Classifications

• • 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
  • H01M4/386—Silicon or alloys based on silicon
• • 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
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
• • 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
  • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • 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
  • H01M4/362—Composites
  • H01M4/364—Composites as mixtures
• • 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
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • 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
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • 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
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • 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
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • 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
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • 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
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2220/00—Batteries for particular applications
  • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
• • 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 disclosure relates to a negative electrode material for a secondary battery, a secondary battery, and a method for manufacturing the negative electrode material for a secondary battery.
• Nonaqueous electrolyte secondary batteries especially lithium ion secondary batteries, have high voltage and high energy density, and are therefore expected to be used as power sources for small consumer applications, power storage devices, and electric vehicles.
• batteries are required to have higher energy densities, there are expectations for the use of silicon (Si)-containing materials that can be alloyed with lithium as negative electrode active materials with high theoretical capacity densities.
• Patent Document 1 discloses that after impregnating a porous resin with one or more organosilicon compounds selected from crosslinkable silanes and siloxanes and forming a crosslinked product of the organosilicon compound in the porous resin, A porous amorphous material that is heated and reacted in a non-oxidizing gas at a temperature of 650 to 1350°C to obtain an amorphous material that contains silicon, carbon, and oxygen as constituent elements and has oxidation resistance.
• the amorphous material obtained by the manufacturing method of Patent Document 1 has a large irreversible capacity.
• one aspect of the present disclosure includes a composite material including an amorphous material phase and a silicate phase, wherein the silicate phase is dispersed within the amorphous material phase, and the silicate phase is dispersed within the amorphous material phase.
• the element M is at least one selected from the group consisting of Li, Na, K, Mg, Ca, B and Al. , relating to negative electrode materials for secondary batteries.
• Another aspect of the present disclosure relates to a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, the negative electrode containing the above negative electrode material for a secondary battery.
• Yet another aspect of the present disclosure provides a raw material mixture containing a first polymer that is an organosilicon polymer containing Si, O, and C, a material constituting an active phase that reacts with Li, and a compound containing element M. and firing the raw material mixture to produce a composite material, the composite material including an amorphous material phase, the active phase, and a silicate phase, the active phase and the silicate phase.
• Each silicate phase is dispersed within the amorphous material phase, the amorphous material phase includes Si, O, and C, and the silicate phase and the amorphous material phase each independently contain the elements.
• the present invention relates to a method for producing a negative electrode material for a secondary battery, wherein the element M is at least one selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al.
• the irreversible capacity of a negative electrode material for a secondary battery can be reduced.
• FIG. 1 is a cross-sectional SEM image showing an example of a composite material included in a negative electrode material according to an embodiment of the present disclosure.
• FIG. 1 is a cross-sectional view schematically showing an example of a negative electrode material according to an embodiment of the present disclosure.
• FIG. 1 is a partially cutaway schematic perspective view of a secondary battery according to an embodiment of the present disclosure.
• a negative electrode material for a secondary battery includes a composite material including an amorphous material phase and a silicate phase.
• the form of the composite material is not particularly limited, but it may be supplied in a bulk state, a sheet state, a powder containing a plurality of particles, or the like.
• the particles of the composite material will also be referred to as "composite particles.”
• the silicate phase is dispersed within the amorphous material phase containing Si, O and C.
• the silicate phase contains element M (cationic species).
• Element M is at least one selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al.
• the silicate phase is composed of silicates. Silicates are compounds containing elemental silicon (Si) and anions.
• silicate phase containing an element M with a small irreversible capacity in the amorphous material phase By including a silicate phase containing an element M with a small irreversible capacity in the amorphous material phase and replacing a part of the amorphous material with the silicate phase, it is possible to reduce the large irreversible capacity due to the amorphous material phase. can. By dispersing the silicate phase containing element M in the amorphous material phase, the effect of reducing irreversible capacity can be stably obtained.
• the composite material preferably contains an active phase that reacts with Li.
• the active phase is dispersed within the amorphous material phase together with the silicate phase.
• a high initial capacity is obtained, charge and discharge efficiency is improved, and excellent charge and discharge cycle characteristics are obtained.
• the amorphous material phase and the silicate phase are formed of a material that has a lower capacity per unit mass (mAh/g) than the active phase.
• the amorphous material phase and the silicate phase have a smaller volume change than the active phase due to charging and discharging, or no volume change.
• the amorphous material phase with the silicate phase dispersed therein relieves stress due to expansion and contraction of the active phase. By dispersing the active phase within the amorphous material phase, side reactions between the active phase and the electrolyte are suppressed.
• the composite material may have a sea-island structure.
• the silicate phase (or silicate phase and active phase) constitutes the island portion and the amorphous material phase constitutes the continuous sea portion or matrix.
• the composite material is a powder, a plurality of island portions are dispersed in a sea portion within one particle of the composite material. It is desirable that the island portion be buried in the sea. In some island portions, at least a portion of the surface of the island portion may be exposed without being covered by the sea portion.
• the amorphous material phase includes Si (silicon), O (oxygen) and C (carbon).
• the amorphous material phase forms a compound in which Si, O, and C are randomly bonded by covalent bonds.
• the amorphous material phase has, for example, Si--O--C bonds (covalent bonds). That is, the amorphous material phase is not a simple mixture or a simple composite of multiple types of compounds (SiO, SiC, etc.).
• An amorphous material phase is a phase in which the crystal structure is not specified.
