All solid state battery

Abstract

To provide an all-solid battery that can increase the capacity retention rate.SOLUTION: An all-solid battery includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, a binder obtained from a material having a double bond, and a conductive material containing a material having a needle-like structure, and the binder is 5 volume% or more and 20 volume% or less with respect to the negative electrode active material layer, and the volume ratio of conductive material / binder is 0.4 or more and 1.0 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] An all-solid-state battery includes a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and a solid electrolyte layer including a solid electrolyte disposed therebetween.

[0003] Patent Document 1 discloses an all-solid-state battery that uses a Si-containing active material as the negative electrode active material. Patent Document 2 discloses an electrode active material (vapor grown carbon fiber) / conductive material composite containing an electrode active material and a conductive material, and discloses that SBR (styrene butadiene rubber) may be used as a dispersant therefor. Patent Document 3 discloses an electrode for an all-solid-state battery that contains vapor-grown carbon fibers. Patent Document 4 discloses that SBR may be used as the binder, and vapor-grown carbon fiber may be used as the conductive material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-112029 A [Patent Document 2] JP 2013-135223 A [Patent Document 3] Special Publication No. 2020-507893 [Patent Document 4] JP 2020-177904 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned conventional techniques, it is disclosed that the negative electrode active material layer contains a binder and a conductive material, but there is a problem that the capacity retention rate after charging and discharging is low. In view of the above, an object of the present disclosure is to provide an all-solid-state battery capable of increasing the capacity retention rate. [Means for solving the problem]

[0006] As one means for solving the above problems, the present disclosure discloses an all-solid-state battery having a negative electrode active material layer, in which the negative electrode active material layer contains a negative electrode active material, a binder obtained from a material having a double bond, and a conductive material including a material having a needle-like structure, in which the binder accounts for 5 vol% or more and 20 vol% or less of the negative electrode active material layer, and the volume ratio of the conductive material / binder is 0.4 or more and 1.0 or less. Effect of the Invention

[0007] According to the all-solid-state battery of the present disclosure, the capacity retention rate can be increased. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating a layer structure of the all-solid-state battery 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1.All-solid-state battery A schematic cross-sectional view showing an example of an all-solid-state battery 10 according to the present disclosure is shown in Fig. 1. As shown in Fig. 1, the all-solid-state battery 10 has a positive electrode active material layer 11 containing a positive electrode active material, a negative electrode active material layer 12 containing a negative electrode active material, a solid electrolyte layer 13 formed between the positive electrode active material layer 11 and the negative electrode active material layer 12, a positive electrode current collector layer 14 that collects current from the positive electrode active material layer 11, and a negative electrode current collector layer 15 that collects current from the negative electrode active material layer 12. The positive electrode active material layer 11 and the positive electrode current collector layer 14 may be collectively referred to as a positive electrode, and the negative electrode active material layer 12 and the negative electrode current collector layer 15 may be collectively referred to as a negative electrode. Each component of the all-solid-state battery 10 will be described below.

[0010] 1.1.Cathode active material layer The positive electrode active material layer 11 is a layer containing a positive electrode active material, and may further contain at least one of a solid electrolyte material, a conductive material, and a binder, as necessary. The positive electrode active material may be a known active material. For example, cobalt-based (LiCoO2, etc.), nickel-based (LiNiO2, etc.), manganese-based (LiMn2O4, Li2Mn2O3, etc.), iron phosphate-based (LiFePO4, Li2FeP2O7, etc.), NCA-based (nickel, cobalt, aluminum compound), NMC-based (nickel, manganese, cobalt compound), etc. are listed. More specifically, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. The surface of the positive electrode active material may be covered with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer. The particle size of the positive electrode active material is not particularly limited, but is preferably in the range of, for example, 5 μm to 50 μm. In this specification, the term "particle size" refers to the particle size at 50% cumulative value (D50) in the volume-based particle size distribution measured by a laser diffraction / scattering method. The content of the positive electrode active material in the positive electrode active material layer is, for example, in the range of 50% by weight to 99% by weight.

