JP2022158106A - All-solid-state secondary battery and production method thereof - Google Patents

Abstract

To provide an all-solid-state secondary battery suppressed in a short circuit and excellent in load characteristics and cycle characteristics, and a production method thereof.SOLUTION: An all-solid-state secondary battery includes a positive electrode 10, a negative electrode 20 and a solid electrolyte layer 30 containing a sulfide-based solid electrolyte. The solid electrolyte layer 30 has a thickness of 15 μm or more and 120 μm or less. At a central part R2 of a cross section of the solid electrolyte layer 30, a porosity calculated from a scanning electron microscope (SEM) image is 3% or less, and the height of irregularities on the interface between the solid electrolyte layer 30 and the positive electrode 10 and the height of irregularities on the interface between the solid electrolyte layer 30 and the negative electrode 20 each are 7 μm or less. The solid electrolyte layer 30 can be obtained, for example, by a process in which a layered aggregate of sulfide-based solid electrolyte particles charged into a mold without using a solvent is subjected to pressure molding with a surface pressure of 1,000 MPa or more.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an all-solid secondary battery having excellent load characteristics and cycle characteristics and a method for manufacturing the same.

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

With the further development of equipment to which lithium ion secondary batteries are applied, there is a demand for longer life, higher capacity, and higher energy density of lithium ion secondary batteries. Furthermore, the reliability of lithium-ion secondary batteries with longer life, higher capacity, and higher energy density is also highly demanded.

However, the organic electrolyte used in the lithium-ion secondary battery contains an organic solvent, which is a combustible substance. In addition, with the recent trend toward higher energy densities in lithium ion secondary batteries and an increase in the amount of organic solvents in organic electrolytes, the reliability of lithium ion secondary batteries is required to be even higher.

Under the circumstances described above, an all-solid-state lithium secondary battery (all-solid-state secondary battery) that does not use an organic solvent has attracted attention. The all-solid secondary battery uses a molded body of a solid electrolyte that does not use an organic solvent, instead of a conventional organic solvent-based electrolyte.

Various improvements have been attempted in the all-solid secondary battery. For example, in Patent Document 1, the porosity of the solid electrolyte layer is 10% or less, and the surface roughness Rz1 of the positive electrode layer and the surface roughness Rz2 of the negative electrode layer satisfy the relationship Rz1+Rz2≦25. It is shown that a short circuit with the negative electrode layer can be suppressed.

According to Patent Document 1, the thickness of the solid electrolyte layer is preferably 20 μm or less from the viewpoint of improving the energy density of the battery. The positive electrode layer surface and the negative electrode layer surface are less uneven to prevent contact between the positive electrode layer and the negative electrode layer. Even in the case where the cathode layer and the anode layer are formed, short-circuiting between the positive electrode layer and the negative electrode layer is prevented.

In Patent Document 1, a solid electrolyte and a binder are mixed to prepare a mixture powder, and then the mixture powder is dispersed in a solvent to prepare a solid electrolyte layer forming paste. An electrolyte green sheet is formed on the surface of the supporting substrate by uniformly applying the solid electrolyte layer forming paste to the surface of the supporting substrate and drying the paste. Further, a positive electrode green sheet and a negative electrode green sheet are produced in the same manner as the electrolyte green sheet except that the positive electrode paste and the negative electrode paste are used. A positive electrode green sheet, a negative electrode green sheet, and the electrolyte green sheet are laminated, and the binder is burned off at a temperature of 300° C. or higher to assemble a coin-type all-solid battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

Further, in Patent Document 2, in the step of preparing a composition for forming a solid electrolyte layer in which a solid electrolyte is dispersed in a solvent, the solvent contains a compound such as 1-hydroxyethyl-2-alkenylimidazoline as a dispersant. It is disclosed that As a result, aggregation of the solid electrolyte can be suppressed, and unevenness on the surface of the solid electrolyte layer formed by applying and drying the composition for forming a solid electrolyte layer can be reduced. As a result, an all-solid lithium secondary battery having a surface roughness Ra of 1.0 μm or less at the interface between the positive electrode mixture layer and the solid electrolyte layer is assembled.

Japanese Patent No. 6729796 JP 2020-161364 A

However, in the all-solid-state battery of Patent Document 1, although the porosity of the solid electrolyte layer can be reduced, in the case of a material such as a sulfide-based solid electrolyte that may be denatured at high temperatures, the green sheet is heated to a temperature that burns out the binder. Since the binder remains in the solid electrolyte layer, the ionic conductivity of the solid electrolyte layer is lowered, and the problem of not being able to obtain sufficient load characteristics tends to occur. Further, as shown in Table 1, although the sum of the surface roughness Rz1 of the positive electrode layer and the surface roughness Rz2 of the negative electrode layer can be reduced, the surface roughness of the larger one of Rz1 and Rz2 is 10 μm. It is only a relatively large value compared to the above. For this reason, when the thickness of the solid electrolyte layer is reduced, the charge/discharge reaction may become non-uniform depending on the location, and the cycle characteristics may deteriorate.

In addition, in the all-solid-state battery of Patent Document 2, it is necessary to make the solid electrolyte into a paint, and in the case of a material that easily reacts with moisture such as a sulfide-based solid electrolyte, the water contained in the solvent and the solid electrolyte when making the paint , the ionic conductivity of the solid electrolyte layer is lowered, and the problem of not being able to obtain sufficient load characteristics tends to occur.

The present invention has been made in view of the above circumstances, and an object thereof is to improve the load characteristics of an all-solid secondary battery having a solid electrolyte layer containing a sulfide-based solid electrolyte.

An all-solid secondary battery in an embodiment of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer containing a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode. The solid electrolyte layer has a thickness of 15 μm or more and 120 μm or less, and a porosity calculated from a scanning electron microscope (SEM) image of the central portion of the cross section of the solid electrolyte layer is 3% or less, and It is characterized in that the height of unevenness of the interface between the solid electrolyte layer and the positive electrode and the negative electrode is 7 μm or less.

Further, the method for producing an all-solid secondary battery of the present invention includes a step of filling a mold with sulfide-based solid electrolyte particles without using a solvent to form a layered aggregate of sulfide-based solid electrolyte particles. and a step of pressure-molding the layered aggregate of the sulfide-based solid electrolyte particles with a surface pressure of 1000 MPa or more.

According to the present invention, load characteristics can be improved in an all-solid secondary battery having a solid electrolyte layer containing a sulfide-based solid electrolyte.

