JP7313236B2 - Negative electrodes for all-solid-state batteries and all-solid-state batteries - Google Patents

Description

TECHNICAL FIELD The present invention relates to an all-solid battery having excellent output characteristics, and an all-solid battery negative electrode that can constitute the all-solid battery.

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 growing need for secondary batteries that are compact, lightweight, and have high capacity and high energy density.

Currently, in lithium secondary batteries, particularly 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 and the like are used as negative electrode active materials, and organic electrolyte solutions containing organic solvents and lithium salts are used as non-aqueous electrolytes.

With the further development of lithium-ion secondary battery application equipment, there is a demand for longer life, higher capacity, and higher energy density of lithium-ion secondary batteries.

However, since the organic electrolyte used in the lithium-ion secondary battery contains an organic solvent, which is a combustible substance, the organic electrolyte may generate abnormal heat when an abnormal situation such as a short circuit occurs in the battery. In addition, with the recent trends 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 battery) that does not use an organic solvent has attracted attention. The all-solid-state battery uses a molded body of a solid electrolyte that does not use an organic solvent instead of a conventional organic solvent-based electrolyte, and has a high degree of safety without the risk of abnormal heat generation of the solid electrolyte.

Various improvements have also been attempted in all-solid-state batteries. For example, Patent Document 1 proposes an all-solid-state battery that uses a titanium oxide such as lithium titanate as a negative electrode active material and uses an oxide-based solid electrolyte such as a glass electrolyte, a ceramics electrolyte, or a glass ceramics electrolyte. According to Patent Document 1, by adopting the above configuration, the discharge voltage of the all-solid-state battery can be increased, and the energy density can be increased.

By the way, since lithium titanate is a material with very low electronic conductivity, in order to use it as a negative electrode active material, it is necessary to increase the electronic conductivity in the negative electrode by incorporating a relatively large amount of conductive aid. In fact, in Patent Document 1, the upper limit of the preferable content of the conductive aid in the negative electrode material including the negative electrode active material and the solid electrolyte is set to a considerably large amount such as 20% by mass.

JP 2018-190695 A (Claims, [0045] etc.)

However, in the negative electrode of the all-solid-state battery, even if the amount of the conductive aid is increased to increase the electronic conductivity, the battery characteristics cannot be improved as expected, and in particular, the output characteristics (capacity during high-current discharge) are impaired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an all-solid battery having excellent output characteristics, and an all-solid battery negative electrode that can constitute the all-solid battery.

The negative electrode for an all-solid-state battery of the present invention has a molded body of a negative electrode mixture containing a negative electrode active material, a solid electrolyte, and a conductive aid, contains lithium titanium oxide as the negative electrode active material, and contains a sulfide-based solid electrolyte as the solid electrolyte, and the content of the conductive aid in the negative electrode mixture is 6.0 to 13.1% by volume.

Further, the all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and has the negative electrode for an all-solid-state battery of the present invention as the negative electrode.

According to the present invention, it is possible to provide an all-solid battery having excellent output characteristics, and an all-solid battery negative electrode that can constitute the all-solid battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which represents typically an example of the all-solid-state battery of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a top view which represents typically an example of the all-solid-state battery of this invention. FIG. 3 is a sectional view taken along line II of FIG. 2; 4 is a graph showing the evaluation results of the electrical conductivity of model cells using the all-solid-state battery negative electrodes of Examples and Comparative Examples.

<Negative electrode for all-solid-state battery>
The negative electrode for an all-solid-state battery of the present invention (hereinafter sometimes simply referred to as "negative electrode") has a molded body of a negative electrode mixture containing lithium titanium oxide as a negative electrode active material.

