KR102648753B1 - Solid electrolyte sheet and all-solid lithium secondary battery - Google Patents

Abstract

A solid electrolyte sheet that is excellent in shape retention and can be expanded into a large area, and an all-solid lithium secondary battery having excellent discharge characteristics using the solid electrolyte sheet are provided. The solid electrolyte sheet of the present invention uses an insulating porous substrate as a support, the insulating porous substrate is composed of a fibrous material, the inside of the insulating porous substrate is filled with solid electrolyte particles, and the solid electrolyte particles are connected to each other. It contains a binder that binds, and the thickness of the insulating porous substrate is 70% or more of the thickness of the solid electrolyte sheet. The all-solid lithium secondary battery of the present invention is characterized by having a positive electrode, a negative electrode, and the solid electrolyte sheet of the present invention inserted between the positive electrode and the negative electrode.

Description

Solid electrolyte sheet and all-solid lithium secondary battery

The present invention relates to a solid electrolyte sheet that is excellent in shape retention and can be expanded into a large area, and an all-solid-state lithium secondary battery having the solid electrolyte sheet and having excellent discharge characteristics.

Recently, with the development of portable electronic devices such as mobile phones and laptop-type personal computers and the practical use of electric vehicles, there is a need for secondary batteries that are small and light, and have high capacity and high energy density.

Currently, in lithium secondary batteries that can meet this requirement, especially lithium ion secondary batteries, lithium-containing complex oxides such as lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO 2 ) are used as the positive electrode active material, and lithium-containing composite oxides such as lithium cobaltate (LiCoO 2 ) and lithium nickelate (LiNiO ₂ ) are used as the positive electrode active material. Graphite, etc. are used, and an organic electrolyte solution containing an organic solvent and lithium salt is used as a non-aqueous electrolyte.

In addition, with the further development of devices to which lithium ion secondary batteries are applied, there is a demand for further longer lifespan, higher capacity, and higher energy density for lithium ion secondary batteries, and lithium ion with longer life, higher capacity, and higher energy density. The safety and reliability of secondary batteries are also highly demanded.

However, since the organic electrolyte solution used in lithium ion secondary batteries contains an organic solvent, which is a flammable substance, there is a possibility that the organic electrolyte solution abnormally generates heat when an abnormality such as a short circuit occurs in the battery. In addition, with recent trends toward higher energy densities of lithium ion secondary batteries and an increase in the amount of organic solvent in organic electrolyte solutions, further safety and reliability of lithium ion secondary batteries are required.

In the above-mentioned situation, all-solid-state lithium secondary batteries that do not use organic solvents are attracting attention. The all-solid-state lithium secondary battery uses a molded body of a solid electrolyte that does not use an organic solvent instead of the conventional organic solvent-based electrolyte, and there is no risk of abnormal heat generation from the solid electrolyte, so it has high safety.

On the other hand, the molded body of the solid electrolyte is brittle, so it lacks processability, and it is difficult to thin the solid electrolyte and increase the area. For this reason, the handling of the solid electrolyte during battery production is poor, and since the molded body of the solid electrolyte becomes thick, the lithium ion conductivity of the solid electrolyte is lowered and battery performance is reduced.

Meanwhile, technologies to solve this problem are also being reviewed. For example, in Patent Documents 1 and 2, a solid electrolyte sheet that has both lithium ion conductivity and strength is created by filling the pores of a substrate made of a porous substrate such as non-woven fabric with a solid electrolyte, and this solid electrolyte sheet is used to form an all-solid electrolyte sheet. It is proposed to construct a secondary battery.

Among these, Patent Document 1 adopts a method of fixing the solid electrolyte to the pores of the porous substrate by attaching the solid electrolyte to an adhesive attached to the surface of the skeleton portion of the porous substrate. Additionally, in Patent Document 2, as a specific embodiment, only an example using a nonwoven fabric that is very thin compared to the total thickness of the solid electrolyte sheet as a substrate is shown.