FIG. 4 is a diagram for explaining a region for measuring the porosity of a solid electrolyte layer; It is a gradation distribution histogram of the SEM image for explaining binarization. FIG. 4 is a diagram for explaining a method of measuring the thickness of a solid electrolyte layer and the unevenness of an interface; BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which represents typically an example of the all-solid-state secondary battery of this invention.

An all-solid secondary battery in an embodiment of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer containing a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode. The solid electrolyte layer has a thickness of 15 μm or more and 120 μm or less, a central portion of a cross section of the solid electrolyte layer has a porosity of 3% or less calculated from a scanning electron microscope (SEM) image, and The height of the unevenness of the interface between the electrolyte layer and the positive electrode and the negative electrode is 7 μm or less.

The solid electrolyte layer containing the sulfide-based solid electrolyte of the all-solid secondary battery has a thickness of 120 μm or less. This configuration can reduce the internal resistance of the battery. On the other hand, since the solid electrolyte layer has a thickness of 15 μm or more, even if the height of the irregularities at the interface between the solid electrolyte layer and the positive electrode and the interface between the solid electrolyte layer and the negative electrode are both close to 7 μm, the positive electrode It can prevent a short circuit due to contact between the and negative electrodes.

In addition, in the cross section of the solid electrolyte layer, the porosity of a region (central portion) including the center in the width direction and the center in the thickness direction is 3% or less. By configuring the porosity of the central portion of the solid electrolyte layer in such a manner, the filling rate of the solid electrolyte layer can be increased and the ionic conductivity can be improved. Further, the height of the unevenness at the interface between the solid electrolyte layer and the positive electrode (height in the thickness direction) and the height of the unevenness at the interface between the solid electrolyte layer and the negative electrode (height in the thickness direction) are each 7 μm or less. By configuring the interface of the solid electrolyte layer in this way, even if the thickness of the solid electrolyte layer is reduced, short circuits due to contact between the positive electrode and the negative electrode can be prevented, and variations in the thickness of the solid electrolyte layer can be suppressed. It is possible to make the reaction of the battery nearly uniform. As a result, the load characteristics of the all-solid secondary battery are improved.

As a result of the above, it is possible to provide an all-solid-state secondary battery with excellent load characteristics. and Goal 12 “Responsible consumption and production”.

In general, the porosity near the edges in the width direction of the solid electrolyte layer tends to be higher than the porosity in the central portion. By setting the porosity of the solid electrolyte layer to a value close to the porosity of the central portion also in the region (peripheral portion) centered at a position 100 μm from the end in the width direction of the cross section of the solid electrolyte layer and including the center in the thickness direction, the solid electrolyte layer As a whole, the filling factor can be increased and the ion conduction within the solid electrolyte layer can be made uniform. This is preferable because the charge/discharge reaction proceeds uniformly throughout and the load characteristics can be further improved. The difference in porosity between the peripheral portion and the central portion of the solid electrolyte layer is preferably 4% or less, more preferably 3% or less.

The target area of the SEM image for calculating the porosity is a rectangular area with a width direction length of 25 μm and a thickness direction length of 19 μm as a rough guide for both the peripheral portion and the central portion. . That is, as the porosity of the central portion, the porosity is calculated in a rectangular region having the above size including the center in the width direction and the center in the thickness direction of the cross section of the solid electrolyte layer. As the porosity of the peripheral edge portion, the porosity is calculated in a rectangular area of the above size centered at a position 100 μm from the end in the width direction of the cross section of the solid electrolyte layer and including the center in the thickness direction.

However, when the thickness of the solid electrolyte layer is approximately 24 μm or less, the length in the thickness direction of the rectangular region for which the porosity is to be calculated is reduced according to the thickness of the solid electrolyte layer. In this case, the length of the rectangular region in the thickness direction is set to 80% of the thickness of the solid electrolyte layer so that the rectangular region does not include the region near the positive electrode side interface and the region near the negative electrode side interface of the solid electrolyte layer. As a result, measurement variation can be reduced.

The solid electrolyte layer of the all-solid secondary battery has a thickness of 15 μm or more, and both the height of unevenness in the thickness direction of the interface with the positive electrode and the height of unevenness in the thickness direction of the interface with the negative electrode are However, even when the thickness is, for example, about 7 μm, it is possible to prevent a short circuit due to contact between the positive electrode and the negative electrode. Therefore, the restrictions on the conditions for pressure molding the sulfide-based solid electrolyte particles are reduced, making it easier to manufacture an all-solid secondary battery with excellent load characteristics.

The positive electrode may have a molded body of a positive electrode mixture containing a positive electrode active material powder, a conductive aid, and a solid electrolyte. The solid electrolyte of the positive electrode mixture may include, for example, a sulfide-based solid electrolyte. The positive electrode active material powder may be, for example, particles in which a lithium ion conductive coating material is formed on the surface of the positive electrode active material. In this case, the positive electrode active material powder may be, for example, primary particles in which a lithium ion conductive coating material is formed on the surface of the positive electrode active material.

The negative electrode may have a molded negative electrode mixture containing a negative electrode active material powder, a conductive aid, and a solid electrolyte. The solid electrolyte of the negative electrode mixture may include, for example, a sulfide-based solid electrolyte.

The method for producing the all-solid secondary battery includes, for example, a step of filling a mold with sulfide-based solid electrolyte particles without using a solvent to form a layered aggregate of the sulfide-based solid electrolyte particles; A step of pressure-molding the layered aggregate of the sulfide-based solid electrolyte particles with a surface pressure of 1000 MPa or more.

In the above manufacturing method, the mold is filled with the sulfide-based solid electrolyte particles by a dry process that does not use a solvent. This can prevent the reaction between the moisture contained in the solvent and the sulfide-based solid electrolyte particles. Also, by filling the mold and pressurizing, it is not necessary to use a binder. Therefore, it is not necessary to heat the sulfide-based solid electrolyte particles to the burnout temperature of the binder. Modification due to heating of the sulfide-based solid electrolyte particles can be suppressed. In addition, the inventors have found that by pressure-molding a layered aggregate of sulfide-based solid electrolyte particles filled in a mold in a dry manner at a surface pressure of 1000 MPa or more, the porosity is low, and the positive electrode and the negative electrode It has been found that a solid electrolyte layer having an interface roughness of 7 μm or less can be efficiently formed. By the production method described above, an all-solid secondary battery having a solid electrolyte layer containing a sulfide-based solid electrolyte and having excellent load characteristics can be obtained.

