WO2023053946A1 - 二次電池 - Google Patents

二次電池 Download PDF

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WO2023053946A1
WO2023053946A1 PCT/JP2022/034229 JP2022034229W WO2023053946A1 WO 2023053946 A1 WO2023053946 A1 WO 2023053946A1 JP 2022034229 W JP2022034229 W JP 2022034229W WO 2023053946 A1 WO2023053946 A1 WO 2023053946A1
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silicon
carbon
containing material
phase
negative electrode
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French (fr)
Japanese (ja)
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陽祐 佐藤
敬太 岡崎
幸穂 奥野
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Panasonic Intellectual Property Management Co Ltd
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Panasonic Intellectual Property Management Co Ltd
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Priority to CN202280065857.4A priority Critical patent/CN118020174A/zh
Priority to EP22875817.3A priority patent/EP4411883A4/en
Priority to JP2023551283A priority patent/JPWO2023053946A1/ja
Priority to US18/695,547 priority patent/US20240405201A1/en
Publication of WO2023053946A1 publication Critical patent/WO2023053946A1/ja
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    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/38—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
    • H01M4/36—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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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 secondary batteries.
  • Silicon-containing materials such as silicon (Si) and silicon oxides are known to be able to store more lithium ions per unit volume than carbon materials such as graphite. Therefore, it has been proposed to use a silicon-containing material for the negative electrode of a lithium ion secondary battery.
  • Patent Document 1 Japanese Patent Laid-Open No. 2016-110969 discloses that "a negative electrode active material for a lithium ion secondary battery comprising Si or a Si alloy and a carbonaceous material or a carbonaceous material and graphite, wherein the negative electrode active material is A negative electrode active material for a lithium ion secondary battery, characterized by being approximately spherical composite particles having an average particle diameter (D50) of 1 to 40 ⁇ m and an average circularity of 0.7 to 1.0. disclosed.
  • D50 average particle diameter
  • one of the objects of the present disclosure is to provide a secondary battery with a high capacity retention rate in charge/discharge cycles.
  • the secondary battery includes a positive electrode and a negative electrode including a negative electrode active material, the negative electrode active material includes a carbon material and a silicon-containing material, and the average particle size of the silicon-containing material is the average particle size of the carbon material.
  • the average circularity of the silicon-containing material is smaller than the average circularity of the carbon material.
  • FIG. 1 is a cross-sectional view schematically showing a silicon-containing material according to one embodiment of the invention.
  • FIG. 1 is a schematic perspective view of a partially cutaway secondary battery according to an embodiment of the present invention
  • a secondary battery according to the present embodiment includes a positive electrode and a negative electrode containing a negative electrode active material.
  • a negative electrode active material includes a carbon material and a silicon-containing material.
  • the carbon material and the silicon-containing material may be referred to as “carbon material (C)” and “silicon-containing material (S)", respectively.
  • the carbon material (C) and silicon-containing material (S) satisfy the following conditions (1) and (2). (1) The average particle size of the silicon-containing material (S) is smaller than the average particle size of the carbon material (C). (2) The average circularity of the silicon-containing material (S) is less than the average circularity of the carbon material (C).
  • the silicon-containing material (S) may contain carbon, but the carbon material in the silicon-containing material (S) is not included in the carbon material (C), but is included in the silicon-containing material (S).
  • the silicon-containing material (S) and the carbon material (C) are each present in the negative electrode in the form of particles.
  • the circularity of the silicon-containing material (S) and the carbon material (C) in the negative electrode is measured.
  • the area of the cross section of the particle is used as S in formula (M1), and the perimeter of the cross section is used as L in formula (M1).
  • the circularity so measured is the cross-sectional circularity of the silicon-containing material (S) and the carbon material (C).
  • S (particle cross-sectional area) and L (particle cross-sectional perimeter) used in formula (M1) are obtained by the following method. First, after disassembling the battery and taking out the negative electrode, the cross section of the negative electrode is exposed. Next, the section is photographed with a scanning electron microscope to obtain an image. Energy dispersive X-ray spectroscopy (EDS) or the like is then used to distinguish between carbon and silicon-containing materials in the image. By image analysis of the particle image (particle cross section) in the image, the area of the cross section of the particle and the peripheral length of the cross section of the particle are obtained.
  • EDS Energy dispersive X-ray spectroscopy
  • the average circularity is obtained by measuring the circularity of each of 100 arbitrarily selected particles and arithmetically averaging the obtained 100 circularities. If the cross section of the particle is a perfect circle, the degree of circularity is 1. Therefore, it can be considered that the higher the degree of circularity, the closer the particle is to a true sphere.
  • the average particle size of each particle such as silicon-containing material (S) and carbon material (C) can also be similarly determined by image analysis. In that case, first, 100 arbitrary particles in the image are selected and the maximum diameter is measured. Next, 100 measured maximum diameters are arithmetically averaged, and the obtained average value is taken as the average particle diameter.
  • the median diameter (D50) at which the cumulative volume is 50% in the volume-based particle size distribution should be used as the average particle size of particles that can be separated independently (for example, particles before forming a negative electrode mixture). can be done.
  • the median diameter can be determined, for example, using a laser diffraction/scattering particle size distribution analyzer.
  • the average circularity of particles that can be separated independently can be measured by the following method. First, the particles to be measured are dispersed in resin. Next, after exposing the cross section of the resin, the cross section is photographed with a scanning electron microscope to obtain an image. Next, by image analysis of the particle image (the cross section of the particle) in the image, the area of the cross section of the particle and the peripheral length of the cross section of the particle are obtained.
  • Increasing the degree of circularity of the silicon-containing material (S) is preferable in that, for example, the rounded shape increases the bulk density and increases the packing density when used as a negative electrode.