As described above, if the amount of the conductive aid in the negative electrode is increased in order to use lithium titanium oxide with low electronic conductivity as the active material, the output characteristics of the all-solid-state battery will deteriorate. This is because the particles of the conductive additive are relatively bulky, and therefore, when the amount of the conductive additive increases, the proportion of voids in the molded negative electrode mixture increases. In the case of a battery containing an organic electrolyte, if there are many voids in the molded negative electrode mixture, the organic electrolyte will permeate uniformly into the molded body, resulting in good ionic conductivity in the negative electrode. However, in the case of the negative electrode of the all-solid-state battery, ion conduction is performed by the solid electrolyte present in the molded body of the negative electrode mixture. Therefore, if the proportion of voids in the molded body increases, the contact between the lithium titanium oxide and the solid electrolyte becomes poor, and the ionic conductivity in the molded body decreases. In addition, when the amount of the conductive aid is increased, the volume ratio of the solid electrolyte in the electrode layer is decreased, so that the ionic conductivity inside the electrode is decreased.

Therefore, in the negative electrode of the present invention, a sulfide-based solid electrolyte having particularly excellent ionic conductivity is used as the solid electrolyte to be contained in the negative electrode mixture molded body. Furthermore, by determining the amount of the conductive aid that can maintain the ionic conductivity secured by the sulfide-based solid electrolyte as much as possible, the balance between both the ionic conductivity and the electronic conductivity can be adjusted, making it possible to form an all-solid-state battery with excellent output characteristics.

The negative electrode of the present invention has a molded body of a negative electrode mixture containing particles of lithium titanium oxide, which is a negative electrode active material, a solid electrolyte, a conductive aid, and the like.

Examples of lithium titanium oxides include those represented by the following general compositional formula (1).

Li[Li _1/3-a M ¹ _a Ti _5/3-b M ² _b ]O ₄ (1)

In the general composition formula (1), ^M1 is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba, and ^M2 is at least one element selected from the group consisting of Al, V, Cr, Fe, Co, Ni, Zn, Ym, Zr, Nb, Mo, Ta and W, where 0≦a<1/3 and 0≦b≦2/3.

That is, in the lithium titanium oxide represented by the general composition formula (1), part of the Li sites may be substituted with the element ^M1 . However, in the general compositional formula (1), a representing the ratio of the element ^M1 is preferably less than 1/3. In the lithium titanium oxide represented by the general composition formula (1), Li may not be substituted with the element ^M1 , so a representing the ratio of the element ^M1 may be zero.

In addition, in the lithium titanium oxide represented by the general composition formula (1), the element ^M2 is a component for increasing the electronic conductivity of the lithium titanium oxide, and when b representing the ratio of the element ^M2 is 0 ≤ b ≤ 2/3, the effect of improving the electronic conductivity can be satisfactorily secured.

For the negative electrode active material, a negative electrode active material other than the lithium titanium oxide used in lithium ion secondary batteries and the like can be used together with the lithium titanium oxide. However, the proportion of the negative electrode active material other than the lithium titanium oxide in the total amount of the negative electrode active material is preferably 30% by mass or less.

A sulfide-based solid electrolyte is used for the solid electrolyte of the negative electrode. A sulfide-based solid electrolyte has particularly excellent ionic conductivity among solid electrolytes that can be used in all-solid-state batteries, and by using this, it is possible to improve the balance between the ionic conductivity and the electronic conductivity in the molded body when the content of the conductive aid in the molded body of the negative electrode mixture is set to the value described later. In addition, by including the sulfide-based solid electrolyte in the negative electrode mixture, the moldability is improved, so that the productivity of the molded negative electrode mixture (that is, the productivity of the negative electrode) can be increased.

Examples of sulfide-based solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S--SiS _{2 ,} Li _{2 SP 2} S ₅ -GeS ₂ , and Li ₂ S--B ₂ S ₃ -based glasses. ₅ Cl (aldirodite series) can _{also be} used. Among these, an aldirodite-based material having particularly high lithium ion conductivity and high chemical stability is preferably used. As the sulfide-based solid electrolyte, only one type of those exemplified above may be used, or two or more types may be used in combination.

