WO2022168408A1 - 活物質粒子、電気化学素子、および電気化学デバイス - Google Patents

活物質粒子、電気化学素子、および電気化学デバイス Download PDF

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WO2022168408A1
WO2022168408A1 PCT/JP2021/043115 JP2021043115W WO2022168408A1 WO 2022168408 A1 WO2022168408 A1 WO 2022168408A1 JP 2021043115 W JP2021043115 W JP 2021043115W WO 2022168408 A1 WO2022168408 A1 WO 2022168408A1
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Prior art keywords
coating
active material
particles
carbon
lithium silicate
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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 JP2022579353A priority Critical patent/JPWO2022168408A1/ja
Priority to CN202180092466.7A priority patent/CN116830307A/zh
Priority to US18/274,337 priority patent/US20240088372A1/en
Priority to EP21924794.7A priority patent/EP4290608A4/en
Publication of WO2022168408A1 publication Critical patent/WO2022168408A1/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
    • H01M4/366—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
    • H01M4/48—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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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 primarily relates to improvements in active material particles.
  • Patent Document 1 proposes coating the surfaces of the positive electrode and the negative electrode with a metal oxide.
  • One aspect of the present disclosure comprises composite particles including a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase, and a first coating covering at least a portion of a surface of the composite particles, wherein
  • the first coating includes an oxide of a first element with low crystallinity and a carbon material that are mixed with each other, and the first element relates to an active material particle that is an element other than a non-metallic element.
  • Another aspect of the present disclosure relates to an electrochemical device comprising a current collector and an active material layer supported on the current collector, wherein the active material layer contains the active material particles described above.
  • Yet another aspect of the present disclosure includes a first electrode, a second electrode, and an electrolyte, wherein one of the first electrode and the second electrode is composed of the electrochemical element described above. , relating to electrochemical devices.
  • FIG. 1 is a schematic cross-sectional view showing active material particles according to an embodiment of the present disclosure
  • FIG. 2 is a schematic cross-sectional view showing an enlarged main part of the active material particles shown in FIG. 1.
  • FIG. 4 is a TEM image showing a cross-sectional main part of an active material particle according to an embodiment of the present disclosure.
  • FIG. 2 is a schematic cross-sectional view showing details of active material particles according to an embodiment of the present disclosure.
  • 1 is a schematic perspective view of a partially cutaway non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure;
  • An active material particle according to an embodiment of the present disclosure includes a composite particle and a first coating that coats at least part of the surface of the composite particle.
  • the composite particles include a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase.
  • the composite particles are also referred to as "lithium silicate composite particles”.
  • the first coating includes a low-crystalline first element oxide and a carbon material that are mixed with each other. The above-mentioned "mixed" means, for example, a state in which an oxide of the first element with low crystallinity enters the gaps between the carbon materials.
  • the first element is an element other than nonmetallic elements.
  • the first coating contains a low-crystalline oxide of the first element means that the occupancy C of the crystalline domain of the oxide of the first element in the first coating is 30% or less.
  • the occupation rate C may be, for example, 0.5% or more and 30% or less, may be 0.5% or more and 25% or less, or may be 10% or more and 25% or less.
  • the crystalline domain of the oxide of the first element is a region in which the oxide of the first element has crystallinity (a non-amorphous region).
  • the above occupancy rate C (%) is obtained by the following method.
  • a cross-sectional image (for example, 50 nm ⁇ 50 nm) of one active material particle (thickness direction of the first coating) is obtained with a TEM (transmission electron microscope).
  • the cross-sectional image is subjected to elemental mapping by TEM-EELS (electron energy loss spectroscopy) to confirm the oxide of the first element in the first coating.
  • FFT Fast Fourier transform
  • the FFT pattern obtained by fast Fourier transform (FFT) of the TEM image shows that it has crystallinity (amorphous not).
  • a large number of points for example, 100 to 200 points
  • a ratio of the number N1 of the measurement points from which the FFT pattern indicating the crystallinity was obtained to the total number N0 of the measurement points, that is, (N1/N0) ⁇ 100 is calculated.
  • (N1/N0) ⁇ 100 is determined for each of a plurality of (eg, 5 to 10) active material particles, and the average value thereof is determined as the occupancy rate C of the crystalline domains.
  • the first coating can enhance the chemical stability of the lithium silicate composite particles while maintaining electrical conductivity. As a result, the capacity retention rate of the electrochemical device can be increased.
  • the active material particles according to the embodiments of the present disclosure are preferably used as a negative electrode active material for lithium ion secondary batteries.
  • the oxide of the first element contained in the first coating contributes to suppressing corrosion of the lithium silicate composite particles.
  • the carbon material contained in the first coating contributes to improving the conductivity of the active material particles.
  • the oxide of the first element contained in the first coating has low crystallinity.
  • the first coating has appropriate flexibility, and the ability of the first coating to follow expansion and contraction of the lithium silicate composite particles during charging and discharging is improved. Therefore, cracking of the first coating due to expansion and contraction of the lithium silicate composite particles during charge and discharge is suppressed, side reactions due to contact between the lithium silicate composite particles and the electrolyte accompanying cracking of the first coating are suppressed, and the first coating A remarkable effect of suppressing corrosion of the lithium silicate composite particles can be obtained.
