Negative electrode active material for secondary batteries and secondary batteries

Abstract

Provided is a negative electrode active material for secondary batteries that is capable of inhibiting negative electrode swelling and the decline of the charge / discharge cycle characteristics of a battery. A negative electrode active material for secondary batteries according to the present disclosure is characterized by including a Si-based material, activated carbon, and a conductive material, and in that the Si-based material and the conductive material are carried in pores of the activated carbon.

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode active material for secondary batteries and secondary batteries. [Background technology]

[0002] Si-based materials are alloying materials that combine with lithium and are known to be able to absorb more lithium ions per unit volume compared to carbon-based active materials such as graphite. Therefore, they are expected to be used as negative electrode active materials in secondary batteries.

[0003] For example, Patent Document 1 discloses a negative electrode active material comprising a Si-based material, a porous carbon aerogel, a binder material, and a carbon active material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2019-536234 [Overview of the project] [Problems that the invention aims to solve]

[0005] By the way, Si-based materials have problems because they undergo large volume changes (expansion and contraction) during charging and discharging. This can cause the negative electrode to swell, reducing the safety of the battery, or reduce the conductivity of the negative electrode, degrading the charge-discharge cycle characteristics.

[0006] Therefore, the present disclosure aims to provide a negative electrode active material for secondary batteries that can suppress the swelling of the negative electrode and the deterioration of the battery's charge-discharge cycle characteristics. [Means for solving the problem]

[0007] A negative electrode active material for a secondary battery, according to one aspect of the present disclosure, comprises a Si-based material, activated carbon, and a conductive material, characterized in that the Si-based material and the conductive material are supported within the pores of the activated carbon.

[0008] A secondary battery according to one aspect of the present disclosure is characterized by comprising a negative electrode containing the negative electrode active material for the secondary battery. [Effects of the Invention]

[0009] This disclosure makes it possible to provide a negative electrode active material for secondary batteries that can suppress the swelling of the negative electrode and the deterioration of the battery's charge-discharge cycle characteristics. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of a secondary battery, which is an example of an embodiment. [Modes for carrying out the invention]

[0011] One embodiment of the present disclosure of a negative electrode active material for a secondary battery comprises a Si-based material, activated carbon, and a conductive material, wherein the Si-based material and the conductive material are supported within the pores of the activated carbon. According to the present disclosure, the volume change of the Si-based material due to charging and discharging occurs within the pores of the activated carbon, so even if the Si-based material expands, it is less likely to lead to expansion of the negative electrode. Furthermore, the conductive material supported together with the Si-based material within the pores of the activated carbon ensures a conductive path for the Si-based material, thereby suppressing a decrease in the battery's charge-discharge cycle characteristics.

[0012] The embodiments of the negative electrode active material for secondary batteries and the secondary battery according to this disclosure will be described in detail below with reference to the drawings.

[0013] Figure 1 is a cross-sectional view of a secondary battery, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, a non-aqueous electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, and a battery case 15 that houses the above components. The battery case 15 is composed of a bottomed cylindrical case body 16 and a sealing body 17 that closes the opening of the case body 16. In addition, other forms of electrode bodies may be used instead of the wound electrode body 14, such as a laminated electrode body in which the positive electrode and negative electrode are alternately stacked with a separator. Examples of battery cases 15 include metal cases such as cylindrical, rectangular, coin-shaped, and button-shaped cases, and resin cases formed by laminating resin sheets (laminated batteries).

[0014] The case body 16 is, for example, a metal container in the shape of a bottomed cylinder. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and its upper surface supports the sealing body 17.

[0015] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheries. When the internal pressure of the secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the cap 27, thus interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0016] In the secondary battery 10 shown in FIG. 1, the positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing body 17 through the through-hole of the insulating plate 18, and the negative electrode lead 21 attached to the negative electrode 12 extends toward the bottom side of the case body 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected by welding or the like to the lower surface of the filter 23 which is the bottom plate of the sealing body 17, and the cap 27 which is the top plate of the sealing body 17 electrically connected to the filter 23 serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner surface of the bottom of the case body 16, and the case body 16 serves as the negative electrode terminal.

[0017] Hereinafter, the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the secondary battery 10 will be described in detail.

