JP2021128885A - Negative electrode for all-solid-state battery - Google Patents

Abstract

To improve quick charging performance.SOLUTION: A negative electrode for an all-solid-state battery includes a negative electrode active material layer. The negative electrode active material layer includes a first particle group and a second particle group. The first particle group consists of titanium oxide. The second particle group consists of a sulfide solid electrolyte. In the cross section of the negative electrode active material layer, the contact interface length between the first particle group and the second particle group is 3.77 mm or more.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a negative electrode for an all-solid-state battery.

Japanese Unexamined Patent Publication No. 2012-243644 (Patent Document 1) discloses an electrode including an active material layer containing an active material powder and a solid electrolyte powder.

Japanese Unexamined Patent Publication No. 2012-243644

In an all-solid-state battery, it is important to maintain the contact interface between the active material particles and the solid electrolyte particles. If the volume change of the active material particles is large during charging / discharging, it may be difficult to maintain the contact interface.

Titanium oxide is one of the promising materials as a negative electrode active material for all-solid-state batteries. This is because the titanium oxide has a small volume change due to charging and discharging. However, the all-solid-state battery using titanium oxide has room for improvement in quick charging performance.

An object of the present disclosure is to improve quick charging performance.

Hereinafter, the technical configuration and the action and effect of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The correctness of the mechanism of action does not limit the scope of claims.

The negative electrode for an all-solid-state battery includes a negative electrode active material layer. The negative electrode active material layer includes a first particle group and a second particle group. The first particle group consists of titanium oxide. The second particle group consists of a sulfide solid electrolyte. In the cross section of the negative electrode active material layer, the contact interface length between the first particle group and the second particle group is 3.77 mm or more.

According to the new findings of the present disclosure, when the negative electrode active material is titanium oxide, the "contact interface length" is a parameter that affects the quick charging performance. That is, the quick charging performance can change drastically before and after the contact interface length of 3.77 mm as a boundary. When the contact interface length is 3.77 mm or more, the desired quick charging performance can be realized. The method for measuring the contact interface length will be described later.

FIG. 1 is a schematic cross-sectional view of an all-solid-state battery according to the present embodiment. FIG. 2 is a first example of a secondary electron image of a cross section of the negative electrode active material layer. FIG. 3 is a second example of a secondary electron image of a cross section of the negative electrode active material layer. FIG. 4 is an explanatory diagram of the image analysis method. FIG. 5 is a graph showing the relationship between the contact interface length and the charging resistance.

Hereinafter, embodiments of the present disclosure (hereinafter, also referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of claims.

In this embodiment, the "negative electrode for all-solid-state battery" may be abbreviated as "negative electrode".

In the present embodiment, for example, ^{the description such as "8.3 m 2} / g to 9.1 m ² / g" indicates a range including a boundary value unless otherwise specified. For example, "8.3 m ² / g to 9.1 m ² / g" ^{indicates a range of "8.3 m 2} / g or more and 9.1 m ² / g or less".

<All-solid-state battery>
FIG. 1 is a schematic cross-sectional view of an all-solid-state battery according to the present embodiment.
The all-solid-state battery 100 includes a battery element 50. The all-solid-state battery 100 may further include an exterior body (not shown). The battery element 50 may be housed in the exterior body. The exterior body may be, for example, a metal case or the like. The exterior body may be, for example, a pouch made of an aluminum laminated film or the like.

The battery element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. The positive electrode 10 contains a positive electrode active material and a solid electrolyte. The negative electrode 20 will be described later. The separator layer 30 is also referred to as a "solid electrolyte layer". The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 blocks electron conduction between the positive electrode 10 and the negative electrode 20. The separator layer 30 conducts ions. That is, the separator layer 30 ionically connects the positive electrode 10 and the negative electrode 20.

The all-solid-state battery 100 may include one battery element 50 alone. The all-solid-state battery 100 may include a plurality of battery elements 50. The plurality of battery elements 50 may be stacked in the z-axis direction of FIG. The plurality of battery elements 50 may be electrically connected in series. The plurality of battery elements 50 may be electrically connected in parallel.