[0011] The solid electrolyte is preferably an inorganic solid electrolyte, since it has higher ionic conductivity and superior heat resistance compared to organic polymer electrolytes. Examples of inorganic solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes. Examples of sulfide solid electrolyte materials having Li ion conductivity include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S- Examples of the sulfide include SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are positive numbers. Z is any of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-LixMOy (where x and y are positive numbers. M is any of P, Si, Ge, B, Al, Ga, and In). The above description of "Li2S-P2S5" refers to a sulfide solid electrolyte material made using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0012] On the other hand, examples of oxide solid electrolyte materials having Li ion conductivity include compounds having a NASICON structure. An example of a compound having a NASICON structure is a compound represented by the general formula Li 1+x Al x Ge 2-x Compounds represented by the formula (PO4)3 (0≦x≦2) (LAGP), general formula Li 1+x Al x Ti 2-x (PO4)3 (0≦x≦2) (LATP) and the like. Another example of the oxide solid electrolyte material is LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0013] The content of the solid electrolyte in the positive electrode active material layer 11 is not particularly limited, but is, for example, in the range of 1% by weight to 50% by weight.

[0014] The binder is not particularly limited as long as it is chemically and electrically stable, and examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as styrene butadiene rubber (SBR), olefin-based binders such as polypropylene (PP) and polyethylene (PE), and cellulose-based binders such as carboxymethylcellulose (CMC). The content of the binder in the positive electrode active material layer 11 is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0015] As the conductive material, carbon materials such as acetylene black (AB), ketjen black, and carbon fiber, and metal materials such as nickel, aluminum, and stainless steel can be used. The content of the conductive material in the positive electrode active material layer 11 is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0016] A sheet-like positive electrode active material layer 11 is preferable from the viewpoint of facilitating the formation of the all-solid-state battery 10. In this case, the thickness of the positive electrode active material layer 11 is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less.

[0017] 1.2.Negative electrode active material layer The negative electrode active material layer 12 is a layer containing at least a negative electrode active material, a binder, and a conductive material, and may contain a solid electrolyte material as necessary. The solid electrolyte material can be considered to be similar to the positive electrode active material layer 11.

[0018] The negative electrode active material is not particularly limited. In the case of forming a lithium ion battery, examples of the negative electrode active material include carbon materials such as graphite and hard carbon, various oxides such as lithium titanate, Si and Si alloys, metallic lithium and lithium alloys, and the like. Among them, in the present disclosure, Si and Si alloys are preferable, since Si materials expand and contract greatly upon charging and discharging, and therefore the effects of the present disclosure are more prominent.

[0019] In this embodiment, the binder is obtained from a material containing a double bond, and the material is contained in the negative electrode active material layer 12 in an amount of 5 vol % to 20 vol %. Examples of materials containing double bonds include styrene butadiene rubber (SBR) and acrylonitrile butadiene rubber (NBR).

[0020] In this embodiment, the conductive material is a material having a needle-like structure, and in the negative electrode active material layer 12, the ratio by volume of the conductive material to the binder (volume ratio of conductive material / volume ratio of binder) is 0.4 or more and 1.0 or less. Examples of materials having a needle-like structure include carbon fiber (CF) and carbon nanotube (CNT). Here, the "needle-like structure" refers to a fiber diameter of 300 nm or less, and a fiber length relative to the fiber diameter (aspect ratio of fiber length / fiber diameter) of 40 or more.

[0021] With a negative electrode active material layer having such a configuration, even when the negative electrode active material layer expands and contracts, the generation of cracks in the negative electrode active material (particularly between the negative electrode active material and the solid electrolyte) can be suppressed, and the negative electrode active material can be suppressed from becoming isolated and causing a decrease in capacity. Specifically, by containing the binder and conductive material in the above ratio, the negative electrode active material layer has a good balance of flexibility, electronic conductivity, and ionic conductivity, and thus satisfies both the inhibition of cracking and electrical conductivity. It is believed that the use of a material having a needle-like structure as the conductive material can improve the strength of the negative electrode active material layer by acting as a filler, and that the use of a binder obtained from a material containing double bonds as the binder can prevent cracks from occurring by adsorbing the binder to the conductive material and forming a mechanically stronger network.

