Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/20—Silicates
  • C01B33/32—Alkali metal silicates
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to composite particles, a method for producing the composite particles, a negative electrode active material for a secondary battery that includes the composite particles, a negative electrode that includes the negative electrode active material, and a secondary battery that includes the negative electrode.
• LIBs lithium-ion batteries
• EVs electric vehicles
• Patent Document 1 describes an anode active material that includes a carbonaceous matrix containing multiple nanoparticles, the nanoparticles including a silicon core, an oxide film layer containing SiOx (0 ⁇ x ⁇ 2) disposed on the silicon core, and a coating layer containing LiF that covers at least a portion of the surface of the oxide film layer.
• silicon compound SiOx: 0.5 ⁇ x ⁇
• Patent Document 3 describes a Si-O-C-Li composite that includes nanosilicon, a silicon-oxygen-lithium compound, and a carbon coating, the silicon-oxygen-lithium compound being partially crystallized, and the composite further including silicon oxide, in which the nanosilicon is dispersed in the silicon-oxygen-lithium compound to form fused particles, the fused particles are dispersed in a matrix of silicon oxide in an island-like form to form composite particles, and the carbon coating is applied to the surfaces of the composite particles.
• the negative electrode active material described in Patent Document 1 has LiF coated on Si particles, which may not be able to withstand the silicon expansion that accompanies the absorption and release of lithium ions. It is believed that a structure such as a matrix phase is necessary to suppress such Si expansion.
• Li needs to be sufficiently diffused into the interior to improve performance, but this requires an increased amount of Li to be added. Increasing the amount of Li added leads to increased costs and may also reduce the initial efficiency of a secondary battery when stored in air for a long period of time. For this reason, it is preferable to reduce the amount of Li added as much as possible. Also, to improve performance, it is necessary to control the structure of the active material with a small amount of Li. Specifically, it is preferable for Li to be selectively present on the surface of the active material, which suppresses surface side reactions with the electrolyte and improves battery performance.
• Patent Document 3 The composite described in Patent Document 3 above is simply silicon covered with a silicon-oxy-lithium compound, silicon oxide, and a carbon coating, which is not able to withstand the inhibition of expansion of silicon.
• Patent Document 3 also describes that "the obtained composite has a stable structure, and can effectively prevent components such as air from penetrating the inside of the particles and causing the active ingredient to become ineffective, and the structure and properties do not deteriorate even when stored for a long period of time," but this has not been substantiated by quantitative evaluation in the examples, etc., and it cannot necessarily be said that the quality is stable even when stored for a long period of time as described above.
• the object of the present invention is to provide composite particles that can suppress surface side reactions with the electrolyte and Si expansion during repeated charging and discharging, and further improve the initial charge-discharge efficiency and cycle characteristics of the active material, a method for producing the composite particles, a negative electrode active material for secondary batteries containing the composite particles, a negative electrode containing the negative electrode active material, and a secondary battery containing the negative electrode.
• the object of the present invention is to provide composite particles and a negative electrode active material for secondary batteries containing the same that are stable in quality and do not decrease in initial efficiency when used as a secondary battery when stored in air for long periods of time by controlling the amount of Li added.
• the inventors discovered that it was possible to create a composite particle structure containing a matrix phase containing Si and O elements that suppresses the expansion of Si during charging and discharging, and a specific metal silicate. Furthermore, they discovered that by controlling the concentration of the metal portion of this metal silicate and selectively distributing the metal elements, it is possible to suppress side reactions on the surface, leading to improved charging and discharging performance.
• the present invention has the following aspects.
• Composite particles comprising at least one silicon particle and a matrix phase containing Si and O elements outside the silicon particle, and further containing a silicate compound, the silicate compound containing at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg, and Al.
• the metal ion element concentration of the metal element is 0.1 to 40.0 atom % based on the total elements of the composite particle.
• Step 1 A step of mixing at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al with an intermediate derived from a polysiloxane resin containing silicon particles.
• Step 2 A step of firing at 900° C. or less in a non-oxygen atmosphere.
• a negative electrode active material for secondary batteries comprising the composite particles according to any one of [1] to [12].
• a negative electrode comprising the negative electrode active material for a secondary battery according to [14].
• a secondary battery comprising the negative electrode according to [15].
• the composite particles of the present invention can suppress surface side reactions and can maintain high charge/discharge performance, such as the capacity retention rate and initial coulombic efficiency, in secondary batteries.
• the composite particles of the present invention have quality stability, with no decrease in initial efficiency when used as a secondary battery after long-term storage in the atmosphere.
• mass is synonymous with “weight.”
• weight is synonymous with “weight.”
• to indicating a range of values is used to mean that the values before and after the range are included as the lower and upper limits, unless otherwise specified.
• the composite particle of the present embodiment has at least one silicon particle and a matrix phase containing Si and O elements outside the silicon particle, and further contains a silicate compound, and the silicate compound contains at least one metal element selected from the group consisting of Li, K, Na, Ca, Mg, and Al.
• the composite particle of the present embodiment is characterized in that a plurality of silicon particles are dispersed and embedded in a matrix phase, and further, the silicate compound is present as a distributed component.
• the silicate compound may be present outside the matrix phase as a silicate layer, or may be present inside the silicon particles or the matrix phase, or may be both.
• the silicon particles in the composite particles of this embodiment are composed of zero-valent silicon and have an average particle size of 300 nm or less.