Japanese Patent Laid-Open No. 2015-153460 (scope of patent claims, etc.) Japanese Patent Laid-Open No. 2016-139482 (scope of patent claims, examples, etc.)

The technology described in Patent Documents 1 and 2 makes it possible to increase the strength to a certain extent compared to sheets composed only of solid electrolytes, but in order to satisfy the shape retention required for solid electrolyte sheets for all-solid-state lithium secondary batteries, , there is still room for improvement.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a solid electrolyte sheet that is excellent in shape retention and can be expanded into a large area, and an all-solid lithium secondary battery having the solid electrolyte sheet and having excellent discharge characteristics. It's in doing.

The solid electrolyte sheet of the present invention uses an insulating porous substrate as a support, the insulating porous substrate is composed of a fibrous material, and the inside of the insulating porous substrate is filled with solid electrolyte particles, It contains a binder that binds the solid electrolyte particles together, and the thickness of the insulating porous substrate is 70% or more of the thickness of the solid electrolyte sheet.

Additionally, the all-solid lithium secondary battery of the present invention is characterized by having a positive electrode, a negative electrode, and the solid electrolyte sheet of the present invention inserted between the positive electrode and the negative electrode.

According to the present invention, it is possible to provide a solid electrolyte sheet that is excellent in shape retention and can be expanded into a large area, and an all-solid-state lithium secondary battery that has the solid electrolyte sheet and has excellent discharge characteristics.

1 is a plan view schematically showing an example of a solid electrolyte sheet of the present invention.
Figure 2 is a cross-sectional view schematically showing an example of an all-solid lithium secondary battery of the present invention.

The solid electrolyte sheet of the present invention has an insulating porous substrate made of fibrous material as a support, and its interior (i.e., the pores of the insulating porous substrate) is filled with solid electrolyte particles, and the solid electrolyte sheet is It contains a binder that binds electrolyte particles together, and the thickness of the insulating porous substrate has a ratio of 70% or more of the entire thickness of the solid electrolyte sheet.

In the solid electrolyte sheet of the present invention, the thickness of the insulating porous substrate serving as a support is 70% or more of the entire thickness of the solid electrolyte sheet, and the binder contained together with the solid electrolyte particles binds the solid electrolyte particles to each other, thereby providing insulation. It is possible to hold solid electrolyte particles well in a porous substrate, the strength of the sheet itself is increased, a decrease in ion conductivity due to flaking or cracking of the solid electrolyte can be prevented, and shape retention is improved. Larger areas become possible. More specifically, the area of the solid electrolyte sheet may be 1 cm ² or more.

In addition, by constructing an all-solid lithium secondary battery using the solid electrolyte sheet of the present invention, an all-solid lithium secondary battery with excellent discharge characteristics at high capacity and high energy density can be provided.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention will be described in detail.

<Solid electrolyte sheet>

Figure 1 shows a plan view schematically showing an example of a solid electrolyte sheet. The solid electrolyte sheet 10 shown in FIG. 1 includes an insulating porous substrate 11, solid electrolyte particles 12 and a binder 13 filled in the gaps (pores) between the fibrous materials constituting the insulating porous substrate 11. ) has. Then, the solid electrolyte particles 12 are bound and fixed to each other by the binder 13.

The thickness of the insulating porous substrate accounts for 70% or more, preferably 75% or more, of the entire thickness of the solid electrolyte sheet. That is, in the solid electrolyte sheet, if the thickness of the insulating porous substrate is within the range that satisfies the above value, the solid electrolyte particles fixed in a layer by a binder or the layer of the solid electrolyte formed in a sheet shape, It may exist beyond the upper or lower surface of the insulating porous substrate (in a state not held by the insulating porous substrate). Additionally, the thickness of the insulating porous substrate may be the same as the overall thickness of the solid electrolyte sheet (that is, the appropriate upper limit of the ratio of the thickness of the insulating porous substrate is 100% of the entire thickness of the solid electrolyte sheet).