  • the low-crystalline oxide of the first element and the carbon material are mixed in the first coating. Thereby, corrosion of the lithium silicate composite particles can be suppressed by the first coating while sufficiently forming a conductive path in the first coating. That is, the first film can serve as both a protective film and a conductive film for the lithium silicate composite particles.
  • the first coating comprises, in the thickness direction of the first coating from the surface of the lithium silicate composite particles, a region A in which the carbon material and the oxide of the first element with low crystallinity are mixed, and the first from the surface of the lithium silicate composite particles.
  • a region B may be included in which the low-crystalline oxide of the first element is present without the carbon material.
  • the composite particle may include a portion covered by region A and a portion covered by region B.
  • the surface coverage of the lithium silicate composite particles by the first coating is preferably 90% or more, more preferably 90% or more and 100% or less. Moreover, the surface coverage of the lithium silicate composite particles with the carbon material contained in the first coating is preferably 20% or more and 50% or less.
  • the surface coverage ratio of the composite particles by the carbon material contained in the first coating means the ratio of the area A covering the composite particles.
  • the surface coverage ratio of the composite particles by the first coating means the sum of the ratio of the composite particles covered with the region A and the ratio of the composite particles covered with the region B.
  • the surface coverage of the composite particles by the first coating and the surface coverage of the composite particles by the carbon material contained in the first coating are obtained by the following methods.
  • the cross section of one active material particle (the cross section in the thickness direction of the first coating) is observed by SEM or TEM, and elemental mapping is performed by SEM-EDS (energy dispersive X-ray spectroscopy) or TEM-EDS analysis.
  • a region A is defined as a region in which both the first element and carbon are distributed in the thickness direction of the first coating from the surface of the lithium silicate composite particles according to the elemental mapping.
  • a region B is defined as a region in which the first element is distributed and carbon is not distributed in the thickness direction of the first coating from the surface of the lithium silicate composite particles.
  • a ratio P1 at which the surface of the composite particle is covered with the region A and a ratio P2 at which the surface of the composite particle is covered with the region B are obtained.
  • a plurality of (eg, 5 to 10) active material particles are measured in the same way, and P1 and P2 are obtained and averaged.
  • the average value of P1 be the surface coverage (%) of the lithium silicate composite particles by the carbon material contained in the first coating.
  • the sum of the average value of P1 and the average value of P2 is defined as the surface coverage (%) of the lithium silicate composite particles by the first coating.
  • the proportion of the amorphous oxide of the first element may be greater on the side farther from the surface of the composite particle than on the side closer to the surface of the composite particle. In this case, cracks originating from the surface of the first coating in contact with the electrolyte are easily suppressed, and the composite particles are easily protected by the first coating.
  • the first coating has a thickness T1 A , and has a first region and a second region other than the first region, and the first region has a distance of 0 from the surface of the composite particle of the first coating. .75T1 A , and when the second region is a region where the distance from the surface of the composite particle of the first coating is farther than the first region, the second region is The proportion of oxides of the amorphous first element may be high.
  • the occupancy C1 of the crystalline domain of the oxide of the first element in the first region may be 20% or more and 75% or less.
  • the occupancy C2 of the crystalline domain of the oxide of the first element in the second region may be 0.5% or less, or may be 0%.
  • the above occupancy rates C1 and C2 are obtained by obtaining a TEM image in the thickness direction (first region and second region) of the first coating, and are the same as the above occupancy rate C for the first region and the second region, respectively. It is obtained by analyzing by the method of
  • the occupancy rate of the crystalline domain of the oxide of the first element may be 20% or more and 75% or less. In the region where the distance from the surface of the composite particle of the first coating is longer than 0.85T1 A , the occupancy rate of the crystalline domain of the oxide of the first element may be 0.5% or less, or 0% may be
  • the lithium silicate composite particles included in the active material particles according to this embodiment include a lithium silicate phase and a silicon phase dispersed in the lithium silicate phase.
  • Lithium silicate composite particles usually exist as secondary particles in which multiple primary particles are aggregated.
  • the first coating coats at least part of the surface of the secondary particles.
  • Each primary particle comprises a lithium silicate phase and a silicon phase dispersed within the lithium 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 integrated value is 50% in the volume particle size distribution measured by the laser diffraction scattering method.
  • lithium silicate phase Since the lithium silicate phase (hereinafter sometimes simply referred to as the silicate phase) does not have many sites that can react with lithium, it is difficult for new irreversible reactions to occur during charging and discharging. Therefore, excellent charge/discharge efficiency is exhibited at the initial stage of charge/discharge.
  • a silicate phase is an oxide phase containing Li, Si, and O.
  • the silicate phase may further contain the element M.
  • M is for example from Be, Mg, Al, B, Zr, Nb, Ta, La, V, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F and W It may be at least one selected from the group consisting of Among them, B has a low melting point and is advantageous for improving the fluidity of molten silicate. Also, 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, relative to the total amount of elements other than O contained in the silicate phase.
  • the silicon phase dispersed in the silicate phase has a particulate phase of simple silicon (Si) and is composed of single or multiple crystallites.
  • the crystallite size of the silicon phase is not particularly limited.
  • the crystallite size of the silicon phase is more preferably 10 nm or more and 30 nm or less, and still more preferably 15 nm or more and 25 nm or less.
  • the crystallite size of the silicon phase is 10 nm or more, the surface area of the silicon phase can be kept small, so that the deterioration of the silicon phase accompanied by the generation of irreversible capacitance is less likely to occur.