• the average particle size of the silicon particles is preferably 5 nm to 300 nm, more preferably 20 nm to 250 nm, and even more preferably 50 nm to 200 nm.
• the charge/discharge performance such as the capacity retention rate and the initial coulombic efficiency, of the secondary battery can be maintained at a high level.
• the average particle size of the silicon particles can be obtained by observing the composite particles of this embodiment with a TEM and calculating the average particle size of 50 silicon particles randomly selected from the TEM image at a magnification of 50,000.
• the silicon particles constituting the composite particles of this embodiment preferably satisfy the following relationship: peak intensity C corresponding to the (111) plane of the silicon particles in the X-ray diffraction spectrum and peak intensity D corresponding to the (111) plane in the X-ray diffraction spectrum of Li 2 SiO 3 are 0 ⁇ D/C ⁇ 0.6.
• the peak intensity range is more preferably 0.05 ⁇ D/C ⁇ 0.5. When this peak intensity range is satisfied, the charge/discharge performance such as the capacity retention rate and the initial coulombic efficiency in the secondary battery can be maintained at a high level.
• the crystallite size x obtained by Scherrer formula calculation using the peak half-width is preferably 10 nm ⁇ x ⁇ 30 nm
• the crystallite size y is preferably 1 nm ⁇ y ⁇ 40 nm.
• the specific surface area of the silicon particles is preferably 50 m 2 /g to 400 m 2 /g, more preferably 100 m 2 /g to 300 m 2 /g, and even more preferably 150 m 2 /g to 230 m 2 /g.
• the specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measuring device.
• the silicon particles are not particularly limited in shape and may be, for example, granular, needle-like, or flaky, but from the viewpoint of charge/discharge performance when used as a secondary battery, the length in the major axis direction is preferably 30 nm to 300 nm, and the thickness is preferably 1 nm to 60 nm. From the viewpoint of charge/discharge performance when used as a secondary battery, a needle-like or flaky shape having an aspect ratio, which is the ratio of thickness to length, of 0.5 or less is preferred.
• the morphology of silicon particles can be measured by the average particle size using dynamic light scattering, but the aspect ratio of the sample can be more easily and precisely identified by using analytical means such as a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM).
• TEM transmission electron microscope
• FE-SEM field emission scanning electron microscope
• the sample can be cut with a focused ion beam (FIB) and the cross section can be observed with a FE-SEM, or the sample can be sliced and the state can be identified by TEM observation.
• the aspect ratio of silicon particles is a calculation result based on the main part of 50 particles of the sample within the field of view of the TEM image.
• the matrix phase present outside the silicon particles contains at least the elements Si and O.
• the matrix phase preferably has a composition represented by SiOx (1 ⁇ x ⁇ 2), and further preferably contains carbonaceous matter (element C) as a component.
• the matrix phase is a three-dimensional network structure of a silicon-oxygen skeleton containing at least silicon and oxygen elements. It is also preferable that the matrix phase contains silicon, carbon, and oxygen elements and is a three-dimensional network structure of a silicon-oxygen-carbon skeleton.
• This three-dimensional network structure of a silicon-oxygen-carbon skeleton has relatively high chemical stability, has a composite structure with carbon (carbonaceous phase), and exhibits small volumetric change with respect to the absorption and release of lithium.
• the three-dimensional network structure of the matrix phase contains a silicon oxycarbide (SiOC) structure. This three-dimensional network structure may contain a nitrogen element in addition to silicon, carbon, and oxygen elements.
• the silicate compounds are generally compounds containing anions having a structure in which one or more silicon atoms are at the center and electronegative ligands surround the silicon atoms, and the silicate compounds containing at least one metal (element) selected from the group consisting of Li, K, Na, Ca, Mg, and Al are salts of these metals and compounds containing anions.
• Examples of compounds containing the above anions include silicate ions such as orthosilicate ion (SiO 4 4 ⁇ ), metasilicate ion (SiO 3 2 ⁇ ), pyrosilicate ion (Si 2 O 7 6 ⁇ ), and cyclic silicate ion (Si 3 O 9 6 ⁇ or Si 6 O 18 12 ⁇ ).
• silicate ions such as orthosilicate ion (SiO 4 4 ⁇ ), metasilicate ion (SiO 3 2 ⁇ ), pyrosilicate ion (Si 2 O 7 6 ⁇ ), and cyclic silicate ion (Si 3 O 9 6 ⁇ or Si 6 O 18 12 ⁇ ).
• the silicate compound is preferably a lithium silicate compound, a magnesium silicate compound, or a sodium silicate compound, more preferably a lithium silicate compound or a magnesium silicate compound, and particularly preferably a lithium silicate compound.
• Examples of such lithium silicate compounds include lithium metasilicate (Li 2 SiO 3 , Li 2 Si 2 O 5 , Li 4 SiO 4 ), and the lithium silicate compound preferably contains at least one crystal structure selected from the group consisting of Li 2 SiO 3 , Li 4 SiO 4 , and Li 2 Si 2 O 5 .
• the magnesium silicate compound may, for example, be magnesium metasilicate (MgSiO 3 , Mg 2 SiO 4 ).
• sodium silicate compounds include sodium metasilicate (Na 2 SiO 3 , Na 4 SiO 4 , Na 2 Si 2 O 5 , Na 2 Si 4 O 9 ).
