CN118630296A - Secondary battery and method for manufacturing secondary battery - Google Patents

Abstract

The secondary battery disclosed herein is a secondary battery having an electrode body having a positive electrode and a negative electrode, wherein the negative electrode comprises: a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer comprises graphite particles and Si-containing particles as negative electrode active materials, and carbon nanotubes as conductive materials. The Si-containing particles are porous bodies containing Si nanoparticles in a network structure, and carbon nanotubes are disposed in at least some of the pores of the porous body. When the weight of the Si-containing particles is set to 100wt%, the weight ratio X of the carbon nanotubes to the Si-containing particles is 0.02wt% to 4wt%.

Description

Secondary battery and method for manufacturing secondary battery

Technical Field

The present invention relates to a secondary battery and a method for manufacturing the secondary battery.

Background Art

Secondary batteries such as lithium-ion secondary batteries are suitable for use in portable power sources such as personal computers and mobile terminals, and vehicle driving power sources such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The negative electrode used in such a secondary battery generally has a structure in which a negative electrode active material layer containing a negative electrode active material is arranged on a negative electrode current collector.

In recent years, for the purpose of increasing the capacity of secondary batteries, the use of Si-based materials as negative electrode active materials has been studied (for example, Patent Documents 1 to 3). Patent Document 1 discloses a composite of a porous carbon material having micropores, mesopores and/or macropores and silicon. In addition, Patent Document 2 discloses a silicon material with amorphous silicon dioxide generated from plant raw materials as a precursor. Patent Document 3 discloses a negative electrode comprising a negative electrode active material containing a Si-based material, a carbon nanotube having an outermost diameter of less than 5 nm, and a carboxymethyl cellulose having a weight average molecular weight of 150,000 to 450,000.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application No. 2018-534720

Patent Document 2: Japanese Patent Application Publication No. 2021-38114

Patent Document 3: International Publication No. 2022/070895

Summary of the invention

Compared with carbon materials such as graphite particles, Si-based materials have a larger specific capacity. On the other hand, they expand and contract more during charging and discharging, and there is a tendency for the conductive path to be easily disconnected. Therefore, when using Si-based materials, the initial characteristics of the secondary battery (such as the initial charge and discharge efficiency) are easily reduced. Therefore, when using Si-based materials as negative electrode active materials, there is still room for improvement in the initial characteristics of the secondary battery.

The present invention has been made in view of the above-mentioned circumstances, and provides a secondary battery including a negative electrode containing graphite particles and a Si-based material as negative electrode active materials, and having excellent initial charge and discharge efficiency.

The secondary battery disclosed herein is a secondary battery having an electrode body having a positive electrode and a negative electrode, wherein the negative electrode has a negative electrode collector and a negative electrode active material layer disposed on the negative electrode collector, wherein the negative electrode active material layer comprises graphite particles and Si-containing particles as negative electrode active materials, and carbon nanotubes as conductive materials. The Si-containing particles are porous bodies containing Si nanoparticles in a network structure, and the carbon nanotubes are disposed in at least some of the pores of the porous body. When the weight of the Si-containing particles is set to 100wt%, the weight ratio X of the carbon nanotubes to the Si-containing particles is 0.02wt% to 4wt%.

According to the above configuration, the Si-containing particles are porous bodies containing Si nanoparticles with a network structure, and a conductive path is appropriately formed. In addition, the Si-containing particles have a plurality of pores, and carbon nanotubes are appropriately arranged in the pores to form a conductive path between the graphite particles and the Si-containing particles. Therefore, a secondary battery with high initial characteristics can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the internal structure of a secondary battery according to an embodiment.

FIG. 2 is a diagram schematically showing the structure of an electrode body according to one embodiment.

FIG. 3 is a diagram schematically showing a negative electrode according to one embodiment.

FIG. 4 is a flowchart showing a method for manufacturing a secondary battery according to an embodiment.

Explanation of symbols

20 Electrode body

30 Battery Case

36 Safety valve

42 Positive terminal

42a Positive electrode collector plate

44 Negative terminal

44a Negative collector plate

50 positive electrode (positive electrode sheet)

52 positive electrode collector

52a Positive electrode current collector exposed portion

54 Positive electrode active material layer

60 Negative electrode (negative electrode sheet)

62 negative electrode collector

62a Negative electrode current collector exposed portion

64 Negative electrode active material layer

66 Graphite particles

67 Containing Si particles

67a Si nanoparticles

67b Pore

68 Carbon nanotube (CNT)

70 Isolation

100 Secondary batteries

DETAILED DESCRIPTION

Hereinafter, the embodiments of the technology disclosed herein will be described with reference to the accompanying drawings. It should be noted that matters other than matters specifically mentioned in this specification and necessary for the implementation of the technology disclosed herein (for example, the general structure and manufacturing process of secondary batteries that do not characterize the technology disclosed herein, etc.) can be grasped as design matters for those skilled in the art based on the prior art in this field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in this field. It should be noted that each of the drawings is schematically depicted, and the dimensional relationship (length, width, thickness, etc.) does not necessarily reflect the actual dimensional relationship. In addition, in the drawings described below, the same symbols are marked for components and parts that play the same role, and repeated descriptions are sometimes omitted or simplified. In addition, the description of "A to B" (A and B are arbitrary numerical values) indicating a range in this specification means that A is above and B is below.

It should be noted that in this specification, "secondary battery" refers to a battery that can be repeatedly charged and discharged by the migration of charge carriers between the positive electrode and the negative electrode. In addition, in this specification, "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers to achieve charge and discharge by the migration of the charge of lithium ions between the positive and negative electrodes.

FIG. 1 is a diagram schematically showing the internal structure of a secondary battery 100 according to an embodiment. As shown in FIG. 1 , the secondary battery 100 includes an electrode body 20 having a positive electrode 50 and a negative electrode 60, an electrolyte (not shown), and a battery case 30 for accommodating the electrode body 20 and the electrolyte. The secondary battery 100 shown in FIG. 1 is a lithium ion secondary battery. The negative electrode 60 disclosed herein is preferably used as a negative electrode for a lithium ion secondary battery.

