JP7246196B2 - All-solid lithium secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an all-solid lithium secondary battery with good charge-discharge cycle characteristics.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the commercialization of electric vehicles, there is a need for secondary batteries that are compact, lightweight, and have high capacity and high energy density. It has become to.

At present, lithium-containing composite oxides such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) are used as positive electrode active materials in non-aqueous secondary batteries, particularly lithium ion secondary batteries, which can meet this demand. , graphite or the like is used as a negative electrode active material, and an organic electrolyte containing an organic solvent and a lithium salt is used as a non-aqueous electrolyte.

With the further development of equipment to which non-aqueous secondary batteries are applied, there is a demand for longer life, higher capacity, and higher energy density of non-aqueous secondary batteries. There is also a strong demand for reliability of non-aqueous secondary batteries with increased capacity and increased energy density.

However, since the organic electrolyte used in lithium-ion secondary batteries contains an organic solvent, which is a combustible substance, the organic electrolyte generates abnormal heat when an abnormal situation such as a short circuit occurs in the battery. there is a possibility. In addition, with the trend toward higher energy densities in non-aqueous secondary batteries and an increase in the amount of organic solvents in organic electrolytes in recent years, there is a demand for greater reliability of non-aqueous secondary batteries.

Under the circumstances described above, an all-solid-state secondary battery that does not use an organic solvent is also being studied (Patent Documents 1 and 2, etc.). The all-solid secondary battery uses a solid electrolyte molded body that does not use an organic solvent in place of the conventional organic solvent-based electrolyte. ing.

In addition, in the all-solid secondary battery, not only the power generation element but also the exterior material has been studied (Patent Document 3). Specifically, in Patent Document 3, a resin coating layer is formed by insert molding. For example, the resin coatings on the positive electrode side and the negative electrode side are each formed with a thickness of 1 mm.

JP 2017-40531 A JP 2017-168387 A JP 2015-18769 A

By the way, in an all-solid secondary battery, since the electrode expands and contracts when charging and discharging are repeated, contact between the active materials in the electrode or between the active material and the solid electrolyte or the conductive aid added as necessary may occur. becomes worse and the discharge characteristics deteriorate. Therefore, in all-solid-state secondary batteries, it is required to suppress such deterioration in discharge characteristics and improve charge-discharge cycle characteristics.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an all-solid lithium secondary battery with good charge-discharge cycle characteristics.

The all-solid lithium secondary battery of the present invention has an electrode laminate in which a positive electrode and a negative electrode are laminated via a solid electrolyte layer, and the periphery of the electrode laminate is polyimide, polyamideimide, or polyetherimide. , polyphenylene sulfide, polybenzimidazole, polyetheretherketone and polyvinylidene fluoride.

According to the present invention, it is possible to provide an all-solid lithium secondary battery with good charge-discharge cycle characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view schematically showing an example of an electrode laminate according to an all-solid lithium secondary battery of the present invention; FIG. 2 is a sectional view taken along the line II of FIG. 1; FIG. 3 is a plan view schematically showing another example of an electrode laminate according to the all-solid lithium secondary battery of the present invention; FIG. 4 is a sectional view taken along line II-II of FIG. 3; 1 is a cross-sectional view schematically showing an example of an all-solid lithium secondary battery of the present invention; FIG. FIG. 3 is a cross-sectional view schematically showing another example of the all-solid lithium secondary battery of the present invention; 4 is a graph showing evaluation results of charge-discharge cycle characteristics of all-solid-state lithium secondary batteries of Examples and Comparative Examples.

The all-solid lithium secondary battery of the present invention has an electrode laminate in which a positive electrode and a negative electrode are laminated via a solid electrolyte layer.

