JP2020092100A - Negative electrode layer and lithium all-solid battery - Google Patents

Abstract

To provide a lithium all-solid battery good in capacity retention rate.SOLUTION: There is provided a negative electrode layer for use in a lithium all-solid battery, in which a metal particle that can be alloyed with Li is included as an active material. The metal particle has two or more types of crystal orientations in one particle.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a lithium all-solid-state battery having a good capacity retention rate.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones and communication devices in recent years, development of batteries used as power sources thereof has been emphasized. Also in the automobile industry and the like, development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles is under way. At present, among various batteries, a lithium battery is drawing attention because of its high energy density.

For example, Patent Document 1 discloses a lithium ion battery manufactured by a negative electrode composite material having a basis weight of 8.5 mg/cm ² or less, and the negative electrode composite material including a negative electrode containing a negative electrode active material and a solid electrolyte. .. Further, Patent Document 1 discloses that the negative electrode mixture contains a negative electrode active material composed of at least one of silicon, tin, indium, aluminum, and lithium. Patent Document 2 discloses a method for producing a negative electrode using amorphous Si powder. US Pat. No. 6,096,849 comprises a silicon/carbon composite material comprising carbon nano-objects partially or completely covered with silicon, and at least one capsule comprising a silicon shell with silicon nano-objects. , A silicon/carbon composite material is disclosed.

JP, 2013-212138, A JP, 2016-184495, A Japanese Patent Publication No. 2015-501279

For example, the negative electrode active material disclosed in Patent Document 1 has a problem that the volume change due to charge and discharge is large and the capacity retention rate is low. The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a negative electrode layer that improves the capacity retention rate of a lithium all-solid-state battery and a lithium all-solid-state battery.

In order to solve the above problems, in the present disclosure, a negative electrode layer used in a lithium all-solid-state battery has metal particles capable of alloying with Li as an active material, and the metal particles have 2 in 1 particle. Provided is a negative electrode layer having more than one type of crystal orientation.

According to the present disclosure, when the negative electrode layer has the above-described metal particles as an active material, it is possible to improve the capacity retention rate in the case of a lithium all-solid-state battery.

In the above disclosure, the metal particles are preferably Si simple substance or Si alloy.

In the present disclosure, a battery element having a negative electrode layer, a positive electrode layer, and a solid electrolyte layer formed between the negative electrode layer and the positive electrode layer is provided, and the negative electrode layer is the negative electrode layer described above. A featured lithium all-solid-state battery is provided.

According to the present disclosure, since the battery element has the above-described negative electrode layer, a lithium all-solid-state battery having a good capacity retention rate can be obtained.

In the above disclosure, it is preferable that the battery element further has a constraint portion that applies a constraint pressure in the thickness direction, and the constraint pressure is within a range of 3 MPa to 20 MPa. This is because a lithium all-solid-state battery having a good capacity retention rate even under a low constraint can be obtained.

In the above disclosure, a plurality of the battery elements may be included.

The negative electrode layer of the present disclosure can improve the capacity retention rate of a lithium all-solid-state battery.

It is a schematic sectional drawing which shows an example of the negative electrode layer of this indication. It is a schematic sectional drawing which shows an example of the metal particle in this indication. It is a schematic sectional drawing which shows an example of the lithium all-solid-state battery of this indication. It is an EBSD measurement result of Si particle (negative electrode active material) in Examples 1-4 and Comparative Examples 1-4. It is a graph which shows the relationship between binding pressure and capacity retention rate in the evaluation batteries of Examples 1 to 4 and Comparative Examples 1 to 4.

Hereinafter, details of the negative electrode layer and the lithium all-solid-state battery of the present disclosure will be described.

A. Negative Electrode Layer FIG. 1 is a schematic cross-sectional view showing an example of the negative electrode layer of the present disclosure, and FIG. 2 is a schematic cross-sectional view showing an example of metal particles used as a negative electrode active material. The negative electrode layer 1 shown in FIG. 1 is used for a lithium all-solid-state battery. Further, the negative electrode layer 1 has the metal particles 1a shown in FIG. 2 as an active material. The metal particles 1a are metal particles that can be alloyed with Li, and each particle has two or more types of crystal orientations. Specifically, in the EBSD measurement, the metal particle 1a has regions (A1 to A5 in FIG. 2) that are separately coated with two or more different colors in one particle.