<Negative electrode for all-solid-state battery>
The negative electrode 20 includes a negative electrode active material layer. The negative electrode 20 may be substantially composed of a negative electrode active material layer. The negative electrode 20 may further include, for example, a negative electrode current collector. The negative electrode active material layer may be arranged on the surface of the negative electrode current collector. The negative electrode current collector may have a thickness of, for example, 5 μm to 30 μm. The negative electrode current collector may include, for example, nickel (Ni) foil, copper (Cu) foil, or the like.

The negative electrode active material layer may have a thickness of, for example, 10 μm to 200 μm. The negative electrode active material layer includes a first particle group (titanium oxide) and a second particle group (sulfide solid electrolyte). The negative electrode active material layer may substantially consist of a first particle group and a second particle group. The negative electrode active material layer may further contain, for example, a conductive material, a binder, or the like as long as it includes the first particle group and the second particle group.

《Contact interface length》
FIG. 2 is a first example of a secondary electron image of a cross section of the negative electrode active material layer.
In FIG. 2, the first particle group has a relatively dark gray color. In FIG. 2, the second particle group has a relatively light gray color. The present embodiment is characterized by a dispersed state of the first particle group and the second particle group in the negative electrode active material layer. In the present embodiment, the dispersed state of the first particle group and the second particle group is quantified by the "contact interface length". For example, in the dispersed state of FIG. 2, the contact interface length is 3.77 mm or more. When the contact interface length is 3.77 mm or more, improvement in quick charging performance is expected.

The contact interface length may be, for example, 3.83 mm or more, 4.10 mm or more, or 4.56 mm or more. The contact interface length can have any upper limit. The contact interface length may be, for example, 4.56 mm or less.

FIG. 3 is a second example of a secondary electron image of a cross section of the negative electrode active material layer.
In FIG. 3, the first particle group has a relatively dark gray color, as in FIG. 2. In FIG. 3, the second particle group has a relatively light gray color, as in FIG. 2. In the dispersed state of FIG. 3, the contact interface length is less than 3.77 mm. If the contact interface length is less than 3.77 mm, the desired quick charging performance may not be obtained.

Titanium oxide tends to aggregate in the process of forming the negative electrode active material layer. In FIG. 3, since the first particle group (titanium oxide) is aggregated as compared with FIG. 2, it is considered that the surface area of the first particle group is smaller. Therefore, it is considered that there are few points of contact between the first particle group and the second particle group. As a result, it is considered that the diffusion resistance of Li is high.

<< Measurement method of contact interface length >>
The contact interface length is measured by the following procedure.

(Preparation of sample pieces)
The all-solid-state battery 100 is prepared. In an inert atmosphere, at least a part of the exterior body (aluminum laminated film, etc.) is peeled off. As a result, the battery element 50 is exposed. The battery element 50 is cut to an appropriate size in an inert atmosphere. As a result, a sample piece of the battery element 50 or the negative electrode 20 is produced. The cut surface of the sample piece is cross-sectioned by an ion milling device or the like. For example, an ion milling device "IM4000PLUS" (or an equivalent product thereof) manufactured by Hitachi High-Technologies Corporation may be used. The cross-section processing is carried out in a vacuum atmosphere or an inert atmosphere. The sample piece may be cooled during cross-section processing.

(Acquisition of reflected electron image)
After cross-section processing, the sample piece is introduced into a field emission scanning electron microscope (FE-SEM). For example, FE-SEM "Regulus 8220" (or an equivalent product thereof) manufactured by Hitachi High-Technologies Corporation may be used. A vacuum atmosphere is maintained so that the sample pieces are not exposed to the atmosphere between the cross-section processing and the introduction of the SEM.