• the silicate compound may have two or more of the above metals. When two or more metals are contained, one silicate ion may have a plurality of metals, or a mixture of silicate compounds having different metals may be used.
• the silicate compound may also have a metal other than the above metals. When the silicate compound is in a crystalline state, it can be detected by powder X-ray diffraction measurement (XRD), and when it is amorphous, it can be confirmed by solid-state 29Si -NMR measurement.
• XRD powder X-ray diffraction measurement
• the content of the metal elements is preferably 25% by mass or less, more preferably 0.1 to 20% by mass, even more preferably 0.2 to 18% by mass, and particularly preferably 0.3 to 15% by mass, relative to the total mass of the composite particles.
• the content of the metal elements is within this range, side reactions on the surface of the composite particles can be suppressed, and the charge/discharge performance can be further improved when the composite particles are used as secondary batteries.
• the metal elements are uniformly dispersed (distributed) within the composite particles, rather than being localized as metal ions in only a few areas.
• the content of the metal elements can be measured, for example, by Auger electron spectroscopy (AES) or an ICP-OES analyzer.
• the silicate compound preferably contains Li element, and the content of Li element is preferably 20 mass% or less, more preferably 0.1 to 19 mass%, even more preferably 0.2 to 17 mass%, and particularly preferably 0.3 to 15 mass%, relative to the total mass of the composite particle.
• the content of Li element is within this range, surface side reactions of the composite particle can be suppressed, and the charge/discharge performance can be further improved when the composite particle is used as a secondary battery.
• the metal ion element concentration of the metal element in the total elements of the composite particle is preferably 0.1 to 40.0 atom%, more preferably 0.3 to 35.0 atom%, and particularly preferably 0.5 to 30.0 atom%.
• the metal ion element concentration is in this range, side reactions on the surface of the composite particle can be suppressed, and the charge/discharge performance when used as a secondary battery can be further improved.
• the metal ion element concentration of the metal element can also be measured, for example, by Auger electron spectroscopy (AES).
• a concentration gradient of the metal ion element may exist, and it is preferable that the concentration is higher on the surface than inside the composite particle.
• the ratio A of the metal ion element to all elements present in a region 30% inward from the surface of the composite particle is taken as the ratio B of the metal ion element to all elements present in the other region, it is preferable that the metal ion element abundance ratio satisfies 0.5 ⁇ A/(A+B) ⁇ 1.0. It is more preferable that the metal ion element abundance ratio is 0.6 ⁇ A/(A+B) ⁇ 0.99, and even more preferable that it is 0.7 ⁇ A/(A+B) ⁇ 0.98.
• the metal ion element abundance ratio is within this range, side reactions on the surface can be suppressed, and the charge/discharge performance can be further improved when the composite particle is used as a secondary battery.
• the composite particles of this embodiment have an average particle size x of preferably 1 ⁇ m ⁇ x ⁇ 15 ⁇ m, more preferably 2 ⁇ m ⁇ x ⁇ 13 ⁇ m, and even more preferably 3 ⁇ m ⁇ x ⁇ 10 ⁇ m, and a specific surface area n of preferably 0.1 m 2 /g ⁇ n ⁇ 20 m 2 /g, more preferably 0.5 m 2 /g ⁇ n ⁇ 18 m 2 /g, and even more preferably 0.7 m 2 /g ⁇ n ⁇ 15 m 2 /g.
• the average particle size and specific surface area of the composite particles are within these ranges, side reactions on the surface can be suppressed and the charge/discharge performance of the secondary battery can be further improved.
• the average particle size x is 1 ⁇ m ⁇ x ⁇ 15 ⁇ m and the specific surface area n is 0.1 m 2 /g ⁇ n ⁇ 20 m 2 /g.
• the negative electrode active material for a secondary battery of this embodiment includes the composite particles of this embodiment.
• the composite particles of this embodiment themselves have the performance as a negative electrode active material, but the negative electrode active material for a secondary battery is
• the composite particles may contain components other than the composite particles.
• the negative electrode active material for secondary batteries may have a carbon layer on the surface of the composite particles. That is, at least a part of the surface of the composite particles may have a carbon coating.
• the carbon layer (carbon coating) is preferably a coating made of low crystalline carbon. From the viewpoint of improving chemical stability and thermal stability, the amount of the carbon layer (carbon coating) is preferably 0.1% by mass to 30% by mass, more preferably 1% by mass to 25% by mass, and even more preferably 5% by mass to 20% by mass, based on the mass of the composite active material for secondary batteries being 100% by mass.
• the composite active material for secondary batteries may have a carbon layer (carbon coating) on its surface, either continuously or intermittently. The carbon layer (carbon coating) is preferably formed on the surface of the active material by chemical vapor deposition.
• the true density of the negative electrode active material for secondary batteries is preferably 1.6 g/cm 3 or more and 2.6 g/cm 3 or less. From the viewpoint of improving the energy density of the resulting secondary battery, the true density is more preferably 1.75 g/cm 3 or more, and further preferably 1.80 g/cm 3 or more.
• the true density is a value measured using a true density measuring device.
• the average particle size of the negative electrode active material for secondary batteries is preferably 2 ⁇ m or more and 15 ⁇ m or less. If the average particle size is 2 ⁇ m or more, a significant increase in the specific surface area can be suppressed, and when used as a secondary battery, the reversible charge/discharge capacity per unit volume can be improved by suppressing the amount of SEI generated during charging and discharging. Furthermore, if the average particle size is 15 ⁇ m or less, the adhesion strength with the current collector is improved, thereby suppressing peeling from the current collector.
