WO2020138313A1 - Composite particle for negative electrode of lithium ion secondary battery - Google Patents

Abstract

In this invention, through a method including mixing together porous silicon particles and a carbon precursor, and heat processing the obtained mixture to graphitize or carbonize the carbon precursor, composite particles containing a carbon material and Si-containing particles are obtained, wherein the porosity is 30 to 50% in a range from the complex particle center to 80% of the complex particle diameter, and the ratio, of the porosity in the range from the complex particle external surface to 10% of the complex particle diameter with respect to the porosity in the range from the complex particle center to 80% of the complex particle diameter, is 0.5 or lower.

Description

Composite particles for negative electrode of lithium-ion secondary battery

The present invention relates to composite particles for a negative electrode of a lithium ion secondary battery. More specifically, the present invention relates to composite particles for a negative electrode that can obtain a lithium ion secondary battery having excellent cycle characteristics.

Various negative electrode materials for lithium-ion secondary batteries have been proposed. For example, Patent Document 1 includes Si-polymer carbonized matrix particles formed from a Si-polymer matrix slurry containing a Si slurry, a polymer monomer, and a cross-linking agent, and a first carbon matrix. Disclosed is a carbon-silicon composite wherein molecular carbonized matrix particles are entrapped and dispersed within the first carbon matrix, the polymeric carbonized matrix particles having a higher porosity than the first carbon matrix. ..

Patent Document 2 includes an outer shell portion and a core portion, and the outer shell portion and the core portion are formed by binding an electrode active material and a conductive material with a dispersion type binder to form the outer shell portion. Disclosed is a composite particle in which the weight average particle diameter of the electrode active material and the conductive material is smaller than the weight average particle diameter of the electrode active material and the conductive material forming the core.

Patent Document 3 discloses a porous silicon particle in which a plurality of silicon fine particles are bonded, and the average particle diameter of the porous silicon particle is 0.1 μm to 1000 μm, and the porous silicon particle has continuous voids. Having a three-dimensional network structure, the average porosity of the porous silicon particles is 15 to 93%, the porosity Xs of the surface vicinity region of 50% or more in the radial direction and the particle interior of 50% or less in the radial direction. Disclosed is a porous silicon particle characterized in that a ratio of porosity Xi of a region, Xs/Xi, is 0.5 to 1.5, and contains 80 atomic% or more of silicon in a ratio of elements other than oxygen. ing.

Patent Document 4 is a porous silicon particle in which a plurality of silicon particles are joined and have continuous voids, and the particle size of the silicon particles, the pillar diameter or the mean x of the pillar sides is 2 nm to 2 μm, The particle size of silicon fine particles, the standard diameter σ of the pillar diameter or the pillar side is 1 to 500 nm, and the ratio (σ/x) between the average x and the standard deviation σ is 0.01 to 0.5. The porous silicon particles are divided into 90% or more of the surface vicinity area S in the radial direction and 90% or less of the particle interior area I in the radial direction, and the average particle size of the silicon fine particles forming the surface vicinity area S is Disclosed is porous silicon particles having Es/Ei of 0.01 to 1.0, where Es is Ei and the average particle diameter of the silicon fine particles forming the particle inner region I is Ei.

Patent Document 5 has a three-dimensional network structure in which silicon fine particles are bonded and has continuous voids, and the average particle diameter or average pillar diameter (μ) of the silicon fine particles is 2 nm to 2 μm. The value of σ/μ, which is a ratio of the standard deviation (σ) of the particle size or the column diameter of the column to the average particle diameter or the average column diameter (μ) of the silicon fine particles, is 0.03 to 1.50. A featured porous silicon particle is disclosed.

Patent Document 6 contains porous silicon particles as an essential component, and includes graphite, amorphous carbon, a polymer compound fired body (for example, pitch coke, needle coke, petroleum coke), carbon fiber, and a conductive polymer (for example, polyacetylene). , Polypyrrole) or tin as an optional component is disclosed.

JP, 2016-13967, A WO2006/118235A JP2012-82125A JP, 2013-193933, A JP, 2013-203626, A JP, 2016-51622, A

An object of the present invention is to provide composite particles for a negative electrode that can obtain a lithium ion secondary battery having excellent charge/discharge cycle characteristics.

The present invention includes the following aspects.
[1] A composite particle containing Si-containing particles and a carbon material,
The porosity in the range from the center of the composite particle to 80% of the diameter of the composite particle is 30 to 50%, and the porosity outside the range from the center of the composite particle to 80% of the diameter of the composite particle The ratio of the porosity in the range from the surface to 10% of the diameter of the composite particles is 0.5 or less,
Composite particles for a negative electrode of a lithium ion secondary battery.

[2] The composite particles according to [1], wherein the 50% diameter in the volume-based particle size distribution is 2 to 50 μm. [3] The Si-containing particles are porous silicon particles formed by aggregating or bonding a plurality of Si fine particles. The composite particle according to [1] or [2].
[4] The composite particle according to [3], wherein the carbon material covers a part or all of the outer surface of the porous silicon particle.
[5] The composite particle according to any one of [1] to [4], wherein the carbon material is a carbonaceous carbon material.

[6] A negative electrode material for a lithium ion secondary battery, containing the composite particle according to any one of [1] to [5].
[7] A negative electrode sheet for a lithium ion secondary battery, which has an electrode layer containing the negative electrode material according to [6].
[8] A lithium ion secondary battery having the negative electrode sheet according to [7].

[9] 100 parts by mass of Si-containing particles and 5 to 95 parts by mass of carbon precursor are mixed,
Heating the obtained mixture from 100° C. to 350° C. at 110 to 290° C./hour, reaching a predetermined temperature, and then maintaining at the predetermined temperature for 0.5 hours or more and 6 hours or less. , Including carbonizing the carbon precursor by heat treatment,
The predetermined temperature is 400° C. or higher and lower than 1800° C.,
A method for producing composite particles for a negative electrode of a lithium ion secondary battery.

[10] Mix Si-containing particles and a carbon precursor,
Heat treating the resulting mixture to graphitize or carbonize the carbon precursor,
The method for producing composite particles according to any one of [1] to [5].
[11] The production method according to [9] or [10], wherein the Si-containing particles are porous silicon particles formed by aggregating or bonding a plurality of Si fine particles.