The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 36 set in a manner to release the internal pressure of the battery case 30 when the internal pressure rises to a predetermined level or more. In addition, the battery case 30 is provided with an injection port (not shown) for injecting a non-aqueous electrolyte. The positive terminal 42 is electrically connected to the positive electrode collector plate 42a. The negative terminal 44 is electrically connected to the negative electrode collector plate 44a. As the material of the battery case 30, a metal material such as aluminum, which is lightweight and has good thermal conductivity, is used.

FIG. 2 is a diagram schematically showing the structure of the electrode body 20. Here, the electrode body 20 is a flat wound electrode body. As shown in FIG. 2 , the electrode body 20 has a shape in which a long sheet-shaped positive electrode 50 (hereinafter, also referred to as a "positive electrode sheet 50") and a long sheet-shaped negative electrode 60 (hereinafter, also referred to as a "negative electrode sheet 60") are overlapped with two long strips of separators 70 and wound in the long side direction. The positive electrode sheet 50 has a structure in which a positive electrode active material layer 54 is formed on one side or both sides (here both sides) of a long strip-shaped positive electrode collector 52 along the long side direction. The negative electrode sheet 60 has a structure in which a negative electrode active material layer 64 is formed on one side or both sides (here both sides) of a long strip-shaped negative electrode collector 62 along the long side direction. As shown in FIGS. 1 and 2 , the positive electrode current collector exposed portion 52a (i.e., the portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode current collector exposed portion 62a (i.e., the portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) are formed so as to protrude outward from both ends of the winding axial direction (i.e., the sheet width direction orthogonal to the above-mentioned long side direction) of the electrode body 20. The positive electrode current collector exposed portion 52a and the negative electrode current collector exposed portion 62a are respectively joined to the positive electrode current collector plate 42a and the negative electrode current collector plate 44a.

As the positive electrode collector 52 constituting the positive electrode sheet 50, a known positive electrode collector used in a lithium-ion secondary battery can be used without particular limitation. For example, sheets or foils made of metals with good electrical conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) can be cited. As the positive electrode collector 52, aluminum foil is preferred. The size of the positive electrode collector 52 is not particularly limited, as long as it is appropriately determined according to the battery design. When aluminum foil is used as the positive electrode collector 52, its thickness is not particularly limited, for example, 5μm to 35μm, preferably 7μm to 20μm.

The positive electrode active material layer 54 contains a positive electrode active material. As the positive electrode active material, a known positive electrode active material used in a lithium ion secondary battery can be used. Specifically, for example, as the positive electrode active material, a lithium composite oxide, a lithium transition metal phosphate compound (for example, lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ )) or the like can be used. The crystal structure of the positive electrode active material is not particularly limited, and may be a layered structure, a spinel structure, an olivine structure, or the like.

As the lithium composite oxide, it is preferred that at least one of Ni, Co, and Mn is contained as a transition metal element in a lithium transition metal composite oxide, and as a specific example thereof, lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, lithium iron nickel manganese composite oxides, etc. can be cited. These positive electrode active materials can be used alone or in combination of two or more. Among them, lithium nickel cobalt manganese composite oxides can be preferably used as the positive electrode active material.

It should be noted that in this specification, "lithium nickel cobalt manganese composite oxide" refers to a term for an oxide containing one or more additional elements other than oxides with Li, Ni, Co, Mn, and O as constituent elements. Examples of the above-mentioned additional elements include transition metal elements or typical metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. In addition, the additional element may also be a semi-metal element such as Y/Z, Si, and P, or a non-metal element such as S, F, Cl, Br, and I. This provision also applies to the above-mentioned lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide.

The positive electrode active material layer 54 may also contain components other than the positive electrode active material, such as a conductive material, a binder, etc. As the conductive material, for example, carbon black such as acetylene black (AB); carbon fibers such as vapor grown carbon fiber (VGCF) and carbon nanotubes (CNT); and carbon materials (such as graphite, etc.) may be used appropriately. As the binder, for example, polyvinylidene fluoride (PVdF) may be used.

Although not particularly limited, the content of the conductive material is preferably 0.1wt% to 10wt%, more preferably 1wt% to 5wt%, when the positive electrode active material is 100wt%. In addition, the content of the binder is preferably 0.1wt% to 10wt%, more preferably 1wt% to 5wt%, when the positive electrode active material is 100wt%.

The thickness per one side of the positive electrode active material layer 54 is not particularly limited, and is, for example, 20 μm or more, preferably 50 μm or more, and, for example, 300 μm or less, preferably 200 μm or less.

As the separator 70, various microporous sheets similar to those in the past can be used, for example, microporous resin sheets made of resins such as polyethylene (PE) and polypropylene (PP). The microporous resin sheet can be a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are stacked on both sides of a PE layer). In addition, the separator 70 can have a heat-resistant layer (HRL).

The electrolyte may be the same as that used in the past. For example, a non-aqueous electrolyte containing a supporting salt in an organic solvent (non-aqueous solvent) may be used. As a non-aqueous solvent, aprotic solvents such as carbonates, esters, and ethers may be used. Among them, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. may be appropriately used. Alternatively, fluorinated solvents such as fluorinated carbonates such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluoromethyl carbonate (TFDMC) may be preferably used. Such non-aqueous solvents may be used alone or in combination of two or more. As a supporting salt, for example, lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ may be appropriately used. The concentration of the supporting salt is not particularly limited, and is preferably about 0.7 mol/L to 1.3 mol/L.

It should be noted that the non-aqueous electrolyte may contain components other than the non-aqueous solvent and supporting salt, for example, various additives such as a gas generator, a film forming agent, a dispersant, and a thickener, as long as the effects of the present technology are not significantly impaired.

The negative electrode 60 of the secondary battery disclosed herein is described below. FIG. 3 is a diagram schematically showing the negative electrode 60 of the secondary battery 100 disclosed herein. As shown in FIG. 3 , the negative electrode 60 includes a negative electrode collector 62 and a negative electrode active material layer 64 disposed on the negative electrode collector 62. The negative electrode collector 62 can use a conventionally known collector without particular limitation. For example, sheets or foils made of metals such as copper, nickel, titanium, and stainless steel can be cited. When copper foil is used as the negative electrode collector 62, its average thickness is not particularly limited, and is, for example, 5 μm to 30 μm, preferably 5 μm to 20 μm, and more preferably 5 μm to 15 μm.