  • the crystallite size of the silicon phase is calculated by Scherrer's formula from the half width of the diffraction peak attributed to the Si (111) plane in the X-ray diffraction (XRD) pattern of the silicon phase.
  • the content of the silicon phase in the lithium silicate composite particles should be, for example, 30% by mass or more and 80% by mass or less.
  • the content of the silicon phase By setting the content of the silicon phase to 30% by mass or more, the ratio of the silicate phase is reduced, and the initial charge/discharge efficiency is likely to be improved.
  • the content of the silicon phase By setting the content of the silicon phase to 80% by mass or less, it becomes easier 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 together with a silicate phase and a silicon phase.
  • the carbon phase for example, covers at least part of the surface of the silicon phase and exists at least part of the interface between 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 lithium silicate composite particles in a discharged state. A powder sample is analyzed and the spectral intensity of each element is measured. Subsequently, standard samples of commercially available elements are used to create a calibration curve, and the content of each element contained in the silicate phase is calculated.
  • ICP-AES analysis inductively coupled plasma atomic emission spectroscopy
  • Auger electron spectroscopy AES
  • LA-ICP-MS laser ablation ICP mass spectroscopy
  • XPS X-ray photoelectron spectroscopy
  • the first coating coats at least part of the surface of the lithium silicate composite particles, which are secondary particles.
  • the first coating contains a low-crystalline oxide of the first element and a carbon material.
  • the low-crystalline oxide of the first element and the carbon material may be mixed in at least part of the first coating.
  • a large amount of the first element may be present near the surface of the lithium silicate composite particles. This improves the effect of suppressing corrosion of the lithium silicate composite particles.
  • the average elemental ratio RA of the first element to the carbon material in the first coating is not particularly limited.
  • the element ratio RA may be, for example, 0.01 or more and 99 or less.
  • the first element is an element other than non-metallic elements, including metallic elements and so-called metalloid elements.
  • the first element is selected from the group consisting of the elements of Group 3, Group 4, Group 5 and Group 6 of the periodic table in that the corrosion inhibition effect of the lithium silicate composite particles is high. 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 conductivity of the lithium silicate composite particles tends to be low.
  • the conductivity of the lithium silicate composite particles can be dramatically increased.
  • Examples of carbon materials include amorphous carbon with low crystallinity such as carbon black, coal, coke, charcoal, and activated carbon, and graphite with high crystallinity. Among them, amorphous carbon is preferable because it has a low hardness and a large buffering effect on the silicon phase that changes in volume due to 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 and ketjen black.
  • Graphite means a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, and graphitized mesophase carbon particles.
  • the thickness of the first coating is not particularly limited. From the viewpoint of corrosion suppression, the thickness of the first coating may be 0.1 nm or more, 0.5 nm or more, or 1 nm or more. From the viewpoint of conductivity and lithium ion diffusibility, the thickness of the first coating may be 50 nm or less, 10 nm or less, or 2 nm or less. The thickness of the first coating may be, for example, 0.1 nm or more and 50 nm or less, or 0.1 nm or more and 10 nm or less.
  • the thickness of the first coating can be measured by cross-sectional observation of the active material particles using SEM or TEM.
  • an electrochemical device is disassembled to take out an electrochemical element (for example, an electrode), and a cross section of the element is obtained using a cross-section polisher (CP).
  • Ten active material particles having a maximum diameter of 5 ⁇ m or more are randomly selected from the cross-sectional image obtained using SEM or TEM.
  • the thickness of the first coating is measured at five arbitrary points for each particle. An average value of the thickness at these 50 points is calculated. After calculating this average value, data different from the obtained average value by 20% or more are excluded, and the average value is calculated again. This corrected average value is taken as the thickness T1A of the first coating.
  • the starting point of the first coating is the interface between the base particles (see below) formed by the lithium silicate composite particles and the first coating.
  • the point 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.
  • the end point of the first coating can be regarded as a point at which the intensity of the peak attributed to the first element obtained by SEM-EDS analysis is 5% or less of its maximum value.
  • the endpoint of the first coating is the interface between the first coating and the second coating.
  • At least part of the first coating may be covered with a conductive second coating. This further improves the conductivity of the active material particles.
  • the second coating does not substantially contain oxides of the first element.
  • the fact that the second coating does not substantially contain the oxide of the first element means 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 because it is electrochemically stable. Examples of the conductive carbon material include the carbon material contained in the first coating as described above.
  • the thickness of the second coating is not particularly limited. It is preferable that the second coating be thin enough not to substantially affect the average particle size of the lithium silicate composite particles.
  • the thickness of the second coating may be 1 nm or more, and may be 5 nm or more.
  • the thickness of the second coating may be 200 nm or less, and may be 100 nm or less.
  • the thickness of the second coating can be measured by cross-sectional observation of the lithium silicate composite particles using SEM or TEM, as in the case of the first coating.
  • 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 images.
  • the end point of the second coating is, alternatively, the point at which the intensity of the peak attributed to C obtained by SEM-EDS analysis is 5% or less of its maximum value.
  • the thickness T1A of the first coating and the thickness T2A of the second coating preferably satisfy the relationship 0 ⁇ T2A / T1A ⁇ 1500. This makes it easier to achieve both corrosion resistance and improved conductivity.
