WO2017130674A1

WO2017130674A1 - Solid electrolyte and all-solid-state lithium battery using solid electrolyte

Info

Publication number: WO2017130674A1
Application number: PCT/JP2017/000372
Authority: WO
Inventors: 渉平鈴木; 純川治; 慎一折茂; 篤宇根本; 吉田　浩二
Original assignee: 株式会社日立製作所
Priority date: 2016-01-27
Filing date: 2017-01-10
Publication date: 2017-08-03
Also published as: JP2019071164A

Abstract

The purpose of the present invention is to provide a solid electrolyte which has a low contact resistance with respect to an electrode. In order to solve the above-described problem, a solid electrolyte according to the present invention contains Li, I, BH₄ and K, and is characterized in that x₁ and y satisfy 0.05 < x₁ ≤ 0.275, 0 < y ≤ 0.50 and 0.15 ≤ (y - x₁)/(1 - x₁), where X₁ is the molar fraction of K relative to the sum of Li and K, and y is the molar fraction of I relative to the sum of I and BH₄.

Description

All-solid lithium battery using fixed electrolyte and solid electrolyte

The present invention relates to a solid electrolyte and an all-solid lithium battery using the solid electrolyte.

An all-solid secondary battery using a solid electrolyte can improve high heat resistance. Further, since the electrolyte does not leak and does not volatilize, safety can be improved. Therefore, the module cost can be reduced and the energy density can be increased.

One example of this solid electrolyte is a hydride-based solid electrolyte. The hydride-based solid electrolyte is excellent in reduction resistance, and can generally be used without forming a high resistance layer with a highly reducing material used for the negative electrode of a lithium ion secondary battery.

Patent Document 1 discloses a LiBH ₄ -based solid electrolyte in which LiBH ₄ and an alkali metal compound are mixed as a solid electrolyte. It has been shown that high ionic conductivity can be obtained over a wide temperature range by mixing LiBH ₄ and an alkali metal compound.

Patent No. 5187703

The solid electrolyte described in Patent Document 1 has a problem that when the proportion of potassium atoms contained in the solid electrolyte is large, a large amount of potassium compound is precipitated in the solid electrolyte, thereby increasing the contact resistance with the electrode. Furthermore, when the proportion of potassium atoms contained in the solid electrolyte is small, the proportion of partial melting even when the solid electrolyte is heated to join the electrode is small, so the solid electrolyte and the electrode cannot be joined well. There is a problem that the contact resistance increases.

An object of the present invention is to provide a solid electrolyte having a low contact resistance with an electrode.

The features of the present invention for solving the above problems are as follows, for example.

A solid electrolyte containing Li, I, BH ₄ and K, wherein the molar fraction of K contained in the solid electrolyte relative to the sum of Li and K contained in the solid electrolyte is x ₁ , When the molar fraction of I contained in the solid electrolyte with respect to the sum of I and BH ₄ contained is y, 0.05 <x ₁ ≦ 0.275 and 0 <y ≦ 0.50 and 0.15 ≦ A solid electrolyte satisfying (yx ₁ ) / (1-x ₁ ).

According to the present invention, a solid electrolyte having a low contact resistance with an electrode can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a schematic cross-sectional view showing an all-solid lithium battery in one embodiment of the present invention. The fragmentary sectional view which shows the solid electrolyte before heat-melting process in one Embodiment of this invention The fragmentary sectional view which shows the solid electrolyte after heat-melting process in one Embodiment of this invention 1 is a partial cross-sectional view showing a solid electrolyte layer and a bonding agent layer before heating and melting treatment in an embodiment of the present invention. The fragmentary sectional view which shows the solid electrolyte layer and bonding agent layer after heat-melting process in one Embodiment of this invention The fragmentary sectional view which shows the state of the all-solid-state lithium battery before heat-melting process in one Embodiment of this invention The fragmentary sectional view which shows the state of the all-solid-state lithium battery after heat-melting process in one Embodiment of this invention The fragmentary sectional view which shows the state of the all-solid-state lithium battery before heat-melting process in one Embodiment of this invention

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

FIG. 1 is a cross-sectional view showing an all-solid-state lithium battery in one embodiment of the present invention. The all solid lithium battery 500 includes a negative electrode 70, a positive electrode 80, a solid electrolyte 100 disposed between the negative electrode 70 and the positive electrode 80, and a battery case 30 that houses the negative electrode 70, the positive electrode 80, and the solid electrolyte 100. I have. The negative electrode 70 includes the negative electrode current collector 10 and the negative electrode mixture layer 40. The positive electrode 80 includes the positive electrode current collector 20 and the positive electrode mixture layer 60. The solid electrolyte 100 has a solid electrolyte layer 50 and a bonding agent layer 90.

The negative electrode current collector 10 is electrically connected to the negative electrode mixture layer 40. As the negative electrode current collector 10, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like is used. In addition to copper, those formed of stainless steel, titanium, nickel or the like are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

The positive electrode current collector 20 is electrically connected to the positive electrode mixture layer 60. For the positive electrode current collector 20, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to aluminum, those formed of stainless steel, titanium or the like are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

The shape of the battery case 30 may be selected from shapes such as a cylindrical shape, a flat oval shape, a flat oval shape, and a square shape according to the shape of the electrode group composed of the negative electrode 70, the positive electrode 80, and the solid electrolyte 100. . The material of the battery case 30 is selected from materials that are corrosion resistant to the nonaqueous electrolyte, such as aluminum, stainless steel, nickel-plated steel, and the like.

<Example of solid electrolyte in which solid electrolyte and bonding agent are integrated before heating and melting treatment>
FIG. 2 is a partial cross-sectional view of solid electrolyte 100 before the heat-melting process in one embodiment of the present invention. The solid electrolyte 100 before the heat melting treatment includes solid electrolyte particles 63 and bonding agent particles 91. As the solid electrolyte particles 63, a hydride-based solid electrolyte can be used. Specifically, it is a solid solution (LiI—Li (BH ₄ ) solid solution) of lithium iodide and lithium borohydride. As the bonding agent particles 91, a mixture of lithium borohydride (Li (BH ₄ )) and potassium borohydride (K (BH ₄ )) (Li (BH ₄ ) -K (BH ₄ ) mixture) is used.

A method for manufacturing the solid electrolyte 100 shown in FIG. Specifically, (i) a step of producing a LiI-Li (BH ₄ ) solid solution, (ii) a step of mixing Li (BH ₄ ) and K (BH ₄ ), (iii) LiI-Li (BH ₄₎ ) A step of mixing the solid solution with the Li (BH ₄ ) —K (BH ₄ ) mixture, and (iv) a step of forming the solid electrolyte 100.

