JP2020170605A - Negative electrode mixture layer - Google Patents

Abstract

To provide a negative electrode mixture layer for an all-solid lithium ion secondary battery, which can suppress the increase in the binding pressure of a battery when charging it, and which is low in battery resistance.SOLUTION: A negative electrode mixture layer for an all-solid lithium ion secondary battery comprises porous silicon particles as a negative electrode active material, and a sulfide-based solid electrolyte. The porous silicon particles are each a silicon fine particle-binding body having a three-dimensional cancellous structure and continuous pores. The porous silicon particles have a porosity of 12-51%. The rate of contact of the porous silicon particles and the sulfide-based solid electrolyte is 20-44%.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a negative electrode mixture layer.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles.
Among all-solid-state batteries, all-solid-state lithium-ion batteries have a high energy density because they utilize a battery reaction that involves the movement of lithium ions, and an electrolyte solution containing an organic solvent as an electrolyte interposed between the positive electrode and the negative electrode. It is attracting attention in that it uses a solid electrolyte instead of.

In Patent Document 1, as a negative electrode material for a lithium ion battery that realizes high capacity and good cycle characteristics, it has a three-dimensional network structure in which silicon fine particles are bonded and has continuous voids, and has an average porosity. Porous silicon particles, which are 15-93%, are disclosed.

Patent Document 2 describes a negative electrode for an all-solid-state battery having a sulfide solid electrolyte and a negative electrode active material for the purpose of obtaining an all-solid-state battery having both a high cell volume energy density and an excellent capacity retention rate. The negative electrode active material is a composite particle having a carbon material containing Si or Sn, the particle size of the Si or Sn is 94 nm or less, and the particle size of the negative electrode active material is 15 μm or less, and the negative electrode is used. A negative electrode for an all-solid-state battery having a void ratio of 5% to 30% is disclosed.

Patent Document 3 discloses a method for manufacturing an all-solid-state lithium ion secondary battery, wherein the porosity V in the negative electrode mixture is 43% or more and 54% or less.

Japanese Unexamined Patent Publication No. 2013-203626 JP-A-2017-054720 Japanese Unexamined Patent Publication No. 2018-181702

The conventional all-solid-state lithium-ion secondary battery has a problem that the binding pressure of the battery at the time of charging is high and the resistance of the battery is high.
In view of the above circumstances, it is an object of the present disclosure to provide a negative electrode mixture layer for an all-solid-state lithium ion secondary battery, which suppresses an increase in the restraining pressure of the battery during charging and has a low battery resistance.

The present disclosure is a negative electrode mixture layer for an all-solid-state lithium ion secondary battery containing porous silicon particles as a negative electrode active material and a sulfide-based solid electrolyte.
The porous silicon particles are a conjugate of a plurality of silicon fine particles, and have a three-dimensional network structure having continuous voids.
The porosity of the porous silicon particles is 12% to 51%.
Provided is a negative electrode mixture layer characterized in that the contact ratio between the porous silicon particles and the sulfide-based solid electrolyte is 20% to 44%.

The present disclosure can provide a negative electrode mixture layer for an all-solid-state lithium ion secondary battery, which suppresses an increase in the restraining pressure of the battery during charging and has a low battery resistance.

It is sectional drawing which shows an example of the all-solid-state lithium ion secondary battery of this disclosure. 6 is an SEM image of a cross section of the porous silicon particles of Example 1.

The present disclosure is a negative electrode mixture layer for an all-solid-state lithium ion secondary battery containing porous silicon particles as a negative electrode active material and a sulfide-based solid electrolyte.
The porous silicon particles are a conjugate of a plurality of silicon fine particles, and have a three-dimensional network structure having continuous voids.
The porosity of the porous silicon particles is 12% to 51%.
Provided is a negative electrode mixture layer characterized in that the contact ratio between the porous silicon particles and the sulfide-based solid electrolyte is 20% to 44%.