According to the present disclosure, when the negative electrode layer has the above-described metal particles as an active material, it is possible to improve the capacity retention rate in the case of a lithium all-solid-state battery. Further, according to the present disclosure, since the negative electrode layer has the above-described metal particles as an active material, cracking inside the negative electrode layer during charging and discharging can be suppressed, and a negative electrode layer having good durability can be obtained. it can.

As an active material used in a lithium all-solid-state battery, for example, an alloy-based active material such as Si (an alloy-based active material that is a metal that can be alloyed with Li) is known. The alloy-based active material generally has a problem of large volume change due to charge/discharge and a low capacity retention rate.
With respect to this problem, the inventors of the present disclosure conducted an examination focusing on the crystallinity of the alloy-based active material, and found that the capacity retention rate was improved by controlling the crystallinity of the alloy-based active material. I found that I can do it. Specifically, as compared with the case of using metal particles having a single crystal orientation (hereinafter, also referred to as single crystal particles), metal particles having two or more types of crystal orientations in one particle (hereinafter , Sometimes referred to as twin grains), the capacity retention rate was improved.

The reason is presumed as follows. The alloy-based active material undergoes a large volume change due to charge/discharge (alloying with Li and dealloying). Therefore, stress due to the volume change of the alloy-based active material is generated inside the negative electrode layer, and “cracking” (for example, cracking of the negative electrode layer or cracking of the active material) occurs inside the negative electrode layer due to stress concentration. It is estimated that the capacity retention rate will decrease.
In the present disclosure, it is presumed that the presence of twin grains inside the negative electrode layer allows the twin portion to receive the generated stress, thereby alleviating the stress concentration. That is, it is presumed that by releasing the stress generated inside the negative electrode layer to the twin crystal grains, “cracking” inside the negative electrode can be suppressed and the capacity retention ratio can be improved.
On the other hand, for example, when single crystal particles are used, it is presumed that the single crystal particles cannot have a role of relaxing the stress generated inside the negative electrode layer. Therefore, it is presumed that the stress generated inside the negative electrode layer cannot be released, local stress concentration is likely to occur, and “cracking” inside the negative electrode layer is likely to occur.

Note that Patent Document 2 describes that amorphous Si is used in place of crystalline Si to improve the capacity retention rate of the battery, but there is no disclosure or suggestion about using twin particles. It has not been.

By the way, in a battery using an alloy-based active material, it is assumed that volume change is controlled, specifically, the binding pressure is increased, as one of the solutions for suppressing the decrease in capacity retention rate. However, from the viewpoint of cost, energy density, etc., it is desired that the binding pressure of the battery be as low as possible.

The inventors of the present disclosure can improve the capacity retention rate of a lithium all-solid-state battery by using the above-mentioned metal particles even under a low constraint (for example, about 3 MPa to 20 MPa). I found that I could do it.
Hereinafter, the negative electrode layer of the present disclosure will be described for each configuration.

1. Active Material The negative electrode layer in the present disclosure has, as an active material, metal particles that can be alloyed with Li. Further, the metal particles have two or more kinds of crystal orientations within one particle.

(1) Metal Particles Metal particles in the present disclosure are characterized by having two or more types of crystal orientations in one particle.
"A metal particle has two or more types of crystal orientations in one particle" means that two or more colors can be applied separately in a mapping image obtained by Electron Backscatter Diffraction Pattern (EBSD) measurement. There is something. EBSD measurement is a kind of crystal analysis by SEM (scanning electron microscope).
The specific measuring method is as follows.
First, metal particles are embedded in a resin, and the resin is cut to form a cross section. EBSD measurement is performed on the obtained cross section at a magnification that includes, for example, about 5 metal particles. The obtained diffraction pattern is analyzed and a mapping image is obtained by IPF (Inverce Pole Figure) mapping.
The measurement conditions are as follows.
・Cross-section fabrication device: JEOL SM-09010 cross section polisher, ion source: argon, accelerating voltage: 5.5 kV
・SEM
Apparatus: JEOL JSM-7000F field emission scanning electron microscope, accelerating voltage: 7.5 kV
・EBSD
Equipment: TSL OIM crystal orientation analyzer, acceleration voltage: 15 kV
Note that, in the cross-section production, in addition to the above-described conditions, for example, conditions of an apparatus: IM-4000 manufactured by Hitachi High-Technologies Corporation, an ion source: Ar, and an acceleration voltage: 5.0 kV may be used.