In (i), it manufactures, for example by the method of patent 5187703. In (ii), Li (BH ₄ ) and K (BH ₄ ) are mixed by, for example, a mixer or a planetary ball mill. In (iii), the LiI—Li (BH ₄ ) solid solution and the Li (BH ₄ ) —K (BH ₄ ) mixture are mixed by, for example, a mixer or a planetary ball mill. In (iv), the mixture obtained in (iii) is formed with a tableting machine, for example. Further, for example, the sheet-like solid electrolyte 100 is prepared by dispersing and coating the mixture with N-methyl-2-pyrrolidone (NMP) or tetrahydrofuran (THF), drying, and roll pressing.

As shown in FIG. 2, the entire solid electrolyte 100 can be melted by including the bonding agent particles 91 in the entire solid electrolyte 100. Therefore, when joining the solid electrolyte 100 and an electrode, it becomes easy to process the solid electrolyte 100 thinly by melting.

<Example of solid electrolyte in which solid electrolyte and bonding agent are integrated after heat-melting treatment>
FIG. 3 is a partial cross-sectional view of solid electrolyte 100 after the heat-melting process in one embodiment of the present invention.

A method for manufacturing the solid electrolyte 100 shown in FIG. Compared with the method for manufacturing the solid electrolyte 100 of FIG. 2, the above two steps are newly added: (v) a step of heating and melting treatment, (vi) a step of cooling.

In (v), the Li (BH ₄ ) -K (BH ₄ ) mixture as the bonding agent particles 91 is partially melted by the heat melting treatment, and the partially melted bonding agent particles 91 and the solid electrolyte particles 63 are LiI-Li. The (BH ₄ ) solid solution reacts with the reaction product Li _1-x1 K _x1 (BH ₄ ) _(1-y) I
_y is generated. x ₁ is the molar fraction of potassium (K) with respect to the amount of substance of the solid electrolyte particles 63 and the bonding agent particles 91. y is the molar fraction of iodine (I) with respect to the amount of substance of the solid electrolyte particles 63 and the bonding agent particles 91. At this time, in order to stabilize the shape of the molten electrolyte, it may be soaked into a thin film of cellulose fiber or glass fiber. Further, the higher the x ₁ , the higher the proportion of the volume to be melted, and the proportion of the bonded portion 95 and the precipitated phase particles 94 increases. On the other hand, a portion of the solid electrolyte particles 63 when x ₁ is less remains rest, the adhesive portion 95 and the precipitated phase particles 94 and the solid electrolyte particles 63 and is mixed electrolyte solid.

In (vi), the reactant Li _1-x1 K _x1 (BH ₄ ) _(1-y) I _y is cooled to room temperature, and as shown in the following (formula 1), the precipitated phase particle 94 is iodine Phase separation is performed into potassium halide (KI) and Li (BH ₄ ) _{(1-y) / (1-x1)} I _{(y-x1) / (1-x1)} which is the bonding portion 95.

Li _1-x1 K _x1 (BH ₄ ) _(1-y) I _y → x ₁ KI + (1-x ₁ ) Li (BH ₄ ) _{(1-y) / (1-x1)} I _{(y-x1) / (1-x1)} (Formula 1)
Through the above steps, the solid electrolyte 100 in which the precipitated phase particles 94 are deposited on the bonding portion 95 can be obtained.

<Mole fraction of I and room temperature conductivity>
When the molar fraction of I in the solid electrolyte 100, that is, the molar fraction of I with respect to the sum of the substance amounts of the solid electrolyte particles 63 and the bonding agent particles 91 is small, the solid electrolyte particles 63 undergo a phase transition to a low-temperature phase. The conductivity at room temperature (25 ° C. to 30 ° C.) is significantly reduced. That is, in order to improve the electrical conductivity at room temperature, y is desirably larger than a certain value. The electrical conductivity of the solid electrolyte 100 at room temperature is desirably 1 × 10 ⁻⁵ Scm ⁻¹ or more. Hereinafter, the conductivity at room temperature is referred to as room temperature conductivity.

<Mole fraction of I and contact resistance>
On the other hand, when y is large, there is a possibility that lithium iodide (LiI) precipitates at the bonding portion 95. Since LiI is a hard material, it causes peeling of the electrode mixture and the electrolyte layer, resulting in a solid electrolyte 100 having high contact resistance with the electrode. Therefore, in order to reduce the contact resistance, it is desirable to set the upper limit of y, and it is desirable that 0 <y ≦ 0.5.

<Relationship between K and I>
The larger the molar fraction of I in the solid electrolyte 100, the greater the room temperature conductivity of the solid electrolyte 100. However, when the precipitated phase particles 94 are precipitated in the solid electrolyte 100, the molar fraction of I decreases according to the amount of precipitated phase particles 94 deposited. That is, the room temperature conductivity of the solid electrolyte 100 becomes small. Therefore, by increasing the molar fraction of I as the molar fraction of K in the solid electrolyte 100 is increased, even when the precipitated phase particles 94 are precipitated, the molar fraction of I can be kept high. It can suppress that the room temperature conductivity of 100 becomes small. Therefore, it is desirable to increase the molar fraction of I as the molar fraction of K increases.

As described above, in the solid electrolyte 100 according to one embodiment of the present invention, the molar fraction of K and I is preferably within the following (formula 2).

0.15 ≦ (y−x ₁ ) / (1−x ₁ ) (Formula 2)
For simplification, (y−x ₁ ) / (1−x ₁ ) = X.

<Mole fraction of K and contact resistance>
As x ₁ is higher as described above, the ratio of the volume of melt is increased. In addition, the amount of precipitated phase particles 94 (KI) deposited in the solid electrolyte 100 increases. On the other hand, when x ₁ is too high, the number of precipitation amount of KI is stiff material, not withstand the volumetric expansion and shrinkage due to charge and discharge, poor bonding between the electrodes. Therefore, it is desirable that x ₁ ≦ 0.275.

Further, the bonding agent particles 91 need to be sufficiently melted in order to form the bonding portion 95. Bonding agent particles 91, the rate of melting as x ₁ is high increases. That is, the contact resistance between the electrode and lower solid electrolyte 100, desirably a 0.05 _{<x 1.}

As described above, in the solid electrolyte 100 of the present invention, it is desirable that 0.05 <x ₁ ≦ 0.275.

<Example of solid electrolyte before heat melting treatment>
FIG. 4 is a partial cross-sectional view of solid electrolyte 100 before the heat-melting process in one embodiment of the present invention. The bonding agent layer 90 before the heat melting treatment includes bonding agent particles 91. As the bonding agent particles 91, the same material as described in FIG. 2 is used. As the solid electrolyte particles 63 used for the solid electrolyte layer 50, the same materials as described in FIG. 2 are used.

Unlike FIG. 2, in the embodiment of the present invention shown in FIG. 4, the location where the bonding agent particles 91 are included and the location where the solid electrolyte particles 63 are included in the solid electrolyte 100 are separated.