• the amorphous material phase may form a single phase without interfaces between different materials, such as composites of two or more materials have.
• the amorphous material phase contains Si, O, and C as essential components and has an unspecified crystal structure, which increases the hardness of the composite material and provides elasticity that relieves stress caused by expansion and contraction of the active phase. Or you can become more flexible.
• the amorphous material phase have no substantial grain boundaries in the cross-section of the composite material. Since the amorphous material phase has a continuous structure with virtually no grain boundaries, the hardness of the composite material is increased, and the phenomenon of electrolyte seeping into grain boundaries is reduced, reducing the side effects associated with decomposition of the electrolyte. Reactions are suppressed and the material is less susceptible to deterioration. In this case, the composite material may be formed as primary particles. However, the amorphous material phase may have some grain boundaries. The state in which the amorphous material phase has substantially no grain boundaries can be confirmed in a cross-sectional SEM image of the composite material.
• amorphous material phase In a cross-sectional SEM image of a composite material when the field of view is 500 nm2 , if the total length of grain boundaries in the amorphous material phase is 1 nm or less, the amorphous material phase is considered to have substantially no grain boundaries. I can say that. It is desirable to perform similar measurements on any ten composite particles and average the measured values to determine the grain boundary length.
• the amorphous material phase preferably contains an element M (at least one element selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al).
• the amorphous material phase and the silicate phase may contain the same type of element M, or may contain different types of element M from each other. Among these, it is more preferable that the amorphous material phase contains at least Li as the element M.
• the element M included in the amorphous material phase is an element other than Li
• the element other than Li is replaced with Li during charging and discharging of a lithium ion secondary battery equipped with a negative electrode containing a composite material, and the amorphous material phase Li ions may be irreversibly trapped, thereby reducing capacity.
• element M contains Li
• the above-mentioned capacity decrease can be suppressed.
• the amorphous material phase is represented by the general formula (1): M a SiO x N y C z , the general formula (1) is, for example, 0 ⁇ a ⁇ 4, 0.1 ⁇ x ⁇ 2.5, 0 ⁇ y ⁇ 0.5 and 0 ⁇ 1-0.5x-0.75y ⁇ z ⁇ 6.
• M is at least one selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al.
• Such a composition is a composition determined empirically from the composition of an amorphous material phase produced by the production method described below. Li can be trapped as irreversible capacitance during charging and discharging.
• the amorphous material phase contains element M. It is preferable that the amorphous material phase is doped with the element M (for example, Li) during production of the composite material (before the first charge). That is, in general formula (1), it is preferable to satisfy 0 ⁇ a ⁇ 4. Further, a in general formula (1) is more preferably 0.1 or more, and even more preferably 1 or more. Further, from the viewpoint that when M is Li, elution of the amorphous material phase into water is easily suppressed, a in general formula (1) may be 2 or less.
• the range of z indicating the atomic ratio of C to Si may be 0.1 ⁇ z ⁇ 6, 0.5 ⁇ z ⁇ 4, or 0.5 ⁇ z ⁇ 3 may be satisfied.
• M is preferably Li.
• the composition of the amorphous material phase can be analyzed by scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analysis.
• SEM-EDX analysis a cross section of the composite material is observed using SEM, and elemental mapping analysis is performed using EDX.
• the observation magnification is preferably 2,000 to 20,000 times. It is desirable that the mapping analysis be performed on a region 1 ⁇ m or more inside from the peripheral edge of the cross section of the particle of the composite material.
• the content ratio (ie, composition) of elements can be calculated using image analysis software.
• the composition may be determined by performing similar measurements on any 10 particles and averaging the measured values.
• the cross section of the particles of the composite material may be formed, for example, by filling the composite material in a thermosetting resin and curing it and using a cross section polisher (CP), or by disassembling the battery and taking out the negative electrode. may be formed on the cross section of the negative electrode by immersing it in a thermosetting resin and curing it.
• CP cross section polisher
• Desirable measurement conditions for cross-sectional SEM-EDX analysis are shown below.
• Processing equipment JEOL Ltd., IB-19520CCP (cross section polisher) Processing conditions: Acceleration voltage 6kV Current value: 150-180 ⁇ A Vacuum degree: 5 ⁇ 10 -4 ⁇ 2 ⁇ 10 -3 Pa
• C1s peaks contained in the amorphous material phase are observed.
• C1s peaks attributed to Si--C bonds, Si--O--C bonds, C--O bonds, CC bonds, etc. are observed.
• the presence of such a peak indicates that the amorphous material phase contains significant amounts of non-oxide regions.
• the C1s peak attributed to the CC bond is a characteristic peak of the composite material according to the present disclosure, and indicates that the amorphous material phase includes a region composed of carbon.
• a peak derived from the CC bond is observed, for example, around 284.8 eV.
• the ratio of the peak area Sx derived from the CC bond to the total area St of all C1s peaks is, for example, 2% or more, may be 3% or more, or may be 5% or more. Further, the ratio of Sx to St is, for example, 90% or less, may be 70% or less, or may be 20% or less. The ratio of Sx to St may be 2% or more and 90% or less, or 2% or more and 20% or less.
• the ratio of the sum of the peak area Sy originating from the C--Si bond and the peak area Sz originating from the C-O-Si bond to the total area St may be 50% or more, 60% or more, and 70% or more. It may be % or more.
