CN109904523B - Method for manufacturing sulfide solid-state battery - Google Patents

Method for manufacturing sulfide solid-state battery Download PDF

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CN109904523B
CN109904523B CN201811186908.0A CN201811186908A CN109904523B CN 109904523 B CN109904523 B CN 109904523B CN 201811186908 A CN201811186908 A CN 201811186908A CN 109904523 B CN109904523 B CN 109904523B
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negative electrode
sulfide solid
lithium
active material
solid electrolyte
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CN109904523A (en
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濑上正晴
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Toyota Motor Corp
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Abstract

The problem of the present application is that, when a negative electrode is configured by laminating a negative electrode mixture containing a silicon-based active material and a sulfide solid electrolyte on the surface of a negative electrode current collector containing copper, the sulfide solid electrolyte reacts with copper at OCV of the silicon-based active material, copper diffuses from the negative electrode current collector to the positive electrode side via the sulfide solid electrolyte, and a slight short circuit occurs between the positive electrode and the negative electrode. The solution of the present application is to diffuse lithium into a silicon-based active material and lower the potential when a negative electrode mixture is produced. Specifically, a sulfide solid battery is manufactured through a 1 st step of doping one material selected from graphite and lithium titanate with lithium to obtain a pre-doped material, a 2 nd step of mixing a sulfide solid electrolyte, a silicon-based active material, and the pre-doped material to obtain a negative electrode mix, and a 3 rd step of laminating the negative electrode mix on the surface of a copper-containing negative electrode current collector to obtain a negative electrode.

Description

Method for manufacturing sulfide solid-state battery
Technical Field
The present application relates to a method for manufacturing a sulfide solid-state battery.
Background
Patent documents 1to 3 disclose a sulfide solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer provided between the positive electrode and the negative electrode. In the technique disclosed in patent document 1, a negative electrode mixture containing a sulfide solid electrolyte, a silicon-based active material, and a carbon-based active material is laminated on the surface of a negative electrode current collector made of copper, thereby obtaining a negative electrode. In the technique disclosed in patent document 2, lithium is supplied from the positive electrode to the negative electrode during the period from the initial charge of the sulfide solid-state battery to the battery use voltage, and the negative electrode active material is doped with lithium. In the technique disclosed in patent document 3, a sulfidation resistant layer is provided on the surface of a negative electrode current collector before a negative electrode mixture containing a sulfide solid electrolyte is laminated on the surface of the negative electrode current collector.
Prior art documents
Patent document 1: japanese patent laid-open publication No. 2017-054720
Patent document 2: japanese patent laid-open publication No. 2017-147158
Patent document 3: international publication No. 2014/156638
Disclosure of Invention
The lithium standard potential of the electrode of the sulfide solid-state battery is equal to the OCV of the active material before charge and discharge. For example, when a negative electrode mixture containing a silicon-based active material is laminated on the surface of a negative electrode current collector to form a negative electrode, the negative electrode has a lithium standard potential of about 2.8V.
On the other hand, according to the findings of the present inventors, when a negative electrode mixture containing a sulfide solid electrolyte is laminated on the surface of a negative electrode current collector containing copper to form a negative electrode, the sulfide solid electrolyte reacts with copper at a potential lower than 2.8V to generate electrically conductive CuS or the like.
That is, when a negative electrode mixture containing a silicon-based active material and a sulfide solid electrolyte is laminated on the surface of a negative electrode current collector containing copper to form a negative electrode, the sulfide solid electrolyte reacts with copper at OCV of the silicon-based active material, and copper diffuses from the negative electrode current collector to the positive electrode side via the sulfide solid electrolyte. When a sulfide solid-state battery is produced using such a negative electrode, self-discharge or the like may occur due to a micro short circuit between the positive electrode and the negative electrode.
As one of means for solving the above problems, the present application discloses a method for manufacturing a sulfide solid-state battery, comprising: a step 1 of doping at least one material selected from graphite and lithium titanate with lithium to obtain a pre-doped material; a step 2 of mixing a sulfide solid electrolyte, a silicon-based active material, and the predoped material to obtain a negative electrode mixture; and a 3 rd step of laminating the negative electrode mixture on the surface of a negative electrode current collector containing copper to obtain a negative electrode.
In the production method of the present disclosure, it is preferable that a ratio (X/Y) of a capacity conversion value (X) of the total amount of lithium doped in the predoped material contained in the negative electrode mix and a total capacity (Y) of the silicon-based active material contained in the negative electrode mix is 0.0005 or more.
In the production method of the present disclosure, in the step 1, it is preferable that lithium is doped into the material by an electrochemical reaction in a lithium ion battery.
In the manufacturing method of the present disclosure, a predetermined pre-doping material is mixed with a silicon-based active material to prepare a negative electrode mixture. In this case, immediately after the negative electrode mixture is prepared, lithium diffuses from the predoped material to the silicon-based active material, and the potential in the case of the negative electrode decreases. That is, the reaction between the sulfide solid electrolyte and copper can be suppressed, diffusion of copper from the negative electrode current collector to the positive electrode side via the sulfide solid electrolyte can be suppressed, and self-discharge or the like due to a micro short circuit between the positive electrode and the negative electrode can be suppressed. In addition, since the predoped material exists in the negative electrode in a state of having electrical conductivity and/or ion conductivity, it is difficult to have a negative influence on the battery characteristics.