The thickness of the bonding agent layer 90 formed on the solid electrolyte 100 is desirably 5 μm or more. If the bonding agent layer 90 is thinner than this, the bonding effect may be insufficient.

A method for manufacturing the solid electrolyte 100 shown in FIG. Specifically, (i) a step of manufacturing a LiI-Li (BH ₄ ) solid solution, (ii) a step of mixing Li (BH ₄ ) and K (BH ₄ ), (iii) forming the solid electrolyte layer 50 And (iv) a step of forming the bonding agent layer 90 on one surface of the solid electrolyte layer 50.

(I) and (ii) are the same as the method described in FIG. In (iii), the manufactured LiI—Li (BH ₄ ) solid solution is formed on the pellet-shaped solid electrolyte layer 50 by, for example, a tableting machine. Further, for example, the sheet-like solid electrolyte layer 50 is formed by dispersing and applying the mixture with N-methyl-2-pyrrolidone (NMP) or tetrahydrofuran (THF), drying, and roll pressing. In (iv), the bonding agent layer 90 is formed on the pellet-shaped solid electrolyte layer 50 obtained in (iii) with, for example, a tableting machine. Further, for example, the bonding agent layer 90 is formed by dispersing and applying a bonding agent on the sheet-like solid electrolyte layer 50 with N-methyl-2-pyrrolidone (NMP) or tetrahydrofuran (THF), drying, and roll pressing. .

As shown in FIG. 4, the solid electrolyte layer 50 on the bonding agent layer 90 side can be melted by forming the solid electrolyte layer 50 and the bonding agent layer 90 separately. As a result, when the solid electrolyte 100 and the electrode are joined, the joining of the solid electrolyte 100 and the positive electrode mixture layer 60 is improved without partially melting a hydride-based solid electrolyte 67 in the negative electrode mixture layer 40 described later. it can.

<Example of solid electrolyte after heat melting treatment>
FIG. 5 is a partial cross-sectional view of solid electrolyte 100 after the heat-melting treatment in one embodiment of the present invention. By the heat melting treatment, the bonding agent particles 91 of the bonding agent layer 90 are partially melted. Then, the partially melted bonding agent particles 91 react with the solid electrolyte particles 63 in the solid electrolyte layer 50 in contact with the partially melted bonding agent particles 91, and Li _1-x2 K _x2 (BH ₄ ) _{(1-y )} I _y is generated. x ₂ is the molar fraction of potassium (K) with respect to the amount of the bonding agent particles 91 contained in the bonding agent layer 90. When this reaction product Li _1-x2 K _x2 (BH ₄ ) _(1-y) I _y is cooled to room temperature, it phase-separates as shown in (Formula 1), and an adhesive portion 95 and precipitated phase particles 94 are generated. The bonding portion 95 penetrates a part between the solid electrolyte particles 63 constituting the solid electrolyte layer 50.

As shown in FIG. 5, the solid electrolyte 100 after the heat-melting treatment indicates the solid electrolyte layer 50 and the adhesive portion 95. The room temperature conductivity of the solid electrolyte 100 after the heat-melting treatment is preferably 1 × 10 ⁻⁵ Scm ⁻¹ or more.

A manufacturing method of the solid electrolyte 100 shown in FIG. Compared with the manufacturing method of the solid electrolyte 100 of FIG. 4, (v) the process of heat-melting treatment and (vi) the process of cooling are performed.

In (v), the partially melted bonding agent particles 91 react with the solid electrolyte particles 63 that are in contact with each other by the heat melting treatment to become Li _1-x2 K _x2 (BH ₄ ) _(1-y) I _y .

In (vi), the reactant Li _1-x2 K _x2 (BH ₄ ) _(1-y) I _y is cooled to cause phase separation, and the adhesion portion 95 and the precipitated phase particles 94 are precipitated. Here, the molar fraction of I at the bonding portion 95 is represented by (yx ₁ ) / (1-x ₁ ) after the following (Formula 3), This is because I and BH ₄ are interdiffused between the solid electrolyte layer 50 and the bonding portion 95 until the rate is not biased.

Li _1-x2 K _x2 (BH ₄ ) _(1-y) I _y → x ₂ KI + (1-x ₂ ) Li (BH ₄ ) _{(1-y) / (1-x2)} I _{(y-x2) / (1-x2)} (Formula 3)
For the above-described reason, it is desirable that the values of y and x ₁ fall within the range of (Expression 2).

Through the above steps, the bonding portion 95 in which the precipitated phase particles 94 are deposited can be generated in the vicinity of the bonding agent layer 90 or the bonding surface between the bonding agent layer 90 and the solid electrolyte layer 50.

<Example of an all-solid-state lithium battery when the solid electrolyte and the bonding agent are different>
FIG. 6 is a partial cross-sectional view schematically showing a part of the inside of the battery in one embodiment of the present invention, showing the negative electrode mixture layer 40, the solid electrolyte 100, and the positive electrode mixture layer 60.

6, the solid electrolyte 100 includes the solid electrolyte layer 50 and the bonding agent layer 90, and is sandwiched between the negative electrode mixture layer 40 and the positive electrode mixture layer 60. The solid electrolyte layer 50 includes solid electrolyte particles 63. And between the solid electrolyte layer 50 and the positive mix layer 60, the bonding agent layer 90 is arrange | positioned in order to improve both bondability. The bonding agent layer 90 is composed of bonding agent particles 91.

In the negative electrode mixture layer 40, a negative electrode active material 54 and a hydride-based solid electrolyte 67 are dispersed. In addition, in this drawing, the negative electrode mixture layer 40 includes a negative electrode conductive additive or a negative electrode binder 69. In addition, although it is not essential about the negative electrode conductive support agent or the negative electrode binder 69, it may be contained.

Meanwhile, a positive electrode active material 62 and a positive electrode Li conductive binder 66 (a positive electrode lithium conductive binder) are dispersed in the positive electrode mixture layer 60. In addition, in this drawing, the positive electrode mixture layer 60 includes a positive electrode conductive additive or a positive electrode binder 68. In addition, although it is not essential about the positive electrode conductive support agent or the positive electrode binder 68, it may be contained.

FIG. 7 is a partial cross-sectional view showing a state after the heat-melting treatment of the bonding agent layer 90 in the all solid lithium battery of FIG.