In this way, in the solid electrolyte sheet of the present invention, the thickness of the insulating porous substrate occupies a large portion of the entire thickness of the solid electrolyte sheet, and the solid electrolyte particles are bound together by the binder present with the solid electrolyte particles. It is fixed. For this reason, the mechanical strength of the solid electrolyte sheet can be improved, the solid electrolyte particles are not damaged even if the area of the solid electrolyte sheet is increased, and it is also possible to prevent the solid electrolyte particles from falling off from the insulating porous substrate. . Additionally, by disposing the solid electrolyte sheet between the positive electrode and the negative electrode, short circuit between the positive electrode and the negative electrode can be prevented while maintaining lithium ion conductivity between the positive electrode and the negative electrode.

The solid electrolyte constituting the solid electrolyte particles that can be used in the solid electrolyte sheet is not particularly limited as long as it has lithium ion conductivity. For example, sulfide-based solid electrolyte, hydride-based solid electrolyte, oxide-based solid electrolyte, etc. can be used. .

Examples of the sulfide-based solid electrolyte include Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ SP ₂ S ₅ -GeS ₂ , and Li ₂ SB ₂ S _3- based glass. Recently, Li ₁₀ GeP ₂ S ₁₂ (LGPS-based) and Li ₆ PS ₅ Cl (agyrodite-based), which have attracted attention as having high lithium ion conductivity, can also be used. Among these, agrodite-based materials with particularly high lithium ion conductivity and high chemical stability are preferably used.

Examples of hydride-based solid electrolytes include LiBH ₄ , solid solutions of LiBH ₄ and the following alkali metal compounds (for example, those with a molar ratio of LiBH ₄ to alkali metal compounds of 1:1 to 20:1), etc. can be mentioned. Examples of alkali metal compounds in the solid solution include lithium halide (LiI, LiBr, LiF, LiCl, etc.), rubidium halide (RbI, RbBr, RbiF, RbCl, etc.), cesium halide (CsI, CsBr, CsF, CsCl, etc.), lithium At least one type selected from the group consisting of amides, rubidium amides, and cesium amides can be mentioned.

Examples of the oxide-based solid electrolyte include Li ₇ La ₃ Zr ₂ O ₁₂ , LiTi(PO ₄ ) ₃ , LiGe(PO ₄ ) ₃ , and LiLaTiO ₃ .

Among the solid electrolytes in the examples above, it is more preferable to use a sulfide-based solid electrolyte with high lithium ion conductivity.

Solid electrolyte particles can be used individually, but two or more types can also be used in combination. In addition, when two or more types of solid electrolyte particles of the above example are used in combination, the individual solid electrolyte particles may be mixed, and each solid electrolyte particle exists so as to form a different region in a layered manner in the thickness direction of the solid electrolyte sheet. You can do it.

As for the size of the solid electrolyte particles, the average particle diameter is preferably 5 μm or less, and more preferably 2 μm or less, from the viewpoint of further increasing the filling ability into 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 handleability may deteriorate or a larger amount of binder will be required, leading to an increase in resistance value. Therefore, the average particle diameter of the solid electrolyte particles is preferably 0.3 μm or more, and more preferably 0.5 μm or more.

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

The insulating porous substrate is composed of a fibrous material, and examples include woven fabric, non-woven fabric, and mesh. Among these, woven fabric and non-woven fabric are preferable.

The fiber diameter of the fibrous material constituting the insulating porous substrate is preferably 5 μm or less, and more preferably 0.5 μm or more.

The material of the fibrous material is not particularly limited as long as it does not react with lithium metal and has insulating properties, and examples include polyolefins such as polypropylene and polyethylene; polystyrene; aramid; polyamideimide; polyimide; nylon; Polyester such as polyethylene terephthalate (PET); polyarylate; Cellulose or modified cellulose; Resins such as these can be used. Additionally, inorganic materials such as glass, alumina, silica, and zirconia may be used.