  • T2 A /T1 A is preferably 5 or more, and preferably 10 or more.
  • T2 A /T1 A is preferably 500 or less, more preferably 100 or less.
  • FIG. 1 is a schematic cross-sectional view showing active material particles according to one embodiment of the present disclosure.
  • FIG. 2 is a schematic cross-sectional view showing an enlarged main part of the active material particles shown in FIG.
  • the active material particles 20 include lithium silicate composite particles 23 , a first coating 27 covering the surfaces thereof, and a second coating 26 covering the first coating 27 .
  • FIG. 3 shows a TEM image of an example of active material particles according to an embodiment of the present disclosure. The TEM image in FIG. 3 shows a portion of the cross section of the active material particles.
  • FIG. 4 is a schematic cross-sectional view showing in detail a cross section of an example of active material particles.
  • the lithium silicate composite particles 23 are secondary particles (mother particles) in which a plurality of primary particles 24 are aggregated.
  • Each primary particle 24 comprises a silicate phase 21 and a silicon phase 22 dispersed within the silicate phase 21 .
  • the silicon phase 22 is dispersed substantially uniformly within the silicate phase 21 .
  • a carbon phase (not shown) is arranged on at least part of the interface S between the adjacent primary particles 24 .
  • the carbon phase may cover at least part of the surface of the silicon phase 22 .
  • the surfaces of the lithium silicate composite particles (mother particles) 23 are covered with a first film 27 .
  • the first coating 27 is covered with the second coating 26 .
  • Electrochemical Device An electrochemical device according to an embodiment of the present disclosure includes a current collector and an active material layer supported on the current collector.
  • the active material layer contains the active material particles described above. Since such an electrochemical element has excellent conductivity and is suppressed from deterioration, an electrochemical device with high capacity and long life can be provided.
  • An example of an electrochemical element is an electrode.
  • 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 embodiments of the present disclosure is preferably used as a negative electrode for lithium ion secondary batteries.
  • Electrochemical Device An electrochemical device according to embodiments of the present disclosure comprises a first electrode, a second electrode, and an electrolyte.
  • One of the first electrode and the second electrode is composed of the electrochemical element described above.
  • Such electrochemical devices have high capacity and long life.
  • An electrochemical device is a device that transfers electrons between substances and causes a chemical reaction through the transfer of electrons.
  • Examples of electrochemical devices include primary batteries, secondary batteries, capacitors, and electric double layer capacitors.
  • 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 a negative electrode active material.
  • the negative electrode active material includes at least the above active material particles (hereinafter sometimes referred to as 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 (hereinafter sometimes referred to as a second active material).
  • a second active material examples include conductive carbon materials that electrochemically occlude and release lithium ions.
  • Examples of conductive carbon materials include graphite, graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Among them, graphite is preferable because it has excellent charging/discharging stability and low irreversible capacity.
  • Graphite means a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, and graphitized mesophase carbon particles. The conductive carbon materials may be used singly or in combination of two or more.
  • 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-porous conductive substrate (metal foil, etc.) or a porous conductive substrate (mesh body, net body, punching sheet, etc.) is used.
  • materials for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.
  • the thickness of the negative electrode current collector is not particularly limited, but is preferably 1 ⁇ m or more and 50 ⁇ m or less, more preferably 5 ⁇ m or more and 20 ⁇ m or less, from the viewpoint of the balance between strength and weight reduction of the negative electrode.
  • binders include at least one selected from the group consisting of polyacrylic acid, polyacrylic acid salts, and derivatives thereof.
  • Li salt or Na salt is preferably used as the polyacrylate. Among them, it is preferable to use crosslinked lithium polyacrylate.
  • Conductive agents include, for example, carbon blacks such as acetylene black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum; and conductive whiskers such as zinc oxide and potassium titanate.
  • conductive metal oxides such as titanium oxide; organic conductive materials such as phenylene derivatives; These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • thickeners examples include carboxymethyl cellulose (CMC) and modified products thereof (including salts such as Na salts), cellulose derivatives such as methyl cellulose (cellulose ethers, etc.); polymer cellulose having a vinyl acetate unit such as polyvinyl alcohol; compound; polyether (polyalkylene oxide such as polyethylene oxide, etc.), and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.
  • CMC carboxymethyl cellulose
  • modified products thereof including salts such as Na salts
  • cellulose derivatives such as methyl cellulose (cellulose ethers, etc.
  • polymer cellulose having a vinyl acetate unit such as polyvinyl alcohol
  • compound compound
  • polyether polyalkylene oxide such as polyethylene oxide, etc.
  • 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.
  • 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, 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.
  • the binder and conductive agent the same ones as exemplified for the negative electrode can be used.
  • the conductive agent graphite such as natural graphite and 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 materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium.
  • the electrolyte includes, for example, a solvent and a lithium salt dissolved in the solvent.
  • the lithium salt concentration in the electrolyte is, for example, 0.5 mol/L or more and 2 mol/L or less.
  • the electrolyte may contain known additives.
  • Aqueous solvents or non-aqueous solvents are used as solvents.
  • 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 ).
  • LiN( SO2F ) 2 LiN ( CF3SO2 ) 2 , LiN ( CF3SO2 ) ( C4F9SO2 ), LiN ( C2F5SO2 ) 2 , etc.
