WO2023026921A1 - 電気化学デバイス - Google Patents

電気化学デバイス Download PDF

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WO2023026921A1
WO2023026921A1 PCT/JP2022/031067 JP2022031067W WO2023026921A1 WO 2023026921 A1 WO2023026921 A1 WO 2023026921A1 JP 2022031067 W JP2022031067 W JP 2022031067W WO 2023026921 A1 WO2023026921 A1 WO 2023026921A1
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negative electrode
layer
positive electrode
peak
electrochemical device
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French (fr)
Japanese (ja)
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祥平 増田
健一 永光
宣寛 島村
信敬 武田
英郎 坂田
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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 CN202280057633.9A priority Critical patent/CN117836886A/zh
Priority to US18/686,257 priority patent/US20250023196A1/en
Priority to JP2023543843A priority patent/JPWO2023026921A1/ja
Publication of WO2023026921A1 publication Critical patent/WO2023026921A1/ja
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    • H—ELECTRICITY
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/04—Hybrid capacitors
    • H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/52—Separators
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • 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
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/443—Particulate material
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    • 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
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to electrochemical devices.
  • An electrochemical device using a carbon material in which lithium ions are occluded in a negative electrode material layer is known (see Patent Documents 1 to 3).
  • An electrochemical device includes a positive electrode, a negative electrode and an electrolyte.
  • As a lithium ion conductive electrolyte an electrolytic solution in which a lithium salt such as LiPF 6 is dissolved in a non-aqueous solvent is known.
  • Patent Document 4 discloses an electrolytic solution containing a mixture of lithium bis(fluorosulfonyl)imide (LiFSI) and LiBF4 , a solvent containing at least one cyclic or chain carbonate compound, and a film-forming agent.
  • LiFSI lithium bis(fluorosulfonyl)imide
  • LiBF4 a solvent containing at least one cyclic or chain carbonate compound
  • a film-forming agent a film-forming agent.
  • lithium ion capacitors have been proposed in which the molar ratio of LiFSI to LiBF 4 is 90/10 to 30/70 and the concentration of the mixture in the electrolyte is 1.2 to 1.8 mol/L.
  • a solid electrolyte interfacial coating that is, SEI coating
  • SEI coating plays an important role in charge/discharge reactions, but if the SEI coating is excessively thick, the internal resistance of the electrochemical device increases.
  • the negative electrode is pre-doped with lithium ions before charging and discharging. Pre-doping is performed, for example, by immersing the negative electrode in an electrolytic solution containing lithium ions and applying a voltage to the negative electrode.
  • the main component of the SEI coating is LiF.
  • the SEI coating mainly composed of LiF is stable to the electrolyte, but has high resistance.
  • LiPF 6 when using an electrolyte in which a fluorine-containing phosphate such as LiPF 6 is dissolved, LiPF 6 is highly reactive with water and easily decomposed. Decomposition produces HF. The HF produced disrupts the SEI coating. For this reason, it is difficult to form a good quality SEI film, and the internal resistance of the device tends to increase.
  • LiFSI hardly reacts with water, and HF is hardly generated.
  • an SEI film containing LiF as a main component is likely to be formed, increasing the internal resistance of the device.
  • One aspect of the present invention includes a positive electrode, a negative electrode, a separator and a lithium ion conductive electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material layer carried on the negative electrode current collector;
  • the negative electrode material layer includes a negative electrode active material reversibly doped with lithium ions, a surface layer portion of the negative electrode material layer has a coating region, the separator includes an olefin resin, and the coating region is
  • X-ray photoelectron spectroscopy in the O1s spectrum, a peak is observed in the binding energy range of 530 to 534 eV, and the intensity of the peak in the O1s spectrum increases from the surface layer of the coating region toward the inside. , relating to electrochemical devices.
  • an increase in internal resistance of an electrochemical device is suppressed.
  • FIG. 1 is a longitudinal sectional view showing the configuration of an electrochemical device according to one embodiment of the present invention
  • FIG. 1 is a graph showing the XPS analysis results of a coating region formed so that the first layer containing lithium fluoride covers the second layer containing lithium carbonate, and the top of the peak attributed to the lithium carbonate bond in the O1s spectrum
  • the peak intensity A, the peak intensity B at the peak apex of the F1s spectrum, and the variation of the peak intensity ratio A/B in the depth direction of the coated region are shown.
  • An electrochemical device includes a positive electrode, a negative electrode and a lithium ion conductive electrolyte.
  • a positive electrode and a negative electrode constitute an electrode body together with a separator interposed therebetween.
  • the electrode body is configured as a columnar wound body by, for example, winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator interposed therebetween.
  • the electrode body may be configured as a laminate by laminating a plate-like positive electrode and a plate-like negative electrode with a separator interposed therebetween.
  • the separator contains an olefinic resin.
  • the negative electrode includes a negative electrode current collector and a negative electrode material layer carried on the negative electrode current collector.
  • the negative electrode material layer includes a negative active material reversibly doped with lithium ions.
  • a negative electrode active material contains a carbon material.
  • the doping of lithium ions into the negative electrode active material includes at least the absorption phenomenon of lithium ions into the negative electrode active material, such as the adsorption of lithium ions to the negative electrode active material and the chemical interaction between the negative electrode active material and lithium ions. It is a concept that can also include
  • a surface layer portion of the negative electrode material layer has a coating region.