The thickness of the insulating porous substrate is not particularly limited, and can be, for example, 10 ㎛ or more and 100 ㎛ or less. From the viewpoint of ensuring a balance between securing the mechanical strength of the insulating porous substrate and preventing an increase in the electrical resistance of the substrate, , it is preferable that it is 20㎛ or more and 50㎛ or less.

In addition, the basis weight of the insulating porous substrate is preferably 10 g/m ² or less, more preferably 8 g/m ² or less, so as to sufficiently retain an amount of solid electrolyte particles sufficient to ensure good lithium ion conductivity. Additionally, from the viewpoint of ensuring sufficient strength, it is preferably 3 g/m ² or more, and more preferably 4 g/m ² or more.

The binder of the solid electrolyte sheet preferably does not react with the solid electrolyte, and at least one type of resin selected from the group consisting of butyl rubber, chloroprene rubber, acrylic resin, and fluororesin is preferably used.

From the viewpoint of ensuring good lithium ion conductivity, the ratio of the insulating porous substrate in the solid electrolyte sheet (the ratio of the actual volume excluding the pores) is preferably 30 volume% or less, and more preferably 25 volume% or less. However, if the ratio of the insulating porous substrate in the solid electrolyte sheet is too small, the effect of improving the shape retention of the solid electrolyte sheet may be reduced. Therefore, from the viewpoint of further increasing the strength of the solid electrolyte sheet, the proportion of the insulating porous substrate in the solid electrolyte sheet is preferably 5 volume% or more, and more preferably 10 volume% or more.

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

The thickness of the solid electrolyte sheet is preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of suppressing the occurrence of short circuits or increase in resistance by ensuring an appropriate distance between the positive electrode and negative electrode of a battery using the solid electrolyte sheet. , Moreover, it is preferable that it is 50 micrometers or less, and it is more preferable that it is 30 micrometers or less.

By using the configuration described so far, the tensile strength of the solid electrolyte sheet measured by the method employed in the later examples can be 4 N/cm or more.

There are no particular restrictions on the manufacturing method of the solid electrolyte sheet, but it is preferable to produce it by dispersing the solid electrolyte particles in a solvent together with a binder to make a slurry, etc., and including the step of filling the pores of the insulating porous substrate in a wet manner. do. Accordingly, the strength of the solid electrolyte sheet is improved, making it easier to manufacture a large-area solid electrolyte sheet.

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

The slurry is prepared by adding solid electrolyte particles and a binder to a solvent and mixing them. It is desirable to select a solvent for the slurry that is less likely to deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes cause chemical reactions due to a small amount of moisture, so non-polar aprotic solvents such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene are used. It is preferable to use a solvent. In particular, it is more preferable to use a super-dehydrating solvent with a moisture content of 0.001% by mass (10ppm) or less. In addition, fluorine-based solvents such as “Vatorell (registered trademark)” manufactured by Mitsui-DuPont Fluorochemicals, “Zeolara (registered trademark)” manufactured by Nippon Zeon, and “Novec (registered trademark)” manufactured by Sumitomo 3M. , and non-aqueous organic solvents such as dichloromethane and diethyl ether can also be used.

After filling the pores of the insulating porous substrate with the slurry as described above, the solvent of the slurry is removed by drying and, if necessary, pressure molding is performed to obtain a solid electrolyte sheet.

In addition, as described above, the method for producing a solid electrolyte sheet is not limited to the wet method. For example, the pores of an insulating porous substrate are filled with a mixture of solid electrolyte particles and binder particles in a dry manner, and then The solid electrolyte sheet may be manufactured by pressure molding.

Additionally, a sheet obtained by molding a mixture of a solid electrolyte and a binder may be affixed to one or both sides of a sheet in which the pores of an insulating porous substrate are filled with solid electrolyte particles and a binder to form a solid electrolyte sheet. In this case, in the sheet obtained by molding a mixture of a solid electrolyte and a binder, it is preferable to use a sulfide-based solid electrolyte with relatively high flexibility as the solid electrolyte.