The composite particles of the present invention have high strength against compression and can maintain their shape without being crushed even during the production of the electrode layer. In the composite particles of the present invention, the size of the composite particles themselves does not substantially change even if the volume of the Si fine particles changes due to the insertion and desorption of lithium ions. By using the negative electrode material of the present invention, a lithium ion secondary battery having excellent charge/discharge cycle characteristics can be obtained.

FIG. 3 is a view showing an SEM image of the composite particles obtained in Example 1. FIG. 3 is a diagram showing an SEM image after compressing the composite particles obtained in Example 1. FIG. 3 is a view showing an SEM image of Si-containing particles used in Example 1. FIG. 3 is a diagram showing an SEM image after compressing the Si-containing particles used in Example 1. It is a figure which shows the concept of the range (outer shell) from the outer surface of a composite particle to 10% of the diameter of a composite particle, and the range (core) from the center of a composite particle to 80% of the diameter of a composite particle.

The composite particle of the present invention is for a negative electrode of a lithium ion secondary battery. The composite particles of the present invention include Si-containing particles and a carbon material.

The Si-containing particles used in the present invention are preferably porous silicon particles formed by aggregating or bonding a plurality of Si fine particles (see FIG. 3). When the Si-containing particles are compressed at 25 MPa, as shown in FIG. 4, some of the Si fine particles are agglomerated or joined.

The surface layer of the Si fine particles preferably contains SiO _x (0<x≦2). The portion (core) other than the surface layer may be made of elemental silicon or SiO _x (0<x≦2). The average thickness of the surface layer containing SiO _x is preferably 0.5 nm or more and 10 nm or less. When the average thickness of the surface layer containing SiO _x is 0.5 nm or more, oxidation by air or oxidizing gas can be suppressed. If the average thickness of the surface layer containing SiO _x is 10 nm or less, the increase in irreversible capacity can be suppressed. This average thickness can be measured by a TEM photograph.

The 90% diameter D _{90 of the} Si fine particles in the number-based cumulative distribution of the primary particle diameter is preferably 1000 nm or less, more preferably 600 nm or less, still more preferably 400 nm or less. The primary particle size can be measured by observation with a microscope such as SEM or TEM. Further, the primary particle diameter of Si fine particles in the composite material can be calculated by performing image analysis of an image of spherical particles observed with a transmission electron microscope at a magnification of 100,000.

The oxygen content of the Si-containing particles is preferably 1% by mass or more and 18% by mass or less, more preferably 2% by mass or more and 10% by mass or less. Within this range, an increase in irreversible capacity can be suppressed. The oxygen content can be quantified by, for example, an oxygen-nitrogen simultaneous analyzer (inert gas melting-infrared absorption method).

The Si-containing particles can include an element M selected from other metal elements and metalloid elements in addition to Si. Specifically, as the element M, for example, Ag, Al, As, Au, B, Ba, Ca, Ce, Co, Cr, Cu, Er, Fe, Ga, Gd, Ge, Hf, In, Ir, Lu, Group consisting of Mg, Mn, Mo, Nb, Nd, Ni, Pd, Pr, Pt, Re, Rh, Ru, Sc, Sm, Sn, Ta, Te, Ti, V, W, Y, Yb, Zn, Zr. At least one selected from The content of the element M is not particularly limited as long as it does not significantly hinder the action of silicon, and is, for example, preferably 2 to 90 atom %, more preferably 50 to 85 atom% in the Si-containing particles. The element M may contribute to the aggregation or bonding of the Si particles.

The porous silicon particles as Si-containing particles are not particularly limited by the manufacturing method. For example, it can be manufactured by referring to the methods disclosed in Patent Document 3, Patent Document 4, Patent Document 5, and the like. A commercially available product may be used as the Si-containing particles. For example, ANSY360 and ANSY160 manufactured by AUO Crystal Corp. can be cited.

Regarding the amount of Si-containing particles contained in the composite particles of the present invention, the lower limit is preferably 55% by mass, more preferably 60% by mass, further preferably 65% by mass, and the upper limit is preferable, with respect to the composite particles. Is 95% by mass, more preferably 90% by mass, and even more preferably 85% by mass.

The carbon material used in the present invention is a graphitic carbon material or a carbonaceous carbon material, preferably a carbonaceous carbon material.

The graphitic carbon material is a carbon material in which crystals formed by carbon atoms are greatly developed. The graphitic carbon material is a carbon material that is more slippery, softer, and has a lower scratch strength than the carbonaceous carbon material. The graphitic carbon material can be produced, for example, by graphitizing a carbon precursor. The graphite carbon material moves flexibly with the pressing at the time of manufacturing the electrode, which may contribute to the improvement of the electrode density. Examples of the graphite carbon material include artificial graphite, pyrolytic graphite, expanded graphite, natural graphite, scaly graphite, and scaly graphite.

≪Carbonaceous carbon material is a carbon material with low growth of crystals formed by carbon atoms. The carbonaceous carbon material can be produced, for example, by carbonizing a carbon precursor.

The carbon precursor is not particularly limited, thermal heavy oil, pyrolysis oil, straight asphalt, blown asphalt, petroleum-derived substances such as tar or petroleum pitch by-produced during ethylene production, or coal tar produced during coal carbonization, Heavy components obtained by distilling off low-boiling components of coal tar, coal-derived substances such as coal tar pitch (coal pitch) are preferable, petroleum pitch or coal pitch is more preferable, and coal tar pitch is further preferable. Pitch is a mixture of polycyclic aromatic compounds. When pitch is used, a carbonaceous carbon material having a high carbonization rate and low impurities can be produced. Since the pitch has a low oxygen content, the Si-containing particles are less likely to be oxidized in carbonization or graphitization after being mixed with Si-containing particles.

The softening point of pitch as a carbon precursor is preferably 80°C or higher and 300°C or lower. The softening point of the pitch can be measured by the Mettler method described in ASTM-D3104-77.

The pitch as the carbon precursor has a residual carbon rate of preferably 20% by mass or more and 85% by mass or less, more preferably 25% by mass or more and 80% by mass or less.
The residual coal rate is determined by the following method. The solid pitch is ground in a mortar or the like, and the ground product is subjected to mass thermal analysis under a nitrogen gas flow. The ratio of the mass at 1100° C. to the charged mass is defined as the residual coal rate. The residual coal rate corresponds to the fixed carbon amount measured at a carbonization temperature of 1100° C. according to JIS K2425.