In order to realize a high energy density of an all-solid-state lithium-ion secondary battery, it is necessary to use a high-capacity Si material as a negative electrode active material.
When a normal diamond-structured Si material is used as the negative electrode active material, repeated charging and discharging of the all-solid-state lithium-ion secondary battery causes cracks inside the electrode, which significantly shortens the battery life and is all-solid-state. In the charged state of the lithium ion secondary battery, an extremely large stress is applied to the restraint parts, which causes problems such as the need for a highly rigid restraint structure.
For example, when Li ions are inserted into Si particles having a diamond structure as a charging reaction, Li ions are incorporated into the crystal structure of the Si particles. At this time, the crystal lattice of Si becomes large and the Si particles expand.

The present researchers have found that by using porous silicon particles having voids inside as a negative electrode active material, the silicon fine particles expand in the porous silicon particles and the expansion of the negative electrode can be suppressed.
In addition, by increasing the contact rate between the porous silicon particles and the sulfide-based solid electrolyte, the researchers will further suppress the expansion of the negative electrode and further reduce the resistance of the all-solid-state lithium-ion secondary battery. I found that I could do it.
The reason why the expansion of the negative electrode can be further suppressed is that Li is uniformly inserted into the porous silicon particles in the negative electrode by increasing the contact rate between the porous silicon particles and the sulfide-based solid electrolyte. Presumed.
In addition, the resistance of the all-solid-state lithium-ion secondary battery can be further reduced by increasing the contact rate between the porous silicon particles and the sulfide-based solid electrolyte, thereby increasing the number of ion conduction paths and Li ions. It is presumed that this is because the movement between the porous silicon particles and the sulfide-based solid electrolyte is not easily hindered.

[Negative electrode mixture layer]
The negative electrode mixture layer is made of a negative electrode mixture, and the negative electrode mixture contains porous silicon particles as a negative electrode active material and a sulfide-based solid electrolyte, and if necessary, further contains a conductive material, a binder, and the like. Including.

Porous silicon particles are a conjugate of a plurality of silicon fine particles, and have a three-dimensional network structure having continuous voids.
Examples of the method for producing the porous silicon particles include the following methods.
[1-1]
First, a predetermined amount of silicon fine particles and metallic Li are mixed in an Ar atmosphere to obtain a LiSi precursor.
[1-2]
The LiSi precursor is reacted with ethanol at a predetermined temperature in a glass reactor under an Ar atmosphere for 120 minutes, and then the liquid 1 and the solid reaction product 1 are separated by suction filtration.
[1-3]
The obtained solid reaction product 1 is reacted with acetic acid in a glass reactor in an air atmosphere for 60 minutes, and then the liquid 2 and the solid reaction product 2 are separated by suction filtration.
[1-4]
The solid reaction product 2 is vacuum dried at 100 ° C. for 2 hours to obtain porous silicon particles.

The porous silicon particles have a porosity of 12% to 51%.
The method for calculating the porosity in the porous silicon particles is not particularly limited, and for example, it may be calculated by observing a scanning electron microscope (SEM) image of a cross section of the porous silicon particles.
The porosity of the porous silicon particles can be controlled, for example, by varying the temperature of ethanol in the range of 0 ° C. to 25 ° C. in the above procedure [1-2].

The average particle size (D50) of the porous silicon particles may be, for example, 50 nm or more and 100 μm or less, or 100 nm or more and 30 μm or less.
The average particle size (D50) of the silicon fine particles may be, for example, 2 nm to 10 μm, or 5 nm to 5 μm.

Examples of the sulfide-based solid electrolyte include Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , LiX-Li ₂ S-SiS ₂ , LiX-Li ₂ S-P ₂ S ₅ , LiX-Li _2. Examples thereof include O-Li ₂ SP ₂ S ₅ , LiX-Li ₂ S-P ₂ O ₅ , LiX-Li ₃ PO _4- P ₂ S ₅ , Li ₃ PS ₄ , and the like. The above description of "Li ₂ SP ₂ S ₅ " means a material made of a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. Further, "X" of the above LiX indicates a halogen element. The raw material composition containing LiX may contain one or more LiX. When two or more types of LiX are contained, the mixing ratio of the two or more types is not particularly limited.
The content of the sulfide-based solid electrolyte in the negative electrode mixture layer is 1 to 80 mass when the total mass of the negative electrode active material, the sulfide-based solid electrolyte, the conductive material, and the binder in the negative electrode mixture layer is 100% by mass. May be%.
The shape of the sulfide-based solid electrolyte is preferably particulate from the viewpoint of good handleability.