The manufacturing method may further include a step of stacking the positive electrode, the negative electrode and the solid electrolyte layer. In this case, the solid electrolyte layer is laminated so as to be arranged between the positive electrode and the negative electrode. The step of pressure-molding the layered aggregate of the sulfide-based solid electrolyte particles at a surface pressure of 1000 MPa or more includes stacking the layered aggregate of the sulfide-based solid electrolyte particles on at least one of the positive electrode and the negative electrode. It may be press-molded in a state. Alternatively, a layered assembly of sulfide-based solid electrolyte particles may be pressure-molded before being laminated on the positive electrode and the negative electrode.

From the viewpoint of manufacturing efficiency, it is preferable that the layered aggregate of the sulfide-based solid electrolyte particles is pressure-molded before being laminated on the positive electrode and the negative electrode. This is because this makes it easier to adjust the height of the unevenness at the interface between the solid electrolyte layer and the positive electrode and at the interface between the solid electrolyte layer and the negative electrode to 7 μm or less.

For example, the manufacturing method includes a first pressure molding step of pressure-molding a layered assembly of the sulfide-based solid electrolyte particles, and a pressure-molded layered assembly of the sulfide-based solid electrolyte particles. A second pressure molding step in which the negative electrode material is laminated on one surface and pressure molded, and a positive electrode material is laminated on the other surface of the pressure-molded layered assembly of the sulfide-based solid electrolyte particles. and a third pressure molding step of performing pressure molding. In this case, pressure molding may be performed at a surface pressure of 1000 MPa or more in at least one of the first pressure molding step, the second pressure molding step and the third pressure molding step. This makes it easier to adjust the height of the unevenness of each of the interfaces between the solid electrolyte layer and the positive and negative electrodes to 7 μm or less.

Hereinafter, embodiments will be described in detail. The same reference numerals are given to the same and corresponding configurations in the drawings, and the same description will not be repeated. In addition, in order to make the description easier to understand, in the drawings referred to below, the configuration may be shown in a simplified or schematic form, or some constituent members may be omitted.

(positive electrode)
The positive electrode of the all-solid secondary battery has a molded body of a positive electrode mixture containing a positive electrode active material, a conductive aid, a solid electrolyte, and the like. It is also possible to integrate the molded body and the current collector.

The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in conventionally known lithium ion secondary batteries, that is, an active material capable of absorbing and releasing Li ions. One type of substance may be used alone, or two or more types may be used in combination. For example, 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, In, A spinel-type lithium-manganese-containing oxide, Lix, which is at least one element selected from the group consisting of Nb, Mo, W, Y, Ru and Rh and is represented by 0.01≦ _x ≦0.5) Ni _{(1-yz) CoyMzO ( 2-k) Fl} (wherein M is Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, at least one element selected from the group consisting of Sn, Ca, Sr and W, 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 nickel-containing oxide having a layered structure, Li _x Co _{(1-y) My} O _(2-k) F _l (wherein M is at least one selected from the group consisting of Ni, Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W) 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, k + l < 1, −0.1 ≤ k ≤ 0.2, 0 ≤ l ≤ 0.1) LiM _1-x Q _x PO ₄ (where M is at least one element selected from the group consisting of Fe, Mn and Co, Q is Al, Mg, at least one element selected from the group consisting of Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, and represented by 0≦x≦0.5) An olivine-type lithium complex compound and the like can be mentioned.

In order to cope with the increase in voltage of batteries, it is preferable to contain a lithium-cobalt-containing oxide having a layered structure as a positive electrode active material.

When a sulfide-based solid electrolyte is used as the positive electrode solid electrolyte, the surface of the positive electrode active material is less likely to react with the sulfide-based solid electrolyte in order to prevent direct reaction between the solid electrolyte and the positive electrode active material. It is desirable to form a lithium ion conductive coating. Lithium niobium-containing oxides such as LiNbO ₃ are preferably used for the lithium ion conductive coating.

When a positive electrode mixture is pressure-molded to form a compact, or when a layered aggregate of sulfide-based solid electrolyte particles is pressure-molded to form a solid electrolyte layer, the positive electrode does not function even when a high pressure is applied. In order to prevent cracks or the like from occurring in the mixture compact, it is desirable to use the positive electrode active material as a powder of primary particles (positive electrode active material powder).

By using a powder of primary particles as the positive electrode active material, the powder having the surface coated with the lithium ion conductive coating material can also be composed of the primary particles.

In addition, if the average particle size of the positive electrode active material powder composed of primary particles having a lithium ion conductive coating material formed on the surface becomes too large, the particles will crack when pressed at high pressure, and the active material will break. Since the sulfide-based solid electrolyte may react, the average particle size of the positive electrode active material powder is 8 μm or less, preferably 6 μm or less.

On the other hand, if the average particle size of the positive electrode active material powder is too small, it becomes difficult to pack the positive electrode at a high density, resulting in a decrease in the capacity of the positive electrode. is preferred.

By using the positive electrode active material powder composed of the primary particles having the average particle size within the above range, the porosity of the positive electrode mixture compact can be set to, for example, 10% or less.

The average particle size of the positive electrode active material powder can be measured using a particle size distribution measuring device (particle size distribution measuring device manufactured by Microtrac Bell: (trade name) Microtrac “MT3300EXII”, etc.). It is obtained as the 50% diameter value (d50) in the volume-based integrated fraction when the integrated volume is determined from the particles. The same applies to the negative electrode active material and the solid electrolyte.

A commercial product can be used as the positive electrode active material powder composed of the primary particles. The positive electrode active material powder is desirably composed only of primary particles, but secondary particles may be partially mixed. However, in order to prevent the above-mentioned problems, the ratio of the secondary particles in the positive electrode active material powder is preferably 30% by mass or less, more preferably 15% by mass or less, and preferably 10% by mass or less. Especially preferred.

Moreover, the lithium ion conductive coating material can be formed on the surface of the positive electrode active material by a sol-gel method, a mechanofusion method, a CVD method, a PVD method, or the like.

The amount of the lithium ion conductive coating material to be formed increases the coverage of the surface of the positive electrode active material and facilitates its action. The amount is preferably 1% by mass or more, and more preferably 0.5% by mass or more. On the other hand, if the amount of the lithium ion conductive coating material formed is too large, the capacity per unit weight of the positive electrode active material powder will decrease. and more preferably 2% by mass or less.

