RU2695127C1 - Method of producing sulphide solid-state batteries - Google Patents

Abstract

FIELD: manufacturing technology.SUBSTANCE: invention relates to a method of producing a sulphide solid-state battery. Method of producing sulphide solid-state battery comprises first step of lithium doping with at least one material selected from graphite and lithium titanate to obtain pre-alloyed material; second step of mixing sulphide solid electrolyte, an active material based on silicon and pre-alloyed material to obtain an anode mixture; third step of applying anode mixture in form of coating on surface of anode current collector containing copper to obtain anode.EFFECT: invention allows reducing self-discharge of battery.3 cl, 3 dwg, 1 tbl

Description

FIELD OF TECHNOLOGY

[0001] The present application discloses a method for manufacturing a sulfide solid state battery.

BACKGROUND

[0002] Patent documents 1-3 disclose sulfide solid state batteries containing positive electrodes, negative electrodes and layers of solid electrolyte sandwiched between the positive and negative electrodes. According to the technology described in Patent Document 1, for preparing a negative electrode, a negative electrode mixture comprising a sulfide solid electrolyte, a silicon-based active material, and a carbon-based active material is coated onto a surface of a current collector of a negative electrode formed of copper. According to the technology described in Patent Document 2, when the sulfide solid state battery is first charged, before the operating voltage appears on it, lithium enters from the cathode to the anode, doping the active material of the anode. According to the technology described in Patent Document 3, before an anode mixture containing a sulfide solid electrolyte is applied to the surface of the anode current collector, a sulfation resistant layer is created on this surface.

List of cited materials

Patent Literature

[0003] Patent Document 1: JP 2017-054720 A

Patent Document 2: JP 2017-147158 A

Patent Document 3: WO 2014/156638 A1

SUMMARY OF THE INVENTION Technical Problem

[0004] The standard electrode potential of a sulfide solid state battery with respect to lithium is equivalent to the NRC of the active material before charging and discharging. For example, when an anode mixture containing silicon-based active material is applied to the surface of the anode current collector to form the anode, the standard potential of the anode with respect to lithium is approximately 2.8 V.

[0005] On the other hand, according to the research results of the present inventor, when an anode mixture containing a sulfide solid electrolyte is deposited on the surface of an anode current collector containing copper to form an anode, the sulfide solid electrolyte reacts with copper at a potential below 2.8 V, s the formation of CuS having conductivity, etc.

[0006] That is, when the anode mixture containing the silicon-based active material and the sulfide solid electrolyte is deposited on the surface of the anode current collector containing copper to form the anode, the sulfide solid electrolyte reacts with copper in the silicon-based NRC, and copper diffuses from the anode current collector through a sulfide solid electrolyte in the direction of the cathode side. The manufacture of a sulfide solid state battery using such an anode can lead to self-discharges caused by small short circuits of the cathode and anode, etc.

Solution to the problem

[0007] The present application discloses, as one of the means of solving the above problem, a method for manufacturing a sulfide solid state battery, this method comprising: a first step of doping with lithium at least one material selected from graphite and lithium titanate to obtain pre-alloyed material; a second step of mixing a sulfide solid electrolyte, a silicon-based active material and a pre-alloyed material to form an anode mixture; and the third step of applying the anode mixture in the form of a coating on the surface of the anode current collector containing copper, to obtain the anode.

[0008] According to the manufacturing method of the present invention, the ratio (X / Y) of the converted value (X) obtained by converting the total amount of lithium by which the pre-alloyed material of the anode mixture is doped into an electrical capacitance to a common electrical the capacitance (Y) of the silicon-based active material contained in the anode mixture is preferably at least 0.0005.

[0009] According to the manufacturing method of this invention, in a first step, said at least one material is preferably doped with lithium using an electrochemical reaction in a lithium-ion battery.

Beneficial effects of the invention

[0010] According to the manufacturing method of the present invention, an anode mixture is obtained by mixing a predetermined pre-alloyed material with a silicon-based active material. In this case, immediately after the manufacture of the anode mixture, lithium diffuses from the pre-alloyed material into the silicon-based active material, which leads to a decrease in potential when using the anode mixture for the anode. That is, the reaction of a sulfide solid electrolyte with copper can be suppressed, diffusion of copper from the anode current collector through the sulfide solid electrolyte in the direction of the cathode can also be suppressed, therefore, self-discharges caused by small short circuits of the cathode and anode, etc. can be suppressed. In addition, due to the presence in the anode, as preserved, of its electrical and / or ionic conductivity, pre-alloyed material will not be able to adversely affect the properties of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is an explanatory block diagram of a method for manufacturing a sulfide solid state battery 100 S10;

FIG. 2A-2C are explanatory schematic views of a process flow diagram of a manufacturing method of a sulfide solid state battery 100 S10; and

FIG. 3 shows an explanatory schematic diagram of the structure of a sulfide solid state battery 100.

DETAILED DISCLOSURE OF OPTIONS FOR CARRYING OUT THE INVENTION

[0012] 1. A method of manufacturing sulfide solid state batteries

The process flow of a method for manufacturing a sulfide solid state battery 100 S10 will be described with reference to FIG. 1-3. A method of manufacturing a sulfide solid state battery 100 S10 includes: a first step S1 of doping with lithium at least one material 1 selected from graphite and lithium titanate to obtain pre-alloyed material 2; a second step S2 of mixing a sulfide solid electrolyte 3, silicon-based active material 4 and pre-alloyed material 2 to obtain an anode mixture 5; and the third step S3 of applying the anode mixture 5 in the form of a coating on the surface of the anode current collector 6 containing copper, to obtain the anode 10.