  • the coating region is the region where the SEI coating is formed.
  • the SEI coating includes lithium carbonate ( Li2CO3 ).
  • An SEI coating containing lithium carbonate has low resistance to movement of lithium ions, and by forming an SEI coating containing lithium carbonate as a main component, the internal resistance of an electrochemical device can be reduced.
  • the SEI coating containing lithium carbonate as a main component easily reacts with HF generated by the decomposition reaction of the electrolytic solution or the like, and the SEI coating easily collapses.
  • the SEI coating may also contain lithium fluoride (LiF).
  • LiF lithium fluoride
  • SEI coatings containing lithium fluoride are stable to electrolytes and have low reactivity with HF.
  • the SEI film containing lithium fluoride as a main component has high resistance to lithium ion migration, and the internal resistance of the electrochemical device tends to increase.
  • a peak attributed to the lithium carbonate bond is a peak attributed to the C ⁇ O bond (or C—O bond) of lithium carbonate, and can appear in a binding energy range of 530 to 534 eV.
  • XPS X-ray photoelectron spectroscopy
  • the intensity of the peak observed in the binding energy range of 530 to 534 eV increases from the surface of the coating region toward the inside. This is because, in the coating region, lithium carbonate is unevenly distributed in the depth direction so that more lithium carbonate is present in the central portion and deep portion (negative electrode active material side) of the coating region. It means that the amount of lithium is reduced. As a result, contact of the SEI coating containing a large amount of lithium carbonate with the electrolyte is regulated, and collapse of the SEI coating is suppressed while maintaining low lithium ion transfer resistance.
  • the intensity of the peak observed in the binding energy range of 530 to 534 eV may increase from the surface layer of the coating region to an arbitrary depth inward.
  • the intensity of the peak observed in the binding energy range of 530 to 534 eV may increase inward from the surface of the film region and then decrease.
  • the intensity of the peak observed in the binding energy range of 684.8 to 685.3 eV is the intensity of the peak attributed to the above lithium carbonate bond in the O1s spectrum. It may decrease from the surface of the coating region toward the inside in a region of depth that increases from the surface to the inside. That is, an SEI coating containing a large amount of lithium fluoride can be formed on the surface layer of the coating region that contacts the electrolytic solution.
  • the SEI coating containing a large amount of lithium fluoride is stable against the electrolytic solution, and the SEI coating is difficult to collapse.
  • the thickness of the SEI coating containing a large amount of lithium fluoride may be small, and an increase in lithium ion migration resistance is suppressed.
  • the coating region includes a first layer containing a large amount of lithium fluoride formed on the surface layer in contact with the electrolytic solution, and a carbonic acid layer formed inside the first layer (on the side in contact with the negative electrode active material). It has a lithium-rich second layer.
  • the lithium fluoride concentration (per unit volume content) in the first layer is higher than the lithium fluoride concentration in the second layer.
  • the lithium carbonate concentration (content per unit volume) in the second layer is higher than the lithium carbonate concentration in the first layer.
  • the concentration may gradually decrease and/or the concentration of lithium carbonate may gradually increase from the first layer to the second layer.
  • A the peak intensity at the top of the above peak in the O1s spectrum
  • B the peak intensity at the top of the above peak in the F1s spectrum.
  • the distribution of the peak intensity B in the depth direction (thickness direction of the surface layer portion) can have a peak at the surface layer (first layer) of the coating region.
  • the peak intensity A in the depth direction (thickness direction of the surface layer) increases toward the negative electrode active material side in the surface layer of the coating region, and the inner side (negative electrode active material side) of the surface layer. can have a maximum vertex in the second layer of .
  • the peak intensity ratio A/B increases inward from the surface layer of the coated region and then decreases.
  • the peak intensity ratio A/B has a maximum value within the coating region.
  • the surface layer portion of the negative electrode material layer is measured by X-ray photoelectron spectroscopy, a peak attributed to the carbon material is substantially observed in the C1s spectrum at the depth position where the peak intensity ratio A / B is maximum. not.
  • the peak attributed to the carbon material in the C1s spectrum is the peak attributed to the in-plane C—C bond of graphite, and can appear in the range of binding energy from 281 to 283 eV.
  • the fact that no peak attributed to the carbon material is substantially observed means that the peak intensity at the apex of the above peak is 0.2 times or less of the peak intensity A.
  • the maximum value of the peak intensity ratio A/B in the depth direction is, for example, 0.5 or more and 2 or less, and may be 1 or more and 1.8 or less. Note that the peak intensities A and B are obtained from the height of the peaks from the baseline.
  • a layer (second layer) containing a large amount of lithium carbonate may be formed on the surface layer of the negative electrode material layer before assembling the electrochemical device.
  • the first layer containing a large amount of lithium fluoride on the surface of the negative electrode active material is uniform and has an appropriate thickness
  • the second layer is the base layer.
  • the first layer is formed, for example, by reaction between an electrolyte and a negative electrode in an electrochemical device.
  • the second layer containing lithium carbonate has the effect of promoting the formation of the first layer, which is a good SEI film, and maintaining the SEI film in a good state when charging and discharging are repeated.