In order to increase the capacity of the positive electrode, the content of the positive electrode active material powder in the positive electrode mixture is 65% by mass or more, preferably 70% by mass or more. On the other hand, in order to make the positive electrode mixture have excellent ionic conductivity and electronic conductivity by setting the content ratio of the solid electrolyte and the conductive aid in the positive electrode mixture to a certain level or more, the positive electrode in the positive electrode mixture The content of the active material powder is 85% by mass or less, preferably 80% by mass or less.

Carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, vapor grown carbon fiber (VGCF), carbon nanofiber, carbon nanotube, and the like can be used as the conductive additive for the positive electrode.

A sulfide-based solid electrolyte is desirably used for the solid electrolyte of the positive electrode in order to increase ion conductivity. Examples of sulfide-based solid electrolytes include compounds composed of Li, S, and P and, if necessary, halogen elements and Si as constituent elements, such as Li ₂ SP ₂ S ₅ and Li ₂ S—SiS. ₂ , Li ₂ SP ₂ S ₅ —GeS ₂ , Li ₂ S—B ₂ S ₃ system glass; Li ₁₀ GeP ₂ S ₁₂ (LGPS system); Li _7+x P _1-y Si _y S ₆ (−0. 6≦x≦0.6, 0.1≦y≦0.6), Li _7−x+y PS _6−x Cl _x+y (0.05≦y≦0.9, −3x+1.8≦y≦−3x+5. 7), Li _7-x PS _6-x Cl _y Br _z (x=y+z, 1<x≦1.8, 0.1≦z/y≦10). Among them, Li _7-x+y PS _6-x Cl _x+y (0.05≦y≦0.9, −3x+1.8≦y≦-3x+5.7), Li _7-x PS _6- Compounds having an aldirodite-type crystal structure such as xClyBrz ( _x = _y + _z , 1 < x ≤ 1.8, 0.1 ≤ z/y ≤ 10) are more preferable, and highly stable Li _7-x+y PS _6-x Cl _x+y (0.05≤y≤0.9, -3x+1.8≤y≤-3x+5.7) is particularly preferably used.

The average particle size of the sulfide-based solid electrolyte is preferably 0.1 μm or more in order to increase the filling property of the positive electrode mixture molded body having the positive electrode active material powder of the above particle size and to reduce the porosity. It is more preferably 5 μm or more, and preferably 5 μm or less.

The positive electrode mixture may contain other solid electrolytes together with the sulfide-based solid electrolyte or in place of the sulfide-based solid electrolyte. Solid electrolytes, oxide-based solid electrolytes, and the like are included.

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 alkali metal compounds of 1:1 to 20:1), and the like. 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.

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

However, in order to prevent the ionic conductivity of the positive electrode mixture from deteriorating, the proportion of solid electrolytes other than sulfide-based solid electrolytes in the total amount of solid electrolytes used in the positive electrode mixture should be 30% by mass or less. It is preferably 10% by mass or less, and particularly preferably does not contain other solid electrolytes.

The content of the solid electrolyte in the positive electrode mixture is preferably 15% by mass or more, more preferably 20% by mass or more, in order to increase ion conductivity. In order to ensure this, the content is preferably 35% by mass or less, more preferably 30% by mass or less.

The positive electrode mixture may contain a resin binder as necessary. Examples of resin binders include fluororesins such as polyvinylidene fluoride (PVDF) and acrylic resins such as acrylic acid-acrylic acid ester copolymers. However, since the resin binder acts as a resistance component in the positive electrode mixture, when the resin binder is contained, it is desirable to reduce the amount as much as possible. , more preferably 0.3% by mass or less, and most preferably 0% by mass (that is, containing no resin binder).

When a current collector is used for the positive electrode, the current collector may be foil of metal such as aluminum or stainless steel, punching metal, net, expanded metal, foamed metal, carbon sheet, or the like.

The thickness of the molded positive electrode mixture is preferably 200 μm or more, more preferably 500 μm or more, from the viewpoint of increasing the capacity of the battery. On the other hand, from the viewpoint of facilitating the formation of a molded body with a low porosity and improving load characteristics, the thickness of the positive electrode mixture molded body is preferably 2 mm or less, and preferably 1.2 mm or less. is more preferred.

In the case of a positive electrode having a current collector, the thickness of the molded positive electrode mixture per one side of the current collector may be within the above range.

(negative electrode)
The negative electrode of the all-solid secondary battery has a molded body of a negative electrode mixture containing a negative electrode active material, a conductive aid, a solid electrolyte, and the like. It is also possible to integrate the molded body and the current collector.

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. In addition, single elements such as Si, Sn, Ge, Bi, Sb, In, and Al that can form an alloy with lithium, alloys with elements that do not form alloys with lithium, and oxides of the above elements Lithium-containing nitrides; composite oxides such as lithium titanium oxides having a spinel structure; lithium metal; can also be used as the negative electrode active material.

In order to increase the capacity of the negative electrode, the content of the negative electrode active material in the negative electrode mixture is preferably 45% by mass or more, more preferably 50% by mass or more. On the other hand, in order to make the content ratio of the solid electrolyte and the conductive aid in the negative electrode mixture more than a certain level and to make the negative electrode mixture excellent in ionic conductivity and electronic conductivity, the negative electrode in the negative electrode mixture The content of the active material is preferably 65% by mass or less, more preferably 60% by mass or less.

Carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes can be used as the conductive aid for the negative electrode. The content of the conductive aid in the negative electrode mixture is preferably 5% by mass or more, more preferably 7% by mass or more, from the viewpoint of improving the electron conductivity in the negative electrode mixture molded body. . In addition, if the amount of the conductive agent in the negative electrode mixture is too large, voids tend to increase in the molded negative electrode mixture, making it difficult to increase the filling rate of the voids. There is a possibility that the energy density will become smaller. Therefore, from the viewpoint of reducing the porosity of the molded negative electrode mixture, the content of the conductive aid in the negative electrode mixture is preferably 15% by mass or less, more preferably 12% by mass or less.

It is desirable to use a sulfide-based solid electrolyte also for the solid electrolyte of the negative electrode in order to increase ion conductivity. As the sulfide-based solid electrolyte, the same solid electrolyte as exemplified as the sulfide-based solid electrolyte that can be used for the positive electrode mixture can be used, but a compound having an aldirodite-type crystal structure with higher ionic conductivity Li _7-x PS _6-x Cl _y Br _z (x=y+z, 1<x≦1.8, 0.1≦z /y≦10) is more preferably used. By using the solid electrolyte, the porosity of the negative electrode mixture during pressure molding, which will be described later, can be set to, for example, 20% or less, preferably 15% or less.