Examples of the conductive material contained in the negative electrode mixture layer include a carbon material and metal particles. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). .. The CNTs and CNFs may be vapor phase carbon fibers (VGCF). Examples of the metal particles include Ni, Cu, Fe, and SUS.
When the total mass of the negative electrode active material, the sulfide-based solid electrolyte, the conductive material, and the binder of the negative electrode mixture layer is 100% by mass, the content ratio of the conductive material contained in the negative electrode mixture layer is 0.1. It may be 10% by mass by mass.

The contact rate between the porous silicon particles and the sulfide-based solid electrolyte in the negative electrode mixture layer is 20% to 44%.
The contact ratio between the porous silicon particles and the sulfide-based solid electrolyte may be calculated according to the following formula (1) by observing the SEM image of the cross section of the negative electrode mixture layer. In the following formula (1), the unit of contact area is [μm ² ].
Equation (1)
Contact rate between porous silicon particles and sulfide-based solid electrolyte [%] = [Contact area between porous silicon particles and sulfide-based solid electrolyte ÷ (contact area between porous silicon particles and sulfide-based solid electrolyte + porous Contact area between quality silicon particles and conductive material + Contact area between porous silicon particles and porous silicon particles)] x 100
The contact rate between the porous silicon particles and the sulfide-based solid electrolyte can be controlled, for example, by varying the amount of the conductive material in the negative electrode mixture layer.

The binder contained in the negative electrode mixture layer is a rubber-based binder such as butadiene rubber, hydride butadiene rubber, styrene butadiene rubber (SBR), hydride styrene butadiene rubber, nitrile butadiene rubber, hydride nitrile butadiene rubber, and ethylene propylene rubber. , Polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), fluoride-based binders such as polytetrafluoroethylene and fluororubber, polyolefin-based thermoplastics such as polyethylene, polypropylene and polystyrene. Examples thereof include imide-based resins such as resins, polyimides and polyamideimides, amide-based resins such as polyamides, acrylic resins such as polymethylacrylate and polyethylacrylate, and methacrylic resins such as polymethylmethacrylate and polyethylmethacrylate.
When the total mass of the negative electrode active material, the sulfide-based solid electrolyte, the conductive material, and the binder of the negative electrode mixture layer is 100% by mass, the content ratio of the binder contained in the negative electrode mixture layer is 0.1 mass. It may be% to 10% by mass.

[All-solid-state lithium-ion secondary battery]
The negative electrode mixture layer of the present disclosure is used for the negative electrode of an all-solid-state lithium ion secondary battery.
The all-solid-state lithium ion secondary battery of the present disclosure is characterized by having a positive electrode, a negative electrode, and a solid electrolyte layer arranged between the positive electrode and the negative electrode.
FIG. 1 is a schematic cross-sectional view showing an example of the all-solid-state lithium ion secondary battery of the present disclosure. In the drawings attached to the present specification, the scale, aspect ratio, etc. are appropriately changed from those of the actual product and exaggerated for the convenience of illustration and comprehension.
As shown in FIG. 1, the all-solid-state lithium ion secondary battery 100 includes a positive electrode 16 including a positive electrode mixture layer 12 and a positive electrode current collector 14, and a negative electrode 17 including a negative electrode mixture layer 13 and a negative electrode current collector 15. A solid electrolyte layer 11 is provided between the positive electrode 16 and the negative electrode 17.

[Positive electrode]
The positive electrode includes at least a positive electrode mixture layer and, if necessary, a positive electrode current collector.
The positive electrode mixture layer is made of a positive electrode mixture, and the positive electrode mixture contains a positive electrode active material, and may contain a solid electrolyte, a conductive material, a binder, and the like as optional components.

