All-solid-state secondary batteries were fabricated in the same manner as in Example 1, except that the particle size of the iron particles, which are the second element of the negative electrode active material, was set to 800 nm and their weights were set to 2 g and 6 g, respectively. The charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0094] <Examples 6 and 7> All-solid-state secondary batteries were fabricated in the same manner as in Example 1, except that copper particles with a particle size of 70 nm were used instead of iron particles, which are the second element of the negative electrode active material, and the weights were set to 2 g and 6 g, respectively. The charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0095] <Examples 8 and 9> All-solid-state secondary batteries were fabricated in the same manner as in Example 1, except that titanium particles with a particle size of 70 nm were used instead of iron particles, which are the second element of the negative electrode active material, and the weights were set to 2 g and 6 g, respectively. The charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0096] <Comparative Example 1> In this example, 2g of silver particles with a particle size of 60nm were added instead of iron particles, which are the second element of the negative electrode active material. Specifically, 12g of carbon black was used as amorphous carbon and 4g of silver particles as the first element. Except for this difference, an all-solid-state secondary battery was fabricated in the same manner as in Example 1, and its charge-discharge characteristics were evaluated using the same procedure as in Example 1. As a result, the discharge ratio capacities for the first and third cycles were 178.4mAh / g and 73.1mAh / g, respectively. The results are shown in Table 1.

[0097] <Comparative Example 2> An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that 2 g of zinc particles with a particle size of 80 nm were added instead of iron particles, which are the second element of the negative electrode active material. Its charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0098] <Comparative Example 3> An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that 2 g of tin particles with a particle size of 60-80 nm were added instead of iron particles, which are the second element of the negative electrode active material. Its charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0099] <Comparative Example 4> An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that 2 g of aluminum particles with a particle size of 40-50 nm were added instead of iron particles, which are the second element of the negative electrode active material. Its charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0100] <Comparative Example 5> An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that 2 g of bismuth particles with a particle size of 40-60 nm were added instead of iron particles, which are the second element of the negative electrode active material. Its charge and discharge characteristics were evaluated using the same procedure as in Example 1. The results are shown in Table 1.

[0101] <Comparative Example 6> An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that iron particles, which are the second element, were removed from the negative electrode active material. Its charge-discharge characteristics were evaluated using the same procedure as in Example 1. As a result, the discharge ratio capacities for the first and third cycles were 179.0 mAh / g and 66.5 mAh / g, respectively. The results are shown in Table 1.

[0102] [Table 1]

[0103] (2. Evaluation of Results) Table 1 shows the results for the examples and comparative examples. This shows that there was no significant difference in the discharge capacity of the first cycle, but a clear difference was observed in the discharge capacity of the third cycle among the solid-state batteries. This is thought to be because the high current density during the third cycle discharge makes the differences in output characteristics more apparent. Therefore, the effect of the additive elements in the negative electrode active material will be evaluated based on the discharge capacity of the third cycle. In this embodiment, when a portion of the first element, silver, is replaced with a second element that does not form an alloy or compound with lithium, a significant improvement compared to Comparative Example 1, which used only silver, is considered effective (indicated by ○ in the table), and an equivalent or less effective result is considered ineffective (indicated by × in the table). "Significantly improved" refers to a case where the discharge capacity in the third cycle is increased by 10% or more compared to the silver-added case (Comparative Example 1) (80.4 mAh / g or more).

[0104] In all of Examples 1 to 9, the discharge capacity in the third cycle was 80.4 mAh / g or higher, which is significantly higher than that of Comparative Example 1. In other words, it can be seen that Examples 1 to 9, which contain the second element, exhibit superior charge-discharge characteristics compared to Comparative Example 1, which contains only amorphous carbon and the first element in the negative electrode active material layer.

[0105] On the other hand, in Comparative Examples 2-5, the improvement was not as significant as that achieved with the addition of silver particles (Comparative Example 1). This indicates that the type and amount of metal particles added as the second element affect the improvement in output characteristics.

[0106] Looking at the examples and comparative examples in the table, it can be seen that there is no effect when zinc, tin, aluminum, or bismuth are added as the second element, but there is an effect when iron, copper, or titanium, which are elements belonging to the 4th period of the periodic table and belonging to groups 3 through 11, are added. Examples 1 to 9 demonstrate sufficient effectiveness even when compared to Comparative Example 6, in which the amount of silver, the first element, is simply reduced. From these results, it was confirmed that in Examples 1 to 9, the discharge ratio capacity of the third cycle is improved by the addition of the second element, rather than by a decrease in the content of the first element in the negative electrode active material.

[0107] Furthermore, looking at Examples 1 to 5, it can be seen that the effect is observed when the weight of iron in the negative electrode layer is between 8.3% and 50% of the weight of carbon black, and even with a large particle size of 800 nm, the effect is reduced, but still present.

[0108] These results show that by replacing a portion of the first element with an inexpensive second element, compared to when the negative electrode active material layer contains amorphous carbon and the first element, it is possible to significantly improve the charge-discharge characteristics of an all-solid-state secondary battery in which lithium is deposited in the negative electrode layer, while keeping the manufacturing cost of the all-solid-state secondary battery low. Furthermore, similar effects can be expected even if the type and shape of the first element used, or the content ratio of amorphous carbon to the first element, are changed in the aforementioned Examples 1 to 9. [Explanation of Symbols]

[0109] 1, 1a All-solid-state secondary battery 10 Positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 20 Negative electrode layer 21 Negative electrode current collector 22 Negative electrode active material layer 23 Metal layer 24 Thin film 30 Solid electrolyte layer

Claims

1. Amorphous carbon and, A first element in its elemental form, contained in a state that allows it to form an alloy or compound with lithium through an electrochemical reaction, It contains a second element in its elemental form that does not form an alloy or compound with lithium through an electrochemical reaction. The amorphous carbon is contained in an amount of 33 parts by mass or more and 95 parts by mass or less per 100 parts by mass of the total content of the amorphous carbon and the first element. The first element is contained in an amount of 10 parts by mass or more and 20 parts by mass or less per 100 parts by mass of amorphous carbon. The second element is contained in an amount of 8 parts by mass or more and 50 parts by mass or less per 100 parts by mass of amorphous carbon. The first element is silver, A negative electrode active material layer material for an all-solid-state battery, characterized in that the second element is one or more selected from the group consisting of iron, copper, and titanium.

2. The negative electrode active material layer material for an all-solid-state battery according to claim 1, wherein the amorphous carbon is carbon black.

3. The positive electrode layer, The negative electrode layer, A solid-state secondary battery comprising a solid electrolyte layer, An all-solid-state secondary battery characterized in that the negative electrode layer includes a negative electrode active material layer formed of the negative electrode active material layer material for all-solid-state batteries described in claim 1 or 2.

4. The all-solid-state secondary battery according to claim 3, characterized in that the ratio of the initial charge capacity of the positive electrode layer to the initial charge capacity of the negative electrode layer satisfies the requirements of the following formula (1). 0.01<b / a<0.5 (1) a: Initial charge capacity of the positive electrode layer (mAh) b: Initial charge capacity of the negative electrode layer (mAh)

5. A method for charging an all-solid-state secondary battery, characterized by charging the all-solid-state secondary battery described in claim 4 to a level exceeding the charging capacity of the negative electrode layer.

6. The charging method according to claim 5, wherein the negative electrode layer is charged in a range of 2 to 100 times the charging capacity of the negative electrode layer.

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