The metal particles according to the present disclosure have two or more types of crystal orientations within one particle.
The number of crystal orientations of the metal particles may be two or more, for example, three or more, or four or more. The upper limit of the number of crystal orientations is not particularly limited, and may be, for example, 10 types or less, 9 types or less, and 7 types or less.
The number of crystal orientations can be measured by the number of color-coded regions and the difference in color in the map diagram obtained by EBSD measurement. For example, as shown in FIG. 2, there are five color-coded regions (A1 to A5) in the metal particle 1a (one particle), and in the case of being colored in three colors, the number of crystal orientations is three.

In the cross section of the metal particles, of the two or more crystal orientations contained in one particle, the area of the crystal orientation having the smallest area is S _Min, and the total area of one particle is S _tot , S _Min /S The ratio of _tot is, for example, 1% or more, preferably 3% or more, and more preferably 10% or more. Since the single crystal and the twin crystal are in reality very different systems, it is presumed that the judgment is possible even if the ratio of S _Min /S _tot is small.

Examples of the metal particles include a simple substance or an alloy containing at least one metal element of Si element, Sn element, In element, and Al element. The metal particles are preferably Si simple substance or Si alloy, and more preferably Si simple substance.
When the metal particles are a Si alloy, the proportion of the Si element in the Si alloy may be, for example, 50 mol% or more, 70 mol% or more, and 90 mol% or more. Moreover, the ratio of the Si element in the simple substance of Si is usually 100 mol %.

The average particle diameter (D ₅₀ ) of the metal particles is, for example, in the range of 10 nm to ₅₀ μm, and preferably in the range of 100 nm to 20 μm.

Examples of the method of preparing the metal particles include a method of mechanically crushing single crystal metal particles to form twin crystal particles. For example, it is presumed that when single-crystal metal particles are mechanically pulverized by applying a shearing force, the crystallinity is lowered to form twin crystal particles. In addition, as a method for preparing the metal particles, for example, a method of changing the crystal growth rate in the middle to form twin particles can be mentioned.

(2) Active Material The negative electrode layer has at least the above metal particles as an active material. The negative electrode layer may have only the above metal particles as an active material, or may further contain an active material other than the above metal particles. Other active materials include amorphous alloys that can be alloyed with Li and single crystals that can be alloyed with Li. The ratio of the metal particles (metal particles having two or more kinds of crystal orientations in one particle) to all active materials is, for example, preferably 50 mol% or more, preferably 70 mol% or more, and 90 mol% or more. Is preferred. The ratio of the single crystal particles to the total active material is, for example, preferably 10% or less, preferably 5% or less, and more preferably 2% or less.

The ratio of the active material in the negative electrode layer is, for example, 30% by weight or more, and preferably 50% by weight or more. The ratio of the negative electrode active material is, for example, 99% by weight or less, may be 85% by weight or less, and may be 80% by weight or less.

(3) Negative Electrode Layer The negative electrode layer in the present disclosure usually contains the above-mentioned active material, and may further contain at least one of a solid electrolyte material, a conductive auxiliary agent, and a binder, if necessary. good.

Examples of the solid electrolyte material include inorganic solid electrolyte materials such as sulfide solid electrolyte materials. The sulfide-based solid electrolyte material, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -Li 3 PO 4, LiI-P 2 S 5 -Li 3 PO 4, Li 2 S-P _{2 S 5 -LiI, Li 2 S} -P 2 S 5 -LiI-LiBr, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S _{-P 2 O 5, LiI-Li} 2 S-P 2 O 5, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiI-LiBr, Li 2 S-SiS 2 _{-LiBr, Li 2 S-SiS 2} -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li _{2 S-P 2 S 5 -Z} m S n ( however, m, n is the number of positive .Z is, Ge, Zn, one of _{Ga.), Li 2 S-} GeS 2, Li 2 S-SiS 2 _{-Li 3 PO 4, Li 2 S} -SiS 2 -Li x MO y ( provided that, x, y is a positive number .M is, P, Si, Ge, B , Al, Ga, either an in.) or the like Can be mentioned. Incidentally, the above description _"Li 2 _S-P 2 _{S 5"} means a sulfide solid electrolyte material obtained by using a raw material composition containing Li ₂ S and _P 2 _{S 5,} the same for the other described is there.

