Negative electrode layer

Abstract

To provide a negative electrode layer that can suppress the decrease in discharge capacity of a secondary battery.SOLUTION: A negative electrode layer for a secondary battery includes a negative electrode active material, the negative electrode active material includes granules of nanoporous Si particles, the granules include SBR (styrene butadiene rubber) as a binder, the nanoporous Si particles are bound by the SBR in the granules, and the content of the SBR in the granules is 4.5 mass% to 8 mass% relative to 100 mass% of the nanoporous Si particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode layer. [Background technology]

[0002] Various technologies have been proposed regarding batteries such as those disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-213094 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-118330 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses granulating silicon using polyimide as a binder. If the negative electrode layer contains a large amount of binder, the discharge capacity of the secondary battery decreases, which is a problem.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a negative electrode layer that can suppress a decrease in the discharge capacity of a secondary battery. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A negative electrode layer for a secondary battery, the negative electrode layer contains a negative electrode active material, the negative electrode active material contains granulated nanoporous Si particles, The granules contain SBR (styrene butadiene rubber) as a binder, In the granules, the nanoporous Si particles are bound by the SBR, The negative electrode layer, wherein the content of the SBR in the granules is 4.5% by mass to 8% by mass with respect to 100% by mass of the nanoporous Si particles. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a negative electrode layer that can suppress a decrease in the discharge capacity of a secondary battery. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a graph showing the standard discharge capacity of each of the secondary batteries of Example 1 and Comparative Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described. Matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, a negative electrode layer that does not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In the present disclosure, unless otherwise specified, the average particle size of particles is the median diameter (D50) value, which is the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.

[0010] In the present disclosure, there is provided a negative electrode layer for a secondary battery, comprising: the negative electrode layer contains a negative electrode active material, the negative electrode active material contains granulated nanoporous Si particles, The granules contain SBR (styrene butadiene rubber) as a binder, In the granules, the nanoporous Si particles are bound by the SBR, The negative electrode layer is provided, wherein the content of the SBR in the granules is 4.5% by mass to 8% by mass with respect to 100% by mass of the nanoporous Si particles.

[0011] In the present disclosure, by using SBR as the binder used in the granules, the amount of binder that reacts with Li is reduced while maintaining the granule shape, and a decrease in the discharge capacity of the secondary battery is suppressed.

[0012] [Negative electrode layer] The negative electrode layer contains granulated nanoporous Si particles as a negative electrode active material. The granules serving as the negative electrode active material contain nanoporous Si particles and SBR (styrene butadiene rubber) as a binder (first binder). In the granules, the nanoporous Si particles are bound together by SBR. The content of SBR in the granules is 4.5 to 8% by mass relative to 100% by mass of nanoporous Si particles. If the content of SBR is less than 4.5% by mass, granulation may not be possible. If the content of SBR exceeds 8% by mass, the discharge capacity of the secondary battery may decrease. The granules can be obtained, for example, by dispersing and dissolving nanoporous Si particles and SBR in a solvent such as dimethyl carbonate to obtain a slurry, and then spraying this slurry into a spray dryer and drying it. The nanoporous Si particles may have an average particle size D50 of 0.3 to 2 μm. The thickness of the negative electrode layer is not particularly limited and may be 1 μm or more and 1000 μm or less. The negative electrode layer may contain a solid electrolyte, a conductive material, a second binder, and the like, as needed.

[0013] The solid electrolyte may be a sulfide solid electrolyte. The content of the solid electrolyte in the negative electrode layer is not particularly limited, but may be, for example, in the range of 1% to 80% by mass when the total mass of the negative electrode layer is taken as 100% by mass.

[0014] Known conductive materials can be used, such as carbon materials and metal particles. Examples of carbon materials include acetylene black (AB), furnace black, vapor grown carbon fiber (VGCF), carbon nanotubes, multi-walled carbon nanotubes (MWCNT), and carbon nanofibers. Examples of metal particles include particles of Ni, Cu, Fe, and SUS. The content of the conductive material in the negative electrode layer is not particularly limited.

[0015] Examples of the second binder include rubber-based binders and fluoride-based binders. Examples of the rubber-based binder include BR-based binders such as butadiene rubber, acrylonitrile butadiene rubber (ABR), hydrogenated butadiene rubber, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, and ethylene propylene rubber. Examples of the fluoride-based binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The content of the second binder in the negative electrode layer is not particularly limited.

[0016] The negative electrode layer can be formed by a conventionally known method. For example, the negative electrode active material and, if necessary, other components are put into a solvent and stirred to prepare a negative electrode slurry, and the negative electrode slurry is applied to one surface of a support such as a negative electrode current collector and dried to obtain a negative electrode layer. Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone. The method for applying the negative electrode slurry onto one surface of a support such as a negative electrode current collector is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method. The support can be appropriately selected from those having self-supporting properties and is not particularly limited, and examples thereof include metal foils such as Ni, Cu, and Al.