[0022] The shape of the negative electrode active material layer 12 may be the same as that of a conventional negative electrode active material layer. From the viewpoint of easily constructing the all-solid-state battery 10, a sheet-shaped negative electrode active material layer 12 is preferable. In this case, the thickness of the negative electrode active material layer 12 is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less.

[0023] 1.3.Solid electrolyte layer The solid electrolyte layer 13 is a solid electrolyte layer disposed between the positive electrode active material layer 11 and the negative electrode active material layer 12. The solid electrolyte layer 13 contains at least a solid electrolyte material. The solid electrolyte material can be considered to be the same as the solid electrolyte material described for the positive electrode active material layer 11.

[0024] The solid electrolyte layer 13 may optionally include a binder. The type of binder may be the same as that used in the positive electrode active material layer 11. The content of the binder in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0025] 1.4.Current collector layer The current collectors are a positive electrode current collector layer 14 that collects current from the positive electrode active material layer 11, and a negative electrode current collector layer 15 that collects current from the negative electrode active material layer 12. Examples of materials constituting the positive electrode current collector layer 14 include stainless steel, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials constituting the negative electrode current collector layer 15 include stainless steel, copper, nickel, and carbon. There are no particular limitations on the thickness of the positive electrode current collector layer 14 and the negative electrode current collector layer 15, and the thickness may be appropriately set according to the desired battery performance, for example, in the range of 0.1 μm to 1 mm.

[0026] 1.5.Battery case The all-solid-state battery may include a battery case (not shown) for housing each component, and may be, for example, a stainless steel battery case.

[0027] 2. Effects etc. In an all-solid-state battery including the above-described negative electrode active material layer, even when the negative electrode active material layer expands and contracts, the generation of cracks in the negative electrode active material (particularly between the negative electrode active material and the solid electrolyte) can be suppressed, and the negative electrode active material can be suppressed from being isolated and causing a decrease in capacity.

[0028] 3. Manufacturing method of all-solid-state batteries A method for producing an all-solid-state battery will be described below. The method for producing an all-solid-state battery may be carried out as known in the art, and may be carried out, for example, as follows.

[0029] [Fabrication of the positive electrode structure] The materials constituting the positive electrode active material layer are mixed to obtain a slurry positive electrode composition, which is then applied to the surface of a material that will become the positive electrode current collector layer, and a layer that will become the positive electrode active material layer is formed through a process of heating and drying, and then pressed to obtain a positive electrode structure having a layer that will become the positive electrode current collector layer and a layer that will become the positive electrode active material layer.

[0030] [Fabrication of negative electrode structure] The materials constituting the negative electrode active material layer are mixed to obtain a slurry negative electrode composition, and then the slurry negative electrode composition is applied to the surface of the material that will become the negative electrode current collector layer, and a layer that will become the negative electrode active material layer is formed through a process of heating and drying, and then pressed to obtain a negative electrode structure having a layer that will become the negative electrode current collector layer and a layer that will become the negative electrode active material layer.

[0031] [Solid electrolyte layer and all-solid-state battery fabrication] Materials for the solid electrolyte layer are mixed to obtain a slurry of a solid electrolyte composition, which is then applied to the surface of, for example, an aluminum foil, and dried by heating to form a layer that will become the solid electrolyte layer. Then, a layer that will become a solid electrolyte is transferred to the above-prepared positive electrode structure, and then a negative electrode structure is transferred to the positive electrode structure, thereby producing an all-solid-state battery.

[0032] 4. Working Example 4.1. Fabrication of all-solid-state batteries according to each example [Fabrication of the positive electrode structure] Cathode active material (LiNi 0.33 Co 0.33 Mn 0.33 The positive electrode active material was weighed out so that the volume ratio of the positive electrode active material to the solid electrolyte was 75:25. The PVDF binder was weighed out at 1.5 parts by weight per 100 parts by weight of the positive electrode active material, and the conductive material (VGCF (registered trademark), Showa Denko K.K.) was weighed out at 3.0 parts by weight per 100 parts by weight of the positive electrode active material. Next, these were mixed together so that the solid content was 63% by weight, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a positive electrode composition in a slurry form. Thereafter, the slurry positive electrode composition was applied to the surface of an aluminum foil that would become the positive electrode current collector layer, and a layer that would become the positive electrode active material layer was formed through a process of heating and drying. The layer was then pressed at 25°C with a linear pressure of 1 t / cm to produce a positive electrode structure having a layer that would become the positive electrode current collector layer and a layer that would become the positive electrode active material layer.