Particularly, the sulfide solid electrolyte material preferably includes an ion conductor containing Li, A (A is at least one of P, Si, Ge, Al and B) and S. Furthermore, the ionic conductor has an anion structure of an ortho composition (PS ₄ ³⁻ structure, SiS ₄ ⁴⁻ structure, GeS ₄ ⁴⁻ structure, AlS ₃ ³⁻ structure, BS ₃ ³⁻ structure) as a main component of anion. It is preferable to have. This is because a sulfide solid electrolyte with high chemical stability can be obtained. The ratio of the anion structure of the ortho composition is preferably 70 mol% or more, and more preferably 90 mol% or more, based on the total anion structure in the ionic conductor. The ratio of the anion structure in the ortho composition can be determined by Raman spectroscopy, NMR, XPS or the like.

The sulfide solid electrolyte material may contain lithium halide in addition to the above ion conductor. Examples of lithium halides include LiF, LiCl, LiBr, and LiI, and among them, LiCl, LiBr, and LiI are preferable. The ratio of LiX (X=I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 5 mol% to 30 mol%, and preferably in the range of 15 mol% to 25 mol%. The ratio of LiX refers to the total ratio of LiX contained in the sulfide solid electrolyte.

The sulfide solid electrolyte material may be a crystalline material or an amorphous material. Further, the sulfide solid electrolyte may be glass or crystallized glass (glass ceramics). Examples of the shape of the sulfide solid electrolyte material include a particulate shape.

The weight ratio (active material/solid electrolyte material) of the active material and the solid electrolyte material in the negative electrode layer is, for example, preferably in the range of 30/70 to 85/15, and in the range of 40/60 to 80/20. May be

Examples of the conductive aid include carbon materials such as acetylene black (AB), Ketjen black (KB), carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). More specifically, vapor grown carbon fiber (VGCF) may be used as the carbon material. Further, as the vapor grown carbon fiber, for example, VGCF manufactured by Showa Denko KK may be used.
Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). .. Further, the thickness of the negative electrode layer is, for example, preferably in the range of 1 μm to 100 μm, and more preferably in the range of 30 μm to 100 μm. The negative electrode layer of the present disclosure is used for a lithium all-solid-state battery.

B. Lithium All Solid State Battery FIG. 3 is a schematic cross-sectional view showing an example of the lithium all solid state battery of the present disclosure. The all-solid-state battery 100 shown in FIG. 3 has a battery element 10 having a negative electrode layer 1, a positive electrode layer 2, and a solid electrolyte layer 3 formed between the negative electrode layer 1 and the positive electrode 2. Further, the all-solid-state battery 100 has a negative electrode current collector 4 that collects current from the negative electrode layer 1, a positive electrode current collector 5 that collects current from the positive electrode layer 2, and a battery case 6 that houses these members. .. In the present disclosure, the negative electrode layer 1 is the above-mentioned “A. negative electrode layer”.
In the present disclosure, the lithium all-solid-state battery 100 may further include the restraint member 20. The restraint member 20 is a member that applies a restraint pressure to the battery element 10 in the thickness direction D _T. Specifically, the restraint member 20 is connected to the sandwiched plate-shaped portions 11 arranged on both surface sides of the battery element 10, the rod-shaped portion 12 that connects the two plate-shaped portions 11, and the rod-shaped portion 12, and has a screw structure or the like. And an adjusting unit 13 for adjusting the restraining pressure. In the present disclosure, the restraint member 20 applies a predetermined restraint pressure to the battery element 10.

According to the present disclosure, since the battery element has the above-described negative electrode layer, a lithium all-solid-state battery having a good capacity retention rate can be obtained.
Hereinafter, the lithium all-solid-state battery of the present disclosure will be described for each configuration.

1. Battery Element The battery element in the present disclosure has a negative electrode layer, a positive electrode layer, and a solid electrolyte layer formed between the negative electrode layer and the positive electrode layer.

(1) Negative Electrode Layer The negative electrode layer in the present disclosure can be the same as the content described in the above-mentioned section “A. Negative electrode layer”, and thus the description thereof is omitted here.