  • lithium halides LiCl, LiBr, LiI, etc.
  • Lithium salts may be used singly or in combination of two or more.
  • a separator may be interposed between the positive electrode and the negative electrode.
  • the separator has high ion permeability and moderate mechanical strength and insulation.
  • Examples of separators include microporous thin films, woven fabrics, non-woven fabrics, and the like.
  • Polyolefin such as polypropylene or polyethylene is used as the material of the separator.
  • An example of the structure of a secondary battery is a structure in which an electrode group formed by winding a positive electrode, a negative electrode, and a separator, and an electrolyte are housed in an exterior body.
  • a laminated electrode group in which a positive electrode and a negative electrode are laminated via a separator is also used instead of the wound electrode group.
  • Other forms of electrode groups may also be applied.
  • the secondary battery may be of any shape such as cylindrical, square, coin, button, and laminate.
  • FIG. 5 is a partially cutaway schematic perspective view of a prismatic secondary battery according to an embodiment of the present disclosure.
  • 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 negative electrode, the positive electrode, and the separator are wound around a flat core, and the electrode group 1 is formed by removing the core.
  • 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 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 lead 3 is electrically connected to the negative terminal 6 .
  • the other end of the positive electrode lead 2 is electrically connected to the sealing plate 5 .
  • a frame made of resin is disposed above the electrode group 1 to separate the electrode group 1 from the sealing plate 5 and to separate the negative electrode lead 3 from the battery case 4 .
  • a method for producing an active material particle according to an embodiment of the present disclosure includes a silicate phase, a silicon phase dispersed in the silicate phase, and a carbon film containing a carbon material.
  • the first coating is formed by introducing the oxide of the first element inside the carbon coating that coats the lithium silicate composite particles.
  • FIG. 6 is a flow chart showing a method for manufacturing active material particles according to an embodiment of the present disclosure.
  • silicon particles are prepared. Silicon particles can be obtained by a chemical vapor deposition method (CVD method), a thermal plasma method, a physical pulverization method, or the like. Silicon nanoparticles having an average particle size of 10 nm or more and 200 nm or less can be synthesized by the following method.
  • the average particle size of silicon particles means the particle size (volume average particle size) at which the volume integrated value is 50% in the volume particle size distribution measured by the laser diffraction scattering method.
  • reaction temperature may be set to, for example, 400° C. or higher and 1300° C. or lower.
  • silane compound silicon hydrides such as silane and disilane, halogenated silanes, alkoxysilanes, and the like can be used.
  • Halogenated silanes include dichlorosilane, trichlorosilane, tetrachlorosilane, and the like.
  • 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 is obtained. That is, the atmosphere of the vapor phase may be an oxidizing gas atmosphere. Silicon oxide is removed by washing the composite with, for example, hydrofluoric acid, yielding silicon particles.
  • the molten metal finely divided by the atomization method may be brought into contact with the silane compound.
  • the molten metal Na, K, Mg, Ca, Zn, Al, etc. can be used.
  • An inert gas, halogenated silane, hydrogen gas, or the like may be used as the atomizing gas. That is, the gas phase atmosphere may be an atmosphere of an inert gas or a reducing gas.
  • Thermal Plasma method is a method in which silicon raw materials are introduced into the generated thermal plasma to generate silicon particles in the high-temperature plasma.
  • Thermal plasma may be generated by arc discharge, high frequency discharge, microwave discharge, laser light irradiation, or the like.
  • radio frequency (RF) discharge is non-polar discharge, and is desirable in that impurities are less likely to be mixed into the silicon particles.
  • silicon oxide can be used as the raw material.
  • silicon and oxygen in the state of atoms or ions are instantly generated, and during cooling, the silicon bonds and solidifies to generate silicon particles.
  • a physical pulverization method (mechanical milling method) is a method of pulverizing coarse silicon particles with a pulverizer such as a ball mill or a bead mill.
  • the interior of the grinder may be, for example, an inert gas atmosphere.
  • (i-ii) Coating of Silicon Particles with Carbon Phase At least part of the surface of the silicon particles may be coated with a carbon phase.
  • Methods for coating silicon particles with a carbon phase include chemical vapor deposition (CVD), sputtering, atomic layer deposition (ALD), wet mixing, and dry mixing. Among them, CVD method, wet mixing method and the like are preferable.
  • (a) Chemical Vapor Deposition Method silicon particles are introduced into a hydrocarbon-based gas atmosphere and heated to deposit a carbon material generated by thermal decomposition of the hydrocarbon-based gas on the surface of the particles to form a carbon phase. is formed.
  • the temperature of the hydrocarbon-based gas atmosphere may be, for example, 500° C. or higher and 1000° C. or lower.
  • Chain hydrocarbon gases such as acetylene and methane, and aromatic hydrocarbons such as benzene, toluene and xylene can be used as the hydrocarbon-based gas.
  • a carbon precursor such as coal pitch, petroleum pitch, or tar is dissolved in a solvent, and the obtained solution and silicon particles are mixed and dried. After that, the silicon particles coated with the carbon precursor are heated in an inert gas atmosphere at, for example, 600° C. or less and 1000° C. or less to carbonize the carbon precursor and form a carbon phase.
  • a raw material for the silicate phase is prepared.
  • 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 melting the raw material mixture and passing the melt through a metal roll to form flakes.