[0033] [Fabrication of negative electrode structure] The negative electrode active material (Si) and the sulfide solid electrolyte (Li2S-P2S5) were weighed out to make a composite material with a volume ratio of negative electrode active material:sulfide solid electrolyte = 60:40, and the binder and conductive material were weighed out to make the volume ratios shown in Table 1. In Table 1, the binder "SBR" is styrene butadiene rubber, "PVDF" is polyvinylidene fluoride, the conductive material "CF" is carbon fiber (in this example, VGCF (registered trademark) from Showa Denko K.K. was used as CF. Note that VGCF (registered trademark) is a type of carbon fiber called vapor grown carbon fiber), and "AB" is acetylene black. Next, these were mixed together so that the solid content was 45% by weight, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a negative electrode composition in a slurry form. Thereafter, the slurry-like negative electrode composition was applied to the surface of nickel foil that would become the negative electrode current collector, and a layer that would become the negative electrode active material layer was formed through a process of heating and drying. The layer was then pressed at 25°C with a linear pressure of 1 t / cm to produce a negative electrode structure having a layer that would become the negative electrode current collector layer and a layer that would become the negative electrode active material layer.

[0034] [Solid electrolyte layer and all-solid-state battery fabrication] The sulfide solid electrolyte (Li2S-P2S5) and the PVDF binder were weighed out so that the PVDF binder was 1 part by weight per 100 parts by weight of the sulfide solid electrolyte. Next, these were mixed together so that the solid content was 63% by weight, and kneaded for 1 minute using an ultrasonic homogenizer to prepare a slurry-like solid electrolyte composition. Thereafter, a slurry-like solid electrolyte composition was applied to the surface of the aluminum foil, and a layer that would become a solid electrolyte layer was formed through a process of heating and drying. The layer was then transferred to a positive electrode structure, and then a negative electrode structure was transferred to the positive electrode structure, thereby producing an all-solid-state battery.

[0035] Evaluation The produced all-solid-state battery was charged and discharged for 500 cycles at 2.5-4.2 V and 0.1 C CCCV, and the capacity retention rate was calculated from the change in discharge capacity between the 1st cycle and the 500th cycle. The capacity retention rate of Comparative Example 1 was set to 1, and the capacity retention rate ratio was calculated for each example.

[0036] 4.3.Results Table 1 shows the main conditions and results of each example.

[0037] [Table 1]

[0038] As can be seen from Table 1, by using the above-mentioned negative electrode active material layer, i.e., by containing a binder obtained from a material having a double bond and a conductive material including a material having a needle-like structure, with the binder being 5 vol% or more and 20 vol% or less with respect to the negative electrode active material layer, and with the conductive material / binder volume ratio being 0.4 or more and 1.0 or less, the capacity retention rate ratio could be increased by 8% or more compared to Comparative Example 1. On the other hand, in the examples in which the content ratios of the binder and conductive material were not satisfied (Comparative Examples 1 to 4), in the examples in which PVDF obtained from a material having no double bonds was used as the binder (Comparative Examples 5 to 8), and in the examples in which AB having a spherical structure was used as the conductive material (Comparative Examples 9 to 12), the capacity retention rate ratio could not be increased by 3% or more. [Explanation of symbols]

[0039] 10 All-solid-state battery 11 Cathode active material layer 12 Negative electrode active material layer 13 Solid electrolyte layer 14 Positive electrode current collector layer 15 Negative electrode current collector layer

Claims

[Claim 1] An all-solid-state battery having a negative electrode active material layer, The negative electrode active material layer contains a negative electrode active material, styrene butadiene rubber or acrylonitrile butadiene rubber as a binder, and a conductive material including a material having a needle-shaped structure, The binder is 5% by volume or more and 20% by volume or less with respect to the negative electrode active material layer, The volume ratio of the conductive material to the binder is 0.4 or more and 1.0 or less. All-solid-state battery.

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