(2) Positive Electrode Layer The positive electrode layer in the present disclosure is a layer containing at least a positive electrode active material, and contains at least one of a solid electrolyte material, a conductive auxiliary agent, a binder, and a thickener, if necessary. It may be. Examples of the positive electrode active material include oxide active materials.

Examples of the oxide active material include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li _{4 and the like.} Examples thereof include spinel-type active materials such as Ti ₅ O ₁₂ and Li(Ni _0.5 Mn _1.5 )O ₄ , and olivine-type active materials such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO ₄ . Further, LiMn as an oxide active _{material, Li 1 + x Mn 2-} x-y M y O 4 (M is, Al, Mg, Co, Fe , Ni, at least one of Zn, 0 <x + y < 2) is represented by A spinel active material, lithium titanate or the like may be used.

Further, it is preferable that a coat layer composed of a Li ion conductive oxide is formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte material can be suppressed. Examples of the Li ion conductive oxide include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , and Li ₃ PO ₄ . The coat layer has a thickness of, for example, 0.1 nm to 100 nm, preferably 1 nm to 20 nm. The coverage of the coating layer on the surface of the positive electrode active material is, for example, 50% or more, preferably 80% or more.

The solid electrolyte material, the conductive additive, the binder, and the like used in the positive electrode layer are the same as those in the above-described negative electrode layer. The weight ratio (active material/solid electrolyte material) of the active material and the solid electrolyte material in the positive electrode layer is preferably, for example, in the range of 30/70 to 85/15, and in the range of 50/50 to 80/20. May be Further, the thickness of the positive electrode layer is, for example, preferably in the range of 1 μm to 100 μm, and more preferably in the range of 3 μm to 100 μm.

(3) Solid Electrolyte Layer The solid electrolyte layer in the present disclosure is a layer formed between the positive electrode layer and the negative electrode layer. Further, the solid electrolyte layer is a layer containing at least a solid electrolyte material, and may further contain a binder if necessary.

The solid electrolyte material and the binder used in the solid electrolyte layer are the same as those in the above-mentioned negative electrode layer. In addition, the content of the solid electrolyte material in the solid electrolyte layer is, for example, in the range of 10% by weight to 100% by weight, and preferably in the range of 50% by weight to 100% by weight. Further, the thickness of the solid electrolyte layer is, for example, in the range of 0.1 μm to 300 μm, and preferably in the range of 0.1 μm to 100 μm.

2. Restraint Member The restraint member in the present disclosure is a member that applies a restraint pressure in the thickness direction of the battery element. The configuration of the restraint member is not particularly limited, but examples thereof include a restraint member having a plate-shaped portion, a rod-shaped portion, and an adjustment portion as shown in FIG. 3 described above. The restraint member may be subjected to necessary insulation treatment so that the positive and negative electrodes are not short-circuited.

The binding pressure applied to the lithium all-solid-state battery by the binding member can be appropriately selected according to the type of the battery and is not particularly limited. The binding pressure may be, for example, 3 MPa or more, or 5 MPa or more. Further, the binding pressure may be, for example, 100 MPa or less, 50 MPa or less, 45 MPa or less, or 20 MPa or less. In the present disclosure, the binding pressure is preferably in the range of 3 MPa to 20 MPa, among others. In the present disclosure, it is possible to provide a lithium all-solid-state battery having a good capacity retention rate even under a low constraint.

3. Other Configurations The lithium all-solid-state battery of the present disclosure usually has a positive electrode current collector that collects current in the positive electrode layer and a negative electrode current collector that collects current in the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, Ni, Cr, Au, Pt, Al, Fe, Ti and Zn. A coating layer of Ni, Cr, C or the like may be formed on the surface of the positive electrode current collector. The coat layer may be, for example, a plating layer or a vapor deposition layer. On the other hand, examples of the material of the negative electrode current collector include Cu and Cu alloys. A coating layer of Ni, Cr, C or the like may be formed on the surface of the negative electrode current collector. The coat layer may be, for example, a plating layer or a vapor deposition layer. Further, as the battery case, for example, a SUS battery case or the like can be used. Note that, as shown in FIG. 3, the restraint member 20 preferably restrains the battery element 10 from the outside of the battery case 6.