Although only a sulfide-based solid electrolyte may be used for the negative electrode, other solid electrolytes can also be used together with the sulfide-based solid electrolyte. Solid electrolytes that can be used in combination with sulfide-based solid electrolytes include hydride-based solid electrolytes and oxide-based solid electrolytes.

Examples of hydride-based solid electrolytes include solid solutions of LiBH ₄ , 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). Examples of the alkali metal compound in the solid solution include at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbiF, RbCl, etc.), 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, the proportion of solid electrolytes other than sulfide-based solid electrolytes in the total amount of solid electrolytes used in the negative electrode mixture is preferably 30% by mass or less.

Examples of conductive aids for the negative electrode include highly crystalline carbon materials such as graphite (natural graphite, artificial graphite), graphene (single-layer graphene, multi-layer graphene) and carbon nanotubes; low crystallinity carbon materials such as carbon black; and the like, and one or more of these can be used. Among these, highly crystalline carbon materials are preferable, graphite and graphene are more preferable, and graphene is even more preferable, because they are less bulky and less likely to form voids in the molded negative electrode mixture.

In the negative electrode mixture, the content of the conductive aid is 6% by volume or more, preferably 8% by volume or more, and 13.1% by volume or less, preferably 12% by volume or less. By setting the amount of the conductive additive in the negative electrode mixture to the above value, coupled with the use of the sulfide-based solid electrolyte, it is possible to ensure well-balanced ionic conductivity and electronic conductivity in the negative electrode mixture molded body, and it is possible to obtain a negative electrode that can form an all-solid-state battery with excellent output characteristics.

In order to improve the balance between the ionic conductivity and the electronic conductivity in the molded negative electrode mixture, when the volume of the lithium titanate is 100, the volume of the sulfide-based solid electrolyte is preferably 20 or more, more preferably 30 or more, preferably 160 or less, more preferably 150 or less, and the volume of the conductive aid is preferably 5 or more, more preferably 10 or more, and 35 or less. Preferably, it is 30 or less.

In the negative electrode mixture, the content of the negative electrode active material is preferably 30 to 70% by volume, and the content of the solid electrolyte is preferably 10 to 60% by volume.

The negative electrode mixture may or may not contain a binder. When the negative electrode mixture contains a binder, a fluororesin such as polyvinylidene fluoride (PVDF) can be used as the binder. When using a binder, the content of the binder in the negative electrode mixture is preferably 0 to 5% by volume.

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

The negative electrode can be manufactured by mixing lithium titanium oxide, which is an active material, a solid electrolyte, a conductive agent, etc., without using a solvent, for example, to prepare a negative electrode mixture, and molding this into a pellet shape or the like. Further, the molded body of the negative electrode mixture obtained as described above may be bonded to a current collector to form a negative electrode.

Alternatively, the negative electrode mixture and a solvent may be mixed to prepare a negative electrode mixture-containing composition, which may be coated on a base material such as a current collector or a solid electrolyte layer facing the negative electrode, dried, and then subjected to a press treatment to form a molded body of the negative electrode mixture.

It is preferable to select a solvent that does not easily deteriorate the solid electrolyte as the solvent used in the negative electrode mixture-containing composition. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes cause chemical reactions with minute amounts of water, so it is preferable to use nonpolar aprotic solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. 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 Co., Ltd., and "Novec (registered trademark)" manufactured by Sumitomo 3M Co., Ltd., and non-aqueous organic solvents such as dichloromethane and diethyl ether can also be used.

The thickness of the molded negative electrode mixture (including both cases where the negative electrode does not have a current collector and where the negative electrode has a current collector) is preferably 50 to 1000 μm.

The negative electrode mixture molded body preferably has a density (calculated from the mass and thickness per unit area of the negative electrode mixture molded body) of 1.9 g/cm or ^more . In order to increase the density of the molded negative electrode mixture, it is preferable to use a highly crystalline carbon material (preferably graphite or graphene), which makes it easy to adjust the density to the above value. Since the molded body of the negative electrode mixture does not need to be a porous body like the negative electrode of a battery containing an organic electrolyte, the upper limit of the density is a value (theoretical density) calculated from the density of each material constituting the negative electrode mixture.

