WO2021153076A1 - 電気化学素子およびその製造方法、ならびに電気化学デバイス - Google Patents

電気化学素子およびその製造方法、ならびに電気化学デバイス Download PDF

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Publication number
WO2021153076A1
WO2021153076A1 PCT/JP2020/047195 JP2020047195W WO2021153076A1 WO 2021153076 A1 WO2021153076 A1 WO 2021153076A1 JP 2020047195 W JP2020047195 W JP 2020047195W WO 2021153076 A1 WO2021153076 A1 WO 2021153076A1
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Prior art keywords
coating
lithium silicate
silicate composite
thickness
active material
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English (en)
French (fr)
Japanese (ja)
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修平 内田
吉宣 佐藤
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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 JP2021574529A priority Critical patent/JP7617438B2/ja
Priority to US17/796,173 priority patent/US12597601B2/en
Priority to CN202080094777.2A priority patent/CN115004404B/zh
Priority to EP20916316.1A priority patent/EP4099434A4/en
Publication of WO2021153076A1 publication Critical patent/WO2021153076A1/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
    • H01M4/58—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
    • H01M4/48—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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0421—Methods of deposition of the material involving vapour deposition
    • H01M4/0428—Chemical vapour deposition
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of 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
    • 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
    • H01M4/62—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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • 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

  • This disclosure is mainly related to the improvement of the active material layer.
  • Patent Document 1 proposes to coat the surfaces of the positive electrode and the negative electrode with a metal oxide.
  • the active material repeats expansion and contraction as it is charged and discharged. Therefore, the durability of the electrochemical device tends to decrease. Silicon compounds expand and contract particularly significantly.
  • One aspect of the present disclosure comprises a current collector and an active material layer supported on the current collector, wherein the active material layer contains active material particles, and the active material particles are a lithium silicate phase and.
  • a lithium silicate composite particle containing silicon particles dispersed in the lithium silicate phase and a first coating film covering at least a part of the surface of the lithium silicate composite particle are provided, and the first coating film is a non-metal.
  • the thickness of the active material layer is TA, which contains an oxide of a first element other than the element, the lithium silicate composite particles at a position of 0.25 TA from the surface of the current collector of the active material layer are coated.
  • the thickness T1b of the first coating film and the thickness T1t of the first coating film covering the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer are T1b. ⁇ Regarding an electrochemical element that satisfies T1t.
  • Another aspect of the present disclosure comprises a first electrode, a second electrode and a separator interposed between them, one of the first electrode and the second electrode comprising the electrochemical element described above. Regarding electrochemical devices.
  • Yet another aspect of the present disclosure is a preparatory step of preparing a lithium silicate composite particle containing a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and the lithium silicate composite particle being placed on the surface of a current collector.
  • the lithium silicate composite particles are placed in a gas phase containing a first element other than a non-metal element.
  • the present invention relates to a method for producing an electrochemical element, which comprises a film forming step of forming a first film containing an oxide of the first element on at least a part of the surface thereof by exposure.
  • the expansion of the active material layer is suppressed. Therefore, it is possible to provide an electrochemical device having a long life.
  • FIG. 1 is a schematic cross-sectional view showing a main part of an electrochemical device according to an embodiment of the present disclosure.
  • FIG. 2 is a schematic cross-sectional view showing a main part of the electrochemical element shown in FIG. 1 in a further enlarged manner.
  • FIG. 3 is a schematic cross-sectional view showing in detail the active material particles according to the embodiment of the present disclosure.
  • FIG. 4 is a schematic perspective view in which a part of the non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure is cut out.
  • FIG. 5 is a flowchart showing a method for manufacturing an electrochemical device according to an embodiment of the present disclosure.
  • Electrochemical element The electrochemical element according to the embodiment of the present disclosure includes a current collector and an active material layer supported on the current collector.
  • the active material layer contains active material particles.
  • the active material particles include a lithium silicate phase and a lithium silicate composite particle containing silicon particles dispersed in the lithium silicate phase, and a first coating film that covers at least a part of the surface of the lithium silicate composite particle.
  • the first coating contains oxides of first elements other than non-metal elements.
  • the first coating is thicker as the active material particles are farther from the surface of the current collector. Since the active material particles separated from the current collector easily expand, the effect on the expansion of the active material layer is large. By thickening the first coating film of the lithium silicate composite particles arranged apart from the current collector, the effect of suppressing the expansion thereof is improved. Therefore, the durability of the electrochemical device is improved. On the other hand, since the first coating of the lithium silicate composite particles arranged in the vicinity of the current collector is thin, the decrease in conductivity of the active material particles is suppressed.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer and the active material layer are active.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the material layer satisfies T1b ⁇ T1t.
  • the surface of the current collector is synonymous with the interface between the active material layer and the current collector.
  • the position of 0.25TA from the surface of the current collector of the active material layer is synonymous with the position of 0.25TA from the interface between the active material layer and the current collector.
  • the position of 0.75TA from the surface of the current collector of the active material layer is synonymous with the position of 0.75TA from the interface between the active material layer and the current collector.
  • the thickness T1b and the thickness T1t may satisfy 0.02 ⁇ T1b / T1t ⁇ 1, 0.1 ⁇ T1b / T1t ⁇ 0.7, and 0.2 ⁇ T1b / T1t ⁇ . It may satisfy 0.5.
  • the thicknesses T1b and T1t of the first coating film can be measured by observing the cross section of the active material particles using SEM or TEM.
  • the electrochemical device is disassembled, an electrochemical element (for example, an electrode) is taken out, and a cross section of the element is obtained using a cross section polisher (CP).
  • a cross section polisher CP
  • the image of the cross section obtained by using SEM or TEM when the thickness of the active material layer is TA, a part overlaps with the straight line drawn at the position of 0.25 TA from the surface of the current collector of the active material layer.
  • 10 lithium silicate composite particles having a maximum diameter of 5 ⁇ m or more are selected. For each particle, the thickness of the first coating at one or two intersections of the straight line and the outer edge of the lithium silicate composite particle is measured. The average value of the thickness at these maximum 20 points is obtained.
  • the average value is calculated again by removing data that differs by 20% or more from the obtained average value.
  • This corrected average value is defined as the thickness T1b of the first coating film at the 0.25TA point.
  • the thickness T1t of the first coating film at the 0.75TA point is calculated by using a straight line drawn at the position of 0.75TA from the surface of the current collector of the active material layer.
  • the starting point of the first coating is the interface between the mother particles (see below) formed by the lithium silicate composite particles and the first coating.
  • a portion where the intensity of the peak attributed to Li obtained by SEM-EDS analysis is 1/10 or less of the peak attributed to the first element can be regarded as the starting point of the first coating film.
  • the end point of the first coating film can be regarded as, for example, a point where the intensity of the peak attributed to the first element obtained by SEM-EDS analysis is 5% or less of the maximum value.
  • the end point of the first coating is the interface between the first coating and the second coating.
  • the film thickness of the first coating film changes so as to increase from the surface of the current collector toward the outside. This change may be continuous, gradual, and as long as it can be grasped as an overall trend.