<All-solid-state lithium secondary battery>

The all-solid-state lithium secondary battery (hereinafter sometimes simply referred to as “battery”) of the present invention has a positive electrode and a negative electrode, and also has the solid electrolyte sheet of the present invention inserted between the positive electrode and the negative electrode.

A cross-sectional view schematically showing an example of the all-solid-state lithium secondary battery of the present invention is shown in Figure 2. The battery 1 shown in FIG. 2 has a positive electrode 20 and a negative electrode ( 30), and a solid electrolyte sheet 10 inserted between the positive electrode 20 and the negative electrode 30 is enclosed.

The sealed can 50 is fitted to the opening of the external can 40 via a gasket 60, and the open end of the external can 40 is clamped inward, thereby sealing the gasket 60. By coming into contact with the sealed can 50, the opening of the external can 40 is sealed and the inside of the element has a sealed structure.

External cans and sealed cans can be made of stainless steel. In addition, polypropylene, nylon, etc. can be used as the gasket material, and in cases where heat resistance is required in relation to the use of the battery, tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), etc. Melting points of fluororesin, polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), etc. Heat-resistant resin exceeding 240°C can also be used. Additionally, when the battery is applied to applications requiring heat resistance, a glass hermetic seal may be used as the seal.

Next, components of the all-solid-state lithium secondary battery other than the solid electrolyte sheet will be explained.

(positive electrode)

The positive electrode of the all-solid-state lithium secondary battery 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 storing and releasing Li ions.

As the positive electrode active material, LiM _x Mn _2-x O ₄ (where M is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, Spinel _- type lithium manganese composite oxide, _{Li y} M _z O _(2-k) F _l (provided that M is made of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W It is at least one element selected from the group, and is expressed as 0.8≤x≤1.2, 0<y<0.5, 0≤z≤0.5, k+l<1, -0.1≤k≤0.2, 0≤l≤0.1) Layered compound, LiCo _1-x M _x O ₂ (where M is selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba At least one element selected, lithium cobalt composite oxide expressed as 0≤x≤0.5, LiNi _1-x M _x O ₂ (where M is Al, Mg, Ti, Zr, Fe, Co, Cu, Lithium nickel composite oxide, _LiM 1 _{- x} N However, M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, It is at least one element selected from the group consisting of Sb and Ba, and includes olivine-type composite oxides expressed as 0≤x≤0.5), lithium titanium composite oxides represented as Li ₄ Ti ₅ O ₁₂ , and one of these. Only one type may be used, or two or more types may be used together.

The positive electrode can be used as a structure in which a positive electrode mixture layer containing the positive electrode active material of the above example and a conductive additive or binder is formed on one side or both sides of a current collector.

As a binder for the positive electrode, for example, a fluororesin such as polyvinylidene fluoride (PVDF) can be used. In addition, as a conductive additive for the positive electrode, carbon materials such as carbon black can be used, but solid electrolytes (for example, the various solid electrolytes previously exemplified as constituting the solid electrolyte particles of the solid electrolyte sheet) can be used. You may use it.

As the current collector of the positive electrode, foil of metal such as aluminum, punching metal, net, expanded metal, foam metal, etc. can be used.

In manufacturing a positive electrode, for example, a positive electrode mixture-containing composition (paste, slurry, etc.) in which the positive electrode active material, conductive additive, binder, etc. are dispersed in a solvent such as xylene is applied to the current collector, dried, and then added as necessary. Pressure molding methods such as calendering can be adopted. As the solvent, a super-dehydrating solvent with a moisture content of 0.001 mass% (10 ppm) or less is preferably used.

In addition, when using a conductive porous substrate such as a punching metal for the positive electrode current collector, for example, the composition containing the positive electrode mixture is filled into the pores of the conductive porous substrate, dried, and then subjected to pressurization, such as calendering, if necessary. The positive electrode can be manufactured by a molding method. If the positive electrode is manufactured in this way, high strength can be secured, making it possible to hold a larger-area solid electrolyte sheet.