The negative electrode mixture may contain other solid electrolytes together with the sulfide-based solid electrolyte or in place of the sulfide-based solid electrolyte. Solid electrolytes, oxide-based solid electrolytes, and the like are included. For these solid electrolytes, the same solid electrolytes as those exemplified for the positive electrode mixture can be used.

However, in order to prevent the ionic conductivity of the negative electrode mixture from decreasing, the proportion of the solid electrolyte other than the sulfide-based solid electrolyte in the total amount of solid electrolyte used in the negative electrode mixture should be 30% by mass or less. It is preferably 10% by mass or less, and particularly preferably does not contain other solid electrolytes.

The content of the solid electrolyte in the negative electrode mixture is preferably 35% by mass or more, more preferably 40% by mass or more, in order to increase ion conductivity, while securing the content of the negative electrode active material. Therefore, it is preferably 55% by mass or less, more preferably 50% by mass or less.

The negative electrode mixture may contain a resin binder, if necessary. Examples of resin binders include fluororesins such as polyvinylidene fluoride (PVDF) and acrylic resins such as acrylic acid-acrylic acid ester copolymers. However, since the resin binder acts as a resistance component in the negative electrode mixture, when the resin binder is contained, it is desirable to reduce the amount as much as possible, and the content ratio is 0.5% by mass or less. , more preferably 0.3% by mass or less, and most preferably 0% by mass (that is, containing no resin binder).

When a current collector is used for the negative electrode, the current collector may be copper or nickel foil, punching metal, mesh, expanded metal, foamed metal, carbon sheet, or the like.

The thickness of the molded negative electrode mixture is preferably 200 μm or more, more preferably 500 μm or more, from the viewpoint of increasing the capacity of the battery. On the other hand, from the viewpoint of facilitating the formation of a molded body with a low porosity and improving load characteristics, the thickness of the molded body of the negative electrode mixture is preferably 3 mm or less, more preferably 2 mm or less. preferable. In the case of a negative electrode having a current collector, the thickness of the molded negative electrode mixture per one side of the current collector may be within the above range.

(Solid electrolyte layer)
A sulfide-based solid electrolyte is used as the solid electrolyte in the solid electrolyte layer of the all-solid secondary battery in order to increase ion conductivity. As the sulfide-based solid electrolyte, the same solid electrolyte as exemplified as the sulfide-based solid electrolyte that can be used for the positive electrode mixture can be used, but a compound having an aldirodite-type crystal structure with higher ionic conductivity is preferably used, and Li _7-x PS _6-x Cl _y Br _z (x=y+z, 1<x≦1.8, 0.1≦z/y≦10) is more preferably used.

The sulfide-based solid electrolyte preferably has an average particle size of 0.3 to 1.5 μm in order to reduce the porosity during pressure molding.

Note that the solid electrolyte layer may be composed of only one layer, but it can also have a laminated structure. The layer in contact with the positive electrode is made of a highly stable sulfide-based solid electrolyte such as Li _7-x+y PS _6-x Cl _x+y (0.05≦y≦0.9, -3x+1.8≦y≦-3x+5.7 ), and the layer on the negative electrode side is a sulfide-based solid electrolyte having high ion conductivity, such as Li _7-x PS _6-x Cl _y Br _z (x=y+z, 1<x≦1.8, 0.1≤z/y≤10).

The solid electrolyte layer may contain other solid electrolytes together with the sulfide-based solid electrolyte. In order to prevent the ionic conductivity of the solid electrolyte layer from decreasing, the content of the solid electrolyte other than the sulfide-based solid electrolyte in the solid electrolyte layer is preferably 30% by mass or less of the total solid electrolyte, and is preferably 10% by mass. % or less, and it is particularly preferable not to contain other solid electrolytes.

The thickness of the solid electrolyte layer is set to 15 μm or more, preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, in order to ensure insulation between the positive electrode and the negative electrode. On the other hand, in order to reduce the internal resistance of the battery, the thickness of the solid electrolyte layer is 120 μm or less, preferably 100 μm or less, more preferably 80 μm or less, and particularly preferably 60 μm or less.

(Laminate electrode body)
The molded body of the positive electrode mixture is composed of, for example, a positive electrode mixture prepared by mixing a positive electrode active material powder, a conductive aid, a solid electrolyte, and a binder added as necessary. It can be formed by putting the positive electrode material mixture into a mold to form a layer having a predetermined thickness, and then compressing it by pressure molding or the like. In addition, the molded body of the negative electrode mixture is composed of a negative electrode mixture prepared by mixing, for example, a negative electrode active material, a conductive agent, a solid electrolyte, and a binder added as necessary, It can be formed by putting the negative electrode mixture into a mold to form a layer having a predetermined thickness, and then compressing it by pressure molding or the like.

The molded body of the positive electrode mixture and the molded body of the negative electrode mixture are used as electrodes (positive electrode and negative electrode) as they are or by bonding them to a current collector by a method such as pressure bonding.

The solid electrolyte layer is produced, for example, by putting solid electrolyte particles into a mold to form a layer (a layered aggregate of solid electrolyte particles) having a predetermined thickness, and then compressing the layer in the thickness direction by pressure molding or the like. can be formed by The solid electrolyte particles are filled into the mold without any solvent or binder. That is, the solid electrolyte particles are filled into a mold in the form of a layered aggregate of particles without solvent and binder, and pressed. The solid electrolyte layer is used for assembling a battery in a state of being formed into a compact by pressing. The pressure during pressurization may be 1000 MPa or more in terms of surface pressure. This makes it easy to reduce the porosity of the solid electrolyte layer and reduce the height of the irregularities at the interface.

In addition, when pressurization is performed a plurality of times during the formation of the solid electrolyte layer, one pressurization should be 1000 MPa or more in terms of surface pressure. Further, the pressure when pressing the layered assembly of solid electrolyte particles may be 1200 Mpa or more.

The molded body of the positive electrode mixture and the molded body of the negative electrode mixture are laminated via the solid electrolyte layer and integrated to form a laminated electrode body, which is used for assembling a battery.

For example, the following conditions can be used as the conditions for producing the positive electrode mixture compact.

A positive electrode active material powder made of primary particles is mixed with a sulfide-based solid electrolyte or the like to prepare a positive electrode mixture containing the positive electrode active material powder at a ratio of 65 to 85% by mass, and this is put into a mold. A molded body of the positive electrode material mixture is produced by forming a layer of a predetermined thickness and applying pressure. The pressure at the time of pressurization is preferably 1000 MPa (10 ton/cm ² ) or more as surface pressure. This makes it easy to make the porosity of the molded body 10% or less.