  • the inventors of the present application have found that it is difficult to achieve high charge-discharge cycle characteristics when using only a silicon-containing material (S) with a high degree of circularity.
  • the inventors of the present application newly found that a secondary battery with high charge-discharge cycle characteristics can be obtained by satisfying the above conditions (1) and (2). Found it. The present disclosure is based on this new finding.
  • the average circularity of the carbon material (C) may be 0.7 or more or 0.8 or more, and is 1 or less.
  • the average circularity of the silicon-containing material (S) may be 0.6 or less, or 0.5 or less, 0.2 or more, 0.3 or more, or 0.4 or more.
  • the carbon material (C) has an average circularity of 0.7 or more
  • the silicon-containing material (S) has an average circularity of 0.6 or less. According to this configuration, the charge/discharge cycle characteristics are particularly good.
  • the value of (average circularity of silicon-containing material (S))/(average circularity of carbon material (C)) is 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less.
  • the lower limit of this value is not particularly limited, it may be 0.2 or more, 0.3 or more, or 0.4 or more. By setting this value to 0.60 or less, the charge/discharge cycle characteristics become particularly good.
  • the average particle size of the carbon material (C) may be 5 ⁇ m or more, or 10 ⁇ m or more, or may be 50 ⁇ m or less, or 30 ⁇ m or less.
  • the average particle size of the silicon-containing material (S) may be 1 ⁇ m or more, or 5 ⁇ m or more, and may be 20 ⁇ m or less, 15 ⁇ m or less, or 10 ⁇ m or less.
  • the carbon material (C) has an average particle size in the range of 10-30 ⁇ m and the silicon-containing material (S) has an average particle size in the range of 1-15 ⁇ m. According to this configuration, the charge/discharge cycle characteristics are particularly good.
  • the value of (average particle size of silicon-containing material (S))/(average particle size of carbon material (C)) is less than 1 and is 0.8 or less, 0.6 or less, or 0.5 or less.
  • the lower limit of this value is not particularly limited, it may be 0.05 or more, 0.1 or more, or 0.2 or more. By setting the value to 0.5 or less, the charge/discharge cycle characteristics become particularly good.
  • An example of a preferable negative electrode satisfies at least one of the following conditions (J1) to (J4).
  • (J1) and (J2) may be satisfied, and in addition to (J1) and (J2), (J3) and/or (J4) may be satisfied.
  • (J1) The carbon material (C) has an average circularity of 0.7 or more, and the silicon-containing material (S) has an average circularity of 0.6 or less.
  • (J2) The average particle size of the carbon material (C) is in the range of 10-30 ⁇ m, and the average particle size of the silicon-containing material (S) is in the range of 1-15 ⁇ m.
  • (J3) The value of (average circularity of silicon-containing material (S))/(average circularity of carbon material (C)) is 0.60 or less.
  • (J4) The value of (average particle size of silicon-containing material (S))/(average particle size of carbon material (C)) is 0.5 or less.
  • the carbon material (C) contained in the negative electrode as an active material may include at least one selected from the group consisting of graphite, soft carbon (easily graphitizable carbon), and hard carbon (non-graphitizable carbon). At least one may be used.
  • the carbon material (C) may contain at least one selected from the group consisting of graphite and hard carbon, or may be the at least one.
  • One type of the carbon material (C) may be used alone, or two or more types may be used in combination.
  • Graphite is preferable because it has excellent charge-discharge stability and low irreversible capacity.
  • the proportion of graphite in the carbon material (C) may be 50% by mass or more, or 80% by mass or more.
  • Graphite means a material with a developed graphite-type crystal structure, and generally refers to a carbon material having an average interplanar spacing d002 of (002) planes of 0.34 nm or less as measured by X-ray diffraction.
  • natural graphite, artificial graphite, graphitized mesophase carbon particles and the like are typical graphites.
  • Hard carbon is a carbon material in which fine graphite crystals are arranged in random directions and little further graphitization proceeds, and the average interplanar spacing d002 of the 002 plane is larger than 0.38 nm. Hard carbon is preferable because of its low resistance and high capacity.
  • carbon material (C) those having various average particle diameters and average circularities are commercially available, so they may be used. Alternatively, the average particle diameter and/or average circularity of the commercially available carbon material (C) may be adjusted.
  • silicon-containing material (S) examples include silicon alloys, silicon compounds, and composites.
  • the silicon-containing material (S) may be a composite material having a so-called islands-in-the-sea structure.
  • the silicon-containing material (S) may be a composite particle that includes an ion-conducting phase and a silicon phase (in one aspect, silicon particles) dispersed within the ion-conducting phase.
  • the silicon-containing material (S) (for example, the silicon-containing material (S1)) comprises a composite particle containing an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase, and at least a portion of the surface of the composite particle (in one example, and a coating layer covering the entire surface).
  • the silicon-containing material (S) may comprise a coating layer disposed over at least a portion of its surface (in one example the entire surface).
  • the ion-conducting phase is a phase that conducts ions.
  • the ion-conducting phase may be at least one selected from the group consisting of a silicate phase, a carbon phase, and a silicon oxide phase.
  • the carbon phase may be composed of amorphous carbon (amorphous carbon).
  • amorphous carbon examples include hard carbon, soft carbon, and other amorphous carbon.
  • Amorphous carbon is a carbon material in which the average interplanar spacing d002 of the (002) plane exceeds 0.34 nm as measured by X-ray diffraction.
  • a major component (eg, 95-100% by weight) of the silicon oxide phase may be silicon dioxide.
  • the composition of a composite material containing a silicon oxide phase and a silicon phase dispersed therein can be expressed as a whole by SiO x .