In addition, a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, etc., and not a solvent, other than the composition containing the positive electrode mixture, is filled in the pores of the conductive porous substrate in a dry manner, and subjected to pressurization, such as calendering, if necessary. The positive electrode may be manufactured by a molding method.

(negative electrode)

The negative electrode of the all-solid-state lithium secondary battery is not particularly limited as long as it is a negative electrode used in conventionally known lithium ion secondary batteries, that is, a negative electrode containing an active material capable of storing and releasing Li ions.

Examples of negative electrode active materials include carbon-based materials that can absorb and release lithium, such as graphite, pyrolytic carbons, coke, glassy carbons, sintered bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fiber. One type or a mixture of two or more types 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 lithium metal, such as lithium-containing nitride or lithium-containing oxide; lithium metal; Lithium/aluminum alloy; can also be used as a negative electrode active material.

For the negative electrode, a negative electrode mixture is formed by appropriately adding a conductive aid (carbon material such as carbon black, solid electrolyte, etc.) or a binder such as PVDF to the negative electrode active material, and the current collector is used as the core material to form a molded body (negative electrode mixture layer). Those finished with , or foils made of the various alloys or lithium metal mentioned above can be used either alone or laminated as a negative electrode layer on a current collector.

When using a current collector for the negative electrode, copper or nickel foil, punching metal, net, expanded metal, foamed metal, etc. can be used as the current collector.

In manufacturing a negative electrode having a negative electrode mixture layer, for example, a negative electrode mixture-containing composition (paste, slurry, etc.) in which the negative electrode active material, binder, and optionally conductive additives are dispersed in a solvent such as xylene, A method of applying it to a current collector, drying it, and then performing pressure molding, such as calendering, if necessary, can be adopted. As the solvent, a super-dehydrating solvent with a moisture content of 0.001 mass% (10 ppm) or less is preferably used.

In addition, when using a conductive porous substrate such as punching metal as the negative electrode current collector, for example, the composition containing the negative electrode mixture is filled into the pores of the conductive porous substrate, dried, and then subjected to pressurization such as calendering if necessary. A negative electrode can be manufactured by a molding method. A negative electrode manufactured in this way can secure great strength, making it possible to hold a larger-area solid electrolyte sheet.

In addition, a negative electrode mixture containing a negative electrode active material, a binder, and a conductive additive, and not the composition containing the negative electrode mixture, and not containing a solvent, is filled in the pores of the conductive porous substrate in a dry manner, and, if necessary, subjected to calendar treatment, etc. The negative electrode may be manufactured by the method of pressure molding.

(electrode body)

The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body laminated with the solid electrolyte sheet of the present invention interposed, or a wound electrode body obtained by winding this laminated electrode body.

In addition, when forming the electrode body, it is preferable to press mold the positive electrode, the negative electrode, and the solid electrolyte sheet in a laminated state from the viewpoint of increasing the mechanical strength of the electrode body.

(shape of battery)

The form of the all-solid-state lithium secondary battery is not limited to those having an external body composed of an external can, a sealed can, and a gasket as shown in FIG. 2, that is, those generally called coin-type batteries or button-type batteries, for example. For example, it may have an exterior body made of a resin film or a metal-resin laminate film, or it may have a cylindrical (cylindrical or rectangular) exterior can with a metal bottom and an exterior body having a sealing structure that seals the opening. It's okay.

Example

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1

Using xylene (“super dehydration” grade) as a solvent, a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) with an average particle diameter of 1 μm, an acrylic resin binder, and a dispersant were mixed in a mass ratio of 100:3:1. Then, it was mixed so that the solid content ratio was 40%, and stirred for 10 minutes with a sinky mixer to prepare a uniform slurry. Through this slurry, a PET nonwoven fabric (“05TH-8” manufactured by Hirose Seji Co., Ltd.) with a thickness of 40 ㎛ and a basis weight of 8 g/m ² is passed through and then pulled up to apply the slurry to the PET nonwoven fabric at 120°C. Vacuum drying was performed for 1 hour to obtain a solid electrolyte sheet with a thickness of 50 μm. The thickness of the nonwoven fabric was 80% of the entire thickness of the solid electrolyte sheet. Additionally, the proportion of the insulating porous substrate in the solid electrolyte sheet was 25% by volume, and the proportion of the binder out of the total amount of solid electrolyte particles and binder was 2.9% by mass.

