All-solid-state batteries

Abstract

To provide an all-solid battery capable of improving the adhesion between a negative electrode current collector and a negative electrode layer while suppressing the degree of surface roughening of the negative electrode current collector.SOLUTION: The all-solid battery includes: a negative electrode layer containing negative electrode active material particles and solid electrolyte particles; and a negative electrode current collector. In the all-solid battery, the surface of the negative electrode current collector that comes into contact with the negative electrode layer is roughened, and the ratio of the ten-point average roughness of the surface of the negative electrode current collector in contact with the negative electrode layer to the D50 of the solid electrolyte particles included in the negative electrode layer is over 4.2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to all-solid-state batteries. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2018-106984 (Patent Document 1) discloses an all-solid-state lithium-ion battery including a laminate of a positive electrode, a negative electrode, and a solid electrolyte layer (separator layer). The negative electrode contains solid electrolyte particles and a plurality of Si particles as the negative electrode active material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-106984 Summary of the Invention [Problem to be solved by the invention]

[0004] When using an active material with a large volume change rate due to charging and discharging, such as a negative electrode active material containing Si, peeling is likely to occur at the interface between the negative electrode current collector (current collector foil) and the negative electrode layer (active material layer) when the active material shrinks due to charging and discharging. Therefore, repeated charging and discharging can reduce the contact area between the negative electrode current collector and the negative electrode layer, which can gradually increase the battery resistance.

[0005] One method for improving the adhesion between the negative electrode current collector and the negative electrode layer and suppressing peeling is to roughen the surface of the negative electrode current collector that comes into contact with the negative electrode layer. However, if the degree of roughening of the surface of the negative electrode current collector (the roughened portion) becomes too great, the capacity per volume of the battery decreases.

[0006] An object of the present disclosure is to improve the adhesion between the negative electrode current collector and the negative electrode layer while suppressing the degree of roughening of the surface of the negative electrode current collector. [Means for solving the problem]

[0007] [1] An all-solid-state battery comprising: a negative electrode layer including negative electrode active material particles and solid electrolyte particles; and a negative electrode current collector, a surface of the negative electrode current collector in contact with the negative electrode layer is roughened; an all-solid-state battery, wherein a ratio of a ten-point average roughness of a surface of the negative electrode current collector in contact with the negative electrode layer to a D50 of the solid electrolyte particles contained in the negative electrode layer is greater than 4.2.

[0008] According to the all-solid-state battery [1], the degree of roughening of the surface of the negative electrode current collector can be suppressed while improving the adhesion between the negative electrode current collector and the negative electrode layer, thereby suppressing an increase in battery resistance due to charge and discharge.

[0009] In the electrode [1], the D50 (D50 SE ) to the ten-point average roughness (Rz) of the surface of the negative electrode current collector 21 that is in contact with the negative electrode layer 22 (Rz / D50 SE ) is greater than 4.2. SE When the ρ exceeds 4.2, the adhesion between the negative electrode current collector 21 and the negative electrode layer 22 is enhanced. Therefore, small-sized solid electrolyte particles contained in the negative electrode layer enter the gaps in the roughened surface of the negative electrode current collector 21, increasing the contact area between the negative electrode current collector and the negative electrode layer and improving the adhesion at the interface. This is thought to suppress peeling between the negative electrode current collector and the negative electrode layer due to charge and discharge, maintaining contact (interfacial path) between the negative electrode current collector and the negative electrode layer and suppressing an increase in resistance in the all-solid-state battery.

[0010] [2] The all-solid-state battery according to [1], wherein the negative electrode active material particles contain Si.

[0011] A negative electrode active material containing Si (e.g., simple Si or a Si alloy) may be used as the material for the negative electrode active material particles. When the negative electrode active material particles contain Si, which has a higher capacity than carbon-based materials, the capacity and capacity density of the all-solid-state battery can be increased. However, since the volume change rate of negative electrode active material particles containing Si is relatively large during charging and discharging, when the negative electrode active material particles contain Si, peeling is particularly likely to occur at the interface between the negative electrode current collector and the negative electrode layer. For this reason, the present disclosure is particularly useful when the negative electrode active material particles contain Si.