  • lithium silicate composite particles located at a plurality of locations (for example, 5 locations) having different distances from the surface of the current collector on a straight line in the thickness direction of the active material layer are selected, and the straight line and the outer edge of the lithium silicate composite particles are used.
  • the thickness of the first coating at the intersection of one or two of the above is measured.
  • a plurality of straight lines (for example, 5 lines) in the thickness direction of the active material layer are drawn, and the thickness of the first coating film is measured in the same manner.
  • the film thickness calculated in this way is plotted on a graph in which the horizontal axis is the distance from the surface of the current collector and the vertical axis is the film thickness. From this graph, when the approximate straight line or approximate curve obtained by the least squares method is upward-sloping, the overall tendency is that the film thickness of the first coating film increases outward from the surface of the current collector. It can be judged that the thickness is increasing.
  • the first coating can suppress the expansion of lithium silicate composite particles. Therefore, deterioration of the electrochemical element is suppressed, and a high-capacity and long-life electrochemical device can be provided.
  • Examples of the electrochemical element include electrodes.
  • the electrode is, for example, at least one of a positive electrode and a negative electrode used in a secondary battery.
  • the electrode according to the embodiment of the present disclosure is preferably used as a negative electrode for a lithium ion secondary battery.
  • a non-perforated conductive substrate metal foil, etc.
  • a porous conductive substrate meh body, net body, punching sheet, etc.
  • the active material layer contains active material particles.
  • the active material particles include a lithium silicate phase and a lithium silicate composite particle containing silicon particles dispersed in the lithium silicate phase, and a first coating film that covers at least a part of the surface of the lithium silicate composite particle.
  • the active material layer is formed on the surface of the current collector.
  • the active material layer may be formed on one surface of the current collector or on both surfaces.
  • the lithium silicate composite particles include a lithium silicate phase and silicon particles dispersed in the lithium silicate phase.
  • the lithium silicate composite particle has a lithium silicate phase which is a sea portion of a sea-island structure and a silicon particle which is an island portion.
  • Lithium silicate composite particles usually exist as secondary particles in which a plurality of primary particles are aggregated.
  • the first coating covers at least a part of the surface of the secondary particles.
  • Each primary particle comprises a silicate phase and silicon particles dispersed within the silicate phase.
  • the particle size of the lithium silicate composite particles is not particularly limited.
  • the average particle size of the lithium silicate composite particles may be, for example, 1 ⁇ m or more and 20 ⁇ m or less.
  • the average particle size of the lithium silicate composite particles means the particle size (volume average particle size) at which the volume integration value is 50% in the volume particle size distribution measured by the laser diffraction scattering method.
  • Lithium silicate phase The lithium silicate (hereinafter, may be simply referred to as a silicate phase) phase does not have many sites that can react with lithium, and therefore is unlikely to cause a new irreversible reaction during charging and discharging. Therefore, it exhibits excellent charge / discharge efficiency at the initial stage of charge / discharge.
  • the silicate phase is an oxide phase containing Li, Si, and O.
  • the silicate phase may further contain element M.
  • M is derived from, for example, Be, Mg, Al, B, Zr, Nb, Ta, La, V, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F and W. It can be at least one selected from the group.
  • B has a low melting point, which is advantageous for improving the fluidity of the silicate in the molten state.
  • Al, Zr, Nb, Ta and La can improve the Vickers hardness while maintaining the ionic conductivity of the silicate phase.
  • the content of the element M is, for example, 10 mol% or less, and may be 5 mol% or less, based on the total amount of the elements other than O contained in the silicate phase.
  • the silicon particles dispersed in the silicate phase have a particulate phase of silicon (Si) alone, and are composed of a single crystallite or a plurality of crystallites.
  • the crystallite size of the silicon particles is not particularly limited.
  • the crystallite size of the silicon particles is more preferably 10 nm or more and 30 nm or less, and further preferably 15 nm or more and 25 nm or less.
  • the crystallite size of the silicon particles is 10 nm or more, the surface area of the silicon particles can be kept small, so that the deterioration of the silicon particles accompanied by the generation of irreversible capacitance is unlikely to occur.
  • the crystallite size of the silicon particles is calculated by Scherrer's equation from the half width of the diffraction peak attributed to the Si (111) plane of the X-ray diffraction (XRD) pattern of the silicon particles.
  • the content of the silicon particles in the lithium silicate composite particles may be, for example, 30% by mass or more and 80% by mass or less.
  • the content of the silicon particles By setting the content of the silicon particles to 30% by mass or more, the proportion of the silicate phase becomes small, and the initial charge / discharge efficiency can be easily improved.
  • the content of the silicon particles By setting the content of the silicon particles to 80% by mass or less, it becomes easy to reduce the degree of expansion and contraction of the lithium silicate composite particles during charging and discharging.
  • the lithium silicate composite particles may contain a carbon phase as well as the silicate phase and the silicon particles.
  • the carbon phase covers at least a part of the surface of the silicon particles, for example, and is present at least a part of the interface of adjacent primary particles.
  • the content of each element contained in the lithium silicate composite particles can be calculated, for example, by SEM-EDS analysis using a powder sample of the lithium silicate composite particles in a discharged state. The powder sample is analyzed and the spectral intensity of each element is measured. Subsequently, a calibration curve is prepared using a standard sample of commercially available elements, and the content of each element contained in the silicate phase is calculated.
  • ICP-AES analysis inductively coupled plasma emission spectroscopic analysis
  • Auger electron spectroscopic analysis AES
  • LA-ICP-MS laser ablation ICP mass analysis
  • XPS X-ray photoelectron spectroscopy
  • the first coating covers at least a part of the surface of the lithium silicate composite particles which are secondary particles.
  • the first coating contains first elements other than non-metallic elements.
  • the thickness T1b of the first coating film that coats the lithium silicate composite particles located at 0.25TA from the surface of the current collector of the active material layer is not particularly limited. From the viewpoint of corrosion suppression, the thickness T1b may be 0.1 nm or more, 0.5 nm or more, and 1 nm or more. From the viewpoint of conductivity and lithium ion diffusivity, the thickness T1b of the first coating film may be 50 nm or less, 10 nm or less, or 2 nm or less. The thickness T1b of the first coating film may be, for example, 0.1 nm or more and 50 nm or less, and may be 0.1 nm or more and 10 nm or less.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles located at 0.75TA from the surface of the current collector of the active material layer is not particularly limited. From the viewpoint of conductivity and lithium ion diffusivity, the thickness T1t may be 50 nm or less, 30 nm or less, 10 nm or less, or 2 nm or less. From the viewpoint of corrosion suppression, the thickness T1t may be 0.1 nm or more, 0.5 nm or more, and 1 nm or more. The thickness T1t of the first coating film may be, for example, 0.1 nm or more and 50 nm or less, and may be 0.1 nm or more and 30 nm or less. However, T1t is larger than T1b.