A sample piece is observed by FE-SEM. Six observation positions are set at substantially equal intervals in a direction orthogonal to the thickness direction of the negative electrode active material layer. A reflected electron image is taken at each observation position. That is, six reflected electron images are acquired. The observation magnification is 1500 times. The shooting area is a rectangular area. The imaging region has a planar size of 59 ± 6 μm × 84 ± 8 μm. At each observation position, additional imaging of secondary electron images and element mapping by EDX (energy dispersive x-ray spectroscopy) may be performed. The secondary electron image and the element mapping image can be used as reference information in creating the color-coded image described later.

(Image analysis)
FIG. 4 is an explanatory diagram of the image analysis method.
Each process of "1. extraction of components", "2. coloring", and "3. superposition" is performed on the reflected electron image obtained above in this order.

1. 1. Extraction of components Each component contained in the backscattered electron image is extracted separately by the binarization process. First, the reflected electron image is binarized to extract the first particle group (titanium oxide) and the second particle group (sulfide solid electrolyte). The binarization threshold value can be set based on, for example, "volume ratio of titanium oxide" in the negative electrode active material layer, "volume ratio of sulfide solid electrolyte", and the like. The volume ratio of each component can be calculated from, for example, an element mapping image by EDX.

Further, the extracted image composed of the first particle group and the second particle group is subjected to the binarization processing, so that the extracted image composed of the first particle group and the extracted image composed of the second particle group are obtained. Is created. The binarization threshold can be set based on, for example, the volume ratio of each component.

Next, the reflected electron image is subjected to a binarization treatment to extract voids. When the negative electrode active material layer further contains components (other components) other than the first particle group and the second particle group, the other components may be extracted together with the voids. For example, the voids and the conductive material may be extracted. In the backscattered electron image, the brightness of the voids can be approximated to the brightness of the conductive material. When the brightness of the voids is close to the brightness of the conductive material, the conductive material can be extracted together by setting the threshold value for extracting the voids.

Further, the extracted image composed of the voids and the conductive material is subjected to the binarization treatment to create an extracted image composed of the voids and an extracted image composed of the conductive material. For example, the binarization threshold value may be set by referring to the size of each component in the image. For example, it may be determined that the component having a relatively large size is a conductive material and the component having a relatively small size is a void. Further, the size, shape, etc. of the conductive material in the element mapping image by EDX may be referred to.

2. Coloring In the extracted image of each component, each component is colored. Each component is colored differently from each other. The first particle group (titanium oxide) may be colored, for example, "red". The second particle group (sulfide solid electrolyte) may be colored, for example, "yellow". The conductive material may be colored, for example, "green". The voids may be colored, for example, "black".

3. 3. Superposition The extracted images after coloring are superposed. In the examples of FIGS. 2 and 3, the extracted image of the first particle group (red), the extracted image of the second particle group (yellow), the extracted image of the conductive material (green), and the extracted image of the void (black). And are superimposed. As a result, the color-coded images are combined. In the color-coded image, each component is color-coded.

From the scale bar of the backscattered electron image, the length of one pixel in the color-coded image is calculated. In the examples of FIGS. 2 and 3, one pixel has a length of ^{6.6 × 10 -8 m.} In the color-coded image, the pixels in which the first particle group (red) and the second particle group (yellow) are adjacent to each other are counted up. The contact interface length in the color-coded image is calculated by multiplying the number of pixels adjacent to the first particle group and the second particle group by the length of one pixel. That is, the contact interface length indicates the total length of the interface in which the first particle group and the second particle group are in contact in the imaging region of the reflected electron image.

A color-coded image is created from each of the six reflected electron images. The contact interface length is measured in each of the six color-coded images. The arithmetic mean of the six contact interface lengths is considered the "contact interface length" of the entire negative electrode active material layer.