[0013] 1.1. First stage

As shown in FIG. 2A, in the first step S1, at least one material 1 selected from graphite and lithium titanate is doped with lithium to obtain pre-alloyed material 2.

[0014] 1.1.1. Material 1

Material 1 consists of at least one substance selected from graphite and lithium titanate (LT). Both graphite and lithium titanate are materials that can accumulate and release lithium, and are known as the anode active material of a lithium-ion battery. When comparing graphite and LT, graphite is preferred, since graphite has a low anode potential, which makes the technical result of this invention more significant. In addition, graphite has a greater electrical capacity. This is also due to the fact that graphite can perform well as a conductive additive. As the material 1 can serve, both artificial and natural graphite. The composition of lithium titanate is not particularly limited, and, for example, in a preferred embodiment, may be Li ₄ Ti ₅ O ₁₂ . The shape of the material 1 is not particularly limited. Material 1 is most preferred in particulate form.

[0015] 1.1.2. Alloying material with lithium

For alloying material 1 with lithium in order to obtain pre-alloyed material 2, any method can be used. Examples include a method for physically mixing material 1 and a lithium source to dope lithium material 1, and a method for electrochemically introducing lithium into material 1. In a preferred embodiment, material 1 is doped with lithium using an electrochemical reaction in a lithium-ion battery, since the alloying amount of lithium is in material 1 can be easily controlled. For example, in a preferred embodiment, it is possible to combine material 1, an active cathode material that charges and discharges lithium ions with a higher potential than the potential of material 1, and any electrolyte having lithium-ion conductivity to form a lithium-ion battery, and then alloy the material 1 with lithium by using a charging reaction in a lithium-ion battery. The lithium-ion battery used in this case may be a solution-based battery, or it may be a solid state battery. In particular, in order that the pre-alloyed material 2 can be easily separated after the material 1 is lithium-doped, it is preferable to use a battery based on a solution system (a battery based on a system of non-aqueous electrolyte solutions, or an aqueous battery). That is, in a preferred embodiment, it is possible to combine material 1, an active cathode material that charges and discharges lithium ions with a higher potential than the potential of material 1, an electrolyte with lithium-ion conductivity (such as LiPF ₆ ) and a solvent for dissolving the electrolyte ( water or an organic solvent) to form a lithium-ion battery based on a solution system, and then alloy the material with 1 lithium using the charging reaction in a lithium-ion battery. After material 1 is doped with lithium using an electrochemical reaction in a lithium-ion battery, the lithium-ion battery can, for example, be disassembled in order to remove the pre-alloyed material 2 from it, and then this pre-alloyed material 2 is washed and crushed if necessary .

[0016] The doping amount of lithium in material 1 is not particularly limited. It is assumed that as the doping amount of lithium in the material 1 increases, the amount of pre-alloyed material 2 in the anode mixture 5 described below can be reduced. As for the doping of material 1 with lithium using a charging reaction in a lithium-ion battery, in a preferred embodiment, material 1 is doped with lithium until the charging capacity becomes at least 10 mAh / g, which is more preferably at least 50 mAh / g, in an even more preferred embodiment, at least 80 mAh / g and in the most preferred embodiment, at least 100 mAh / g. The upper limit is not particularly limited, but is preferably not more than 200 mAh / g, more preferably not more than 180 mAh / g, and even more preferably not more than 150 mAh / g. Or, when doping the material with 1 lithium using a charging reaction in a lithium-ion battery, in a preferred embodiment, the battery is charged until the charge level (SOC) is at least 5%, in a more preferred embodiment, at least 8% and in the most a preferred embodiment is at least 10%. Its upper limit is not particularly limited and is preferably not more than 50%.

[0017] 1.2. Second phase

As shown in FIG. 2B, in a second step S2, a sulfide solid electrolyte 3, silicon-based active material 4 and pre-alloyed material 2 are mixed to form an anode mixture 5.

[0018] 1.2.1. Sulfide Solid Electrolyte 3

As the sulfide solid electrolyte 3, any sulfide used as a solid electrolyte for a sulfide solid state battery can be used. Examples thereof include Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Si ₂ SP ₂ S ₅ , LiI-LiBr-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ O-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ and Li ₂ SP ₂ S ₅ -GeS ₂ . In particular, in a more preferred embodiment, a sulfide solid electrolyte containing Li ₂ SP ₂ S _{5 is used} . One sulphide solid electrolyte can be used alone or at least two sulphide solid electrolytes can be mixed for use as a sulphide solid electrolyte 3. In a second step S2, the amount of sulphide solid electrolyte 3 is not specifically limited, and can be appropriately determined according to with desired battery performance. For example, the content of sulfide solid electrolyte 3 in the preferred embodiment is from 10% (mass.) To 60% (mass), if the entire anode mixture 5 (total solid content after drying to remove the solvent in the case of wet mixing. And hereinafter referred to same.) is 100% (mass). The lower limit level of its content in a more preferred embodiment is not less than 20% (mass), and the upper limit level of content in a more preferred embodiment is not more than 50% (mass).