In FIG. 7, the bonding agent particles 91 are melted, and a part thereof penetrates into the solid electrolyte layer 50 and the positive electrode mixture layer 60 to form an adhesive portion 95. As described with reference to FIG. 5, KI that is the precipitated phase particles 94 generated by the phase separation is distributed. The bonding portion 95 penetrates a part between the particles constituting the solid electrolyte layer 50 and the positive electrode mixture layer 60. In addition, the adhesion part 95 may be in a state of penetrating all the particles constituting the solid electrolyte layer 50 and the positive electrode mixture layer 60. That is, the configuration may be such that the adhesive portion 95 penetrates and the precipitated phase particles 94 are distributed over the entire region of the solid electrolyte layer 50 and the positive electrode mixture layer 60. Furthermore, the solid electrolyte 100 of FIG. 6 does not need to be divided into the solid electrolyte layer 50 and the bonding agent layer 90, and may be a solid electrolyte such as the solid electrolyte 100 of FIG.

The contact property is improved as compared with a case where the positive electrode mixture layer 60 and the solid electrolyte 100 are mechanically pressurized and brought into contact with each other by the heat melting treatment. And even if the volume change accompanying charging / discharging of a battery arises, a contact interface becomes difficult to peel.

Note that the temperature of the lithium ion secondary battery during heating is lower than the heat resistant temperature of the lithium ion secondary battery. Thereby, the interface between the positive electrode mixture layer 60 and the solid electrolyte 100 does not peel off even when the volume changes due to charging / discharging, and stable battery operation becomes possible.

The bonding agent particles 91 constituting the bonding agent layer 90 are materials that soften at a temperature lower than the melting point of the solid electrolyte layer 50 and fill the physical gap between the positive electrode mixture layer 60 and the solid electrolyte layer 50. It is desirable.

The solid electrolyte particles 63 used in the solid electrolyte layer 50 are excellent in reduction resistance, and are easily deformed by pressurization even at room temperature, so that they can be easily filled between the negative electrode active material particles.

<Positive electrode mixture layer 60>
The positive electrode mixture layer 60 includes at least a positive electrode active material 62 and a positive electrode Li conductive binder 66.

Examples of the positive electrode active material 62 include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M _x O ₂ (where M is And at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ti, and x = 0.01 to 0.2). The positive electrode active material 62 may include one or more of the above materials. In the positive electrode active material 62, lithium ions are desorbed in the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer 40 are inserted in the discharging process.

The particle diameter of the positive electrode active material 62 is normally specified so as to be equal to or less than the thickness of the positive electrode mixture layer 60. When the powder of the positive electrode active material 62 has coarse particles having a size equal to or larger than the thickness of the mixture layer, the coarse particles are previously removed by sieving classification or wind classification to produce particles having a thickness of the mixture layer or less. Is preferred.

The positive electrode Li conductive binder 66 has high Li ion conductivity (lithium ion conductivity), exhibits good oxidation resistance with respect to the potential of the positive electrode active material 62, and enters the gap between the positive electrode active materials 62. Materials that can be used can be used. As for the oxidation resistance, it is desirable that the oxidation resistance is 3.5 V or higher in view of the potential of the positive electrode active material 62 and 4 V or higher from the viewpoint of high energy density. As a material that can enter the gap between the positive electrode active materials 62, a heat-meltable material that melts by heat or a deliquescence material that melts by deliquescence can be used.

Examples of the heat-meltable material that can be used as the positive electrode Li conductive binder 66 include Li ₃ BO ₃ and Li _3-x C _x B _1-x O ₃ (0 <x <1). The heat-meltable material can efficiently enter the gaps between the positive electrode active materials 62 by flowing by heating.

In addition, since the positive electrode active material 62 is generally oxide-based and has high electrical resistance, a conductive aid for supplementing electrical conductivity may be used. When the positive electrode mixture layer 60 includes a positive electrode conductive agent or a positive electrode binder, examples of the positive electrode conductive agent include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. Alternatively, oxide particles exhibiting electronic conductivity such as indium-tin-oxide (ITO) and antimony-tin-oxide (ATO) can be used.

Since both the positive electrode active material 62 and the positive electrode conductive agent are usually powders, a binder having a binding ability can be mixed with the powders to bond the powders to each other and to be bonded to the positive electrode current collector 20 at the same time. Examples of the positive electrode binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVdF), and a mixture thereof.

As shown in FIG. 8, the positive electrode mixture layer 60 may include an oxide solid electrolyte layer 81 made of oxide solid electrolyte particles. In other words, the oxide solid electrolyte layer 81 may be provided in a portion where the positive electrode mixture layer 60 and the bonding agent layer 90 are in contact with each other. In addition, this figure has shown the state before performing the heat-melting process to the binder particle | grains 91 which comprise the binder layer 90. FIG. Although not shown after the heat-melting treatment, the melted bonding agent particles 91 permeate the adjacent solid electrolyte layer 50, oxide solid electrolyte layer 81, and the like to form an adhesive portion. By providing the oxide solid electrolyte layer 81, the deterioration rate of the active material particles at the time of battery use can be suppressed, and it is desirable because the life becomes long.

Examples of the oxide solid electrolyte that can be used include solid oxides such as perovskite oxide, NASICON oxide, LISICON oxide, and garnet oxide, and β-alumina. The thickness of the oxide solid electrolyte layer 81 is 1 μm to 10 μm, preferably 5 μm to 10 μm. When the thickness is less than the above range, the protective effect of the positive electrode active material 62 by the oxide solid electrolyte layer is not exhibited. If the thickness is larger than the above range, the resistance increases in proportion to the film thickness, and the battery characteristics deteriorate, which is not desirable.

<Negative electrode mixture layer 40>
The negative electrode mixture layer 40 includes a negative electrode active material 54 and a hydride-based solid electrolyte 67, and may include a negative electrode conductive additive or a negative electrode binder 69. The hydride-based solid electrolyte 67 is dispersed so as to enter the voids between the particles of the negative electrode active material 54. When the hydride-based solid electrolyte 67 enters the gap, the lithium ion conductivity between the negative electrode active materials 54 is increased. Even when the negative electrode active material 54 expands and contracts, the hydride-based solid electrolyte 67 can maintain the lithium ion path between the negative electrode active materials 54.

As the hydride-based solid electrolyte 67, an electrolyte material that is durable with respect to the negative electrode potential and that can enter the voids formed between the negative electrode active materials 54 can be used. Examples of the hydride-based solid electrolyte 67 include solid solutions of LiBH ₄ and lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH ₂ ).

The particle diameter of the negative electrode active material 54 is normally defined so as to be equal to or less than the thickness of the negative electrode mixture layer 40. In the case where there are coarse particles having a size equal to or larger than the thickness of the mixture layer in the powder of the negative electrode active material 54, the coarse particles are removed in advance by sieving classification, wind classification, etc. It is preferable to produce it. The particle size of the negative electrode active material 54 is 0.1 μm to 5 μm. The smaller the active material particle size, the shorter the Li diffusion distance in the active material, so that the battery resistance is lowered. However, agglomeration is likely to occur, so that the active material utilization rate is lowered. When the negative electrode mixture layer 40 includes a conductive additive or binder, examples of the conductive aid include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. Examples of the binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), and a mixture thereof.

