JP7579643B2 - All-solid-state lithium secondary battery and method for producing same - Google Patents

Description

The present invention relates to a high-capacity all-solid-state lithium secondary battery using a solid electrolyte and a method for manufacturing the same.

The organic electrolyte solution currently used in lithium-ion secondary batteries contains organic solvents, which are flammable substances, and therefore there is a possibility that the organic electrolyte solution will generate abnormal heat if an abnormality such as a short circuit occurs in the battery. In addition, with the recent trend toward higher energy density in lithium-ion secondary batteries and an increasing amount of organic solvent in the organic electrolyte solution, there is an even greater demand for safety and reliability in lithium-ion secondary batteries.

In light of the above, all-solid-state lithium secondary batteries that do not use organic solvents are attracting attention. All-solid-state lithium secondary batteries use a molded solid electrolyte that does not use organic solvents instead of the conventional organic solvent-based electrolyte, and are highly safe with no risk of abnormal heat generation from the solid electrolyte.

All-solid-state lithium secondary batteries generally use a laminated electrode body in which a solid electrolyte layer is disposed between a positive electrode and a negative electrode. The laminated electrode body can be produced by a method of forming a laminated film by applying a paint in which each component material (active material, solid electrolyte) is dispersed in a solvent, or by a method of filling a mold with powder of each component material as is and pressure-molding it to form a pellet.

Currently, development of coin-type solid electrolyte batteries is underway for use in small electronic devices. Coin-type batteries are typically made by producing pellets of laminated electrodes and assembling them in a battery container.

When the laminated electrode body of a coin-type battery is made into a pellet, the powders of the respective constituent materials are pressure-molded in a mold, so that the whole is formed as a cylindrical laminate, and the area of the positive electrode and negative electrode is the same as the area of the solid electrolyte layer. For this reason, if active material particles are detached from the ends of the positive electrode or negative electrode, there is a problem that the outer peripheral end of the positive electrode and the outer peripheral end of the negative electrode come into contact with each other, making it easy for a short circuit to occur. In particular, when an attempt is made to form a thin solid electrolyte layer, which is not related to the battery capacity, in order to increase the capacity of the battery, the above-mentioned short circuit is more likely to occur.

To solve this problem, Patent Document 1 proposes that at least one of the positive and negative electrodes be covered with a solid electrolyte layer. By configuring the laminated electrode body as described above, the short circuit problem can be prevented. However, Patent Document 1 uses a method in which the electrode and solid electrolyte layer, which are separately manufactured, are later integrated, making it difficult to form a thin solid electrolyte layer.

On the other hand, Patent Documents 2 and 3 propose a method in which powders of active material and solid electrolyte are charged, coated, and then pressed to form a film. With this method, the thickness of each layer can be adjusted relatively freely, making it possible to reduce the thickness of the solid electrolyte layer and to create a shape in which the outer periphery of the electrode is covered with solid electrolyte.

JP 2009-64644 A JP 2010-282803 A JP 2019-21428 A

However, the methods described in Patent Documents 2 and 3 only pressurize the coating film in the thickness direction, and do not impose any restrictions on the surface direction of the coating film. Therefore, when a solid electrolyte layer is formed on the outer peripheral surface of the positive or negative electrode to prevent the above-mentioned short circuit, it is difficult to adjust the thickness of the solid electrolyte layer on the outer peripheral surface.

In addition, because the solid electrolyte layer molded body is fragile, when a solid electrolyte layer is formed on the outer peripheral surface of the positive electrode or negative electrode, the solid electrolyte layer formed on the outer peripheral surface of the positive electrode or negative electrode is likely to detach during battery manufacturing, and the outer peripheral end of the positive electrode and the outer peripheral end of the negative electrode may come into contact with each other, causing a short circuit.

This application has been made to solve the above problems, and aims to provide an all-solid-state lithium secondary battery that prevents short circuits at the outer peripheral ends of the positive and negative electrodes, while reducing the thickness of the solid electrolyte layer to increase capacity.

The all-solid-state lithium secondary battery of the present invention comprises a laminated electrode body including a positive electrode, a negative electrode, and a solid electrolyte-containing sheet disposed between the positive electrode and the negative electrode, the solid electrolyte-containing sheet includes an insulating porous substrate and a solid electrolyte filled in the insulating porous substrate, the peripheral portion of the solid electrolyte-containing sheet covers the outer peripheral side portion of the positive electrode or the negative electrode, and the thickness of the solid electrolyte-containing sheet is 5 to 200 μm.