[0018] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. As the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode such as aluminum or an aluminum alloy, a film having the metal disposed on the surface layer, or the like can be used. The positive electrode mixture layer is composed of, for example, a positive electrode active material, a binder, a conductive material, and the like. The positive electrode mixture layer is preferably formed on both sides of the positive electrode current collector. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, and the like onto the positive electrode current collector, drying and rolling the coating film, and forming the positive electrode mixture layer on both sides of the positive electrode current collector.

[0019] As the positive electrode active material, for example, a lithium transition metal composite oxide or the like is used. Examples of the metal element contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, and the like. Among them, it is preferable to contain at least one of Ni, Co, and Mn.

[0020] Examples of the conductive material contained in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, and graphite. Examples of the binder contained in the positive electrode composite layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), and the like.

[0021] [Negative electrode] The negative electrode 12 includes, for example, a negative electrode current collector and a negative electrode composite layer formed on the current collector. For the negative electrode current collector, for example, a foil of a metal stable within the potential range of the negative electrode such as copper or a copper alloy, a film having the metal disposed on the surface layer, or the like can be used. The negative electrode composite layer is composed of a negative electrode active material. The negative electrode composite layer may also contain a binder, a conductive material, and the like. The negative electrode 12 can be manufactured, for example, by applying a negative electrode composite slurry containing a negative electrode active material and the like to the negative electrode current collector, drying and rolling the coating film, and forming the negative electrode composite layer on both sides of the negative electrode current collector.

[0022] The negative electrode active material contains activated carbon, a Si-based material supported in the pores of the activated carbon, and a conductive material. Although it is desirable that all of the Si-based material and the conductive material are supported in the pores of the activated carbon, a part of the Si-based material and the conductive material may be supported on the surface of the activated carbon.

[0023] The method for supporting Si-based materials and conductive materials within the pores of activated carbon is not particularly limited, but one example is to immerse activated carbon in a slurry in which Si-based materials and conductive materials are dispersed in an organic solvent. This allows the slurry to penetrate into the pores of the activated carbon based on capillary action, thereby supporting the Si-based materials and conductive materials within the pores. Heating or degassing the slurry is desirable to facilitate the support of the Si-based materials and conductive materials within the pores. Alternatively, Si-based materials and conductive materials can be supported in the pores of activated carbon by the cold isostatic pressing method (CIP method). Specifically, a mixture is prepared by adding activated carbon to a slurry in which Si-based materials and conductive materials are dispersed in an organic solvent. This mixture is placed in a rubber bag, and pressurized using a pressure medium such as water, thereby injecting the slurry into the pores of the activated carbon. By controlling the Si content and conductive material content of the slurry, the amount of Si and conductive materials within the pores of the activated carbon can be adjusted. It is also possible to combine the aforementioned capillary action-based immersion method with the CIP method.

[0024] <Activated carbon> Activated carbon primarily functions as a carrier for supporting Si-based materials and conductive materials. Activated carbon has a porous structure with numerous pores. The pores of activated carbon are classified into micropores, mesopores, and macropores according to their diameter. Micropores are pores with a diameter of 2 nm or less, mesopores are pores with a diameter between 2 nm and 50 nm, and macropores are pores with a diameter greater than 50 nm.

[0025] The raw materials for activated carbon are not particularly limited, and known raw materials such as carbonized materials of coconut shells, bamboo, wood (i.e., coconut shell charcoal, bamboo charcoal, wood charcoal, etc.) and coal can be used. Among these raw materials, it is preferable to use carbonized materials with high hardness, such as coconut shell charcoal or bamboo charcoal. Furthermore, the method for activating activated carbon is not particularly limited, and known activation methods such as gas activation, which involves treatment at high temperatures using gases such as water vapor or carbon dioxide, and chemical activation, which involves treatment with zinc chloride, phosphoric acid, concentrated sulfuric acid, etc., can be employed.

[0026] Furthermore, the particle form of the activated carbon is not particularly limited; it may be in the form of powder, granules, or other particle shapes, or it may be in the form of fibers.

[0027] The total pore volume of activated carbon (sum of micropore volume, mesopore volume, and macropore volume) is preferably 0.5 mL / g or more and 2.5 mL / g or less, and more preferably 0.7 mL / g or more and 2.2 mL / g or less, in order to allow sufficient Si-based material and conductive material to be supported within the pores. Furthermore, the macropore volume of activated carbon is preferably 1.0 mL / g or more and 2.1 mL / g or less, and more preferably 1.2 mL / g or more and 2.0 mL / g or less, in order to facilitate the support of Si-based material and conductive material within the pores. The micropore distribution and mesopore distribution of activated carbon are calculated using the BJH method of nitrogen adsorption isotherm adsorption curves. The macropore distribution is determined using the mercury intrusion method.