  • the raw material mixture may be baked at a temperature below the melting point to synthesize silicate by a solid phase reaction without melting.
  • Silicon oxide (eg, SiO 2 ) can be used as the Si raw material.
  • Li source or element M source lithium or element M carbonate, oxide, hydroxide, hydride, nitrate, sulfate, or the like can be used, respectively. Among them, carbonates, oxides, hydroxides and the like are preferable.
  • silicon particles whose surfaces are at least partly coated with a carbon phase are added to the silicate, and the two are mixed.
  • carbon-coated silicon particles silicon particles whose surfaces are at least partly coated with a carbon phase
  • lithium silicate composite particles are produced through the following steps.
  • carbon-coated silicon particles and silicate powder are mixed at a mass ratio of, for example, 20:80 to 95:5.
  • a device such as a ball mill is used to stir the mixture of carbon-coated silicon particles and silicate.
  • an organic solvent may be charged into the pulverization vessel at once in the initial stage of pulverization, or may be intermittently introduced into the pulverization vessel in a plurality of times during the pulverization process.
  • the organic solvent plays a role in preventing the material to be ground from adhering to the inner wall of the grinding vessel.
  • organic solvents alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicate esters, metal alkoxides and the like can be used.
  • the mixture is heated and sintered at 450°C or higher and 1000°C or lower while being pressurized, for example, in an inert gas atmosphere (eg, an atmosphere of argon, nitrogen, etc.).
  • an inert gas atmosphere eg, an atmosphere of argon, nitrogen, etc.
  • a sintering apparatus capable of applying pressure in an inert atmosphere, such as hot press or discharge plasma sintering, can be used.
  • the silicate melts and flows to fill the gaps between the silicon particles.
  • the sintered body obtained is pulverized to obtain lithium silicate composite particles.
  • lithium silicate composite particles having a predetermined average particle size can be obtained.
  • Methods for forming a carbon film on the surface of lithium silicate composite particles include chemical vapor deposition using chain hydrocarbon gases such as acetylene and methane, coal pitch, petroleum pitch, phenolic resin, etc., on lithium silicate composite particles. and a method of heating and carbonizing can be exemplified. Carbon black may be adhered to the surface of the lithium silicate composite particles.
  • the carbon coating be thin enough not to substantially affect the average particle size of the lithium silicate composite particles.
  • the thickness of the carbon coating be equal to or greater than the desired thickness of the first coating.
  • the carbon coating 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 coating can be measured by cross-sectional observation of the lithium silicate composite particles using SEM or TEM, similarly to the first coating.
  • a step of washing the lithium silicate composite particles having a carbon coating with an acid may be performed.
  • an acidic aqueous solution it is possible to dissolve and remove trace amounts of alkaline components that may exist on the surfaces of the lithium silicate composite particles.
  • an aqueous solution of inorganic acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid and carbonic acid
  • an aqueous solution of organic acids such as citric acid and acetic acid
  • Step of forming first coating A lithium silicate composite particle having a carbon coating is exposed to a gas phase containing a first element. As a result, the first element is introduced into the carbon coating, and a first coating containing the oxide of the first element and the carbon material is formed on at least part of the surface of the lithium silicate composite particles.
  • vapor phase methods examples include CVD, ALD, and physical vapor deposition (PVD).
  • ALD method is preferable because the first coating can be formed at a relatively low temperature.
  • the first coating can be formed in an atmosphere of 200° C. or less.
  • an organometallic compound (precursor) containing the first element is used as the raw material for the first coating.
  • a raw material gas containing a vaporized precursor and an oxidant are alternately supplied to a reaction chamber in which an object is placed. As a result, a layer containing the oxide of the first element is formed on the surface of the object.
  • At least part of the surface of the target lithium silicate composite particles is covered with a carbon coating.
  • the first element contained in the source gas can pass through the carbon coating and reach the surface of the lithium silicate composite particles. Then, the first element is deposited as it is on the surface of the lithium silicate composite particles. Therefore, more of the first element is arranged near the surface of the lithium silicate composite particles.
  • the formed first coating contains the carbon material derived from the carbon coating together with the oxide of the first element. If there is a portion not covered with the carbon film on the surface of the target lithium silicate composite particles, the first element contained in the raw material gas is deposited on the surface of the lithium silicate composite particles in that portion.
  • the self-limiting action works, so the first element is deposited on the surface of the object in units of atomic layers.
  • the thickness of the first film is determined by the number of cycles in which one cycle is supply of raw material gas (pulse) ⁇ exhaust of raw material gas (purge) ⁇ supply of oxidant (pulse) ⁇ exhaust of oxidant (purge). controlled.
  • oxidant supply (pulse) ⁇ oxidant exhaust (purge) ⁇ source gas supply (pulse) ⁇ source gas exhaust (purge) may be one cycle. If the thickness of the first coating is controlled to be approximately the same as that of the carbon coating, the oxide of the first element can be arranged over the entire carbon coating although there is a concentration gradient.
  • the first coating containing the oxide of the first element and the carbon material is formed on the surface side of the lithium silicate composite particles, and the lithium silicate composite particles are formed.
  • a second coating from the remainder of the carbon coating is formed at a position further away from the surface than the first coating.
  • a precursor is an organometallic compound containing the first element.
  • Various organometallic compounds conventionally used in the ALD method can be used as precursors.