<< First particle swarm >>
The first particle group consists of titanium oxide. Titanium oxide functions as a negative electrode active material. The titanium oxide in this embodiment represents a compound containing at least titanium (Ti) and oxygen (O). The titanium oxide may further contain, for example, Li, niobium (Nb) and the like. Titanium oxide, for example, lithium titanate _{(Li 4 Ti 5 O 12)} , also comprise at least one member selected from the group consisting of titanium oxide (TiO ₂₎ and Chitan'niobu oxide (TiNb ₂ O ₇₎ good. The titanium oxide can have any crystal structure. The titanium oxide may have, for example, a spinel-type structure, a monoclinic crystal system, or the like.

Each of the particles included in the first particle group is a secondary particle (aggregate of primary particles). The secondary particle group of titanium oxide may have a median diameter of, for example, 1 μm to 30 μm. The "median diameter" indicates a particle diameter in which the cumulative particle volume from the small particle size side is 50% of the total particle volume in the volume-based particle size distribution. The secondary particle group of titanium oxide may have, for example, a median diameter of 1 μm to 10 μm.

The primary particle group contained in the secondary particles may have, for example, an average primary particle diameter of 0.1 μm to 1 μm. The "average primary particle size" can be measured by SEM observation. The directional diameter (ferret diameter) of the primary particles in the secondary electron image is regarded as the primary particle diameter. The average primary particle size indicates an arithmetic mean value of 100 or more primary particle sizes. More than 100 primary particles are randomly sampled from the first particle swarm.

<< Second particle swarm >>
The second particle group consists of a sulfide solid electrolyte. The second particle swarm forms an ionic conduction path. The blending amount of the second particle group may be, for example, 10 parts by volume to 150 parts by volume with respect to 100 parts by volume of the first particle group (negative electrode active material). The blending amount of the second particle group may be, for example, 100 parts by volume to 150 parts by volume with respect to 100 parts by volume of the first particle group (negative electrode active material). The blending amount of the second particle group may be, for example, 10 parts by volume to 50 parts by volume with respect to 100 parts by volume of the first particle group (negative electrode active material).

The second particle group may have, for example, a median diameter of 0.05 μm to 5 μm. The second particle group may have, for example, a median diameter of 0.1 μm to 1 μm.

The second particle group may have, for example, a specific surface area of ^{8.3 m 2 / g or more.} When the second particle group has ^{a specific surface area of 8.3 m 2} / g or more, it is expected that, for example, the contact interface length becomes long. The "specific surface area" in this embodiment is measured by the BET multipoint method. The second particle group may have, for example, a specific surface area of ^{8.3 m 2} / g to 9.1 m ^{2 / g.}

The sulfide solid electrolyte may be, for example, glass. The sulfide solid electrolyte may be, for example, glass ceramics (also referred to as “crystallized glass”).

The sulfide solid electrolyte contains sulfur (S) and Li. The sulfide solid electrolyte may further contain, for example, phosphorus (P) and the like. That is, the sulfide solid electrolyte may contain phosphorus lithium sulfide and the like. The sulfide solid electrolyte may further contain, for example, a halogen element and the like. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br) and the like. The sulfide solid electrolyte may further contain, for example, O, silicon (Si), germanium (Ge), tin (Sn) and the like.

Sulfide solid electrolytes include, for example, Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Si _{2 SP 2} S ₅ , LiI-LiBr-Li _{2 SP 2} S ₅ , LiI-Li _{2 SP 2} S ₅ , LiI-Li ₂ O-Li _{2 SP 2} S ₅ , LiI-Li _{2 SP 2} O ₅ , LiI-Li ₃ PO ₄ -P ₂ S _5, and Li may include at least one selected from ₂ S-P ₂ S ₅ group consisting -GeS _2.

Here, for example, "Li ₂ SP ₂ S ₅ " indicates that the sulfide solid electrolyte is composed of _{a component derived from "Li 2} S" and a component derived from "P ₂ S ₅ ". Li ₂ SP ₂ S ₅ can be produced, for example, by a mechanochemical reaction between _{Li 2} S and P ₂ S _5. The mixing ratio of Li ₂ S and P ₂ S _{5 is arbitrary.} For example, Li ₂ S and P ₂ S _{5 satisfy the relationship of "Li 2} S / P ₂ S ₅ = 50/50" to "Li ₂ S / P ₂ S ₅ = 90/10" in terms of molar ratio. You may. The Li ₂ S and P ₂ S _5, for example, meet the relationship of _{"Li 2 S / P 2 S 5} = 80/20 " in a molar ratio from _{"Li 2 S / P 2 S 5} = 60/40 ' You may.