  • the negative electrode on which the second layer containing lithium carbonate is formed is susceptible to deterioration in performance due to deterioration of the separator. It is believed that this is because metallic lithium reacts with the separator during the formation of the first layer or during pre-doping, and the separator is easily damaged.
  • cellulose-based separators which have been generally used in the past, have a large number of functional groups such as OH groups that easily react with lithium ions, and also contain relatively large amounts of water, so they are susceptible to damage due to side reactions. easy.
  • the amount of lithium pre-doped into the negative electrode can be reduced by the reaction of metallic lithium with the separator.
  • the main reason why cellulose-based separators are generally used is that they are excellent in electrolyte permeability and facilitate pre-doping.
  • the formation of the first layer is carried out by bringing the negative electrode material layer, on which the second layer is formed on the surface layer, into contact with the electrolyte.
  • the second layer can be formed by a gas phase method, a coating method, or by vapor-depositing metallic lithium on the surface of the negative electrode material layer and then exposing it to a carbon dioxide gas atmosphere.
  • the first layer is formed by bringing the negative electrode material layer into contact with the electrolyte in a wound body in which the positive electrode and the negative electrode are wound with a separator interposed therebetween. Occasionally the separator is damaged.
  • the electrochemical device uses a separator containing an olefinic resin (olefinic separator). Since the olefinic separator has low reactivity with metallic lithium, the use of a separator containing an olefinic resin suppresses the deterioration of the separator and improves the reliability of the electrochemical device. In addition, the olefin-based separator has high strength, and sufficiently high strength can be obtained even if it is made into a thin film. Therefore, by tightly winding the positive electrode and the negative electrode, a wound body having a high surface pressure can be used, and the performance such as the capacity of the electrochemical device can be improved.
  • olefinic separator has low reactivity with metallic lithium
  • the use of a separator containing an olefinic resin suppresses the deterioration of the separator and improves the reliability of the electrochemical device.
  • the olefin-based separator has high strength, and sufficiently high strength can be obtained even if it is made into a thin
  • the olefin resin contained in the separator preferably contains at least one selected from the group consisting of polypropylene (PP) and polyethylene (PE).
  • PP separators and PE separators have high strength and are stable to electrolytes containing lithium ions, so they can be preferably used in electrochemical devices in which the first layer and the second layer are formed on the surface layer of the negative electrode material layer. .
  • the electrochemical device As described above, according to the electrochemical device according to the present embodiment, by forming a film containing lithium carbonate on the surface layer of the negative electrode material layer, the resistance to lithium ion migration is reduced, and the internal resistance of the electrochemical device is reduced. can. Further, by using a separator containing an olefin resin, deterioration of the separator is suppressed, a state of low internal resistance is maintained for a long period of time, and reliability is improved.
  • olefinic separators have a higher air permeability resistance than cellulose separators, and the passage speed of lithium ions through the separator is slow.
  • Such high air permeability resistance of the olefinic separator does not pose a problem in normal charging and discharging of electrochemical devices, but in the pre-doping process of lithium ions, the passage speed of lithium ions is slow, so it takes time for pre-doping. may be required.
  • the air resistance A of the separator is preferably 70 sec/100 mL or more and 500 sec/100 mL or less. When the air resistance A is within this range, both reduction in internal resistance and improvement in reliability of the electrochemical device can be achieved. More preferably, the permeation resistance A of the palette may be 70 sec/100 mL or more and 300 sec/100 mL or less, 70 sec/100 mL or more and 230 sec/100 mL or less, or 180 sec/100 mL or more and 230 sec/100 mL or less.
  • air resistance A is the time (seconds) required for a given volume (100 mL) of air per unit area of the separator to permeate when a given pressure difference is applied between both sides of the separator. Based on JIS P8117:2009, it is measured by a Gurley tester method with a separator area (permeable portion) of 6.42 cm 2 and an inner cylinder weight of 567 g.
  • the thickness of the separator is preferably 12 ⁇ m or more and 30 ⁇ m or less in terms of easy permeation of lithium ions and sufficient strength.
  • the thickness of the first layer containing a large amount of lithium fluoride may be, for example, 1 nm or more, may be 3 nm or more, and is sufficient if it is 5 nm or more. However, when the thickness of the first layer exceeds 20 nm, the first layer itself can become a resistance component. Therefore, the thickness of the first layer may be 20 nm or less, or 10 nm or less.
  • the thickness of the second layer containing a large amount of lithium carbonate may be, for example, 1 nm or more, and may be 5 nm or more when a longer-term effect is expected, and when a more reliable effect is expected. It may be 10 nm or more.
  • the thickness of the second layer may be 50 nm or less, or 30 nm or less. For example, 1 nm to 50 nm.
  • the thickness of the coating region is measured by analyzing the surface layer portion of the negative electrode material layer at a plurality of locations (at least five locations) of the negative electrode material layer. Then, the average of the thicknesses of the first layer or the second layer obtained at a plurality of locations may be taken as the thickness of the first layer or the second layer.
  • the negative electrode material layer provided for the measurement sample may be peeled off from the negative electrode current collector.
  • the film formed on the surface of the carbon material forming the vicinity of the surface layer of the negative electrode material layer may be analyzed.
  • the carbon material covered with the film may be sampled from the region of the negative electrode material layer disposed on the side opposite to the surface bonded to the negative electrode current collector and used for analysis.