4. Lithium All-Solid-State Battery The lithium all-solid-state battery of the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery among them. This is because it can be repeatedly charged and discharged and is useful as, for example, a vehicle battery. Note that the primary battery also includes use of the secondary battery as a primary battery (use for the purpose of only discharging once after charging). Examples of the shape of the lithium all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type.

The lithium all-solid-state battery may have one battery element or may have a plurality of battery elements. In the latter case, it is preferable that a plurality of battery elements are stacked in the thickness direction.
The plurality of battery elements may be connected in parallel or may be connected in series. The latter case corresponds to a so-called bipolar battery, and usually an intermediate current collector is formed between two adjacent battery elements.

Note that the present disclosure is not limited to the above embodiment. The above-described embodiment is an exemplification, and it has substantially the same configuration as the technical idea described in the claims of the present disclosure, and has any similar effects to the present invention. It is included in the technical scope of the disclosure.

Hereinafter, the present disclosure will be described more specifically with reference to examples.

[Example 1]
(Preparation of metal particles)
Elkem was requested to manufacture Si particles (Supreme microncut Supreme 20) aiming at an average particle size of 20 μm.
When the produced Si particles were examined using the EBSD measurement described in the above section “1. Active material (1) Metal particles”, Si particles having 2 to 7 crystal orientations in one particle were examined. It was confirmed to be (metal particles). The results are shown in Fig. 4(a).
The proportion of single crystal particles in the entire Si particles used in Example 1 was 2% or less. For example, in EBSD measurement, it may be observed at a ratio of about 1 particle in 50 particles.

(Preparation of negative electrode layer)
In a polypropylene (PP) container, butyl butyrate and a butyl butyrate solution containing a PVDF-based binder at a ratio of 5% by weight, a negative electrode active material (metal particles), and a sulfide solid electrolyte material (Li ₂ S-P ₂ (S ₅ type glass ceramics) and a conductive additive (VGCF) were added, and the mixture was stirred for 30 seconds with an ultrasonic dispersion device (UH-50 manufactured by SMT). Then, it was shaken with a shaker (Shibata Scientific Co., Ltd., TTM-1) for 30 minutes. This obtained the negative electrode slurry.
The obtained negative electrode slurry was applied on a negative electrode current collector (Cu foil) by a blade method using an applicator, and dried on a hot plate at 100° C. for 30 minutes. Through the above steps, a negative electrode layer and a negative electrode current collector were obtained.

(Preparation of positive electrode layer)
In a polypropylene (PP) container, butyl butyrate, a butyl butyrate solution containing a PVDF-based binder at a ratio of 5% by weight, a positive electrode active material (LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , average particle size) (Diameter D ₅₀ =6 μm), a sulfide solid electrolyte material (Li ₂ S-P ₂ S ₅ glass ceramics), and a conductive additive (VGCF) are added, and an ultrasonic dispersion device (SH UH-50) is added. And stirred for 30 seconds. Then, it was shaken with a shaker (Shibata Scientific Co., Ltd., TTM-1) for 3 minutes. As a result, a positive electrode slurry was obtained.
The obtained positive electrode slurry was applied on a positive electrode current collector (Al foil, manufactured by Showa Denko KK) by a blade method using an applicator, and dried on a hot plate at 100° C. for 30 minutes. Through the above steps, a positive electrode layer and a positive electrode current collector were obtained.

(Preparation of solid electrolyte layer)
In a polypropylene (PP) container, heptane, a heptane solution containing a butylene rubber (BR) binder at a ratio of 5% by weight, and a sulfide solid electrolyte material (Li ₂ S-P ₂ S ₅ glass ceramics). The mixture was added and stirred with an ultrasonic dispersion device (UH-50 manufactured by SMT) for 30 seconds. Then, it was shaken for 30 minutes with a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.). As a result, a solid electrolyte slurry was obtained.
The obtained slurry was applied onto a substrate (Al foil) by a blade method using an applicator, and dried on a hot plate at 100° C. for 30 minutes. As described above, a base material having a solid electrolyte layer on its surface was obtained.