<All-solid battery>
The all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the negative electrode is the negative electrode for the all-solid-state battery of the present invention.

FIG. 1 shows a cross-sectional view schematically showing an example of the all-solid-state battery of the present invention. In the battery 1 shown in FIG. 1, 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 are enclosed in an outer package formed of an outer can 40, a sealing can 50, and a resin gasket 60 interposed therebetween.

The sealing can 50 is fitted to the opening of the outer can 40 via a gasket 60, and the opening end of the outer can 40 is tightened inward, whereby the gasket 60 comes into contact with the sealing can 50, thereby sealing the opening of the outer can 40 and forming a sealed structure inside the element.

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

2 and 3 show drawings schematically showing other examples of the all-solid-state battery of the present invention. 2 is a plan view of an all-solid-state battery, and FIG. 3 is a cross-sectional view taken along the line II of FIG.

The all-solid-state battery 100 shown in FIGS. 2 and 3 contains an electrode body 200 composed of a positive electrode, a solid electrolyte layer, and the negative electrode of the present invention in a laminate film package 500 made up of two metal laminate films. The laminate film package 500 is sealed at its outer periphery by heat-sealing the upper and lower metal laminate films. In order to avoid complicating the drawing, FIG. 3 does not show each layer constituting the laminate film exterior body 500 or the positive electrode, the negative electrode, and the separator constituting the electrode assembly.

The positive electrode of the electrode assembly 200 is connected to the positive electrode external terminal 300 inside the battery 100 , and the negative electrode of the electrode assembly 200 is also connected to the negative electrode external terminal 400 inside the battery 100 , although not shown. One end of each of the positive electrode external terminal 300 and the negative electrode external terminal 400 is drawn out of the laminate film exterior body 500 so as to be connectable to an external device or the like.

(positive electrode)
A positive electrode of an all-solid-state battery contains a positive electrode active material and usually contains a solid electrolyte.

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 intercalating/releasing Li ions.正極活物質の具体例としては、ＬｉＭ _ｘ Ｍｎ _２－ｘ Ｏ _４ （ただし、Ｍは、Ｌｉ、Ｂ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ａｌ、Ｓｎ、Ｓｂ、Ｉｎ、Ｎｂ、Ｍｏ、Ｗ、Ｙ、ＲｕおよびＲｈよりなる群から選択される少なくとも１種の元素であり、０．０１≦ｘ≦０．５）で表されるスピネル型リチウムマンガン複合酸化物、Ｌｉ _ｘ Ｍｎ _{（１－ｙ－ｘ）} Ｎｉ _ｙ Ｍ _ｚ Ｏ _{（２－ｋ）} Ｆ _ｌ （ただし、Ｍは、Ｃｏ、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｕ、Ｚｎ、Ｚｒ、Ｍｏ、Ｓｎ、Ｃａ、ＳｒおよびＷよりなる群から選択される少なくとも１種の元素であり、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）で表される層状化合物、ＬｉＣｏ _１－ｘ Ｍ _ｘ Ｏ _２ （ただし、Ｍは、Ａｌ、Ｍｇ、Ｔｉ、Ｚｒ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ｎｂ、Ｍｏ、Ｓｎ、ＳｂおよびＢａよりなる群から選択される少なくとも１種の元素であり、０≦ｘ≦０．５）で表されるリチウムコバルト複合酸化物、ＬｉＮｉ _１－ｘ Ｍ _ｘ Ｏ _２ （ただし、Ｍは、Ａｌ、Ｍｇ、Ｔｉ、Ｚｒ、Ｆｅ、Ｃｏ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ｎｂ、Ｍｏ、Ｓｎ、ＳｂおよびＢａよりなる群から選択される少なくとも１種の元素であり、０≦ｘ≦０．５）で表されるリチウムニッケル複合酸化物、ＬｉＭ _１－ｘ Ｎ _ｘ ＰＯ _４ （ただし、Ｍは、Ｆｅ、ＭｎおよびＣｏよりなる群から選択される少なくとも１種の元素で、Ｎは、Ａｌ、Ｍｇ、Ｔｉ、Ｚｒ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ｎｂ、Ｍｏ、Ｓｎ、ＳｂおよびＢａよりなる群から選択される少なくとも１種の元素であり、０≦ｘ≦０．５）で表されるオリビン型複合酸化物、Ｌｉ _４ Ｔｉ _５ Ｏ _１２で表されるリチウムチタン複合酸化物などが挙げられ、これらのうちの１種のみを用いてもよく、２種以上を併用してもよい。