  • the coating formed on the surface layer of the negative electrode material layer or on the surface of the carbon material is removed in the electrochemical device. It has an SEI coating (ie, the first layer) produced. In this case, a peak attributed to lithium carbonate can also be observed in the first layer in the O1s spectrum. However, it is possible to distinguish between the first layer containing the material produced in the electrochemical device, because it has a different composition than the second layer, which is pre-formed prior to assembly of the electrochemical device.
  • there may be a third region which is closer to the outermost surface of the surface layer than the first region and where the first peak is observed and the second peak is not observed. The third region is likely to be observed when the thickness of the second layer is large.
  • XPS analysis of the surface layer of the negative electrode material layer is performed, for example, by irradiating the surface layer or the coating formed on the surface of the carbon material with an argon beam in the chamber of an X-ray photoelectron spectrometer, and measuring the C1s, O1s or F1s electrons with respect to the irradiation time. Observe and record the change in each spectrum attributed to . At this time, from the viewpoint of avoiding analysis errors, the spectrum of the outermost surface of the surface layer may be ignored.
  • the thickness of the region where the peak attributed to lithium fluoride is stably observed corresponds to the thickness of the first layer.
  • the thickness of the region where the peak attributed to lithium carbonate is stably observed corresponds to the thickness of the second layer.
  • a method for forming a coating region on the surface layer of the negative electrode material layer will be described.
  • a second layer containing lithium carbonate is formed on the surface layer of the negative electrode material layer.
  • the step of forming the second layer can be performed by, for example, a vapor phase method, a coating method, a transfer method, or the like.
  • Vapor phase methods include methods such as chemical vapor deposition, physical vapor deposition, and sputtering.
  • lithium carbonate may be deposited on the surface of the negative electrode material layer using a vacuum vapor deposition apparatus.
  • the pressure in the apparatus chamber during vapor deposition may be, for example, 10 ⁇ 2 to 10 ⁇ 5 Pa
  • the temperature of the lithium carbonate evaporation source may be 400 to 600° C.
  • the temperature of the negative electrode material layer may be ⁇ 20 to 80° C. °C.
  • the second layer can be formed by applying a solution or dispersion containing lithium carbonate to the surface of the negative electrode using, for example, a micro gravure coater and drying.
  • the content of lithium carbonate in the solution or dispersion is, for example, 0.3 to 2% by mass, and when a solution is used, the concentration is below the solubility (for example, about 0.9 to 1.3% by mass for an aqueous solution at room temperature). If it is
  • a negative electrode can be obtained by performing a step of forming a first layer containing lithium fluoride so as to cover at least a portion of the second layer.
  • the surface layer portion of the obtained negative electrode material layer has a first layer and a second layer.
  • the first layer is formed so that at least a portion thereof covers at least a portion (preferably the entire surface) of the surface of the negative electrode active material via the second layer (that is, the second layer serves as a base layer).
  • the step of forming the first layer is performed while the negative electrode material layer and the electrolyte are in contact with each other, it may serve as at least part of the step of pre-doping the negative electrode material layer with lithium ions.
  • Metallic lithium for example, may be used as the pre-doped lithium ion source.
  • the metallic lithium may adhere to the surface of the negative electrode material layer.
  • a second layer containing lithium carbonate having a thickness of 1 nm or more and 50 nm or less can be formed by exposing a negative electrode having a negative electrode material layer to which metallic lithium is attached to a carbon dioxide atmosphere.
  • the step of attaching metallic lithium to the surface of the negative electrode material layer can be performed by, for example, a vapor phase method, transfer, or the like.
  • Vapor phase methods include methods such as chemical vapor deposition, physical vapor deposition, and sputtering.
  • a film of metallic lithium may be formed on the surface of the negative electrode material layer using a vacuum deposition apparatus.
  • the pressure in the apparatus chamber during vapor deposition may be, for example, 10 ⁇ 2 to 10 ⁇ 5 Pa
  • the temperature of the lithium evaporation source may be 400 to 600° C.
  • the temperature of the negative electrode mixture layer may be ⁇ 20 to 80° C. °C.
  • the carbon dioxide gas atmosphere is desirably a dry atmosphere that does not contain moisture.
  • the carbon dioxide atmosphere may contain gases other than carbon dioxide, but the molar fraction of carbon dioxide is desirably 80% or more, more desirably 95% or more. It is desirable not to contain an oxidizing gas, and the molar fraction of oxygen should be 0.1% or less.
  • the partial pressure of carbon dioxide In order to form the second layer thicker, it is efficient to increase the partial pressure of carbon dioxide to, for example, 0.5 atm (5.05 ⁇ 10 4 Pa) or more. Pa) or more.
  • the temperature of the negative electrode exposed to the carbon dioxide atmosphere may be, for example, within the range of 15°C to 120°C. The higher the temperature, the thicker the second layer.
  • the thickness of the second layer can be easily controlled by changing the exposure time of the negative electrode to the carbon dioxide atmosphere.
  • the exposure time may be, for example, 12 hours or more and less than 10 days.
  • the step of forming the second layer is desirably performed before forming the electrode body, but it is not excluded that it is performed after forming the electrode body. That is, a positive electrode is prepared, a negative electrode having a negative electrode material layer to which metallic lithium is attached is prepared, an electrode body is formed by interposing a separator between the positive electrode and the negative electrode, and the electrode body is exposed to a carbon dioxide atmosphere.