  • SiOx has a structure in which silicon fine particles are dispersed in amorphous SiO 2 .
  • the content ratio x of oxygen to silicon is, for example, 0.5 ⁇ x ⁇ 2.0, more preferably 0.8 ⁇ x ⁇ 1.5.
  • the silicate phase may satisfy conditions (3) and/or (4) below.
  • (3) The silicate phase contains at least one selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements of the long period periodic table).
  • the silicate phase contains the element L;
  • the element L is selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanides, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W At least one.
  • the lanthanoid is a general term for 15 elements from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.
  • examples of alkali metal elements include lithium (Li), potassium (K), and sodium (Na).
  • Examples of Group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba).
  • a silicate phase containing lithium hereinafter sometimes referred to as a “lithium silicate phase” is preferable in terms of small irreversible capacity and high initial charge/discharge efficiency.
  • Examples of the coating layer present on the surface of the silicon-containing material (S) include a conductive layer, for example a conductive layer made of a conductive carbon material.
  • a conductive layer By forming a conductive layer on the surface of the silicon-containing material (S), the conductivity of the silicon-containing material (S) can be dramatically increased.
  • a conductive material containing carbon As the conductive material forming the conductive layer, a conductive material containing carbon is preferable.
  • Examples of conductive materials containing carbon include conductive carbon materials. Examples of conductive carbon materials include carbon black, graphite, amorphous carbon with low crystallinity (amorphous carbon), and the like. Amorphous carbon is preferable in that it has a large buffering effect on the silicon phase, which changes in volume during charging and discharging.
  • the amorphous carbon may be graphitizable carbon (soft carbon) or non-graphitizable carbon (hard carbon).
  • Examples of carbon black include acetylene black, ketjen
  • the thickness of the conductive layer is preferably thin enough not to affect the average particle size of the silicon-containing material (S).
  • the thickness of the conductive layer is preferably in the range of 1 to 200 nm (for example, in the range of 5 to 100 nm) in consideration of ensuring conductivity and diffusibility of lithium ions.
  • the thickness of the conductive layer can be measured by cross-sectional observation of the silicon-containing material (S) using SEM or TEM (transmission electron microscope).
  • Lithium silicate may be an oxide phase containing Li, Si and O, and may contain other elements.
  • the atomic ratio of O to Si: O/Si in the lithium silicate phase is greater than 2 and less than 4, for example.
  • O/Si is greater than 2 and less than 3.
  • the atomic ratio of Li to Si in the lithium silicate phase: Li/Si is greater than 0 and less than 4, for example.
  • the lithium silicate phase may contain lithium silicate represented by the formula: Li 2z SiO 2+z (0 ⁇ z ⁇ 2), or may be composed of the lithium silicate.
  • the total proportion of the silicon-containing material (S) and the carbon material (C) in the negative electrode active material may be 60% by mass or more, 80% by mass or more, 90% by mass or more, or 90% by mass or more, It may be 100% by mass or less.
  • the mass Ws of the silicon-containing material (S) is 3% or more, 5% or more of the sum of the mass Wc of the carbon material (C) and the mass Ws of the silicon-containing material (S), Alternatively, it may be 10% or more, or 40% or less, 30% or less, or 20% or less.
  • the mass Ws of the silicon-containing material (S) may be in the range of 5-30% of the sum of the mass Wc of the carbon material (C) and the mass Ws of the silicon-containing material. According to this range, it is considered that the expansion and contraction of the entire negative electrode can be controlled within a more suitable range, and the advantage of high capacity due to the silicon-containing material (S) can be maximized.
  • the contents of B, Na, K and Al contained in the silicate layer are determined by quantitative analysis in accordance with, for example, JIS (Japanese Industrial Standard) R3105 (1995) (analytical method for borosilicate glass). Also, the Ca content is determined by quantitative analysis according to JIS R3101 (1995) (analysis method for soda-lime glass).
  • JIS Japanese Industrial Standard
  • R3105 Japanese Industrial Standard
  • Ca content is determined by quantitative analysis according to JIS R3101 (1995) (analysis method for soda-lime glass).
  • the content of each element contained in the silicon-containing material (S) can be measured, for example, by inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, a sample of the silicon-containing material (S) is completely dissolved in a heated acid solution, the carbon remaining in the solution is removed by filtration, and then the obtained filtrate is analyzed by ICP-AES, Measure the spectral intensity of each element. Subsequently, a calibration curve is created using a commercially available standard solution of each element, and the content of each element is calculated.
  • ICP-AES inductively coupled plasma atomic emission spectrometry
  • the silicon-containing material (S) may be removed from the battery, for example, by the following method. Specifically, the battery is disassembled, the negative electrode is taken out, and the negative electrode is washed with anhydrous ethyl methyl carbonate or dimethyl carbonate to remove the electrolyte. Next, the negative electrode mixture layer is peeled off from the negative electrode current collector and pulverized in a mortar to obtain a sample powder. Next, the sample powder is dried in a dry atmosphere for 1 hour and immersed in weakly boiled 6M hydrochloric acid for 10 minutes to remove alkali metals such as Na and Li that may be contained in the binder and the like. Next, the sample powder is washed with ion-exchanged water, filtered, and dried at 200° C. for 1 hour. In this way the silicon-containing material (S) is removed.
  • the battery is disassembled, the negative electrode is taken out, and the negative electrode is washed with anhydrous ethyl methyl carbonate or dimethyl carbonate
  • a silicate phase, a silicon oxide phase, a silicon phase, etc. may exist in the silicon-containing material (S).
  • Si-NMR silicon-containing material
  • the Si content obtained by ICP-AES as described above is the sum of the amount of Si constituting the first silicon phase, the amount of Si in the silicate phase, and the amount of Si in the silicon oxide phase.