[0017] The negative electrode layer of the present disclosure is for use in a secondary battery. The secondary battery of the present disclosure includes a positive electrode, an electrolyte layer, and a negative electrode in this order. The positive electrode includes a positive electrode layer and a positive electrode current collector. The negative electrode includes the negative electrode layer of the present disclosure and a negative electrode current collector. The electrolyte layer may be a liquid electrolyte layer containing an electrolytic solution, or may be a solid electrolyte layer containing a solid electrolyte.

[0018] The secondary battery of the present disclosure may be a liquid battery or a solid battery. In the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid-state battery that contains a solid electrolyte and a liquid-based material, or an all-solid-state battery that does not contain a liquid-based material. When a set of a positive electrode, an electrolyte layer, and a negative electrode is considered to be a power generation unit, the secondary battery may have only one power generation unit or may have two or more power generation units. When the secondary battery has two or more power generation units, the power generation units may be connected in series or in parallel. Examples of uses of secondary batteries include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, secondary batteries may be used as driving power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Secondary batteries may also be used as power sources for mobile objects other than vehicles (for example, trains, ships, and aircraft), and as power sources for electrical appliances such as information processing devices. [Example]

[0019] Example 1 [Fabrication of nanoporous Si] 0.65 g of Si particles (average particle size 0.5 μm, manufactured by Kojundo Chemical Co., Ltd.) and 0.60 g of metallic Li (manufactured by Honjo Metal Co., Ltd.) were mixed in an agate mortar under an Ar atmosphere to obtain a LiSi precursor. In a glass reactor under an Ar atmosphere, 1.0 g of LiSi precursor and 125 ml of a dispersion medium (1,3,5-trimethylbenzene) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation). The LiSi precursor dispersion obtained after mixing was cooled to 0°C, and 125 ml of ethanol (manufactured by Nacalai Tesque) was added dropwise and reacted for 120 minutes. After the reaction, 50 ml of acetic acid was added dropwise and reacted for 60 minutes. After the reaction, the liquid and solid reaction product (nanoporous Si) were separated by suction filtration. The solid reaction product was vacuum dried at 120°C for 2 hours to recover the nanoporous Si (primary particles). [Preparation of granules] The nanoporous Si (primary particles) and SBR (binder) were dispersed and dissolved in dimethyl carbonate at a ratio of primary particles to binder of 100:8 (mass%) to obtain a slurry. This slurry was sprayed into a spray dryer in a nitrogen gas atmosphere at 140°C and dried to obtain granules as the negative electrode active material. The formation of the granules was confirmed using a scanning electron microscope.

[0020] [Preparation of positive electrode layer] A cathode slurry was prepared by ultrasonically stirring a cathode composite containing NCA-based cathode active material, sulfide solid electrolyte, vapor-grown carbon fiber, PVdF-based binder, and butyl butyrate. The mass ratio of NCM-based cathode active material: sulfide solid electrolyte: vapor-grown carbon fiber: PVdF-based binder was 100:16:2:0.75. This cathode slurry was applied to an Al foil cathode current collector using a blade method and dried on a hot plate at 100°C for 30 minutes to obtain a cathode layer. [Creating the negative electrode layer] A granule containing nanoporous Si particles and a binder, a sulfide solid electrolyte, vapor-grown carbon fiber, a second binder (a BR-based binder), mesitylene, and dibutyl ether were added, and the resulting negative electrode mixture was stirred using an ultrasonic disperser and a stirrer to produce a negative electrode slurry. The mass ratio of nanoporous Si particles:binder:sulfide solid electrolyte:vapor-grown carbon fiber:second binder was 100:8:77.6:8.4:1.5. This negative electrode slurry was applied to a Ni foil negative electrode current collector using a blade method and then dried on a hot plate at 100°C for 30 minutes to produce a negative electrode layer. [Preparation of solid electrolyte layer] A solid electrolyte slurry was prepared by stirring a solid electrolyte mixture containing a sulfide solid electrolyte, a BR binder, and butyl butyrate using an ultrasonic disperser. The mass ratio of sulfide solid electrolyte to binder was 99.6:0.4. This solid electrolyte slurry was applied to an Al foil using a blade method and dried at 100°C on a hot plate for 30 minutes to obtain a peelable solid electrolyte layer. [Preparation of positive electrode laminate] The positive electrode layer and the solid electrolyte layer were laminated so that the composite surfaces overlapped. After pressing with a roll press at a pressure of 50 kN / cm and a temperature of 160°C, the Al foil of the solid electrolyte layer was peeled off, and the laminate was separated by 1 cm. 2 A positive electrode laminate was obtained by punching out the sheet into pieces of this size. [Fabrication of negative electrode laminate] The negative electrode layer and the solid electrolyte layer were laminated so that their composite surfaces overlapped. After pressing with a roll press at a pressure of 50 kN / cm, the Al foil of the solid electrolyte layer was peeled off to obtain a negative electrode laminate. Furthermore, a solid electrolyte layer was laminated on the solid electrolyte layer side of the negative electrode laminate so that their composite surfaces overlapped. This laminate was pre-pressed with a flat uniaxial press at a pressure of 100 MPa and a temperature of 25°C, after which the Al foil of the solid electrolyte layer was peeled off and a 1.08 cm 2 By punching out the sheet into a size of 100 mm, a negative electrode laminate having an additional solid electrolyte layer was obtained. [Fabrication of battery stack] The positive electrode laminate and the negative electrode laminate having the additional solid electrolyte layer were stacked so that their composite surfaces overlapped, and the stack was pressed in a flat uniaxial press at a pressure of 600 MPa and a temperature of 160°C to obtain a battery stack. [Battery stack constraints] The battery stack obtained as described above was sandwiched between two restraint plates, and these two restraint plates were fastened with a fastener at a restraint pressure of 1 MPa to fix the distance between the two restraint plates, thereby obtaining a secondary battery.