[0019] 1.2.2. Silicon Based Active Material 4

The silicon-based active material 4 should contain only silicon as a constituent element and have the functions of an anode active material in a sulfide solid state battery. For example, at least one material of silicon, a silicon alloy, and silicon oxide may be used. In particular, silicon or silica is preferred. The shape of the silicon-based active material 4 is not particularly limited, and, for example, in a preferred embodiment, the silicon-based active material 4 is present in particulate form. In the second step S2, the amount of silicon-based active material 4 is not specifically limited and can be appropriately determined in accordance with the desired battery performance. For example, the content of silicon-based active material 4 in a preferred embodiment is from 30% (mass.) To 90% (mass), if the entire anode mixture 5 is 100% (mass). The lower limit level of its content in a more preferred embodiment is not less than 50% (mass), and the upper limit level of its content in a more preferred embodiment is not more than 80% (mass).

[0020] 1.2.3. Pre-alloyed material 2

In the second step S2, the amount of pre-alloyed material 2 is not specifically limited, and can be appropriately determined in accordance with the alloying amount of lithium in the first step S1, etc. In particular, in the second step S2, the ratio of the mixture of the pre-alloyed material 2 and the active material 4 based on silicon is preferably determined so that the ratio (X / Y) of the converted value (X) obtained by converting the total amount of lithium, with which pre-alloyed material 2, which is part of the anode mixture 5, is doped into the electric capacitance, to the total electric capacitance (Y) of the active material 4 based on silicon contained in the anode mixture 5 was not less than 0,0005. The ratio (X / Y) is more preferably not less than 0.0008. According to the results of research by the author of this application, a ratio of (X / Y) of at least 0.0005 can lead to the diffusion of a sufficient amount of lithium into the silicon-based active material 4, which further suppresses self-discharges during the manufacturing process of the sulfide solid state battery 100.

[0021] “The converted value (X) obtained by converting the total amount of lithium with which the pre-alloyed material 2 included in the anode mixture 5 is alloyed” is the value obtained by converting the total amount of lithium, which can diffuse from the pre doped material 2 into the active material 4 based on silicon in the composition of the anode mixture 5, into an electric capacitance. When lithium is alloyed with material 1 using a charging reaction in a lithium-ion battery to obtain pre-alloyed material 2, the converted value (X) can be obtained from the charging capacity (Ah / g). “The total electrical capacitance (Y) of the silicon-based active material 4 contained in the anode mixture 5” is the capacity that the silicon-based active material 4 is contained in the anode mixture 5 in an uncharged state. In particular, Y may be the charging capacity of the active material, which is determined based on the initial charging capacity obtained when a separately prepared mixture for measuring Y is charged and discharged in a battery cell with a Li counter electrode.

[0022] 1.2.4. Other components

In a second step S2, a conductive additive is further mixed with the anode mixture 5 until the problem is resolved. Any conductive additive known as a conductive additive used for a sulfide solid state battery may be used. Examples of these additives include carbon material such as acetylene black (AC), Ketjen black (KB) carbon black, vapor grown carbon fiber (UVPF), carbon nanotubes (CNTs), carbon nanofiber (CNF) and graphite; and metal materials such as nickel, aluminum and stainless steel. Particularly preferred is a carbon material. One conductive additive may be used alone, or two or more conductive additives may be mixed for use as a conductive additive. As a form of the conductive additive, any form, for example, powder and fiber, can be used. In the second step S2, the amount of the conductive additive is not specifically limited and can be appropriately determined in accordance with the desired battery performance. For example, the content of the conductive additive in the preferred embodiment is from 0.5% (mass.) To 20% (mass), if the solids content in the anode mixture 5 is 100% (mass). The lower limit level of its content in a more preferred embodiment is not less than 1% (mass), and the upper limit level of its content in a more preferred embodiment is not more than 10% (mass).

[0023] In the second step S2, in a preferred embodiment, a binder is further mixed with the anode mixture 5 until the problem is solved. Any binder known as a binder used for a sulfide solid state battery may be used. For example, at least one selected from styrene-butadiene rubber (SBK), carboxymethyl cellulose (CMC), acrylonitrile butadiene rubber (ANBK), butadiene rubber (BC), polyvinylidene fluoride (PVDF) and polytetrafluoroethane can be used. In the second step S2, the amount of binder is not specifically limited and can be appropriately determined in accordance with the desired battery performance. For example, the content of the binder in a preferred embodiment is from 1% (mass.) To 30% (mass), if the solids content in the anode mixture 5 is 100% (mass). The lower limit level in a more preferred embodiment is not less than 2% (mass), and the upper limit level in a more preferred embodiment is not more than 15% (mass).

[0024] In the second step S2, a solid electrolyte other than a sulfide solid electrolyte 3 can be further admixed to the anode mixture 5 until the problem is solved. Examples thereof include a solid oxide electrolyte such as lithium lanthanum zirconate, LiPON, Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ , glass based on Li-SiO, and glass based on Li-Al-SO.

[0025] In the second step S2, the anode active material other than the silicon-based active material 4 can be further mixed with the anode mixture 5 until the problem is solved. Examples thereof include carbon material such as graphite and solid carbon; various oxides such as lithium titanate; as well as metallic lithium or a lithium alloy.

[0026] 1.2.5. Mixing

In the second step S2, the method of mixing the sulfide solid electrolyte 3, the silicon-based active material 4 and the pre-alloyed material 2 to form the anode mixture 5 is not specifically limited. The second step S2 can be performed using known mixing means. The mixing in the second step S2 may be wet mixing using a solvent or dry mixing without a solvent (mixing granular materials with each other). From the point of view that the materials can be mixed more evenly and that lithium can diffuse more efficiently from the pre-alloyed material 2 into the silicon-based active material 4, wet mixing using a solvent is preferable. In particular, in a preferred embodiment, it is possible to mix the sulfide solid electrolyte 3, the silicon-based active material 4 and the pre-alloyed material 2 together with the solvent to obtain the anode mixture 5 in the form of a suspension or paste. The solvent used in this case is not specifically limited. Preferred examples include butyl butyrate and N-methylpyrrolidone (NMP).