Drawings
Fig. 1 is a diagram for explaining the flow of the manufacturing method S10 of the sulfide solid-state battery 100.
Fig. 2 is a schematic diagram for explaining the flow of the method S10 for producing the sulfide solid-state battery 100.
Fig. 3 is a schematic diagram for explaining the structure of the sulfide solid-state battery 100.
Description of the reference numerals
10 negative electrode
1 materials made of graphite and/or lithium titanate
2 Pre-doping Material
3 sulfide solid electrolyte
4 silicon-based active material
5 negative electrode mixture
6 negative electrode current collector
20 positive electrode
21 positive electrode current collector
22 positive electrode mixture layer
30 solid electrolyte layer
100 sulfide solid-state battery
Detailed Description
1. Method for manufacturing sulfide solid-state battery
Referring to fig. 1to 3, a flow of a method S10 for manufacturing a sulfide solid-state battery 100 will be described. Method S10 for manufacturing sulfide solid-state battery 100 includes the steps of: a 1 st step S1 of doping at least one material 1 selected from graphite and lithium titanate with lithium to obtain a pre-doped material 2; a 2 nd step S2 of mixing the sulfide solid electrolyte 3, the silicon-based active material 4, and the preliminary doping material 2 to obtain a negative electrode mixture 5; and a 3 rd step S3 of laminating the negative electrode mixture 5 on the surface of the negative electrode current collector 6 containing copper to obtain the negative electrode 10.
1.1. Step 1 of
As shown in fig. 2(a), in the 1 st step S1, at least one material 1 selected from graphite and lithium titanate is doped with lithium to obtain a pre-doped material 2.
1.1.1. Material 1
The material 1 is made of at least one selected from graphite and Lithium Titanate (LTO). Graphite and lithium titanate are both materials capable of occluding and releasing lithium, and are known as negative electrode active materials for lithium ion batteries. In the case of comparing graphite with LTO, graphite is preferable. This is because the negative electrode potential of graphite is low, making the technical effect of the present disclosure more obvious. In addition, the large capacity of graphite is also a factor. Further, graphite can exhibit high performance as a conductive aid. The graphite can be artificial graphite or natural graphite. The composition of lithium titanate is not particularly limited, and for example, Li is preferable4Ti5O12. The shape of the material 1 is not particularly limited, and is particularly preferably a particle shape.
1.1.2. Method for doping lithium
As a method of doping lithium in the material 1to obtain the pre-doped material 2, various methods can be employed. For example, there are a method of doping lithium into the material 1 by physically mixing the material 1 with a lithium source, a method of electrochemically inserting lithium into the material 1, and the like. From the viewpoint of easily controlling the amount of lithium doped into the material 1, it is preferable to dope lithium into the material 1 by utilizing an electrochemical reaction in a lithium ion battery. For example, it is preferable that the material 1 is charged and discharged with lithium ions at a higher potential than the material 1An electric positive electrode active material and an appropriate electrolyte having lithium ion conductivity are combined to form a lithium ion battery, and lithium is doped into the material 1 by utilizing a charging reaction in the lithium ion battery. The lithium ion battery used in this case may be a liquid battery or a solid battery. In particular, from the viewpoint of easily separating the pre-doped material 2 after doping lithium into the material 1, a liquid battery (nonaqueous electrolyte battery, aqueous battery) is preferably used. That is, it is preferable to use the material 1, a positive electrode active material that charges and discharges lithium ions at a higher potential than the material 1, and an electrolyte having lithium ion conductivity (for example, LiPF)6Etc.) and a solvent (water, organic solvent) for dissolving the electrolyte, and doping the material 1 with lithium by utilizing a charging reaction in the lithium ion battery. After doping lithium in the material 1 by using an electrochemical reaction in the lithium ion battery, for example, the lithium ion battery is decomposed, the pre-doped material 2 is peeled off, and the pre-doped material 2 is washed and pulverized as necessary.
The amount of lithium doped into the material 1 is not particularly limited. The amount of the pre-doped material 2 in the negative electrode mix 5 described later can be reduced as the amount of lithium doped into the material 1 is increased. When the material 1 is doped with lithium by utilizing a charging reaction in a lithium ion battery, it is preferable that the material 1 is doped with lithium until the amount of charge becomes 10mAh/g or more. More preferably 50mAh/g or more, still more preferably 80mAh/g or more, and particularly preferably 100mAh/g or more. The upper limit is not particularly limited, but is preferably 200mAh/g or less, more preferably 180mAh/g or less, and further preferably 150mAh/g or less. Alternatively, when the material 1 is doped with lithium by a charging reaction in a lithium ion battery, charging is preferably performed until the SOC is preferably 5% or more, more preferably 8% or more, and still more preferably 10% or more. The upper limit is not particularly limited, and charging is preferably performed until the SOC becomes 50% or less.
1.2. Step 2
As shown in fig. 2(B), in the 2 nd step S2, the sulfide solid electrolyte 3, the silicon-based active material 4, and the preliminary doping material 2 are mixed to obtain the negative electrode mixture 5.