The QI (quinoline insoluble matter) content of the pitch used in the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 2% by mass or less. The QI content of the pitch is a value corresponding to the amount of free carbon. When the QI content is within the above range, the electrode characteristics will be further improved.

Further, the pitch used in the present invention has a TI (toluene insoluble content) content of preferably 10% by mass or more and 70% by mass or less. When the TI content is within the above range, it is possible to uniformly mix the pitch and the other components, and it is possible to obtain composite particles exhibiting properties suitable as a negative electrode active material for a lithium ion secondary battery.

The QI content and TI content of the pitch used in the present invention can be measured by the method described in JIS K2425 or a method equivalent thereto.

Regarding the amount of the carbon material contained in the composite particles of the present invention, the lower limit is preferably 5 parts by mass, more preferably 10 parts by mass, further preferably 15 parts by mass, and the upper limit is 100 parts by mass of the composite particles. , Preferably 45 parts by mass, more preferably 40 parts by mass, further preferably 35 parts by mass.

The composite particle of the present invention has a porosity of 30 to 50%, preferably 33 to 49% in the range (Core) from the center of the composite particle to 80% of the diameter of the composite particle.
The composite particle of the present invention has a porosity in the range from the center of the composite particle to 80% of the diameter of the composite particle (Core) to the outer surface of the composite particle to 10% of the diameter of the composite particle (Outer Shell). The porosity ratio is 0.5 or less, more preferably 0.45 or less.
The porosity in the present invention is a value determined by the method described in the section of Examples.

The 50% diameter in the volume-based particle size distribution of the composite particles of the present invention is preferably 2 to 50 μm, more preferably 2 to 30 μm. The 50% diameter in the volume-based particle size distribution can be measured by a laser diffraction method.
In the composite particles of the present invention, it is preferable that the carbon material covers part or all of the outer surface of the porous silicon particles that are Si-containing particles. Further, the carbon material may cover a part or the whole of the surface in the voids of the surface layer portion of the porous silicon particle (for example, the range from the outer surface of the composite particle to 10% of the diameter of the composite particle). ..

In the method for producing composite particles of the present invention having the porosity as described above, the Si-containing particles are mixed with the carbon precursor, and the resulting mixture is heat treated to graphitize or carbonize the carbon precursor. including.

Further, the method for producing composite particles for a negative electrode of a lithium ion secondary battery of the present invention is 100 parts by mass of Si-containing particles and preferably 5 to 95 parts by mass, more preferably 20 to 70 parts by mass of carbon precursor. And heat treating the resulting mixture to carbonize the carbon precursor.

In the heat treatment, the temperature is raised from room temperature to a predetermined temperature and then kept at the predetermined temperature for a predetermined time. The heating rate from 100° C. to 350° C. is preferably 110 to 290° C./hour, more preferably 130 to 270° C./hour, and further preferably 140 to 250° C./hour.
The heat treatment is preferably performed in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an atmosphere of non-oxidizing gas such as nitrogen gas and argon gas.

The predetermined temperature during the heat treatment for carbonizing the carbon precursor is preferably 400°C or higher and lower than 1800°C, more preferably 600°C or higher and 1500°C or lower. Then, in carbonization, it is preferable to hold at a predetermined temperature for 0.5 hours or more and 6 hours or less. Further, it is preferable that the heat treatment is performed at a constant temperature for a predetermined time within the above temperature range. In carbonization, if the holding time at a predetermined temperature is too short, carbonization tends to be insufficient, and if the holding time at a predetermined temperature is too long, it is not economical.

The temperature during the heat treatment when graphitizing the carbon precursor is preferably 1800° C. or higher and 3500° C. or lower, and more preferably 2000° C. or higher and 3200° C. or lower. Within this range, graphitization is easy. Further, it is preferable that the heat treatment is performed at a constant temperature for a predetermined time within the above temperature range.

After graphitizing or carbonizing, it is preferable to remove coarse particles by sieving.

As shown in FIG. 1, the composite particles of the present invention apparently have the same appearance as the Si-containing particles (see FIG. 3), but as shown in FIG. 2, even if compression treatment is performed at 25 MPa. , Si fine particles cannot be aggregated or joined. It is presumed that the lithium-ion secondary battery using the negative electrode material of the present invention is excellent in charge/discharge cycle characteristics because collapse of the electrode layer is prevented.

The negative electrode material of the present invention is for a lithium ion secondary battery. The negative electrode material of the present invention contains the composite particles. The negative electrode material of the present invention may contain graphitic carbon material particles and the like in addition to the composite particles. The graphitic carbon material particles can be contained in order to make the ratio of the capacity (Q _A ) of the negative electrode sheet to the capacity (Q _C ) of the positive electrode sheet a predetermined value.

The graphitic carbon material particles are particles made of a graphitic carbon material, and are preferably artificial graphite particles. The graphitic carbon material is a carbon material in which crystals formed by carbon atoms are greatly developed. The graphitic carbon material is a carbon material that is more slippery, softer, and has a lower scratch strength than the carbonaceous carbon material. The graphite carbon material particles move flexibly with the pressing at the time of manufacturing the electrode, which contributes to the improvement of the electrode density.

The graphitic carbon material particles are preferably composed of scaly particles. The graphitic carbon material particles have a 50% diameter (also referred to as “D ₅₀ ”) in a volume-based cumulative particle size distribution of preferably 1 μm or more and 50 μm or less, more preferably 5 μm or more and 35 μm or less, and further preferably 10 μm or more and 25 μm or less. Is. When D ₅₀ is 1 μm or more, side reactions are less likely to occur during charge and discharge, and when D ₅₀ is 50 μm or less, diffusion of lithium ions in the negative electrode material tends to be faster, and the charge and discharge rate tends to be improved. When used for a driving power source of an automobile or the like that requires generation of a large current, D ₅₀ is preferably 25 μm or less. D ₅₀ is a laser diffraction particle size distribution meter, for example, be measured using a MICROTRAC Co. particle size analyzer MT3300EXII like.

In the graphitic carbon material particles, the average interplanar spacing d ₀₀₂ of the 002 planes calculated from the analysis of the X-ray diffraction pattern by CuKα ray is preferably 0.337 nm or less. As d ₀₀₂ is smaller, the amount of lithium ions inserted and desorbed per mass increases, which contributes to the improvement of the weight energy density. When d ₀₀₂ is 0.337 nm or less, most of the optical structure observed by the polarization microscope has optical anisotropy.