[0021] Example 2 Granules were obtained in the same manner as in Example 1, except that in [Preparation of Granules], the nanoporous Si (primary particles) and SBR (binder) were dispersed and dissolved in dimethyl carbonate in a ratio (mass %) of primary particles:binder of 100:4.5 to obtain a slurry. The fact that granules had been obtained was confirmed using a scanning electron microscope.

[0022] (Comparative Example 1) A secondary battery was produced in the same manner as in Example 1, except that in [Preparation of granules], the granules were not produced, and in [Preparation of negative electrode layer], the nanoporous Si (primary particles) was used as the negative electrode active material, and a negative electrode slurry was produced with a mass ratio of nanoporous Si particles:sulfide solid electrolyte:vapor grown carbon fiber:second binder of 100:77.6:8:5.

[0023] (Comparative Example 2) In the [Preparation of Granules] step, the nanoporous Si (primary particles) and PVDF-HFP (binder) were dispersed and dissolved in dimethyl carbonate at a ratio (mass %) of primary particles to binder of 100:8 to obtain a slurry, which was then sprayed into a spray dryer in a nitrogen gas atmosphere at 140°C and dried to obtain granules as the negative electrode active material. A secondary battery was fabricated in the same manner as in Example 1, except that the production of granules was confirmed using a scanning electron microscope.

[0024] (Comparative Example 3) A secondary battery was fabricated in the same manner as in Comparative Example 2, except that in [Preparation of Granules], the nanoporous Si (primary particles) and PVDF-HFP (binder) were dispersed and dissolved in dimethyl carbonate at a ratio (mass %) of primary particles:binder = 100:6 to obtain a slurry. The production of granules was confirmed using a scanning electron microscope.

[0025] Comparative Example 4 In the [Preparation of Granules], the nanoporous Si (primary particles) and polyimide (binder) were dispersed and dissolved in dimethylacetamide so that the ratio (mass %) of primary particles to binder was 100:8 to obtain a slurry. This slurry was then sprayed into a spray dryer in a nitrogen gas atmosphere at a temperature of 170°C and dried to obtain granules as the negative electrode active material. A secondary battery was prepared in the same manner as in Example 1, except for this.

[0026] (Comparative Example 5) A secondary battery was produced in the same manner as in Comparative Example 4, except that in [Preparation of granules], the above nanoporous Si (primary particles) and polyimide (binder) were dispersed and dissolved in dimethylacetamide so that the ratio (mass %) of primary particles to binder was 100:16 to obtain a slurry.

[0027] [First charge / discharge] Each of the secondary batteries of Example 1 and Comparative Examples 1 to 5 was subjected to a constant current charge of 1 / 10C to 4.55V, followed by a constant voltage charge of 4.05V to a cut-off current of 1 / 100C, and then a constant current discharge of 1C to 3V, followed by a constant voltage discharge of 2.5V to a cut-off current of 1 / 100C.

[0028] [Evaluation of discharge capacity] Each of the secondary batteries of Example 1 and Comparative Examples 1 to 5 was subjected to constant current charging at 1 / 3C to 4.35V, followed by constant voltage charging at 4.05V to a cut-off current of 1 / 100C, and then constant current discharging at 1 / 3C to 3V, followed by constant voltage discharging at 2.5V to a cut-off current of 1 / 100C, twice each. The discharge capacity of the second discharge was evaluated. The discharge capacity (standard discharge capacity) of each secondary battery, with the discharge capacity of the secondary battery of Comparative Example 1 taken as 100%, is shown in Table 1 and FIG. 1.

[0029] [Table 1]

[0030] FIG. 1 is a graph showing the standard discharge capacity of each of the secondary batteries of Example 1 and Comparative Examples 1 to 5. As shown in Table 1 and FIG. 1, the secondary battery using the granules using SBR as a binder as the negative electrode active material can maintain a discharge capacity equivalent to that of the secondary battery of Comparative Example 1 which does not use the granules as the negative electrode active material, and it can be seen that the decrease in discharge capacity due to the use of a binder can be reduced compared to Comparative Examples 1 to 5.

Claims

[Claim 1] A negative electrode layer for a secondary battery, the negative electrode layer contains a negative electrode active material, the negative electrode active material contains granulated nanoporous Si particles, The granules contain SBR (styrene butadiene rubber) as a binder, In the granules, the nanoporous Si particles are bound by the SBR, The negative electrode layer, wherein the content of the SBR in the granules is 4.5% by mass to 8% by mass with respect to 100% by mass of the nanoporous Si particles.

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