[0028] Activated carbon preferably has macropores with an average pore size of 0.5 μm or more and 2.5 μm or less, and more preferably has macropores with an average pore size of 1 μm or more and 2 μm or less, as this facilitates the loading of Si-based materials and conductive materials into the pores.

[0029] The specific surface area of ​​activated carbon is, for example, 2000 m². 2 / g or less, or 1700m 2 It may be less than / g, and 1000m 2 / g or more, or 1100m 2 It may be 1000 m² or more. The specific surface area of ​​activated carbon is, for example, 1000 m². 2 / g or more, 2000m 2 It may be less than / g. The specific surface area of ​​activated carbon can be measured by the BET method.

[0030] The average particle size of activated carbon may be, for example, 10 μm or more, 30 μm or more, or 40 μm or more, and may be 100 μm or less, 70 μm or less, or 60 μm or less. The average particle size of activated carbon may be 10 μm or more, 100 μm or less, 40 μm or more, 70 μm or less, or 30 μm or more, or 60 μm or less. The average particle size can be measured by laser diffraction scattering.

[0031] <Si-based materials> The Si-based materials are not particularly limited as long as they can reversibly occlude and release ions such as lithium ions. For example, Si particles, alloy particles containing Si, and composite particles containing Si can be mentioned. These may be used alone or in combination of two or more.

[0032] Si particles can be obtained by, for example, a vapor phase method or pulverizing silicon scraps, and any method of production can be used. Alloy particles containing Si include, for example, alloys containing Si and a metal selected from an alkali metal, an alkaline earth metal, a transition metal, a rare earth metal, or a combination thereof. Composite particles containing Si include, for example, a lithium ion conductive phase and Si particles dispersed in the lithium ion conductive phase. The lithium ion conductive phase is at least one selected from, for example, a silicon oxide phase, a silicate phase, and a carbon phase.

[0033] The silicate phase preferably contains at least one element selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium, for example, from the viewpoint of high lithium ion conductivity. Among them, the silicate phase is preferably a lithium-containing silicate phase (hereinafter sometimes referred to as a lithium silicate phase) from the viewpoint of high lithium ion conductivity.

[0034] The lithium silicate phase is represented by, for example, the formula: Li 2z SiO 2+z (0 < z < 2). From the viewpoints of stability, ease of production, lithium ion conductivity, etc., z preferably satisfies the relationship of 0 < z < 1, and z = 1 / 2 is more preferable.

[0035] Composite particles in which Si particles are dispersed in the silicon oxide phase are represented by, for example, the general formula SiO x(The range of 0 < x < 2 is preferred, and the range of 0.5 ≦ x ≦ 1.6 is more preferred). The composite particles in which Si particles are dispersed in the carbon phase are represented by, for example, the general formula SixC1y (the range of 0 < x ≦ 1 and 0 < y ≦ 1 is preferred, and the range of 0.3 ≦ x ≦ 0.45 and 0.7 ≦ y ≦ 0.55 is more preferred).

[0036] Regarding the content of the Si-based material, in terms of increasing the capacity of the battery and suppressing the swelling of the negative electrode, for example, the volume ratio of the Si-based material to the total pore volume of the activated carbon is preferably 20% or more and 40% or less, and more preferably 25% or more and 35% or less.

[0037] The average particle size of the Si-based material is, for example, preferably 10 nm or more and 500 nm or less, more preferably 20 nm or more and 200 nm or less, and even more preferably 50 nm or more and 100 nm or less, in terms of being easily supported in the pores of the activated carbon.

[0038] It is preferable that a conductive coating film made of a material with high conductivity is formed on the particle surface of the Si-based material. Examples of the conductive coating film include a carbon coating film, a metal coating film, and a metal compound coating film. From the viewpoint of electrochemical stability and the like, a carbon coating film is preferred. The carbon coating film can be formed, for example, by a CVD method using acetylene, methane, etc., or a method in which coal pitch, petroleum pitch, phenol resin, etc. are mixed with the silicon-based active material and heat-treated. Also, a conductive coating film may be formed by fixing a conductive filler such as carbon black to the particle surface of the Si-based material using a binder.