In the graphitic carbon material particles, the thickness (Lc) in the crystal C-axis direction of the graphitic carbon material calculated from the analysis of the X-ray diffraction pattern by CuKα ray is preferably 50 nm or more and 1000 nm or less. A large Lc is advantageous in increasing the energy density per volume of the battery. From the viewpoint of increasing the energy density per volume, Lc is preferably 80 nm or more and 300 nm or less, more preferably 100 nm or more and 200 nm or less, still more preferably 100 or more and 150 nm or less. When Lc is small, it is advantageous in maintaining the cycle characteristics of the battery. From the viewpoint of maintaining the cycle characteristics of the battery, Lc is preferably 50 nm or more and 200 nm or less, more preferably 50 nm or more and 100 nm or less, still more preferably 50 nm or more and 90 nm or less.

Note that d ₀₀₂ and Lc can be measured using a powder X-ray diffraction (XRD) method (Inayoshi Noda, Michio Inagaki, Japan Society for the Promotion of Science, 117th Committee sample, 117-71-A-1 ( 1963), Michio Inagaki et al., Japan Society for the Promotion of Science, 117th Committee sample, 117-121-C-5 (1972), Michio Inagaki, "Carbon", 1963, No. 36, pp. 25-34).

The G value of the graphitic carbon material particles is preferably 5.2 or more and 100 or less, more preferably 7.0 or more and 80 or less, and further preferably 10 or more and 60 or less. The G value is in the range of 1580 to 1620 cm ^-1 and the peak area (I _D ) in the range of 1300 to 1400 cm ^-1 in the Raman spectroscopic spectrum observed when the particle end face is measured by the Raman spectroscopic analyzer. It is the ratio I _G /I _D to the area of the peak (I _G ). When the G value is within the above numerical range, self-discharge and deterioration of the battery are suppressed. If the G value is too small, side reactions tend to occur during charge and discharge due to the presence of many defects.

The Raman spectroscopic spectrum of the particle end surface is, for example, a laser Raman spectrophotometer (NRS-5100, manufactured by JASCO Corporation) and an attached microscope, not the smooth portion (basal surface), but the end surface. It is measured by selectively observing the existing part. In the Raman spectroscopic spectrum of the particle end face, the peak in the range of 1300 to 1400 cm ⁻¹ is the peak derived from sp3 bond, and the peak in the range of 1580 to 1620 cm ⁻¹ is the peak derived from sp2 bond. It is suggested that the larger the G value, the higher the proportion of sp2 binding.

The BET specific surface area of the graphitic carbon material particles is preferably 0.4 m ² /g or more and 5 m ² /g or less, more preferably 0.5 m ² /g or more and 3.5 m ² /g or less, still more preferably 0. It is 5 m ² /g or more and 3.0 m ² /g or less. When the BET specific surface area is within this range, it is possible to secure a large area in contact with the electrolytic solution without using the binder excessively, and to smoothly insert and desorb lithium ions to reduce the reaction resistance of the battery. You can The BET specific surface area is calculated from the nitrogen gas adsorption amount. Examples of the measuring device include NOVA-1200 manufactured by Yuasa Ionics Inc.

The graphite carbon material particles have a loosened bulk density (0 times tapping) of preferably 0.7 g/cm ³ or more, and a powder density (tapping density) of 400 times tapping, preferably 0. 8 g/cm ³ or more and 1.6 g/cm ³ or less, more preferably 0.9 g/cm ³ or more and 1.6 g/cm ³ or less, and still more preferably 1.1 g/cm ³ or more and 1.6 g/cm ³ or less. ..
The loosened bulk density is a density obtained by dropping 100 g of a sample from a height of 20 cm into a graduated cylinder and measuring the volume and mass without applying vibration. The tap density is a density obtained by measuring the volume and mass of 100 g of powder tapped 400 times using a Kantachrome auto tap. These are the measurement methods based on ASTM B527 and JIS K5101-12-2. The drop height of the auto tap in the tap density measurement was set to 5 mm.
When the loosened bulk density is 0.7 g/cm ³ or more, the electrode density before pressing tends to increase when applied to the electrode. From this value, it is possible to predict whether it is possible to obtain a sufficient electrode density with one roll press. Further, when the tap density is within the above range, it is easy to make the electrode density reached during pressing to a desired height.

The graphitic carbon material particles are not particularly limited by the manufacturing method thereof. For example, it can be manufactured by the method disclosed in WO 2014/003135A.

For the graphitic carbon material particles, coal-based coke and/or petroleum-based coke can be used as a raw material. The graphitic carbon material particles are produced by heat treating coal-based coke and/or petroleum-based coke at a temperature of preferably 2000° C. or higher, more preferably 2500° C. or higher. The upper limit of the heat treatment temperature is not particularly limited, but 3200° C. is preferable. This heat treatment is preferably performed in an inert atmosphere. The heat treatment can be performed using an Acheson type graphitization furnace or the like.

The amount of the graphitic carbon material particles that can be contained in the negative electrode material is preferably 10 to 95% by mass, more preferably 20 to 90% by mass, based on the mass of the negative electrode material.

The negative electrode material of the present invention may further contain a conductive auxiliary agent.
The conductive auxiliary agent can play a role of imparting conductivity to the electrode layer or a buffering effect against a volume change due to insertion/desorption of lithium ions. Examples of the conductive auxiliary agent include carbon materials such as carbon black, graphite, carbon nanotube (CNT), carbon nanofiber, and vapor grown carbon fiber (VGCF (registered trademark)). Examples of carbon black include Ketjen black, acetylene black, channel black, lamp black, oil furnace black, thermal black and the like. The conductive additive may be used alone or in combination of two or more.

The amount of the conductive additive that can be contained in the negative electrode material of the present invention is preferably 0.5 to 50% by mass, more preferably 0.5 to 30% by mass, and still more preferably 0. It is 5 to 25% by mass. The conductive additive used when preparing the negative electrode material containing the composite particles and the conductive additive described above is preferably in the form of powder, paste or the like.

The negative electrode material of the present invention may further contain a binder. The material used as the binder is not particularly limited, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, epichlorohydrin, Examples thereof include polyphosphazene, polyacrylonitrile, polyvinyl acetate, polymethacrylate, polyacrylate, polyvinyl alcohol, carboxymethyl cellulose and the like.