1.2.1. Sulfide solid electrolyte 3
As the sulfide solid electrolyte 3, a sulfide suitable as a solid electrolyte of a sulfide solid battery can be used. For example, Li is mentioned2S-P2S5、Li2S-SiS2、LiI-Li2S-SiS2、LiI-Si2S-P2S5、LiI-LiBr-Li2S-P2S5、LiI-Li2S-P2S5、LiI-Li2O-Li2S-P2S5、LiI-Li2S-P2O5、LiI-Li3PO4-P2S5、Li2S-P2S5-GeS2And the like. Among these, Li is particularly more preferably contained2S-P2S5The sulfide solid electrolyte of (1). Only one kind of the sulfide solid electrolyte 3 may be used alone, or two or more kinds may be used in combination. In the 2 nd step S2, the amount of the sulfide solid electrolyte 3 is not particularly limited, and may be determined as appropriate in accordance with the performance of the target battery. For example, the entire negative electrode mixture 5 (the entire solid content after drying from which the solvent is removed in the case of wet mixing, the same applies hereinafter) is set to 100 mass%, and the content of the sulfide solid electrolyte 3 is preferably set to 10 mass% or more and 60 mass% or less. The lower limit is more preferably 20% by mass or more, and the upper limit is more preferably 50% by mass or less.
1.2.2. Silicon-based active material 4
The silicon-based active material 4 may be any material that contains Si as a constituent element and functions as a negative electrode active material in the sulfide solid-state battery. For example, at least one selected from among Si, Si alloys, and silicon oxides may be used. Si or silicon oxide is particularly preferred. The shape of the silicon-based active material 4 is not particularly limited. For example, the particles are preferable. In the 2 nd step S2, the amount of the silicon-based active material 4 is not particularly limited, and may be determined as appropriate depending on the performance of the target battery. For example, the negative electrode mixture 5 is 100 mass% as a whole, and the content of the silicon-based active material 4 is preferably 30 mass% or more and 90 mass% or less. The lower limit is more preferably 50% by mass or more, and the upper limit is more preferably 80% by mass or less.
1.2.3. Pre-doped material 2
In the 2 nd step S2, the amount of the preliminary doping material 2 is not particularly limited, and may be determined as appropriate according to the doping amount of lithium in the 1 st step S1, and the like. In particular, in step 2S 2, the mixing ratio of the predoped material 2 and the silicon-based active material 4 is preferably determined so that the ratio (X/Y) of the capacity conversion value (X) of the total amount of lithium doped in the predoped material 2 contained in the negative electrode mix 5 to the total capacity (Y) of the silicon-based active material 4 contained in the negative electrode mix 5 becomes 0.0005 or more. The ratio (X/Y) is more preferably 0.0008 or more. According to the findings of the present inventors, if the ratio (X/Y) is 0.0005 or more, a sufficient amount of lithium can be diffused into the silicon-based active material 4, and self-discharge in the case of constituting the sulfide solid-state battery 100 can be further suppressed.
The "capacity conversion value (X) of the total amount of lithium doped in the predoped material 2 included in the negative electrode mix 5" is a value obtained by converting the total amount of lithium that can diffuse from the predoped material 2 to the silicon-based active material 4 in the negative electrode mix 5 into a capacity. When the pre-doped material 2 is obtained by doping lithium into the material 1 by the charging reaction of the lithium ion battery, the capacity conversion value (X) can be obtained from the charged amount (Ah/g). The "total capacity (Y) of the silicon-based active materials 4 contained in the negative electrode mix 5" refers to a capacity possessed by the silicon-based active materials 4 in an uncharged state contained in the negative electrode mix 5. Specifically, a mixture for measuring Y may be separately prepared, and the charge capacity of the active material may be obtained from the initial charge capacity obtained when the electrode Li battery is charged and discharged.
1.2.4. Other ingredients
In the 2 nd step S2, it is preferable to further mix a conductive additive into the negative electrode mixture 5 within a range capable of solving the above problem. As the conductive aid, a material known as a conductive aid used in a sulfide solid-state battery can be used. For example, carbon materials such as Acetylene Black (AB), Ketjen Black (KB), vapor phase carbon fiber (VGCF), Carbon Nanotube (CNT), Carbon Nanofiber (CNF), and graphite; nickel, aluminum, stainless steel, and the like. Particularly preferred is a carbon material. The conductive additive may be used alone or in combination of two or more. The shape of the conductive aid may be in various forms such as powder and fiber. In the 2 nd step S2, the amount of the conductive aid is not particularly limited, and may be determined as appropriate in accordance with the performance of the target battery. For example, the solid content of the negative electrode mixture 5 is 100 mass% as a whole, and the content of the conductive additive is preferably 0.5 mass% or more and 20 mass% or less. The lower limit is more preferably 1% by mass or more, and the upper limit is more preferably 10% by mass or less.
In step 2S 2, it is preferable to further mix a binder with the negative electrode mixture 5 within a range that can solve the above problem. As the binder, a material known as a binder used in a sulfide solid-state battery can be used. For example, at least one selected from Styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC), Acrylonitrile Butadiene Rubber (ABR), Butadiene Rubber (BR), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and the like may be used. In the 2 nd step S2, the amount of the binder is not particularly limited, and may be appropriately determined according to the performance of the target battery. For example, the solid content of the negative electrode mixture 5 is 100 mass% as a whole, and the content of the binder is preferably 1 mass% or more and 30 mass% or less. The lower limit is more preferably 2% by mass or more, and the upper limit is more preferably 15% by mass or less.