  • Precursors containing Ti include, for example, bis(t-butylcyclopentadienyl)titanium (IV) dichloride (C 18 H 26 Cl 2 Ti), tetrakis(dimethylamino)titanium (IV) ([(CH 3 ) 2 N ]4Ti, TDMAT), tetrakis(diethylamino)titanium( IV ) ([( C2H5 )2N]4Ti), tetrakis(ethylmethylamino)titanium( IV ) ( Ti[N ( C2H5 )(CH 3 )] 4 ), titanium (IV) (diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate (Ti[OCC(CH 3 ) 3 CHCOC( CH3 ) 3 ] 2 ( OC3H7 ) 2 ), titanium tetrachloride ( TiCl4 ),
  • the source gas may contain multiple 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 source 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.
  • oxidizing agents include water, oxygen, and ozone.
  • the oxidant may be supplied to the reaction chamber as an oxidant-based plasma.
  • the conditions for the ALD method are not particularly limited.
  • the crystallinity of the oxide of the first element is determined by, for example, the temperature of the atmosphere containing the precursor or oxidizing agent in the reaction chamber, the pressure of the reaction chamber during processing, the pulse time of the source gas, the back pressure of the reaction chamber before processing, and the like. It can be controlled by adjusting.
  • the temperature of the atmosphere containing the precursor or the oxidizing agent in the reaction chamber may be, for example, 25° C. or higher and 200° C. or lower, It may be 50°C or higher and 150°C or lower.
  • the pressure in the reaction chamber during treatment may be, for example, 1 ⁇ 10 ⁇ 5 Pa or more and 1 ⁇ 10 ⁇ 2 Pa or less, and 1 ⁇ 10 ⁇ 4 Pa or more and 1 ⁇ 10 ⁇ 3 Pa or less.
  • the pulse time of the source gas may be 0.01 seconds or more and 5 seconds or less, or may be 0.05 seconds or more and 3 seconds or less.
  • the amorphous first layer is formed on the side farther from the surface of the composite particle than on the side closer to the surface of the composite particle.
  • a first coating can be formed with a high proportion of elemental oxides.
  • An embodiment electrochemical device of the present disclosure includes the first active material described above. This electrochemical device is obtained by supporting a first active material having a first coating on the surface of a current collector. This electrochemical device can also be obtained by supporting lithium silicate composite particles coated with a carbon film on the surface of a current collector and then forming a first film by a vapor phase method.
  • FIG. 7 is a flow chart showing a method for manufacturing an electrochemical device according to one embodiment of the present disclosure.
  • the manufacturing method shown in FIG. 7 prepares lithium silicate composite particles containing a silicate phase and a silicon phase dispersed in the silicate phase, and at least a portion of the surface of which is coated with a carbon film containing a carbon material.
  • Lithium silicate composite particle preparation step (S21) Lithium silicate composite particles coated with a carbon film are prepared in the same manner as the steps (ii) to (i-iv) of the lithium silicate composite particle preparation step in the method for producing active material particles.
  • Step of supporting lithium silicate composite particles (S22) A slurry obtained by dispersing the prepared negative electrode mixture containing the lithium silicate composite particles in a dispersion medium is applied to the surface of the current collector, and the slurry is dried. Thereby, the precursor of the active material layer is formed on the surface of the current collector.
  • the dispersion medium is not particularly limited, but 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. .
  • Step of forming first coating A current collector comprising a precursor of an active material layer is exposed to a gas phase containing a first element. As a result, the first element is introduced into the carbon coating, and at least part of the surface of the lithium silicate composite particles contained in the precursor is covered with the first coating containing the oxide of the first element and the carbon material. Thereby, an active material layer is formed.
  • the ALD method is preferably used as described above.
  • the precursor and oxidant shown in the first coating forming step (ii) in the method for producing active material particles can be used.
  • the conditions for the ALD method are not particularly limited.
  • the temperature of the atmosphere containing the precursor or oxidant, the pressure of the reaction chamber during treatment, and the pulse time of the raw material gas are the precursor or oxidant shown in the first coating forming step (ii) in the method for producing active material particles. , the pressure of the reaction chamber during processing, and the pulse time of the raw material gas.
  • the active material layer may be rolled.
  • the rolling conditions are not particularly limited, and may be appropriately set so that the active material layer has a predetermined thickness or density. This increases the density of the active material layer and increases the capacity of the electrochemical device.
  • a carbon material was deposited on the surfaces of silicon particles by chemical vapor deposition. 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 was 10 parts by mass with respect to 100 parts by mass of silicon particles.
  • Lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 ⁇ m and carbon-coated silicon were mixed at a mass ratio of 70:30.
  • the mixture is filled into a pot (made of SUS, volume 500 mL) of a planetary ball mill (manufactured by Fritsch, P-5), 24 SUS balls (20 mm in diameter) are placed in the pot, the lid is closed, and in an inert atmosphere, 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 while applying pressure from a hot press to obtain a sintered body of the mixture. After that, the sintered body was pulverized to obtain lithium silicate composite particles.
  • the crystallite size of the silicon phase calculated by Scherrer's formula 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 the silicon phase was 30% by mass).
  • Negative Electrode Precursor Lithium silicate composite particles having a carbon coating and a second active material (graphite) were mixed at a mass ratio of 5:95 and used as a negative electrode active material.