The negative electrode active material layer 64 contains at least a negative electrode active material. The negative electrode active material layer 64 contains at least graphite particles 66 and Si-containing particles 67 as negative electrode active materials. The above-mentioned Si-containing particles 67 are porous bodies containing Si nanoparticles 67a in a network structure. The Si-containing particles 67 have a plurality of pores 67b. Carbon nanotubes 68 are arranged in at least some of the pores 67b of the above-mentioned plurality of pores 67b. Moreover, when the weight of the Si-containing particles 67 is set to 100wt%, the weight ratio X of the carbon nanotubes 68 to the Si-containing particles 67 is adjusted to 0.02wt% to 4wt%. According to the above-mentioned structure, the initial charge and discharge efficiency of the secondary battery 100 can be improved.

It is not intended to limit the technology disclosed herein, but the reasons for obtaining the above-mentioned effects are speculated as follows. The conductive path is appropriately improved by making the Si-containing particles 67 a porous body containing Si nanoparticles 67a having a network structure. In addition, the Si-containing particles 67 have a plurality of pores 67b, so that the carbon nanotubes 68 as a conductive material are appropriately arranged around the Si-containing particles 67, and a good charging path is formed between the graphite particles 66 and the Si-containing particles 67. Therefore, the initial charge and discharge efficiency of the secondary battery 100 is improved. In addition, even if the expansion and contraction are repeatedly accompanied by charging and discharging, it is difficult for the carbon nanotubes 68 to detach from the plurality of pores 67b by exerting the anchoring effect. Moreover, the expansion of the Si nanoparticles 67a can be suppressed by the Si nanoparticles 67a having a network structure, and it is not easy for the Si nanoparticles 67a to be damaged by expansion. Therefore, even if the expansion and contraction are repeatedly accompanied by charging and discharging, it is difficult to cut off the conductive path, and the cycle characteristics of the secondary battery 100 are improved.

As the graphite particles 66, for example, artificial graphite, natural graphite, etc. can be used. The graphite particles 66 may have a coating layer of amorphous carbon on their surfaces. There are no particular restrictions, and the graphite particles 66 may be roughly spherical in shape. It should be noted that in this specification, "roughly spherical" refers to terms including spherical, rugby-shaped, etc., for example, a shape with an average aspect ratio (the ratio of the length in the major axis direction to the length in the minor axis direction in the smallest rectangle circumscribed by the particle) of, for example, 1 to 2 (preferably 1 to 1.5).

The _D50 particle size of the graphite particles 66 is not particularly limited, and is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. It should be noted that in this specification, the " _D50 particle size of the graphite particles" refers to the particle size corresponding to 50% of the cumulative value from the microparticle side in the volume-based particle size distribution measured by the particle size distribution measurement using the laser diffraction scattering method.

The Si-containing particles 67 are porous bodies containing Si nanoparticles 67a having a network structure. As long as the Si-containing particles 67 contain Si, they may also contain components other than Si. As the Si-containing particles 67, for example, SiOx, Si-C composites, particles in which Si nanoparticles are dispersed in porous Si particles, etc. can be cited. The porous body part of the Si-containing particles 67 can be composed of Si as the main component, for example, or can be composed of carbon (C) as the main component. For example, a Si-C composite containing Si nanoparticles having a network structure and porous carbon particles can be preferably used as the Si-containing particles 67. Alternatively, a Si particle containing Si nanoparticles having a network structure and porous Si particles can be preferably used as the Si-containing particles 67. It should be noted that in this specification, "A is composed of B as the main component" means that B is the largest component on a weight basis among the components constituting A.

The Si-containing particle 67 is a porous body having a plurality of pores (pores) 67b. The Si-containing particle 67 may have, for example, micropores, mesopores, and macropores. Here, micropores refer to pores with a diameter of less than 2nm, mesopores refer to pores with a diameter greater than 2nm and less than 50nm, and macropores refer to pores with a diameter greater than 50nm. When the pore size is too large, the cycle characteristics of the secondary battery 100 may be reduced due to erosion by the electrolyte. From the above viewpoints, the pores 67b possessed by the Si-containing particle 67 are preferably, for example, 1nm to 300nm, or 1nm to 250nm. The Si-containing particle 67 may, for example, be a nanoporous structure having a nano-sized porous structure.

Without particular limitation, the Si-containing particles 67 preferably include pores with a diameter of more than 100 nm and pores with a diameter of less than 10 nm. Since the Si-containing particles 67 have pores of more than 100 nm, the anchoring effect can be easily exerted, and carbon nanotubes can be appropriately arranged on the surface of the Si-containing particles 67. Therefore, the initial charge and discharge efficiency of the secondary battery 100 can be improved. In addition, even if the Si-containing particles 67 repeatedly expand and contract with charging and discharging, the conductive material is not easily detached due to the anchoring effect, and the conductive path is not easily disconnected. Therefore, the cycle characteristics of the secondary battery 100 can also be improved. Since the Si-containing particles 67 have pores of less than 10 nm, the erosion of the electrolyte and the expansion and contraction accompanying charging and discharging can be appropriately suppressed. Thus, the cycle characteristics of the secondary battery 100 can be improved.

More preferably, the Si-containing particles 67 can be adjusted so that the ratio of the logarithmic differential pore volume (log differential pore volume) _V10 of pores with a diameter of 10 nm to the logarithmic differential pore volume _V100 of pores with a diameter of 100 nm ( _V10 / _V100 ) is 1 or more. That is, it is preferred that the Si-containing particles 67 have a nanoporous structure in which pores with smaller diameters (for example, pores with a diameter of 10 nm) are more than pores with larger diameters (for example, pores with a diameter of 100 nm). Thus, the initial charge and discharge efficiency and cycle characteristics of the secondary battery 100 can be appropriately combined. The above-mentioned ratio of _V10 to _V100 ( _V10 / _V100 ) is preferably greater than 1, more preferably greater than 1.2, and may also be greater than 1.5. In addition, the ratio of _V10 to _V100 ( _V10 / _V100 ) is, for example, preferably less than 20, and may also be less than 10.