《Conductive material》
The negative electrode active material layer may further contain a conductive material. The conductive material forms an electron conductive path. The conductive material may contain any component. The conductive material may contain, for example, a carbon material. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fibers (VGCF), carbon nanotubes, and graphene flakes.

The blending amount of the conductive material may be, for example, 0 parts by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The blending amount of the conductive material may be, for example, 0.5 parts by mass to 5 parts by mass with respect to 100 parts by mass of the negative electrode active material.

《Binder》
The negative electrode active material layer may further contain a binder. Binders bond solid materials together. The binder may contain any component. The binder is, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), butyl rubber (IIR), and butadiene rubber (BR). It may be included.

The blending amount of the binder may be, for example, 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The blending amount of the binder may be, for example, 0.5 parts by mass to 5 parts by mass with respect to 100 parts by mass of the negative electrode active material.

<Manufacturing method of negative electrode for all-solid-state battery>
For example, a negative electrode active material layer can be formed by applying a negative electrode paste to the surface of a negative electrode current collector and drying it. That is, a negative electrode can be manufactured. In the present embodiment, the negative electrode paste is prepared, for example, by two-step mixing. It is expected that the contact interface length will be lengthened by the two-step mixing of the paste.

First, as a first step, a first paste is prepared by mixing a first particle group (titanium oxide), a conductive material, and a dispersion medium. For example, an ultrasonic homogenizer or the like may be used. The dispersion medium may be, for example, butyl butyrate or the like.

In the first stage, it is expected that the agglutination of the first particle group will be crushed. The mixing time of the first step may be, for example, 15 to 60 minutes. The mixing time of the first step may be, for example, 30 to 60 minutes.

Next, as a second step, a second paste (negative electrode paste) is prepared by mixing the second particle group (sulfide solid electrolyte) with the first paste. That is, after the agglutination of the titanium oxide is crushed, the titanium oxide and the sulfide solid electrolyte are mixed. For example, an ultrasonic homogenizer or the like may be used. The mixing time of the second step may be, for example, 20 to 40 minutes.

At this time, for example, the use of a sulfide solid electrolyte having a large specific surface area is expected to increase the contact interface length. As described above, the second particle group (sulfide solid electrolyte) may have a specific surface area of ^{, for example, 8.3 m 2} / g to 9.1 m ^{2 / g.}

Hereinafter, examples of the present disclosure (hereinafter, also referred to as “the present examples”) will be described. However, the following description does not limit the scope of claims.

<Manufacturing of all-solid-state batteries>
Follow the procedure below to No. 1 to No. The test battery (all-solid-state lithium ion secondary battery) according to No. 8 was manufactured. The sulfide solid electrolytes in this example were all glass ceramics.

<< No. 1 >>
(1. Preparation of negative electrode paste)
The following materials were prepared.
First particle group: Lithium titanate (average primary particle size 0.7 μm)
Second particle group: LiI-LiBr-Li _{2 SP 2} S ₅ (specific surface area 8.3 m ² / g)
Conductive material: VGCF
Dispersion medium: Butyl butyrate

(1st stage)
With an ultrasonic homogenizer (product name "UH-50") manufactured by SMT, 1.0 parts by mass of the first particle group, 0.024 parts by mass of the conductive material, 0.048 parts by mass of the binder, and 1 .6 parts by mass of dispersion medium was mixed. As a result, the first paste was prepared. The mixing time of the first stage was 5 minutes.

(Second stage)
Then, the first paste and the second particle group of 0.336 parts by mass were mixed by the same ultrasonic homogenizer. As a result, a second paste (negative electrode paste) was prepared. The mixing time of the second stage was 30 minutes.