The method for producing the all-solid-state lithium secondary battery of the present invention is a method for producing the all-solid-state lithium secondary battery of the present invention, and includes an electrode preparation step of preparing a positive electrode and a negative electrode, a filling step of filling an insulating porous substrate with solid electrolyte particles to prepare a solid electrolyte-containing sheet, a stacking step of stacking the positive electrode, the solid electrolyte-containing sheet, and the negative electrode in this order, and a folding step of folding back the peripheral portion of the solid electrolyte-containing sheet to the outer periphery of one of the stacked positive electrode or negative electrode, thereby covering the outer periphery of the positive electrode or the negative electrode with the peripheral portion of the solid electrolyte-containing sheet.

According to the present application, even if the thickness of the solid electrolyte layer is thin, it is possible to prevent the occurrence of short circuits at the outer peripheral ends of the positive and negative electrodes, and it is possible to provide an all-solid-state lithium secondary battery with high capacity and high energy density.

FIG. 1 is a cross-sectional view illustrating an example of an all-solid-state lithium secondary battery according to an embodiment. FIG. 2 is a cross-sectional view showing an example of a process for producing a laminated electrode body of an all-solid-state lithium secondary battery according to an embodiment.

(All-solid-state lithium secondary battery)
An embodiment of an all-solid-state lithium secondary battery disclosed in the present application will be described. The all-solid-state lithium secondary battery of this embodiment includes a laminated electrode body including a positive electrode, a negative electrode, and a solid electrolyte-containing sheet disposed between the positive electrode and the negative electrode, the solid electrolyte-containing sheet includes an insulating porous substrate and a solid electrolyte filled in the insulating porous substrate, the peripheral portion of the solid electrolyte-containing sheet covers the outer peripheral side portion of the positive electrode or the negative electrode, and the thickness of the solid electrolyte-containing sheet is 5 to 200 μm.

In the all-solid-state lithium secondary battery of this embodiment, the solid electrolyte is filled into the insulating porous substrate, so that a thin and uniform solid electrolyte layer can be formed. This makes it possible to provide an all-solid-state lithium secondary battery with high capacity and high energy density. In addition, since the peripheral portion of the solid electrolyte-containing sheet covers the outer peripheral side portion of the positive electrode or negative electrode, even if the solid electrolyte layer (solid electrolyte-containing sheet) is formed thin, it is possible to prevent the occurrence of a short circuit at the outer peripheral end portion of the positive electrode and the negative electrode.

In addition, since the thickness of the solid electrolyte-containing sheet is 200 μm or less, a certain degree of flexibility can be imparted to the solid electrolyte-containing sheet, which makes it possible to fold the peripheral portion of the solid electrolyte-containing sheet onto the outer peripheral side portion of the positive electrode or negative electrode, and the outer peripheral side portion of the electrode can be covered with the solid electrolyte-containing sheet in a simple manner. Furthermore, since the thickness of the solid electrolyte-containing sheet is 5 μm or more, the insulating porous substrate holds the solid electrolyte, ensuring the shape retention of the solid electrolyte-containing sheet, and allowing it to be reliably formed into a laminated electrode body by stacking it with the positive electrode and negative electrode.

The all-solid-state lithium secondary battery of this embodiment will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a coin-shaped all-solid-state lithium secondary battery of this embodiment. In FIG. 1, an all-solid-state lithium secondary battery 10 has a laminated electrode body consisting of a negative electrode 14, a positive electrode 15, and a solid electrolyte-containing sheet 16 enclosed inside an exterior body consisting of an exterior can 11, a sealing can 12, and a gasket 13 interposed between them. The solid electrolyte-containing sheet 16 includes an insulating porous substrate (not shown) and a solid electrolyte filled in the insulating porous substrate, and the peripheral portion 16a of the solid electrolyte-containing sheet 16 is folded back to the positive electrode 15 side to cover the outer peripheral side portion of the positive electrode 15. The peripheral portion 16a of the solid electrolyte-containing sheet 16 may be folded back to the negative electrode 14 side to cover the outer peripheral side portion of the negative electrode 14.