1 and 2 show drawings schematically showing an example of an electrode laminate according to an all-solid lithium secondary battery. FIG. 1 is a plan view of the electrode laminate 100, and FIG. 2 is a sectional view taken along line II of FIG. An electrode laminate 100 shown in FIGS. 1 and 2 is configured by laminating a positive electrode 10 and a negative electrode 20 with a solid electrolyte layer 30 interposed therebetween. In the positive electrode 10 , a positive electrode mixture layer 11 containing a positive electrode active material, a solid electrolyte, and the like is formed on one side of a positive electrode current collector 12 . Also, in the negative electrode 20 , a negative electrode mixture layer 21 containing a negative electrode active material, a solid electrolyte, and the like is formed on one side of the negative electrode current collector 22 .

Then, the periphery of the electrode laminate 100, that is, the side surfaces (the end surface of the positive electrode 10, the end surface of the negative electrode 20, and the end surface of the solid electrolyte layer 30), the upper surface (the surface of the negative electrode 20 on the side of the negative electrode current collector 22), and the lower surface (positive electrode 10 ) is covered with a covering layer 40 .

The coating layer covering the periphery of the electrode laminate is made of at least one resin (A ) and has a high intensity. Therefore, even if the electrode expands due to charging and discharging of the all-solid-state lithium secondary battery having the electrode laminate, the volume change of the electrode can be suppressed by the action of the coating layer. Therefore, in the all-solid lithium secondary battery of the present invention, even if charging and discharging are repeated, the active materials in the mixture layer of the electrode, or the active material and the solid electrolyte, and the conductive aid added as necessary. Since good contact can be maintained, it becomes possible to suppress a decrease in charge-discharge capacity, and it becomes possible to ensure excellent charge-discharge cycle characteristics.

In the electrode laminate, as shown in FIGS. 1 and 2, an exposed portion 20a (exposed portion of the negative electrode current collector 22) that is not covered with the coating layer 40 is provided on a part of the periphery (for example, the upper surface). An electrically conductive connection with the outside can be made through the exposed portion. For example, in the case of an all-solid-state lithium secondary battery using an outer package having an outer can and a sealed can, the inner surface of the outer can or the sealed can, which also serves as a positive electrode terminal or a negative electrode terminal, and the outermost electrode of the electrode laminate. In general, a configuration is adopted in which the wires are brought into direct contact with each other to be electrically connected. When an exposed portion that is not covered with a coating layer is provided on a part of the upper surface of the electrode laminate, the exposed portion of the electrode (positive or negative electrode) constituting the upper surface of the electrode laminate and the outer can or the sealed can. The electrode and the outer can or the sealing can can be electrically connected simply by contacting the inner surface. Alternatively, a lead may be attached to the exposed portion, and the electrode and the outer can or the sealing can may be electrically connected via the lead.

In addition, as shown in FIG. 2, the electrode laminate may have an exposed portion 10a (exposed portion of the positive electrode current collector 12) that is not covered with the coating layer 40 at a portion of the lower surface thereof. . In this case also, the exposed portion of the electrode (positive electrode or negative electrode) constituting the lower surface of the electrode laminate is brought into contact with the inner surface of the outer can or the sealed can, or a lead is attached to the exposed portion, and the lead is attached to the outer can. Alternatively, by connecting to the inner surface of the sealing can, the electrode can be electrically connected to the outer can or the sealing can.

In the case of providing an exposed portion on a part of the upper surface and/or a part of the lower surface in the electrode laminate, from the viewpoint of better suppressing the volume change of the electrode due to charging and discharging of the battery, the upper surface and the lower surface It is preferable not to provide an exposed portion at a portion (edges of the upper surface and the lower surface) connected to the side surfaces and in the vicinity thereof.

FIGS. 3 and 4 show drawings schematically showing other examples of electrode laminates related to all-solid lithium secondary batteries. 3 is a plan view of the electrode laminate 100, and FIG. 4 is a cross-sectional view taken along the line II-II of FIG. In the electrode laminate 100 shown in FIGS. 3 and 4, the positive electrode current collector 12 of the positive electrode 10 is provided with a positive electrode current collecting tab portion in which the positive electrode mixture layer 11 is not formed, and the negative electrode current collector 22 of the negative electrode 20 is provided with a negative electrode current collector. In this example, negative electrode current collecting tabs are provided without the agent layer 21 formed thereon, and these current collecting tabs are used as leads for connecting to external terminals of the battery.