• powder of the composite material is used as a sample, and analysis is performed from the sample surface along the depth direction of the composite material (10 to 100 nm) to analyze the internal state of the composite material.
• Measuring device ULVAC-PHI, PHI5000 X-ray used: Monochrome Al-K ⁇ , 25W, 15kV Vacuum degree: 5 ⁇ 10 -7 Pa
• a peak derived from the C--C bond characteristic of the composite material according to the present disclosure is observed.
• the peak area Sv of 9 ppm or more and 30 ppm or less of the spectrum obtained by 13C-NMR measurement of the composite material may be, for example, 10% or more and 90% or less of the area of the entire spectrum.
• the silicate phase contains at least one element M selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al. Among these, it is preferable that the silicate phase contains at least Li as the element M.
• the element M contained in the silicate phase is an element other than Li
• the element other than Li is replaced with Li during charging and discharging of a lithium ion secondary battery equipped with a negative electrode containing a composite material, and Li ions are added to the silicate phase. It may become irreversibly trapped, thereby reducing capacity.
• element M contains Li, the above-mentioned capacity decrease can be suppressed.
• the silicate phase is composed of, for example, elements M, Si, and O.
• the silicate phase may contain at least one member selected from the group consisting of Li 4 SiO 4 , Li 2 SiO 3 and Li 2 Si 2 O 5 .
• the silicate phase preferably contains Li 2 Si 2 O 5 from the viewpoint of reducing the irreversible capacity of the silicate phase and suppressing elution of the amorphous material phase into water.
• the average particle diameter of the silicate phase may be 10 nm or more and 100 ⁇ m or less, or 100 nm or more and 10 ⁇ m or less.
• Particulate is a state in which each silicate phase (or island portion) has the form of a particle.
• the shape of the particles is not particularly limited, but the ratio of the maximum diameter A of the particles to the maximum width B in the direction perpendicular to the maximum diameter: A/B may be, for example, 1 or more and 20 or less; It may be 10 or less, 1 or more and 5 or less, 1 or more and 3 or less.
• A/B may be determined as the average value of 10 arbitrary silicate phases (or island portions) having the form of particles. The smaller the average particle diameter of the silicate phase is, the more advantageous it is in terms of relieving stress due to expansion and contraction during charging and discharging.
• the average particle diameter of the silicate phase is measured using a cross-sectional image of the composite material obtained by SEM.
• the average particle diameter of the silicate phase is determined by averaging the maximum diameters of any 100 silicate phases.
• the composite material may have voids inside the amorphous material phase.
• the silicate phase may be exposed on the inner wall surface of the void.
• the presence of voids tends to relieve stress caused by expansion and contraction of the active phase.
• voids are likely to be formed in the vicinity of the silicate phase, and voids are likely to be formed so that the silicate phase is exposed on the inner wall surface. Exposure of the active phase to the inner wall surface of the void can be reduced to the extent that the silicate phase is exposed on the inner wall surface of the void. In the case of voids that are not completely encapsulated in the composite material (communicating with the outside of the composite material), exposure of the active phase that can come into contact with the electrolyte can be reduced.
• FIG. 1 is a cross-sectional SEM image (backscattered electron image) showing an example of a composite material included in a negative electrode material according to an embodiment of the present disclosure.
• FIG. 1 shows a cross section of composite particles included in negative electrode material A1 of Example 1, which will be described later.
• portions a, b, and c are an amorphous material phase, a silicate phase, and voids, respectively.
• the silicate phase b is exposed on the inner wall surface of the gap c.
• the composite particles shown in FIG. 1 do not include an active phase, the composite particles may further include an active phase dispersed within the amorphous material phase.
• the composition of the silicate phase can be determined by the above SEM-EDX analysis. Since the silicate phase has relatively high crystallinity, the composition of the silicate phase may be confirmed by an X-ray diffraction (XRD) method.
• XRD X-ray diffraction
• the active phase may be made of a material that can electrochemically undergo a reversible reaction with Li during charging and discharging.
• the material constituting the active phase includes, for example, at least one selected from the group consisting of metals and intermetallic compounds.
• the material constituting the active phase may be a silicon compound such as silicon carbide, or a composite oxide such as a lithium titanium composite oxide.
• the active phase may be used alone or in combination of two or more.
• the metal may be at least one selected from the group consisting of Si, Sn, Ti, Al, and Mg. Among them, Si and Sn have a high capacity, and Si is particularly preferable because it is inexpensive.
• the intermetallic compound is CrSi 2 , MnSi 2 , FeSi 2 , CoSi 2 , NiSi 2 , LiNiSn, and M x Si (M is Li, Na, K, Mg , Ca, B, and Al, and satisfies 0 ⁇ x ⁇ 5).
• the above-mentioned intermetallic compound may contain element M derived from a compound containing element M used during production of the composite material.
• Element M derived from a compound containing element M may be doped into the active phase during the preparation process of the composite material.
• the above-mentioned M x Si may be formed as an intermetallic compound.
• the content of the active phase in the composite material can be controlled as appropriate. From the viewpoint of increasing capacity, it is desirable that the content of the active phase in the composite material be as high as possible. On the other hand, from the viewpoint of alleviating stress caused by expansion and contraction of the active phase and suppressing side reactions between the active phase and the electrolyte, the composite material needs to contain a certain amount of amorphous material phase.