The amount of the binder that can be contained in the negative electrode material is preferably 0.5 to 50% by mass, more preferably 0.5 to 30% by mass, still more preferably 0.5 to 20% by mass, still more preferably 0.5. It is up to 10% by mass. The binder used in the preparation of the positive electrode material containing the above-mentioned Prussian blue analog powder and the binder is preferably in the form of powder, solution, emulsion or dispersion.

The negative electrode material of the present invention may be a paste that further contains a liquid medium. The pasty negative electrode material is used for manufacturing a lithium ion secondary battery. The liquid medium may be derived from a conductive auxiliary agent in a paste state; a binder in a solution state, an emulsion state, or a dispersion state. The liquid medium is not particularly limited as long as it can uniformly dissolve or disperse the constituent components of the negative electrode material. As the liquid medium, for example, water, isopropanol, N-methyl-2-pyrrolidone, dimethylformamide or the like can be used. The amount of the liquid medium may be appropriately adjusted so that the paste has a viscosity such that it can be easily applied to the current collector. The pasty negative electrode material may contain a thickener, a leveling agent, etc., if necessary. Examples of the thickener include polycarboxylic acid, polycarboxylic acid salt, carboxymethyl cellulose, carboxymethyl cellulose alkali metal salt and the like.

The negative electrode material of the present invention can be obtained by, for example, supplying the above-mentioned composite particle powder and, if necessary, a binder, a conductive additive, and/or other components to the kneading device simultaneously or in any order and kneading. In the kneading, for example, a kneading device such as a rotation/revolution mixer or a planetary mixer can be used. In the case of using a conductive auxiliary agent, the powder of the composite particles and the conductive auxiliary agent are mixed to obtain a mixed powder, and the mixed powder and, if necessary, a binder and/or other components are simultaneously or in random order placed in a kneading device. It can be supplied and kneaded.

The negative electrode sheet of the present invention is for a lithium ion secondary battery. The negative electrode sheet of the present invention has a current collector and an electrode layer that covers the current collector. The electrode layer contains the negative electrode material of the present invention. The negative electrode material of the present invention contained in the electrode layer is usually in the state of a green compact.

The current collector in the negative electrode sheet is a conductor and is not particularly limited as long as it can hold the electrode layer, but a metal foil or a metal mesh is preferable, and an aluminum foil, a nickel foil, a copper foil, a nickel mesh or a copper mesh is used. More preferable. The current collector may be a metal foil or a metal mesh on which a functional layer such as a conductive layer is laminated or combined.

The electrode layer can be obtained, for example, by applying a paste-like negative electrode material on a current collector and drying it. When applying and drying the paste negative electrode material on the current collector, a coating device such as a doctor blade and a drying device can be used.
The electrode layer can also be obtained, for example, by pressure-molding a granular or powdery negative electrode material together with a current collector.

The thickness of the electrode layer in the negative electrode sheet is preferably 30 to 200 μm. When the thickness of the electrode layer is 200 μm or less, the negative electrode sheet can be housed in a standardized battery container. The thickness of the electrode layer can be adjusted by the coating amount of the paste-like negative electrode material and the like. It can also be adjusted by rolling the paste-form negative electrode material after drying. In the pressure forming or rolling, a press machine such as a pressure roll type or a pressure plate type can be used. The pressure applied in the pressure plate type is preferably 100 to 500 MPa.

The lithium-ion secondary battery of the present invention includes the above-mentioned negative electrode sheet, electrolyte, and positive electrode sheet. The positive electrode sheet and the negative electrode sheet may be arranged to face each other with the separator interposed therebetween.

The positive electrode sheet has a current collector and an electrode layer that covers the current collector. The electrode layer in the positive electrode sheet contains a positive electrode active material capable of inserting and extracting lithium, a binder, and, if necessary, a conductive auxiliary agent. Examples of the current collector in the positive electrode sheet include copper foil and aluminum foil. Examples of the positive electrode active material include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiNi _0.34 Mn _0.33 Co _0.33 O ₂ , and LiFePO ₄ .

The electrolyte is not particularly limited as long as it contains a lithium salt. The electrolyte may be in the form of a solution, a melt or a solid. As the electrolyte as a solution, a solution containing a potassium salt and a non-aqueous solvent is preferably used. 

The non-aqueous electrolyte solution and the non-aqueous polymer electrolyte used in the lithium ion secondary battery are not particularly limited. For example, lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li are converted into ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, propylene. Organic electrolytes dissolved in non-aqueous solvents such as carbonate, butylene carbonate, acetonitrile, propyronitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone; polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethylmethacrylate, etc. Examples thereof include gel polymer electrolytes contained therein; and solid polymer electrolytes containing a polymer having an ethylene oxide bond.

Also, a small amount of a substance that causes a decomposition reaction when the lithium-ion secondary battery is first charged may be added to the electrolytic solution. Examples of the substance include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sultone (ES) and the like. The addition amount is preferably 0.01% by mass or more and 50% by mass or less.

The separator physically separates the positive electrode sheet and the negative electrode sheet to prevent an internal short circuit. Examples of the separator include those using a porous material, a non-woven fabric, or the like. The separator may be formed of only a porous membrane layer or a non-woven fabric layer, or may be formed of a laminate of a plurality of layers having different compositions and forms. Examples of the laminate include a laminate having a plurality of resin porous layers having different compositions, a laminate having a porous membrane layer and a nonwoven fabric layer, and the like.

Examples of the material of the porous film or the nonwoven fabric constituting the separator include polyolefin resins such as polyethylene, polypropylene and ethylene-propylene copolymer; polyphenylene sulfide resins such as polyphenylene sulfide and polyphenylene sulfide ketone; aromatic polyamide resins ( Polyamide resin such as aramid resin); polyimide resin and the like. These resins may be used alone or in combination of two or more. Inorganic fibers such as glass fibers can also be used as the material of the non-woven fabric.

The separator may include an inorganic filler. Examples of the inorganic filler include ceramics (silica, alumina, zeolite, titania, etc.), talc, mica, wollastonite, and the like. The inorganic filler is preferably particulate or fibrous. The amount of the inorganic filler contained in the separator is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, based on the mass of the separator.