The electrode laminate 100 shown in FIGS. 2 and 4 has one positive electrode 10 and one negative electrode 20, and one solid electrolyte layer 30 interposed therebetween. The electrode laminate constituting the solid lithium secondary battery may have two or more positive electrodes, and may have two or more negative electrodes. In this case, the solid electrolyte layer may be interposed between each positive electrode and negative electrode. In the case of an electrode laminate having two or more positive and negative electrodes, the positive and negative electrodes may be connected to each other according to a conventional method, and have a bipolar structure in which one surface of the positive electrode and one surface of the negative electrode are electrically connected. It is also possible to In the electrode laminate 100 shown in FIGS. 2 and 4, the electrode constituting the upper surface is the negative electrode 20 and the electrode constituting the lower surface is the positive electrode 10, but the electrode according to the all-solid lithium secondary battery of the present invention The laminated body is not limited to such a configuration, and the upper surface may be composed of the positive electrode and the lower surface may be composed of the negative electrode. For example, as shown in FIG. In the case of the electrode laminate having a configuration in which the .sup.2 is drawn out, both the upper surface and the lower surface can be made to have the same polarity (positive electrode or negative electrode).

The coating layer covering the periphery of the electrode laminate may be composed of only the resin (A) [only one or more of the resins (A)]. may contain additives such as synthetic fillers. When the coating layer contains a component other than the resin (A), the content of the resin (A) in the coating layer [when two or more resins (A) are used, the total amount thereof. same as below. ] is preferably 80% or more. On the other hand, since the coating layer may be composed only of the resin (A), the upper limit of the content of the resin (A) in the coating layer is 100% by mass.

The thickness of the coating layer is preferably 10 μm or more, more preferably 30 μm or more, from the viewpoint of securing strength sufficient to satisfactorily suppress changes in volume of the electrode due to charging and discharging of the battery. However, the coating layer itself does not contribute to the battery reaction, and if it is too thick, it is disadvantageous in increasing the energy density of the battery. Therefore, from the viewpoint of suppressing such problems, the thickness of the coating layer is preferably 200 μm or less, more preferably 100 μm or less.

The method for forming the resin coating layer around the electrode laminate is not particularly limited. A method such as spray coating can be used. When the coating layer is formed by these methods, in the electrode bodies shown in FIGS. 2 and 4, part of the side coating layer is mixed with the mixture layer at the interface with the mixture layer of the electrode. Conceivable.

As the positive electrode of the all-solid lithium secondary battery, the positive electrode used in conventionally known lithium ion secondary batteries, that is, the positive electrode containing an active material capable of absorbing and releasing Li ions is particularly limited. no.

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, At least one element selected from the group consisting of Sb, In, Nb, Mo, W, Y, Ru and Rh, and a spinel-type lithium-manganese composite oxide represented by 0.01≦x≦0.5) Li _x Mn _(1-y-x) Ni _y M _z O _(2-k) F _l (where M is Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, at least one element selected from the group consisting of 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), LiCo _1-x M _x O ₂ (where M is Al, Mg, At least one element selected from the group consisting of Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, represented by 0 ≤ x ≤ 0.5) lithium cobalt composite oxide, LiNi _1-x M _x O ₂ (where M is Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and LiM _1-x N _x PO ₄ (wherein M is Fe, at least one element selected from the group consisting of Mn and Co, where N is the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba At least one element selected from, olivine-type composite oxides represented by 0 ≤ x ≤ 0.5), lithium titanium composite oxides represented by Li ₄ Ti ₅ O ₁₂ , and the like, Only one of these may be used, or two or more thereof may be used in combination.