  • the amount of Si constituting the silicon phase and the amount of Si in the silicon oxide phase can be separately quantified using Si-NMR. Therefore, by subtracting the amount of Si forming the silicon phase and the amount of Si in the silicon oxide phase from the amount of Si obtained by ICP-AES, the amount of Si in the silicate phase can be quantified.
  • a mixture or the like containing a silicate having a known Si content and a silicon phase at a predetermined ratio may be used as a standard substance necessary for quantification.
  • Si-NMR measurement conditions Desirable Si-NMR measurement conditions are shown below.
  • Measurement device Solid-state nuclear magnetic resonance spectrometer (INOVA-400) manufactured by Varian Probe: Varian 7mm CPMAS-2 MAS: 4.2kHz MAS speed: 4kHz Pulse: DD (45° pulse + signal acquisition time 1H decouple) Repeat time: 1200sec-3000sec Observation width: 100 kHz Observation center: Around -100 ppm Signal capture time: 0.05 sec Cumulative count: 560 Sample amount: 207.6 mg
  • quantification of each element in the silicon-containing material is performed by SEM-EDX analysis, Auger electron spectroscopy (AES), laser ablation ICP mass spectrometry (LA-ICP-MS), and X-ray photoelectron spectroscopy (XPS). etc. is also possible.
  • the average grain size of the silicon phase (eg, the first silicon phase and the second silicon phase) dispersed in the ion-conducting phase may be 1 nm or more, or 5 nm or more.
  • the average particle size may be 1000 nm or less, 500 nm or less, 200 nm or less, 100 nm or less, or 50 nm or less.
  • a fine silicon phase is preferable in that the volume change during charging and discharging is small and the structural stability of the silicon-containing material (S) is improved.
  • the average particle size of the silicon phase can be determined by the method for determining the average particle size of the particles described above.
  • the crystallite size of the silicon phase is preferably 30 nm or less. When the crystallite size is 30 nm or less, the amount of change in volume of the silicon-containing material (S) due to expansion and contraction of the silicon phase accompanying charging and discharging can be made smaller.
  • the crystallite size is more preferably 30 nm or less, still more preferably 20 nm or less. When the crystallite size is 20 nm or less, the expansion and contraction of the silicon phase are made uniform, the microcracks in the silicon phase are reduced, and the cycle characteristics can be further improved.
  • the crystallite size of the silicon phase is calculated by Scherrer's formula from the half width of the diffraction peak attributed to the (111) plane of the silicon phase (simple elemental Si) in the X-ray diffraction pattern.
  • silicon-containing materials (S) having a sea-island structure examples include the first silicon-containing material and the second silicon-containing material described below.
  • the first silicon-containing material and the second silicon-containing material may be referred to as “silicon-containing material (S1)” and “silicon-containing material (S2),” respectively.
  • the silicon-containing material (S1) includes a silicate phase and a silicon phase dispersed within the silicate phase (hereinafter sometimes referred to as "first silicon phase”).
  • the silicon-containing material (S2) also includes a carbon phase and a silicon phase dispersed in the carbon phase (hereinafter sometimes referred to as a "second silicon phase”).
  • the negative electrode active material may include a silicon-containing material (S1) and/or a silicon-containing material (S2), and may be a silicon-containing material (S1) and/or a silicon-containing material (S2).
  • Each of the first silicon phase and the second silicon phase can be considered silicon particles.
  • the silicon-containing material (S1) and the silicon-containing material (S2) can each exist in the form of particles having a so-called sea-island structure.
  • the first or second silicon phases (islands) are dispersed in a matrix (sea) of silicate or carbon phases and covered with a lithium ion conducting phase (silicate or carbon phase).
  • the sea-island structure limits the contact between the first or second silicon phase and the electrolyte, thereby suppressing side reactions. Also, the stress caused by the expansion and contraction of the silicon phase is relieved by the matrix of the lithium ion conductive phase.
  • the relative values of the mass A of the silicon-containing material (S1), the mass B of the silicon-containing material (S2), and the mass C of the carbon material (C) contained in the negative electrode can be obtained by cross-sectional SEM-EDX analysis. .
  • the particles (particles A) of the silicon-containing material (S1), the particles (particles B) of the silicon-containing material (S2), and the particles (particles C) of the carbon material (C) are distinguished.
  • the observation magnification is desirably 2000 to 20000 times.
  • the battery is disassembled, the negative electrode is taken out, and a cross section of the negative electrode is obtained using a cross-section polisher (CP).
  • a cross section of the negative electrode is observed using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • EDX energy dispersive X-ray
  • image analysis software uses image analysis software to calculate the total areas A to C occupied by particles A to C. The area ratio of the total areas A to C may be considered as the volume ratio of the particles A to C.
  • the analysis above and the analysis of the negative electrode described later are preferably performed using the negative electrode in a discharged state.
  • a film is formed on the surface of the silicon-containing material due to the decomposition of the electrolyte during the charging and discharging process.
  • the silicon-containing material may also have a conductive layer on its surface. Therefore, mapping analysis by EDX is performed on a region 1 ⁇ m or more inward from the peripheral edge of the cross-section of the silicon-containing material so that the measurement range does not include the film or the conductive layer.