No particular limitation is imposed on the kind of the positive electrode active material, for example, the general formula _Li x _M y _O z _(M is a transition metal element, x = 0.02~2.2, y = 1~2 , z = 1 The positive electrode active material represented by .4 to 4) can be mentioned. In the above general formula, M is at least one selected from the group consisting of Co, Mn, Ni, V, Fe and Si, and may be at least one selected from the group consisting of Co, Ni and Mn. .. Specific examples of such positive electrode active materials include LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , and Li (Ni _{0). .5} Mn _1.5 ) O ₄ , Li ₂ FeSiO ₄ , Li ₂ MnSiO _{4 and the} like can be mentioned.
As the positive electrode active material other than the above-mentioned general formula _Li x _M y _{O z,} the lithium titanate (for example, _Li 4 _Ti 5 _{O 12),} phosphoric acid metal lithium _{(LiFePO 4, LiMnPO 4, LiCoPO} 4, LiNiPO 4), Transition metal oxides (V ₂ O ₅ , MoO ₃ ), TiS ₂ , LiCoN, Si, SiO ₂ , Li ₂ SiO ₃ , Li ₄ SiO ₄ , and lithium storable metal compounds (eg Mg ₂ Sn, Mg ₂ Ge) , Mg ₂ Sb, Cu ₃ Sb) and the like.
The shape of the positive electrode active material is not particularly limited, but may be in the form of particles.
A coat layer containing a Li ion conductive oxide may be 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 can be suppressed.
Examples of the Li ion conductive oxide include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₃ PO ₄ , and the like.
The content of the positive electrode active material in the positive electrode mixture layer is not particularly limited, but may be in the range of, for example, 10% by mass to 100% by mass.
Examples of the solid electrolyte used for the positive electrode mixture layer include the same solid electrolytes used for the solid electrolyte layer described later. The content ratio of the solid electrolyte in the positive electrode mixture layer is not particularly limited.

Examples of the conductive material include the same conductive materials as those used for the negative electrode mixture described above. The content of the conductive material in the positive electrode mixture layer is not particularly limited.

Examples of the binder include the same binders used for the above-mentioned negative electrode mixture. The content of the binder in the positive electrode mixture layer is not particularly limited.

The thickness of the positive electrode mixture layer is not particularly limited.

The positive electrode mixture layer can be formed by a conventionally known method.
For example, a positive electrode active material and a binder are put into a solvent, and these are stirred to prepare a slurry for a positive electrode mixture layer, and the slurry is applied on one surface of a support such as a positive electrode current collector. By drying, a positive electrode mixture layer is obtained.
Examples of the solvent include butyl acetate, butyl butyrate, heptane, N-methyl-2-pyrrolidone and the like.
The method of applying the slurry for the positive electrode mixture layer on one surface of a support such as a positive electrode current collector is not particularly limited, and is a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, and a spray coating method. , Roll coating method, gravure coating method, screen printing method and the like.
Further, as another method of forming the positive electrode mixture layer, the positive electrode mixture layer may be formed by pressure molding the powder of the positive electrode mixture containing the positive electrode active material and, if necessary, other components.

As the positive electrode current collector, a known metal that can be used as a current collector for an all-solid-state lithium ion secondary battery can be used. Such metals include one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Metallic materials can be exemplified.
The form of the positive electrode current collector is not particularly limited, and various forms such as a foil shape and a mesh shape can be used.

The shape of the positive electrode as a whole is not particularly limited, but it may be in the form of a sheet. In this case, the thickness of the positive electrode as a whole is not particularly limited, and may be appropriately determined according to the desired performance.

[Solid electrolyte layer]
The solid electrolyte layer contains at least a solid electrolyte.

Examples of the solid electrolyte include sulfide-based solid electrolytes and oxide-based solid electrolytes.
Examples of the sulfide-based solid electrolyte include the same sulfide-based solid electrolytes used in the above-mentioned negative electrode mixture.
Examples of the oxide-based solid electrolyte include Li _6.25 La ₃ Zr ₂ Al _0.25 O ₁₂ , Li ₃ PO ₄ , Li _{3 + x} PO _4-x N _x (LiPON), and the like.

The shape of the solid electrolyte is preferably particulate from the viewpoint of good handleability.
The average particle size (D50) of the particles of the solid electrolyte is not particularly limited, but the lower limit is preferably 0.5 μm or more, and the upper limit is preferably 2 μm or less.
As the solid electrolyte, one kind alone or two or more kinds can be used. When two or more kinds of solid electrolytes are used, two or more kinds of solid electrolytes may be mixed.