  • the average thickness T1 A of the first coating film is also not particularly limited. From the viewpoint of corrosion suppression, the average thickness T1 A of the first coating film may be 0.1 nm or more, 0.5 nm or more, and 1 nm or more. From the viewpoint of conductivity and lithium ion diffusivity, the average thickness T1 A of the first coating film may be 50 nm or less, 10 nm or less, or 2 nm or less. The average thickness T1 A of the first coating film is, for example, 0.1 nm or more and 50 nm or less.
  • the average thickness T1 A of the first coating film can be calculated by averaging the thickness T1b and the thickness T1t.
  • the first element is an element other than a non-metal element, and includes a metal element and a so-called metalloid element.
  • the first element is selected from the group consisting of Group 3 elements, Group 4 elements, Group 5 elements and Group 6 elements in the periodic table because the lithium silicate composite particles have a high corrosion suppressing effect. It preferably contains at least one element.
  • the first element preferably contains at least one selected from the group consisting of Al, Ti, Si, Zr, Mg, Nb, Ta, Sn, Ni and Cr.
  • each oxide may be mixed or may be arranged in layers.
  • the first element is present in a larger amount as it is closer to the surface of the lithium silicate composite particles. This improves the effect of suppressing the expansion of the lithium silicate composite particles.
  • the concentration Cb of the first element at a position of 0.25 T1 from the surface of the lithium silicate composite particle of the first coating film is T1
  • the concentration Ct of the first element at the position of 0.75T1 from the surface of the lithium silicate composite particles of the same first coating satisfies Cb> Ct.
  • the surface of the lithium silicate composite particle is synonymous with the interface between the first coating and the lithium silicate composite particle.
  • the concentration Cb and the concentration Ct may satisfy Cb / Ct> 2.
  • the mean concentration C A of the first element in the first coating is not particularly limited.
  • the concentration C A for example, may be 1% or more, may be 3% or more. In other words, when the concentration C A is more than 1%, the coating is a first coating containing a first element.
  • the concentration C A for example, may be 80% or less, it may be 50% or less.
  • the concentration C A of the average can be calculated by averaging the concentration Cb and the concentration Ct.
  • the concentration Cb of the first element inside the first coating film is determined by evaluating the element distribution state (depth profile) using Energy Dispersive X-ray Spectroscopy (EDS). Can be done.
  • the thickness T1 of the first coating is divided into four equal parts, and the profile at the position of 0.25 T1 from the surface of the lithium silicate composite particles is evaluated. By performing this evaluation on any other plurality of lithium silicate composite particles (for example, 5 particles) and averaging them, the concentration Cb of the first element at that point can be determined.
  • X-ray photoelectron spectroscopy X-ray Photoelectron Spectroscopy
  • EELS electron energy loss spectroscopy
  • ESCA Electron Spectroscopy for Chemical Analysis
  • concentration Cb may be obtained by evaluating the distribution of the first element in the thickness direction.
  • concentration Cb may be calculated from the mole fraction of the oxide of the first element in the first coating.
  • the mole fraction can be calculated from the measurement results of EDS and EELS and the calibration curve.
  • the concentration Ct can be determined by evaluating the profile at the position of 0.75T1 from the surface of the lithium silicate composite particles.
  • the first coating may contain carbon atoms together with oxides of first elements other than non-metal elements. This improves the conductivity of the active material particles. It is desirable that the oxide and the carbon atom are mixed in the first film.
  • the element RA may be, for example, 0.01 or more and 99 or less, 0.1 or more and 10 or less, and 0.1 or more and 3 or less.
  • the element of the first element with respect to the carbon atom at the position of 0.25 T1 from the surface of the lithium silicate composite particles of the first film is T1
  • Rb> Rt is satisfied.
  • the element ratio Rb and the element ratio Rt may satisfy Rb / Rt> 1.3, Rb / Rt> 2, or Rb / Rt> 3.
  • the elemental ratio Rb of the first element to the carbon atom at the position of 0.25T1 from the surface of the lithium silicate composite particles of the first coating is not particularly limited.
  • the element ratio Rb may be, for example, 5 or more and 99 or less, 10 or more and 99 or less, and 20 or more and 99 or less.
  • the elemental ratio Rt of the first element to the carbon atom at the position of 0.75T1 from the surface of the lithium silicate composite particles of the first coating is not particularly limited.
  • the element ratio Rt may be, for example, 0.01 or more and 10 or less, and may be 0.01 or more and 5 or less.
  • the element ratio inside the first coating film can be obtained by evaluating the element distribution state of the first element and the carbon atom using EDS or the like in the same manner as described above.
  • the average elemental ratio RA can be calculated by averaging the elemental ratio Rb and the elemental ratio Rt.
  • Examples of carbon include carbon black, coal, coke, charcoal, and amorphous carbon having low crystallinity such as activated carbon, and graphite having high crystallinity. Of these, amorphous carbon is preferable because it has a low hardness and a large buffering action against silicon particles whose volume changes with charge and discharge.
  • the amorphous carbon may be easily graphitized carbon (soft carbon) or non-graphitized carbon (hard carbon).
  • Examples of carbon black include acetylene black and Ketjen black.
  • Graphite means a material having a graphite-type crystal structure, and examples thereof include natural graphite, artificial graphite, and graphitized mesophase carbon particles.
  • At least a part of the first coating may be coated with a conductive second coating. As a result, the conductivity of the active material particles is further improved.
  • the second coating unlike the first coating, does not contain oxides of the first element.
  • the fact that the second film does not contain the oxide of the first element is synonymous with the fact that the intensity of the peak attributed to the first element obtained by SEM-EDS is below the detection limit.
  • the second coating contains a conductive material.
  • the conductive material is preferably a conductive carbon material in that it is electrochemically stable. Examples of the conductive carbon material include carbon that can be contained in the first coating film as described above.
  • the thickness of the second coating film is not particularly limited.
  • the second coating is preferably thin enough to substantially not affect the average particle size of the lithium silicate composite particles.
  • the average thickness of the second coating may be 1 nm or more, and may be 5 nm or more.
  • the average thickness of the second coating may be 200 nm or less, and may be 100 nm or less.
  • the average thickness of the second coating can be calculated in the same manner as the average thickness of the first coating.
  • the average thickness T1 A of the first coating average thickness T2 A second coating it is preferable to satisfy the relationship of 0 ⁇ T2 A / T1 A ⁇ 1500.
  • T2 A / T1 A is preferably 2 or more, preferably 5 or more, and preferably 10 or more.
  • T2 A / T1 A is preferably 500 or less, and preferably 100 or less.
  • the starting point of the second coating is the interface with the first coating.
  • the end point of the second coating is the outermost point of the active material particles that can be confirmed by SEM or TEM image.
  • the end point of the second coating film is also a point where the intensity of the peak attributable to C obtained by SEM-EDS analysis is 5% or less of the maximum value.
  • the thickness T1 of the first coating film covering any lithium silicate composite particle and the thickness T2 of the second coating film satisfy the relationship of 0 ⁇ T2 / T1 ⁇ 1500. This makes it easier to achieve both corrosion resistance and improved conductivity.