  • Water was added to a negative electrode mixture containing a negative electrode active material, sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), and lithium polyacrylate at a mass ratio of 96.5:1:1.5:1. was added, and then stirred using a mixer (TK Hibismix, manufactured by Primix) to prepare a negative electrode slurry.
  • the 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.
  • a negative electrode precursor on which a negative electrode active material layer was formed was produced.
  • the thickness of the negative electrode active material layer in the negative electrode precursor was 202 ⁇ m.
  • a negative electrode precursor was placed in a predetermined reaction chamber, and a first coating was formed on the surface of the negative electrode precursor according to the following procedure by ALD.
  • a vaporized oxidant (H 2 O) was supplied to the reaction chamber containing the negative electrode precursor.
  • the pulse time was 0.015 seconds.
  • the temperature of the atmosphere containing the oxidizing agent in the reaction chamber was controlled to 150° C., and the reaction pressure was controlled to 200 Pa. After 30 seconds, excess oxidant was purged with nitrogen gas. The purge was for 1 minute.
  • a vaporized precursor (TDMAT) serving as a supply source of the first element (Ti) was supplied to the reaction chamber containing the negative electrode precursor.
  • the pulse time was 0.05 seconds.
  • the temperature of the atmosphere containing the precursor in the reaction chamber was controlled at 150° C., and the reaction pressure was controlled at 260 Pa. After 30 seconds, excess precursor was purged with nitrogen gas, assuming that the surface of the negative electrode precursor was covered with a monomolecular layer of precursor. The purge was for 1 minute.
  • a series of operations consisting of supply of oxidant, purge, supply of precursor, and purge were repeated 22 times to form a first film containing titanium.
  • the first coating and the second coating covering the first coating were simultaneously formed by adjusting the thickness of the first coating to be thinner than the carbon coating.
  • the first and second coatings were analyzed by SEM, EDS, ICP, etc.
  • the first coating contained Ti and C.
  • the second coating contained C.
  • the thickness T1A of the first coating was 5 nm.
  • the thickness T2A of the second coating was 45 nm.
  • the occupation rate C obtained by the method described above was 20%, the occupation rate C1 was 50%, and the occupation rate C2 was 0%.
  • the negative electrode active material layer was rolled to obtain a negative electrode.
  • 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) at a volume ratio of 3:7.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • a tab was attached to each electrode, and an electrode group was produced by spirally winding the positive electrode and the negative electrode with the separator interposed therebetween such that the tab was positioned at the outermost periphery. After inserting the electrode group into an outer package made of an aluminum laminate film and vacuum-drying at 105° C. for 2 hours, an electrolytic solution was injected and the opening of the outer package was sealed to obtain a secondary battery A1.
  • the thickness T1 A of the first coating was 5 nm, and the thickness T2 A of the second coating was 45 nm.
  • the surface coverage of the lithium silicate composite particles by the carbon material of the first coating, determined by the method described above, was 30%, and the surface coverage of the lithium silicate composite particles by the first coating was 100%.
  • the occupation rate C obtained by the method described above was 5%, the occupation rate C1 was 20%, and the occupation rate C2 was 0%.
  • the thickness T1 A of the first coating was 5 nm, and the thickness T2 A of the second coating was 45 nm.
  • the surface coverage of the lithium silicate composite particles by the carbon material of the first coating, determined by the method described above, was 30%, and the surface coverage of the lithium silicate composite particles by the first coating was 100%.
  • the occupation rate C obtained by the method described above was 30%, the occupation rate C1 was 60%, and the occupation rate C2 was 0%.
  • the thickness T1 A of the first coating was 5 nm, and the thickness T2 A of the second coating was 45 nm.
  • the surface coverage of the lithium silicate composite particles by the carbon material of the first coating, determined by the method described above, was 30%, and the surface coverage of the lithium silicate composite particles by the first coating was 100%.
  • the occupation rate C obtained by the method described above was 5%, the occupation rate C1 was 20%, and the occupation rate C2 was 0%.
  • a secondary battery B2 was produced by manufacturing an active material in the same manner as in Example 1, except that the formation of the first coating and the second coating (6) was not performed.
  • the active material was coated with a carbon film having a thickness of 50 nm.
  • the thickness T1 A of the first coating was 5 nm, and the thickness T2 A of the second coating was 45 nm.
  • the surface coverage of the lithium silicate composite particles by the carbon material of the first coating, determined by the method described above, was 30%, and the surface coverage of the lithium silicate composite particles by the first coating was 100%.
  • the occupation rate C obtained by the method described above was 100%.
  • the rest period between charging and discharging was 10 minutes.
  • the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle was taken as the capacity retention rate.
  • the DC internal resistance (DCIR) was obtained from the voltage change before and after the 100th cycle discharge and the discharge current value. Table 1 shows the evaluation results.
  • batteries A1 to A4 the crystallinity of the oxide of the first element contained in the first coating was low, and the capacity retention rate after 100 cycles was higher and the internal resistance after 100 cycles was lower than those of batteries B1 and B2. .
  • an electrochemical device with high capacity and long life can be provided.
  • the electrochemical device according to the present disclosure is useful as a main power source for mobile communication equipment, portable electronic equipment, and the like.

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PCT/JP2021/043115 2021-02-03 2021-11-25 活物質粒子、電気化学素子、および電気化学デバイス Ceased WO2022168408A1 (ja)

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