The lithium-ion secondary battery of the present invention is a power source for electronic devices such as mobile phones, portable personal computers, and personal digital assistants; power sources for electric motors such as electric drills, vacuum cleaners, and electric vehicles; fuel cells, solar power generation, wind power generation. It can be used for storage of electric power obtained by the above.

The examples of the present invention will be shown below to explain the present invention more specifically. Note that these are merely examples for description, and the present invention is not limited to these.

<Measurement of porosity>
97 parts by mass of epoxy resin (Resin G-2 manufactured by GATAN Co., Ltd.) and 3 parts by mass of palladium acetate (manufactured by Tokyo Kasei Kogyo Co., Ltd.) were dissolved in 1000 parts of toluene (manufactured by Fuji Film Wako Pure Chemical Industries), and toluene was distilled off under reduced pressure. , Pd-labeled epoxy resin was obtained.
100 parts by mass of the Pd label epoxy resin and 10 parts by mass of a curing agent (Hardener G-2 manufactured by GATAN Co.) were kneaded on a slide glass to which an adhesive tape made of fluororesin was attached. About 2 times the volume of the composite particles was added to the kneaded product, and the mixture was further kneaded.
Then, it was placed on a hot plate at 110° C. for 20 seconds. Immediately, it was put in a desiccator and depressurized. As a result, the molten resin penetrated into the voids of the composite particles.
It was placed on a hot plate at 120° C. for 2 hours and cured to obtain a test piece.

The test piece was subjected to cross section processing at 5 kV for 8 hours using a cross section polisher SM09010 manufactured by JEOL.

)
The SEM (JEOL field emission scanning electron microscope JSM-7000F) equipped with a large-area SDD detector (Oxford Instruments) was used to observe the cross-section processed test piece, and the EDS provided by Oxford Instruments was used. Analysis was performed by the analysis software AZtecEnergy.
In the point analysis mode, the palladium concentration was measured at 30 randomly selected points in the range (Outer Shell) from the outer surface of the composite particle to 10% of the diameter of the composite particle. The porosity P _sn was calculated for each concentration C _sn (n=1 to 30) by the following formula. The average value of P _sn was defined as the porosity P _{s in} the range from the outer surface of the composite particle to 10% of the diameter of the composite particle.
P _sn =(C _sn ×100/3) ^1.5
In the point analysis mode, the palladium concentration was measured by randomly selecting 30 points in the range (Core) from the center of the composite particle to 80% of the diameter of the composite particle. The porosity P _cn for each concentration C _cn (n=1 to 30) was calculated by the following formula. The average value of P _cn was defined as the porosity P _{c in} the range from the center of the composite particle to 80% of the diameter of the composite particle.
P _cn =(C _cn ×100/3) ^1.5

<Compression test>
Approximately 0.6 g of composite particles is put into the hole of the powder load cell (self-made, width 50 mm, height 60 mm, depth 50 mm, polyacetal resin block with 10 mm width, 50 mm height and 5 mm depth) Then, insert a push rod (self-made, width 10 mm, height 50 mm, depth 5 mm polyamide resin piece) from above and load 1.25 kN (pressure 25 MPa) with A&D Tensilon Universal Material Testing Machine RTG-1310. Was added. By observing the composite particles before and after compression with an SEM (JSM-7000F, a field emission scanning electron microscope manufactured by JEOL Ltd.), it was evaluated whether the aggregation or bonding of Si particles in the composite particles was maintained.

<Measurement of particle size distribution>
1 mg of the composite particles was added to 1 mL of a dispersion medium (1 wt% polyoxyethylene (10) octylphenyl ether aqueous solution), and the dispersion liquid was manually stirred, and the particle size distribution was measured using water as a solvent with a particle size analyzer MT3300EXII manufactured by MICROTRAC. ..

Example 1
(Composite particles)
To the container, 100 g of Si-containing particles (ANSY360 manufactured by AUO Crystal Corp., porous silicon particles obtained by bonding Si fine particles, see FIG. 3, porosity 50%) and 50 g of coal tar pitch (carbonization rate 78%) were added. The mixture was stirred at 100 rpm for 6 hours using a mix rotor (VMR-5R manufactured by AsOne). The obtained mixture was placed in an alumina crucible and heat-treated at 1100° C. under an argon atmosphere in a Motoyama atmosphere tubular furnace PCR (heating rate from room temperature to 1100° C. 150° C./h, 1100° C. for 1 hour, 1100° C. A temperature-decreasing rate to room temperature of 150° C./h), and then composite particles A having a sieve opening of 45 μm were obtained. The composite particles A had P _c of 35%, P _s of 13%, P _s /P _c of 0.37, and D ₅₀ of 10.1 μm.

(Positive electrode sheet)
LiNi _0.6 Mn _0.2 Co _0.2 O ₂ 192 g, carbon black 4 g and polyvinylidene fluoride (PVdF) 4 g were stirred and mixed while adding N-methylpyrrolidone to obtain a paste-like positive electrode material. The paste-like positive electrode material was applied to an aluminum foil having a thickness of 20 μm using a roll coater, dried, and then compressed to a density of 3.6 g/cm ³ using a roll press to obtain a positive electrode sheet.

(Negative electrode sheet)
Carboxymethyl cellulose (CMC; manufactured by Daicel, CMC1300) was dissolved in water to obtain a CMC aqueous solution having a concentration of 2%.
3 parts by mass of carbon black, 1 part by mass of carbon nanotube (CNT), and 1 part by mass of vapor grown carbon fiber (VGCF (registered trademark)-H, manufactured by Showa Denko KK) were mixed to obtain a conductive additive. ..
An active material was obtained by mixing the composite particles and the artificial graphite particles in a ratio such that the ratio of the capacity (Q _A ) of the negative electrode sheet to the capacity (Q _C ) of the positive electrode sheet was 1.2.
90 parts by mass of the active material, 2 parts by mass of the conduction aid and 400 parts by mass of the CMC aqueous solution were mixed and then kneaded by a rotation/revolution mixer to obtain a paste-like negative electrode material.
The paste-like negative electrode material was applied onto a copper foil having a thickness of 20 μm using a doctor blade having a gap of 300 μm, dried on a hot plate, and further vacuum dried. This was passed through a roll press having a roll width of 38 mm at a speed of 2.0 m/min and compressed so that the electrode density was 1.6±0.1 g/cm ³ . The linear pressure between the rolls was adjusted between 150 and 250 MPa so that the target electrode density was obtained.