The sealing can 12 fits into the opening of the exterior can 11 via a gasket 13, and the open end of the exterior can 11 is tightened inward, causing the gasket 13 to come into contact with the sealing can 12, sealing the opening of the exterior can 11 and creating an airtight structure inside the exterior body.

Next, we will explain each component of the all-solid-state lithium secondary battery of this embodiment.

<Solid electrolyte-containing sheet>
The solid electrolyte-containing sheet in the all-solid-state lithium secondary battery of this embodiment constitutes the solid electrolyte layer of the laminated electrode body, and includes an insulating porous substrate, and a solid electrolyte and a binder filled in the insulating porous substrate.

As described above, the thickness of the solid electrolyte-containing sheet is set to 5 μm or more, preferably 10 μm or more, so that the solid electrolyte-containing sheet can maintain its shape and can be laminated with the positive and negative electrodes to reliably form a laminated electrode body. In addition, in order to make it possible to fold the peripheral portion of the solid electrolyte-containing sheet to the outer peripheral side portion of the positive or negative electrode, the thickness of the solid electrolyte-containing sheet is set to 200 μm or less, preferably 100 μm or less.

In the laminated electrode body, in order to ensure ion conductivity at the interface between the electrode and the solid electrolyte-containing sheet, it is preferable that the entire surface of the insulating porous substrate is covered with the solid electrolyte.

[Solid electrolyte]
The solid electrolyte is not particularly limited as long as it has lithium ion conductivity, and for example, a sulfide-based solid electrolyte, a hydride-based solid electrolyte, an oxide-based solid electrolyte, etc. can be used.

Examples of the sulfide-based solid electrolyte include sulfide _- based solid electrolyte glasses such as _Li2S - _P2S5 , _Li2S - _SiS2 , _Li2S - _{P2S5 - GeS2} , and _Li2S - _{B2S3 ,} as well as _Li10GeP2S12 (LGPS-based) and _Li6PS5Cl (argyrodite-based ₎ , _which have attracted attention in recent years for their high lithium ion conductivity. Among these, the _argyrodite -based solid electrolyte is preferably used because of its particularly high lithium ion conductivity and high chemical stability.

Examples of the hydride-based solid electrolyte include a solid solution of _LiBH4 and the following alkali metal compounds (for example, a solid solution in which the molar ratio of _LiBH4 to the alkali metal compound is 1:1 to 20:1). The alkali metal compound in the solid solution includes at least one selected from lithium halides (LiI, LiBr, LiF, LiCl), rubidium halides (RbI, RbBr, RbF, RbCl), cesium halides (CsI, CsBr, CsF, CsCl), lithium amide, rubidium amide, and cesium amide.

Examples of the _{oxide-based solid electrolyte include Li7La3Zr2O12 , LiTi} ( _PO4 ) ₃ , _LiGe ( _PO4 ) ₃ , and _LiLaTiO3 .

Among the above-listed solid electrolytes, it is more preferable to use a sulfide-based solid electrolyte, which has high lithium ion conductivity.

The above solid electrolytes can be used alone or in combination of two or more. The solid electrolyte is preferably in particulate form from the viewpoint of filling the insulating porous substrate, but may be in a form other than particulate form. When two or more solid electrolytes are used in combination, the solid electrolytes may be mixed in particulate form or at the molecular level, or the solid electrolytes may be present in a layered form in which the solid electrolyte particles form different regions in the thickness direction of the solid electrolyte-containing sheet.

The average particle diameter of the solid electrolyte particles is preferably 5 μm or less, more preferably 2 μm or less, from the viewpoint of improving the filling of the pores of the insulating porous substrate and ensuring good lithium ion conductivity. However, if the size of the solid electrolyte particles is too small, there is a risk that the handling properties will be reduced or a larger amount of binder will be required, resulting in an increase in the resistance value. Therefore, the average particle diameter of the solid electrolyte particles is preferably 0.3 μm or more, more preferably 0.5 μm or more.

The average particle size of the solid electrolyte particles and other particles (positive electrode active material particles, negative electrode active material particles, etc.) referred to in this specification is the number average particle size measured by dispersing the particles in a medium that does not dissolve or swell the particles using, for example, a laser scattering particle size distribution meter (for example, HORIBA's "LA-920").