^In addition, the negative electrode mixture molded body can be produced, for example, under the same conditions as those for the positive electrode mixture molded body. As described above, the filling rate can be increased.

The positive electrode mixture layer and the negative electrode mixture layer may be pressurized at one time. It may be pressurized with pressure to form the desired compact.

The order of laminating each layer is not limited. For example, a laminate may be formed by first forming a layer of the negative electrode mixture, forming a layer of the solid electrolyte thereon, and further forming a layer of the positive electrode mixture thereon. Alternatively, a solid electrolyte layer is formed first, one layer of the negative electrode mixture and the positive electrode mixture is formed on one side of the solid electrolyte layer, and the negative electrode mixture and the positive electrode mixture are formed on the other side of the solid electrolyte layer. The other layer of the agent may be formed to form a laminate.

Alternatively, the molded body of the positive electrode mixture, the solid electrolyte layer, and the molded body of the negative electrode mixture may be prepared separately in advance, and finally laminated and integrated. For example, the molded body of the positive electrode mixture, the solid electrolyte layer, and the molded body of the negative electrode mixture may be individually pressure-molded in advance.

In this way, a solid electrolyte layer is first produced by pressing a layered aggregate of solid electrolyte particles at a surface pressure of 1000 MPa, and then separately press-molded on both sides of the solid electrolyte layer. From the viewpoint of manufacturing efficiency, it is preferable to form a layer of the negative electrode mixture and a layer of the positive electrode mixture. This is because, in this case, it is easy to reduce the height of irregularities at the interface between the solid electrolyte layer and the positive electrode and the negative electrode, and it is easy to form a homogeneous solid electrolyte layer.

The surface pressure of each layer during pressurization is considered to be normally up to about 2000 MPa (20 ton/cm ² ) in consideration of productivity due to the restrictions of the manufacturing equipment. It is considered that the lower limit of the porosity of the molded body of the negative electrode mixture is about 5%.

The porosity of the molded body of the positive electrode mixture and the negative electrode mixture referred to in this specification is calculated from the thickness of the molded body, the mass per area, and the density of the constituent components using the following formula (1). is a value calculated by summing over

P = 100-(Σai/ρi)×(m/t) (1)

Here, in the above formula (1), ai: ratio of component i expressed in mass %, ρi: density of component i (g/cm ³ ), m: mass per unit area of compact (g/cm ² ), t: thickness (cm) of molded body.

In addition, the cross section of the molded body of the positive electrode mixture and the negative electrode mixture was observed with a scanning electron microscope (SEM), and the ratio of the void portion was obtained by binarization by image processing, and the porosity of the molded body of the positive electrode mixture was calculated. It may be calculated. In this case, it is desirable to determine the conditions of the image processing so that the value matches the porosity obtained by the above method.

The porosities of the central portion and peripheral portion of the solid electrolyte layer are measured as follows. Seen from the thickness direction, the solid electrolyte layer is cut along a plane parallel to the thickness direction through the longest line. SEM images of the peripheral portion and the central portion of the cut cross section are acquired.

FIG. 1 is a diagram for explaining regions (peripheral portion and central portion) where the porosity of a solid electrolyte layer is measured. In the example shown in FIG. 1, a cross section of an all-solid secondary battery including a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20 is cut. When viewed from the thickness direction (z direction in FIG. 1), the solid electrolyte layer 30 is cut in the thickness direction along the longest line in the width direction (x direction). In the example of FIG. 1, the shape of the solid electrolyte layer 30 seen from the thickness direction (top view shape) is circular. In this case, solid electrolyte layer 30 is cut in the thickness direction along a line passing through the center of the circle. If the top view shape is an ellipse, cut along the major axis of the ellipse. If the top view shape is a rectangle, cut along the center line between the two long sides. In the example shown in FIG. 1, R1 is the peripheral portion and R2 is the central portion.

The peripheral portion is a region centered at a position s = 100 μm from the end in the width direction of the cross section of the solid electrolyte layer interposed between the positive electrode and the negative electrode in the cross section and including the center in the thickness direction. length: 25 μm and length in the thickness direction: 19 μm. The central portion is a region including the center of the cross section of the layer (the center in the thickness direction and the center in the width direction) of the solid electrolyte layer interposed between the positive electrode and the negative electrode in the cross section, and has a length in the width direction of 25 μm and a length in the thickness direction of 25 μm. length: a rectangular area of 19 μm.

These SEM images of the peripheral part and the central part are binarized using image analysis software (such as ImageJ). The porosity is calculated by calculating the ratio.

Equipment and conditions to be used can be, for example, as follows.
Scanning electron microscope: Hitachi S4800
Detector: Backscattered electron enhancement mode Accelerating voltage: 2 kV
Magnification: 5,000 times Capture resolution: 2,560 x 1,920
Minimum dot length: 9.9 nm (circle equivalent diameter: 11.2 nm)
Minimum dot area: ^98nm2
Analysis area: 4.81×10 ⁸ nm ²

Grayscale conversion is performed on the obtained SEM image using Photoshop (registered trademark). At this time, a Gaussian filter (0.5 pixels) is used for noise reduction. Next, ImageJ quantifies the histogram of the SEM image. FIG. 2 is a diagram showing an example of a histogram of an SEM image. In the histogram, the luminance at the maximum frequency: a is taken as the central value. On the higher luminance side than the central value, the luminance at the frequency at which the numerical value is 3% of the maximum frequency: Read b, and further, on the lower luminance side than the central value, the numerical values are b and a than the central value A luminance d (=a−c) that is reduced by a difference: c (=b−a) is obtained, and the luminance d is used as a threshold value.

Further, the SEM image is divided into a low-luminance portion and a high-luminance portion by performing binarization with the threshold value d previously obtained using the image analysis software "Eizo-kun". The ratio of the area of the low-luminance portion in the SEM image is calculated as the porosity. At this time, the porosity is calculated by excluding the low-luminance portion below the threshold whose area is less than 900 nm ² (0.09×10 ⁻² μm ² ) because it is judged as a noise component.

It should be noted that the size of the rectangular region for acquiring the SEM image (backscattered electron image) can be changed according to the thickness of the solid electrolyte layer when the solid electrolyte layer is thin. When the thickness of the solid electrolyte layer is about 24 μm or less, the length of the rectangular region in the thickness direction is adjusted so that the rectangular region does not include the region near the positive electrode side interface and the region near the negative electrode side interface of the solid electrolyte layer. It may be 80% of the thickness of the electrolyte layer.