<Mole fraction of K>
In the configuration of the present invention, when x ₂ is too high, the surface contacting the solid electrolyte 100 and the positive electrode 80, the number precipitation amount of KI is stiff material, not withstand the volumetric expansion and shrinkage due to charge and discharge, the electrode The joint is not good. Therefore, it is desirable that x ₂ is smaller than a certain value. On the other hand, when y is too high, Li (BH ₄ ) _{(1-y) / (1-x1)} I _(y-x1 ₎ which is the bonding portion 95.
_{) / (1-x1)} , LiI may be precipitated. Since LiI is a hard material, it causes peeling of the electrode mixture and the electrolyte layer, resulting in a solid electrolyte 100 having high contact resistance with the electrode. Therefore, in order to reduce the contact resistance, y is preferably smaller than a certain value.

If the solid electrolyte 100 is joined to the positive electrode 80 before the heat-melting treatment, the bonding agent particles 91 and the positive electrode 80 are in point contact with each other, so that the all solid lithium battery 500 having poor contact resistance between the solid electrolyte 100 and the electrode is obtained. . On the other hand, by performing the heat melting treatment, an adhesive portion 95 is generated, the contact area with the positive electrode 80 is increased, and the all solid lithium battery 500 capable of being efficiently charged and discharged is obtained. The adhesive portion 95 is formed must cement particles 91 is sufficiently melted, the bonding agent particles 91 percentage melting the higher x ₂ in the bonding agent layer 90 is increased. That is, in order to improve the contact resistance between the solid electrolyte 100 and the electrode, it is desirable that the bonding agent particles 91 include a predetermined amount of potassium borohydride (KBH ₄ ). From the above, x ₂ in the bonding agent layer 90 is greater than a certain value is desirable.

In addition, the solid electrolyte 100 in FIG. 6 was demonstrated using the solid electrolyte 100 shown in FIG. However, an electrolyte that is not separated into the solid electrolyte layer 50 and the bonding agent layer 90, such as the solid electrolyte 100 shown in FIG. 2, may be used in the structure shown in FIG. Also in this case, as described above, y is preferably smaller than a certain value, and x ₁ is desirably larger than a certain value.

Hereinafter, FIGS. 2 and 3 which are one embodiment of the present invention will be described in more detail.

<Preparation of Sheet-shaped Solid Electrolyte 100>
A slurry obtained by dispersing solid electrolyte particles 63 and bonding agent particles 91 in NMP was applied onto a glass fiber thin film having a thickness of 30 μm and dried. By heating and melting, a sheet-like solid electrolyte 100 having a thickness of 30 μm, in which the solid electrolyte 100 was filled in the fiber thin film, was obtained. The XRD measurement, it was confirmed that a low-temperature phase and a mixture of KI in Li high temperature phase or Li (BH ₄₎ of (BH _4).

<Measuring method of melting point>
The melting point of the mixture of the solid electrolyte particles 63 and the bonding agent particles 91 was measured by differential scanning calorimetry (DSC). A sample weighed so as to have a volume of 2 μL was placed in a high-pressure pan made of SUS steel and sealed by caulking. Measurement was performed using Rigaku's Thermo plus Evo 2 / DSC 8230. The sample atmosphere was Ar, and the temperature was raised at 5 ° C./min ⁻¹ . The peak temperature of the endothermic peak obtained at the time of temperature rise was taken as the melting point. In many cases, a plurality of endothermic peaks are obtained, but the lowest temperature among the endothermic peaks attributed to the melting point is defined as the first melting point. This temperature is the onset temperature of partial melting and is most important for bonding.

<Electrode peeling test method>
This is a method for determining whether or not the solid electrolyte 100 and the electrode are sufficiently joined. First, the sheet-shaped solid electrolyte 100 and the electrode produced on the current collector foil were brought into contact with each other, heated at the first melting point, and joined. Thereafter, the current collector foil was picked up with tweezers at room temperature and peeled off from the sheet-like solid electrolyte 100. The case where bonding was insufficient and the current collector foil and the electrode mixture peeled was evaluated as x, and the case where bonding was sufficient and only the current collector foil was peeled and the electrode mixture remained in the solid electrolyte was judged as ◯.

<Method of measuring room temperature conductivity and battery resistance>
Room temperature conductivity and battery resistance were measured at room temperature by an AC impedance method using a resistance measuring device (HIOKI CHEMICAL IMPEDANCE METER 3532-80).

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.25, _{x 1} is 0.10.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.28, _{x 1} is 0.15.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.32, _{x 1} is 0.20.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.37, _{x 1} is 0.25.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.33, _{x 1} is 0.10.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.36, _{x 1} is 0.15.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.40, _{x 1} is 0.20.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.44, _{x 1} is 0.25.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.42, _{x 1} is 0.10.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.45, _{x 1} is 0.15.

A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.48, _{x 1} is 0.20.

(Comparative Example 1)
Free of solid electrolyte particles 63, to prepare a sheet-like solid electrolyte 100 in bonding agent particles 91 _{x 1} 0.15.

(Comparative Example 2)
The sheet-like solid electrolyte 100 was made of the solid electrolyte particles 63 not including the bonding agent particles 91 and y of 0.25.

(Comparative Example 3)
A sheet-like solid electrolyte 100 was created with the solid electrolyte particles 63 and the bonding agent particles 91. Y of a sheet-like solid in the electrolyte 100 is 0.25, _{x 1} is 0.05.

(Comparative Example 4)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.25, _{x 1} is 0.15.

(Comparative Example 5)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.25, _{x 1} is 0.20.

(Comparative Example 6)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.25, _{x 1} is 0.25.

(Comparative Example 7)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.51, _{x 1} is 0.25.

(Comparative Example 8)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.52, _{x 1} is 0.15.

(Comparative Example 9)
A sheet-like solid electrolyte 100 was made of the same material as in Comparative Example 3. Y of a sheet-like solid in the electrolyte 100 is 0.39, _{x 1} is 0.28.

Table 1 shows determination results as to whether solid electrolytes having good bonding with electrodes and good room temperature conductivity in Examples and Comparative Examples. Y in the solid electrolyte 100, x ₁ in the solid electrolyte 100, the value of X, the melting point measured by the melting point measurement method described above, the presence or absence of electrode peeling tested by the electrode peeling test method described above, and the battery resistance measurement method described above Based on the measured room temperature conductivity value, the above numerical values, and the presence or absence of electrode peeling, it is determined whether or not the solid electrolyte 100 has good bonding with the electrode and good room temperature conductivity.

As shown in Comparative Example 1, when the sheet-shaped solid electrolyte 100 is composed of the bonding agent particles 91, the sheet-shaped solid electrolyte 100 and the electrode are sufficiently bonded. However, the room temperature conductivity is as low as 1.0 × 10 ⁻⁸ Scm ⁻¹ .