  • the second layer may be formed on the surface layer of the negative electrode material layer.
  • the step of pre-doping lithium ions into the negative electrode material layer is, for example, further advanced by bringing the negative electrode material layer and the electrolyte into contact with each other after that, and completed by allowing to stand for a predetermined time.
  • Such a step may be a step of forming the first layer to cover at least a portion of the second layer.
  • a predetermined charging voltage for example, 3.4 to 4.0 V
  • a predetermined time for example, 1 to 75 hours
  • Electrochemical devices according to the present invention include electrochemical devices such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors.
  • a positive electrode material layer containing a carbon material as a positive electrode active material may be used to form a polarizable electrode layer.
  • an electric double layer is formed by adsorption of ions to the positive electrode active material, and capacity is developed on the positive electrode side.
  • the carbon material may be activated carbon, for example.
  • the carbon material for example, activated carbon
  • the carbon material has a specific surface area of 1500 m 2 /g or more and 2500 m 2 /g or less, an average particle size of 10 ⁇ m or less, a total pore volume of 0.5 cm 3 /g or more and 1.5 cm 3 /g or less, and , an average pore diameter of 1 nm or more and 3 nm or less can be preferably used.
  • FIG. 1 schematically shows the configuration of an electrochemical device 200 according to one embodiment of the invention.
  • the electrochemical device 200 includes an electrode body 100, a non-aqueous electrolyte (not shown), a metallic bottomed cell case 210 that houses the electrode body 100 and the non-aqueous electrolyte, and an opening of the cell case 210 is sealed.
  • a sealing plate 220 is provided.
  • a gasket 221 is arranged on the peripheral edge of the sealing plate 220 , and the inside of the cell case 210 is sealed by crimping the open end of the cell case 210 to the gasket 221 .
  • a positive electrode current collector plate 13 having a through hole 13h in the center is welded to the positive electrode core exposed portion 11x.
  • the other end of the tab lead 15 is connected to the inner surface of the sealing plate 220 . Therefore, the sealing plate 220 functions as an external positive electrode terminal.
  • the negative electrode current collector plate 23 is welded to the negative electrode core exposed portion 21x. The negative electrode current collector plate 23 is directly welded to a welding member provided on the inner bottom surface of the cell case 210 . Therefore, the cell case 210 functions as an external negative electrode terminal.
  • the negative electrode includes a negative electrode current collector and a negative electrode material layer (negative electrode mixture layer) supported on the negative electrode current collector.
  • a sheet-like metal material is used for the negative electrode current collector.
  • the sheet-shaped metal material may be a metal foil, a metal porous body, an etched metal, or the like.
  • metal materials copper, copper alloys, nickel, stainless steel, and the like can be used.
  • the negative electrode current collector plate is a generally disk-shaped metal plate.
  • the material of the negative electrode current collector plate is, for example, copper, copper alloy, nickel, stainless steel, or the like.
  • the material of the negative electrode current collector may be the same as the material of the negative electrode current collector.
  • the negative electrode material layer includes, as a negative electrode active material, a carbon material that electrochemically absorbs and releases lithium ions.
  • a carbon material that electrochemically absorbs and releases lithium ions.
  • As the carbon material graphite, non-graphitizable carbon (hard carbon), and graphitizable carbon (soft carbon) are preferable, and graphite and hard carbon are particularly preferable.
  • a carbon material and other materials may be used together.
  • the non-graphitizable carbon may have an interplanar spacing of (002) planes (that is, an interplanar spacing between carbon layers) d 002 of 3.8 ⁇ or more as measured by an X-ray diffraction method.
  • the theoretical capacity of non-graphitizable carbon is desirably 150 mAh/g or more, for example.
  • the non-graphitizable carbon preferably accounts for 50 mass % or more, further 80 mass % or more, furthermore 95 mass % or more of the negative electrode active material.
  • Non-graphitizable carbon and materials other than non-graphitizable carbon may be used together as the negative electrode active material.
  • Materials other than non-graphitizable carbon that can be used as the negative electrode active material include graphitizable carbon (soft carbon), graphite (natural graphite, artificial graphite, etc.), lithium titanium oxide (spinel-type lithium titanium oxide, etc.), silicon Examples include oxides, silicon alloys, tin oxides, and tin alloys.
  • the average particle size of the negative electrode active material (especially non-graphitizable carbon) is preferably 1 ⁇ m to 20 ⁇ m, more preferably 2 ⁇ m to 2 ⁇ m, from the viewpoint of high filling properties of the negative electrode active material in the negative electrode and easy suppression of side reactions with the electrolyte. More preferably, it is 15 ⁇ m.
  • the average particle diameter means the volume-based median diameter (D 50 ) in the particle size distribution obtained by laser diffraction particle size distribution measurement.
  • the negative electrode material layer contains a negative electrode active material as an essential component, and a conductive material, a binder, and the like as optional components.
  • conductive agents include carbon black and carbon fiber.
  • binders include fluorine resins, acrylic resins, rubber materials, and cellulose derivatives.
  • a negative electrode active material, a conductive agent, a binder, and the like are mixed together with a dispersion medium to prepare a negative electrode mixture slurry. Formed by drying.