For the solid electrolyte of the positive electrode, one or more of the solid electrolytes exemplified above that can be used for the negative electrode can be used. In order to improve the battery characteristics, it is desirable to contain a sulfide-based solid electrolyte.

For the positive electrode, for example, a layer (positive electrode mixture layer) made of a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and optionally a conductive aid and a binder is formed on one or both sides of a current collector.

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.

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.

When manufacturing a positive electrode, for example, in the case of a positive electrode having a current collector, a positive electrode mixture-containing composition (paste, slurry, etc.) obtained by dispersing a positive electrode active material, a solid electrolyte, a conductive aid added as necessary, a binder, etc. in a solvent such as xylene is applied to the current collector, dried, and optionally subjected to pressure molding such as calendering to form a positive electrode mixture layer (positive electrode mixture layer) on the surface of the current collector.

As with the solvent used for the negative electrode mixture-containing composition, the solvent used for the positive electrode mixture-containing composition is preferably selected from those that do not easily deteriorate the solid electrolyte. It is preferable to use the various solvents exemplified above as the solvent for the negative electrode mixture-containing composition, and it is particularly preferable to use a super-dehydrated solvent having a water content of 0.001% by mass (10 ppm) or less.

Further, in the case of a positive electrode made of a molded positive electrode mixture, the positive electrode mixture prepared by mixing the positive electrode active material, the solid electrolyte, and optionally added conductive aid, binder, etc. can be formed by compression molding or the like.

As for the composition of the positive electrode mixture in the positive electrode, for example, the content of the positive electrode active material is preferably 50 to 90% by mass, the content of the solid electrolyte is preferably 10 to 50% by mass, and the binder content is preferably 0.1 to 10% by mass. Further, when the positive electrode mixture contains a conductive agent, the content is preferably 0.1 to 10% by mass. Furthermore, the thickness of the positive electrode mixture layer and the thickness of the positive electrode mixture molding in the positive electrode having a current collector is preferably 50 to 1000 μm.

(Solid electrolyte layer)
For the solid electrolyte in the solid electrolyte layer of the all-solid-state battery, one or more of the same solid electrolytes as exemplified above as the solid electrolyte for the negative electrode can be used. However, in order to improve the battery characteristics, it is desirable to contain a sulfide-based solid electrolyte, and it is more desirable to include a sulfide-based solid electrolyte in all of the positive electrode, the negative electrode, and the solid electrolyte layer.

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

As for the solvent used in the solid electrolyte layer-forming composition, it is desirable to select a solvent that does not easily deteriorate the solid electrolyte, similarly to the solvent used in the negative electrode mixture-containing composition. It is preferable to use the various solvents exemplified above as the solvent for the negative electrode mixture-containing composition, and it is particularly preferable to use an ultra-dehydrated solvent having a water content of 0.001% by mass (10 ppm) or less.

The thickness of the solid electrolyte layer is preferably 50-200 μm.

(electrode body)
The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body in which a solid electrolyte layer is interposed, or a wound electrode body in which the laminated electrode body is further wound.

When forming the electrode body, it is preferable from the viewpoint of increasing the mechanical strength of the electrode body that the positive electrode, the negative electrode, and the solid electrolyte layer are laminated and pressure-molded.