• the specific surface area of the negative electrode active material for secondary batteries is preferably 0.1 m 2 /g or more and 10 m 2 /g or less.
• the specific surface area is more preferably 0.3 m 2 /g or more, and particularly preferably 0.5 m 2 /g or more.
• the specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measurement device.
• the method for producing composite particles of the present embodiment includes the following steps 1 and 2.
• Step 1 Mixing at least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg and Al with an intermediate derived from a polysiloxane resin containing silicon particles.
• Step 2 Sintering at 900°C or less in a non-oxygen atmosphere.
• the composite particles of this embodiment are not limited to those obtained by the above manufacturing method.
• the description of the manufacturing method below is only one aspect of the manufacturing method of the composite particles of this embodiment, and may include steps other than the above steps 1 and 2, and the order of steps 1 and 2 is not particularly limited.
• the silicon particles used in step 1 are obtained by wet grinding the raw silicon.
• the raw silicon is dispersed in a solvent such as an organic solvent in the wet grinding to obtain a silicon slurry, which is a dispersion of silicon particles.
• the silicon slurry can be prepared while grinding the raw silicon in a wet powder grinding device. It is preferable to add a dispersant to the organic solvent to promote the grinding of the raw silicon.
• wet grinding devices include roller mills, high-speed rotary grinders, container-driven mills, and bead mills.
• the preferred range of the average particle size of the silicon particles in the obtained silicon slurry is as described above.
• organic solvent examples include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohols such as ethanol, methanol, normal propyl alcohol, and isopropyl alcohol; and aromatics such as benzene, toluene, and xylene.
• ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone
• alcohols such as ethanol, methanol, normal propyl alcohol, and isopropyl alcohol
• aromatics such as benzene, toluene, and xylene.
• the above-mentioned dispersants include aqueous and non-aqueous dispersants, with non-aqueous dispersants being preferred.
• non-aqueous dispersants include polymeric types such as polyethers, alcohols, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters, low molecular weight types such as polyhydric alcohol esters and alkyl polyamines, and inorganic types such as polyphosphates.
• the solids concentration of the silicon particles and dispersant in the silicon slurry is not particularly limited, but is preferably in the range of 5% to 40% by mass, and more preferably 10% to 30% by mass, with the total amount of the solvent, dispersant, and silicon particles being 100% by mass.
• the amount of dispersant added is preferably in the range of 2% to 60% by mass, and more preferably 5% to 50% by mass, relative to the total mass of the silicon particles.
• the polysiloxane compound is mixed uniformly with the silicon slurry obtained by the wet grinding process, and then the solvent is removed, dried, and treated at high temperature to obtain an intermediate derived from polysiloxane resin containing silicon particles.
• the matrix phase which is a three-dimensional network structure of a silicon-oxygen skeleton, is mixed with the silicon particles and homogenized, and then the solvent is removed, dried, and treated at high temperature to obtain the intermediate.
• the polysiloxane compound may be, for example, a resin containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure. It may be a resin containing only these structures, or a composite resin having at least one of these structures as a segment and chemically bonded to other polymer segments.
• the form of the composite may be graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, etc.
• a composite resin having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment there may be a composite resin having a block structure in which a polysiloxane segment is chemically bonded to the end of a polymer segment.
• the polysiloxane segment is preferably a polysiloxane compound having a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2).
• the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group on the side chain or terminal of the main siloxane bond (Si-O-Si) skeleton.
• R1 represents an aromatic hydrocarbon group or an alkyl group which may have a substituent, an epoxy group, a carboxy group, etc.
• R2 and R3 each represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, etc.
• alkyl group examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl, 1-ethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-2-methylpropyl, and 1-ethyl-1-methylpropyl.
• cycloalkyl group examples include cyclopropyl, cyclobutyl, cyclopentyl,
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• aralkyl groups examples include benzyl, diphenylmethyl, and naphthylmethyl groups.
• polymer segments other than polysiloxane segments contained in polysiloxane compounds include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and olefin polymers, as well as polymer segments such as urethane polymer segments, ester polymer segments, and ether polymer segments. Among these, vinyl polymer segments are preferred.
• the polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure shown in the following structural formula (S-3), or may have a three-dimensional network-like polysiloxane structure.
• the carbon atom is a carbon atom that constitutes a polymer segment
• the two silicon atoms are silicon atoms that constitute a polysiloxane segment.
• the polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, in the polysiloxane segment.
• a functional group capable of reacting by heating such as a polymerizable double bond
• the crosslinking reaction proceeds, and the compound becomes solid, making it easier to carry out the thermal decomposition treatment.
• polymerizable double bond examples include vinyl groups and (meth)acryloyl groups. It is preferable that there are two or more polymerizable double bonds in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. In addition, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the crosslinking reaction can be easily promoted.
• the polysiloxane segment may have a silanol group and/or a hydrolyzable silyl group.
• the hydrolyzable group in the hydrolyzable silyl group include a halogen atom, an alkoxy group, a substituted alkoxy group, an acyloxy group, a phenoxy group, a mercapto group, an amino group, an amide group, an aminooxy group, an iminoxy group, and an alkenyloxy group.