[Insulating porous substrate]
The insulating porous substrate is not particularly limited as long as it can be filled with and hold a solid electrolyte, but a nonwoven fabric is preferred because it is easy to handle and form into a thin film.

The porosity of the insulating porous substrate is preferably 30% by volume or more, more preferably 40% by volume or more, from the viewpoint of ensuring a certain amount of solid electrolyte filling and good lithium ion conductivity. However, if the porosity of the insulating porous substrate is too high, the shape retention of the solid electrolyte-containing sheet may decrease. Therefore, from the viewpoint of further increasing the strength of the solid electrolyte-containing sheet, the porosity of the insulating porous substrate is preferably 90% by volume or less, more preferably 85% by volume or less.

As described above, since it is preferable to cover the entire surface of the insulating porous substrate with the solid electrolyte, the thickness of the insulating porous substrate is made slightly thinner than the thickness of the solid electrolyte-containing sheet described above, and it is preferable that the thickness of the solid electrolyte-containing sheet is in the range of 5 to 200 μm when the entire surface of the insulating porous substrate is covered with the solid electrolyte. Therefore, the thickness of the insulating porous substrate is preferably set to 3.5 to 195 μm, and more preferably 8.5 to 137 μm.

When a nonwoven fabric is used as the insulating porous substrate, the fiber diameter of the fibrous material constituting the nonwoven fabric substrate is preferably 20 μm or less, and more preferably 0.5 μm or more.

The material of the fibrous material constituting the nonwoven fabric is not particularly limited as long as it does not react with lithium metal and has insulating properties. For example, resins such as polyolefins such as polypropylene and polyethylene; polystyrene; aramid; polyamide-imide; polyimide; nylon; polyesters such as polyethylene terephthalate (PET); polyarylate; cellulose and modified cellulose; etc. can also be used. Inorganic materials such as glass, alumina, silica, and zirconia can also be used.

The nonwoven fabric has a basis weight of preferably 10 g/m2 ^{or less} , and more preferably 8 g/m2 or less, so as to be able to hold a sufficient amount of solid electrolyte particles to ensure good lithium ion conductivity, and from the viewpoint of ensuring sufficient strength, the basis weight is preferably 3 g/m2 ^{or more} , and more preferably 4 g/m2 or ^more .

[Binder]
The binder is preferably one that does not react with the solid electrolyte, and at least one resin selected from butyl rubber, chloroprene rubber, acrylic resin, and fluororesin is preferably used.

The content of the binder is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on the total mass of the solid electrolyte and the binder, from the viewpoint of further improving the shape retention of the solid electrolyte-containing sheet, and is preferably 5% by mass or less, and more preferably 3% by mass or less, based on the viewpoint of limiting the amount of the binder to a certain extent and suppressing the decrease in lithium ion conductivity.

There are no particular limitations on the method for producing the solid electrolyte-containing sheet, but it is preferable to produce the sheet by dispersing solid electrolyte particles together with a binder in a solvent to prepare a slurry or the like, and then wet-filling the slurry into the pores of an insulating porous substrate (such as a resin nonwoven fabric). This improves the strength of the solid electrolyte-containing sheet, making it easier to produce a large-area solid electrolyte-containing sheet.

The above-mentioned slurry is prepared by adding solid electrolyte particles and a binder to a solvent and mixing them. It is preferable to select a solvent for the slurry that is unlikely to deteriorate the solid electrolyte. In particular, since sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with trace amounts of moisture, it is more preferable to use a non-polar aprotic solvent, such as a hydrocarbon solvent such as hexane, heptane, octane, nonane, decane, decalin, toluene, or xylene, as an ultra-dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less.

As the above solvent, fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by DuPont-Mitsui Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Zeon Corporation, and "Novec (registered trademark)" manufactured by Sumitomo 3M Limited, as well as non-aqueous organic solvents such as dichloromethane and diethyl ether can also be used.

The method of filling the pores of the insulating porous substrate with a slurry containing solid electrolyte particles and a binder can be a coating method such as screen printing, doctor blade, or dipping.

After filling the pores of the insulating porous substrate with the slurry, the solvent in the slurry is removed by drying, and a solid electrolyte-containing sheet can be obtained by performing pressure molding as necessary.