[0012] [3] The all-solid-state battery according to [1] or [2], wherein a ratio of the ten-point average roughness of the surface of the negative electrode current collector in contact with the negative electrode layer to D50 of the solid electrolyte particles contained in the negative electrode layer is 5.0 or more and 100 or less.

[0013] According to the all-solid-state battery [3] above, it is possible to more reliably improve the adhesion between the negative electrode current collector and the negative electrode layer while suppressing the degree of roughening of the surface of the negative electrode current collector.

[0014] [4] The all-solid-state battery according to any one of [1] to [3], further comprising a positive electrode and a separator layer. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a conceptual diagram illustrating an example of an all-solid-state battery according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between negative electrode peel strength and Rz / D50SE in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0017] In this specification, elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)."

[0018] When a compound is expressed by a stoichiometric formula (e.g., "LiCoO2"), the stoichiometric formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobalt oxide is expressed as "LiCoO2," unless otherwise specified, the lithium cobalt oxide is not limited to a composition ratio of "Li / Co / O=1 / 1 / 2" and may contain Li, Co, and O in any composition ratio. Furthermore, doping or substitution with trace elements may be permitted.

[0019] <All-solid-state battery> Fig. 1 is a conceptual diagram showing an example of an all-solid-state battery according to this embodiment. The all-solid-state battery 100 shown in Fig. 1 includes an electricity storage element 5. The electricity storage element 5 includes a positive electrode 1, a negative electrode 2, and a separator layer 3. The positive electrode 1 includes a positive electrode current collector 11 and a positive electrode layer 12. The negative electrode 2 includes a negative electrode current collector 21 and a negative electrode layer 22.

[0020] The all-solid-state battery 100 may include, for example, an exterior body (not shown) that houses the electricity storage element 5. The exterior body may be, for example, a pouch made of a metal foil laminate film.

[0021] 《Negative electrode》 The negative electrode 2 includes a negative electrode current collector 21 and a negative electrode layer 22. The negative electrode 2 is layered.

[0022] (Negative electrode current collector) The negative electrode current collector 21 may include, for example, Cu foil, Ni foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm. For example, the negative electrode layer may be formed by applying a negative electrode composite material to the surface of the negative electrode current collector.

[0023] The ten-point mean roughness of the surface of the negative electrode current collector 21 that comes into contact with the negative electrode layer 22 is, for example, 1 to 10 μm.

[0024] The ten-point average roughness of the surface of the negative electrode current collector 21 in contact with the negative electrode layer 22 can be measured by obtaining an SEM image of a cross section parallel to the lamination direction of the negative electrode layer 22, reading the roughness of the interface of the negative electrode layer (the portion of the negative electrode layer in contact with the negative electrode current collector) from the SEM image, and measuring the ten-point average roughness (Rz) as specified in JIS B 0601:2001.

[0025] (negative electrode layer) The negative electrode layer 22 is in close contact with the separator layer 3. The negative electrode layer 22 may have a thickness of, for example, 10 to 200 μm.

[0026] The negative electrode layer 22 may include negative electrode active material particles and solid electrolyte particles.

[0027] The components of the negative electrode active material particles include, for example, carbon materials such as graphite, Si, SiO x (0 <x<2)、Li4Ti5O 12 Examples include:

[0028] The negative electrode active material particles may contain a negative electrode active material whose volume change rate due to charging and discharging of the all-solid-state battery is 10% or more, 100% or more, or 200% or more.