  • the thickness of the negative electrode material layer is, for example, 10 to 300 ⁇ m per side.
  • the negative electrode material layer is pre-doped with lithium ions in advance. This lowers the potential of the negative electrode, increasing the potential difference (that is, voltage) between the positive electrode and the negative electrode, thereby improving the energy density of the electrochemical device.
  • the amount of lithium to be pre-doped may be, for example, about 50% to 95% of the maximum amount that can be occluded in the negative electrode material layer.
  • the positive electrode includes a positive electrode current collector and a positive electrode material layer (positive electrode mixture layer) supported by the positive electrode current collector.
  • a sheet-like metal material is used for the positive electrode current collector.
  • the sheet-shaped metal material may be a metal foil, a metal porous body, an etched metal, or the like. Aluminum, an aluminum alloy, nickel, titanium, etc. can be used as the metal material.
  • the positive electrode current collector plate is a generally disk-shaped metal plate. It is preferable to form a through-hole as a passage for the non-aqueous electrolyte in the central portion of the positive electrode current collector plate.
  • the material of the positive electrode current collector plate is, for example, aluminum, an aluminum alloy, titanium, stainless steel, or the like. The material of the positive electrode current collector may be the same as the material of the positive electrode current collector.
  • the positive electrode material layer contains a material reversibly doped with anions as a positive electrode active material.
  • the positive electrode active material is, for example, a carbon material, a conductive polymer, or the like.
  • the carbon material used as the positive electrode active material is preferably a porous carbon material, such as activated carbon or the carbon materials exemplified as the negative electrode active material (for example, non-graphitizable carbon).
  • Raw materials for activated carbon include, for example, wood, coconut shells, coal, pitch, and phenolic resin.
  • Activated carbon is preferably activated.
  • the average particle diameter (volume-based median diameter D50) of the carbon material is not particularly limited, it is preferably 20 ⁇ m or less, more preferably 10 ⁇ m or less.
  • the carbon material may have an average particle size of 3 ⁇ m to 10 ⁇ m.
  • the specific surface area of the positive electrode material layer generally reflects the specific surface area of the positive electrode active material.
  • the specific surface area of the positive electrode material layer may be, for example, 600 m 2 /g or more and 4000 m 2 /g or less, and preferably 800 m 2 /g or more and 3000 m 2 /g or less. More desirably, the specific surface area of the positive electrode material layer may be 1500 m 2 /g or more and 2500 m 2 /g or less.
  • the specific surface area of the positive electrode mixture layer is the BET specific surface area obtained using a measuring device (for example, Tristar II3020 manufactured by Shimadzu Corporation) that conforms to JIS Z8830. Specifically, the electrochemical device is disassembled and the positive electrode is taken out. The positive electrode is then washed with dimethyl carbonate (DMC) and dried. Thereafter, the positive electrode mixture layer is peeled off from the positive electrode current collector, and about 0.5 g of a sample of the positive electrode mixture layer is collected.
  • a measuring device for example, Tristar II3020 manufactured by Shimadzu Corporation
  • DMC dimethyl carbonate
  • the collected sample is heated at 150 ° C. for 12 hours under a reduced pressure of 95 kPa or less, and then nitrogen gas is adsorbed on the sample with a known mass to determine the adsorption isotherm in the range of 0 to 1 relative pressure. obtain.
  • the surface area of the sample is calculated from the monomolecular layer adsorption amount of the gas obtained from the adsorption isotherm.
  • the specific surface area is obtained from the following BET formula by the BET one-point method (relative pressure 0.3).
  • P/V (P0-P) (1/VmC) + ⁇ (C-1)/VmC ⁇ (P/P0) (1)
  • P0 saturated vapor pressure
  • V adsorption amount at adsorption equilibrium pressure
  • Vm monomolecular layer adsorption amount
  • C parameter related to heat of adsorption
  • S specific surface area k: nitrogen single molecule occupied area 0.162 nm 2
  • the active carbon accounts for 50% by mass or more, further 80% by mass or more, furthermore 95% by mass or more of the positive electrode active material. In addition, it is desirable that the active carbon accounts for 40% by mass or more, further 70% by mass or more, furthermore 90% by mass or more of the positive electrode material layer.
  • the positive electrode material layer contains a positive electrode active material as an essential component, and a conductive material, a binder, and the like as optional components.
  • conductive agents include carbon black and carbon fiber.
  • binders include fluorine resins, acrylic resins, rubber materials, and cellulose derivatives.
  • the positive electrode material layer is formed, for example, by mixing a positive electrode active material, a conductive agent, a binder, and the like with a dispersion medium to prepare a positive electrode mixture slurry, applying the positive electrode mixture slurry to a positive electrode current collector, Formed by drying.
  • the thickness of the positive electrode material layer is, for example, 10 to 300 ⁇ m per side of the positive electrode current collector.
  • a ⁇ -conjugated polymer is preferable as the conductive polymer used as the positive electrode active material.
  • the ⁇ -conjugated polymer for example, polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, polypyridine, or derivatives thereof can be used. These may be used alone or in combination of two or more.
  • the weight average molecular weight of the conductive polymer is, for example, 1000-100000.
  • the derivative of a ⁇ -conjugated polymer means a polymer having a ⁇ -conjugated polymer as a basic skeleton, such as polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, and polypyridine.