[0039] Similarly, it is preferable that a conductive coating film is formed on the surface of the activated carbon in which the Si-based material and the conductive material are supported in the pores. Examples of the conductive coating film include a carbon coating film, a metal coating film, and a metal compound coating film. From the viewpoint of electrochemical stability and the like, a carbon coating film is preferred.

[0040] <Conductive material> Examples of conductive materials include carbon black, acetylene black, Ketjenblack, graphite, and carbon nanotubes. Among these, carbon nanotubes are preferred because they can suppress the deterioration of the battery's charge-discharge cycle characteristics while keeping the amount added low. Carbon nanotubes include single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Among these, single-walled carbon nanotubes are preferred because they can further suppress the deterioration of the battery's charge-discharge cycle characteristics. Single-walled carbon nanotubes (SWCNTs) are carbon nanostructures in which one layer of graphene sheet forms a single cylindrical shape, double-walled carbon nanotubes are carbon nanostructures in which two layers of graphene sheet are stacked concentrically to form a single cylindrical shape, and multi-walled carbon nanotubes are carbon nanostructures in which three or more layers of graphene sheet are stacked concentrically to form a single cylindrical shape. A graphene sheet refers to a layer in which carbon atoms with sp2 hybrid orbitals that make up the crystal of graphite are located at the vertices of a regular hexagon. The shape of the carbon nanotube is not limited. Such shapes include a variety of forms, such as needle-shaped, cylindrical tube-shaped, fishbone-shaped (fishbone or cup-stacked type), playing card-shaped (platelet), and coil-shaped.

[0041] The content of the conductive material may be, for example, 0.01% by mass or more and 1.0% by mass or less relative to the mass of the Si-based material.

[0042] The negative electrode active material may include, in addition to activated carbon in which Si-based materials and conductive materials are supported within its pores, known negative electrode active materials such as carbon materials that electrochemically absorb and release lithium ions. The content of the negative electrode active material may be, for example, 85% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the negative electrode composite layer.

[0043] Examples of binders include the binder exemplified in the positive electrode 11. The binder content is preferably 0.5% to 10% by mass, and more preferably 1% to 5% by mass, relative to the total amount of the negative electrode composite layer.

[0044] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include olefin resins such as copolymers containing polyethylene, polypropylene, ethylene, and propylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0045] [Non-aqueous electrolytes] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt. Non-aqueous electrolytes are not limited to liquid electrolytes and may also be solid electrolytes using gel-like polymers, etc. Examples of lithium salts used as electrolyte salts include LiFSI, LiTFSI, LiBF4, and LiPF6. Examples of solvents include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl acetate (MA), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixtures of two or more of these. Non-aqueous solvents may contain halogen-substituted solvents in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine.

[0046] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). [Examples]

[0047] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0048] <Example 1> Silicon chips were used as a raw material and pulverized to produce Si particles with a particle size of 50 nm to 100 nm. These Si particles were mixed with acetylene black (AB) as a conductive material in a mass ratio of 100:0.5. A slurry was prepared by dispersing this mixture in propylene carbonate solvent (PC solvent). Next, the slurry was added to activated carbon (macropores: pore size 1 μm to 2 μm, total pore volume: 1.5 mL / g) so that the volume ratio of Si to the total pore volume of the activated carbon was 33%. Then, pressure molding was performed by the CIP method to produce a negative electrode active material in which Si-based material and conductive material were supported within the pores of the activated carbon.

[0049] The above-mentioned negative electrode active material, sodium carboxymethylcellulose, and styrene-butadiene rubber were mixed in a mass ratio of 100:1.3:1.0, and an appropriate amount of water was added to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a negative electrode current collector made of copper foil, and after the coating film was dried, the coating film was rolled with a rolling roller to produce a negative electrode in which a negative electrode composite layer was formed on both sides of the negative electrode current collector.

[0050] Composition is LiNi 0.88 Co 0.09 Al 0.03 A lithium transition metal composite oxide of O2, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 100:0.75:0.6, and then N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry. This slurry was applied to both sides of an aluminum foil, and after the coating was dried, the coating was rolled using a rolling roller to produce a positive electrode in which a positive electrode composite layer was formed on both sides of the positive electrode current collector.