• the hydrolyzable silyl group becomes a silanol group.
• a hydrolysis condensation reaction proceeds between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound.
• the silanol group in this invention is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom.
• the hydrolyzable silyl group in this invention is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, and specific examples include groups represented by the following general formula (S-4).
• R4 is a monovalent organic group such as an alkyl group, an aryl group, or an aralkyl group
• R5 is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, an iminoxy group, or an alkenyloxy group
• b is an integer of 0 to 2.
• alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl, 1-ethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-2-methylpropyl, and 1-ethyl-1-methylpropyl.
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• aralkyl groups examples include benzyl groups, diphenylmethyl groups, and naphthylmethyl groups.
• Halogen atoms include, for example, fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.
• alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups.
• acyloxy groups include formyloxy groups, acetoxy groups, propanoyloxy groups, butanoyloxy groups, pivaloyloxy groups, pentanoyloxy groups, phenylacetoxy groups, acetoacetoxy groups, benzoyloxy groups, and naphthoyloxy groups.
• allyloxy group examples include a phenyloxy group and a naphthyloxy group.
• alkenyloxy groups include vinyloxy groups, allyloxy groups, 1-propenyloxy groups, isopropenyloxy groups, 2-butenyloxy groups, 3-butenyloxy groups, 2-pentenyloxy groups, 3-methyl-3-butenyloxy groups, and 2-hexenyloxy groups.
• polysiloxane segments having structural units represented by the above general formula (S-1) and/or general formula (S-2) include those having the following structures:
• R6 in the structural formulae (1) to (3) above has the same meaning as R1 above.
• R7 and R8 in the structural formulae (4) to (8) above have the same meaning as R2 and R3 above, respectively.
• the polymer segment may have various functional groups as necessary, as long as they do not impair the effects of the present invention.
• functional groups include a carboxyl group, a blocked carboxyl group, a carboxylic anhydride group, a tertiary amino group, a hydroxyl group, a blocked hydroxyl group, a cyclocarbonate group, an epoxy group, a carbonyl group, a primary amide group, a secondary amide, a carbamate group, and a functional group represented by the following structural formula (S-5).
• the polymer segment may also have a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.
• the polysiloxane compound is preferably produced, for example, by the methods shown in (1) to (3) below.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance as the raw material for the polymer segment.
• a polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and/or a hydrolyzable silyl group and a polymerizable double bond to a hydrolysis and condensation reaction. The polymer segment and the polysiloxane are then mixed together to carry out a hydrolysis and condensation reaction.
• polysiloxane compounds such as the Ceranate (registered trademark) series (organic/inorganic hybrid coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane hybrid; manufactured by Arakawa Chemical Industries, Ltd.).
• a carbon source resin that is compatible with the polysiloxane compound may be used.
• carbon source resins include thermosetting resins and thermoplastic resins that contain molecular structures with benzene rings or aromatic functional groups.
• Thermosetting resins include, for example, phenolic resins such as novolac-type phenolic resins and resol-type phenolic resins; epoxy resins such as bisphenol-type epoxy resins and novolac-type epoxy resins; melamine resins; urea resins; aniline resins; cyanate resins; furan resins; ketone resins; unsaturated polyester resins; and urethane resins.
• Thermoplastic resins are not particularly limited, and examples include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, and polyphthalamide.
• an intermediate derived from polysiloxane resin containing silicon particles is obtained. Drying is performed, for example, using a dryer, a vacuum dryer, a spray dryer, etc.
• the drying temperature is preferably 80°C or higher, and preferably 150°C or lower. Drying may be performed while reducing the pressure.
• the high-temperature treatment is performed according to a firing program that is specified by the heating rate, the holding time at a constant temperature, etc.
• the treatment temperature is preferably, for example, a maximum reaching temperature of 1000°C or higher.
• the treatment equipment can be appropriately selected according to the purpose, from among fluidized bed reactors, rotary furnaces, vertical moving bed reactors, tunnel furnaces, batch furnaces, rotary kilns, etc.
• Step 1 At least one metal element compound selected from the group consisting of Li, K, Na, Ca, Mg, and Al is mixed with the intermediate derived from the polysiloxane resin containing silicon particles obtained above (mixing step). Note that in the description of step 1 below, some steps may be omitted, and there is no particular restriction on the mixing method.
• the metal element compound is not particularly limited as long as it contains the above-mentioned elements, and metal element compounds such as oxides, hydroxides, oxyhydroxides, nitrates, oxalates, acetates, and carbonates can be used.
• metal element compounds such as oxides, hydroxides, oxyhydroxides, nitrates, oxalates, acetates, and carbonates can be used.
• metal element lithium oxide and anhydrous lithium acetate are typical examples, and when the metal element is Mg, anhydrous magnesium acetate is typical examples.
• anhydrous magnesium acetate is typical examples.
• these metal element compounds may be added by dispersing them in a suitable organic solvent (polar or non-polar) such as ethanol, MEK, etc.
• the amount of the metal element compound added is preferably 0.1 to 30% by mass based on the total mass of the composite particles.
• mixing is performed to uniformly disperse the metal element in the polysiloxane resin-derived intermediate.
• the mixing method can be performed, for example, with a stirrer equipped with a stirring blade, and the stirring time is, for example, 1 minute to 2 hours, preferably 2 minutes to 1 hour. Stirring can be performed at room temperature, or while heating to about 30 to 50°C.