(2. Preparation of positive electrode paste)
The following materials were prepared.
Positive electrode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ / LiNbO ₃
Conductive material: VGCF
Sulfide solid electrolyte: LiI-LiBr-Li _{2 SP 2} S ₅
Binder: PVdF
Dispersion medium: Butyl butyrate

A positive electrode active material was prepared by coating _{the surface of LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (particles) with LiNbO _3.

With an ultrasonic homogenizer (product name "UH-50") manufactured by SMT, 2.0 parts by mass of positive electrode active material, 0.048 parts by mass of conductive material, and 0.407 parts by mass of sulfide solid electrolyte. , 0.016 parts by mass of binder and 1.3 parts by mass of dispersion medium were mixed. As a result, a positive electrode paste was prepared.

(3. Preparation of solid electrolyte paste)
The following materials were prepared.
Sulfide solid electrolyte: LiI-LiBr-Li _{2 SP 2} S ₅ (median diameter 2.5 μm)
Binder solution: Solute butadiene rubber binder (concentration 5% by mass), solvent heptane Dispersion medium: heptane

A polypropylene container was prepared. The container was filled with a sulfide solid electrolyte, a binder solution, and a dispersion medium. The material in the container was agitated for 30 seconds by the ultrasonic disperser. After stirring, the container was set in the shaker. The container was shaken by a shaker for 3 minutes. From the above, a solid electrolyte paste was prepared.

(4. Manufacture of positive and negative electrodes)
The positive electrode paste was applied to the surface of the positive electrode current collector (aluminum foil) by a blade type applicator. The positive electrode paste was dried on a hot plate at 100 ° C. for 30 minutes. As a result, a positive electrode active material layer was formed on the surface of the positive electrode current collector. From the above, the positive electrode was manufactured.

Similarly, the negative electrode paste was applied to the surface of the negative electrode current collector (nickel foil) and dried to form a negative electrode active material layer. From the above, the negative electrode was manufactured.

The amount of the positive electrode active material layer and the negative electrode active material layer was adjusted so that the ratio of the negative electrode capacity to the positive electrode capacity (negative electrode capacity / positive electrode capacity) was 1.15. The positive electrode capacity was calculated assuming that the specific volume of the positive electrode active material was 185 mAh / g.

(5. Formation of separator layer (positive electrode side))
The positive electrode was first pressed. After the first press working, the solid electrolyte paste was applied to the surface of the positive electrode active material layer by a blade type applicator. The solid electrolyte paste was dried on a hot plate at 100 ° C. for 30 minutes. By drying the solid electrolyte paste, a part of the separator layer was formed on the surface of the positive electrode active material layer. As a result, the first laminated body was formed. The first laminated body was subjected to the second press working by the roll press device. The pressure of the second press working was ² ton / cm 2 (2 × 10 ³ kg / cm ² ). After the second press working, the first laminated body was processed into a predetermined planar shape by punching.

(6. Formation of separator layer (negative electrode side))
The negative electrode was first pressed. After the first press working, the solid electrolyte paste was applied to the surface of the negative electrode active material layer by a blade type applicator. The solid electrolyte paste was dried on a hot plate at 100 ° C. for 30 minutes. By drying the solid electrolyte paste, a part of the separator layer was formed on the surface of the negative electrode active material layer. As a result, a second laminated body was formed. The second laminated body was subjected to the second press working by the roll press device. The pressure of the second press working was ^{2 ton / cm 2.} After the second press working, the second laminated body was processed into a predetermined planar shape by punching.

(7. Assembly)
Aluminum foil was prepared as a temporary support. A solid electrolyte paste was applied to the surface of the temporary support and dried to form a part of the separator layer (unpressed state).