[0051] [Nonaqueous electrolyte] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1.2 mol / L in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (MA) in a volume ratio of 20:40:40.

[0052] [Test cell] The positive electrode and the negative electrode were stacked facing each other with a separator in between, and this was wound to create an electrode body. Next, the electrode body and the non-aqueous electrolyte were placed in a bottomed cylindrical battery case body, and after the non-aqueous electrolyte was injected, the opening of the battery case body was sealed with a gasket and a sealing body to create a test cell.

[0053] <Example 2> A test cell was prepared in the same manner as in Example 1, except that Si particles with a carbon coating formed on their surface were used.

[0054] <Example 3> A test cell was prepared in the same manner as in Example 2, except that single-walled carbon nanotubes (SWCNTs) were used as the conductive material, and Si particles and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 100:0.01.

[0055] <Example 4> A test cell was prepared in the same manner as in Example 3, except that a carbon film was formed on the surface of activated carbon supporting a Si-based material and a conductive material within its pores.

[0056] <Comparative Example 1> A test cell was prepared in the same manner as in the examples, except that Si particles were used as the negative electrode active material.

[0057] <Comparative Example 2> A test cell was prepared in the same manner as in Example 1, except that a slurry was prepared by dispersing only Si particles in a PC solvent, and the slurry was added to activated carbon so that the volume ratio of Si to the total pore volume of the activated carbon was 50%.

[0058] <Comparative Example 3> A test cell was prepared in the same manner as in Example 1, except that a slurry was prepared in which only Si particles were dispersed in a PC solvent.

[0059] [Charge-discharge cycle test] The test cells for each example and comparative example were charged at a constant current of 0.3C at a temperature of 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage until the current value was 0.05C at 4.2V. Subsequently, constant current discharge was performed at a constant current of 0.5C until the battery voltage reached 2.5V. This was repeated 300 times, and the capacity retention rate after 300 cycles was calculated using the following formula. A higher capacity retention rate indicates that the degradation of charge-discharge cycle characteristics is suppressed. Capacity retention rate (%) = (Discharge capacity at 300 cycles / Discharge capacity at 1 cycle) × 100

[0060] [Evaluation of negative electrode expansion rate] The test cells for each example and comparative example were charged at a constant current of 0.3C under a temperature of 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage until the current value reached 0.05C at 4.2V. The charged test cells were disassembled, the negative electrode was removed, and the thickness of the negative electrode was measured (measurement of the negative electrode thickness after charging). The negative electrode expansion rate was then calculated by applying the negative electrode thickness at the time of fabrication and the negative electrode thickness after charging to the following formula. Negative electrode expansion rate (%) = (Negative electrode thickness after charging / Negative electrode thickness during manufacturing) × 100

[0061] Table 1 summarizes the results for the negative electrode expansion rate and capacity retention rate in each example and comparative example.

[0062] [Table 1]

[0063] In the example using a negative electrode active material in which Si-based materials and conductive materials are supported within the pores of activated carbon, the negative electrode expansion rate was lower and the capacity retention rate was higher compared to Comparative Example 1, in which only Si-based materials were used as the negative electrode active material. Therefore, it can be said that by using a negative electrode active material in which Si-based materials and conductive materials are supported within the pores of activated carbon, it is possible to suppress the expansion of the negative electrode and the deterioration of charge-discharge cycle characteristics. [Explanation of symbols]

[0064] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18,19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating material, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. It contains a Si-based material, activated carbon, and a conductive material. The Si-based material and the conductive material are supported within the pores of the activated carbon. The activated carbon has macropores with an average pore size of 1 μm or more and 2 μm or less, and the macropore volume measured by the mercury intrusion method is 1.0 mL / g or more and 2.1 mL / g or less. A negative electrode active material for a secondary battery, wherein the volume ratio of the Si-based material to the total pore volume of the activated carbon is 20% or more and 40% or less.

2. The negative electrode active material for a secondary battery according to claim 1, wherein a carbon film is formed on the surface of the Si-based material.

3. The conductive material comprises single-walled carbon nanotubes, as described in claim 1 or 2, for a negative electrode active material for a secondary battery.

4. The negative electrode active material for a secondary battery according to any one of claims 1 to 3, wherein a carbon film is formed on the surface of the activated carbon.

5. A secondary battery comprising a negative electrode containing the negative electrode active material for a secondary battery described in any one of claims 1 to 4.

Images