The method for producing the solid electrolyte-containing sheet is not limited to the wet method. For example, the solid electrolyte-containing sheet may be produced by a method in which the pores of the insulating porous substrate are dry-filled with a mixture of solid electrolyte particles and binder particles, and then pressure-molded.

<Positive electrode>
The positive electrode is not particularly limited as long as it is a positive electrode used in conventionally known lithium ion secondary batteries, that is, a positive electrode containing an active material capable of absorbing and releasing Li ions. For example, the positive electrode active material may be a spinel type lithium manganese composite oxide represented by LiM _x Mn _2-x O ₄ (wherein M is at least one element selected from the group consisting of Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru, and Rh, and 0.01≦x≦0.5), Li _x Mn _(1-yx) Ni _y M _z O _(2-k) F _l a layered compound represented by LiCo1-xMxO2 (wherein M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and _W , and 0.8≦x≦1.2, 0<y<0.5, 0≦z≦0.5, k+l<1, -0.1≦k≦0.2, 0≦l≦0.1); a lithium cobalt composite oxide represented by LiCo1 _{- xMxO2} (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, _{and Ba} , and ₀ ≦x≦0.5); (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, _Ga , Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦0.5); an olivine type composite oxide represented by LiM1 _{- xNxPO4} (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦0.5); and a lithium _{titanium composite oxide represented by Li4Ti5O12 . Among} these, only one may be used, or two or more may be used in combination.

The positive electrode may have a structure in which a positive electrode mixture layer containing the positive electrode active material, a conductive additive, and a binder is formed on one or both sides of a current collector.

As the binder for the positive electrode, for example, a fluororesin such as polyvinylidene fluoride (PVDF) can be used, and as the conductive assistant for the positive electrode, for example, a carbon material such as carbon black can be used, but the solid electrolyte used in the above-mentioned solid electrolyte-containing sheet can also be used as the conductive assistant.

The positive electrode current collector can be made of a metal such as aluminum foil, punched metal, mesh, expanded metal, foamed metal, etc.

When manufacturing the positive electrode, for example, a method can be used in which a positive electrode mixture-containing paste, slurry, etc., in which a positive electrode active material, a conductive additive, a binder, etc. are dispersed in a solvent such as xylene, is applied to a current collector, dried, and then pressure-molded, such as by calendaring, as necessary. As the solvent, a highly dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less is preferably used.

In addition, when a conductive porous substrate such as punched metal is used for the positive electrode current collector, the positive electrode can be manufactured, for example, by filling the pores of the conductive porous substrate with the above-mentioned positive electrode mixture-containing paste, slurry, etc., drying, and then, if necessary, performing pressure molding such as calendaring. A positive electrode manufactured in this manner can ensure high strength, making it possible to hold a larger area of a solid electrolyte-containing sheet.

In addition, instead of the above-mentioned positive electrode mixture-containing paste, slurry, etc., a positive electrode mixture that contains a positive electrode active material, a conductive assistant, a binder, etc. and does not contain a solvent may be dry-filled into the pores of a conductive porous substrate, and the positive electrode may be produced by a method of pressure molding such as calendaring as necessary.

<Negative Electrode>
The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known lithium ion secondary battery, that is, a negative electrode containing an active material capable of absorbing and releasing Li ions. For example, as the negative electrode active material, one or a mixture of two or more types of carbon-based materials capable of absorbing and releasing lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, baked bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, is used. In addition, simple substances, compounds, and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In; compounds that can be charged and discharged at a low voltage close to that of lithium metal, such as lithium-containing nitrides or lithium-containing oxides; lithium metal; lithium/aluminum alloys, etc., can also be used as the negative electrode active material.

The above-mentioned negative electrode is made by adding an appropriate amount of conductive additives (carbon materials such as carbon black, solid electrolytes, etc.) and binders such as PVDF to the negative electrode active material, and forming a negative electrode mixture layer using a current collector as the core material, or by laminating the above-mentioned various alloys or lithium metal foils alone or on the current collector as a negative electrode mixture layer.

When a current collector is used for the negative electrode, the current collector can be made of copper or nickel foil, punched metal, mesh, expanded metal, foamed metal, etc.