(Battery form)
The form of the all-solid-state battery has an exterior body composed of an exterior can, a sealing can, and a gasket, as shown in FIG.

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

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

Example 1
(Formation of solid electrolyte layer)
A sulfide-based solid electrolyte (Li ₆ PS ₅ Cl): 80 mg was placed in a powder molding die with a diameter of 10 mm, and pressure-molded using a press to form a solid electrolyte layer.

(Preparation of negative electrode)
Lithium titanate (Li ₄ Ti ₅ O ₁₂ ), the sulfide-based solid electrolyte, and graphite powder as a conductive aid were mixed at a mass ratio of 60: 31.5 : 8.5 and well kneaded to prepare a negative electrode mixture. Next, 15 mg of the negative electrode mixture was placed on the solid electrolyte layer in the powder molding mold, and pressure molding was performed using a press to form a negative electrode made of the negative electrode mixture compact on the solid electrolyte layer. The thickness of the negative electrode at this time was 91 μm.

(Formation of laminated electrode body)
As the counter electrode, a Li metal and an In metal were each formed into a cylindrical shape and bonded together. This counter electrode was placed on the surface of the solid electrolyte layer in the powder molding die on the side opposite to the negative electrode, and pressure molding was performed using a pressing machine to prepare a laminated electrode body.

(Assembly of model cell)
A model cell having a planar structure similar to that shown in FIG. 2 was fabricated using the laminated electrode assembly described above. A negative electrode current collector foil (SUS foil) and a counter electrode current collector foil (SUS foil) were placed side by side with a certain amount of space between them on the inner surface of the aluminum laminate film constituting the laminate film outer package. Each of the current collector foils was cut into a shape having a main body portion facing the negative electrode side surface or the counter electrode side surface of the laminated electrode body, and a portion to be the negative electrode external terminal 400 and the counter electrode external terminal 300 projecting from the main body portion toward the outside of the battery.

The laminated electrode body was placed on the negative electrode current collector foil of the laminated film outer body, the laminated electrode body was wrapped in the laminated film outer body so that the counter current collector foil was arranged on the counter electrode of the laminated electrode body, and the remaining three sides of the laminated film outer body were sealed by heat sealing under vacuum to obtain a model cell.

Example 2
A negative electrode mixture was prepared in the same manner as in Example 1 except that the mass ratio of lithium titanate, sulfide-based solid electrolyte, and graphite powder as a conductive aid in the negative electrode mixture was changed to 55: 40 : 5 , and a model cell was produced in the same manner as in Example 1 except that this was used. The thickness of the negative electrode (molded body of negative electrode mixture) was 100 μm.

Example 3
A negative electrode mixture was prepared in the same manner as in Example 1, except that the mass ratio of the lithium titanate, the sulfide-based solid electrolyte, and the graphite powder as the conductive aid in the negative electrode mixture was changed to 70: 25 : 5 , and a model cell was produced in the same manner as in Example 1, except that this was used. The thickness of the negative electrode (molded body of negative electrode mixture) was 97 μm.

Example 4
A negative electrode mixture was prepared in the same manner as in Example 1, except that the mass ratio of the lithium titanate, the sulfide-based solid electrolyte, and the graphite powder as the conductive aid in the negative electrode mixture was changed to 60:30:10 , and a model cell was produced in the same manner as in Example 1 , except that this was used. The thickness of the negative electrode (molded body of negative electrode mixture) was 91 μm.

Comparative example 1
A negative electrode mixture was prepared in the same manner as in Example 1, except that the mass ratio of the lithium titanate, the sulfide-based solid electrolyte, and the graphite powder as the conductive aid in the negative electrode mixture was changed to 41: 55 : 4 , and a model cell was produced in the same manner as in Example 1, except that this was used. The thickness of the negative electrode (molded body of negative electrode mixture) was 106 μm.