The logarithmic differential pore volume _V100 of pores with a diameter of 100 nm and the logarithmic differential pore volume _V10 of pores with a diameter of 10 nm can be calculated using a specific surface area/pore distribution measuring device using the BJH method. First, the Si-containing particles are heated and dried under vacuum to prepare a measurement sample. Next, liquid nitrogen is used as a refrigerant and nitrogen ( _N2 gas) is used as an adsorption gas to obtain an adsorption isotherm of the measurement sample, and the obtained adsorption isotherm is analyzed using the BJH method to obtain the logarithmic differential pore volume distribution. Then, the logarithmic differential pore volume _V100 of pores with a diameter of 100 nm and the logarithmic differential pore volume _V10 of pores with a diameter of 10 nm can be obtained based on the logarithmic differential pore volume distribution.

The Si-containing particles 67 have Si nanoparticles 67a with a network structure. The Si nanoparticles 67a are Si particles of nanometer size (i.e., less than 1 μm). The Si nanoparticles 67a may be present on the surface of the above-mentioned porous body and/or inside the pores 67b of the porous body. The Si nanoparticles 67a are preferably less than 100 nm, and more preferably less than 50 nm. As a result, the amount of expansion and contraction of each Si nanoparticle 67a during charge and discharge can be reduced, and it is not easy to break even if it is repeatedly expanded and contracted. In addition, there is no particular limitation, and the average particle size of the Si nanoparticles 67a can be, for example, more than 5 nm. It should be noted that in this specification, the "average particle size of Si nanoparticles" can be calculated as follows. First, the negative electrode active material layer is processed by FIB (focused ion beam) to prepare a sample for observation by a scanning transmission electron microscope (STEM). Then, the sample is subjected to elemental analysis by EDX element mapping, and a BF image (bright field image) and a HAADF image (high-angle annular dark field image) are obtained. The diameter of the Si nanoparticles can be determined from the contrast and shape obtained from the BF image and the HAADF image. The arithmetic mean of the diameters of at least 10 Si nanoparticles is referred to as the "average particle size of the Si nanoparticles" herein.

The Si nanoparticles 67a have a network structure. The network structure forms a plurality of gaps randomly or regularly. The conductive path is appropriately improved by the Si nanoparticles 67a having a network structure. In addition, the Si nanoparticles 67a have a network structure, so that the excessive expansion and contraction of the Si nanoparticles 67a accompanying charge and discharge is suppressed.

Although not particularly limited, the Si-containing particles 67 preferably have a plurality of pores 67b around the Si nanoparticles 67a. It is particularly preferred that there are many pores with smaller diameters (e.g., pores with a diameter of less than 10 nm) around the Si nanoparticles 67a. This can alleviate the expansion and contraction associated with charge and discharge, and appropriately suppress the erosion of the electrolyte.

Although not particularly limited, the oxygen content of the Si-containing particles is preferably 10 wt% or less when all Si-containing particles are set to 100 wt%. Thus, the side reactions caused by excessive oxygen content can be reduced, and the capacity and cycle characteristics of the secondary battery can be appropriately improved. It should be noted that the oxygen content can be measured by heating and melting in an inert gas using an oxygen analyzer.

The _D50 particle size of the Si-containing particles 67 is not particularly limited, and is preferably 1 μm to 15 μm, and more preferably 2 μm to 10 μm. It should be noted that in this specification, the " _D50 particle size of the Si-containing particles" refers to the particle size corresponding to 50% of the cumulative value from the microparticle side in the volume-based particle size distribution measured by the particle size distribution measurement using the laser diffraction scattering method.

The above-mentioned Si-containing particles 67 can be obtained, for example, by calcining plants containing Si. That is, the Si-containing particles 67 are preferably of plant origin. Specifically, rice (paddy rice), barley, wheat, rye, etc., rice husks, coconut shells, tea leaves, sugar cane, corn and other plants can be used as raw materials. Among them, the Si-containing particles 67 are preferably made from rice husks. Plants accumulate silicate absorbed from the soil around their cell walls. By calcining it, a porous body containing Si nanoparticles 67a with a network structure of plant origin can be obtained. Among them, the Si-containing particles 67 can also be prepared by separately preparing a porous body composed mainly of Si or C and Si nanoparticles with a network structure and introducing Si nanoparticles into the porous body.

The negative electrode active material layer 64 may contain components other than the graphite particles 66 and Si-containing particles (for example, SiOx or hard carbon not having the above structure) as a negative electrode active material unless the effect of the present technology is significantly impaired.

Although not particularly limited, when the total mass of the negative electrode active material (the total weight of the weight of the graphite particles 66, the weight of the Si-containing particles 67, and the weight of other components that can be contained as the negative electrode active material) is set to 100wt%, the content of the Si-containing particles 67 is preferably 10wt% to 60wt%, and more preferably 20wt% to 40wt% or less. When the total mass of the negative electrode active material is set to 100wt%, the content of the graphite particles 66 is preferably 40wt% to 90wt%, and more preferably 60wt% to 80wt%. That is, the weight ratio of the weight of the graphite particles 66 to the weight of the Si-containing particles is preferably adjusted to 90:10 to 40:60, and can also be adjusted to 80:20 to 60:40. By adjusting the weight of the Si-containing particles 67 to the above range, it is possible to appropriately achieve both initial charge and discharge efficiency and cycle characteristics.

In the secondary battery 100 disclosed herein, carbon nanotubes (CNT) 68 are used as conductive materials. Carbon nanotubes 68 are fibrous carbon having a structure in which graphene forming a carbon hexagonal network is rolled into a cylindrical shape. Carbon nanotubes 68 have the properties of high aspect ratio and excellent conductivity. Therefore, carbon nanotubes 68 are easily entangled with graphite particles 66 and Si-containing particles 67, and the conductive path is properly maintained. In addition, as described above, Si-containing particles 67 have a plurality of pores 67b, and by configuring carbon nanotubes 68 in the above-mentioned pores 67b, it is not easy to detach from Si-containing particles 67 even if they expand and contract repeatedly with charge and discharge, and the conductive path is properly maintained.

As the carbon nanotube 68, for example, there can be mentioned a single-layer carbon nanotube (SWCNT) composed of one layer of graphene, a two-layer carbon nanotube (DWCNT) composed of two different layers of SWCNT, a multilayer carbon nanotube (MWCNT) composed of three or more different layers of SWCNT, etc. From the viewpoint of further increasing the capacity of the secondary battery 100, a single-layer carbon nanotube (SWCNT) is preferred.