The positive electrode has a structure in which a positive electrode mixture layer containing the above-exemplified positive electrode active material and solid electrolyte, as well as a conductive aid and a binder added as necessary, is formed on one or both sides of a current collector. can be used.

For the solid electrolyte of the positive electrode, one or more of various solid electrolytes exemplified later can be used for the solid electrolyte layer.

As the binder for the positive electrode, for example, a fluorine resin such as polyvinylidene fluoride (PVDF) can be used. Moreover, as a conductive additive for the positive electrode, for example, a carbon material such as carbon black can be used.

As the current collector of the positive electrode, metal foil such as aluminum or stainless steel, punching metal, mesh, expanded metal, foam metal, or the like can be used.

When manufacturing a positive electrode, for example, a positive electrode mixture-containing composition (paste, slurry etc.) is applied to the current collector, dried, and then pressure molding such as calendering can be employed as necessary. As the solvent, a super dehydrated solvent having a water content of 0.001% by mass (10 ppm) or less is preferably used.

When a conductive porous substrate such as punching metal is used as the positive electrode current collector, for example, the positive electrode mixture-containing composition is filled into the pores of the conductive porous substrate, After drying, the positive electrode can be manufactured by a method of pressure molding such as calendering, if necessary. A positive electrode manufactured by such a method can secure a large strength, so that a solid electrolyte sheet having a larger area can be held.

Furthermore, instead of the positive electrode mixture-containing composition, a positive electrode mixture containing a positive electrode active material, a solid electrolyte, a conductive aid and a binder added as necessary, and not containing a solvent is used as a conductive material. The positive electrode may be manufactured by a method of filling the pores of the porous base material in a dry manner and, if necessary, performing pressure molding such as calendering.

In addition, depending on the form of the outer package of the battery, a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and optionally a conductive aid and a binder may be used without using a positive electrode current collector. A molded body (positive electrode mixture molded body) press-molded into a pellet can also be used as the positive electrode.

As the negative electrode of the all-solid lithium secondary battery, the negative electrode used in conventionally known lithium ion secondary batteries, that is, the negative electrode containing an active material capable of absorbing and releasing Li ions is particularly limited. no.

Examples of negative electrode active materials include graphite, pyrolytic carbons, cokes, vitreous carbons, sintered organic polymer compounds, mesocarbon microbeads (MCMB), carbon fibers, and the like, which can occlude and release lithium. One or a mixture of two or more carbonaceous materials is used. Elements, compounds, and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In; compounds that can be charged and discharged at low voltages close to lithium metal, such as lithium-containing nitrides or lithium-containing oxides; lithium metal a lithium/aluminum alloy; can also be used as the negative electrode active material.

For the negative electrode, a negative electrode mixture obtained by appropriately adding a conductive aid (carbon material such as carbon black, etc.) and a binder such as PVDF to the negative electrode active material and solid electrolyte is formed into a molded body (negative electrode mixture) using a current collector as a core material. or a foil of the various alloys or lithium metal described above alone or laminated on a current collector as a negative electrode layer.

For the solid electrolyte of the negative electrode, one or more of various solid electrolytes exemplified later can be used for the solid electrolyte layer.

When a current collector is used for the negative electrode, the current collector may be copper, nickel or stainless steel foil, punching metal, mesh, expanded metal, foam metal, or the like.

When manufacturing a negative electrode having a negative electrode mixture layer, for example, a negative electrode mixture containing a negative electrode active material, a solid electrolyte, and optionally a binder, a conductive aid, etc. dispersed in a solvent such as xylene. A method of applying a composition (paste, slurry, etc.) to a current collector, drying it, and subjecting it to pressure molding such as calendering, if necessary, can be employed. As the solvent, a super dehydrated solvent having a water content of 0.001% by mass (10 ppm) or less is preferably used.