• the content of the active phase in the composite material is, for example, 20% by mass or more and 95% by mass or less, and may be 35% by mass or more and 75% by mass or less.
• the content of the Si phase contained in the composite material can be measured by Si-NMR.
• the average particle diameter of the active phase may be 1 nm or more and 1000 nm or less.
• Particulate is a state in which each active phase (or island portion) has the form of a particle.
• the shape of the particles is not particularly limited, but the ratio of the maximum diameter A of the particles to the maximum width B in the direction perpendicular to the maximum diameter: A/B may be, for example, 1 or more and 20 or less, and 1 or more and 10 or less. It may be 1 or more and 5 or less, or 1 or more and 3 or less.
• A/B may be determined as the average value of 10 arbitrary active phases (or island portions) having the form of particles.
• the average particle diameter of the active phase may be 200 nm or less, 100 nm or less, or 50 nm or less.
• the average particle diameter of the active phase is measured using a cross-sectional image of the composite material obtained by SEM.
• the average particle diameter of the active phase is determined by averaging the maximum diameters of any 100 active phases.
• the negative electrode material may include at least one carbon material selected from the group consisting of graphite (natural graphite, artificial graphite), hard carbon, and soft carbon.
• the carbon material may be composited with an amorphous material phase.
• a silicate phase (or a silicate phase and an active phase) may be dispersed in a composite material of a carbon material and an amorphous material phase.
• the proportion of the carbon material in the total of the composite material and the carbon material may be, for example, 70% by mass or more and 99% by mass or less, 85% by mass or more and 95% by mass or less, and 90% by mass or more and 95% by mass. It may be less than %. This makes it easier to achieve both higher capacity and better cycle characteristics.
• the negative electrode material may include a conductive layer covering the surface of the composite material.
• the conductive layer may include a carbon material having conductivity.
• the thickness of the conductive layer is preferably so thin that it does not substantially affect the average particle size of the composite particles.
• the thickness of the conductive layer is, for example, 1 nm or more and 10 nm or less.
• the conductive layer is formed by mixing the raw material of the conductive carbon material and the composite material, and firing the mixture to carbonize the raw material of the conductive carbon material.
• a raw material for the conductive material for example, coal pitch or coal tar pitch, petroleum pitch, phenol resin, etc. can be used.
• the mixture of the raw material of the conductive carbon material and the composite material is fired, for example, in an inert atmosphere (for example, an atmosphere of argon, nitrogen, etc.).
• the firing temperature is, for example, 450°C or higher and 1000°C or lower.
• the firing time is, for example, 1 hour or more and 10 hours or less.
• FIG. 2 is a cross-sectional view schematically showing an example of a negative electrode material according to an embodiment of the present disclosure.
• the negative electrode material 20 includes composite particles 21 and a conductive layer 25 covering the surfaces of the composite particles 21.
• Composite particle 21 includes an amorphous material phase 22, an active phase 23, and a silicate phase 24.
• the composite particles 21 have a sea-island structure in which an active phase 23 and a silicate phase 24 are dispersed in a matrix of an amorphous material phase 22 .
• voids 26 may be formed within the amorphous material phase 22.
• the silicate phase 24 may be exposed on the inner wall surface of the void 26.
• a method for producing a negative electrode material for a secondary battery comprising a composite material in which a silicate phase and an active phase are dispersed in an amorphous material phase includes, for example, the following first step and second step.
• the first step is a step of obtaining a raw material mixture containing the first polymer, a material constituting the active phase that reacts with Li, and a compound containing element M.
• the first polymer is a source of an amorphous material phase containing Si, O and C, and contains Si, O and C. Further, a part of the first polymer (Si, O) is used together with a compound containing element M to form a silicate phase.
• the first polymer may be an organosilicon polymer.
• the organosilicon polymer those used as ceramic precursor polymers can be used. Ceramic precursor polymers can produce ceramics by controlling firing conditions. Many organosilicon polymers have thermoplastic properties and become liquid when heated in the subsequent second step.
• the organosilicon polymer may be a polymer that is liquid at room temperature (25°C to 35°C). By using the first polymer that is liquid at room temperature or when heated, an amorphous material phase having substantially no grain boundaries can be generated, and a composite material with high particle fracture strength can be obtained.
• Organosilicon polymers are generally soluble in organic solvents and easy to handle.
• the organosilicon polymer may be used in a mixed state with an organic solvent in order to obtain a uniform raw material mixture. Most of the organic solvent evaporates during the second step of baking.
• the organosilicon polymer When the organosilicon polymer is solid at room temperature, the organosilicon polymer may be dissolved in an organic solvent.
• an organosilicon polymer (or a mixture of an organosilicon polymer and an organic solvent) that is liquid at room temperature has a kinematic viscosity of 0.1 mm 2 /s or more at 25°C, for example. It is 500 mm 2 /s or less.
• polysiloxane, polycarbosilane, polysilazane, polyorganoborosilazane, polymetalloxane, polyborosiloxane, polycarbosilazane, etc. can be used. These may be used alone or in combination of two or more. For example, at least one selected from the group consisting of polysiloxane, polycarbosilane, and polysilazane may be used.
• Polysiloxane is a polymer compound with a basic skeleton of Si--O bonds.
• Polycarbosilane is a polymer compound having a basic skeleton of Si--C bonds.
• Polysilazane is a polymer compound having a basic skeleton of Si--N bonds.