In step 2, S2, solid electrolytes other than sulfide solid electrolyte 3 may be further mixed into negative electrode mixture 5 within a range capable of solving the above problems. For example, lanthanum zirconate lithium, LiPON, Li can be mixed1+XAlXGe2-X(PO4)3And oxide solid electrolytes such as Li-SiO glass and Li-Al-S-O glass.
In the 2 nd step S2, the negative electrode mixture 5 may be further mixed with a negative electrode active material other than the silicon-based active material 4 within a range in which the above-described problems can be solved. For example, a carbon material such as graphite or hard carbon may be mixed; various oxides such as lithium titanate; metallic lithium, lithium alloys, and the like.
1.2.5. Mixing method
In the 2 nd step S2, the method of mixing the sulfide solid electrolyte 3, the silicon-based active material 4, and the predoping material 2 to form the negative electrode mixture 5 is not particularly limited. Step 2S 2 can be performed by a known mixing means. The mixing in the 2 nd step S2 may be wet mixing using a solvent or dry mixing (mixing of powders) without using a solvent. Wet mixing using a solvent is preferred from the viewpoint of more uniformly mixing the materials and better diffusing lithium from the pre-doped material 2 to the silicon-based active material 4. Specifically, the sulfide solid electrolyte 3, the silicon-based active material 4, and the preliminary doping material 2 are preferably mixed together with a solvent to obtain the negative electrode mixture 5 in a slurry or paste form. The type of solvent used in this case is not particularly limited. For example, butyl butyrate and N-methylpyrrolidone (NMP) are preferably used.
1.3. Step 3 of
As shown in fig. 2(C), in step S3, a negative electrode mixture 5 is laminated on the surface of the negative electrode current collector 6 containing copper, to obtain a negative electrode 10.
1.3.1. Negative electrode current collector 6 containing copper
The negative electrode current collector 6 may contain copper. Examples thereof include metal foils and metal meshes containing copper or copper alloys. Alternatively, the substrate may be plated, copper or copper alloy evaporated. A metal foil (copper foil) made of copper is particularly preferable. The thickness of the negative electrode current collector 6 is not particularly limited. For example, it is preferably 0.1 μm or more and 1mm or less, and more preferably 1 μm or more and 100 μm or less.
1.3.2. Lamination method
The method for laminating the negative electrode mixture 5 on the surface of the negative electrode current collector 6 is not particularly limited. The negative electrode mixture 5 may be laminated on the surface of the negative electrode current collector 6 by applying the negative electrode mixture 5 to the surface of the negative electrode current collector 6 in a wet manner, followed by drying and optionally press-molding, or the negative electrode mixture 5 may be formed on the surface of the negative electrode current collector 6 by press-molding the negative electrode mixture 5 together with the negative electrode current collector 6 in a dry manner. In the case of a wet type, it is preferable to disperse the negative electrode mixture 5 in a solvent or the like to prepare a slurry or paste as described above. In the case of pressure molding in step S3, the contact between the sulfide solid electrolyte 3, the silicon-based active material 4, and the predoping material 2 is further improved in the negative electrode mixture 5, and therefore lithium can be more uniformly diffused from the predoping material 2 to the silicon-based active material 4, and a more significant effect can be exhibited.
The thickness of the layer of the negative electrode mixture 5 laminated on the surface of the negative electrode current collector 6 after the 3 rd step S3 (the thickness after the solvent is removed and dried in the case of wet) is not particularly limited. For example, it is preferably 0.1 μm or more and 1mm or less, and more preferably 1 μm or more and 100 μm or less. Alternatively, the thickness may be increased for higher capacity. The thickness of the layer of the negative electrode mixture 5 is preferably determined so that the capacity of the negative electrode 10 is larger than the capacity of the positive electrode 20.
As described above, through steps S1 to S3, negative electrode 10 of sulfide solid-state battery 100 can be manufactured. In the negative electrode 10, a layer of a negative electrode mixture different from the negative electrode mixture 5 may be further provided on the surface of the layer of the negative electrode mixture 5 opposite to the negative electrode current collector 6 (the surface on the positive electrode side in the case of a battery). For example, a layer containing only an active material (for example, a carbon-based active material) other than the silicon-based active material as the negative electrode active material may be used.
1.4. Supplement
As shown in fig. 3, the sulfide solid-state battery 100 includes a positive electrode 20 and a solid electrolyte layer 30 in addition to the negative electrode 10 manufactured in the above steps S1 to S3. Methods for manufacturing the positive electrode 20 and the solid electrolyte layer 30 are well known. That is, the sulfide solid-state battery 100 can be manufactured by the same method as the conventional method except that the manufacturing method S10 is provided.
1.4.1. Positive electrode 20
A structure of the positive electrode 20 in the sulfide solid state battery 100 will be known to those skilled in the art, and an example will be described below. The positive electrode 20 generally includes a positive electrode mixture layer 22 containing a positive electrode active material, and a solid electrolyte, a binder, a conductive auxiliary agent, and other additives (such as a thickener) as optional components. Further, it is preferable to provide a positive electrode current collector 21 in contact with the positive electrode mixture layer 22.
The positive electrode current collector 21 may be made of a metal foil, a metal mesh, or the like. Metal foils are particularly preferred. Examples of the metal that can constitute the positive electrode current collector include stainless steel, nickel, chromium, gold, platinum, aluminum, iron, titanium, zinc, and the like. These materials may be plated or evaporated on a metal foil or a substrate.