Although not particularly limited, the average length of the carbon nanotubes 68 is preferably 1 μm to 10 μm, and more preferably 1 μm to 5 μm. The carbon nanotubes 68 are in the above-mentioned range of length, so that the carbon nanotubes 68 are appropriately dispersed to form an appropriate conductive path. In addition, the average diameter of the carbon nanotubes 68 is not particularly limited, but is preferably 1 nm to 100 nm, and more preferably 10 nm to 50 nm. The average length and average diameter of the carbon nanotubes 68 can be obtained, for example, by taking an electron microscope photograph of the carbon nanotubes and measuring the lengths and diameters of more than 30 carbon nanotubes, and then calculating the average values thereof.

Since the Si-containing particles 67 have pores 67b and the weight ratio of the Si-containing particles 67 to the carbon nanotubes 68 is appropriately adjusted, the carbon nanotubes 68 are appropriately arranged around the Si-containing particles 67 (specifically, at least a portion of the pores 67b of the Si-containing particles 67). As a result, a conductive path is appropriately formed in the negative electrode active material layer 64, so that the initial charge and discharge efficiency is improved. When the weight of the Si-containing particles 67 is set to 100wt%, the weight ratio X of the carbon nanotubes 68 to the Si-containing particles 67 is preferably 0.02wt% to 4wt%, more preferably 0.2wt% to 1wt%, and further preferably 0.2wt% to 0.6wt%. In other words, the ratio (CNT/Si-containing particles) of the content (wt%) of the carbon nanotubes 68 to the content (wt%) of the Si-containing particles 67 in the secondary battery 100 disclosed herein is preferably 0.0002 to 0.04, more preferably 0.002 to 0.01, and further preferably 0.002 to 0.006.

Although not particularly limited, the content of carbon nanotubes is preferably 0.01 wt% to 1.4 wt%, more preferably 0.1 wt% to 1 wt%, and further preferably 0.1 wt% to 0.2 wt% when the total mass of the negative electrode active material is 100 wt%. That is, the negative electrode active material and the carbon nanotubes are preferably negative electrode active material: CNT = 100: 0.01 to 100: 1.4, more preferably negative electrode active material: CNT = 100: 0.1 to 100: 1, and further preferably negative electrode active material: CNT = 100: 0.1 to 100: 0.2.

The negative electrode active material layer 64 may contain components (such as a binder, etc.) other than the above-mentioned negative electrode active material (graphite particles 66 and Si-containing particles 67) and the conductive material (carbon nanotubes). As a binder, a conventionally known binder can be used. As a binder, for example, carboxymethyl cellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), etc. can be cited. Among them, CMC, PAA, and SBR can be preferably used. In addition, although not particularly limited, it is more preferred to use CMC, PAA and SBR in combination.

The content of the binder as a whole is, for example, 1 wt% or more, preferably 3 wt% or more, and more preferably 3.5 wt% or more, when the negative electrode active material is 100 wt%. In addition, the content of the binder as a whole is 10 wt% or less, preferably 8 wt% or less, and more preferably 5 wt% or less, when the negative electrode active material is 100 wt%.

It is speculated that since Si-containing particles 67 are porous bodies having a plurality of pores, not only carbon nanotubes 68 but also a binder (not shown) are arranged around Si-containing particles 67. As a result, carbon nanotubes 68 are less likely to be separated from Si-containing particles 67, and initial charge and discharge efficiency and cycle characteristics can be improved.

The thickness per one side of the negative electrode active material layer 64 is not particularly limited, and is, for example, 20 μm or more, preferably 50 μm or more, and, for example, 300 μm or less, preferably 200 μm or less.

Although not particularly limited, the proportion of the negative electrode active material in the entire negative electrode active material layer 64 is, for example, 80 mass % or more, preferably 90 mass % or more, and more preferably 95 mass % or more. In addition, although not particularly limited, the proportion of the negative electrode active material in the entire negative electrode active material layer 64 may be, for example, 98 mass % or less.

<Method for producing secondary battery>

As described above, the secondary battery 100 disclosed herein includes graphite particles 66, Si-containing particles 67, and carbon nanotubes 68, and the carbon nanotubes 68 are disposed in at least a portion of the pores of the Si-containing particles 67. The secondary battery 100 can be manufactured, for example, as follows.

FIG4 is a flow chart showing one preferred embodiment of the manufacturing method of the secondary battery 100 disclosed herein. As shown in FIG4 , the manufacturing method of the secondary battery 100 disclosed herein includes: a preparation step S10 of preparing each material, and a mixing step S20 of mixing the prepared materials. The mixing step S20 preferably includes: a first mixing step S21 of mixing Si-containing particles and carbon nanotubes to prepare a first mixture, and a second mixing step S22 of mixing the first mixture, graphite particles, a binder and a solvent to prepare a second mixture. Among them, the manufacturing method disclosed herein may further include other steps at any stage.

In the preparation step S10, at least graphite particles 66, Si-containing particles 67 and carbon nanotubes 68 are prepared. In addition, in the preparation step S10, other necessary components (for example, a binder, a solvent, etc.) can be prepared. As described above, the graphite particles 66 can preferably use natural graphite or artificial graphite. As the Si-containing particles 67, a porous body containing Si nanoparticles 67a having a network structure is prepared. As the above-mentioned Si-containing particles 67, for example, a Si-C complex and/or Si particles of plant origin can be prepared. It is more preferable to prepare a Si-C complex and/or Si particles of rice husk origin as the Si-containing particles 67. As the carbon nanotubes 68, a water-soluble paste having a solid content of about 1% to 10% can be prepared.

As a binder, the binder exemplified above can be used without particular limitation. As a solvent, any of an aqueous solvent and a non-aqueous solvent can be used. Typically, water or a mixed solvent with water as the main body is preferably used. As a solvent component other than water constituting the above-mentioned mixed solvent, one or more than two organic solvents (lower alcohols, lower ketones, etc.) that can be uniformly mixed with water can be appropriately selected. For example, it is preferred to use an aqueous solvent in which more than 80% by mass (more preferably more than 90% by mass, and further preferably more than 95% by mass) of the aqueous solvent is water. As a particularly preferred example, an aqueous solvent substantially consisting of water can be cited.