  • SEM-EDX measurement conditions Processing equipment: SM-09010 (Cross Section Polisher) manufactured by JEOL Processing conditions: acceleration voltage 6 kV Current value: 140 ⁇ A Degree of vacuum: 1 ⁇ 10 -3 to 2 ⁇ 10 -3 Pa Measuring device: Electron microscope SU-70 manufactured by HITACHI Acceleration voltage during analysis: 10 kV Field: Free Mode Probe Current Mode: Medium Probe current range: High Anode Ap.: 3 OBJ App.: 2 Analysis area: 1 ⁇ m square Analysis software: EDAX Genesis CPS: 20500 Lsec: 50 Time constant: 3.2
  • the average particle diameter Da of the silicon-containing material (S1) may be 2 ⁇ m or more, 3 ⁇ m or more, or 5 ⁇ m or more, and may be 15 ⁇ m or less, 12 ⁇ m or less, or 10 ⁇ m or less. Within such a range, voids that may occur due to expansion and contraction of the silicon-containing material (S1) are moderately suppressed, and cracks in the silicon-containing material (S1) that may occur due to expansion and contraction are easily suppressed. it is conceivable that.
  • the average particle size Db of the silicon-containing material (S2) may be 3 ⁇ m or more, 6 ⁇ m or more, or 8 ⁇ m or more, or may be 18 ⁇ m or less, 15 ⁇ m or less, or 12 ⁇ m or less.
  • the content of the first silicon phase in the silicon-containing material (S1) may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and 80% by mass or less, or 70% by mass or less. may Within this range, not only is a sufficiently high capacity of the negative electrode achieved, but side effects due to expansion and contraction of the first silicon phase are limited, so that cycle characteristics are likely to be improved. This is because while the silicon-containing material (S1) contains a sufficient amount of the first silicon phase, the proportion of the silicate phase in the silicon-containing material (S1) does not become too small. By maintaining the ratio of the silicate phase at a certain level or more, the contact between the first silicon phase and the electrolyte is significantly restricted, and side reactions are also significantly suppressed. Also, the stress caused by the expansion and contraction of the first silicon phase is easily relieved by the matrix of the silicate phase.
  • the content of the second silicon phase in the silicon-containing material (S2) may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, and 80% by mass or less, or 70% by mass or less. may Within such a range, as in the case of the silicon-containing material (S1), a sufficiently high capacity of the negative electrode is achieved, and the cycle characteristics are likely to be improved. In addition, by maintaining a considerable proportion of the carbon phase, the carbon phase can easily enter into voids that are subsequently generated due to charging and discharging. Electrical connections are easier to maintain.
  • the method for adjusting the average particle size and average circularity of the carbon material (C) is not particularly limited, and known methods may be used. For example, a method similar to the mechanofusion method or a pulverization method may be used alone or in combination. For example, after adjusting the average particle size with a jet mill or the like, the average circularity may be adjusted using an apparatus used for mechanofusion or the like.
  • the method for adjusting the average particle size and average circularity of the silicon-containing material (S) is not particularly limited, and known methods may be used.
  • the silicon-containing material is pulverized into particles using a jet mill or the like
  • the average particle size and average circularity may be adjusted by changing conditions such as pulverization time.
  • the average circularity can be lowered by increasing the pressure during pulverization and shortening the pulverization time.
  • a raw material for lithium silicate As a raw material for lithium silicate, a raw material mixture containing a Si raw material and a Li raw material in a predetermined ratio is used.
  • the raw material mixture may contain the alkali metal element, the Group 2 element, and/or the element L described above.
  • the raw material mixture is melted, and the melt is passed through metal rolls to form flakes to produce lithium silicate.
  • the flaked silicate is crystallized by heat treatment in an air atmosphere at a temperature above the glass transition point and below the melting point. Note that the flaked silicate can also be used without being crystallized. It is also possible to produce silicate by solid-phase reaction by firing at a temperature below the melting point without melting the raw material mixture.
  • Silicon oxide can be used as the Si raw material.
  • Li raw materials that can be used include lithium carbonate, lithium oxide, lithium hydroxide, and lithium hydride. These may be used alone or in combination of two or more.
  • oxides, hydroxides, carbonate compounds, hydrides, nitrates, sulfates, and the like of each element can be used.
  • Step (ii) Next, raw material silicon is mixed with lithium silicate to form a composite.
  • a silicon-containing material (S1) that is composite particles of lithium silicate and a first silicon phase (hereinafter also referred to as silicate composite particles) is produced through the following steps (a) to (c).
  • step (a) Raw material silicon powder and lithium silicate powder are mixed at a mass ratio of, for example, 20:80 to 95:5. Coarse silicon particles having an average particle size of several ⁇ m to several tens of ⁇ m may be used as the raw material silicon.
  • step (b) Next, using a pulverizing device such as a ball mill, the mixture of raw material silicon and lithium silicate is pulverized and compounded while being finely divided. At this time, an organic solvent may be added to the mixture for wet pulverization. The organic solvent plays a role in preventing the material to be ground from adhering to the inner wall of the grinding vessel.
  • a pulverizing device such as a ball mill
  • organic solvents alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicate esters, metal alkoxides, etc. can be used.
  • the raw material silicon and the lithium silicate may be separately pulverized and then mixed. Silicon nanoparticles and amorphous lithium silicate nanoparticles may also be produced and mixed without using a pulverizer.
  • a known method such as a vapor phase method (eg, plasma method) or a liquid phase method (eg, liquid phase reduction method) may be used to prepare nanoparticles.
  • step (c) the mixture is heated to 600° C. to 1000° C., for example, in an inert gas atmosphere (eg, an atmosphere of argon, nitrogen, etc.) and pressurized to sinter.
  • an inert gas atmosphere eg, an atmosphere of argon, nitrogen, etc.
  • a sintering apparatus capable of applying pressure under an inert atmosphere, such as a hot press, can be used.
  • the silicate softens and flows to fill the gaps between the first silicon phases.
  • a dense block-shaped sintered body having the silicate phase as the sea portion and the first silicon phase as the island portion.
  • the resulting sintered body is pulverized to obtain silicate composite particles.