As the positive electrode active material contained in the positive electrode mixture layer 22, a material known as a positive electrode active material of a sulfide solid-state battery can be used. Among known active materials, a material that exhibits a higher charge/discharge potential than the silicon-based active material 4 may be used as the positive electrode active material. For example, lithium cobaltate, lithium nickelate, and Li (Ni, Mn, Co) O can be used as the positive electrode active material2(Li1+αNi1/3Mn1/3Co1/3O2) Lithium manganate, spinel-type lithium composite oxide, lithium titanate, and lithium metal phosphate (LiMPO)4And M is at least one selected from Fe, Mn, Co and Ni). The positive electrode active material may be used alone or in combination of two or more. The positive electrode active material may have a coating layer such as lithium niobate, lithium titanate, or lithium phosphate on the surface. The shape of the positive electrode active material is not particularly limited. For example, the particles are preferably in the form of particles or films. The content of the positive electrode active material in the positive electrode mixture layer is not particularly limited, and may be equal to the amount of the positive electrode active material contained in the positive electrode mixture layer of the conventional sulfide solid-state battery.
As the solid electrolyte, a material known as a solid electrolyte of a sulfide solid battery can be used, and for example, the sulfide solid electrolyte is preferably used. The inorganic solid electrolyte other than the sulfide solid electrolyte may be included in addition to the sulfide solid electrolyte within a range in which a desired effect can be exerted. The same materials as those used for negative electrode 10 may be used for the conductive auxiliary agent and the binder. The solid electrolyte, the conductive assistant and the binder may be used alone or in combination of two or more. The shape of the solid electrolyte and the conductive aid is not particularly limited. For example, the particles are preferable. The content of the solid electrolyte, the conductive additive and the binder in the positive electrode mixture layer is not particularly limited, and may be equal to the amount of the solid electrolyte, the conductive additive and the binder contained in the positive electrode mixture layer of the conventional sulfide solid battery.
The positive electrode 20 having the above structure can be easily manufactured by a process of adding a positive electrode active material, and optionally a solid electrolyte, a binder, and a conductive additive to a solvent, kneading them to obtain an electrode composition in a slurry state, applying the electrode composition to the surface of a positive electrode current collector, and drying it. However, the method is not limited to the wet method, and the positive electrode may be produced by a dry method. When the sheet-shaped positive electrode mixture layer is formed on the surface of the positive electrode current collector in this manner, the thickness of the positive electrode mixture layer is, for example, preferably 0.1 μm or more and 1mm or less, and more preferably 1 μm or more and 100 μm or less.
1.4.2. Solid electrolyte layer 30
The structure of the solid electrolyte layer 30 in the sulfide solid state battery 100 can be understood by those skilled in the art, and an example will be described below. The solid electrolyte layer 30 contains a solid electrolyte and an optional binder. The solid electrolyte is preferably the sulfide solid electrolyte described above. The electrolyte may include, for example, an inorganic solid electrolyte other than the sulfide solid electrolyte in addition to the sulfide solid electrolyte within a range in which a desired effect can be exerted. The binder may be suitably selected from the same materials as those described above. The content of each component in the solid electrolyte layer 30 may be the same as that of the conventional one. The shape of the solid electrolyte layer 30 may be the same as that of the conventional one. The sheet-like solid electrolyte layer 30 is particularly preferable. The sheet-shaped solid electrolyte layer 30 can be easily manufactured, for example, by a process of kneading a solid electrolyte and an optional binder in a solvent to obtain an electrolyte composition in a slurry state, applying the electrolyte composition to the surface of a substrate and drying the electrolyte composition, or applying the electrolyte composition to the surface of a positive electrode material mixture layer and/or a negative electrode material mixture layer and drying the electrolyte composition. In this case, the thickness of the solid electrolyte layer 30 is, for example, preferably 0.1 μm or more and 300 μm or less, and more preferably 0.1 μm or more and 100 μm or less.
1.4.3. Other parts
Of course, the sulfide solid-state battery 100 may be provided with necessary terminals, battery cases, and the like, in addition to the negative electrode 10, the positive electrode 20, and the solid electrolyte layer 30. These components are well known and a detailed description thereof will be omitted.
1.5. Sulfide solid-state battery 100
The sulfide solid-state battery 100 manufactured by the manufacturing method S10 of the present disclosure has the following structural features, for example. That is, the sulfide solid-state battery 100 includes a negative electrode 10, a positive electrode 20, and a solid electrolyte layer 30 provided between the negative electrode 10 and the positive electrode 20, wherein the negative electrode 10 includes a negative electrode current collector 6 containing copper and a layer formed of a negative electrode mix 5 provided on a surface of the negative electrode current collector 6, the negative electrode mix 5 includes a sulfide solid electrolyte 3, a silicon-based active material 4, and a pre-doped material 2, and the pre-doped material 2 is doped with lithium in at least one material 1 (preferably, a material 1 made of graphite) selected from graphite and lithium titanate. The structures of the respective members are as described above, and detailed description thereof is omitted here.