On the other hand, when the sheet-like solid electrolyte 100 is composed of the solid electrolyte particles 63 as shown in Comparative Example 2, the room temperature conductivity is 2.0 × 10 ⁻⁵ Scm ⁻¹ , and the solid electrolyte used in the battery is Indicates a sufficient value. However, since the bonding agent particles 91 are not present in the sheet-like solid electrolyte 100, the adhesive portion 95 is not generated by melting, and the bonding between the sheet-like solid electrolyte 100 and the electrode is insufficient and peeling occurs.

Example 1 to Example 11 and Comparative Example 3 to Comparative Example 9 are examples in which the sheet-like solid electrolyte 100 is composed of solid electrolyte particles 63 and bonding agent particles 91.

Example 1, as shown from Comparative Example 3 Comparative Example 6, with the x ₁ is increased, the smaller the room temperature electrical conductivity. This is because, as described above, KI is deposited on the sheet-like solid electrolyte 100, so that y is reduced in the sheet-like solid electrolyte 100.

In Comparative Examples 4 to 6, the room temperature conductivity was below 1.0 × 10 ⁻⁵ Scm ^−1, which was an insufficient value for the sheet-like solid electrolyte 100 used in the battery.

In Example 2 to Example 11 and Comparative Example 7 to Comparative Example 9, y is increased in order to increase the room temperature conductivity. In this case, the room temperature conductivity was improved and became a sufficient value.

On the other hand, as shown in Comparative Examples 3 and 9, when x ₁ in the sheet-like solid electrolyte 100 is 0.05 and 0.28, peeling occurs, and the joining of the sheet-like solid electrolyte 100 and the electrode is caused. It turns out that it is insufficient. This small amount of the solid electrolyte 100 to partially melt when x ₁ is too low, because the greater the amount of precipitation of solid KI particles when x ₁ is too high.

Then, as shown in Comparative Examples 7 and 8, when y is large, it can be seen that hard LiI precipitates at the bonding portion 95 and the bonding between the sheet-like solid electrolyte 100 and the electrode becomes insufficient.

From the above, it can be seen that 0.15 ≦ X must be satisfied in order to obtain the solid electrolyte 100 having sufficient room temperature conductivity. Then, it can be seen that 0.05 <x ₁ ≦ 0.275 and 0 <y ≦ 0.50 are necessary to obtain a solid electrolyte 100 with good bonding to the electrode. These ranges preferably satisfy 0.20 ≦ X and 0.05 <x ₁ ≦ 0.275 and 0 <y ≦ 0.50, and more preferably 0.20 ≦ X and 0.10 ≦ x ₁ ≦. 0.275 and 0 <y ≦ 0.50 are satisfied.

Hereinafter, FIGS. 4 and 5 which are one embodiment of the present invention will be described more specifically.

<Preparation of Sheet-shaped Solid Electrolyte 100>
A slurry obtained by dispersing solid electrolyte particles 63 in NMP was applied, dried, and then uniaxially pressurized to obtain a sheet-like solid electrolyte layer 50. On this sheet-like solid electrolyte layer 50, a slurry obtained by dispersing the bonding agent particles 91 in NMP was applied, dried, and then uniaxially pressurized. And it heat-processed with 1st melting | fusing point, and obtained the sheet-like solid electrolyte 100 of thickness 200 micrometers. It was confirmed by XRD measurement that the solid electrolyte layer 50 side was a high temperature phase of LiBH ₄ .

4 and FIG. 5 are the same as the methods in FIG. 2 and FIG. 3 in the melting point measurement method, electrode peel test method, room temperature conductivity and battery resistance measurement method.

A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.02. _{X 2} in the bonding agent layer 90 was 0.10.

A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.03. _{X 2} in the bonding agent layer 90 was 0.15.

A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.04. _{X 2} in the bonding agent layer 90 was 0.20.

A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.05. _{X 2} in the bonding agent layer 90 was 0.25.

A bonding agent layer 90 having a thickness of 10 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.23, _{x 1} is 0.05. _{X 2} in the bonding agent layer 90 was 0.15.

(Comparative Example 10)
On the solid electrolyte layer 50, a bonding agent layer 90 of a Li (BH ₄ ) —K (BH ₄ ) mixture having a thickness of 5 μm was placed to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.01. _{X 2} in the bonding agent layer 90 was 0.05.

(Comparative Example 11)
A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.06. _{X 2} in the bonding agent layer 90 was 0.30.

(Comparative Example 12)
A bonding agent layer 90 having a thickness of 5 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.20, _{x 1} is 0.07. _{X 2} in the bonding agent layer 90 was 0.35.

(Comparative Example 13)
A bonding agent layer 90 having a thickness of 10 μm was placed on the solid electrolyte layer 50 to prepare a sheet-like solid electrolyte 100. The y in the solid electrolyte 100 0.17, _{x 1} is 0.05. _{X 2} in the bonding agent layer 90 was 0.15.

Similar to Table 1, Table 2 shows the determination results as to whether or not the solid electrolyte 100 has good bonding with the electrode and good room temperature conductivity in Examples and Comparative Examples. In addition to Table 1, x ₂ in the bonding agent layer 90, the thickness of the solid electrolyte layer 50, and the thickness of the bonding agent layer 90 are described. Note that the thicknesses of the solid electrolyte layers 50 in the comparative examples and examples shown in Table 2 are all 20 μm.

Example 12 to Example 16 and Comparative Example 10 to Comparative Example 13 are examples in which the sheet-like solid electrolyte 100 is composed of the bonding agent layer 90 and the solid electrolyte layer 50.

As shown in Examples 12 to 15 and Comparative Examples 10 to 12, the room temperature conductivity decreases as x ₁ and x ₂ in the sheet-like solid electrolyte 100 increase. This is because LI, which is the precipitated phase particles 94, is deposited on the sheet-like solid electrolyte 100, thereby reducing LiI from the LiI—Li (BH ₄ ) solid solution.

As shown in Comparative Examples 10 to 12, when x ₂ in the bonding agent layer 90 is 0.05 or 0.30 and 0.35, peeling occurs, and the bonding between the sheet-like solid electrolyte 100 and the electrode occurs. It turns out that it is insufficient.

In Comparative Example 13, since the thickness of the bonding agent layer 90 was 10 μm, precipitation of KI, which is the precipitated phase particle 94, increased, and the room temperature conductivity was below 1.0 × 10 ⁻⁵ Scm ^−1, and the solid electrolyte used in the battery As a result, it was insufficient.

In Example 16, y is increased as compared with Comparative Example 13. The room temperature conductivity of Example 16 was 1 × 10 ⁻⁵ Scm ⁻¹ or more, which was a sufficient value.