  • Step (iii) Subsequently, at least part of the surface of the composite particles may be coated with a conductive material to form a conductive layer.
  • a method of coating the surface of the composite particles with a conductive carbon material there is a CVD method using hydrocarbon gas such as acetylene and methane as a raw material, coal pitch, petroleum pitch, phenol resin, etc. are mixed with composite particles, and an inert atmosphere is used.
  • a method of carbonizing by heating at 700° C. to 950° C. in for example, an atmosphere of argon, nitrogen, etc.
  • carbon black may be attached to the surface of the composite particles.
  • Step (iv) A step of washing the composite particles (including those having a conductive layer on the surface) with an acid may be performed.
  • an acidic aqueous solution it is possible to dissolve and remove trace amounts of alkaline components that may be generated when the raw material silicon and lithium silicate are composited.
  • an aqueous solution of inorganic acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid and carbonic acid
  • organic acids such as citric acid and acetic acid
  • FIG. 1 schematically shows a cross section of a silicate composite particle 20 coated with a conductive layer.
  • the silicate composite particles (mother particles) 23 include a lithium silicate phase 21 and silicon phases 22 dispersed within the lithium silicate phase 21 .
  • a silicate composite particle (mother particle) 23 has a sea-island structure in which fine silicon phases 22 are dispersed in a matrix of a lithium silicate phase 21 .
  • the surfaces of the silicate composite particles (mother particles) 23 are covered with a conductive layer 26 .
  • a silicon oxide phase (not shown) may be dispersed in the lithium silicate phase 21 .
  • the SiO 2 content in the silicate composite particles (mother particles) 23 measured by Si-NMR is, for example, preferably 30% by mass or less, more preferably less than 7% by mass.
  • the silicate composite particles (mother particles) 23 may contain other components in addition to the above.
  • reinforcing materials such as carbon materials, oxides such as ZrO 2 , and carbides may be contained in an amount of less than 10% by mass relative to the base particles 23 .
  • a raw material silicon and a carbon source are mixed, and a pulverizing device such as a ball mill is used to pulverize and compound the mixture of the raw material silicon and the carbon source while pulverizing the mixture.
  • An organic solvent may be added to the mixture.
  • the raw material silicon is pulverized to form a second silicon phase.
  • a second silicon phase is dispersed in the matrix of the carbon source.
  • carbon sources include water-soluble resins such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, polyacrylates, polyacrylamide, polyvinyl alcohol, polyethylene oxide, and polyvinylpyrrolidone, sugars such as cellulose and sucrose, petroleum pitch, and coal pitch. , tar, and the like can be used, but are not particularly limited.
  • CMC carboxymethyl cellulose
  • hydroxyethyl cellulose polyacrylates
  • polyacrylamide polyacrylamide
  • polyvinyl alcohol polyethylene oxide
  • polyvinylpyrrolidone sugars such as cellulose and sucrose
  • petroleum pitch and coal pitch.
  • tar tar, and the like can be used, but are not particularly limited.
  • organic solvents alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicate esters, metal alkoxides, etc. can be used.
  • the composite of the second silicon phase and the carbon source is heated to 700° C. to 1200° C. in an inert gas atmosphere (eg, an atmosphere of argon, nitrogen, etc.) to carbonize the carbon source and convert amorphous carbon. generate.
  • an inert gas atmosphere eg, an atmosphere of argon, nitrogen, etc.
  • (b) Second method The raw material silicon and the carbon material are mixed, and the mixture of the raw material silicon and the carbon material is pulverized and compounded by using a pulverizing device such as a ball mill while pulverizing the mixture. An organic solvent may be added to the mixture. At this time, the raw material silicon is pulverized to form a second silicon phase. A second silicon phase is dispersed in the matrix of the carbon material.
  • a silicon-containing material (S2) in which the second silicon is dispersed in the carbon phase of amorphous carbon is obtained by compositing the raw material silicon and the carbon material as described above.
  • the silicon-containing material (S2) may then be heated to 700° C.-1200° C. in an inert gas atmosphere.
  • Amorphous carbon is preferable as the carbon material, and easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon black, and the like can be used.
  • Examples of carbon black include acetylene black and ketjen black. Even when graphite is used as the carbon material, most of the crystal structure of graphite is lost when a composite of the second silicon and the carbon material is obtained using a pulverizer, and a carbon phase of amorphous carbon is formed.
  • a configuration example of the secondary battery according to the present disclosure will be described below.
  • Various selections can be made for other components except for using the negative electrode active material described above as the negative electrode active material.
  • known constituents may be used as constituents other than the negative electrode active material.
  • a secondary battery according to the present disclosure typically includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode. These components are described below.
  • the manufacturing method of the secondary battery is not limited except for using the negative electrode active material described above, and a known manufacturing method may be used.
  • the negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector and containing a negative electrode active material.
  • the negative electrode mixture layer can be formed by coating the surface of the negative electrode current collector with a negative electrode slurry in which the components of the negative electrode mixture are dispersed in a dispersion medium, and drying the slurry. You may roll the coating film after drying as needed.
  • the negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, etc. as optional components.
  • the negative electrode active material contains a carbon material (C) and a silicon-containing material (S).
  • a non-porous conductive substrate metal foil, etc.
  • a porous conductive substrate meh body, net body, punching sheet, etc.
  • materials for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.
  • binders include fluorine resins, polyolefin resins, polyamide resins, polyimide resins, vinyl resins, styrene-butadiene copolymer rubber (SBR), polyacrylic acid and derivatives thereof. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • Examples of conductive agents include carbon black, conductive fibers, carbon fluoride, and organic conductive materials. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • thickeners examples include carboxymethylcellulose (CMC) and polyvinyl alcohol. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • CMC carboxymethylcellulose
  • polyvinyl alcohol examples include polyvinyl alcohol. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • dispersion media examples include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.