As described above, in the manufacturing method S10 of the present disclosure, the predetermined preliminary doping material 2 is prepared in the 1 st step S1, and the preliminary doping material 2 and the silicon-based active material 4 are mixed in the 2 nd step S2 to prepare the negative electrode mixture 5. In this case, immediately after the negative electrode mixture 5 is produced, lithium diffuses from the predoped material 2 into the silicon-based active material 4, and the standard lithium potential in the case of the negative electrode 10 is lowered. That is, the reaction between the sulfide solid electrolyte 3 and copper (copper in the negative electrode current collector 6) can be suppressed, diffusion of copper from the negative electrode current collector 6to the positive electrode 20 side via the sulfide solid electrolyte 3 can be suppressed, and self-discharge or the like due to a micro short circuit between the positive electrode 20 and the negative electrode 10 in the sulfide solid-state battery 100 can be suppressed. In addition, since the pre-doped material 2 exists in the negative electrode 10 in a state of having electrical conductivity and ion conductivity, it is difficult to adversely affect the characteristics of the sulfide solid-state battery 100.
2. Supplement to the advantages related to the manufacturing method of the present disclosure
Further, the same effect can be obtained by doping the silicon-based active material used as the negative electrode active material with lithium in advance by the electrochemical reaction in the lithium ion battery before the negative electrode mixture is produced. However, in this case, it is necessary to perform doping treatment or the like on a larger amount of active material than in the above-described production method S10, and this is not realistic from the viewpoint of cost.
In addition, the problem of producing CuS can also be solved by using a material made of a metal other than copper as the negative electrode current collector. However, in this case, the performance of the battery such as the cycle characteristics may be degraded.
3. Authentication on the market
Whether or not the sulfide solid-state battery is a battery manufactured by the manufacturing method of the present disclosure can be confirmed, for example, by the following method. That is, in the sulfide solid-state battery, whether or not the sulfide solid-state battery is a battery manufactured by the manufacturing method of the present disclosure can be confirmed by analyzing the negative electrode active material in the portion where the positive electrode and the negative electrode do not face each other, and observing the balance and balance of the positive and negative electrode potentials due to the three-stage battery formation. Alternatively, when a pre-doped material is obtained by an electrochemical reaction in a liquid battery, an SEI is formed on the surface of the pre-doped material. Therefore, it is possible to confirm whether or not the sulfide solid-state battery is a battery manufactured by the manufacturing method of the present disclosure by confirming whether or not the surface of graphite or lithium titanate contained in the negative electrode has SEI. Examples of the compound constituting the SEI include LiF and LiCO3Phosphoric esters, and the like. Examples of the method for confirming the presence or absence of the SEI-constituting compound include elemental analysis by TEM-EELS, ICP, EPS, mass analysis by TOF-SIMS, and a combination thereof. For example, it can be determined whether or not the manufacturing method of the present disclosure is performed by confirming that an element, such as fluorine, which is not included in the solid electrolyte raw material is included only in the SEI formed on the surface of the pre-doped material.
Examples
< example 1 >
1. Fabrication of sulfide solid state battery
1.1. Production of Positive electrode active Material
Preparation of LiNi1/3Mn1/3Co1/3O2Particles (average particle diameter (D)50)6 μm). Coating LiNbO on the surface of the particle by a sol-gel method3. Specifically, equimolar LiOC was dissolved in a solvent by a rotary flow coater (SFP-01, Powrex Co., Ltd.) under atmospheric pressure2H5And Nb (OC)2H5)5The ethanol solution of (3) is applied to the surface of the particles. The treatment time was adjusted so that the thickness of the coating became 5 nm. Then, the coated particles were subjected to heat treatment at 350 ℃ for 1 hour under atmospheric pressure, thereby obtaining a positive electrode active material.
1.2. Production of positive electrode
The obtained positive electrode active material and sulfide solid electrolyte (LiI-Li)2O-Li2S-P2S5Average particle diameter (D)50)2.5 μm) was weighed in a mass ratio of the positive electrode active material to the sulfide solid electrolyte of 75:25, and further, 4 parts by mass of a PVDF-based binder (manufactured by wuhui chemical corporation) and 6 parts by mass of acetylene black as a conductive auxiliary agent were weighed with respect to 100 parts by mass of the positive electrode active material. These were blended with butyl butyrate so that the solid content became 70 mass%, and the resulting mixture was kneaded with a mixer to obtain a positive electrode paste. The obtained positive electrode paste was weighed at 30mg/cm in terms of weight per unit area by a doctor blade method using an applicator2The resultant was coated on an aluminum foil having a thickness of 15 μm and dried at 120 ℃ for 3 minutes to obtain a positive electrode having a positive electrode mixture layer on the aluminum foil.
1.3. Fabrication of solid electrolyte layer
95 parts by mass of the same sulfide solid electrolyte as described above and 5 parts by mass of a butene rubber as a binder were weighed, and the solid content was adjusted to 70% by mass in a heptane solvent, and stirred for 2 minutes by an ultrasonic dispersion device (UH-50 manufactured by SMT) to obtain a solid electrolyte paste. The obtained solid electrolyte paste was weighed to 60mg/cm in terms of basis weight in the same manner as in the case of the positive electrode paste2Coated on a substrate (aluminum foil), naturally dried, and then dried at 100 ℃ for 30 minutes, thereby obtaining a substrate having a solid electrolyte layer.