  • T2 / T1 is preferably 5 or more, and preferably 10 or more.
  • T2 / T1 is preferably 500 or less, and preferably 100 or less.
  • the thickness of the first coating and the second coating for coating any lithium silicate composite particle is determined by observing the cross section of the lithium silicate composite particle using SEM or TEM, as in the case of determining the average thickness of the first coating. Can be measured. From the cross-sectional image of the electrochemical device obtained in the same manner as above, one active material particle having a maximum diameter of 5 ⁇ m or more was randomly selected, and the thickness of the first coating film and the second coating film at any five points. Are measured respectively. The average value of the thickness at each of these five points is calculated. Let the average value be the thicknesses T1 and T2 of the first and second coatings covering any lithium silicate composite particles.
  • FIG. 1 is a schematic cross-sectional view showing a main part of an electrochemical device according to an embodiment of the present disclosure.
  • FIG. 2 is a schematic cross-sectional view showing a main part of the electrochemical element shown in FIG. 1 in a further enlarged manner.
  • the electrochemical element 10 includes a current collector 11 and an active material layer 12.
  • the active material layer 12 contains the active material particles 20.
  • the active material particle 20 includes a lithium silicate composite particle 23 and a first coating film 27 that covers the surface of the lithium silicate composite particle 23.
  • FIG. 2 shows only two lithium silicate composite particles.
  • the thickness T1t can also be calculated in the same manner.
  • the thickness of the active material layer is TA
  • the thickness of the first coating T11, T12, T13, T14, ...) At one or two intersections of the straight line and the outer edge of the lithium silicate composite particle is measured. The average value of the thickness at these maximum 20 points is obtained. After calculating this average value, the average value is calculated again by removing data that differs by 20% or more from the obtained average value. This corrected average value is defined as the thickness T1b of the first coating film at the 0.25TA point.
  • FIG. 3 is a schematic cross-sectional view showing in detail a cross section of an example of active material particles.
  • the lithium silicate composite particle 23 is a secondary particle (mother particle) in which a plurality of primary particles 24 are aggregated.
  • Each primary particle 24 includes a silicate phase 21 and silicon particles 22 dispersed in the silicate phase 21.
  • the silicon particles 22 are substantially uniformly dispersed in the silicate phase 21.
  • a carbon phase is arranged at least a part of the interface S of the adjacent primary particles 24.
  • the carbon phase may cover at least a part of the surface of the silicon particles 22.
  • the surface of the lithium silicate composite particles (mother particles) 23 is covered with the first coating film 27.
  • the first coating 27 is covered with a second coating 26.
  • Electrochemical device The electrochemical device according to the embodiment of the present disclosure includes a first electrode, a second electrode, and a separator interposed therein.
  • One of the first electrode and the second electrode is composed of the above-mentioned electrochemical element.
  • Such an electrochemical device has a high capacity and a long life.
  • An electrochemical device is a device that transfers electrons between substances and causes a chemical reaction by the transfer of electrons.
  • Examples of the electrochemical device include a primary battery, a secondary battery, a capacitor, and an air double layer capacitor.
  • the electrochemical device according to the embodiment of the present disclosure is preferably a lithium ion secondary battery using lithium silicate composite particles as a negative electrode active material.
  • the negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer.
  • the negative electrode active material layer contains the negative electrode active material.
  • the negative electrode active material includes at least the above-mentioned active material particles (hereinafter, may be referred to as a first active material).
  • the negative electrode active material layer is formed as a layer containing a negative electrode mixture on the surface of the negative electrode current collector.
  • the negative electrode active material layer may be formed on one surface of the negative electrode current collector, or may be formed on both surfaces.
  • the negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, and the like as optional components.
  • the negative electrode active material may further contain another active material material (hereinafter, may be referred to as a second active material).
  • a second active material include a conductive carbon material that electrochemically occludes and releases lithium ions.
  • Examples of the conductive carbon material include graphite, easily graphitized carbon (soft carbon), and non-graphitized carbon (hard carbon). Among them, graphite having excellent charge / discharge stability and a small irreversible capacity is preferable.
  • Graphite means a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, graphitized mesophase carbon particles, and the like. As the conductive carbon material, one type may be used alone, or two or more types may be used in combination.
  • the particle size of the conductive carbon material is not particularly limited.
  • the average particle size of the conductive carbon material may be, for example, 1 ⁇ m or more and 30 ⁇ m or less.
  • the ratio of the first active material to the total of the first and second active materials may be, for example, 3% by mass or more and 30% by mass or less. This makes it easier to achieve both high capacity and long life.
  • the negative electrode current collector a non-perforated conductive substrate (metal foil, etc.) and a porous conductive substrate (mesh body, net body, punching sheet, etc.) are used.
  • the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.
  • the thickness of the negative electrode current collector is not particularly limited, but is preferably 1 ⁇ m or more and 50 ⁇ m or less, and more preferably 5 ⁇ m or more and 20 ⁇ m or less, from the viewpoint of balancing the strength and weight reduction of the negative electrode.
  • binder examples include at least one selected from the group consisting of polyacrylic acid, polyacrylic acid salt and derivatives thereof.
  • polyacrylate a Li salt or a Na salt is preferably used. Of these, it is preferable to use crosslinked lithium polyacrylate.
  • the conductive agent examples include carbon blacks such as acetylene black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate. ; Conductive metal oxides such as titanium oxide; Organic conductive materials such as phenylene derivatives and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • the thickener examples include carboxymethyl cellulose (CMC) and its modified product (including salts such as Na salt), cellulose derivatives such as methyl cellulose (cellulose ether and the like); and ken, which is a polymer having a vinyl acetate unit such as polyvinyl alcohol.
  • CMC carboxymethyl cellulose
  • cellulose ether and the like examples include cellulose derivatives such as methyl cellulose (cellulose ether and the like); and ken, which is a polymer having a vinyl acetate unit such as polyvinyl alcohol.
  • Compounds Polyethers (polyalkylene oxides such as polyethylene oxide, etc.) and the like can be mentioned. One of these may be used alone, or two or more thereof may be used in combination.
  • the positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector.
  • the positive electrode active material layer may be formed on one surface of the positive electrode current collector, or may be formed on both surfaces.
  • the positive electrode active material layer is formed as a layer containing a positive electrode mixture on the surface of the positive electrode current collector.
  • the positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a conductive agent, and the like as optional components.
  • a lithium composite metal oxide can be used as the positive electrode active material.
  • the lithium composite metal oxide include 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 , and Li a Ni. 1-b M b O c, Li a Mn 2 O 4, Li a Mn 2-b M b O 4, LiMePO 4, Li 2 MePO 4 F can be mentioned.
  • 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 (eg, at least one selected from the group consisting of Mn, Fe, Co, Ni). 0 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.9, 2.0 ⁇ c ⁇ 2.3.
  • the binder and the conductive agent the same ones as those exemplified for the negative electrode can be used.