[0029] The volume change rate of an active material due to charging and discharging is the rate of change in the volume of the active material when it is most expanded relative to the volume of the active material when it is most contracted, for an active material that expands and contracts due to charging and discharging. That is, the volume change rate of an active material due to charging and discharging of an all-solid-state battery is expressed by the following formula: "Volume change rate of active material" (%) = [("Volume of active material when most expanded" - "Volume of active material when most contracted") / "Volume of active material when most contracted"] x 100

[0030] The volume change rate of the above active material can be measured by a known method, and for each common active material material, the volume change rate due to charge and discharge is known. The volume change rate (expansion rate) of the active material due to charge and discharge can be measured, for example, by calculating the lattice volume before and after charging using in-situ XRD. The volume change rate (expansion rate) of each active material measured by such a method is as follows. Si (single substance): 300% Carbon-based negative electrode active material (graphite): 10%

[0031] When a negative electrode active material with a relatively large volume change rate due to charge and discharge is used, peeling is likely to occur at the interface between the negative electrode (negative electrode layer) and the separator layer. Therefore, the present disclosure is particularly useful when the negative electrode active material particles contain an active material with a volume change rate of 10% or more due to charge and discharge of the all-solid-state battery.

[0032] The active material (negative electrode active material) with a volume change rate of 10% or more due to charge and discharge of the all-solid-state battery is not particularly limited, and examples thereof include a negative electrode active material containing Si (silicon element). Examples of the negative electrode active material containing Si include Si (single substance) or Si alloy. Examples of the Si alloy include SiO x (0 < x < 2). Since the negative electrode active material containing Si has a higher capacity than the carbon-based negative electrode active material, the capacity of the all-solid-state battery can be improved by including Si in the negative electrode active material particles. However, carbon materials such as graphite can also be included in the active material (negative electrode active material) with a volume change rate of 10% or more due to charge and discharge of the all-solid-state battery.

[0033] The negative electrode active material particles may be secondary particles (aggregates of primary particles). The negative electrode active material particles (secondary particles) may have, for example, a D50 (average particle diameter) of 1 to 50 μm, or a D50 of 1 to 20 μm, or a D50 of 5 to 15 μm. The primary particles may have, for example, a maximum Feret diameter of 0.1 to 3 μm.

[0034] In this specification, "D50" refers to the particle size at which the cumulative frequency from the smaller particle size side reaches 50% in a volume-based particle size distribution. D50 can be measured by a laser diffraction method.

[0035] The components of the solid electrolyte particles used in the negative electrode layer 22 may be the same as or different from the components of the solid electrolyte particles used in the separator layer 3 described below.

[0036] The components of the solid electrolyte particles are not particularly limited, and may be any of sulfide solid electrolytes, oxide solid electrolytes, hydrogen boron solid electrolytes, and the like.

[0037] The sulfide solid electrolyte may contain S and P. The sulfide solid electrolyte may further contain Li. The sulfide solid electrolyte may further contain, for example, O, Si, etc. The sulfide solid electrolyte may further contain, for example, a halogen such as iodine (I) or bromine (Br).

[0038] Examples of sulfide solid electrolytes include LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, and LiCl-LiBr-Li3PS 4、 LiCl-LiBr-Li2S-P2S5, LiCl-LiBr-Li2S-SiS2, etc. can be used.

[0039] For example, "LiI-LiBr-Li3PS4" refers to a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. "Li2S-P2S5" includes Li3PS4. Li3PS4 can be produced, for example, by mixing Li2S and P2S5 in a molar ratio of Li2S / P2S5 = 75 / 25.

[0040] The solid electrolyte may be any of argyrodite type, perovskite type, glass ceramic type, and the like.

[0041] In this embodiment, the D50 (D50 SE ) to the ten-point average roughness (Rz) of the surface of the negative electrode current collector 21 that is in contact with the negative electrode layer 22 (Rz / D50 SE ) is greater than 4.2. SE When the value exceeds 4.2, the adhesion between the negative electrode current collector 21 and the negative electrode layer 22 is improved.

[0042] Rz / D50 SE is preferably 5.0 or more and 100 or less, and more preferably 6.0 or more and 80 or less.

[0043] The D50 (D50 SE ) is preferably 0.01 to 2.5 μm, more preferably 0.02 to 1.5 μm, and even more preferably 0.05 to 1.0 μm.

[0044] The solid electrolyte particles used to form the negative electrode layer 22 may be fine particles obtained by, for example, atomizing larger solid electrolyte particles by mechanical grinding or the like.