• the molecules of these polymer compounds may be linear, branched, or three-dimensional network-like.
• Examples of the polysiloxane include silicone resin and silicone oil.
• the silicone resin for example, the product name "KR-112" manufactured by Shin-Etsu Chemical Co., Ltd. can be used.
• the polysiloxane has the formula (2):
• polycarbosilane has the formula (3):
• polysilazane has the formula (4):
• These first polymers may produce an amorphous material phase of general formula (1).
• R 1 and R 2 are each independently, for example, a hydrogen atom or an organic group having 1 to 8 carbon atoms.
• the organic group includes a hydrocarbon group having a substituent (or functional group), a hydrocarbon group having no substituent (or functional group), and the like.
• the functional group may be a hydroxyl group, a cyano group, an amino group, etc., but is not particularly limited.
• the hydrocarbon group may be, for example, an alkyl group, a vinyl group, an alkoxy group, an aryl group, an aryloxy group, a ketone group, a carboxyl group, an ester group, or the like.
• the plurality of repeating units of the first polymer may have the same structure or different structures. That is, in the plurality of repeating units of the first polymer, R 1 and R 2 may be the same or different.
• Examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, pentyl group, and hexyl group.
• Examples of the aryl group include a phenyl group, a benzyl group, and a tolyl group.
• Examples of the aryloxy group include a phenoxy group.
• Examples of the alkoxy group include oxyalkyl groups having 1 to 8 carbon atoms.
• Examples of the ester group include a condensed group of an alcohol having 1 to 8 carbon atoms and a carboxylic acid having 1 to 8 carbon atoms.
• R 1 and R 2 can each independently be a phenyl group, a methyl group, an ethyl group, or the like.
• the weight average molecular weight (Mw) of the first polymer may be, for example, 1000 or more and 100000 or less, 1000 or more and 10000 or less, or 2000 or more and 10000 or less.
• particles constituting the active phase As the material constituting the active phase, particles of the materials described above (hereinafter also referred to as "active particles") can be used.
• the active particles may be nanoparticles.
• the average particle diameter of the active particles may be 1 nm or more and 1000 nm or less, 200 nm or less, 100 nm or less, or 50 nm or less.
• active particles for example, silicon nanoparticles may be used.
• the average particle diameter of the active particles is measured using a cross-sectional image of the composite material obtained by SEM.
• the average particle diameter of the active particles is determined by averaging the maximum diameter of 100 arbitrary active particles.
• the amount of the material constituting the active phase relative to 100 parts by mass of the first polymer may be set as appropriate depending on the desired ratio of the active phase of the composite material, but for example, 20 parts by mass or more, 250 parts by mass. or less, and may be 50 parts by mass or more and 200 parts by mass or less.
• Element M is at least one selected from the group consisting of Li, Na, K, Mg, Ca, B, and Al.
• the compound containing element M preferably contains at least Li as element M.
• a composite material can be produced in which the amorphous material phase and the silicate phase each contain at least Li as the element M.
• the compound containing element M contributes to the formation of a silicate phase containing element M and doping of element M into the amorphous material phase.
• a silicate phase containing element M is formed using particles of a compound containing element M as nuclei.
• Si in the silicate phase is supplied from the first polymer surrounding particles of the compound containing element M.
• the anionic species (eg O) of the silicate phase is provided by the compound containing the element M and/or the first polymer.
• a part of the element M is also supplied into the amorphous material phase formed by firing.
• Examples of compounds containing element M include salts formed from an anion of carbonic acid or carboxylic acid (formic acid, acetic acid, benzoic acid, etc.) and a cation of element M.
• the compound containing element M is, for example, at least one selected from the group consisting of lithium carbonate, lithium formate, lithium acetate, and lithium benzoate.
• the compound containing element M is preferably lithium carbonate.
• the compound containing element M is preferably lithium carbonate.
• CO 2 gas is generated as the lithium carbonate decomposes during firing in the second step, resulting in the formation of voids within the amorphous material phase.
• voids are likely to be formed near the silicate phase. Voids are likely to be formed so that the silicate phase is exposed on the inner wall surface.
• the compound containing element M may be used in the form of powder (particles).
• the maximum diameter of the particles of the compound containing element M is, for example, in the range of 0.01 ⁇ m or more and 100 ⁇ m or less.
• the blending ratio of the first polymer and the compound containing element M may be adjusted as appropriate depending on the proportion of the silicate phase to be dispersed within the amorphous material phase.
• the molar ratio of element M derived from the compound containing element M to Si derived from the first polymer: M/Si may be 0.01 or more and 5 or less, 0.1 or more, It may be 2 or less.
• the second step is a step of firing the raw material mixture to produce a composite material.
• the composite material includes an amorphous material phase, an active phase, and a silicate phase.
• the active phase and the silicate phase are each dispersed within the amorphous material phase.
• the amorphous material phase includes Si, O and C.
• the silicate phase and the amorphous material phase each independently contain the element M.
• the raw material mixture containing the first polymer, the material constituting the active phase, and the compound containing element M is in the form of a paste (or slurry) that is fluid at room temperature, or at least during heating for firing. It goes through a state of fluidity. As a result, during the second firing step, most of the surfaces of the material constituting the active phase and the compound containing element M are covered with the first polymer having fluidity. It is desirable to use a raw material mixture in such a state in order to obtain a dense composite material in the second step.