  • the 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 the shape and range according to the negative electrode current collector.
  • Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.
  • the separator is interposed between the positive electrode and the negative electrode.
  • the separator has high ion permeability and has appropriate mechanical strength and insulation.
  • Examples of the separator include a microporous thin film, a woven fabric, and a non-woven fabric.
  • As the material of the separator for example, polyolefins such as polypropylene and polyethylene are used.
  • the electrochemical device further comprises an electrolyte.
  • the electrolyte contains a solvent and a lithium salt dissolved in the solvent.
  • the concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.
  • the electrolyte may contain known additives.
  • an aqueous solvent or a non-aqueous solvent is used.
  • a non-aqueous solvent for example, a cyclic carbonate ester, a chain carbonate ester, a cyclic carboxylic acid ester, or the like is used.
  • the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC).
  • the chain carbonic acid ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
  • GBL ⁇ -butyrolactone
  • GVL ⁇ -valerolactone
  • lithium salt examples include a lithium salt of a chlorine-containing acid (LiClO 4 , LiAlCl 4 , LiB 10 Cl 10, etc.) and a lithium salt of a fluorine-containing acid (LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiCF 3 SO 3). , LiCF 3 CO 2 etc.), Lithium salt of fluorine-containing acidimide (LiN (SO 2 F) 2 , LiN (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ), LiN (C 2 F 5 SO 2 ) 2, etc.), lithium halide (LiCl, LiBr, LiI, etc.) and the like.
  • One type of lithium salt may be used alone, or two or more types may be used in combination.
  • the structure of the secondary battery there is a structure in which the positive electrode, the negative electrode, the electrode group formed by winding the separator, and the electrolyte are housed in the exterior body.
  • a laminated type electrode group in which the positive electrode and the negative electrode are laminated via a separator is also used.
  • other forms of electrodes may be applied.
  • the secondary battery may be in any form such as a cylindrical type, a square type, a coin type, a button type, and a laminated type.
  • FIG. 4 is a schematic perspective view in which a part of the square secondary battery according to the embodiment of the present disclosure is cut out.
  • the battery includes a bottomed square battery case 4, an electrode group 1 and an electrolyte housed in the battery case 4, and a sealing plate 5 for sealing 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 between them.
  • the negative electrode, the positive electrode, and the separator are wound around a flat plate-shaped winding core, and the electrode group 1 is formed by pulling out the winding core.
  • the sealing plate 5 has a liquid injection port closed by the sealing 8 and a negative electrode terminal 6 insulated from the sealing plate 5 by a gasket 7.
  • One end of the negative electrode lead 3 is attached to the negative electrode current collector of the negative electrode by welding or the like.
  • One end of the positive electrode lead 2 is attached to the positive electrode current collector of the positive electrode by welding or the like.
  • the other end of the negative electrode lead 3 is electrically connected to the negative electrode terminal 6.
  • the other end of the positive electrode lead 2 is electrically connected to the sealing plate 5.
  • a resin frame that separates the electrode group 1 and the sealing plate 5 and the negative electrode lead 3 and the battery case 4 is arranged above the electrode group 1.
  • the method for producing an electrochemical element includes a preparatory step for preparing a lithium silicate composite particle containing silicon particles dispersed in a silicate phase and a silicate phase, and a surface of a current collector.
  • a preparatory step for preparing a lithium silicate composite particle containing silicon particles dispersed in a silicate phase and a silicate phase, and a surface of a current collector After the supporting step of supporting the lithium silicate composite particles to form the precursor layer, the rolling step of rolling the precursor layer, and the rolling step, lithium is added to the gas phase containing the first element other than the non-metal element. It comprises a film forming step of exposing the silicate composite particles to form a first film containing an oxide of the first element on at least a part of the surface thereof.
  • FIG. 5 is a flowchart showing a method for producing active material particles according to an embodiment of the present disclosure.
  • Silicon particles can be obtained by a chemical vapor deposition method (CVD method), a thermal plasma method, a physical pulverization method, or the like.
  • CVD method chemical vapor deposition method
  • thermal plasma method a thermal plasma method
  • physical pulverization method a physical pulverization method
  • silicon nanoparticles having an average particle size of 10 to 200 nm can be synthesized.
  • the average particle size of the silicon particles means the particle size (volume average particle size) at which the volume integration value is 50% in the volume particle size distribution measured by the laser diffraction / scattering method.
  • the CVD method is, for example, a method of oxidizing or reducing a silane compound in a gas phase to generate silicon particles.
  • the reaction temperature may be set to, for example, 400 ° C. or higher and 1300 ° C. or lower.
  • silane compound silicon hydride such as silane and disilane, silane halide, alkoxysilane and the like can be used.
  • halogenated silane dichlorosilane, trichlorosilane, tetrachlorosilane and the like can be used.
  • alkoxysilane tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane and the like can be used.
  • silicon hydride when silicon hydride is brought into contact with an oxidizing gas in the gas phase, a composite of silicon particles and silicon oxide particles can be obtained. That is, the atmosphere of the gas phase may be an oxidizing gas atmosphere. Silicon oxides are removed by washing the complex with, for example, hydrofluoric acid, resulting in silicon particles.
  • the molten metal micronized by the atomizing method may be brought into contact with the silane compound.
  • the molten metal Na, K, Mg, Ca, Zn, Al and the like can be used.
  • the atomizing gas an inert gas, silane halide, hydrogen gas or the like may be used. That is, the atmosphere of the gas phase may be an inert gas or reducing gas atmosphere.
  • the thermal plasma method is a method in which a silicon raw material is introduced into the generated thermal plasma to generate silicon particles in a high-temperature plasma.
  • the thermal plasma may be generated by arc discharge, high frequency discharge, microwave discharge, laser light irradiation, or the like.
  • the discharge by radio frequency (RF) is a non-polar discharge, which is desirable in that impurities are less likely to be mixed in the silicon particles.
  • silicon oxide can be used as a raw material.
  • silicon and oxygen in the state of atoms or ions are instantly generated, and silicon is bonded and solidified during cooling to generate silicon particles.
  • the physical crushing method (mechanical milling method) is a method of crushing coarse particles of silicon with a crusher such as a ball mill or a bead mill.
  • the inside of the crusher may have, for example, an inert gas atmosphere.
  • Examples of the method of coating silicon particles with a carbon phase include a chemical vapor deposition method (CVD method), sputtering, an atomic layer deposition method (ALD method: Atomic Layer Deposition), a wet mixing method, and a dry mixing method.
  • CVD method chemical vapor deposition method
  • ALD method Atomic Layer Deposition
  • wet mixing method a wet mixing method
  • dry mixing method a dry mixing method.
  • silicon particles are introduced into a hydrocarbon-based gas atmosphere, heated, and a carbon material generated by thermal decomposition of the hydrocarbon-based gas is deposited on the particle surface to form a carbon phase. Is formed.
  • the temperature of the hydrocarbon gas atmosphere may be, for example, 500 ° C. or higher and 1000 ° C. or lower.