The solid electrolyte layer is formed such that the porosity of the central portion of the cross section of the solid electrolyte layer measured as described above is 3% or less, preferably 2% or less, and 1% or less. is more preferred.

Moreover, the porosity of the periphery of the solid electrolyte layer measured as described above is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less.

As for the thickness of the solid electrolyte layer and the height of the irregularities at the interface, values near the central portion measured as follows are used. Regarding the cross section of the solid electrolyte layer set when measuring the porosity, the unevenness of the interface between the positive electrode and the solid electrolyte layer and the unevenness of the interface between the solid electrolyte layer and the negative electrode in the cross section can be understood. An SEM image including regions of 100 μm each on both sides (regions with a length of 200 μm in the width direction as a whole) is obtained from the center of the cross section in the width direction. The SEM image may be an image of the entire region by combining a plurality of images acquired while shifting in the width direction. In the obtained SEM image of the entire region, as shown in FIG. 3, at the interface between the positive electrode and the solid electrolyte layer, a line L1 perpendicular to the thickness direction passing through the point closest to the solid electrolyte layer and a line L1 located closest to the positive electrode A line L2 passing through the point and perpendicular to the thickness direction is drawn. Similarly, at the interface between the negative electrode and the solid electrolyte layer, a line L3 passing through the point closest to the solid electrolyte layer and perpendicular to the thickness direction, and a line L4 passing through the point closest to the negative electrode and perpendicular to the thickness direction. Pull. In this case, the distance T1 between L1 and L3 is the thickness of the solid electrolyte layer. A distance H1 between the lines L1 and L2 is a value indicating the height of unevenness in the thickness direction of the interface between the positive electrode and the solid electrolyte layer. A distance H2 between the lines L3 and L4 is a value indicating the height of unevenness in the thickness direction of the interface between the negative electrode and the solid electrolyte layer.

The thickness of the solid electrolyte layer measured as described above is 15 μm or more. As a result, a short circuit can be prevented even if the thickness of the solid electrolyte layer formed by pressure-molding the sulfide-based solid electrolyte particles varies, that is, even if unevenness occurs to some extent at the interface of the solid electrolyte layer.

The height of the unevenness at the interface between the solid electrolyte and the positive electrode and the height of the unevenness at the interface between the solid electrolyte and the negative electrode, which are measured as described above, should be is 7 μm or less, preferably 5 μm or less, more preferably 3 μm or less.

At least one of the positive electrode mixture, the negative electrode mixture, and the composition for forming the solid electrolyte layer may be pressure-molded in a heated state. Since the solid electrolyte material is molded in a state of being softened by heating, the contact area between the active material and the solid electrolyte material or between the solid electrolyte materials increases, and the fillability of the compact can be improved.

The heating temperature may be, for example, 60 to 200° C., depending on the composition of the solid electrolyte material. From the viewpoint of suppressing denaturation of the sulfide-based solid electrolyte due to heating, the heating temperature in the step of forming the solid electrolyte layer is preferably 200° C. or lower, more preferably 150° C. or lower, and even more preferably 100° C. or lower.

(Battery form)
The all-solid secondary battery of the present invention can be configured as, for example, a coin-shaped battery. FIG. 4 is a schematic cross-sectional view of a coin-shaped battery. The battery 1 shown in FIG. 4 is formed of an outer can 40, a sealing can 50, and a resin gasket 60 interposed therebetween. The positive electrode 10 , the negative electrode 20 , and the solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20 are enclosed in the outer package.

The sealing can 50 is fitted to the opening of the outer can 40 via a gasket 60, and the open end of the outer can 40 is tightened inward, whereby the gasket 60 abuts the sealing can 50. , the opening of the exterior can 40 is sealed to form a sealed structure inside the device.

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.

The form of the all-solid secondary battery is not limited to a flat shape having an exterior body composed of an exterior can, a sealing can, and a gasket, as shown in FIG. Those having an exterior made of a film, or those having an exterior made of metal and having a bottomed cylindrical (cylindrical or rectangular) outer can and a sealing structure for sealing the opening. may be

The all-solid secondary battery of the present invention can be applied to the same uses as conventionally known secondary batteries, but has excellent heat resistance because it has a solid electrolyte instead of an electrolytic solution. It can be preferably used for 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)
<Production of laminated electrode body>
A sulfide-based solid electrolyte having an average particle size of 0.7 μm: 9.6 mg of powder of Li _5.4 PS _4.4 Cl _0.8 Br _0.8 is put into a powder molding mold and pressed at 70 MPa ( Pressure molding was performed at a pressure of 0.7 tf/cm ² ) to form a temporary molding layer of the solid electrolyte.

Next, lithium titanate (Li ₄ Ti ₅ O ₁₂ , negative electrode active material) having an average particle size of 2 μm and a Sulfide-based solid electrolyte: Negative electrode produced by mixing Li _5.4 PS _4.4 Cl _0.8 Br _0.8 and graphene (conductive assistant) at a mass ratio of 50:41:9 Mixture: 101 mg was added and press-molded at a pressure of 300 MPa (3 tf/cm ² ) to produce a laminate in which a temporary molded layer of the negative electrode was formed on one side of the temporary molded layer of the solid electrolyte.

Furthermore, after the mold having the laminate was turned upside down, LiCoO with an average particle size of 5 μm having a LiNbO ₃ coating layer formed on the surface was formed on the temporary molding layer of the solid electrolyte placed on the upper side. ₂ (positive electrode active material), a sulfide-based solid electrolyte: Li _7.0 PS _5.4 Cl _1.2 having an average particle size of 3 μm, carbon black, and vapor grown carbon fiber (VGCF), 73 mg of a positive electrode mixture prepared by mixing at a ratio of 70:26.8:1.1:2.1 was added, and pressure molding was performed at a pressure of 1300 MPa (13 tf/cm ² ) to form a negative electrode. The temporary molding layer, the temporary molding layer of the solid electrolyte, and the positive electrode mixture were compressed to obtain a laminated electrode body in which the negative electrode layer, the solid electrolyte layer having a thickness of 110 μm, and the positive electrode layer were integrated. The ratio of the weight of the coating layer to the total weight of the positive electrode active material powder including the coating layer was 2% by mass.