In the present disclosure, the average particle size of the particles is a volume-based median diameter (D50) value measured by laser diffraction / scattering type particle size distribution measurement, unless otherwise specified. Further, in the present disclosure, the median diameter (D50) is a diameter (volume average diameter) at which the cumulative volume of the particles is half (50%) of the total volume when the particles are arranged in ascending order.

The content ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited.

The solid electrolyte layer may also contain a binder that binds the solid electrolytes to each other from the viewpoint of exhibiting plasticity and the like. As such a binder, a binder or the like that can be contained in the above-mentioned positive electrode can be exemplified. However, in order to facilitate high output of the battery, the solid electrolyte layer may be used from the viewpoint of preventing excessive aggregation of the solid electrolyte and making it possible to form a solid electrolyte layer having a uniformly dispersed solid electrolyte. The binder to be contained is preferably 5.0% by mass or less.

The thickness of the solid electrolyte layer is appropriately adjusted depending on the configuration of the battery, and is not particularly limited, and is usually 0.1 μm or more and 1 mm or less.
As a method for forming the solid electrolyte layer, for example, the solid electrolyte layer may be formed by pressure molding a powder of the material of the solid electrolyte layer containing the solid electrolyte and, if necessary, other components.

[Negative electrode]
The negative electrode includes at least a negative electrode mixture layer and, if necessary, a negative electrode current collector.
The negative electrode mixture layer is made of the above-mentioned negative electrode mixture.

The method for forming the negative electrode mixture layer is not particularly limited, but the powder of the negative electrode mixture containing the negative electrode active material, the sulfide-based solid electrolyte, and if necessary, other components such as a conductive material and a binder is pressure-molded. The method of doing this can be mentioned.

As the negative electrode current collector, a metal similar to the metal used as the positive electrode current collector can be used.
The form of the negative electrode current collector is not particularly limited, and various forms such as a foil shape and a mesh shape can be used.

The shape of the negative electrode as a whole is not particularly limited, but it may be in the form of a sheet. In this case, the thickness of the negative electrode as a whole is not particularly limited, and may be appropriately determined according to the desired performance.

The all-solid-state lithium-ion secondary battery includes, if necessary, a positive electrode, a negative electrode, and an exterior body that houses the solid electrolyte layer.
The shape of the exterior body is not particularly limited, and examples thereof include a laminated type.
The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

Examples of the shape of the all-solid-state lithium ion secondary battery include a coin type, a laminated type, a cylindrical type, and a square type.

In the method for producing an all-solid-state lithium-ion secondary battery of the present disclosure, for example, first, a solid electrolyte layer is formed by pressure molding a powder of a solid electrolyte material. Then, the positive electrode mixture layer is obtained by pressure molding the positive electrode mixture powder on one surface of the solid electrolyte layer. Then, the negative electrode mixture layer is obtained by pressure molding the powder of the negative electrode mixture on the surface of the solid electrolyte layer opposite to the surface on which the positive electrode mixture layer is formed. Then, an all-solid-state lithium ion secondary battery may be obtained by attaching a current collector to the obtained positive electrode mixture layer-solid electrolyte layer-negative electrode mixture layer joint body as needed.
In this case, the press pressure when the powder of the solid electrolyte material, the powder of the positive electrode mixture, and the powder of the negative electrode mixture are pressure-molded is usually about 1 MPa or more and 600 MPa or less.
The pressurizing method is not particularly limited, and examples thereof include a pressing method in which pressure is applied using a flat plate press, a roll press, or the like.
The all-solid-state lithium-ion secondary battery should be manufactured in a state where the water content in the system is removed as much as possible. For example, in each manufacturing process, it is considered effective to reduce the pressure in the system and to replace the inside of the system with a gas that does not substantially contain water such as an inert gas.

(Example 1)
[1] Preparation of Porous Silicon Particles [1-1]
0.65 g of silicon fine particles (high-purity chemistry, particle size 5 μm) and 0.60 g of metal Li (Honjo Metal) were mixed in an agate mortar under an Ar atmosphere to obtain a LiSi precursor.

[1-2]
After reacting 1.0 g of the LiSi precursor with 250 ml of ethanol (Nacalai Tesque) at 0 ° C. for 120 minutes in a glass reactor under an Ar atmosphere, the liquid 1 and the solid reaction product 1 were separated by suction filtration.