(Bipolar laminated full cell)
The following operation was carried out in a glove box kept in a dry argon gas atmosphere with a dew point of −80° C. or lower.
The negative electrode sheet and the positive electrode sheet were punched out to obtain a negative electrode piece and a positive electrode piece having an area of 20 cm ² . An Al tab was attached to the Al foil of the positive electrode piece, and a Ni tab was attached to the Cu foil of the negative electrode piece. A polypropylene film microporous film was sandwiched between a negative electrode piece and a positive electrode piece, and in that state, it was packed with an aluminum laminate packaging material. Then, 700 μL of the electrolytic solution was injected thereinto. Then, the opening was sealed by heat fusion to obtain a bipolar laminated full cell. The electrolytic solution was prepared by adding 1% by mass of vinylene carbonate (VC) and 10% by mass of fluoroethylene carbonate (FEC) to a mixed solution of 3 parts by volume of ethylene carbonate, 5 parts by volume of ethylmethyl carbonate and 2 parts by volume of diethyl carbonate, Further, this is a liquid obtained by dissolving electrolyte LiPF _{6 in} this to a concentration of 1 mol/L.

[Bipolar laminated full cell/charge/discharge cycle test]
(aging)
The bipolar laminated full cell was subjected to constant current charging from rest potential at 0.025 C for 6 hours and 45 minutes. I rested for 12 hours.
Constant current charging was performed at 0.05 C up to 4.2V. A constant current discharge was performed at 0.05 C to 2.7 V.
Constant current charging was performed at 0.1 C until the voltage became 4.3 V. After reaching 4.3 V, constant voltage charging was performed until the voltage reached 0.025 C. A constant current discharge was performed at 0.1 C until 2.7 V was reached.
Constant current charging was performed at 0.2 C until the voltage became 4.3 V. After reaching 4.3 V, constant voltage charging was performed until the voltage reached 0.025 C. Constant current discharge was performed at 0.2 C until the voltage reached 2.7 V. This charging/discharging operation was performed once more.
Constant current charging was performed at 0.1 C until the voltage became 4.3 V. After reaching 4.3 V, constant voltage charging was performed until the voltage reached 0.025 C. A constant current discharge was performed at 0.1 C until 2.7 V was reached.

(200 cycles charge/discharge)
Next, constant current charging was performed at 1C until the voltage became 4.3V. After reaching 4.3 V, constant voltage charging was performed until the voltage reached 0.05 C. Constant current discharge was performed until the voltage became 3.0 V at 1 C (first cycle). This charging/discharging operation was further performed 19 times (second cycle to 20th cycle).
Subsequently, constant current charging was performed at 0.1 C until the voltage became 4.3 V. After reaching 4.3 V, constant voltage charging was performed until the voltage reached 0.05 C. Constant-current discharge was performed at 0.1 C until the voltage reached 3.0 V (21st cycle).
Ten sets of charging/discharging operations in the first to 21st cycles were performed as one set.
The full-cell 200-cycle discharge capacity retention rate defined by the following formula was 64.3%.
Full-cell 200-cycle discharge capacity maintenance rate Crr200 (%) =
{200th cycle discharge capacity/first cycle discharge capacity}×100

(Tripolar laminated half cell)
The following operation was carried out in a glove box kept in a dry argon gas atmosphere with a dew point of −80° C. or lower.
The negative electrode sheet was punched out to obtain a negative electrode piece with a Cu foil tab having an area of 4 cm ² . A Ni tab having a width of 5 mm was attached to the Cu foil tab of the negative electrode piece.
A counter electrode Li piece having an area of 7.5 cm ² (3.0 cm×2.5 cm) and a reference electrode Li piece having an area of 3.75 cm ² (1.5 cm×2.5 cm) were prepared.
A Ni tab having a width of 5 mm was attached at a length of its tip of 5 mm in accordance with a 5 mm width of a 5 mm×20 mm Ni mesh. The Ni mesh to which the Ni tab was attached was attached to a corner of the counter electrode Li piece so as to intersect with a 3.0 cm side of the counter electrode Li piece at a right angle.
The Ni mesh to which the Ni tab was attached was attached to the center of the 1.5 cm side of the Li piece for reference electrode so as to intersect with the 1.5 cm side of the Li piece for reference electrode at a right angle.
A polypropylene microporous membrane was sandwiched between the reference electrode and the working electrode and between the working electrode and the counter electrode, respectively. In that state, it was packed in an aluminum laminate packaging material. Then, an electrolytic solution was injected into it. The opening was sealed by heat fusion to obtain a tripolar laminate type half cell.
The electrolytic solution was prepared by adding 1% by mass of vinylene carbonate (VC) and 10% by mass of fluoroethylene carbonate (FEC) to a mixed solution of 3 parts by volume of ethylene carbonate, 5 parts by volume of ethyl methyl carbonate and 2 parts by volume of diethyl carbonate, and further adding It is a liquid obtained by dissolving the electrolyte LiPF ₆ in the solution to a concentration of 1 mol/L.

[Tripolar laminate type half cell/charge/discharge cycle test]
(aging)
0.005V vs. rest potential in a tripolar laminated half cell. A constant current discharge was performed at 0.05 C until it became Li/Li ⁺ . 1.5V vs. 0.05C. Constant current charging was performed until Li/Li ^{+ was} reached.
Continuously, 0.005 Vvs. Constant current discharge was performed at 0.2 C until it became Li/Li+. 0.005 Vvs. After reaching Li/Li ⁺ , constant voltage discharge was performed until the temperature reached 0.025C. 1.5 V vs. 0.2 C Constant current charging was performed until it became Li/Li ⁺ . This charging/discharging operation was further performed 5 times.