• the powdered metal element compound can be added directly to the polysiloxane resin-derived intermediate and mixed. In the case of mixing in powder, it can be performed with a ball mill or bead mill, and the mixing time is, for example, 1 minute to 2 hours, preferably 2 minutes to 1 hour. Stirring can be performed at room temperature, or while heating to about 30 to 50°C.
• the solvent is removed and the mixture is dried.
• the solvent can be removed by a common method such as filtration. Drying can be performed, for example, using a dryer, a vacuum dryer, or a spray dryer.
• the drying temperature is preferably 80°C or higher and 150°C or lower. Drying can also be performed under reduced pressure.
• Step 2 After the drying, the mixture is fired at 900°C or less in an oxygen-free atmosphere (firing step).
• the firing apparatus may be selected from fluidized bed reactors, rotary furnaces, vertical moving bed reactors, tunnel furnaces, batch furnaces, rotary kilns, etc., depending on the purpose.
• the firing is performed according to a firing program that is determined by the heating rate, holding time at a constant temperature, etc.
• the firing temperature is preferably, for example, a maximum reaching temperature of 900°C or less. This allows composite particles to be obtained that contain the metal element of the metal element compound added in the mixing step as a compound.
• the non-oxidizing atmosphere during the firing process is not particularly limited in terms of the type of gas used, but examples include nitrogen, argon, hydrogen, and nitrogen/hydrogen mixed gas.
• the fired product obtained above may be further pulverized and classified as necessary.
• the pulverization may be performed in one stage until the desired particle size is reached, or may be performed in several stages.
• the particles may be coarsely pulverized using a jaw crusher, roll crusher, etc., and then pulverized using a glow mill, ball mill, etc., and further pulverized using a bead mill, jet mill, etc.
• Classification may be performed using an air classifier, wet classifier, etc.
• the composite particles thus obtained may be used as they are as the negative electrode active material for secondary batteries.
• the negative electrode active material for secondary batteries further has carbon (carbon coating) on the surface
• the obtained active material is coated with a carbon coating in a chemical vapor deposition apparatus at a temperature range of 700°C to 1000°C in a flow of pyrolytic carbon source gas and carrier inert gas.
• pyrolytic carbon source gas include acetylene, ethylene, acetone, alcohol, propane, methane, and ethane.
• inert gas include nitrogen, helium, and argon, and nitrogen is usually used.
• a metal element compound may be added to the intermediate after the high-temperature treatment, and the mixture may be mixed and fired, or a metal element compound may be added to an intermediate that has not been subjected to high-temperature treatment, and the mixture may be mixed and fired.
• the composite particles obtained by firing may be washed with a liquid in order to remove impurities and unreacted substances, and the liquid is preferably one having an OH group, such as water or alcohol.
• the negative electrode of this embodiment is not particularly limited as long as it contains the above-mentioned negative electrode active material for secondary batteries, but may also contain other components such as an organic binder and a conductive assistant.
• the negative electrode of this embodiment can be produced by applying a slurry containing the composite particles of this embodiment, an organic binder, and other components such as conductive assistants as necessary, onto a copper foil current collector in the form of a thin film.
• the negative electrode can also be produced by adding a carbon material such as graphite to the slurry. Examples of the carbon material include natural graphite, artificial graphite, and amorphous carbon such as hard carbon or soft carbon.
• the negative electrode active material for secondary batteries and a binder which is an organic binding material
• a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader to prepare a negative electrode material slurry, which is then applied to a current collector to form a negative electrode layer.
• a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader
• a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader
• It can also be obtained by forming the paste-like negative electrode material slurry into a sheet, pellet, or other shape and integrating it with the current collector.
• organic binder examples include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR”); ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and unsaturated carboxylic acid copolymers such as (meth)acrylic copolymers made of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymeric compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethylcellulose (hereinafter also referred to as "CMC").
• SBR styrene
• these organic binders may be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP).
• NMP N-methyl-2-pyrrolidone
• the content of the organic binder in the negative electrode layer of the lithium ion secondary battery negative electrode is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, and even more preferably 3% by mass to 15% by mass.
• the organic binder content is 1% by mass or more, adhesion is better and damage to the negative electrode structure caused by expansion and contraction during charging and discharging is more effectively prevented.
• the content is 30% by mass or less, an increase in electrode resistance is more effectively prevented.
• a conductive additive may be mixed into the negative electrode material slurry as necessary.
• conductive additives include carbon black, graphite, acetylene black, and oxides and nitrides that exhibit electrical conductivity.
• the amount of conductive additive used may be, for example, 1% by mass to 15% by mass with respect to the negative electrode active material of this embodiment.
• the material and shape of the current collector can be, for example, copper, nickel, titanium, stainless steel, or the like, in the form of a foil, perforated foil, mesh, or other strip. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.
• Methods for applying the negative electrode material slurry to the current collector include, for example, metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calendar roll, etc., as necessary.
• the negative electrode material slurry can also be made into a sheet or pellet shape, and integrated with the current collector by, for example, rolling, pressing, or a combination of these.
• the negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated according to the organic binder used.
• the organic binder used For example, when using a water-based styrene-butadiene rubber copolymer (SBR), heat treatment at 100 to 130°C is sufficient, and when using an organic binder with a polyimide or polyamideimide as the main skeleton, heat treatment at 150 to 450°C is preferable.