• a silicate phase containing element M By including a compound containing element M in the raw material mixture, a silicate phase containing element M can be formed, and the amorphous material phase can be doped with element M. Thereby, a composite material with a small irreversible capacity can be obtained.
• the raw material mixture can be fired, for example, at a temperature of 600°C or higher and 1000°C or lower in an inert atmosphere.
• the inert atmosphere may be a reduced pressure atmosphere or may be under the flow of an inert gas.
• Argon, nitrogen, helium, etc. can be used as the inert gas.
• the firing time may be any time as long as the carbon atoms contained in the first polymer are sufficiently carbonized.
• the composite material obtained after firing is a solid with no fluidity. By pulverizing the composite material, a composite material in a powder state is generated.
• the raw material mixture may contain a second polymer that carbonizes together with the carbon atoms in the first polymer when the raw material mixture is fired.
• the second polymer may be included in the mixture as at least one raw material selected from the group consisting of graphite (natural graphite, artificial graphite), hard carbon, and soft carbon.
• the second polymer is not particularly limited, but is preferably a material that has excellent compatibility with the first polymer.
• the second polymer may be, for example, at least one selected from the group consisting of polyvinyl resin, polyimide resin, polyacrylonitrile, acrylic resin, and polyolefin resin.
• a secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte.
• the negative electrode contains the above negative electrode material for secondary batteries.
• the negative electrode includes, for example, a sheet-like negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.
• the negative electrode mixture layer is a negative electrode mixture formed in the form of a layer or a coating.
• the negative electrode mixture contains a negative electrode active material as an essential component, and can contain a binder, a conductive aid, a thickener, etc. as optional components.
• the negative electrode active material includes a negative electrode material for secondary batteries.
• the negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry in which the negative electrode mixture is dispersed in a dispersion medium onto the surface of the negative electrode current collector and drying it.
• the dried coating film may be rolled if necessary.
• a non-porous conductive substrate metal foil, etc.
• a porous conductive substrate meh body, net body, punched sheet, etc.
• the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.
• resin materials such as fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride (PVDF); polyolefin resins such as polyethylene and polypropylene; polyamide resins such as aramid resins; polyimide resins such as polyimide and polyamideimide; ; Acrylic resins such as polyacrylic acid, polymethyl acrylate, and ethylene-acrylic acid copolymers; Vinyl resins such as polyacrylonitrile and polyvinyl acetate; Polyvinylpyrrolidone; Polyethersulfone; Styrene-butadiene copolymer rubber (SBR) Examples include rubber-like materials such as. These may be used alone or in combination of two or more.
• PVDF polytetrafluoroethylene and polyvinylidene fluoride
• polyamide resins such as aramid resins
• polyimide resins such as polyimide and polyamideimide
• Acrylic resins such as polyacrylic acid, polymethyl acrylate
• conductive aids include carbon black such as acetylene black, carbon nanotubes (hereinafter also referred to as CNT), metal fibers, carbon fluoride, metal powders, conductive whiskers such as zinc oxide and potassium titanate, and titanium oxide.
• CNT carbon nanotubes
• metal fibers such as carbon fibers
• carbon fluoride such as aluminum oxide
• metal powders such as aluminum oxide
• conductive whiskers such as zinc oxide and potassium titanate
• titanium oxide examples include conductive metal oxides such as, organic conductive materials such as phenylene derivatives, and the like. These may be used alone or in combination of two or more.
• the positive electrode includes a positive electrode active material that can electrochemically insert and release lithium ions.
• the positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector.
• the positive electrode mixture layer can be formed by applying a positive electrode slurry in which the positive electrode mixture is dispersed in a dispersion medium onto the surface of the positive electrode current collector and drying the slurry. The dried coating film may be rolled if necessary.
• the positive electrode mixture contains a positive electrode active material as an essential component, and can contain a binder, a conductive agent, etc. as optional components.
• a lithium-containing composite oxide can be used as the positive electrode active material.
• a lithium-containing composite oxide can be used as the positive electrode active material.
• M is Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, at least one selected from the group consisting of Al, Cr, Pb, Sb, and B.
• a 0 to 1.2
• b 0 to 0.9
• c 2.0 to 2.3. Note that the a value indicating the molar ratio of lithium increases or decreases due to charging and discharging.
• binder and conductive agent those similar to those exemplified for the negative electrode can be used.
• conductive agent graphite such as natural graphite or artificial graphite may be used.
• the shape and thickness of the positive electrode current collector can be selected from a shape and range similar to those of the negative electrode current collector.
• Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, titanium, and the like.
• the electrolyte has lithium ion conductivity.
• the electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.
• the solid electrolyte for example, a solid or gel polymer electrolyte, an inorganic solid electrolyte, etc.
• an inorganic solid electrolyte materials known for use in all-solid lithium ion secondary batteries and the like (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used.
• the polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a nonaqueous solvent, a lithium salt, and a matrix polymer.
• the matrix polymer for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, and the like.
• the electrolytic solution includes a solvent and an electrolyte salt.
• a solvent a non-aqueous solvent can be used, and water may also be used.
• the electrolyte salt contains at least a lithium salt.
• the concentration of the lithium salt in the electrolytic solution is preferably, for example, 0.5 mol/L or more and 2 mol/L or less. By controlling the lithium salt concentration within the above range, an electrolytic solution having excellent ionic conductivity and appropriate viscosity can be obtained.
• the lithium salt concentration is not limited to the above.