[0045] The content of solid electrolyte particles in the negative electrode layer 22 may be, for example, 70 to 100 mass %, 80 to 99.9 mass %, or 90 to 99.8 mass %.

[0046] The surface of the negative electrode active material particles may be covered with, for example, a coating film to suppress reaction with the solid electrolyte particles and the like.

[0047] The negative electrode layer 22 may further contain, for example, a conductive material. The conductive material can form an electron conduction path within the negative electrode layer. The conductive material can contain any component. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes. The blending amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material particles.

[0048] The negative electrode layer 22 may further include, for example, a binder. The binder may include any component. The binder may include, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material particles.

[0049] 《Positive electrode》 The positive electrode 1 includes a positive electrode current collector 11 and a positive electrode layer 12. The positive electrode 1 is layered.

[0050] The positive electrode current collector 11 may be, for example, an Al foil. The positive electrode current collector 11 may have a thickness of, for example, 5 to 50 μm. For example, the positive electrode layer 12 may be formed by applying a positive electrode mixture to the surface of the positive electrode current collector 11.

[0051] The positive electrode layer 12 is in close contact with the separator layer 3. The positive electrode layer 12 may have a thickness of, for example, 10 to 200 μm.

[0052] The positive electrode layer 12 may include positive electrode active material particles and solid electrolyte particles.

[0053] Examples of components of the positive electrode active material particles include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, LiFePO4, Li2S, and P2S. 5、For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in the parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 is, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 ) O2, etc.

[0054] The positive electrode active material particles may be secondary particles (aggregates of primary particles). The secondary particles of the positive electrode active material particles may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm. The primary particles of the positive electrode active material particles may have a maximum Feret diameter of, for example, 0.1 to 3 μm.

[0055] The surfaces of the positive electrode active material particles may be covered with, for example, a coating film to suppress reaction with the solid electrolyte particles and the like.

[0056] The components of the solid electrolyte particles used in the positive electrode layer 12 may be the same as or different from the components of the solid electrolyte particles used in the separator layer 3 described below.

[0057] The positive electrode layer 12 may further include, for example, a conductive material and a binder. As the conductive material and binder, for example, the same conductive material and binder as those of the negative electrode layer 22 may be used.

[0058] The positive electrode active material particles may be subjected to heat treatment (baking). The heat treatment temperature may be, for example, 150 to 300°C. The heat treatment time may be, for example, 1 to 10 hours. For example, the heat treatment may be performed in air or in an inert atmosphere.

[0059] <Separator layer> The separator layer 3 is interposed between the positive electrode 1 and the negative electrode 2 . The separator layer 3 contains solid electrolyte particles. The solid electrolyte (solid electrolyte particles) used in the separator layer 3 may be the same type as or different from that of at least one of the negative electrode layer 22 and the positive electrode layer 12.

[0060] The separator layer 3 may further contain a binder. The blending amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the solid electrolyte particles. [Example]

[0061] Example 1 (Preparation of negative electrode) The following materials were prepared: Negative electrode active material particles: D50 is 3 μm, specific surface area is 4 m 2 / g Si powder Solid electrolyte particles: D50 (D50 SE ) powder of sulfide solid electrolyte (15LiBr 10LiI 75 (0.75Li2S 0.25P2S5) glass ceramics) with a particle size of 0.1 μm Conductive material: CNF (specific surface area: 14m 2 / g) Binder: SBR (styrene-butadiene rubber) binder Dispersion medium: butyl butyrate Negative electrode current collector: surface-roughened Ni foil (thickness: 10 μm, ten-point average roughness (Rz) of the roughened surface): 1.6 μm )

[0062] [Measurement of Ten-Point Average Roughness of Negative Electrode Current Collector] The ten-point average roughness (Rz) of the surface of the prepared negative electrode current collector, which was in contact with the negative electrode layer, was measured in advance. An SEM image of the surface was taken, and the surface roughness was read from the SEM image to measure the ten-point average roughness (Rz) as specified in JIS B 0601:2001. The measurement results are shown in Table 1.