From the above, it can be seen that 0.15 ≦ X must be satisfied in order to obtain the solid electrolyte 100 having sufficient room temperature conductivity. Moreover, it can be seen that 0.05 <x ₂ ≦ 0.275 and 0 <y ≦ 0.50 are necessary to improve the bonding with the electrode. These ranges preferably satisfy 0.20 ≦ X and 5 <x ₂ ≦ 0.275 and 0 <y ≦ 0.50, and more preferably 0.20 ≦ X and 0.10 ≦ x ₂ ≦ 0.275. And it is desirable to satisfy 0 <y ≦ 0.50.

Hereinafter, FIGS. 7 and 8 which are one embodiment of the present invention will be described in more detail.

<Preparation of Sheet-shaped Solid Electrolyte 100>
This is a manufacturing method similar to that of the sheet-like solid electrolyte 100 of FIGS.

<Synthesis of Positive Electrode Li Conductive Binder 66 (Li ₃ BO ₃ )>
Lithium carbonate Li ₂ CO ₃ 3.92 g and boron oxide B ₂ O ₃ 11.08 g were blended and mixed in a planetary ball mill using zirconia balls. After mixing, the mixed powder was added to the alumina crucible and heat-treated at 600 ° C. for 24 hours. As a result of analyzing the crystal structure of the obtained powder by XRD, it was confirmed to be Li ₃ BO ₃ . This was used as a Li ₃ BO ₃ binder. It was 690 degreeC when melting | fusing point was measured by the differential scanning calorimetry (DSC).

<Preparation of positive electrode 80>
0.3 g of Li ₃ BO ₃ powder was added to 1.5 g of LiCoO ₂ powder having an average particle size of 10 μm, and after mixing and mixing in a mortar, 1.5 g of 5% by mass ethylcellulose solution was added and kneaded. . The kneaded positive electrode paste was screen-coated on a 10 mm diameter Al foil. After drying at 150 ° C. to evaporate the solvent, it was cold pressed with a hand press. The sample was placed on an alumina plate and heated at 700 ° C. to decompose and remove ethyl cellulose, and Li ₃ BO ₃ was melted. As a result of measuring the mass after cooling, the coating amount was 3 mg / cm ² in terms of the mass of LiCoO ₂ per 1 cm ² of the electrode.

<Joining of positive electrode 80 and bonding agent layer 90>
The produced positive electrode 80 was disposed so that the positive electrode mixture layer 60 and the bonding agent layer 90 were in contact with each other. Thereafter, the positive electrode 80 and the bonding agent layer 90 were bonded by heating at a temperature equal to or higher than the first melting point of the bonding agent. This sample was used as a positive electrode-electrolyte assembly.

<Preparation of negative electrode 70>
Li as the negative electrode active material 54 was disposed so as to be in contact with the solid electrolyte layer 50 of the produced positive electrode-electrolyte assembly, thereby forming the negative electrode 70.

<Evaluation method of charge / discharge characteristics of battery>
The charge / discharge characteristics of the battery were evaluated using a charge / discharge tester (manufactured by Sorartron, model 1470). The set temperature of the mantle heater during the charge / discharge test is 150 ° C. The applied current at the time of charging / discharging was set to a current (0.1 C) at which the fully charged battery would be discharged in 10 hours.

The discharge capacity (Ah) after 20 cycles was measured, and the percentage calculated by dividing this by 1 cycle discharge capacity (Ah) was defined as “capacity maintenance ratio after 20 cycles” (%).

Also, the percentage calculated by dividing the initial charge capacity (Ah) by the initial discharge capacity (Ah) was defined as “initial Coulomb efficiency” (%).

7 and FIG. 8 are the same as the methods in FIG. 2 and FIG. 3 for measuring the room temperature conductivity and battery resistance.

On the electrolyte layer side of the negative electrode-electrolyte assembly in which Li is used for the negative electrode active material 54 and the solid electrolyte layer 50 made of LiI-Li (BH ₄ ) solid solution is 50 μm, the K mole fraction x ₂ is 0.15. A bonding agent layer 90 made of a LiBH ₄ -KBH ₄ mixture of 10 μm in thickness was prepared, and a positive electrode layer made of Li conductive binder LBO and an active material NMC was brought into contact with pressure, and set in a SUS cell. The SUS cell was heated to the first melting point in a state where pressure was applied in the sample film thickness direction, so that the bonding agent layer 90 was softened and the positive electrode and the solid electrolyte 100 were bonded. Y in the solid electrolyte 100 is 0.21.

The same as Example 17 except that the oxide solid electrolyte layer LLZ having a thickness of 10 μm was provided between the positive electrode mixture layer and the bonding agent layer.

The thickness of the solid electrolyte layer 50 made of a LiI-Li (BH ₄ ) solid solution is changed from 50 μm to 5 μm, the thickness of the bonding agent layer 90 is changed from 10 μm to 5 μm, and y in the solid electrolyte 100 is 0.25. Example 17 is the same as Example 17 except for the above.

Example 17 is the same as Example 17 except that the thickness of the bonding agent layer 90 made of the LiBH ₄ -KBH ₄ mixture is changed from 10 μm to 5 μm so that y becomes 0.23.

Example 17 is the same as Example 17 except that the thickness of the solid electrolyte layer 50 made of a LiI—Li (BH ₄ ) solid solution is changed from 50 μm to 200 μm so that y becomes 0.24.

Example 17 is the same as Example 17 except that the bonding agent layer 90 is changed to a mixture of LiBH ₄ -KBH ₄ and LiI—Li (BH ₄ ) solid solution having y of 0.25 and x ₂ of 0.15.

A solid electrolyte layer 50 is not provided, and a mixture of a LiBH ₄ -KBH ₄ mixture having x ₁ of 0.15 and y of 0.36 and a LiI-Li (BH ₄ ) solid solution is melted in a glass fiber thin film having a thickness of 30 μm. The same as Example 17 except for impregnation.

The same as Example 17 except that the y in the solid electrolyte 100 was changed to 0.42.

Example 17 is the same as Example 17 except that the thickness of the solid electrolyte layer 50 made of LiI—Li (BH ₄ ) solid solution is changed from 50 μm to 500 μm so that y becomes 0.25.

Example 17 is the same as Example 17 except that the thickness of the bonding agent layer 90 made of the LiBH ₄ -KBH ₄ mixture is changed from 10 μm to 3 μm so that y becomes 0.24.

(Comparative Example 14)
The negative electrode active material 54 is made of Li, and a solid electrolyte layer 50 made of LiI—Li (BH ₄ ) solid solution having y of 0.25 is 50 μm in the negative electrode-electrolyte assembly. A sample in which a positive electrode layer made of an adhesive (lithium borate Li ₃ BO ₃ : LBO) and an active material (layered lithium / nickel / manganese / cobalt composite oxide: NMC) was brought into contact by pressurization was used as Comparative Example 14. .