[1-3]
The obtained 0.5 g of the solid reaction product 1 was reacted with 50 ml of acetic acid (Nacalai Tesque) in a glass reactor under an air atmosphere for 60 minutes, and then the liquid 2 and the solid reaction product 2 were separated by suction filtration. ..

[1-4]
The solid reaction product 2 was vacuum dried at 100 ° C. for 2 hours to obtain nanosheets of porous silicon particles.

[Cross-section observation of porous silicon particles (porosity)
The porous silicon particles were subjected to cross-section processing by ion milling, and the cross-section of the porous silicon particles was observed with a secondary electron microscope.
FIG. 2 is a scanning electron microscope (SEM) image of a cross section of the porous silicon particles of Example 1.
From the obtained observation image, the porosity in the porous silicon particles was calculated after binarizing the silicon (Si) and the voids in the porous silicon particles in the white part and the ash part. The results are shown in Table 1.

[2] Synthesis of sulfide-based solid electrolytes Li ₂ S (Furuuchi Chemistry) 0.550 g, P ₂ S ₅ (Aldrich) 0.887 g, LiI (Nippoh Chemicals) 0.285 g and LiBr (High Purity Chemistry) 0. 277 g was weighed, mixed in a Menou dairy pot for 5 minutes, then 4 g of n-heptane (dehydrated grade, Kanto Chemical Co., Inc.) was added, and mechanical milling was performed for 40 hours using a planetary ball mill to obtain a sulfide-based solid electrolyte.

[3] Preparation of all-solid-state lithium-ion secondary battery [3-1] Positive electrode mixture LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (Nichia Corporation) was used as the positive electrode active material.
The positive electrode active material was surface-treated with LiNbO ₃ . 1.5 g of this positive electrode active material, 0.023 g of VGCF (Showa Denko) as a conductive material, 0.239 g of the sulfide-based solid electrolyte, 0.011 g of PVdF (Kureha) as a binder, and butyl butyrate (xida) as a solvent. (Chemistry) was weighed in 0.8 g and mixed with an ultrasonic homogenizer (UH-50 manufactured by SMT) to prepare a positive electrode mixture.

[3-2] Negative electrode mixture 1.0 g of nanosheet of porous silicon particles synthesized in [1] as negative electrode active material, 0.04 g of VGCF (Showa Denko) as conductive material, 0.776 g of the sulfide-based solid electrolyte. , 0.02 g of PVdF (Kureha) as a binder and 1.7 g of butyl butyrate (Kishida Chemical) as a solvent were weighed and mixed using an ultrasonic homogenizer (UH-50 manufactured by SMT) to prepare a negative electrode mixture.

[3-3] Solid Electrolyte Layer 0.065 g of a sulfide-based solid electrolyte was weighed in a 1 cm ² ceramic mold and pressed at 1 ton / cm ² to prepare a solid electrolyte layer.

[3-4]
0.018 g of the positive electrode mixture was placed on one side of the solid electrolyte layer and pressed at 1 ton / cm ² to prepare a positive electrode mixture layer. A negative electrode mixture layer of 0.0054 g is placed on the opposite side and pressed at 4 ton / cm ² , and an aluminum foil is used for the positive electrode current collector and a copper foil is used for the negative electrode current collector. , An all-solid-state lithium-ion secondary battery was obtained.

[Cross-sectional observation of the negative electrode mixture layer (contact rate between porous silicon particles and sulfide-based solid electrolyte)
The negative electrode mixture layer was subjected to cross-section processing by ion milling, and the cross section of the negative electrode mixture layer was observed with a secondary electron microscope.
From the obtained observation image, the porous silicon particles in the negative electrode mixture layer, the sulfide-based solid electrolyte, and the conductive material were ternaryized, and then the contact rate between the porous silicon particles and the sulfide-based solid electrolyte was determined as described above. It was calculated using the above equation (1). The results are shown in Table 1.