(Comparative Example 1)

A solid electrolyte sheet with a thickness of 50 μm was prepared in the same manner as in Example ¹ , except that instead of the PET nonwoven fabric, a polyolefin nonwoven fabric (“HOP-4” manufactured by Hirose Seji Co., Ltd.) with a thickness of 20 μm and a basis weight of 4 g/m 2 was used. got it The thickness of the nonwoven fabric was 40% of the entire thickness of the solid electrolyte sheet.

From the solid electrolyte sheets of Example 1 and Comparative Example 1, test pieces with a length of 50 mm and a width of 20 mm were cut out, and a tensile force test was performed at a tensile speed of 120 mm/min to measure the tensile strength of each test piece. As a result, in the test piece of Example 1 in which the thickness of the nonwoven fabric was 70% or more of the entire thickness of the solid electrolyte sheet, the tensile strength was 5 N/cm, and peeling of the solid electrolyte was not confirmed during the test, whereas solid In the test piece of Comparative Example 1 in which the ratio of the thickness of the nonwoven fabric to the overall thickness of the electrolyte sheet was too small, the tensile strength decreased to 3 N/cm, and further peeling of the solid electrolyte and cracking of the sheet were observed from the start of the test. Therefore, it can be said that the solid electrolyte sheet of Example 1 is superior in shape retention compared to the sheet of Comparative Example 1.

Example 2

Using the solid electrolyte sheet of Example 1, an all-solid lithium secondary battery was produced as follows.

<Positive pole>

Using xylene (“super dehydration” grade) as a solvent, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ with an average particle diameter of 3 ㎛ with an amorphous composite oxide of Li and Nb formed on the surface, and a sulfide solid electrolyte (Li ₆ PS ₅ Cl) , carbon nanotubes as a conductive aid (“VGCF” (brand name) manufactured by Showa Denko) and an acrylic resin binder are mixed at a mass ratio of 50:44:3:3 so that the solid content ratio is 50%, and the sinky The mixture was stirred with a mixer for 10 minutes to prepare a uniform slurry. This slurry was applied onto Al foil with a thickness of 20 μm using an applicator with a gap of 200 μm, and vacuum dried at 120°C to obtain a positive electrode.

<Negative pole>

Xylene (“super dehydration” grade) is used as a solvent, and graphite with an average particle diameter of 20㎛, sulfide solid electrolyte (Li ₆ PS ₅ Cl), and acrylic resin binder are used in a mass ratio of 50:47:3. , mixed so that the solid content ratio was 50%, and stirred for 10 minutes with a sinky mixer to prepare a uniform slurry. This slurry was applied onto SUS foil with a thickness of 20 μm using an applicator with a gap of 200 μm, and vacuum dried at 120°C to obtain a negative electrode.

<Assembly of the battery>

The positive electrode, negative electrode, and solid electrolyte sheet of Example 1 were punched out to a size of 10 mmΦ, overlapped in the order of positive electrode, solid electrolyte sheet, and negative electrode between the upper and lower pins of SUS, and placed in a PET container to weigh 10 tons/kg. It was pressurized to cm ² and made into a cell (all-solid-state lithium secondary battery) that can be charged and discharged in a sealed state so as not to contact the atmosphere.

(Comparative Example 2)

An all-solid lithium secondary battery was produced in the same manner as in Example 2, except that the solid electrolyte sheet produced in Comparative Example 1 was used.

For Example 2 and Comparative Example 2, 10 batteries each were manufactured, and the number of batteries in which short circuit occurred after assembly was investigated.