When manufacturing a negative electrode having a negative electrode mixture layer, for example, a method can be used in which a negative electrode mixture-containing paste, slurry, etc., in which the negative electrode active material, binder, and optionally conductive assistants are dispersed in a solvent such as xylene, is applied to a current collector, dried, and then pressure-molded, such as by calendaring, if necessary. As the above-mentioned solvent, a highly dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less is preferably used.

In addition, when a conductive porous substrate such as punched metal is used for the negative electrode current collector, the negative electrode can be manufactured, for example, by filling the pores of the conductive porous substrate with the above-mentioned negative electrode mixture-containing paste, slurry, etc., drying, and then, if necessary, performing pressure molding such as calendaring. A negative electrode manufactured in this manner can ensure high strength, making it possible to hold a larger area of solid electrolyte-containing sheet.

In addition, the negative electrode may be produced by dry-filling the pores of the conductive porous substrate with a negative electrode mixture that does not contain a solvent but contains a negative electrode active material, a binder, and a conductive assistant, instead of the above-mentioned negative electrode mixture-containing paste, slurry, etc., and then applying pressure molding such as calendaring as necessary.

<Exterior body>
The materials of the outer can and the sealing can constituting the outer casing can include, for example, stainless steel. The materials of the gasket can include polypropylene, nylon, etc., and in addition, when heat resistance is required in relation to the use of the battery, a heat-resistant resin having a melting point exceeding 240° C. can be used. As the heat-resistant resin, for example, fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA); polyphenylene ether (PPE); polysulfone (PSF); polyarylate (PAR); polyethersulfone (PES); polyphenylene sulfide (PPS); polyetheretherketone (PEEK), etc. can be used. In addition, when the battery is applied to an application requiring heat resistance, a glass hermetic seal can be used for sealing the battery.

<Electrode body>
The positive electrode and the negative electrode can be used in the form of a laminated electrode body in which the above-mentioned solid electrolyte-containing sheet is laminated with each other, or in the form of a wound electrode body in which this laminated electrode body is wound.

When forming the laminated electrode body, the positive electrode, the negative electrode, and the solid electrolyte-containing sheet are pressure-molded in a laminated state, and the interfaces between the positive electrode, the negative electrode, and the solid electrolyte-containing sheet are joined and integrated. Also, instead of pressing and joining the positive electrode, the negative electrode, and the solid electrolyte-containing sheet all at once, one electrode may be joined to the solid electrolyte-containing sheet first, and then the other electrode may be laminated and joined to the opposite side of the solid electrolyte-containing sheet to form the laminated electrode body.

<Battery type>
The form of the all-solid-state lithium secondary battery of this embodiment is not limited to one having an exterior body composed of an exterior can, a sealing can, and a gasket as shown in FIG. 1 , that is, one generally called a coin-type battery or a button-type battery, but may be, for example, one having an exterior body composed of a resin film or a metal-resin laminate film, or one having an exterior body having a metallic cylindrical or square-tubular exterior can and a sealing structure that seals the opening of the can.

(Method of manufacturing all-solid-state lithium secondary battery)
Next, an embodiment of the manufacturing method of the all-solid-state lithium secondary battery disclosed in the present application will be described. A suitable aspect of the manufacturing method of the all-solid-state lithium secondary battery of this embodiment includes, as a manufacturing process of a laminated electrode body, an electrode preparation process for preparing a positive electrode and a negative electrode, a filling process for filling an insulating porous substrate with solid electrolyte particles to prepare a solid electrolyte-containing sheet, a stacking process for stacking the positive electrode, the solid electrolyte-containing sheet, and the negative electrode in this order, and a folding process for folding back the peripheral portion of the solid electrolyte-containing sheet to the outer periphery side of one of the stacked positive electrode or negative electrode, and covering the outer periphery side portion of the positive electrode or the negative electrode with the peripheral portion of the solid electrolyte-containing sheet. In the filling process, it is preferable to further fill the insulating porous substrate with a binder.

The above-mentioned method for manufacturing an all-solid-state lithium secondary battery can be used to manufacture the laminated electrode body for the all-solid-state lithium secondary battery disclosed above. After that, the laminated electrode body can be housed in the aforementioned exterior body in a conventional manner to form a sealed structure.

Next, the manufacturing method of the laminated electrode body will be explained with reference to the drawings. However, the manufacturing method of the laminated electrode body is not limited to the manufacturing method shown below.