Regarding the cross section of the solid electrolyte layer, the porosity of the peripheral portion and the porosity of the central portion were determined by subjecting the SEM image obtained at a magnification of 5000 times to the image processing described above. The obtained porosity was 2.9% for the peripheral portion and 0.8% for the central portion. Further, the heights of the irregularities at the interfaces between the solid electrolyte layer and the positive and negative electrodes were 3.9 μm and 4.4 μm, respectively.

<Battery assembly>

A sealing can and an outer can made of stainless steel are used as an outer package, and a porous carbon sheet having a thickness of 0.1 mm is arranged between the sealing can and the outer can and the laminated electrode body for sealing. A coin-shaped all-solid-state secondary battery was assembled by performing.

(Comparative example 1)
A laminated electrode body was produced in the same manner as in Example 1 except that the pressure for pressure molding performed using a press after forming a laminate of three layers was 600 MPa (6 ton/cm ² ). An all-solid secondary battery was assembled.

Regarding the cross section of the solid electrolyte layer, the porosity obtained by image processing the SEM image obtained at a magnification of 5000 was 5.2% in the central portion and 7.9% in the peripheral portion. Further, the heights of the irregularities at the interfaces between the solid electrolyte layer and the positive and negative electrodes were 4.2 μm and 4.8 μm, respectively. The thickness of the solid electrolyte layer was 115 μm.

(Comparative example 2)
101 mg of the negative electrode mixture prepared in Example 1 was placed in a powder molding die and press-molded at a pressure of 300 MPa (3 tf/cm ² ) using a pressing machine to form a temporary molded layer of the negative electrode.
Next, 9.6 mg of powder of sulfide-based solid electrolyte: Li _5.4 PS _4.4 Cl _0.8 Br _0.8 having an average particle size of 0.7 μm is put on the temporary molded layer of the negative electrode. Then, pressure molding was performed at a pressure of 70 MPa (0.7 tf/cm ² ) to produce a laminate in which a temporary molded layer of solid electrolyte was formed on one side of the temporary molded layer of negative electrode.
Furthermore, 73 mg of the positive electrode mixture prepared in Example 1 was put on the temporary molding layer of the solid electrolyte, and pressure molding was performed at a pressure of 1300 MPa (13 tf/cm ² ) to temporarily mold the negative electrode. A laminated electrode body in which the negative electrode layer, the solid electrolyte layer, and the positive electrode layer were integrated was obtained by compressing the layer, the temporary molded layer of the solid electrolyte, and the positive electrode mixture.

Regarding the cross section of the solid electrolyte layer, the porosity obtained by image processing the SEM image obtained at a magnification of 5000 times was 1.0% in the central portion and 3.3% in the peripheral portion. Further, the heights of the irregularities at the interfaces between the solid electrolyte layer and the positive and negative electrodes were 7.8 μm and 8.8 μm, respectively. The thickness of the solid electrolyte layer was 111 µm.

(Comparative Example 3)
An all-solid coin-shaped electrode body was produced in the same manner as in Example 1, except that the amount of the sulfide-based solid electrolyte powder added was adjusted so that the thickness of the solid electrolyte layer after pressure molding was 10 μm. A secondary battery was assembled.

The following evaluations were performed on the all-solid secondary batteries of Example 1 and Comparative Examples 1 and 2. The all-solid secondary battery of Comparative Example 3 was not evaluated because a short circuit occurred.

<Load characteristics evaluation>
For the fabricated batteries of Example 1 and Comparative Examples 1 and 2, constant current charging was performed at a current value of 0.2 C until the battery voltage reached 3.1 V, and at a voltage of 3.1 V the current value reached 0.02 C. Constant-current-constant-voltage charging is performed by combining constant-voltage charging until the battery voltage reaches 0.1C. It was measured.

Next, constant current-constant voltage charging is performed in the same manner as described above, and constant current discharging is performed at a current value of 0.5 C until the battery voltage reaches 1.2 V, and the discharge capacity at 0.5 C is measured. did. The value (%) obtained by dividing the discharge capacity at 0.5C by the discharge capacity at 0.1C was obtained, and the load characteristics of each battery were evaluated.

<Cycle characteristics evaluation>
The batteries of Examples and Comparative Examples were subjected to 50 charge-discharge cycles in an environment of 100° C. under the following conditions.

Constant-current charging was performed at a current value of 0.2C until the voltage reached 3.1V, followed by constant-voltage charging at a voltage of 3.1V until the current value reached 0.02C, and then charging at a voltage of 0.2C. Repeat 50 cycles of charging and discharging cycles in which constant current discharge is performed until the voltage reaches 1.2 V at the current value. evaluated. Table 1 shows the evaluation results.

In the all-solid secondary battery of Example 1, a solid electrolyte layer having a thickness of 15 μm or more is formed by pressure-molding sulfide-based solid electrolyte particles, and the porosity of the central portion is 35% or less, and By setting the height of the irregularities at the interface between the solid electrolyte layer and the positive electrode and the negative electrode to 7 μm or less, the battery was excellent in load characteristics and cycle characteristics.

On the other hand, in the battery of Comparative Example 1, since the porosity of the central portion of the solid electrolyte layer exceeded 5%, the load characteristics and cycle characteristics were degraded. In the battery of Comparative Example 2, the height of the irregularities at the interface between the solid electrolyte layer and the positive electrode and negative electrode exceeded 7 μm, so that the cycle characteristics were degraded. Also, in the battery of Comparative Example 3 in which the thickness of the solid electrolyte layer was less than 15 μm, a short circuit occurred.

1 All Solid Secondary Battery 10 Positive Electrode 20 Negative Electrode 30 Solid Electrolyte Layer 40 Outer Can 50 Sealing Can 60 Gasket

Claims (2)

An all-solid secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer containing a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode,
The solid electrolyte layer has a thickness of 15 μm or more and 120 μm or less, and a porosity calculated from a scanning electron microscope (SEM) image of the central portion of the cross section of the solid electrolyte layer is 3% or less, and An all-solid secondary battery, wherein heights of irregularities at interfaces between a solid electrolyte layer and the positive electrode and the negative electrode are each 7 μm or less. A method for manufacturing the all-solid secondary battery according to claim 1,
filling a mold with sulfide-based solid electrolyte particles without using a solvent to form a layered aggregate of the sulfide-based solid electrolyte particles;
A method for producing an all-solid secondary battery, comprising a step of pressure-molding the layered aggregate of the sulfide-based solid electrolyte particles with a surface pressure of 1000 MPa or more.

Images