The separator layer formed on the surface of the temporary support was transferred to the surface of the first laminated body. Further, the battery element was formed by superimposing the second laminated body on the first laminated body. In the battery element, the positive electrode current collector, the positive electrode active material layer, the separator layer, the negative electrode active material layer, and the negative electrode current collector were laminated in this order. The battery element was hot pressed. The temperature of the hot press was 130 ° C. The pressure of the hot press was ^{2 ton / cm 2.}

The exterior was prepared. The exterior was a pouch made of aluminum laminated film. A battery element was enclosed in the exterior. The perimeter of the exterior was constrained so that a pressure of 5 MPa was applied to the battery element. From the above, the test battery was manufactured.

(8. Activation)
“1C” in this embodiment indicates the current rate at which the fully charged capacity is charged in one hour. At a current rate of 1C, the test battery was charged with a constant current up to 2.95V. After reaching 2.95V, constant current charging was switched to constant voltage charging. Constant voltage charging was continued until the current rate dropped to 0.01C.

After the constant voltage charging was completed, the test battery was discharged to 1.5 V at a current rate of 1 C.

<< No. 2 to No. 5 >>
In "1. Preparation of negative electrode paste", as shown in Table 1 below, No. 1 except that the mixing time of the first step is changed. Similar to No. 1, test batteries were manufactured respectively.

<< No. 6 >>
In "1. Preparation of negative electrode paste", No. 1 except that the second particle group (sulfide solid electrolyte) having the specific surface area shown in Table 1 below is used. Similar to No. 2, a test battery was manufactured.

<< No. 7 >>
In "1. Preparation of negative electrode paste", No. 1 except that the second particle group (sulfide solid electrolyte) having the specific surface area shown in Table 1 below is used. Similar to No. 5, a test battery was manufactured.

<< No. 8 >>
No. In No. 8, a negative electrode paste was prepared by batch mixing.
With an ultrasonic homogenizer (product name "UH-50") manufactured by SMT, 1.0 parts by mass of the first particle group, 0.024 parts by mass of the conductive material, 0.048 parts by mass of the binder, and 1 A dispersion medium of 0.6 parts by mass and a second particle group (specific surface area of 8.3 m ² / g) of 0.336 parts by mass were mixed together. As a result, a negative electrode paste was prepared. The mixing time was 90 minutes. Except for these, No. Similar to No. 1, a test battery was manufactured.

<Evaluation>
《Quick charging performance》
The test battery was charged for 10 seconds by a constant current method at a current rate of 3C. As a result, the amount of voltage rise (ΔV) was measured. The amount of voltage increase is the difference between the voltage at the time of charging for 10 seconds and the voltage before the start of charging. The charging resistance was calculated by dividing the amount of voltage rise by the charging current. The charging resistance is shown in Table 1 below. It is considered that the lower the charging resistance, the better the quick charging performance.

《Contact interface length》
The contact interface length in the cross section of the negative electrode active material layer was measured by the above procedure. The contact interface lengths are shown in Table 1 below.

<Result>
FIG. 5 is a graph showing the relationship between the contact interface length and the charging resistance.
FIG. 5 shows the relationship between the contact interface length and the charging resistance in Table 1 above. In FIG. 5, there is a tendency that the quick charging performance drastically changes before and after the contact interface length of 3.77 mm as a boundary. That is, when the contact interface length is less than 3.77 mm, the charging resistance tends to increase sharply. When the contact interface length is 3.77 mm or more, the charging resistance tends to be stable at a low value. That is, when the contact interface length is 3.77 mm or more, excellent quick charging performance tends to be exhibited.

10 positive electrode, 20 negative electrode (negative electrode for all-solid-state battery), 30 separator layer, 50 battery elements, 100 all-solid-state battery.

Claims (1)

Contains the negative electrode active material layer,
The negative electrode active material layer includes a first particle group and a second particle group.
The first particle group is made of titanium oxide.
The second particle group consists of a sulfide solid electrolyte.
In the cross section of the negative electrode active material layer, the contact interface length between the first particle group and the second particle group is 3.77 mm or more.
Negative electrode for all-solid-state batteries.

Images