2 is a cross-sectional view showing an example of a process for manufacturing a laminated electrode body of an all-solid-state lithium secondary battery. First, as shown in FIG. 2A, for example, the above-mentioned negative electrode 14, solid electrolyte-containing sheet 16, and positive electrode 15 are sequentially placed in a mold 20. At this time, the outer periphery of the solid electrolyte-containing sheet 16 is set to be larger than the outer periphery of the positive electrode 15. Also, the size of the negative electrode 14 is set to be the same as that of the positive electrode 15. Next, as shown in FIG. 2B, the laminated negative electrode 14, solid electrolyte-containing sheet 16, and positive electrode 15 are all pressed from above, so that the peripheral portion 16a of the solid electrolyte-containing sheet 16 is folded back to the positive electrode 15 side, and the peripheral portion 16a of the solid electrolyte-containing sheet 16 covers the outer periphery side portion of the positive electrode 15, and the negative electrode 14, solid electrolyte-containing sheet 16, and positive electrode 15 are integrated. As a result, the laminated electrode body shown in FIG. 2C is obtained.

The laminated electrode body is then housed in the aforementioned exterior body in a conventional manner to form a sealed structure, thereby producing an all-solid-state lithium secondary battery.

The all-solid-state lithium secondary battery disclosed in this application will be described in detail below based on examples. However, the following examples do not limit the all-solid-state lithium secondary battery disclosed in this application.

Example 1
<Preparation of solid electrolyte-containing sheet>
Xylene ("ultra-dehydrated" grade with a water content of 10 ppm or less) was used as a solvent, and sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) particles with an average particle size of 1 μm and an acrylic resin binder (butyl acrylate-acrylic acid copolymer) were mixed with the above solvent in a mass ratio of 100:3 to give a solid content ratio of 40 mass%, and the mixture was stirred with a Thinky mixer for 10 minutes to prepare a uniform slurry. A PET nonwoven fabric (Hirose Paper Co., Ltd. "05TH-8") with a thickness of 38 μm and a basis weight of 8 g/m ² was passed through the slurry, and then pulled up, so that the slurry was applied to the PET nonwoven fabric. Thereafter, the mixture was vacuum dried at 120° C. for 1 hour to obtain a solid electrolyte-containing sheet with a thickness of 50 μm. The thickness of the nonwoven fabric in the prepared solid electrolyte-containing sheet was 80% of the thickness of the entire solid electrolyte-containing sheet. The proportion of the PET nonwoven fabric in the solid electrolyte-containing sheet was 25% by volume, and the proportion of the binder in the total mass of the solid electrolyte particles and the binder was 2.9% by mass.

Finally, the solid electrolyte-containing sheet was punched out into a circle with a diameter of 11 mm and used to fabricate a laminated electrode body.

<Preparation of Positive Electrode>
Xylene ("ultra- _dehydrated " grade with a water content of 10 ppm or less) was used as a solvent, and _{LiNi0.6Co0.2Mn0.2O2 with} an average particle diameter of 3 μm on which an amorphous composite oxide of Li and _Nb was formed on the surface, sulfide-based solid electrolyte ( _Li6PS5Cl ) particles, carbon nanotubes as a conductive assistant ["VGCF" (trade name) manufactured by Showa Denko K.K.], and _an acrylic resin binder (butyl acrylate-acrylic acid copolymer) were mixed with the above solvent in a mass ratio of 50:44:3:3 to give a solid content ratio of 50 mass%, and the mixture was stirred with a Thinky mixer for 10 minutes to prepare a uniform slurry. This slurry was applied to an Al foil with a thickness of 20 μm using an applicator with a gap of 200 μm, and the mixture was vacuum dried at 120 ° C to obtain a positive electrode.

Finally, the prepared positive electrode was punched out into a circle with a diameter of 10 mm and used to prepare a laminated electrode body.

<Preparation of negative electrode>
Using xylene ("ultra-dehydrated" grade with a water content of 10 ppm or less) as a solvent, graphite with an average particle size of 20 μm, sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) particles, and acrylic resin binder (butyl acrylate-acrylic acid copolymer) were mixed with the above solvent in a mass ratio of 50:47:3 to give a solid content ratio of 50 mass%, and the mixture was stirred for 10 minutes with a Thinky mixer to prepare a uniform slurry. This slurry was applied to a 20 μm-thick stainless steel foil with an applicator leaving a gap of 200 μm, and the negative electrode was obtained by vacuum drying at 120° C.