When a conductive porous substrate such as punching metal is used as the negative electrode current collector, for example, the negative electrode mixture-containing composition is filled into the pores of the conductive porous substrate, After drying, the negative electrode can be manufactured by a method of pressure molding such as calendering, if necessary. A negative electrode manufactured by such a method can secure a large strength, so that a solid electrolyte sheet having a larger area can be held.

Furthermore, instead of the negative electrode mixture-containing composition, a negative electrode mixture containing a negative electrode active material, a solid electrolyte, a binder and a conductive aid added as necessary, and not containing a solvent, is used as a conductive material. The negative electrode may be produced by a method of filling the pores of the porous base material in a dry process and, if necessary, performing pressure molding such as calendering.

In addition, depending on the form of the outer package of the battery, a negative electrode mixture containing a negative electrode active material, a solid electrolyte, and optionally a binder, a conductive aid, etc., may be used without using a negative electrode current collector. A molded body (negative electrode mixture molded body) press-molded into a pellet can also be used as the negative electrode.

A hydride-based solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or the like can be used as the solid electrolyte that constitutes the solid electrolyte layer of the all-solid-state lithium secondary battery. may be used, or two or more may be used in combination.

Specific examples of hydride-based solid electrolytes include LiBH ₄ , solid solutions of LIBH ₄ and the following alkali metal compounds (for example, those having a molar ratio of LiBH ₄ to the alkali metal compound of 1:1 to 20:1), and the like. is mentioned. Examples of alkali metal compounds in the solid solution include lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbiF, RbCl, etc.), and cesium halides (CsI, CsBr, CsF, CsCl, etc.). , lithium amide, rubidium amide and cesium amide.

Specific examples of sulfide-based solid electrolytes include Li ₂ SP ₂ S ₃ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₃ —P ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—SiS ₂ —P ₂ S ₅ , Li ₂ S—SiS ₂ —Li ₄ SiO ₄ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li _{3PS 4} —Li ₄ GeS ₄ , Li _3.4 P _0.6 Si _0.4 S ₄ , Li _3.25 P _0.25 Ge _0.76 S ₄ , Li _4-x Ge _1-x P _x S ₄ , _{Li7P3S11 ,} and the _like .

Specific examples of oxide- _based solid electrolytes include _Li7La3Zr2O12 , LiTi( _PO4 ) ₃ , LiGe _{( PO4} ) ₃ , _{LiLaTiO3 ,} and the like.

The solid electrolyte layer is formed by applying a composition for forming a solid electrolyte layer prepared by dispersing the solid electrolyte in a solvent onto the base material, the positive electrode, and the negative electrode, drying it, and performing pressure molding such as press treatment as necessary. It can be formed by doing.

As the solvent used in the solid electrolyte layer-forming composition, it is preferable to select a solvent that does not easily deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes are represented by hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene because they cause chemical reactions with minute amounts of moisture. Preference is given to using non-polar aprotic solvents. In particular, it is more preferable to use a super-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. In addition, fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by Mitsui-DuPont Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Nippon Zeon, "Novec (registered trademark)" manufactured by Sumitomo 3M, and , dichloromethane, and diethyl ether can also be used.

In addition, it is preferable to select solvents for the positive electrode mixture-containing composition and the negative electrode mixture-containing composition that do not easily deteriorate the solid electrolyte. It is desirable to use the same solvents as those described above.

The thickness of the solid electrolyte layer is preferably 10 to 200 μm.

A laminated electrode body configured by laminating a positive electrode and a negative electrode with a solid electrolyte interposed therebetween is enclosed in an outer package to form an all-solid lithium secondary battery.