(Comparative Example 15)
The thickness of the solid electrolyte layer 50 made of a LiI-Li (BH ₄ ) solid solution was changed from 50 μm to 3 μm, the thickness of the bonding agent layer 90 was changed from 10 μm to 5 μm, and y in the solid electrolyte 100 was 0.19. Example 17 is the same as Example 17 except that

(Comparative Example 16)
The bonding agent layer _{x 2} in 90 was changed from 0.15 to 0.05 is similar to that in Example 17.

(Comparative Example 17)
The bonding agent layer _{x 2} in 90 was changed from 0.15 to 0.28 is similar to that in Example 17.

(Comparative Example 18)
Example 17 is the same as Example 17 except that y in the solid electrolyte 100 is changed to 0.62.

As in Tables 1 and 2, Table 3 shows the determination results as to whether or not the solid electrolyte 100 has good bonding with electrodes and good room temperature conductivity in Examples and Comparative Examples. The higher the capacity retention rate, the better the bonding with the electrode, and the more difficult it is to peel off. Therefore, the capacity maintenance rate was set to 70% or more, and it was determined as acceptable. In addition, the battery resistance is lower as the conductivity is higher, and is lower as the thickness of the solid electrolyte 100 is thinner. Therefore, the battery resistance was 50 Ωcm ² or less, which was regarded as acceptable.

When the bonding agent layer 90 is not included as in Comparative Example 14, the bonding between the positive electrode and the solid electrolyte layer 50 cannot be performed well, and the battery has a low capacity retention rate. On the other hand, by providing a bonding agent layer as in Example 17, bonding is improved, and a battery having a low resistance and a high capacity retention rate can be obtained.

Furthermore, as shown in Example 18, when the oxide solid electrolyte layer 81 is used, a battery having a low resistance and a high capacity retention rate can be obtained.

Comparative Example 15, Example 25, and Examples 19 and 21 are results when the thickness of the solid electrolyte layer 50 is changed. If the solid electrolyte layer 50 is too thick, the battery resistance increases, and in the case of 3 μm, the thin film is too thin, causing a short circuit. From these results, the thickness of the solid electrolyte layer is desirably 5 μm or more and 200 μm or less.

In Example 20 and Example 26, the thickness of the bonding agent layer 90 is made thinner than 10 μm. If it is too thin, bonding becomes insufficient, and a battery with a low performance with a 20-cycle capacity retention rate of 55% is obtained. Therefore, the thickness of the bonding agent layer 90 is desirably 5 μm or more.

In Comparative Example 16 and Comparative Example 17, the K mole fraction in the bonding agent layer 90 is changed. If the K mole fraction is too low, melting of the bonding agent layer 90 is suppressed and bonding cannot be performed well, resulting in a low capacity retention rate. On the other hand, if the K mole fraction is too high, the amount of precipitation of KI, which is a hard material, increases, it cannot withstand volume expansion / contraction due to charge / discharge, and the capacity retention rate decreases. Therefore, x ₂ is desirably 0.05 <x ₂ ≦ 0.275.

The bonding agent layer 90 of Example 22 includes solid electrolyte particles 63 and bonding agent particles 91 as in the case of the solid electrolyte 100 of FIG. Thus, even a solid electrolyte 100 in which the solid electrolyte layer 50 and the solid electrolyte 100 of FIG. 2 are combined is a battery with high performance. In Example 23, the bonding agent layer 90 is the solid electrolyte 100 of FIG. Also in this case, the bonding can be improved, and the battery has high performance.

In Example 24 and Comparative Example 18, y is increased. If y increases too much, LiI will precipitate in the solid electrolyte 100 and lower the room temperature conductivity. Furthermore, since LiI is hard, it cannot follow volume expansion / contraction, resulting in a battery with a low capacity retention rate. Therefore, 0 <y ≦ 0.5 is desirable.

10: negative electrode current collector, 20: positive electrode current collector, 30: battery case, 40: negative electrode mixture layer, 50: solid electrolyte layer, 54: negative electrode active material, 60: positive electrode mixture layer, 62: positive electrode active material 63: solid electrolyte particles, 66: positive electrode Li conductive binder, 67: hydride-based solid electrolyte, 68: positive electrode conductive auxiliary or positive electrode binder, 69: negative electrode conductive auxiliary or negative electrode binder, 70: negative electrode, 80 : Positive electrode, 81: oxide solid electrolyte layer, 90: bonding agent layer, 94: deposited phase particles, 95: adhesion part, 100: solid electrolyte, 500: all solid lithium battery

Claims

A solid electrolyte comprising Li, I, BH 4 , and K,
X 1 represents the molar fraction of K contained in the solid electrolyte with respect to the sum of LiK contained in the solid electrolyte.
When the molar fraction of I with respect to the sum of I and BH 4 contained in the solid electrolyte is y,
0.05 <x 1 ≦ 0.275,
0 <y ≦ 0.50,
0.15 ≦ (y−x 1 ) / (1−x 1 ),
Meet solid electrolyte.
A solid electrolyte comprising a bonding agent layer and a solid electrolyte layer,
The bonding agent layer includes Li, BH 4 , and K,
The solid electrolyte layer includes Li, I, and BH 4 ;
The molar fraction of K contained in the binder layer relative to the sum of Li and K contained in the binder layer is x 2 ,
X 1 represents the molar fraction of K contained in the solid electrolyte with respect to the sum of Li and K contained in the solid electrolyte.
When the molar fraction of I with respect to the sum of I and BH 4 contained in the solid electrolyte is y,
0.05 <x 2 ≦ 0.275
0 <y ≦ 0.50,
0.15 ≦ (y−x 1 ) / (1−x 1 ),
Meet solid electrolyte.
The solid electrolyte according to claim 2,
The bonding agent layer has a thickness of 5 μm or more and 30 μm or less.
The solid electrolyte according to claim 2,
The solid electrolyte layer has a thickness of 5 μm or more and 200 μm or less.
A solid electrolyte according to claim 1, a negative electrode mixture layer, and a positive electrode mixture layer,
The negative electrode mixture layer includes a negative electrode active material,
The positive electrode mixture layer includes a positive electrode active material and a positive electrode lithium conductive binder,
The solid electrolyte is provided between the positive electrode mixture layer and the negative electrode mixture layer.
All solid lithium battery.
A solid electrolyte according to claim 2, a negative electrode mixture layer, and a positive electrode mixture layer,
The negative electrode mixture layer includes a negative electrode active material,
The positive electrode mixture layer includes a positive electrode active material and a positive electrode lithium conductive binder,
Between the positive electrode mixture layer and the solid electrolyte layer, the bonding agent layer is provided,
All solid lithium battery.