  • chain hydrocarbon gases such as acetylene and methane
  • aromatic hydrocarbons such as benzene, toluene, and xylene
  • (B) Wet Mixing Method for example, carbon precursors such as coal pitch, petroleum pitch, and tar are dissolved in a solvent, and the obtained solution and silicon particles are mixed and dried. Then, the silicon particles coated with the carbon precursor are heated in an inert gas atmosphere at, for example, 600 ° C. or lower and 1000 ° C. or lower to carbonize the carbon precursor to form a carbon phase.
  • carbon precursors such as coal pitch, petroleum pitch, and tar
  • a raw material mixture containing a Si raw material and a Li raw material in a predetermined ratio may be used as the raw material for the silicate phase.
  • a silicate can be obtained by dissolving the raw material mixture and passing the melt through a metal roll to form flakes.
  • the silicate may be synthesized by solid-phase reaction by firing at a temperature below the melting point without dissolving the raw material mixture.
  • Silicon oxide (for example, SiO 2 ) can be used as the Si raw material.
  • the raw material of Li or the raw material of element M carbonates, oxides, hydroxides, hydrides, nitrates, sulfates and the like of lithium or element M can be used, respectively. Of these, carbonates, oxides, hydroxides and the like are preferable.
  • the silicate is mixed with silicon particles having at least a part of the surface coated with a carbon phase (hereinafter, also referred to as carbon-coated silicon particles) and mixed.
  • silicon particles having at least a part of the surface coated with a carbon phase hereinafter, also referred to as carbon-coated silicon particles
  • lithium silicate composite particles are produced through the following steps.
  • the carbon-coated silicon particles and the silicate powder are mixed at a mass ratio of, for example, 20:80 to 95: 5.
  • the mixture of carbon-coated silicon particles and silicate is agitated using a device such as a ball mill.
  • a device such as a ball mill.
  • an organic solvent may be put into the crushing container at one time at the initial stage of crushing, or may be intermittently put into the crushing container in a plurality of times in the crushing process.
  • the organic solvent plays a role of preventing the object to be crushed from adhering to the inner wall of the crushing container.
  • the organic solvent alcohol, ether, fatty acid, alkane, cycloalkane, silicate ester, metal alkoxide and the like can be used.
  • the mixture is heated at 450 ° C. or higher and 1000 ° C. or lower while pressurizing in an inert gas atmosphere (for example, an atmosphere of argon, nitrogen, etc.) and sintered.
  • an inert gas atmosphere for example, an atmosphere of argon, nitrogen, etc.
  • a sintering apparatus capable of pressurizing under an inert atmosphere, such as hot pressing or discharge plasma sintering, can be used.
  • the silicate melts and flows to fill the gaps between the silicon particles.
  • Lithium silicate composite particles can be obtained by crushing the last obtained sintered body. By appropriately selecting the pulverization conditions, lithium silicate composite particles having a predetermined average particle size can be obtained.
  • lithium silicate composite particles As a method for forming a carbon film on the surface of lithium silicate composite particles, a chemical vapor phase growth method using a chain hydrocarbon gas such as acetylene or methane as a raw material, coal pitch, petroleum pitch, phenol resin, etc. are used as lithium silicate composite particles. Examples thereof include a method of mixing with and heating to carbonize. Carbon black may be attached to the surface of the lithium silicate composite particles.
  • the carbon film is thin enough not to affect the average particle size of the lithium silicate composite particles.
  • the thickness of the carbon coating film is preferably greater than or equal to the desired first coating film.
  • the carbon film may be 0.1 nm or more, and may be 1 nm or more.
  • the carbon film is preferably 300 nm or less, more preferably 200 nm or less. The thickness of the carbon film can be measured by observing the cross section of the lithium silicate composite particles using SEM or TEM, as in the case of the first film.
  • a step of washing the lithium silicate composite particles having a carbon film with an acid may be performed.
  • an acidic aqueous solution for example, by washing the composite particles with an acidic aqueous solution, a trace amount of alkaline components that may be present on the surface of the lithium silicate composite particles can be dissolved and removed.
  • an aqueous solution of an inorganic acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid or carbon dioxide, or an aqueous solution of an organic acid such as citric acid or acetic acid can be used.
  • Step of supporting lithium silicate composite particles (S2) A slurry in which a negative electrode mixture containing the prepared lithium silicate composite particles is dispersed in a dispersion medium is applied to the surface of the current collector, and the slurry is dried. As a result, a precursor layer of the active material layer is formed on the surface of the current collector.
  • the dispersion medium is not particularly limited, and examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof. ..
  • the rolling conditions are not particularly limited.
  • the rolling is preferably carried out so that the density of the precursor layer is 0.9 g / cm 3 or more and 1.8 g / cm 3 or less, preferably 1.0 g / cm 3 or more and 1.8 g / cm 3 or less.
  • the precursor layer is not excessively rolled, and in particular, densification of the precursor layer on the outer surface side of the active material layer is suppressed. Therefore, in the film forming step, the gas phase containing the first element can come into contact with the lithium silicate composite particles located near the outer surface of the active material layer in a larger amount. Therefore, a thicker first film is likely to be formed on the lithium silicate composite particles relatively separated from the surface of the current collector.
  • First film forming step (S4) Lithium silicate composite particles are exposed to a gas phase containing the first element. As a result, a first film containing an oxide of the first element is formed on at least a part of the surface of the lithium silicate composite particles. When the lithium silicate composite particle has a carbon film, this step introduces the first element into the carbon film to form the first film containing the oxide of the first element and the carbon atom.
  • the vapor phase method examples include a CVD method, an ALD method, and a physical vapor deposition method (PVD).
  • the ALD method is preferable in that the first film can be formed at a relatively low temperature.
  • the first film can be formed in an atmosphere of 200 ° C. or lower.
  • an organometallic compound (plicasa) containing the first element is used as a raw material for the first coating film.
  • the vaporized precursor (raw material gas) and the oxidizing agent are alternately supplied to the reaction chamber in which the object is arranged. As a result, a layer containing an oxide of the first element is formed on the surface of the object.
  • the first element contained in the raw material gas passes through the carbon film and reaches the surface of the lithium silicate composite particle. can do. Then, the first element is deposited as it is on the surface of the lithium silicate composite particles. Therefore, more first elements are likely to be arranged near the surface of the lithium silicate composite particles.
  • the first film formed contains carbon atoms derived from the carbon film together with the oxide of the first element.
  • the self-limiting action works, so the first element is deposited on the surface of the object in atomic layer units.
  • the entire first coating film is formed by the number of cycles in which the supply of the raw material gas (pulse) ⁇ the exhaust of the raw material gas (purge) ⁇ the supply of the oxidant (pulse) ⁇ the exhaust of the oxidant (purge) is set as one cycle. Thickness is controlled.
  • the oxide of the first element can be arranged on the entire carbon film.
  • the thickness of the first film is controlled to be thinner than the carbon film, a first film containing an oxide of the first element and a carbon atom is formed on the surface side of the lithium silicate composite particles, and the first film is formed.