• SBR water-based styrene-butadiene rubber copolymer
• This heat treatment removes the solvent and hardens the binder, increasing strength and improving adhesion between particles and between the particles and the current collector. It is preferable to carry out these heat treatments in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, to prevent oxidation of the current collector during treatment.
• an inert atmosphere such as helium, argon, or nitrogen
• the negative electrode is preferably subjected to pressure treatment.
• the electrode density is preferably 1 g/cm 3 to 1.8 g/cm 3 , more preferably 1.1 g/cm 3 to 1.7 g/cm 3 , and even more preferably 1.2 g/cm 3 to 1.6 g/cm 3.
• the higher the electrode density the more the adhesion and the volume capacity density of the electrode tend to improve.
• the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon, etc., and the capacity retention rate may decrease. Therefore, the optimal range of the electrode density is selected.
• the secondary battery of the present embodiment includes the negative electrode of the present embodiment.
• a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferable, and the negative electrode of the present embodiment exhibits excellent performance particularly when used as the negative electrode of a non-aqueous electrolyte secondary battery.
• the secondary battery of this embodiment When the secondary battery of this embodiment is used as, for example, a wet electrolyte secondary battery, it can be constructed by arranging a positive electrode and a negative electrode containing the negative electrode active material for secondary batteries of this embodiment so as to face each other with a separator interposed therebetween, and injecting an electrolyte solution.
• the positive electrode can be obtained by forming a positive electrode layer on the surface of a current collector in the same manner as the negative electrode.
• the current collector can be a strip of metal or alloy such as aluminum, titanium, or stainless steel in the form of foil, perforated foil, mesh, or the like.
• the positive electrode material used in the positive electrode layer is not particularly limited.
• a metal compound, a metal oxide, a metal sulfide, or a conductive polymer material capable of doping or intercalating lithium ions may be used.
• lithium cobalt oxide LiCoO2
• lithium nickel oxide LiNiO2
• lithium manganese oxide LiMnO2
• lithium manganese spinel LiMn2O4
• lithium vanadium compounds V2O5 , V6O13 , VO2 , MnO2
• TiO2 , MoV2O8 TiS2 , V2S5 , VS2
• MoS2 , MoS3 , Cr3O8 , Cr2O5 olivine type LiMPO4 (wherein M is Co, Ni, Mn or Fe)
• conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used alone or in combination.
• separator for example, a nonwoven fabric, cloth, microporous film, or a combination of these, whose main component is a polyolefin such as polyethylene or polypropylene, can be used. Note that if the positive and negative electrodes of the nonaqueous electrolyte secondary battery to be fabricated are not in direct contact with each other, there is no need to use a separator.
• a so-called organic electrolyte can be used in which a lithium salt such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , or LiSO 3 CF 3 is dissolved in a non-aqueous solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, ⁇ -butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetra
• the structure of the secondary battery of this embodiment is not particularly limited, but typically, the positive and negative electrodes and a separator, which is provided as necessary, are wound into a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and the electrode plate group is enclosed in an exterior body.
• the half cells used in the examples of the present invention are mainly composed of the present negative electrode active material in the negative electrode, and a simplified evaluation is performed using metallic lithium as the counter electrode, in order to more clearly compare the cycle characteristics of the active material itself.
• the secondary battery of this embodiment is not particularly limited, but may be used as a paper battery, a button battery, a coin battery, a laminated battery, a cylindrical battery, a square battery, or the like.
• the negative electrode active material of this embodiment described above can also be applied to electrochemical devices in general that use the insertion and removal of lithium ions as a charging and discharging mechanism, such as hybrid capacitors and solid-state lithium secondary batteries.
• polysiloxane resin CERANATE SSA-500: manufactured by DIC Corporation
• the black fired product was pulverized with a planetary ball mill (ball mill P-6 classic line: manufactured by FRITSCH) to obtain a composite particle intermediate.
• Lithium oxide (LiO 2 ) (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the prepared composite particle intermediate in an amount of 0.1 equivalent to the silicon particles, and mixed with a planetary ball mill.
• the mixture was sintered at a high temperature of 800° C. for 2 hours in a nitrogen atmosphere, washed with distilled water, and dried under reduced pressure to obtain composite particles with an average particle size of 6.4 ⁇ m and a specific surface area (SSA) of 5.1 m 2 /g.
• SSA specific surface area
• the amount of metal ion elements relative to the total mass of the obtained composite particles was measured using an ICP-OES analyzer (ICAP-7400, manufactured by Thermo Fisher Scientific Co., Ltd.), and the amount of metal elements present was 4.2% by mass.
• the metal ion element concentration distribution ratio between the surface and interior of the composite particle was measured by Auger electron spectroscopy (AES), and the result was that A/(A+B) was 0.9, where A is the ratio of the metal ion element to all elements in a region 30% inward from the particle surface and B is the ratio of the metal ion element to all elements in the other regions.
• the composite particles (8 parts) obtained above, acetylene black (1 part) as a conductive assistant, and an organic binder (1 part, consisting of SBR (0.75 parts) + CMC (0.25 parts)) were mixed and stirred for 10 minutes with a rotating and revolving type foaming blender to prepare a slurry.
• a rotating and revolving type foaming blender After coating a copper foil with a thickness of 20 ⁇ m using an applicator, the film was dried under reduced pressure at 110 ° C. to obtain a thin electrode film.