(60 cycles charge/discharge)
Then, 0.005V vs. 1C. Constant current discharge was performed until it became Li/Li ⁺ . 0.005V vs. After reaching Li/Li ⁺ , constant voltage discharge was performed until the temperature reached 0.025C. 1.5V vs. 1C. Constant current charging was performed until it became Li/Li ⁺ (first cycle). This charging/discharging operation was further performed 19 times (second cycle to 20th cycle).
0.005 V vs. 0.1 C Constant current discharge was performed until it became Li/Li ⁺ . 0.005V vs. After reaching Li/Li ⁺ , constant voltage discharge was performed until the temperature reached 0.025C. 1.5 V vs. 0.1 C Constant current charging was performed until it became Li/Li ⁺ (21st cycle).
Three sets of charging/discharging operations in the 1st to 21st cycles were performed as one set.
The half-cell 60-cycle charge capacity retention rate defined by the following formula was 89.8%.
Half-cell 60-cycle charge capacity maintenance rate Crr60 (%) =
{Charge capacity of 60th cycle/Charge capacity of 1st cycle}×100

Example 2
Composite particles B were obtained in the same manner as in Example 1 except that the amount of coal tar pitch was changed to 25 g. The composite particles B had P _c of 45%, P _s of 20%, Ps/Pc of 0.44, and D ₅₀ of 9.6 μm. The full-cell 200-cycle discharge capacity retention rate was 63.6%, and the half-cell 60-cycle charge capacity retention rate was 89.4%.

Example 3
Composite particles C were obtained in the same manner as in Example 1 except that the temperature rising rate was changed to 200° C./h. The composite particles C had P _c of 48%, P _s of 8%, Ps/Pc of 0.17, and D ₅₀ of 10.0 μm. The full-cell 200-cycle discharge capacity retention rate was 63.5%, and the half-cell 60-cycle charge capacity retention rate was 89.2%.

Comparative Example 1
Composite particles D were obtained in the same manner as in Example 1 except that the temperature rising rate was changed to 300° C./h. The composite particles D had P _c of 55%, P _s of 7%, Ps/Pc of 0.13, and D ₅₀ of 9.9 μm. The full-cell 200-cycle discharge capacity retention rate was 60.9%, and the half-cell 60-cycle charge capacity retention rate was 87.5%.

Comparative example 2
Composite particles E were obtained in the same manner as in Example 1 except that the temperature rising rate was changed to 100° C./h. The composite particles E had P _c of 38%, P _s of 21%, Ps/Pc of 0.55, and D ₅₀ of 9.5 μm. The full-cell 200-cycle discharge capacity retention rate was 60.3%, and the half-cell 60-cycle charge capacity retention rate was 88.5%.

Comparative Example 3
Composite particles F were obtained in the same manner as in Example 1 except that the amount of coal tar pitch was changed to 100 g. The composite particles F had P _c of 28%, P _s of 18%, Ps/Pc of 0.64, and D ₅₀ of 10.3 μm. The full-cell 200-cycle discharge capacity retention rate was 61.5%, and the half-cell 60-cycle charge capacity retention rate was 87.9%.

Comparative Example 4
Si-containing particles (porous silicon particles formed by joining Si particles, see FIG. 3) were directly used as composite particles G. The composite particles G had P _c of 55%, P _s of 48%, P _s /P _c of 0.87, and D ₅₀ of 9.4 μm. The full-cell 200-cycle discharge capacity retention rate was 60.7%, and the half-cell 60-cycle charge capacity retention rate was 86.2%.

Comparative Example 5
50 g of solid Si particles (ANI720 manufactured by AUO Crystal Corp.) and 90 g of coal tar pitch (carbonization rate 78%) were added to a container, and the mixture was stirred at 100 rpm for 6 hours using a mix rotor (VMR-5R manufactured by AsOne). The obtained mixture was placed in an alumina crucible and heat-treated at 1100° C. under an argon atmosphere (rate of temperature increase from room temperature to 1100° C. 150° C./h), then crushed in a mortar, and composite particles under sieve of 45 μm sieve. H was obtained. The composite particles H had P _c of 3%, P _s of 3%, Ps/Pc of 1.00, and D ₅₀ of 16.2 μm. The full-cell 200-cycle discharge capacity retention rate was 54.8% and the half-cell 60-cycle charge capacity retention rate was 87.5%.

As shown above, the porosity in the range from the center of the composite particle to 80% of the diameter of the composite particle is 30 to 50%, and the porosity in the range of from the center of the composite particle to 80% of the diameter of the composite particle. When a composite particle containing Si-containing particles and a carbon material having a porosity ratio of 0.5 or less in the range from the outer surface of the composite particle to 10% of the diameter of the composite particle is used for the negative electrode, a charge-discharge cycle A lithium ion secondary battery having excellent characteristics can be obtained.

Claims (11)

1. A composite particle containing Si-containing particles and a carbon material,
   The porosity in the range from the center of the composite particle to 80% of the diameter of the composite particle is 30 to 50%, and the porosity outside the range from the center of the composite particle to 80% of the diameter of the composite particle The ratio of the porosity in the range from the surface to 10% of the diameter of the composite particles is 0.5 or less,
   Composite particles for a negative electrode of a lithium ion secondary battery.
2. The composite particle according to claim 1, wherein the 50% diameter in the volume-based particle size distribution is 2 to 50 μm.
3. The composite particle according to claim 1 or 2, wherein the Si-containing particle is a porous silicon particle formed by aggregating or bonding a plurality of Si particles.
4. The composite particle according to claim 3, wherein the carbon material covers part or all of the outer surface of the porous silicon particle.
5. The composite particles according to any one of claims 1 to 4, wherein the carbon material is a carbonaceous carbon material.
6. A negative electrode material for a lithium ion secondary battery, containing the composite particle according to any one of claims 1 to 5.
7. A negative electrode sheet of a lithium ion secondary battery, which has an electrode layer containing the negative electrode material according to claim 6.
8. A lithium-ion secondary battery having the negative electrode sheet according to claim 7.
9. 100 parts by mass of Si-containing particles and 5 to 95 parts by mass of carbon precursor are mixed,
   Heating the obtained mixture from 100° C. to 350° C. at 110 to 290° C./hour, reaching a predetermined temperature, and then maintaining at the predetermined temperature for 0.5 hours or more and 6 hours or less. , Including carbonizing the carbon precursor by heat treatment,
   The predetermined temperature is 400° C. or higher and lower than 1800° C.,
   A method for producing composite particles for a negative electrode of a lithium ion secondary battery.
10. Mixing the Si-containing particles and the carbon precursor,
    Heat treating the resulting mixture to graphitize or carbonize the carbon precursor,
    The method for producing composite particles according to any one of claims 1 to 5.
11. The manufacturing method according to claim 9 or 10, wherein the Si-containing particles are porous silicon particles formed by aggregating or bonding a plurality of Si fine particles.

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