FIG. 5 shows a cross-sectional view schematically showing an example of the all-solid lithium secondary battery of the present invention. The all-solid lithium secondary battery 1 shown in FIG. 5 is an example having the electrode laminate 100 configured as shown in FIGS. , and a gasket 70 (a flat-shaped outer body called a coin-shaped or button-shaped outer body). In the all-solid-state lithium secondary battery 1 shown in FIG. 5, the sealing can 50 is fitted to the opening of the outer can 60 via the gasket 70, and the open end of the outer can 50 is tightened inward. As a result, the gasket 70 comes into contact with the sealing can 60, thereby sealing the opening of the outer can 50 and forming a sealed structure inside the battery. Then, the exposed portion on the upper surface side of the electrode laminate 100 (exposed portion of the negative electrode current collector) is electrically connected by contacting the inner surface of the sealing can 60 that also serves as the negative electrode terminal, and the exposed portion on the lower surface side (positive electrode collector) is electrically connected. The exposed portion of the conductor) contacts the inner surface of the outer can 50, which also serves as the positive electrode terminal, for electrical connection.

In the case of an outer package composed of an outer can and a sealed can, the shape thereof may be polygonal (triangle, quadrangle, pentagon, hexagon, heptagon, octagon) in plan view, circular or circular in plan view. It may be oval.

A stainless steel can or the like can be used for the outer can and the sealing can. In addition, polypropylene, nylon, etc. can be used for gasket materials, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), etc., can be used when heat resistance is required in relation to battery applications. Heat resistance with a melting point exceeding 240°C such as fluorine resin, polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), etc. Resin can also be used. Moreover, when the battery is applied to applications requiring heat resistance, a glass hermetic seal can be used for the sealing.

FIG. 6 shows a cross-sectional view schematically showing another example of the all-solid lithium secondary battery of the present invention. The all-solid lithium secondary battery 1 shown in FIG. 6 is an example having the electrode laminate 100 configured as shown in FIGS. .

In the all-solid-state lithium secondary battery 1 shown in FIG. 6, the positive electrode terminal portion 13 is connected at one end thereof to the current collecting tab portion of the positive electrode of the laminated electrode assembly 100 by welding or the like, and at the other end thereof is a sheet-shaped outer package 80. One end of the negative electrode terminal portion 23 is connected to the current collecting tab portion of the negative electrode of the laminated electrode body 100 by welding or the like, and the other end is pulled out of the sheet-shaped exterior body 80. is

The sheet-like exterior body can be composed of, for example, a resin film, such as a nylon film (nylon 66 film, etc.), a polyester film (polyethylene terephthalate (PET) film, etc.), and the like. The thickness of the resin film is preferably 20-100 μm.

The sealing of the sheet-shaped exterior body is generally performed by heat-sealing the end portion of the resin film on the upper side of the sheet-shaped exterior body and the end portion of the resin film on the lower side of the sheet-shaped exterior body. For the purpose of facilitating the attachment, a heat-sealable resin layer may be laminated on the above-exemplified resin film for use in the sheet-like exterior body. Examples of the heat-sealable resin forming the heat-sealable resin layer include modified polyolefin films (modified polyolefin ionomer films, etc.), polypropylene and copolymers thereof. It is preferable that the thickness of the heat-sealable resin layer is 20 to 100 μm.

Also, a metal layer may be laminated on the resin film. The metal layer can be composed of an aluminum film (aluminum foil, including aluminum alloy foil), a stainless steel film (stainless steel foil), or the like. It is preferable that the thickness of the metal layer is 10 to 150 μm.

Moreover, the resin film that constitutes the sheet-like exterior body may be a film having a configuration in which the heat-sealable resin layer and the metal layer are laminated.

The shape of the sheet-like exterior body may be polygonal (triangle, quadrangle, pentagon, hexagon, heptagon, octagon) in plan view, or may be circular or elliptical in plan view. In the case of a polygonal sheet-like exterior body in a plan view, the positive electrode terminal portion and the negative electrode terminal portion may be pulled out from the same side or may be pulled out from different sides.