Finally, the prepared negative electrode was punched out into a circle with a diameter of 10 mm and used to prepare a laminated electrode body.

<Battery assembly>
First, as shown in Fig. 2A, the prepared negative electrode, solid electrolyte-containing sheet, and positive electrode were placed in a mold so that the negative electrode mixture layer and the positive electrode mixture layer were arranged on the solid electrolyte-containing sheet side. At this time, the center point of the solid electrolyte-containing sheet was aligned with the center points of the negative electrode and the positive electrode. Next, as shown in Fig. 2B, the entire stacked negative electrode, solid electrolyte-containing sheet, and positive electrode were pressed from above with a pressure of 392 MPa (4 tf/cm ² ), so that the peripheral part of the solid electrolyte-containing sheet was folded back to the positive electrode side, and the peripheral part of the solid electrolyte-containing sheet covered the outer peripheral side part of the positive electrode, and the negative electrode, solid electrolyte-containing sheet, and positive electrode were integrated to obtain a stacked electrode body shown in Fig. 2C.

Finally, as shown in FIG. 1, the laminated electrode body was placed in a stainless steel exterior body to produce the all-solid-state lithium secondary battery of Example 1.

(Comparative Example 1)
The solid electrolyte-containing sheet, the positive electrode, and the negative electrode were all punched out into circles with a diameter of 10 mm, and the centers of the sheets were aligned and stacked together, and the whole was pressed at a pressure of 392 MPa (4 tf/ ^cm2 ) to produce a laminated electrode body. Finally, an all-solid-state lithium secondary battery of Comparative Example 1 was produced in the same manner as in Example 1.

<Evaluation of all-solid-state lithium secondary batteries>
When the voltages of the batteries of Example 1 and Comparative Example 1 were measured, 0.4 V was measured for the battery of Example 1, but no voltage could be measured for Comparative Example 1. This is thought to be because, in the laminated electrode body of Comparative Example 1, the solid electrolyte-containing sheet, the positive electrode, and the negative electrode are all formed to the same size, and the solid electrolyte-containing sheet does not cover the outer peripheral side portion of the positive electrode or the negative electrode, so that the outer peripheral end of the positive electrode comes into contact with the outer peripheral end of the negative electrode, causing a short circuit. In contrast, in the laminated electrode body of Example 1, the peripheral portion of the solid electrolyte-containing sheet is folded back to the positive electrode side, and the peripheral portion of the solid electrolyte-containing sheet covers the outer peripheral side portion of the positive electrode, so that the contact between the outer peripheral end of the positive electrode and the outer peripheral end of the negative electrode is prevented, and it is thought that no short circuit occurs.

The all-solid-state lithium secondary battery disclosed in this application can prevent short circuits from occurring at the outer peripheral ends of the positive and negative electrodes even if the thickness of the solid electrolyte layer is thin, and can realize an all-solid-state lithium secondary battery with high capacity and high energy density, which can be preferably used as a power source for various electronic devices (especially portable electronic devices such as mobile phones and notebook personal computers).

REFERENCE SIGNS LIST 10 All-solid-state lithium secondary battery 11 Outer can 12 Sealing can 13 Gasket 14 Negative electrode 15 Positive electrode 16 Solid electrolyte-containing sheet 16a Periphery 20 Mold

Claims (2)

an electrode preparation step of preparing a positive electrode and a negative electrode having the same size as the positive electrode;
a filling step of filling an insulating porous substrate with solid electrolyte particles to prepare a solid electrolyte-containing sheet;
a lamination step of laminating the positive electrode, the solid electrolyte-containing sheet, and the negative electrode in this order;
and a folding step of folding back a peripheral portion of the solid electrolyte-containing sheet onto an outer periphery of one of the stacked positive electrode or negative electrode to cover an outer periphery of the positive electrode or the negative electrode with the peripheral portion of the solid electrolyte-containing sheet. The method for producing an all-solid-state lithium secondary battery according to claim 1 , wherein the insulating porous substrate is further filled with a binder in the filling step.

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