[Restriction pressure]
As the initial charge, the all-solid-state lithium-ion secondary battery was CC-CV charged at 0.245 mA to 4.35 V.
In the initial charging, the confining pressure of the all-solid-state lithium-ion secondary battery is monitored, and the confining pressure of the all-solid-state lithium-ion secondary battery of Comparative Example 1 described later is used as a reference for the all-solid-state lithium-ion secondary battery of Comparative Example 1. The ratio of the restraint pressure to the restraint pressure at the time of initial charging of the all-solid-state lithium ion secondary battery of Example 1 was calculated. Regarding the restraint pressure at the time of initial charging of the all-solid-state lithium ion secondary batteries of Examples 2 to 3 and Comparative Examples 2 to 3 described later, the ratio to the restraint pressure of the all-solid-state lithium ion secondary battery of Comparative Example 1 described later is calculated. did. The results are shown in Table 1.

[Internal resistance of all-solid-state lithium-ion secondary battery]
After the initial charge, the all-solid-state lithium-ion secondary battery was CC-CV discharged to 3.0 V at 0.245 mA.
After that, the all-solid-state lithium-ion secondary battery was charged to a voltage of 3.7 V at 0.245 mA, and then 7.35 mA was passed for 5 seconds to reduce the internal resistance of the all-solid-state lithium-ion secondary battery from the change in voltage. It was measured.
Based on the internal resistance of the all-solid-state lithium-ion secondary battery of Comparative Example 1 described later, the internal resistance of the all-solid-state lithium-ion secondary battery of Example 1 with respect to the internal resistance of the all-solid-state lithium-ion secondary battery of Comparative Example 1 The ratio was calculated. The ratio of the internal resistance of the all-solid-state lithium-ion secondary battery of Examples 2 to 3 and Comparative Examples 2 to 3 described later to the internal resistance of the all-solid-state lithium-ion secondary battery of Comparative Example 1 described later was calculated. The results are shown in Table 1.

(Example 2)
An all-solid-state lithium-ion secondary battery was prepared in the same procedure as in Example 1 except that the temperature of ethanol was set to 15 ° C. in the procedure [1-2] of Example 1, and the all-solid-state lithium ion secondary battery was prepared. Evaluation was performed.

(Example 3)
An all-solid-state lithium-ion secondary battery was prepared in the same procedure as in Example 1 except that the ethanol temperature was set to 25 ° C. in the procedure [1-2] of Example 1, and the all-solid-state lithium ion secondary battery was prepared. Evaluation was performed.

(Comparative Example 1)
An all-solid-state lithium-ion secondary battery was prepared in the same procedure as in Example 1 except that the VGCF was 0.12 g in the procedure [3-2] of Example 1, and the all-solid-state lithium-ion secondary battery was evaluated. Was done.

(Comparative Example 2)
In the procedure [3-2] of Example 1, the VGCF was 0.12 g, and an all-solid-state lithium ion secondary battery was prepared in the same procedure as in Example 2 except for that, and the evaluation of the all-solid-state lithium ion secondary battery was performed. Was done.

(Comparative Example 3)
In the procedure [3-2] of Example 1, the VGCF was 0.12 g, and an all-solid-state lithium ion secondary battery was prepared in the same procedure as in Example 3 except for that, and the evaluation of the all-solid-state lithium ion secondary battery was performed. Was done.

As shown in Table 1, a negative electrode mixture layer is used in which the void ratio of the porous silicon particles is 12% to 51% and the contact ratio between the porous silicon particles and the sulfide-based solid electrolyte is 20% to 44%. It has been demonstrated that the all-solid-state lithium-ion secondary battery can reduce the confining pressure and internal resistance.

11 Solid electrolyte layer 12 Positive electrode mixture layer 13 Negative electrode mixture layer 14 Positive electrode current collector 15 Negative electrode current collector 16 Positive electrode 17 Negative electrode 100 All-solid-state lithium ion secondary battery

Claims (1)

A negative electrode mixture layer for an all-solid-state lithium-ion secondary battery containing porous silicon particles as a negative electrode active material and a sulfide-based solid electrolyte.
The porous silicon particles are a conjugate of a plurality of silicon fine particles, and have a three-dimensional network structure having continuous voids.
The porosity of the porous silicon particles is 12% to 51%.
A negative electrode mixture layer characterized in that the contact ratio between the porous silicon particles and the sulfide-based solid electrolyte is 20% to 44%.