  • polythiophene derivatives include poly(3,4-ethylenedioxythiophene) (PEDOT) and the like.
  • the conductive polymer is formed by, for example, immersing a positive electrode current collector having a carbon layer in a reaction solution containing raw material monomers of the conductive polymer, and electrolytically polymerizing the raw material monomers in the presence of the positive electrode current collector. be.
  • the positive electrode current collector and the counter electrode are immersed in a reaction solution containing raw material monomers, and current is passed between them using the positive electrode current collector as an anode.
  • the conductive polymer may be formed by methods other than electropolymerization.
  • the conductive polymer may be formed by chemical polymerization of raw material monomers. In chemical polymerization, raw material monomers may be polymerized with an oxidizing agent or the like in the presence of the positive electrode current collector.
  • the raw material monomer used in electrolytic polymerization or chemical polymerization may be any polymerizable compound capable of producing a conductive polymer by polymerization.
  • Raw material monomers may include oligomers. Examples of raw material monomers include aniline, pyrrole, thiophene, furan, thiophene vinylene, pyridine, and derivatives thereof. These may be used alone or in combination of two or more. Among them, aniline is easily grown on the surface of the carbon layer by electropolymerization.
  • Electropolymerization or chemical polymerization can be performed using a reaction solution containing anions (dopants).
  • dopants include sulfate ion, nitrate ion, phosphate ion, borate ion, benzenesulfonate ion, naphthalenesulfonate ion, toluenesulfonate ion, methanesulfonate ion, perchlorate ion, tetrafluoroborate ion, and hexafluorophosphate ion.
  • the dopant may be a polyion.
  • Polymer ions include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylsulfonic acid, polymethacrylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic Examples include ions such as acids.
  • the separator contains an olefinic resin.
  • An olefin resin refers to a resin containing olefin units as a main component.
  • the olefin-based resin contains, for example, 50% by mass or more, and further 70% by mass or more of olefin units.
  • Olefin units refer to monomer units derived from olefins (alkenes) such as ethylene, propylene and butene.
  • the divalent group (diyl group) formed by polymerizing a monomer is referred to as the "unit" of that monomer. At least a portion of the olefin may be a derivative thereof.
  • the olefin-based resin may be a homopolymer or a copolymer synthesized from multiple types of olefins. A portion of the hydrogen atoms of the olefin may be substituted with halogen atoms.
  • olefinic resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), chlorinated polyethylene (CPE), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer. Coalescing (EEA) and the like may be included.
  • a separator containing an olefin resin for example, a polyolefin microporous membrane, woven fabric, or non-woven fabric can be used.
  • the thickness of the separator is, for example, 8 to 40 ⁇ m, preferably 12 to 30 ⁇ m, more preferably 14 to 25 ⁇ m or 16 to 25 ⁇ m.
  • microporous membranes, woven fabrics, and non-woven fabrics microporous membranes, which are non-fibrous porous films, are particularly preferred because they are particularly strong and suitable for thinning.
  • the electrolyte has lithium ion conductivity and includes a lithium salt and a solvent that dissolves the lithium salt.
  • the anion of the lithium salt reversibly repeats doping and dedoping of the positive electrode.
  • Lithium ions derived from the lithium salt are reversibly absorbed and released by the negative electrode.
  • lithium salts examples include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCF 3 SO 3 , LiFSO 3 , LiCF 3 CO 2 , LiAsF 6 , LiB 10 Cl 10 , LiCl, LiBr, LiI , LiBCl 4 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 and the like. These may be used individually by 1 type, or may combine 2 or more types.
  • Lithium salts are preferably salts having a fluorine-containing anion because they have a high degree of dissociation, yield a low-viscosity electrolytic solution, and can improve the withstand voltage characteristics of electrochemical devices.
  • the electrolyte preferably contains an imide-based electrolyte.
  • the imide-based electrolyte contains an imide-based anion as an anion of a lithium salt.
  • the imide anion may be an anion containing fluorine and sulfur, and it is particularly preferred to use lithium bis(fluorosulfonyl)imide, LiN(SO 2 F) 2 (LiFSI).
  • LiFSI lithium bis(fluorosulfonyl)imide
  • 80 mass % or more of the lithium salt may be LiFSI.
  • LiFSI has the effect of reducing the deterioration of the positive electrode active material and the negative electrode active material.
  • the FSI anion is excellent in stability, so it is thought that by-products are unlikely to be produced, and the surface of the active material is not damaged, thus contributing to smooth charging and discharging.
  • the SEI coating formed on the surface layer of the negative electrode material layer by LiFSI contains a large amount of lithium fluoride and a small content of lithium carbonate. Thereby, a stable coating (first layer) mainly composed of lithium fluoride can be formed so as to cover the second layer mainly composed of lithium carbonate.
  • the concentration of the lithium salt in the non-aqueous electrolyte in the charged state (state of charge (SOC) 90-100%) is, for example, 0.2-5 mol/L.
  • the solvent examples include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; and aliphatic carboxylic acids such as methyl formate, methyl acetate, methyl propionate and ethyl propionate.
  • cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate
  • chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate
  • aliphatic carboxylic acids such as methyl formate, methyl acetate, methyl propionate and ethyl propionate.