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

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

Example 1
<Positive electrode>
LiNi _0.6 Co _0.2 Mn _0.2 O ₂ having an average particle size of 3 μm and having an amorphous composite oxide of Li and Nb formed on the surface, using xylene (“ultra-dehydrated” grade) as a solvent; A sulfide solid electrolyte (Li ₆ PS ₅ Cl), a carbon nanotube ("VGCF" (trade name) manufactured by Showa Denko Co., Ltd.) as a conductive agent, and an acrylic resin binder were mixed at a mass ratio of 50:44:3. 3 and mixed with the solvent so that the solid content ratio is 50%, and stirred for 10 minutes with a Thinky mixer to prepare a uniform slurry.This slurry is applied to an Al foil having a thickness of 20 μm with an applicator. was applied with a gap of 200 μm, and vacuum drying was performed at 120° C. to obtain a positive electrode.

<Negative Electrode>
Using xylene (“super dehydrated” grade) as a solvent, graphite with an average particle size of 20 μm, a sulfide solid electrolyte (Li ₆ PS ₅ Cl), and an acrylic resin binder were mixed in a mass ratio of 50:47:3. was mixed with the solvent so that the solid content ratio was 50%, and stirred for 10 minutes with a thinky mixer to prepare a uniform slurry. This slurry was applied to a SUS foil having a thickness of 20 μm using an applicator with a gap of 200 μm, followed by vacuum drying at 120° C. to obtain a negative electrode.

<Solid electrolyte layer>
Using xylene (“super-dehydrated” grade) as a solvent, a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) with an average particle size of 1 μm, an acrylic resin binder, and a dispersant were mixed in a mass ratio of 100:3:1. and a solid content ratio of 40%, and stirred for 10 minutes with a Thinky mixer to prepare a uniform slurry. This slurry was applied onto a SUS foil having a thickness of 20 μm using an applicator with a gap of 200 μm, followed by vacuum drying at 120°C. The obtained solid electrolyte sheet was punched into a size of 10 mmφ, and the SUS foil was separated by pressing at 3.5 tons/cm ² to obtain a solid electrolyte layer.

<Assembly of electrode laminate>
The obtained positive electrode and negative electrode sheets are both punched into a size of 10 mmφ, and the positive electrode, the solid electrolyte layer, and the negative electrode are stacked in this order between the upper and lower pins of SUS, placed in a SUS cylinder, and pressed at 10 tons/cm ² . Thus, an electrode laminate was obtained.

<Coating>
In order to form the exposed portions 10a and 20a shown in FIG. 2, a masking tape having a diameter of 5 mm was put on the central portions of the Al foil of the positive electrode and the SUS foil of the negative electrode. The taped electrode laminate was immersed in a polyimide solution having a concentration of 10% by mass, immediately pulled out, and vacuum-dried at 150°C. After that, the tape was peeled off to form an exposed portion. The thickness of the coating layer was 40 μm.

<Battery assembly>
A SUS mesh is placed as a current collector on the inner bottom surface of a sealing can made of stainless steel, and the electrode laminate is stacked on the current collector so that the negative electrode faces the current collector. After arranging the mesh on the positive electrode of the laminate, the SUS mesh was arranged so as to be in contact with the upper and lower surfaces of the electrode laminate by covering and sealing with a stainless steel outer can. A coin-shaped all-solid-state lithium secondary battery having the same structure as that of No. 5 was produced.

Example 2
An electrode laminate was produced in the same manner as in Example 1, except that current collecting tabs were provided on the positive electrode and the negative electrode, the respective electrodes were punched into the shape shown in FIG. It was created. After that, a masking tape was put on the current collecting tab portion, and coating was performed in the same manner as in Example 1. A nickel tab with a sealant was connected to the current collecting tab by ultrasonic welding, an aluminum laminate film with a thickness of 150 μm was used as an exterior material, and the ends were sealed by heat welding to form a coin with a structure similar to that shown in FIG. A type all-solid-state lithium secondary battery was fabricated.

Comparative example 1
A coin-type all-solid lithium secondary battery was produced in the same manner as in Example 1, except that the electrode laminate was used as it was for battery assembly without forming a coating layer around it.