[0027] 1.3. Third stage

As shown in FIG. 2C, in the third step S3, the anode mixture 5 is applied in the form of a coating on the surface of the anode current collector 6 containing copper to obtain the anode 10.

[0028] 1.3.1. Anode current collector 6 containing copper

The anode current collector 6 must contain copper. Examples of such a current collector include a metal foil or wire mesh containing copper or a copper alloy. Alternatively, the anode current collector 6 may consist of a substrate material coated with a layer of copper or a copper alloy, or of a substrate material, sputtered from copper or a copper alloy. In particular, in a preferred embodiment, said current collector consists of a metal foil made of copper (copper foil). The thickness of the anode current collector 6 is not particularly limited and, in particular, in a preferred embodiment is from 0.1 μm to 1 mm, and in a more preferred embodiment is from 1 μm to 100 μm.

[0029] 1.3.2. Coating

The method of applying the anode mixture 5 in the form of a coating on the surface of the anode current collector 6 is not specifically limited. You can apply the anode mixture 5 to the surface of the anode current collector 6 using a wet process and dry and, alternatively, use the mold for the anode current collector 6 to apply the anode mixture 5 to the surface of the current collector 6. You can also press the anode mixture 5 together with the anode current collector 6 in the mold by means of a dry process with the formation of the anode mixture 5 on the surface of the anode current collector 6. In the case of a wet process, in the preferred embodiment, the anode mixture 5 is dispersed over a solvent or the like, with the floor HAND slurry or paste as described above. It is believed that the molding in the third step S3 leads to better contact between the sulfide solid electrolyte 3, the silicon-based active material 4 and the pre-alloyed material 2 in the anode mixture 5, which makes it possible to more uniformly diffuse lithium from the pre-alloyed material 2 into the active material 4 is based on silicon and produces a more significant effect.

[0030] The thickness of the layer of the anode mixture 5 that is applied to the surface of the anode current collector 6 in the third step S3 (thickness after drying to remove the solvent in the case of a wet process) is not specifically limited, and, for example, in the preferred embodiment, is from 0.1 μm to 1 mm and more preferably from 1 μm to 100 μm. Or the thickness may be greater than the above to increase the electric capacitance. The thickness of the layer of the anode mixture 5 is preferably determined so that the capacity of the anode 10 is greater than the capacity of the cathode 20.

[0031] As described above, the anode 10 of the sulfide solid state battery 100 can be obtained in steps S1-S3. In the anode 10, on the surface of the layer of the anode mixture 5, which is located on the opposite side from the anode current collector 6 (turned towards the cathode, if the anode 10 is used in the battery), an additional layer of the anode mixture can be deposited, which differs from the anode mixture 5. Examples of it include layers containing only the active material other than silicon active material (e.g., carbon active material) as the anode active material.

[0032] 1.4. Additives

As shown in FIG. 3, the sulfide solid state battery 100 includes a cathode 20 and a solid electrolyte layer 30 as an additive to the anode 10 fabricated according to steps S1 to S3. Methods of manufacturing a cathode 20 and a solid electrolyte layer 30 are well known. That is, the sulfide solid state battery 100 can be manufactured in the same manner as a conventional one, except that this method includes a manufacturing method S10.

[0033] 1.4.1. Cathode 20

Although the structure of the cathode 20 in the sulfide solid state battery 100 is obvious to a person skilled in the art, an example thereof will be described below. The cathode 20 usually contains a cathode active material and a layer of cathode mixture 22, which contains as an optional component a solid electrolyte, a binder, a conductive additive and other additives (thickener, etc.). In a preferred embodiment, it includes a cathode current collector 21, which is in contact with the layer 22 of the cathode mixture.

[0034] The cathode current collector 21 may be made of metal foil, metal mesh, or the like. Most preferred is a metal foil. Examples of metals from which a cathode current collector can be formed are stainless steel, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, etc. The cathode current collector 21 may also be a metal foil on which, or on whose substrate material, such metal is applied in the form of a coating, or this metal is sprayed onto the substrate material.

[0035] Any material known as cathode active material for use in a sulfide solid state battery can be used as the cathode active material contained in the cathode mixture layer 22. Among the known active materials, a material having more than higher potential for charging and discharging than silicon-based active material 4. Examples thereof include lithium oxide, such as lithium cobaltate, lithium nickelate, Li (Ni, Mn, Co) O ₂ (Li _{1 + α} Ni _1/3 Mn _1/3 Co _1/3 O ₂ ), lithium manganate, spinel composite and lithium oxide, lithium titanate and lithium phosphate (LiMPO ₄ , where M is at least one substance selected from Fe, Mn, Co and Ni). One cathode active material may be used alone or two or more cathode active materials may be mixed for such use. The active cathode material may have a coating layer of lithium niobate, lithium titanate, lithium phosphate, and the like on its surface. The shape of the cathode active material is not particularly limited, and, for example, in a preferred embodiment, the cathode active material is in the form of particles or a thin film. The content of the cathode active material in the cathode layer is not particularly limited and may be equivalent to the amount of cathode active material contained in the cathode layer of a conventional sulfide solid state battery.