• a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester, a chain carboxylic ester, etc. are used.
• the cyclic carbonate ester include propylene carbonate (PC), ethylene carbonate (EC), and the like.
• chain carbonate esters include diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), and the like.
• Examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
• chain carboxylic acid ester examples include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and the like.
• the non-aqueous solvents may be used alone or in combination of two or more.
• lithium salts examples include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiB 10 Cl 10 , lower aliphatic carboxylic acid lithium, LiCl , LiBr, LiI, borates, imide salts, and the like.
• One type of lithium salt may be used alone, or two or more types may be used in combination.
• the electrolytic solution may further contain additives.
• additives include vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethyl carbonate (VEC), and the like.
• separator usually, it is desirable to interpose a separator between the positive electrode and the negative electrode.
• the separator has ion permeability and insulation properties.
• a microporous thin film, woven fabric, nonwoven fabric, etc. can be used.
• polyolefins such as polypropylene and polyethylene are preferred.
• An example of the structure of a secondary battery is a structure in which an electrode group in which a positive electrode and a negative electrode are wound with a separator in between and an electrolyte are housed in an exterior body.
• a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may be applied.
• the secondary battery may have, for example, a cylindrical shape, a square shape, a coin shape, a button shape, a sheet shape, or the like.
• the battery includes a rectangular battery case 4 with a bottom, an electrode group 1 and an electrolyte (not shown) housed in the battery case 4.
• the electrode group 1 includes a strip-shaped negative electrode, a strip-shaped positive electrode, and a separator interposed between them.
• the negative electrode current collector of the negative electrode is electrically connected to a negative electrode terminal 6 provided on the sealing plate 5 via the negative electrode lead 3 .
• the negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7.
• the positive current collector of the positive electrode is electrically connected to the back surface of the sealing plate 5 via the positive electrode lead 2 . That is, the positive electrode is electrically connected to the battery case 4 which also serves as a positive electrode terminal.
• the peripheral edge of the sealing plate 5 fits into the open end of the battery case 4, and the fitting portion is laser welded.
• the sealing plate 5 has an electrolyte injection hole, which is closed with a sealing plug 8 after injection.
• the silicate phase contains at least one selected from the group consisting of Li 4 SiO 4 , Li 2 SiO 3 and Li 2 Si 2 O 5 Negative electrode material.
• the silicate phase is particulate, The negative electrode material for a secondary battery according to any one of Techniques 1 to 6, wherein the silicate phase has an average particle diameter of 10 nm or more and 100 ⁇ m or less.
• the amorphous material phase is represented by the general formula: M a SiO x N y C z , 0 ⁇ a ⁇ 4, 0.1 ⁇ x ⁇ 2.5, 0 ⁇ y ⁇ 0.5, and A negative electrode material for a secondary battery according to technology 3, which satisfies 0 ⁇ 1-0.5x-0.75y ⁇ z ⁇ 6.
• M includes at least Li, the negative electrode material for a secondary battery according to technique 8.
• the composite material has voids inside the amorphous material phase, The negative electrode material for a secondary battery according to any one of Techniques 1 to 9, wherein the silicate phase is exposed on the inner wall surface of the void.
• the composite material further comprising a conductive layer covering the surface of the composite material, The negative electrode material for a secondary battery according to any one of Techniques 1 to 10, wherein the conductive layer includes a carbon material having conductivity.
• the composite material further includes an active phase that reacts with Li, The negative electrode material for a secondary battery according to any one of Techniques 1 to 11, wherein the active phase is dispersed within the amorphous material phase.
• the metal is at least one selected from the group consisting of Si, Sn, Ti, Al and Mg
• the intermetallic compound is selected from the group consisting of CrSi 2 , MnSi 2 , FeSi 2 , CoSi 2 , NiSi 2 , LiNiSn and M x Si (M is selected from the group consisting of Li, Na, K, Mg, Ca, B and Al).
• the active phase is particulate;
• the negative electrode material for a secondary battery according to any one of Techniques 1 to 16 further comprising at least one selected from the group consisting of graphite, hard carbon, and soft carbon.
• (Technology 18) Comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery, wherein the negative electrode includes the secondary battery negative electrode material according to any one of Techniques 1 to 17.
• (Technology 19) Obtaining a raw material mixture containing a first polymer that is an organosilicon polymer containing Si, O and C, a material constituting an active phase that reacts with Li, and a compound containing element M; firing the raw material mixture to produce a composite material,
• the composite material includes an amorphous material phase, the active phase, and a silicate phase, the active phase and the silicate phase are each dispersed within the amorphous material phase;
• the amorphous material phase includes Si, O and C,
• the silicate phase and the amorphous material phase each independently contain the element M,
• (Technology 20) The method for producing a negative electrode material for a secondary battery according to technique 19, wherein the silicate phase and the amorphous material phase each contain at least Li as the element M.
• (Technology 21) The method for producing a negative electrode material for a secondary battery according to technology 19 or 20, wherein the compound containing the element M is at least one selected from the group consisting of lithium carbonate, lithium formate, lithium acetate, and lithium benzoate.
• (Technology 22) The method for producing a negative electrode material for a secondary battery according to any one of Techniques 19 to 21, wherein the first polymer is at least one selected from the group consisting of polysiloxane, polycarbosilane, and polysilazane.
• the raw material mixture includes a second polymer that carbonizes together with the carbon atoms in the first polymer when the raw material mixture is fired.