The mixing step S20 may include a first mixing step S21 and a second mixing step S22. In the first mixing step S21, the Si-containing particles 67 and the carbon nanotubes 68 are mixed to prepare a first mixture. By mixing the Si-containing particles 67 and the carbon nanotubes 68 in advance and then mixing with other materials, the carbon nanotubes 68 can be appropriately arranged in a part of the pores 67b of the Si-containing particles 67. Therefore, a conductive path is easily formed, and the initial charge and discharge efficiency of the secondary battery 100 can be improved.

In the first mixing step S21, for example, powdered Si-containing particles 67 and paste-like carbon nanotubes 68 are put into a stirring device for mixing. The stirring device is not particularly limited as long as it has a rotating stirring blade (a stirring blade such as a dispersing blade or a turbine blade, or a stirring blade). The stirring speed is not particularly limited, and for example, it can be about 1000 rpm to 5000 rpm.

In the second mixing step S22, the first mixture prepared in the first mixing step S21, the graphite particles 66, the binder, and the solvent are mixed to prepare the second mixture. The stirring device is not particularly limited, and the same stirring device as the first mixing step S21 can be used. Although not particularly limited, when a powdered binder is used in the second mixing step S22, it is preferred that the graphite particles 66 in powder form and the binder are dry-mixed, and then the first mixture and the solvent are added for kneading (solid kneading). In this way, the dispersibility can be improved.

The second mixture prepared above is applied to the negative electrode current collector 62 and dried. It should be noted that the negative electrode active material layer 64 disposed on the negative electrode current collector 62 may be dried and pressed as needed. In this way, the thickness and density of the negative electrode active material layer 64 may be adjusted.

The positive electrode active material layer 54 can be formed by dispersing the positive electrode active material, the conductive material and the binder in an appropriate solvent (e.g., NMP) to prepare a paste (or slurry) composition and applying the composition to the surface of the positive electrode collector 52 and drying it. Then, pressurization is performed as needed to adjust the thickness and density of the positive electrode active material layer 54.

The negative electrode 60 and the positive electrode 50 prepared above are stacked in an insulated state using two separators 70. As needed, the prepared stack is wound along the long side direction with the winding axis as the center, and the wound stack is pressurized to prepare a flat wound electrode body. The wound electrode body is accommodated in the battery case 30, and a non-aqueous electrolyte is injected from the injection hole. Then, the injection hole is sealed to close the secondary battery 100. In this way, the secondary battery 100 can be manufactured.

The above describes the structure of the secondary battery 100 and the manufacturing method of the secondary battery 100 according to one embodiment. The secondary battery 100 includes graphite particles 66, Si-containing particles 67 and carbon nanotubes 68, and the carbon nanotubes 68 are arranged in at least a part of the pores 67b of the Si-containing particles 67 to improve the initial charge and discharge efficiency. Furthermore, by arranging the carbon nanotubes 68 in the pores 67b, the situation where the conductive path is disconnected due to expansion and contraction caused by repeated charge and discharge is appropriately suppressed, and the cycle characteristics of the secondary battery 100 are improved. The secondary battery 100 can be used for various purposes, for example, it can be appropriately used as a motor power source (driving power source) mounted in vehicles such as passenger cars and trucks. It is particularly suitable as a power source for electric vehicles (BEV; Battery Electric Vehicle). The secondary battery 100 can also be appropriately used to construct a battery pack.

In the secondary battery 100 described above, a wound electrode body is exemplified as the electrode body 20 , but the present invention is not limited thereto. For example, a stacked electrode body may be formed by alternately stacking a plurality of substantially rectangular positive electrodes and a plurality of substantially rectangular negative electrodes with separators interposed therebetween.

Hereinafter, test examples related to the present invention will be described, but the present invention is not intended to be limited to the embodiments shown in the following test examples.

1. Test 1

In the first test, the type of Si-containing particles, the weight ratio of the Si-containing particles to CNTs, and the mixing method were changed to evaluate the initial charge and discharge efficiency of the secondary battery.

<Example 1>

First, prepare graphite particles and Si-containing particles as negative electrode active materials. The Si-containing particles in Example 1 are plant-derived Si-C composite particles using rice husks as raw materials. In addition, prepare single-layer carbon nanotubes (SWCNTs) as conductive materials. Then, prepare carboxymethyl cellulose (CMC), polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) as binders. They are mixed with water as a solvent in a weight basis of graphite particles: Si-containing particles: SWCNT: CMC: PAA: SBR = 65:35:0.1:1:1:1.5 to prepare a slurry for forming a negative electrode active material layer.

Specifically, the mixing and kneading of the slurry for forming the negative electrode active material layer is carried out as follows. First, Si-containing particles, paste-like SWCNT (solid content 2%) and a solvent are put into a container. Use a disperser to mix at a rotation speed of 3000 rpm to prepare a first mixture. Next, use a stirring granulator to dry-mix the graphite particles, CMC and PAA, add the above-prepared first mixture and solvent to the mixed powder, and knead and knead. The solid content during kneading and kneading is 65%. SBR and a solvent are further added to the mixture after kneading and mixing. In this way, a slurry for forming the negative electrode active material layer is prepared.

It should be noted that the solid content C (%) during kneading is determined as follows. Water is added to the mixed powder of graphite particles and Si-containing particles in the above ratio, and the moisture content at which the torque required for mixing is the maximum is set to A (%). The amount of water per 100g of the mixed powder equivalent to the moisture content A (%) is set to B (ml). At this time, the solid content C (%) that can provide the maximum torque can be calculated by the formula: C (%) = 100-A = (100/(100+B)) × 100.

The prepared negative electrode active material layer forming slurry was applied in strips on both sides of a copper foil (thickness 10 μm). The slurry on the copper foil was then dried, pressed to a predetermined thickness, and processed into a predetermined size to prepare a negative electrode sheet.

Next, prepare lithium nickel cobalt manganese composite oxide (NCM) as a positive electrode active material, acetylene black (AB) as a conductive material, and PVDF as a binder. Mix them with N-methylpyrrolidone (NMP) as a solvent in a weight ratio of NCM:AB:PVDF=100:1:1 to prepare a slurry for forming a positive electrode active material layer. Apply the slurry in a strip shape to both sides of an aluminum foil (thickness 15μm). Then, dry the slurry on the aluminum foil, press it to a specified thickness, and process it into a specified size to make a positive electrode sheet.