[0036] As the solid electrolyte, any material known as solid electrolyte for use in a sulfide solid state battery may be used. Preferred examples include a sulfide solid electrolyte as described above. In addition to the sulfide solid electrolyte, an inorganic solid electrolyte other than the sulfide solid electrolyte may be added to achieve the desired effect. As the conductive additive and the binder, the same materials can be used that are used for this purpose in the anode 10. One solid electrolyte (conductive additive, binder) can be used separately or two or more solid electrolytes (conductive additives, binders) can be mixed for such use. The forms of the solid electrolyte and the conductive additive are not particularly limited, and, for example, they are preferably contained in particulate form. The content of the solid electrolyte, the conductive additive and the binder in the layer of the cathode mixture is not particularly limited, and may be equivalent to the content of the solid electrolyte, the conductive additive and the binder in the layer of the cathode mixture of a conventional sulfide solid state battery.

[0037] A cathode 20 having the structure described above can be easily obtained by performing steps such as placing the cathode active material and a solid electrolyte, as well as optionally incorporating a binder and a conductive additive in a solvent, mixing them to form an electrode composition in suspension and then applying this electrode composition to the surface of the cathode current collector and drying the surface. The cathode can be made not only using such a wet process, but also using a dry process. After the cathode mixture layer in the form of a sheet is formed, as described above, on the surface of the cathode current collector, the thickness of the cathode mixture layer is, for example, preferably from 0.1 to 1 mm, and more preferably from 1 μm to 100 microns.

[0038] 1.4.2. Solid electrolyte layer 30

Although the structure of the solid electrolyte layer 30 in the sulfide solid state battery 100 is obvious to a person skilled in the art, one example thereof will be described below. The solid electrolyte layer 30 contains a solid electrolyte and, optionally, a binder. For example, in a preferred embodiment, a sulfide solid electrolyte is used as the solid electrolyte, as described above. For example, in addition to a sulfide solid electrolyte, an inorganic solid electrolyte other than a sulfide solid electrolyte may additionally be contained until the desired effect is achieved. For use, a binder may be appropriately selected, the same as described above. The content of the constituents in the solid electrolyte layer 30 may be the same as in the normal case. The shape of the solid electrolyte layer 30 may be the same as in the normal case. In particular, a sheet-like solid electrolyte layer 30 is preferred. The solid electrolyte layer 30 in the form of a sheet can be easily obtained by going through such steps as placing a solid electrolyte and, optionally, binder in a solvent, mixing them to obtain an electrolyte composition in the form of a suspension, then applying this electrolyte composition to the surface of the substrate material or ( a) on the surface (surface) of the layer of the cathode mixture and / or layer of the anode mixture and drying the surface (surfaces). In this case, the thickness of the layer of solid electrolyte 30 is, for example, in a preferred embodiment, from 0.1 to 300 μm, and in a more preferred embodiment, from 0.1 μm to 100 μm.

[0039] 1.4.3. Other details

Needless to say, the sulfide solid state battery 100 may include the necessary terminals, a battery compartment, etc. in addition to the anode 10, the cathode 20, and the solid electrolyte layer 30. These details are well known, and a detailed description thereof is omitted here.

[0040] 1.5. 100 Sulfide Solid State Battery

For example, the sulfide solid state battery 100, which is manufactured by the manufacturing method S10 of the present invention, has the following structural feature: the sulfide solid state battery 100 comprises an anode 10, a cathode 20 and a solid electrolyte layer 30 located between the anode 10 and the cathode 20, while the anode 10 contains a layer formed by the anode current collector 6 containing copper and the anode mixture 5 deposited on the surface of the anode current collector 6, wherein the anode mixture 5 contains a sulfide solid electrolyte 3, an active material silicon-based rial 4 and pre-alloyed material 2, and pre-alloyed material 2 is obtained by alloying material 1, which is at least one material selected from graphite and lithium titanate (in the preferred embodiment, material 1 consists of graphite), lithium . The structure of the battery parts are as described above, and their detailed description is omitted here.

[0041] As described above, in the manufacturing method S10 of the present invention, the preselected pre-alloyed material 2 is manufactured in the first step S1, and in the second step S2, the pre-alloyed material 2 is mixed together with the silicon-based active material 4 to obtain an anode mixture 5. In this case, if the anode mixture 5 is used for the anode 10, immediately after the formation of the anode mixture 5, lithium diffuses from the pre-alloyed material 2 into the silicon-based active material 4, which leads to a decrease in the standard deleterious potential with respect to lithium. Thus, in the sulfide solid state battery 100, the reaction of the sulfide solid electrolyte 3 with copper (copper in the anode current collector 6) can be suppressed, the diffusion of copper from the anode current collector 6 through the sulfide solid electrolyte 3 in the direction of the side of the cathode 20 can be suppressed, therefore, self-discharge caused by small short circuits of the cathode 20 and the anode 10, etc., can be suppressed. In addition, since the anode 10 exists as its stored electrical and / or ionic conductivity, the pre-alloyed material 2 will not be able to adversely affect the properties of the battery 100.

[0042] 2. Addition to the description of the beneficial effect in the manufacturing method of this invention

It seems that the same effect can be obtained by pre-alloying lithium with an active material based on silicon, which is used as the anode active material using the electrochemical reaction in a lithium-ion battery before making the anode mixture. However, this seems unfeasible in view of the costs; for example, in this case a much larger amount of active material must be doped than in the manufacturing method S10.