  • a second coating derived from the rest of the carbon coating is formed so as to cover the coating of.
  • Pricasa is an organometallic compound containing the first element.
  • As the precursor various organometallic compounds conventionally used in the ALD method can be used.
  • Ti-containing precursor examples include bis (t-butylcyclopentadienyl) titanium (IV) dichloride (C 18 H 26 Cl2 Ti) and tetrakis (dimethylamino) titanium (IV) ([(CH 3 ) 2 ).
  • the raw material gas may contain a plurality of types of precursors. Different types of precursors may be supplied to the reaction chamber simultaneously or sequentially. Alternatively, the type of precursor contained in the raw material gas may be changed for each cycle.
  • the oxidizing agent As the oxidizing agent, the oxidizing agent conventionally used in the ALD method can be used.
  • the oxidizing agent include water, oxygen, ozone and the like.
  • the oxidant may be supplied to the reaction chamber as plasma using the oxidant as a raw material.
  • the conditions of the ALD method are not particularly limited.
  • the temperature of the atmosphere containing the precursor or the oxidizing agent may be 10 ° C. or higher and 200 ° C. or lower, and 25 ° C. or higher and 200 ° C. or higher, in that the first film is more likely to be formed on the lithium silicate composite particles in the vicinity of the current collector. It may be below ° C.
  • the pressure in the reaction chamber during the treatment may be 1 ⁇ 10 -5 Pa or more and 1 ⁇ 10 5 Pa or less, and may be 1 ⁇ 10 -4 Pa or more and 1 ⁇ 10 4 Pa or less.
  • the temperature of the atmosphere containing the precursor or oxidant in the reaction chamber is 10 ° C. or higher and 200 ° C. or lower, and the reaction during the treatment is in that the first film is more likely to be formed on the lithium silicate composite particles near the current collector.
  • the pulse time of the raw material gas may be 0.01 seconds or more, and may be 0.05 seconds or more.
  • the pulse time of the raw material gas may be 5 seconds or less, and may be 3 seconds or less.
  • the active material layer may be rolled.
  • the rolling conditions are not particularly limited, and the active material layer may be appropriately set to have a predetermined thickness or density.
  • Example 1 [Preparation of negative electrode] (1) Preparation of silicon particles Coarse silicon particles (3N, average particle size 10 ⁇ m) are filled in a pot (SUS, volume 500 mL) of a planetary ball mill (Fritsch, P-5), and the pot is filled with SUS balls (US ball). Twenty-four pieces (diameter 20 mm) were put in, the lid was closed, and the particles were pulverized at 200 rpm until the average particle size became 150 nm in an inert atmosphere to prepare silicon particles.
  • SUS volume 500 mL
  • SUS balls US ball
  • a carbon material was deposited on the surface of silicon particles by a chemical vapor deposition method. Specifically, silicon particles were introduced into an acetylene gas atmosphere and heated at 700 ° C. to thermally decompose the acetylene gas and deposit it on the surface of the silicon particles to form a carbon phase. The amount of carbon material with respect to 100 parts by mass of silicon particles was 10 parts by mass.
  • Lithium Silicate Composite Particles Silicon dioxide and lithium carbonate are mixed so that the atomic ratio ( Si / Li) is 1.05, and the mixture is calcined in air at 950 ° C. for 10 hours to obtain Li.
  • a lithium silicate represented by 2 Si 2 O 5 (z 0.5) was obtained.
  • the obtained lithium silicate was pulverized so as to have an average particle size of 10 ⁇ m.
  • Lithium silicate (Li 2 Si 2 O 5 ) having an average particle size of 10 ⁇ m and carbon-coated silicon were mixed at a mass ratio of 70:30.
  • the mixture was stirred at 200 rpm for 50 hours.
  • the powdery mixture was taken out in an inert atmosphere and fired at 800 ° C. for 4 hours in an inert atmosphere under pressure from a hot press to obtain a sinter of the mixture. Then, the sintered body was crushed to obtain lithium silicate composite particles.
  • the crystallite size of the silicon particles calculated by Scherrer's equation from the diffraction peak attributed to the Si (111) plane by XRD analysis 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 silicon particles was 30% by mass).
  • a lithium silicate composite particle having a carbon film and a second active material (graphite) were mixed at a mass ratio of 5:95 and used as the negative electrode active material.
  • Water is added to a negative electrode mixture containing a negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), and a lithium polyacrylic acid salt in a mass ratio of 96.5: 1: 1.5: 1.
  • a mixer TK Hibismix manufactured by Primix
  • a negative electrode slurry was applied to the surface of the copper foil so that the mass of the negative electrode mixture per 1 m 2 was 190 g, and the coating film was dried to form a precursor layer. Then, it was rolled so that the density of the precursor layer became 1.1 g / cm 3. The thickness of the precursor layer was 202 ⁇ m.
  • the negative electrode precursor was housed in a predetermined reaction chamber, and the first film was formed on the surface of the negative electrode precursor according to the following procedure by the ALD method.
  • the temperature of the atmosphere containing the precursor in the reaction chamber was controlled to 200 ° C., and the pressure was controlled to 260 Pa. After 30 seconds, the surface of the negative electrode precursor was covered with a monolayer of the precursor, and the excess precursor was purged with nitrogen gas.
  • reaction chamber negative electrode precursor is accommodated and fed by vaporizing an oxidizing agent (H 2 O).
  • the pulse time was 0.015 seconds.
  • the temperature of the atmosphere containing the oxidizing agent was controlled to 200 ° C., and the pressure was controlled to 260 Pa. After 30 seconds, excess oxidant was purged with nitrogen gas.
  • a first film containing titanium was formed by repeating a series of operations consisting of supplying the precursor, purging, supplying the oxidizing agent, and purging 400 times.
  • the first coating was adjusted to be thinner than the carbon coating, and a first coating and a second coating covering the first coating were formed at the same time.
  • the first coating was analyzed by SEM, EDS, ICP and the like.
  • the first coating contained Ti and C.
  • the thickness T1b of the first coating film for coating the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 6 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 20 nm.
  • the average thickness T1 A of the first coating was 13 nm.
  • the first coating for coating the lithium silicate composite particles at the position of 0.25TA from the surface of the current collector of the active material layer the first coating at the position of 0.25T1 from the surface of the lithium silicate composite particles of the first coating.
  • the element concentration Cb was 6%.
  • the concentration Ct of the first element at the position of 0.75T1 from the surface of the lithium silicate composite particles of the first coating was 2%.
  • the first element In the first coating for coating the lithium silicate composite particles at 075TA from the surface of the current collector in the active material layer, the first element at 0.25T1 from the surface of the lithium silicate composite particles in the first coating.
  • the concentration Cb was 3%.
  • the concentration Ct of the first element at the position of 0.75T1 from the surface of the lithium silicate composite particles of the first coating was 0.5%.
  • the minimum value of the element ratio R of the first element to the carbon atom was 0.03, and the maximum value was 8.