The prepared negative electrode sheet and the positive electrode sheet are stacked with a separator to produce a stacked electrode body. Collecting leads are respectively installed on the positive electrode plate and the negative electrode plate, and the stacked electrode body is inserted into an outer casing composed of an aluminum laminate. A non-aqueous electrolyte is injected into the interior of the outer casing, and the opening of the outer casing is sealed to produce the evaluation battery of Example 1. It should be noted that as a separator, a porous polyolefin sheet having a three-layer structure of PP/PE/PP is used. In addition, as a non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol/L in a mixed solvent in which ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a volume ratio of EC:FEC:EMC:DMC=15:5:40:40 is used.

Table 1 shows the content (wt%) of Si-containing particles when the weight of the negative electrode active material is 100wt%, the weight ratio X (wt%) of SWCNT to the Si-containing particles when the weight of the Si-containing particles is 100wt%, and the content (wt%) of SWCNT when the weight of the negative electrode active material is 100wt%. It should be noted that the weight ratio X of SWCNT can be obtained by the formula: weight ratio X of SWCNT = ((content of SWCNT)/(content of Si-containing particles))×100.

<Example 2, Example 3, Example 5 and Example 6>

Evaluation batteries of Examples 2, 3, 5 and 6 were prepared in the same manner as in Example 1 except that the weight ratio X (wt %) of SWCNT to the Si-containing particles was changed as shown in Table 1 when the weight of the Si-containing particles was 100 wt %.

<Example 4>

In Example 4, the step of mixing Si-containing particles with SWCNTs is not performed. That is, Si-containing particles, graphite particles, CMC and PAA are dry-mixed using a stirring granulator, and paste-like SWCNTs (solid content 2%) and a solvent are added to the mixed powder, and kneading is performed. The solid content during kneading is 65%. SBR and a solvent are further added to the mixture after kneading and mixing, and mixed. Thus, a slurry for forming a negative electrode active material layer is prepared. Except for the above, the evaluation battery of Example 4 is prepared in the same manner as Example 1.

<Example 7>

As Si-containing particles, Si—C composite particles produced by CVD were prepared. A battery for evaluation of Example 7 was produced in the same manner as in Example 1 except for the above.

＜Evaluation of initial charge and discharge efficiency＞

In the first cycle of CCCV charging (0.05C to 4.2V, then 0.05C cut-off) followed by CC discharge (0.05C at 2.5V cut-off) at 25°C, the first charge capacity and the first discharge capacity were measured. The initial charge and discharge efficiency was calculated according to the following formula (1). The results are shown in Table 1.

Initial charge and discharge efficiency (%) = ((first discharge capacity)/(first charge capacity)) × 100···Formula (1)

[Table 1]

According to Table 1, the initial charge and discharge efficiency of the evaluation batteries of Examples 1 to 4 is 82% or more. According to these results, it can be seen that by using graphite particles and Si-containing particles as a porous body containing Si nanoparticles in a network structure as negative electrode active materials, the weight ratio X of carbon nanotubes to the Si-containing particles is 0.02wt% to 4wt% when the weight of the Si-containing particles is set to 100wt%, and CNTs are arranged in at least some of the holes in the porous body, thereby realizing a secondary battery with excellent initial charge and discharge efficiency.

In addition, when comparing Examples 1 to 3 in Table 1 with Example 4, it can be seen that by performing the first mixing step of mixing Si-containing particles with SWCNTs first and then performing the second mixing step, CNTs are easily arranged in the holes of the porous body, and the initial charge and discharge efficiency is further improved.

2. Test 2

In the second test, the weight ratio of the Si-containing particles to the CNTs and the pore distribution ratio of the porous body were changed to evaluate the cycle characteristics of the secondary battery.

<Example 11>

An evaluation battery of Example 11 was prepared in the same manner as in Example 1 except that the pore distribution ratio (V ₁₀ /V ₁₀₀ ) of the porous body containing Si particles was 1.5.

<Example 12 to Example 15>

As Si-containing particles, Si-containing particles having a porous body with a pore distribution ratio ( _V10 / _V100 ) of the value shown in Table 2 were prepared. Furthermore, the weight ratio X of the carbon nanotubes to the Si-containing particles when the weight of the Si-containing particles was 100 wt% was changed as shown in Table 2. Except for this, evaluation batteries of Examples 12 to 15 were prepared in the same manner as in Example 1.

＜Calculation of pore distribution ratio＞

The pore distribution ratio is calculated using the BJH method using a specific surface area and a pore distribution measuring device (ASAP2020 manufactured by Micromeritics). First, the Si-containing particles are heated and dried under vacuum to form a measurement sample. Next, liquid nitrogen is used as a refrigerant, and nitrogen ( _N2 gas) is used as an adsorbed gas to obtain the adsorption isotherm of the measurement sample. The obtained adsorption isotherm is analyzed using the BJH method to obtain the logarithmic differential pore volume distribution. Then, the logarithmic differential pore volume _V100 of a pore with a diameter of 100nm and the logarithmic differential pore volume _V10 of a pore with a diameter of 10nm are obtained according to the logarithmic differential pore volume distribution, and the ratio of _V10 to _V100 ( _V10 / _V100 ) is obtained. The results are shown in Table 2.

＜Evaluation of Cycle Capacity Retention Rate＞

Under 25°C environment, CCCV charging (at a rate of 0.4C to 4.2V, then 0.1C cut-off) followed by CC discharge (at a rate of 0.4C to 2.5V cut-off) was performed as one cycle, and a cycle test was repeated for 250 cycles of charge and discharge. The discharge capacity (initial capacity) of the first cycle and the discharge capacity of the 250th cycle were measured, and the cycle capacity maintenance rate was calculated according to the following formula (2). It can be said that the higher the cycle capacity maintenance rate, the higher the cycle characteristics of the secondary battery. The results are shown in Table 2.

Cycle capacity retention rate (%) = ((discharge capacity at the 250th cycle)/(discharge capacity at the first cycle)) × 100 Formula (2)

[Table 2]

According to Table 2, in the evaluation batteries of Examples 11 to 13, the capacity retention rate is 79% or more. According to these results, it can be seen that by using graphite particles and Si-containing particles as a porous body containing Si nanoparticles in a network structure as negative electrode active materials, the weight ratio X of carbon nanotubes to the Si-containing particles is 0.02wt% to 4wt% when the weight of the Si-containing particles is set to 100wt%, and CNTs are arranged in at least some of the holes in the porous body, the cycle characteristics of the secondary battery can be improved.