[0043] It also seems that the problem of the formation of CuS should be solved using an anode current collector made of a metal other than copper. However, in this case, some properties of the battery, including cycle characteristics, etc., may deteriorate.

[0044] 3. Market information

This can be confirmed, for example, by checking whether a sulfide solid state battery can be manufactured by the method of the present invention or not. That is, the fact that a sulfide solid state battery may (or cannot) be produced by the method of the present invention can be confirmed by analyzing in the sulfide solid state battery a portion of the anode active material that is not facing toward the cathode or anode, or by checking the balance cathode and anode potentials in a three-electrode cell. Alternatively, if a pre-alloyed material is prepared using an electrochemical reaction in a battery based on a solution system, a solid electrolyte layer (SEI) is formed on the surface of the pre-alloyed material. Then it is possible to confirm the possibility of manufacturing a sulfide solid-state battery by the manufacturing method of the present invention, making sure that the lithium graphite or titanate contained in the anode has SEI on its surface. Examples of compounds that can form SEI include LiF, LiCO _3, and phosphoric ester. Examples of a method for confirming the presence or absence of compounds that can form SEIs are elemental analysis using TEM-EELS, ICP and EPS, mass spectrometry using TOF-SIMS, and analysis using a combination of these methods. For example, whether a given embodiment of the invention can be implemented or not, it can be determined by establishing that an element such as fluorine, which is not normally found in raw materials for solid electrolyte, is contained only in the SEI formed on the surface of the pre-alloyed material.

Examples

[0045] <Example 1>

1. Manufacture of sulfide solid state batteries

1.1. Preparation of the cathode active material. LiNi particles _1/3 Mn _1/3 Co _1/3 O ₂ were obtained (average particle size (D ₅₀ ): 6 μm). LiNbO _{3 was} applied to the surface of the particles using a sol-gel process. In particular, an ethanol solution in which equimolar amounts of LiOC ₂ H ₅ and Nb (OC ₂ H ₅ ) ₅ were dissolved covered the surface of the particles at atmospheric pressure using a fluid bed granulation and coating apparatus (SFP-01 manufactured by Powrex Corporation ) The processing time was adjusted so that the thickness of this coating was 5 nm. After that, the coated particles were subjected to heat treatment at 350 ° C at atmospheric pressure for 1 hour to obtain a cathode active material.

[0046] 1.2. Cathode fabrication

The obtained cathode active material and sulfide solid electrolyte (LiI-Li ₂ O-Li ₂ SP ₂ S ₅ , average particle size (D ₅₀ ): 2.5 μm) was weighed so that their mass ratio was: cathode active material: sulfide solid electrolyte = 75: 25. Further, to 100 mass parts of the cathode active material, 4 mass parts of a PVDF-based binder (manufactured by Kureha Corporation) and 6 mass parts of acetylene carbon black as a conductive additive were added. The resulting mixture was added to butyl butyrate so that the solids content was 70% (mass), and then stirred with a stirrer until a cathode paste formed. An aluminum foil of a thickness of 15 μm was coated with the obtained cathode paste in accordance with the scraper method using an applicator, so that the paste was 30 mg / cm in weight, and then the foil was dried at 120 ° C for 3 minutes to obtain a cathode containing a layer of the cathode mixture on the surface of aluminum foil.

[0047] 1.3. Production of a solid electrolyte layer

95 parts by weight of the same sulfide solid electrolyte as above and 5 parts by weight of butylene rubber as a binder were weighed, and this mixture was added to the heptane solvent so that the solids content was 70% (mass). The resulting mixture was mixed using an ultrasonic dispersing device (UH-50 manufactured by SMT Corporation) for 2 minutes to obtain a solid electrolyte paste. The substrate material (aluminum foil) was coated with the obtained solid electrolyte paste in the same manner as in the case of the cathode paste, so that the paste was 60 mg / cm ² and the substrate material was dried in air and then dried at 100 ° C for 30 minutes to obtain a substrate material comprising a layer of solid electrolyte.

[0048] 1.4. Anode fabrication

1.4.1. Preparation of Pre-Alloyed Material 99.7 parts by weight of finely divided particles of natural graphite (average particle size (D ₅₀ ): 15 μm) and 0.3 parts by weight of carboxymethyl cellulose were weighed, they were added to ion-exchanged water so that the solids content was 60 % (mass), and mixed using a planetary mixer to obtain a paste. The resulting paste was uniformly applied to the copper foil in accordance with the method of scraper coating, and the copper foil was dried at 120 ° C for 5 minutes to obtain an electrode. A coin-type battery with a diameter of 16 mm was cut out from the obtained electrode, in which metallic Li served as a counter electrode, PE (ie, with a “zero” phase), a 20 μm thick separator was used as a separating pad, and a non-aqueous electrolyte solution (ethyl carbonate mixture) (EC) and diethyl carbonate (DEC) ratio (EC: DEC = 1: 1) in which LiPF ₆ was dissolved at a concentration of 1 mol / kg) was used as an electrolyte solution. This coin-type battery was charged using a charging and discharging device. The charging capacity was adjusted so that it was 100 mAh / kg in relation to the total mass of graphite contained in this battery. After charging, the coin-type battery was disassembled in an argon atmosphere and the electrode was removed from it. After the electrode was washed in ethyl methyl carbonate, graphite was separated from the copper foil using a spatula, thereby obtaining a pre-alloyed material.