(Preparation of evaluation battery)
The solid electrolyte layer was laminated on the positive electrode layer so that the solid electrolyte layer was in contact with the positive electrode layer, and pressed at 1 ton/cm ² . Next, the Al foil as the base material of the solid electrolyte layer was peeled off to prepare a laminate of the solid electrolyte layer and the positive electrode layer. A negative electrode layer was placed on the solid electrolyte layer side of the laminate and pressed at 6 ton/cm ² to obtain a cell. The diameter of the negative electrode layer was made larger than that of the positive electrode layer.
The produced cell was restrained at 15 MPa using a restraint jig to obtain an evaluation battery.

[Comparative Example 1]
A battery for evaluation was obtained in the same manner as in Example 1 except that Si particles (SIE23PB manufactured by Kojundo Chemical Laboratory Co., Ltd.) were used as the negative electrode active material. When the Si particles used in Comparative Example 1 were examined by EBSD measurement, it was confirmed to be Si particles having one type of crystal orientation. The results are shown in Fig. 4(b).

[Examples 2 to 4]
An evaluation battery was obtained in the same manner as in Example 1 except that the binding pressure of the cell was set to 5 MPa (Example 2), 20 MPa (Example 3), and 45 MPa (Example 4).

[Comparative Examples 2 to 4]
An evaluation battery was obtained in the same manner as in Comparative Example 1 except that the cell confining pressure was 3 MPa (Comparative Example 2), 30 MPa (Comparative Example 3), and 45 MPa (Comparative Example 4).

[Evaluation]
The batteries for evaluation were subjected to the following treatments (1) to (4).
(1) Activation Constant current-constant voltage charge up to 4.55V (final current 1/100C) at a rate of 10 hours (1/10C), and then constant current-constant voltage discharge up to 2.5V to activate the battery. Turned into
(2) Measurement of initial discharge capacity Constant current-constant voltage charge was charged to 4.35 V, constant current-constant voltage discharge was discharged to 3.0 V, and the initial discharge capacity was measured.
(3) Durability test After charging to 4.08 V, charging and discharging were changed every one second, and discharging corresponding to SOC 61.6% was performed so that discharge capacity>charge capacity. After discharging, the battery was charged again to 4.08V. This charge/discharge treatment was repeated for 28 days.
(4) Discharge capacity measurement after durability test Charging and discharging were performed under the same conditions as in (2), and the discharge capacity after durability test was measured.

The value of the discharge capacity after the durability test with respect to the initial discharge capacity was determined as the capacity retention rate (%).
The results are shown in Table 1 and FIG. The capacity retention rate in Table 1 is a relative value when the capacity retention rate in Comparative Example 1 is 100%.

As shown in FIG. 5, from the results of Examples 1 to 4 and Comparative Examples 1 to 4, single crystal particles having one type of crystal orientation were used when the constraining pressure was constant (the horizontal axis was constant). Compared with the case, it was confirmed that the capacity retention ratio can be improved when twin grains having two or more crystal orientations are used.
Further, in the range of the binding pressure of 3 MPa to 20 MPa (corresponding to 1 N·m or less), the effect of holding the capacity retention ratio was found to be higher in the example than in the comparative example. Therefore, it was suggested from the examples that the negative electrode layer of the present disclosure can improve the capacity retention rate particularly under low restraint.

DESCRIPTION OF SYMBOLS 1... Negative electrode layer 2... Positive electrode layer 3... Solid electrolyte layer 4... Negative electrode collector 5... Positive electrode collector 10... Battery element 20... Restraint member 100... Lithium all-solid-state battery

Claims (5)

A negative electrode layer used in a lithium all-solid-state battery,
Having metal particles capable of alloying with Li as an active material,
The metal particles are twin particles having two or more types of crystal orientations in one particle,
In the EBSD measurement, a negative electrode layer having regions which are separately coated with different colors of 2 to 7 colors in one particle. The negative electrode layer according to claim 1, wherein the metal particles are a simple substance of Si or a Si alloy. A battery element having a negative electrode layer, a positive electrode layer, and a solid electrolyte layer formed between the negative electrode layer and the positive electrode layer, wherein the negative electrode layer is the negative electrode layer according to claim 1 or 2. A lithium all-solid-state battery characterized in that The lithium all-solid-state battery according to claim 3, further comprising a constraint portion that applies a constraint pressure in a thickness direction of the battery element, the constraint pressure being within a range of 3 MPa to 20 MPa. The lithium all-solid-state battery according to claim 3 or 4, comprising a plurality of the battery elements.