• a circular electrode with a diameter of 14 mm was punched out and pressed using a tablet molder so that the thickness was about 40 ⁇ m. The thickness was measured by calculating the average value of five points on the electrode using a thickness gauge.
• Battery characteristics were measured using a secondary battery charge/discharge tester (Hokuto Denko Co., Ltd.), and an evaluation test of charge/discharge characteristics was performed under the set conditions of constant current/low voltage charge/discharge/constant current charge/discharge at room temperature of 25°C, cutoff voltage range of 0.005-1.5 V, and charge rate of 0.1 C (1-3 times) and 0.2 C (after 4 cycles).
• the initial efficiency was 86%.
• composite particles stored in a vial at room temperature in the atmosphere were evaluated using a half cell. The initial efficiency of the sample stored in the atmosphere for 7 days was 85%, and the initial efficiency of the sample stored in the atmosphere for 14 days was also 85%.
• a positive electrode film was prepared using a single-layer sheet using LiCoO2 as the positive electrode active material and aluminum foil as the current collector, and a negative electrode film was prepared by mixing graphite powder, active material powder, and binder at a design value of 450 mAh/g discharge capacity.
• a non-aqueous electrolyte solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol/L in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1/1 was used as the non-aqueous electrolyte, and a laminated lithium ion secondary battery was prepared using a polyethylene microporous film having a thickness of 30 ⁇ m as the separator.
• the laminated lithium ion secondary battery was charged at a constant current of 1.2 mA (0.25c based on the positive electrode) at room temperature until the voltage of the test cell reached 4.2 V, and after reaching 4.2 V, the current was reduced to keep the cell voltage at 4.2 V and charging was performed, and the discharge capacity was obtained.
• the capacity retention rate after 300 cycles at room temperature was 89%.
• Example 2 Polysiloxane resin (CERANATE SSA-934: manufactured by DIC Corporation) and phenolic resin (SUMILITE RESIN: PR-53570, manufactured by Sumitomo Bakelite Co., Ltd.) were thoroughly mixed in a stirrer in a resin solid matter composition ratio (5:5), and mixed with the silicon slurry so that the silicon element content after high-temperature firing was 50% to produce a mixed and dried product.
• the procedure was the same as in Example 1, except that when the Li source was added, the amount of Li 2 O added was 0.05 equivalents relative to the silicon particles.
• Example 3 The same procedure as in Example 2 was repeated except that the amount of Li 2 O added was 0.2 equivalents relative to the silicon particles.
• Example 4 The same procedure as in Example 1 was carried out except that the amount of Li 2 O added was 0.1 equivalent relative to the silicon particles and the firing temperature was 800° C./hour.
• Example 5 The same procedure as in Example 2 was repeated except that Li 2 O was changed to Li 2 CO 3 , the amount added was 1.0 equivalent relative to the silicon particles, and the firing temperature was 800° C./4 h.
• Example 6 The same procedure as in Example 2 was carried out except that the amount of Li 2 O added was 0.07 equivalent relative to the silicon particles and the firing temperature was 800° C./hour.
• Example 7 The same procedure as in Example 2 was repeated except that the amount of Li 2 O added was 0.25 equivalents relative to the silicon particles and the firing temperature was 800° C. for 6 hours.
• Example 8 The same procedure as in Example 2 was carried out except that the amount of Li 2 O added was 0.3 equivalents relative to the silicon particles and the firing temperature was 800° C./4 hours.
• Example 9 The black fired product was ground in a planetary ball mill at 220 rpm for 10 minutes, and the procedure was the same as in Example 2 except that the amount of Li 2 O added was 0.5 equivalents relative to the silicon particles and the firing temperature was 800° C./6 hours.
• Example 10 The same procedures as in Example 2 were carried out except that the amount of Li 2 O added was 0.4 equivalents relative to the silicon particles and the firing temperature was other than 700° C./6 hours.
• Example 11 The same procedure as in Example 2 was repeated except that the amount of Li 2 O added was 0.5 equivalents relative to the silicon particles and the firing temperature was 900° C./2 hours.
• Example 12 The same procedure as in Example 2 was repeated except that the amount of Li 2 O added was 0.1 equivalent relative to the silicon particles and the firing temperature was 800° C./24 hours.
• Example 13 The same procedure as in Example 2 was repeated, except that Li 2 O was changed to Na 2 CO 3 in an amount of 0.5 equivalents relative to the silicon particles.
• Example 14 The same procedure as in Example 2 was repeated, except that Li 2 O was changed to K 2 CO 3 in an amount of 0.5 equivalents relative to the silicon particles.
• Comparative Example 1 The same procedure as in Example 2 was carried out except that Li 2 O was not added.
• Comparative Example 2 The same procedure as in Example 2 was repeated except that no polysiloxane resin or phenolic resin was used, the amount of Li 2 O added was 0.1 equivalent relative to the silicon particles, and the firing temperature was 800° C./2 hours.
• Comparative Example 3 The same procedure as in Example 2 was repeated except that no silicon particles were used and the amount of Li 2 O added was 0.3 equivalents relative to the material after firing at 1100° C. for 6 hours.
• Comparative Example 4 The same procedure as in Example 2 was repeated except that Li 2 O was changed to Fe 2 O 3 , the amount of Fe 2 O 3 added was 0.1 equivalent relative to the silicon particles, and the firing temperature was 800° C./2 h.

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