[0049] 1.4.2. The manufacture of the anode mixture and the application of this anode mixture in the form of a coating on a copper foil

Sulphide solid electrolyte, as described above, fine silicon particles (average particle size (D ₅₀ ): 6 μm) and pre-alloyed material were weighed so as to obtain a mass ratio of sulfide solid electrolyte: fine silicon particles: pre-alloyed material = 45:53, 4: 1.6 (silicon active material: pre-alloyed material = 97: 3). In addition, 6 parts by weight of a PVDF-based binder (manufactured by Kureha Corporation) and 6 parts by weight of acetylene carbon black as a conductive additive were added to 100 parts by weight of finely divided silicon particles. The resulting mixture was added to butyl butyrate so that the solids content was 70% (mass), and then stirred with a stirrer until an anode paste formed. A 15 μm thick copper foil was uniformly coated with the obtained cathode paste in accordance with a scraper coating method using an applicator, and this copper foil was dried at 120 ° C. for 3 minutes to obtain an anode comprising an anode mixture layer on the surface of the copper foil.

[0050] 1.5. Layering of the cathode, solid electrolyte layer and anode

From the above-described layer of solid electrolyte, a 1 cm ² area was cut down for processing by pressing under a pressure of 1 ton / cm ² . The cathode was layered on one of the surfaces obtained by pressing a layer of solid electrolyte (face side opposite to the substrate material) and processed by pressing under a pressure of 1 ton / cm ² . The backing material has been removed. The anode was layered on the surface from which the substrate was removed, and processed by pressing under a pressure of 6 tons / cm ² to obtain a multilayer product formed from a cathode / layer of solid electrolyte / anode. The resulting multilayer product was hermetically sealed with an aluminum laminated film provided with leads so as to obtain a sulfide solid state battery for evaluation. The characteristics of the resulting battery are shown in the following Table 1.

[0051] 2. Self-discharge sulfide solid state battery test

As described above, there is a case where the reaction of a copper foil, which serves as an anode collector with a sulfide solid electrolyte, leads to the formation of CuS with high conductivity, while Cu diffuses from the anode collector towards the cathode, resulting in small short circuits of the cathode and anode, and the voltage of a sulfide solid state battery spontaneously decreases. To evaluate this, a sulfide solid state battery was subjected to a self-discharge test using the following procedures. Firstly, after the sulfide solid-state battery was charged (charging conditions: 4.4 V CCCV mode, current 2 mA, cut-off current 0.1 mA), the battery was kept in a furnace with a constant temperature at 25 ° C for 25 hours, and throughout this process, the voltage (ΔV) was measured. The results are shown in Table 1.

[0052] 3. Evaluation of the characteristics of the cycle

It is expected that if the carbon-based active material is used together with the silicon-based active material, then the expansion rate as a whole of the anode active material is reduced, and the cycle characteristics of the sulfide solid state battery during charging / discharging are improved compared to the case when as the anode active material only silicon-based active material is used. To confirm this effect, a cycle test was performed under the following conditions. The charge retention value was calculated using the discharge capacity after the 150th cycle with respect to the discharge capacity after the first cycle (in%). This cyclic testing was carried out under conditions of battery limitation using a restrictive device with a strain gauge so that a pressure of 5 MPa was uniformly applied to the surface of the anode and cathode. The results are shown in the following Table 1.

(Conditions for testing the cycle)

charging: 4.4 V CCCV mode, current 10 mA, cut-off current 0.5 mA

discharge: 3.0 V SS mode, current 10 mA

temperature: 25 ° C

[0053] <Examples 2-4 and Comparative example 1>

A sulfide solid state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that the mixture ratio of the anode active material and the pre-alloyed material was changed as shown in the following Table 1. Battery characteristics as well as the results of self-discharge tests and evaluation of cycle characteristics are presented in the following Table 1.

[0054] <Example 5>

A sulfide solid state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that the charging capacity in the manufacture of pre-alloyed material was changed to 150 mAh / g. Battery characteristics, as well as self-discharge test results and cycle characteristics estimates, are presented in the following Table 1.

[0055] <Example 6>

A sulfide solid state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that in the material used as a pre-alloyed material, graphite was replaced by lithium titanate (average particle size (D ₅₀ ): 2 μm) in order to obtain pre-alloyed material using the following procedures. Battery characteristics, as well as self-discharge test results and cycle characteristics estimates, are presented in the following Table 1.

[0056] In NMP, 92 parts by weight of lithium titanate, 3 parts by weight of a binder based on PVDF and 5 parts by weight of acetylene carbon black were weighed so that the solids content was 70% (mass) and mixed using a planetary mixer until receiving pasta. The resulting paste was applied to copper foil in accordance with the method of scraper coating, and dried copper foil to obtain an electrode in the same manner as in Example 1. A coin-type battery was made using the obtained electrode in the same manner as in Example 1. Coin battery type charged in the same manner as in Example 5 (charging capacity: 150 mAh / g). After the coin-type battery was disassembled and separated from the copper foil in the same manner as in Example 1, the separated powder was dispersed in NMP, approximately 10 times larger than the powder, and centrifuged again three times to remove the binder bonded to lithium titanate based on PVDF, etc. Fine particles obtained after centrifugation were used as pre-alloyed material.

[0057] <Example 7>

A sulfide solid state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that silicon was replaced with silicon oxide (average particle size (D ₅₀ ): 5 μm) and the mass of the obtained paste in the anode has been changed. Battery characteristics, as well as self-discharge test results and cycle characteristics estimates, are presented in the following Table 1.