  • 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 coating the surface of the positive electrode current collector with a positive electrode slurry in which the components of the positive electrode mixture are dispersed in a dispersion medium, and drying the slurry. You may roll the coating film after drying as needed.
  • the positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a conductive agent, etc. as optional components.
  • a material that absorbs and releases lithium ions can be used as the positive electrode active material.
  • a known positive electrode active material used for non-aqueous electrolyte secondary batteries may be used as the positive electrode active material.
  • positive electrode active materials include lithium mixed metal oxides.
  • Lithium composite metal oxides include, for example, Li a CoO 2 , Li a NiO 2 , Li a MnO 2 , Li a Co b Ni 1-b O 2 , Li a Co b M 1-b O c , Li a Ni 1- bMbOc , LiaMn2O4 , LiaMn2 - bMbO4 , LiMePO4 , Li2MePO4F .
  • M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B.
  • Me contains at least a transition element (for example, contains at least one selected from the group consisting of Mn, Fe, Co, and Ni).
  • 0 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.9, and 2.0 ⁇ c ⁇ 2.3 0 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.9, and 2.0 ⁇ c ⁇ 2.3.
  • the value a which indicates the molar ratio of lithium, is the value immediately after the preparation of the active material, and increases or decreases due to charging and discharging.
  • the binder and conductive agent the same materials as those exemplified for the negative electrode can be used.
  • Graphite such as natural graphite and artificial graphite may be used as the conductive agent.
  • a conductive substrate having the same shape as the shape described for the negative electrode current collector can be used for the positive electrode current collector.
  • materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium.
  • the electrolyte (or liquid electrolyte) includes a solvent and a lithium salt dissolved in the solvent.
  • concentration of lithium salt in the electrolyte is, for example, 0.5-2 mol/L.
  • the electrolyte may contain known additives.
  • aqueous solvent or a non-aqueous solvent as the solvent.
  • the non-aqueous solvent for example, cyclic carbonate, chain carbonate, cyclic carboxylate, and the like are used.
  • Cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC).
  • Chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and the like.
  • Cyclic carboxylic acid esters include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
  • the non-aqueous solvent may be used singly or in combination of two or more.
  • Lithium salts include, for example, lithium salts of chlorine-containing acids ( LiClO4 , LiAlCl4 , LiB10Cl10 , etc.), lithium salts of fluorine-containing acids ( LiPF6 , LiBF4 , LiSbF6 , LiAsF6 , LiCF3SO3 ) . , LiCF3CO2 , etc. ), lithium salts of fluorine - containing acid imides (LiN( CF3SO2 ) 2 , LiN( CF3SO2 ) ( C4F9SO2 ) , LiN( C2F5SO2 ) 2, etc.), lithium halides (LiCl, LiBr, LiI, etc.) can be used. Lithium salts may be used singly or in combination of two or more.
  • the secondary battery of this embodiment may be a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte.
  • a non-aqueous electrolyte is obtained, for example, by dissolving a lithium salt in a non-aqueous solvent.
  • Separator It is desirable to interpose a separator between the positive electrode and the negative electrode.
  • the separator has high ion permeability and moderate mechanical strength and insulation.
  • a microporous thin film, a woven fabric, a nonwoven fabric, or the like can be used as the separator.
  • Polyolefins such as polypropylene and polyethylene can be used as the material of the separator, for example.
  • An example of a secondary battery includes an electrode group, an electrolyte, and an exterior housing them.
  • the electrode group may be a wound electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween.
  • the electrodes may have other forms.
  • the electrode group may be a laminated electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween.
  • the form of the secondary battery is not particularly limited, and may be, for example, cylindrical, rectangular, coin-shaped, button-shaped, laminate-shaped, or the like.
  • FIG. 2 is a partially cutaway schematic perspective view of a prismatic secondary battery according to an embodiment of the present disclosure. Note that the battery shown in FIG. 2 is an example, and the secondary battery of the present disclosure is not limited to the battery shown in FIG.
  • the battery includes a bottomed prismatic battery case 4 , an electrode group 1 and an electrolyte (not shown) housed in the battery case 4 , and a sealing plate 5 that seals the opening of the battery case 4 .
  • the electrode group 1 has a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed therebetween.
  • the sealing plate 5 has a liquid inlet closed with a sealing plug 8 and a negative electrode terminal 6 insulated from the sealing plate 5 with a gasket 7 .
  • One end of the negative electrode lead 3 is attached to the negative electrode current collector by welding or the like.
  • One end of the positive electrode lead 2 is attached to the positive electrode current collector by welding or the like.
  • the other end of the negative lead 3 is electrically connected to the negative terminal 6 .
  • the other end of positive electrode lead 2 is electrically connected to sealing plate 5 .
  • a plurality of secondary batteries were produced by the following procedure.
  • Pulverized lithium silicate (Li 2 Si 2 O 5 ) and raw material silicon (3N, average particle size 10 ⁇ m) were mixed at a mass ratio of 40:60.
  • the mixture was filled in a pot (manufactured by SUS, volume: 500 mL) of a planetary ball mill (manufactured by Fritsch, P-5).
  • 24 SUS balls (20 mm in diameter) were placed in the pot, the lid was closed, and the mixture was pulverized at 200 rpm for 50 hours in an inert atmosphere.
  • the powdery mixture is taken out in an inert atmosphere, and fired at 800 ° C. for 4 hours in an inert atmosphere while applying pressure from a hot press to obtain a sintered body of the mixture (silicon-silicate composite ).