  • the elemental ratio Rb of the first element to the carbon atom at the position of 0.25 T1 A from the surface of the lithium silicate composite particles of the first coating was 6.2.
  • Element ratio Rt of the first element to the carbon atoms at the position of 0.75T1 A from the surface of the lithium silicate composite particles of the first coating was 0.08.
  • composition of the second coating film was analyzed in the same manner, it contained C.
  • the sum of the thickness of the first coating and the thickness of the second coating was 50 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles at a position of 0.5 TA from the surface of the current collector of the active material layer is 6 nm
  • the thickness of the second coating film is 44 nm
  • the thickness of the first coating film is 44 nm.
  • the sum of the thickness of the coating film and the thickness of the second coating film was 50 nm.
  • An electrolytic solution was prepared by dissolving LiPF 6 at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • Electrode group was inserted into the outer body made of an aluminum laminated film, vacuum dried at 105 ° C. for 2 hours, then the electrolytic solution was injected, and the opening of the outer body was sealed to obtain a secondary battery A1.
  • Example 2 In the formation of the first and second coating films (6), the first active material is the same as in Example 1 except that a series of operations including the supply of the precursor, the purge, the supply of the oxidizing agent, and the purge are repeated 100 times. Was manufactured to produce a secondary battery A2.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film for coating the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 6 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 10 nm.
  • the average thickness T1 A of the first coating was 8 nm. In each lithium silicate composite particle, the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 6 nm, and the thickness T2 of the second coating film was 44 nm.
  • Example 3 In the formation of the first and second coating films (6), the first active material is the same as in Example 1 except that a series of operations including the supply of the precursor, the purge, the supply of the oxidizing agent, and the purge are repeated 300 times. Was manufactured to produce a secondary battery A3.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 3 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 20 nm.
  • the average thickness T1 A of the first coating was 11.5 nm.
  • the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 3 nm, and the thickness T2 of the second coating film was 47 nm.
  • Example 4 In the formation of the first and second coating films (6), the first active material was the same as in Example 1 except that a series of operations including the supply of the precursor, the purge, the supply of the oxidizing agent, and the purge were repeated 70 times. Was manufactured to produce a secondary battery A4.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 3 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 10 nm.
  • the average thickness T1 A of the first coating was 6.5 nm. In each lithium silicate composite particle, the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 3 nm, and the thickness T2 of the second coating film was 47 nm.
  • Example 5 In the formation of the first and second coating films (6), the first active material was the same as in Example 1 except that a series of operations including the supply of the precursor, the purge, the supply of the oxidizing agent, and the purge were repeated 50 times. Was manufactured to produce a secondary battery A5.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles at a position of 0.25 TA from the surface of the current collector of the active material layer was 1 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 10 nm.
  • the average thickness T1 A of the first coating was 5.5 nm. In each lithium silicate composite particle, the sum of the thickness of the first coating film and the thickness of the second coating film was 50 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 1 nm, and the thickness T2 of the second coating film was 49 nm.
  • Example 6 In the coating of the lithium silicate composite particles with the carbon coating (5), the thickness of the carbon coating was set to 100 nm, and in the formation of the first and second coatings (6), the supply of the precursor, the purge, and the supply of the oxidizing agent.
  • the first active material was produced in the same manner as in Example 1 except that the series of operations including the purge was repeated 300 times, and the secondary battery A6 was produced.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 3 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 20 nm.
  • the average thickness T1 A of the first coating was 11.5 nm. In each lithium silicate composite particle, the sum of the thickness of the first coating film and the thickness of the second coating film was 100 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 3 nm, and the thickness T2 of the second coating film was 97 nm.
  • Example 7 In the coating of the lithium silicate composite particles with the carbon coating (5), the thickness of the carbon coating was set to 100 nm, and in the formation of the first and second coatings (6), the supply of the precursor, the purge, and the supply of the oxidizing agent.
  • the first active material was produced in the same manner as in Example 1 except that the series of operations including the purge was repeated 70 times, and the secondary battery A7 was produced.
  • the first coating and the second coating were analyzed in the same manner as in Example 1.
  • the first coating coating the lithium silicate composite particles contained Ti and C
  • the first coating coating the conductive carbon material contained Ti.
  • the second coating contained C.
  • the thickness T1b of the first coating film covering the lithium silicate composite particles located at 0.25 TA from the surface of the current collector of the active material layer was 3 nm.
  • the thickness T1t of the first coating film for coating the lithium silicate composite particles at a position of 0.75TA from the surface of the current collector of the active material layer was 10 nm.
  • the average thickness T1 A of the first coating was 5.5 nm. In each lithium silicate composite particle, the sum of the thickness of the first coating film and the thickness of the second coating film was 100 nm.
  • the thickness T1 of the first coating film covering the lithium silicate composite particles located 0.5 TA from the surface of the current collector of the active material layer was 3 nm, and the thickness T2 of the second coating film was 97 nm.
  • Comparative Example 1 An active material was produced in the same manner as in Example 1 except that the lithium silicate composite particles were not coated with the carbon film (4) and the first film was not formed (6), and the secondary battery B1 was produced.
  • Comparative Example 2 The active material was produced in the same manner as in Example 1 except that the formation of the first and second coating films (6) was not performed, and the secondary battery B2 was produced.
  • the thickness of the carbon film was 50 nm.
  • Comparative Example 3 For the lithium silicate composite particles before being supported on the copper foil, instead of coating the lithium silicate composite particles with the carbon film (4) and forming the first and second coatings (6). An active material was produced in the same manner as in Example 1 except that the treatment using the ALD method was performed, and a secondary battery B3 was produced.
  • the treatment using the ALD method on the silicate composite particles was performed under the same conditions as in Example 1 except that a series of operations including the supply of the precursor, the purge, the supply of the oxidizing agent, and the purge were repeated 100 times.
  • the thickness T1b of the first coating coating the lithium silicate composite particles at 0.25 TA from the surface of the current collector of the active material layer and 0.75 TA from the surface of the current collector of the active material layer.
  • the thickness of the first coating film for coating the lithium silicate composite particles was T1t, which was the same as 10 nm.
  • the pause period between charging and discharging was set to 10 minutes.
  • the ratio of the discharge capacity of the 100th cycle to the discharge capacity of the 1st cycle was calculated, and the average value of 20 batteries was obtained. This average value was taken as the capacity retention rate.
  • the evaluation results are shown in Table 1.
  • each battery was disassembled, the negative electrode was taken out, and the thickness was measured. The average value of the thicknesses at any five points was taken as the thickness of the negative electrode after the charge / discharge cycle. About 20 of the negative electrode after charging and discharging cycles, respectively determine the thickness T A.
  • the electrochemical device according to the present disclosure is useful as a main power source for mobile communication devices, portable electronic devices, and the like.
  • Electrode group 2 Positive electrode lead 3 Negative electrode lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8 Sealing 10 Electrochemical element 11 Current collector 12 Active material layer 20 Active material particles 21 Silicate phase 22 Silicon particles 23 Lithium silicate composite particles 24 Primary particles 26 Second coating 27 First coating

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