[0063] The negative electrode active material particles, solid electrolyte particles, conductive material, binder, and dispersion medium were mixed to prepare a composition for forming a negative electrode layer (negative electrode slurry). The solid electrolyte particles were mixed in an amount of 100 parts by mass, the conductive material was mixed in an amount of 10 parts by mass, and the binder was mixed in an amount of 5 parts by mass, relative to 100 parts by mass of the negative electrode active material particles. The solid content of the negative electrode slurry was 40% by mass.

[0064] The negative electrode slurry was thoroughly stirred by ultrasonic dispersion treatment for 1 minute using an ultrasonic dispersion device. The negative electrode slurry was then applied to the negative electrode current collector by blade coating using a commercially available applicator until the coating weight (solid content) was 3 mg / cm. 2 The coating was then dried at 100°C for 60 minutes to form a negative electrode layer on the negative electrode current collector (on the roughened surface). In this way, the negative electrode of Example 1 was obtained.

[0065] <Examples 2 to 4 and Comparative Examples 1 and 2> In Example 2, the thickness and ten-point average roughness (Rz) of the negative electrode current collector, and the D50 of the solid electrolyte particles in the negative electrode layer were changed as shown in Table 1. Otherwise, all-solid-state batteries of Examples 2 to 4 and Comparative Examples 1 and 2 were fabricated using the same materials and processes as in Example 1.

[0066] <Peel strength> The peel strength (negative electrode peel strength) of the negative electrodes of the above examples and comparative examples was measured. Specifically, the negative electrode was cut into a 2cm x 10cm strip and pressed at 150°C and 10t for 1 minute using a uniaxial press. The surface of the negative electrode layer opposite the negative electrode current collector was then attached to the base of a tensile tester with double-sided tape. The edge of the negative electrode current collector (Ni foil) was peeled off and clamped in the tester's clamp, and the negative electrode current collector was pulled to measure the peel strength (negative electrode peel strength).

[0067] [Table 1]

[0068] From the results shown in Table 1 and Figure 2, Rz / D50 SE In Examples 1 to 4, where Rz / D50 is greater than 4.2, SE It can be seen that the peel strength (adhesion between the negative electrode layer and the negative electrode current collector) is significantly improved compared to Comparative Examples 1 and 2, in which the peel strength is 4.2 or less.

[0069] In the examples, by using solid electrolyte particles with a small D50 relative to the ten-point height average roughness (Rz) of the negative electrode current collector, the solid electrolyte (SE) particles penetrate into the irregularities or gaps on the roughened surface of the negative electrode current collector foil, increasing the contact area between the negative electrode layer and the negative electrode current collector, presumably improving the adhesion (peel strength) between the negative electrode layer and the negative electrode current collector. Thus, according to the present disclosure, by using solid electrolyte particles with a small D50, it is possible to reduce the degree of roughening of the surface of the negative electrode current collector (without increasing the thickness of the negative electrode current collector) and improve the adhesion between the negative electrode layer and the negative electrode current collector without reducing the battery capacity per volume. [Explanation of symbols]

[0070] 1 positive electrode, 11 positive electrode current collector, 12 positive electrode layer, 2 negative electrode, 21 negative electrode current collector, 22 negative electrode layer, 3 separator layer, 5 power storage element, 100 all-solid-state battery.

Claims

1. An all-solid-state battery comprising: a negative electrode layer including negative electrode active material particles and solid electrolyte particles; and a negative electrode current collector, the negative electrode active material particles contain Si, the negative electrode current collector is a Cu foil or a Ni foil, a surface of the negative electrode current collector in contact with the negative electrode layer is roughened; the surface of the negative electrode current collector in contact with the negative electrode layer has a ten-point average roughness of 1.6 μm or more and 3.9 μm or less; a ratio of the ten-point average roughness to D50 of the solid electrolyte particles contained in the negative electrode layer is 15.5 or more and 37.8 or less.

2. The all-solid-state battery according to claim 1 , wherein the negative electrode current collector is a Ni foil.

3. Further, the battery includes a positive electrode and a separator layer, The all-solid-state battery according to claim 1 or 2, wherein the separator layer contains solid electrolyte particles.

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