Comparing Examples 11 and 12 with Example 13 in Table 2, it can be seen that the capacity retention rate is 86% or more when the pore distribution ratio ( _V10 / _V100 ) of the porous body is 1 or more. That is, when the pore distribution ratio ( _V10 / _V100 ) of the porous body is 1 or more, the cycle characteristics of the secondary battery can be further improved.

Some embodiments of the present invention have been described above, but the above embodiment is only an example. The present invention may also be implemented in various other ways. The present invention may be implemented based on the contents disclosed in this specification and the technical common sense in this field. The technology described in the scope of protection requested includes technologies obtained by various deformations and changes to the above-illustrated embodiments. For example, part of the above embodiment may be replaced with other deformation modes, and other deformation modes may be added to the above embodiment. In addition, as long as the technical feature is not described as a necessary technical feature, it may be appropriately deleted.

In summary, as specific aspects of the technology disclosed herein, the following items can be cited.

Item 1: A secondary battery comprising an electrode body having a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, wherein the negative electrode active material layer comprises graphite particles and Si-containing particles as negative electrode active materials, and carbon nanotubes as conductive materials, wherein the Si-containing particles are porous bodies containing Si nanoparticles in a network structure, wherein the carbon nanotubes are arranged in at least some of the pores of the porous body, and when the weight of the Si-containing particles is set to 100wt%, the weight ratio X of the carbon nanotubes to the Si-containing particles is 0.02wt% to 4wt%.

Item 2: The secondary battery according to Item 1, wherein the Si-containing particles are of plant origin.

Item 3: The secondary battery according to Item 1 or Item 2, wherein the Si-containing particles have pores with a diameter of 100 nm or more and pores with a diameter of 10 nm or less, and when the logarithmic differential pore volume of the pores with a diameter of 100 nm is set to _V100 and the logarithmic differential pore volume of the pores with a diameter of 10 nm is set to _V10 , the ratio of _V10 to _V100 ( _V10 / _V100 ) is 1 or more.

Item 4: The secondary battery according to any one of Items 1 to 3, wherein the average particle diameter of the Si nanoparticles is 50 nm or less.

Item 5: The secondary battery according to any one of Items 1 to 4, wherein the Si-containing particles are Si-C composite compounds containing the network-structured Si nanoparticles and porous carbon particles, and/or Si particles containing the network-structured Si nanoparticles and porous Si particles.

Item 6: The secondary battery according to any one of Items 1 to 5, wherein the Si-containing particles have an oxygen content of 10 wt % or less.

Item 7: The secondary battery according to any one of Items 1 to 6, wherein the content of the Si-containing particles is 10 wt % to 60 wt % when the total mass of the negative electrode active material is 100 wt %.

Item 8: A method for manufacturing a secondary battery, comprising:

a preparation step of preparing at least graphite particles and Si-containing particles as negative electrode active materials and carbon nanotubes as conductive materials,

a first mixing step of mixing the Si-containing particles and carbon nanotubes prepared above to prepare a first mixture, and

a second mixing step of mixing the first mixture, the graphite particles, a binder and a solvent to prepare a second mixture;

The Si-containing particles prepared in the above-mentioned preparation step are porous bodies containing Si nanoparticles in a network structure.

Item 9: The production method according to Item 8, wherein in the first mixing step, a weight ratio X of the carbon nanotubes to the Si-containing particles is 0.02 wt% to 4 wt% when the weight of the Si-containing particles is 100 wt%.

Item 10: The production method according to Item 8 or Item 9, wherein in the second mixing step, when the weight of the negative electrode active material is 100 wt %, the content of the graphite particles is 40 wt % to 90 wt %.

Claims (10)

1. A secondary battery includes an electrode body having a positive electrode and a negative electrode,

The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector,

The negative electrode active material layer contains graphite particles and Si-containing particles as a negative electrode active material, and carbon nanotubes as a conductive material,

The Si-containing particles are porous bodies containing network-structured Si nanoparticles,

The carbon nanotubes are disposed in at least some of the pores of the porous body,

The weight ratio X of the carbon nanotubes to the Si-containing particles is 0.02 to 4wt% based on 100wt% of the Si-containing particles.

2. The secondary battery according to claim 1, wherein the Si-containing particles are of vegetable origin.

3. The secondary battery according to claim 1 or 2, wherein the Si-containing particles have pores having a diameter of 100nm or more and pores having a diameter of 10nm or less,

When V ₁₀₀ is the logarithmic differential pore volume of a pore having a diameter of 100nm and V ₁₀ is the logarithmic differential pore volume of a pore having a diameter of 10nm, V ₁₀/V₁₀₀, which is the ratio of V ₁₀ to V ₁₀₀, is 1 or more.

4. The secondary battery according to claim 1 or 2, wherein the average particle diameter of the Si nanoparticle is 50nm or less.

5. The secondary battery according to claim 1 or 2, wherein the Si-containing particles are Si-C composite compounds containing the network-structured Si nanoparticles and porous carbon particles, and/or Si particles containing the network-structured Si nanoparticles and porous Si particles.

6. The secondary battery according to claim 1 or 2, wherein the Si-containing particles have an oxygen content of 10wt% or less.

7. The secondary battery according to claim 1 or 2, wherein the content of the Si-containing particles is 10wt% to 60wt%, with the total weight of the anode active material set to 100 wt%.

8. A method of manufacturing a secondary battery, comprising:

A preparation step of preparing at least graphite particles and Si-containing particles as negative electrode active materials, and carbon nanotubes as conductive materials,

A1 st mixing step of mixing the prepared Si-containing particles with carbon nanotubes, preparing a1 st mixture, and

A 2 nd mixing step of mixing the 1 st mixture, the graphite particles, a binder, and a solvent to prepare a 2 nd mixture;

The Si-containing particles prepared in the preparation step are porous bodies containing network-structured Si nanoparticles.

9. The method according to claim 8, wherein in the 1 st mixing step, the weight ratio X of the carbon nanotube to the Si-containing particles is 0.02 to 4wt% based on 100wt% of the Si-containing particles.

10. The production method according to claim 8 or 9, wherein in the 2 nd mixing step, the content of the graphite particles is 40wt% to 90wt% based on 100wt% of the negative electrode active material.