Comparative example 2
A negative electrode mixture was prepared in the same manner as in Example 1, except that the mass ratio of the lithium titanate, the sulfide-based solid electrolyte, and the graphite powder as the conductive aid in the negative electrode mixture was changed to 60:28:12 , and a model cell was produced in the same manner as in Example 1 , except that this was used. The thickness of the negative electrode (molded body of the negative electrode mixture) was 92 μm.

Output characteristics were evaluated under the following conditions for model cells having negative electrodes of Examples and Comparative Examples. First, each model cell was pressurized (1 t/cm ² ) and was subjected to constant current charging at a current value of 0.05 C until the voltage reached 0.38 V, followed by constant voltage charging at a voltage of 0.38 V until the current value reached 0.01 C, and then discharged at 0.05 C to 1.88 V. Next, each battery was subjected to constant-current charging at a current value of 0.05 C until the voltage reached 0.38 V, followed by constant-voltage charging at a voltage of 0.38 V until the current value reached 0.01 C. Then, the battery was discharged at a current value of 0.05 C until the depth of charge (SOC) reached 50%, and then rested for 1 hour. After that, each model cell was pulse-discharged at a current value of 0.05 C for 10 seconds, then the voltage was obtained, and the DCR was calculated from the value.

Then, from the obtained DCR of each model cell, the conductivity of each model cell was calculated using the following formula.
σ = (1/DCR) x (t/S)
In the above formula, σ: conductivity, t: thickness (cm) of electrode laminate, S: area of electrode laminate in plan view (cm ² )

The higher the conductivity obtained by this method, the better the output characteristics of the model cell (the larger the capacity during high-current discharge), and the negative electrode of the model cell can constitute an all-solid-state battery with excellent output characteristics.

Table 1 shows the structure of each negative electrode of Examples and Comparative Examples and the above evaluation results. The "volume ratio of sulfide-based solid electrolyte" and "volume ratio of conductive aid" in Table 1 mean values when the volume of lithium titanate in the negative electrode mixture is 100, and "conductivity" is expressed as a relative value when the value of Example 1 is 100.

FIG. 4 shows a graph in which the horizontal axis represents the content of the conductive aid in the negative electrode mixture and the vertical axis represents the conductivity. As shown in Table 1 and FIG. 4, the model cells having the negative electrodes of Examples 1 to 4, which are formed of negative electrode mixture compacts containing lithium titanate (lithium titanium oxide), a sulfide-based solid electrolyte, and an appropriate amount of conductive aid, have higher conductivity than the model cell having the negative electrode of Comparative Example 1 in which the amount of conductive aid is too small and the model cell having the negative electrode of Comparative Example 2 in which the amount of conductive aid is too large. had

1, 100 All-solid battery 10 Positive electrode 20 Negative electrode 30 Solid electrolyte layer 40 Packaging can 50 Sealing can 60 Gasket 200 Electrode assembly 300 Positive electrode external terminal 400 Negative electrode external terminal 500 Laminated film packaging

Claims (3)

A negative electrode used in an all-solid-state battery,
It has a molded body of a negative electrode mixture containing a negative electrode active material, a solid electrolyte and a conductive aid,
containing lithium titanium oxide as the negative electrode active material,
Containing a sulfide-based solid electrolyte as the solid electrolyte,
The content of the conductive aid in the negative electrode mixture is 6.0 to 13.1% by volume,
In the negative electrode mixture, when the volume of the lithium titanium oxide is 100, the volume of the sulfide-based solid electrolyte is 20 to 160, and the volume of the conductive aid is 5 to 35. A negative electrode for an all-solid battery. As the lithium titanium oxide, the following general composition formula (1)
Li[Li _1/3-a M ¹ _a Ti _5/3-b M ² _b ]O ₄ (1)
[In the general compositional formula (1), ^M1 is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba; ^M2 is at least one element selected from the group consisting of Al, V, Cr, Fe, Co, Ni, Zn, Ym, Zr, Nb, Mo, Ta and W;
The negative electrode for an all-solid-state battery according to claim 1, containing the compound represented by An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and having the negative electrode for an all-solid-state battery according to claim 1 or 2 as the negative electrode.

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