Next, while pressurizing the battery in which a short circuit has not occurred, constant current charging is performed at a current value of 0.05C until the voltage reaches 4.2V, and then constant current discharge is performed at a predetermined current value until the voltage reaches 2.7V. A charge/discharge test was conducted. Additionally, the current values during constant current discharge during the charge/discharge test were 0.05C (0.05C discharge), 0.1C (0.1C discharge), 0.5C (0.5C discharge), and 1.0C (1.0C discharge).

In the above charge/discharge test, the charge/discharge efficiency when discharging at a current value of 0.05C was determined, and the capacity (capacity per mass of the battery) during discharge at each current value was measured.

The evaluation results of the all-solid lithium secondary batteries of Example 2 and Comparative Example 2 are shown in Table 1.

As shown in Table 1, the all-solid lithium secondary battery of Example 2 was assembled using a solid electrolyte sheet with excellent shape retention, so there was no occurrence of short circuit, and compared to the battery of Comparative Example 2, , charge/discharge efficiency, and discharge capacity at each current value were all excellent, and had good discharge characteristics.

On the other hand, in the battery of Comparative Example 2, it was confirmed that a short circuit occurred after assembly due to separation of solid electrolyte particles from the solid electrolyte sheet or cracking of the sheet during manufacture.

The present invention can be implemented in forms other than those described above, without departing from its spirit. The embodiments disclosed in this application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is interpreted by giving priority to the description of the appended claims over the description of the above specification, and all changes within the scope equivalent to the claims are included in the scope of the claims.

The all-solid lithium secondary battery of the present invention can be applied for the same purposes as conventionally known secondary batteries, but has excellent heat resistance because it has a solid electrolyte instead of an organic electrolyte, and is preferably used for applications exposed to high temperatures. You can use it.

1 All solid lithium secondary battery
10 solid electrolyte sheet
11 Insulating porous substrate
12 Solid electrolyte particles
13 binder
20 positive electrode
30 negative electrode
40 external can
50 sealed cans
60 gasket

Claims (12)

A solid electrolyte sheet using an insulating porous substrate as a support,
The thickness is 5㎛ or more and 50㎛ or less,
The insulating porous substrate is composed of a fibrous material,
The interior of the insulating porous substrate is filled with solid electrolyte particles,
In addition, it contains a binder that binds the solid electrolyte particles together,
A solid electrolyte sheet, wherein the thickness of the insulating porous substrate is 70% or more of the thickness of the solid electrolyte sheet. According to claim 1,
A solid electrolyte sheet wherein the ratio of the binder to the total amount of the solid electrolyte particles and the binder is 0.5 to 5% by mass. According to claim 1,
A solid electrolyte sheet wherein the insulating porous substrate is woven or non-woven. According to claim 1,
A solid electrolyte sheet containing sulfide-based solid electrolyte particles as the solid electrolyte particles. According to claim 1,
A solid electrolyte sheet wherein the fibrous material is made of cellulose, modified cellulose, polyolefin, polyester, aramid, polyamidoimide, polyimide, glass, alumina, or silica. According to claim 1,
A solid electrolyte sheet wherein the proportion of the insulating porous substrate is 20% by volume or less. According to claim 6,
A solid electrolyte sheet wherein the proportion of the insulating porous substrate is 5% by volume or more. According to claim 1,
Solid electrolyte sheet with a tensile strength of 4N/cm or more. According to claim 1,
A solid electrolyte sheet wherein the average particle diameter of the solid electrolyte particles is 0.3 to 5 μm. According to claim 1,
A solid electrolyte sheet wherein the basis weight of the insulating porous substrate is 3 g/m ² or more. According to claim 1,
A solid electrolyte sheet wherein the basis weight of the insulating porous substrate is 10 g/m ² or less. An all-solid-state lithium secondary battery comprising a positive electrode, a negative electrode, and the solid electrolyte sheet according to any one of claims 1 to 11 inserted between the positive electrode and the negative electrode.