1.4. Production of negative electrode
1.4.1. Fabrication of pre-doped materials
99.7 parts by mass of fine particles (average particle diameter (D)) of natural graphite were weighed out separately50)15 μm), and 0.3 part by mass of carboxymethyl cellulose, and these were mixed in ion-exchanged water so that the solid content became 60 mass%, and kneaded by a planetary mixer to obtain a paste. The obtained paste was uniformly coated on a copper foil by a doctor blade method, and dried at 120 ℃ for 5 minutes to obtain an electrode. The obtained electrode was punched out to a diameter of 16mm, and a separator made of Li metal as a counter electrode, PE having a thickness of 20 μm as a separator, and a nonaqueous electrolyte solution (a mixed solvent of EC and DEC (EC: DEC: 1)) as an electrolyte solution were used, and LiPF was dissolved at a concentration of 1mol/kg6 -) And (5) manufacturing a coin battery. The coin cell is charged by a charging and discharging device. The amount of charge was adjusted to 100mAh/kg relative to the total weight of graphite contained in the coin cell. After charging, the coin cell was decomposed in an argon atmosphere, the electrodes were taken out, cleaned with EMC, and graphite was peeled off from the copper foil with a scraper to obtain a pre-doped material.
1.4.2. Production of negative electrode mixture and lamination to copper foil
The sulfide solid electrolyte and fine particles of silicon (average particle diameter (D)50)6 μm) and a predoping material were weighed in a mass ratio of sulfide solid electrolyte to fine particles of silicon to predoping material of 45:53.4:1.6 (silicon-based active material to predoping material of 97:3), and 6 parts by mass of PVDF-based binder (manufactured by wu-seye chemical corporation) and 6 parts by mass of acetylene black as a conductive assistant were weighed per 100 parts by mass of the fine particles of silicon. These were blended with butyl butyrate so that the solid content became 70 mass%, and kneaded with a mixer to obtain a paste-like negative electrode mixture. The obtained paste was uniformly applied to a copper foil having a thickness of 15 μm by a doctor blade method using an applicator, and dried at 120 ℃ for 3 minutes, thereby obtaining a negative electrode having a negative electrode mixture layer on the copper foil.
1.5. Lamination of positive electrode, solid electrolyte layer and negative electrode
Punching the solid electrolyte layer to an area of 1cm2At a rate of 1ton/cm2And (4) pressing. Under pressureThe positive electrode was stacked on one surface (the surface opposite to the substrate) of the solid electrolyte layer, and the thickness of the positive electrode was 1ton/cm2And (4) pressing. Peeling off the substrate, and superposing the negative electrode on the surface of the peeled substrate of the solid electrolyte layer at a ratio of 6ton/cm2Pressing was performed to obtain a laminate made of the positive electrode/the solid electrolyte layer/the negative electrode. The obtained laminate was sealed in an aluminum laminate film with a terminal to obtain a sulfide solid-state battery for evaluation. The specifications of the obtained battery are shown in table 1 below.
2. Self-discharge inspection of sulfide solid-state battery
As described above, if the copper foil as the negative electrode current collector reacts with the sulfide solid electrolyte, CuS having high conductivity is formed, Cu diffuses from the negative electrode current collector to the positive electrode side, a micro short circuit occurs between the positive electrode and the negative electrode, and the voltage of the sulfide solid battery spontaneously decreases. To evaluate this, a self-discharge inspection of the sulfide solid state battery was performed by the following procedure. That is, after the sulfide solid-state battery was first charged (charging condition: 4.4cccv, current rate 2mA, off-current 0.1mA), it was left to stand in a thermostatic bath at 25 ℃ for 25 hours, and voltage Δ V in the rest was measured. The results are shown in Table 1 below.
3. Evaluation of cycle characteristics
In the case where a silicon-based active material and a carbon-based active material are used, the expansion rate of the entire negative electrode active material is reduced during charge and discharge, and improvement in the cycle characteristics of the sulfide solid-state battery can be expected, as compared with the case where only a silicon-based active material is used as the negative electrode active material. To confirm this effect, a cycle test was performed under the following conditions. The ratio of the discharge capacity after 150 cycles to the initial discharge capacity was calculated as the capacity maintenance rate [% ]. In the cycle test, the test was carried out while the positive and negative electrode surfaces were held by a jig with a load cell so as to uniformly apply a pressure of 5MPa to the surface. The results are shown in table 1 below.
(conditions of cycle test)
Charging: 4.4Vcccv, current rate 10mA, cutoff current 0.5mA
Discharging: 3.0Vcc and current rate 10mA
Temperature: 25 deg.C
< examples 2 to 4, comparative example 1 >
A sulfide solid state battery was produced in the same manner as in example 1, except that the mixing ratio of the negative electrode active material and the predoped material was changed as shown in table 1 below, and self-discharge test and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
< example 5 >
A sulfide solid state battery was produced in the same manner as in example 1, except that the charge amount in the production of the predoped material was changed to 150mAh/g, and self-discharge test and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
< example 6 >
The material used as the pre-doped material was changed from graphite to lithium titanate (average particle size (D)50)2 μm) and a predoped material was obtained by the following procedure, and a sulfide solid-state battery was produced in the same manner as in example 1, and self-discharge inspection and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
92 parts by mass of lithium titanate, 3 parts by mass of PVDF binder, and 5 parts by mass of acetylene black were weighed, and the weighed materials were mixed with NMP so that the solid content became 70% by mass, and kneaded by a planetary mixer to obtain a paste. The obtained paste was applied to a copper foil by the same doctor blade method as in example 1 and dried to obtain an electrode. A coin cell was produced in the same manner as in example 1 using the obtained electrode, charged in the same manner as in example 5 (charge amount of 150mAh/g), decomposed and peeled from the copper foil in the same manner as in example 1, and then the peeled powder was dispersed in NMP of about 10 times the volume thereof, and centrifugation was repeated 3 times to remove the PVDF-based binder and the like adhering to the lithium titanate. The particles obtained after centrifugation were used as a pre-doped material.