  • the silicon-silicate composite was pulverized and passed through a mesh of 40 ⁇ m, and the obtained silicate composite particles were mixed with coal pitch (manufactured by JFE Chemical Co., Ltd., MCP250), and the mixture was heated at 800 ° C. in an inert atmosphere. to coat the surface of the silicate composite particles with conductive carbon to form a conductive layer.
  • the coating amount of the conductive layer was 5% by mass with respect to the total mass of the silicate composite particles and the conductive layer.
  • silicate composite particles P1 silicon-containing material (S1)) having a conductive layer were obtained.
  • a sieve was used to adjust the average particle size of the silicate composite particles P1.
  • the crystallite size of the silicate composite particles P1 calculated from the diffraction peak attributed to the Si (111) plane by the XRD analysis of the silicate composite particles P1 using the Scherrer formula was 15 nm.
  • the Si/Li ratio was 1.0
  • the content of Li 2 Si 2 O 5 measured by Si-NMR. was 70% by mass (the content of the first silicon phase was 30% by mass).
  • Carbon material (C) Spherical graphite particles having an average particle diameter Dc of 24 ⁇ m were prepared.
  • the negative electrode slurry was applied to the surface of the copper foil to form a coating film so that the mass of the negative electrode mixture per 1 m 2 was 190 g.
  • the coating film was dried and then rolled to obtain a negative electrode having negative electrode mixture layers (density: 1.5 g/cm 3 ) formed on both sides of the copper foil.
  • Lithium-nickel composite oxide LiNi 0.8 Co 0.18 Al 0.02 O 2
  • a mixture was obtained by mixing at a mass ratio of 5:2.5.
  • NMP N-methyl-2-pyrrolidone
  • the mixture was stirred using a mixer (TK Hibismix manufactured by Primix) to prepare a positive electrode slurry.
  • the surface of the aluminum foil was coated with the positive electrode slurry to form a coating film.
  • the coating film was dried and then rolled to obtain a positive electrode having positive electrode mixture layers (density: 3.6 g/cm 3 ) formed on both sides of an aluminum foil.
  • An electrolyte was prepared by dissolving a lithium salt in a non-aqueous solvent.
  • the concentration of LiPF 6 in the electrolyte was set to 1.0 mol/L.
  • a tab was attached to each electrode.
  • an electrode group was produced by spirally winding the positive electrode and the negative electrode with the separator interposed therebetween. At this time, the winding was performed so that the tab was positioned at the outermost periphery.
  • the electrode group was inserted into an outer package made of an aluminum laminate film, and vacuum-dried at 105° C. for 2 hours. Next, an electrolytic solution was injected into the exterior body, and the opening of the exterior body was sealed. Battery A1 was thus obtained.
  • ⁇ Batteries A2 to A7 and Batteries CA1 to CA4> The average particle size and average circularity of the silicate composite particles P1 (silicon-containing material (S)) described above, the average particle size and average circularity of the graphite particles (carbon material (C)) described above, and the mixture ratio thereof A plurality of negative electrodes were produced in the same manner and under the same conditions as those for producing the negative electrode of Battery A1, except for the changes. Batteries A2 to A7 and batteries CA1 to CA4 were produced in the same manner and under the same conditions as those for battery A1, except that the produced negative electrode was used.
  • the average particle diameter and average circularity of the silicate composite particles P1 (silicon-containing material (S)) were changed by the method described above. Carbon materials (C) having different average particle diameters and average circularities were purchased and used.
  • the average particle size and average circularity of the silicate composite particles P1 (silicon-containing material (S)) and graphite particles (carbon material (C)) were measured by the following methods.
  • the volume-based particle size distribution of each particle was measured using a laser diffraction particle size distribution analyzer (MT3300EXII manufactured by Microtrack Co., Ltd.).
  • the particle diameter (median diameter D50) when the cumulative volume is 50% was taken as the average particle diameter.
  • the average circularity was measured by the method described above, that is, by dispersing particles in a resin and measuring.
  • (1/X) It current
  • (1/X) It (A) rated capacity (Ah) / X (h)
  • Capacity deterioration rate (%) 100 ⁇ (C1-C300) / C1
  • the evaluation results are shown in Tables 1 to 3.
  • the capacity deterioration rate of the battery in Table 1 is shown as a relative value when the capacity deterioration rate of the battery C1 is set to 100.
  • the capacity deterioration rate of the battery in Table 2 is shown as a relative value when the capacity deterioration rate of the battery C3 is set to 100.
  • the capacity deterioration rate of the battery in Table 3 is shown as a relative value when the capacity deterioration rate of the battery C4 is set to 100.
  • a smaller value of the capacity deterioration rate indicates a higher capacity retention rate.
  • the "average circularity ratio" column indicates the value of (average circularity of silicon-containing material (S))/(average circularity of carbon material (C)).
  • Batteries C1 to C4 are comparative example batteries, and batteries A1 to A7 are example batteries. As shown in Tables 1 to 3, (1) the average particle size of the silicon-containing material (S) is smaller than the average particle size of the carbon material (C), and (2) the average circularity of the silicon-containing material (S) is smaller than the average circularity of the carbon material (C). That is, batteries A1 to A7 had higher capacity retention rates than batteries C1 to C4.
  • the carbon material (C) has an average circularity of 0.70 or more and the silicon-containing material (S) has an average circularity of 0.60 or less. Furthermore, as shown in the table, the above average circularity ratio is more preferably 0.60 or less.

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WO2024225132A1 (ja) * 2023-04-27 2024-10-31 パナソニックＩｐマネジメント株式会社 二次電池用負極活物質、および二次電池

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CN119275238B (zh) * 2024-12-12 2025-05-30 宁德新能源科技有限公司 二次电池及电子设备

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