• a method for producing a negative electrode material for secondary batteries (Technology 24) The method for producing a negative electrode material for a secondary battery according to technique 23, wherein the second polymer is at least one selected from the group consisting of polyvinyl resin, polyimide resin, polyacrylonitrile, acrylic resin, and polyolefin resin.
• Example 1 A silicone resin (solvent-containing type) was prepared as an organosilicon polymer. Specifically, the product name is "KR-112" manufactured by Shin-Etsu Chemical Co., Ltd. (contains organic solvents (toluene, xylene), non-volatile content (105°C x 3h): 70%, kinematic viscosity (25°C): 200mm 2 /s) was prepared.
• lithium carbonate (Li 2 CO 3 ) powder (the maximum diameter of particles is in the range of 1 ⁇ m or more and less than 100 ⁇ m) was prepared.
• Lithium carbonate powder was added to "KR-112" and mixed to obtain a uniform paste-like raw material mixture.
• the mixing was carried out in an air atmosphere at room temperature by stirring at 20,000 rpm for 3 minutes using a thin film rotating high speed mixer "Filmix” manufactured by Primix Co., Ltd.
• the raw material mixture was transferred to an alumina crucible and fired in a nitrogen atmosphere at 875°C for 5 hours.
• the fired product was pulverized using a mortar, and the pulverized product was passed through a sieve with an opening of 75 ⁇ m to obtain composite particles (negative electrode material A1).
• Example 2 ⁇ A composite material (anode material A2 ) was obtained.
• Test cells were prepared using the negative electrode materials of Examples 1 and 2 and Comparative Example 1 according to the following procedure, and the irreversible capacity was determined.
• a negative electrode slurry was prepared by mixing negative electrode materials, carbon nanotubes (CNT), polyacrylic acid (PAA), styrene-butadiene copolymer rubber (SBR), carboxymethyl cellulose (CMC), and an appropriate amount of water. .
• the amounts of CNT, PAA, CMC, and SBR added to 100 parts by mass of the negative electrode material were 0.5 parts by mass, 5 parts by mass, 5 parts by mass, and 5 parts by mass, respectively.
• a negative electrode slurry was applied to one side of an electrolytic copper foil serving as a current collector, punched out into a size of 2 cm x 2 cm, and then dried to form a negative electrode mixture layer. In this way, a negative electrode was obtained.
• a counter electrode was prepared by pasting a lithium metal foil on one side of an electrolytic copper foil (current collector) and punching it out into a square shape of 2.5 cm on each side.
• LiPF 6 was dissolved in a mixed solvent at a concentration of 1.3 mol/L to prepare an electrolytic solution.
• An electrode body was constructed by disposing a negative electrode and a counter electrode facing each other with a separator in between. A microporous polyolefin film was used as the separator.
• the electrode body was housed in an exterior body made of an aluminum laminate sheet, and after injecting an electrolyte, the opening of the exterior body was sealed. At this time, parts of the leads attached to the negative electrode and the counter electrode were each exposed from the exterior body. A test cell was thus obtained.
• Constant current charging was performed at 0.1C (1C is a current value that discharges the designed capacity in 1 hour) until the cell voltage reached 0.005V. The rest time thereafter was 20 minutes. Next, constant current charging was performed at 0.01C until the cell voltage reached 0.005V. The rest time thereafter was 20 minutes. Further, constant current charging was performed at 0.001C until the cell voltage reached 0.005V.
• the charge capacity and discharge capacity per unit mass of the negative electrode material were determined, and the value obtained by subtracting the discharge capacity from the charge capacity was determined as the irreversible capacity.
• the irreversible capacity was expressed as a relative value when the irreversible capacity of battery B1 of Comparative Example 1 was set to 100.
• negative electrode materials A1 and A2 the irreversible capacity was significantly reduced compared to negative electrode material B1.
• Example 3 The same silicone resin (solvent-containing type) as in Example 1 was prepared as an organosilicon polymer.
• the same lithium carbonate powder as in Example 1 was prepared as a compound containing Li.
• Silicon nanoparticles (average particle diameter: 40 nm) were prepared as a material constituting the active phase.
• Lithium carbonate powder and silicon nanoparticles were added to "KR-112" and mixed to obtain a uniform paste-like raw material mixture.
• the mixing was carried out in an air atmosphere at room temperature by stirring at 20,000 rpm for 3 minutes using a thin film rotating high speed mixer "Filmix” manufactured by Primix Co., Ltd.
• the amount of silicon nanoparticles added was 11.9 parts by mass per 100 parts by mass of "KR-112".
• the raw material mixture was transferred to an alumina crucible and fired in a nitrogen atmosphere at 875°C for 5 hours.
• the fired product was pulverized using a mortar, and the pulverized product was passed through a sieve with an opening of 75 ⁇ m to obtain composite particles (negative electrode material A3).
• the amount of silicon nanoparticles added was 11.2 parts by mass per 100 parts by mass of "KR-112". Except for the above, composite particles (negative electrode material A4) were obtained in the same manner as in Example 3.
• negative electrode materials A3 and A4 irreversible capacity was significantly reduced and charge/discharge efficiency was improved compared to negative electrode material B2.
• the negative electrode material for secondary batteries according to the present disclosure is useful for secondary batteries used as main power sources for mobile communication devices, portable electronic devices, and the like.

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