Each of the prepared batteries was subjected to constant current charging at a current value of 0.05 C until the battery voltage reached 4.2 V under a room temperature environment, followed by constant voltage charging at a voltage of 4.2 V until the current value reached 0.01 C. After charging, the battery was discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V, thereby measuring the discharge capacity (initial discharge capacity) at room temperature. Thereafter, each battery was charged again, and the impedance was measured at 0.1 Hz with an applied voltage of 10 mV in a fully charged state. Table 1 shows the result of converting the measured initial discharge capacity per 1 g of the positive electrode active material and the measurement result of the impedance.

As shown in Table 1, the batteries of Examples 1 and 2 had higher initial discharge capacity and lower impedance than the battery of Comparative Example 1, and had excellent discharge characteristics. This is probably because the coating layer suppressed the expansion and contraction of the electrode due to charging and discharging of the battery, and maintained good contact between the constituent materials of the electrode.

Each battery whose impedance was measured was subjected to constant current discharge at a current value of 0.5 C until the battery voltage reached 2.5 V. After measuring the discharge capacity at that time, the charge/discharge cycle was repeated under the following conditions at room temperature. . The charge/discharge in the measurement of the initial discharge capacity was regarded as the first cycle, and the charge/discharge in the measurement of the impedance was regarded as the second cycle, and the number of cycles was counted.

The charging is constant current charging at a current value of 0.5C until the battery voltage reaches 4.2V, and then constant voltage charging at a voltage of 4.2V until the current value reaches 0.05C. Voltage charging was performed, and constant current discharging was performed at a current value of 0.5C until the battery voltage reached 2.5V. In the discharge process of the 22nd cycle and the discharge process of the 43rd cycle, the current value was changed from 0.5C to 0.05C, and the discharge capacity was measured. FIG. 7 shows the result of converting the measured discharge capacity per 1 g of the positive electrode active material.

As shown in FIG. 7, the batteries of Examples 1 and 2 have low impedance and excellent discharge characteristics, so that even if the discharge current value is increased, there is little decrease in capacity, and charging and discharging can be continued even after the 22nd cycle. I was able to do it. On the other hand, in the battery of Comparative Example 1, the electrodes swelled and shrunk significantly as the battery was charged and discharged, and the contact between the electrode constituent materials could not be maintained as the cycles progressed. is no longer possible.

Reference Signs List 1 All-solid lithium secondary battery 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode current collector 13 Positive electrode terminal portion 10a Exposed portion 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode current collector 23 Negative electrode terminal portion 20a Exposed portion 30 Solid electrolyte layer 40 Coating layer 50 outer can 60 sealing can 70 gasket 80 sheet-like outer package 100 electrode laminate

Claims (4)

An all-solid lithium secondary battery having an electrode laminate in which a positive electrode and a negative electrode are laminated via a solid electrolyte layer, and an outer package provided with an outer can and a sealing can ,
The electrode laminate is surrounded by at least one resin (A) selected from the group consisting of polyimide, polyamideimide, polyetherimide, polyphenylene sulfide, polybenzimidazole, polyetheretherketone and polyvinylidene fluoride. an all-solid lithium secondary battery, wherein the all-solid lithium secondary battery is covered with a coating layer containing the lithium secondary battery, is enclosed in the exterior body, and is fixed by being sandwiched between the exterior can and the sealing can . 2. The all-solid lithium secondary battery according to claim 1, wherein an exposed portion not covered by the covering layer is provided in a portion of the periphery of the electrode laminate, and conductive connection with the outside is made through the exposed portion. next battery. 3. The all-solid lithium secondary battery according to claim 1, wherein the coating layer has a thickness of 10 to 200 μm. 4. The all-solid lithium secondary battery in accordance with claim 1, wherein at least one of said positive electrode, said negative electrode and said solid electrolyte layer contains a sulfide-based solid electrolyte.

Images