< example 7 >
Silicon was replaced by silicon oxide (average particle diameter (D)50)5 μm) and the weight per unit area of the negative electrode was changed, a sulfide solid state battery was produced in the same manner as in example 1, and self-discharge test and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
< example 8 >
A sulfide solid state battery was produced in the same manner as in example 1, except that the charge amount in the production of the predoped material was changed to 10mAh/g and the mixing ratio of the negative electrode active material and the predoped material was changed as shown in table 1 below, and a self-discharge test and a cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
< comparative example 2 >
A sulfide solid state battery was produced in the same manner as in comparative example 1, except that a stainless steel foil having the same thickness was used as a negative electrode current collector instead of the copper foil, and self-discharge test and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
< reference example 1 >
A sulfide solid state battery was produced in the same manner as in example 1, except that a stainless steel foil having the same thickness was used as a negative electrode current collector instead of the copper foil, and a self-discharge test and cycle characteristic evaluation were performed. The specifications of the battery, the self-discharge inspection results, and the cycle characteristic evaluation results are shown in table 1 below.
Figure BDA0001826431910000171
As is clear from the results shown in table 1, the self-discharge amount was significantly reduced by including the predoped material in the negative electrode mixture. The pre-doped material reduces the initial negative electrode potential of the sulfide solid-state battery, and inhibits the reaction of the copper foil and the sulfide solid electrolyte. The amount of the predoping material contained in the negative electrode mixture is not particularly limited, and a certain effect can be exhibited even if the predoping material is contained in a small amount in the negative electrode mixture, but it is understood from examples 1to 8 that the ratio (X/Y) of the capacity conversion value (X) of the total amount of lithium doped in the predoping material contained in the negative electrode mixture to the total capacity (Y) of the silicon-based active material contained in the negative electrode mixture is preferably 0.0005 or more. In particular, when X/Y is 0.0008 or more, the self-discharge amount is suppressed to about 0.18V, and the self-discharge suppression effect is saturated. Alternatively, it is apparent from examples 1to 8 that the total amount of the negative electrode active material and the predoping material is 100 mass%, the negative electrode active material is preferably 70 mass% or more and less than 100 mass%, and the predoping material is preferably more than 0 mass% and 30 mass% or less. In consideration of the negative electrode capacity and the like, for example, the negative electrode active material is more preferably 90% by mass or more, further preferably 93% by mass or more, and particularly preferably 96% by mass or more, and the predoped material is more preferably 10% by mass or less, further preferably 7% by mass or less, and particularly preferably 4% by mass or less.
Further, from the results of examples 1to 8 and comparative example 1, it is understood that when a copper foil is used as the negative electrode current collector, the cycle characteristics of the sulfide solid-state battery are improved by including the predoping material in the negative electrode mixture.
Further, from the results of examples 6 and 7, it is understood that the same effect can be obtained even when the kind of the negative electrode active material and/or the kind of the predoping material is changed.
As shown in comparative example 2 and reference example 1, by changing the material of the negative electrode current collector to a metal other than copper (such as stainless steel), it is possible to avoid the generation of CuS and reduce the self-discharge amount. However, in this case, the performance of the battery other than self-discharge is degraded. For example, the cycle characteristics of the battery shown in comparative example 2 were degraded. Further, from the results of comparative example 2 and reference example 1, it is clear that when a stainless steel foil is used as a negative electrode current collector, even if a predoping material is contained in the negative electrode mixture, the cycle characteristics are difficult to improve. This is because stainless steel foil is harder than copper foil and is difficult to follow expansion and contraction of the negative electrode active material during charge and discharge.
As described above, when the negative electrode mixture layer containing the silicon-based active material and the sulfide solid electrolyte is provided on the surface of the negative electrode current collector, it is possible to suppress the generation of CuS more effectively by using the negative electrode current collector containing copper and by including a predetermined predoping material in the negative electrode mixture than by using a negative electrode current collector made of a material other than copper to avoid the generation of CuS.
Industrial applicability
The sulfide solid-state battery produced by the production method of the present disclosure can be widely used, for example, for a small-sized power supply for portable equipment or a large-sized power supply for vehicle mounting.

Claims (2)

1. A method for manufacturing a sulfide solid-state battery, comprising the steps of:
a step 1 of doping at least one material selected from graphite and lithium titanate with lithium to obtain a pre-doped material;
a step 2 of mixing a sulfide solid electrolyte, a silicon-based active material, and the predoped material to obtain a negative electrode mixture; and
a 3 rd step of laminating the negative electrode mixture on the surface of a negative electrode current collector containing copper to obtain a negative electrode,
the ratio X/Y between a capacity conversion value X of the total amount of lithium doped in the predoped material contained in the negative electrode mix and a total capacity Y of the silicon-based active material contained in the negative electrode mix is set to 0.0005 or more.
2. The sulfide solid-state battery manufacturing method according to claim 1,
in the step 1, lithium is doped into the material by an electrochemical reaction in a lithium ion battery.
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