[0058] <Example 8>

A sulfide solid state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that the charging capacity in the manufacture of pre-alloyed material was changed to 10 mAh / g, and the ratio of the mixture of the anode active material and preliminary alloyed material was changed as shown in the following Table 1. Battery characteristics, as well as the results of self-discharge tests and evaluation of cycle characteristics are presented in the following th below Table 1.

[0059] <Comparative example 2>

A sulphide solid state battery was made and subjected to a self-discharge test and evaluation of cycle characteristics in the same manner as in Comparative Example 1, except that stainless steel foil of the same thickness was used instead of copper foil as the anode current collector. Battery characteristics, as well as self-discharge test results and cycle characteristics estimates, are presented in the following Table 1.

[0060] <Reference example 1>

A sulfide solid-state battery was made and subjected to a self-discharge test and evaluation of the cycle characteristics in the same manner as in Example 1, except that stainless steel foil of the same thickness was used instead of copper foil as the anode current collector. Battery characteristics, as well as self-discharge test results and cycle characteristics estimates, are presented in the following Table 1.

[0062] As can be seen from the results shown in Table 1, the presence of pre-alloyed material in the anode mixture led to a significant decrease in self-discharge. It can be assumed that the pre-alloyed material decreased the initial anode potential of the sulfide solid state battery, which led to the suppression of the reaction of copper foil and sulfide solid electrolyte. Despite the fact that the amount of pre-alloyed material contained in the anode mixture was not specifically limited, and a certain effect was manifested if only a small amount of pre-alloyed material was contained in the anode mixture, from Examples 1-8 we can conclude that the ratio (X / Y ) the converted value (X) obtained by converting the total amount of lithium, with which pre-alloyed material included in the anode mixture is alloyed into an electric capacitance, to the total electric the capacitance (Y) of the silicon-based active material contained in the anode mixture is preferably at least 0.0005. In particular, if X / Y is not less than 0.0008, while suppressing self-discharge by about 0.18 V, then the limit of the effect of suppressing self-discharge is reached. Or, based on Examples 1-8, it can also be said that the anode active material in the preferred embodiment is not less than 70% (mass.) And not more than 100% (mass), and the pre-alloyed material in the preferred embodiment is more than 0% (mass. ) and not more than 30% (mass) if the total amount of anode active material and pre-alloyed material is 100% (mass). Given the electrical capacity of the anode, etc., in particular, the anode active material may more preferably be at least 90% (mass), even more preferably at least 93% (mass), and in a particularly preferred embodiment at least 96 % (mass); and pre-alloyed material in a more preferred embodiment can be no more than 10% (mass), in an even more preferred embodiment, not more than 7% (mass) and in a particularly preferred embodiment, not more than 4% (mass).

As can be seen from the results of Examples 1-8 and Comparative Example 1, if a copper foil containing pre-alloyed material in the anode mixture was used as the anode current collector, the cycle characteristics of the sulfide solid state battery improved.

In addition, as can be seen from the results of Examples 6 and 7, the same effect was obtained even if the anode active material and / or pre-alloyed material was / were replaced (s).

[0063] Replacing the material of the anode current collector with a metal other than copper (for example, stainless steel), as in Comparative Example 2 and Reference Example 1, also avoids the formation of CuS and reduces self-discharge. However, in this case, some other properties of the battery, in addition to self-discharge, worsened. For example, as shown in Comparative Example 2, battery cycle performance is degraded. As can be seen from the results of Comparative Example 2 and Reference Example 1, if stainless steel foil was used as the anode current collector, it was difficult to improve the cycle characteristics even if the pre-alloyed material was contained in the anode mixture. It is believed that the reason is that the stainless steel foil is harder than the copper foil, and therefore it is difficult to follow the expansion / contraction of the anode active material in the charging / discharging mode.

From the foregoing, it can be said that if a layer of the anode mixture containing a silicon-based active material and a sulfide solid electrolyte is deposited on the surface of the anode current collector, then in order to avoid the formation of CuS, it is advisable to use an anode current collector containing copper, and containing pre-alloyed material in the anode mixture in order to suppress the formation of CuS, compared with the use of the anode current collector formed from a material other than copper.

Industrial applicability

[0064] A sulfide solid state battery manufactured according to the manufacturing method of the present invention can be used in a wide range of power sources, such as a small sized power supply for portable devices and a large built-in power supply.

List of Reference Items

[0065] 10 anode

1 material consisting of graphite and / or lithium titanate

2 pre-alloyed material

3 solid sulfide electrolyte

4 silicon-based active material

5 anode mixture

6 anode current collector

20 cathode

21 cathode current collector

22 layer cathode mixture

30 layer solid electrolyte

100 sulfide solid state battery

Claims (8)

1. A method of manufacturing a sulfide solid state battery, comprising: a first lithium alloying step of at least one material selected from graphite and lithium titanate to produce pre-alloyed material; a second step of mixing a sulfide solid electrolyte, a silicon-based active material and a pre-alloyed material to form an anode mixture; and the third stage of applying the anode mixture in the form of a coating on the surface of the anode current collector containing copper, to obtain the anode. 2. The method according to p. 1, in which the ratio (X / Y) of the converted value (X) obtained by converting the total amount of lithium with which the pre-alloyed material included in the anode mixture is doped into an electric capacitance to the total electric capacitance (Y) of the silicon-based active material, contained in the anode mixture is at least 0,0005. 3. The method according to p. 1 or 2, in which in a first step, said at least one material is doped with lithium using an electrochemical reaction in a lithium-ion battery.

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