  • acid esters lactones such as ⁇ -butyrolactone and ⁇ -valerolactone, chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), tetrahydrofuran , cyclic ethers such as 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethylmonoglyme, trimethoxymethane, sulfolane, methylsulfolane, 1 , 3-propanesultone and the like can be used. These may be used alone or in combination of two or more.
  • the electrolyte may contain various additives as necessary.
  • an unsaturated carbonate such as vinylene carbonate, vinylethylene carbonate, or divinylethylene carbonate may be added as an additive that forms a lithium ion conductive film on the surface of the negative electrode.
  • Example 1 (1) Production of Positive Electrode An aluminum foil (positive electrode current collector) having a thickness of 30 ⁇ m was prepared. On the other hand, 88 parts by mass of activated carbon (average particle size 5.5 ⁇ m) as a positive electrode active material, 6 parts by mass of polytetrafluoroethylene as a binder, and 6 parts by mass of acetylene black as a conductive material were dispersed in water. to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry was applied to both sides of an aluminum foil, and the coating film was dried and rolled to form a positive electrode material layer, thereby obtaining a positive electrode. A 10 mm-wide positive electrode current collector exposed portion was formed at the end portion along the longitudinal direction of the positive electrode current collector.
  • a copper foil (negative electrode current collector) having a thickness of 10 ⁇ m was prepared.
  • 97 parts by mass of non-graphitizable carbon (average particle size 5 ⁇ m), 1 part by mass of carboxycellulose, and 2 parts by mass of styrene-butadiene rubber were dispersed in water to prepare a negative electrode mixture slurry.
  • the resulting negative electrode mixture slurry was applied to both sides of a copper foil, and the coating film was dried and rolled to form a negative electrode material layer, thereby obtaining a negative electrode.
  • a thin film of metallic lithium for pre-doping was formed on the entire surface of the negative electrode material layer by vacuum deposition.
  • the amount of lithium to be pre-doped was set so that the negative electrode potential in the non-aqueous electrolyte after pre-doping was completed was 0.2 V or less with respect to metallic lithium.
  • the inside of the chamber of the apparatus was purged with carbon dioxide to create a carbon dioxide atmosphere, thereby forming a coating (second layer) containing lithium carbonate on the surface layer portion of the negative electrode mixture layer.
  • the dew point of the carbon dioxide atmosphere was ⁇ 40° C.
  • the mole fraction of carbon dioxide was 100%
  • the pressure in the chamber was 1 atm (1.01 ⁇ 10 5 Pa).
  • the temperature of the negative electrode exposed to a carbon dioxide gas atmosphere of 1 atm is 25°C and The time for exposing the negative electrode to the carbon dioxide atmosphere was 22 hours.
  • a separator made of a polyolefin microporous film was prepared.
  • the separator used had a three-layer structure in which both sides of a polyethylene (PE) sheet were coated with polypropylene (PP).
  • the thickness of the PE layer was 8.5 ⁇ m
  • the thickness of the PP layer was 11.5 ⁇ m on both sides
  • the total thickness of the separator was 20 ⁇ m.
  • the air resistance of the separator was 200 sec/100 mL.
  • An electrode body was formed by winding the positive electrode and the negative electrode in a columnar shape with a separator interposed therebetween. At this time, the positive electrode core exposed portion was projected from one end surface of the wound body, and the negative electrode core exposed portion was projected from the other end surface of the electrode assembly.
  • a disk-shaped positive current collector plate and a negative current collector plate were welded to the positive electrode core exposed portion and the negative electrode core exposed portion, respectively.
  • Non-Aqueous Electrolyte A solvent was prepared by adding 0.2% by mass of vinylene carbonate to a mixture of propylene carbonate and dimethyl carbonate in a volume ratio of 1:1.
  • a non-aqueous electrolyte was prepared by dissolving LiFSI as a lithium salt in the obtained solvent at a concentration of 1.2 mol/L.
  • Electrode body is housed in a bottomed cell case having an opening, the tab lead connected to the positive electrode current collector is connected to the inner surface of the sealing plate, and the negative electrode current collector is connected to the cell. Welded to the inner bottom of the case. After putting the non-aqueous electrolyte into the cell case, the opening of the cell case was closed with a sealing plate to assemble an electrochemical device A1 as shown in FIG.
  • aging was performed at 60°C while applying a charging voltage of 3.8 V between the terminals of the positive electrode and the negative electrode to complete the pre-doping of lithium ions to the negative electrode.
  • Example 2 In the preparation of the electrode body, the material, thickness and air resistance of the separator were changed as shown in Table 1. Except for this, electrochemical devices A2 to A9 were produced in the same manner as in Example 1 and evaluated in the same manner.
  • Example 2 As in Example 1, a three-layer structure in which both sides of a polyethylene (PE) sheet were coated with polypropylene (PP) was used.
  • the thickness of the PE layer was 7 ⁇ m
  • the thickness of the PP layer was 9 ⁇ m on both sides
  • the total thickness of the separator was 16 ⁇ m.
  • the air permeability resistance of the separator was 300 sec/100 mL in Example 2 and 500 sec/100 mL in Example 3.
  • Examples 4 to 9 a single-layer separator made of a polypropylene (PP) microporous film was used, but the thickness and air resistance of the separator were changed as shown in Table 1.
  • PP polypropylene
  • Example 1 A cellulose non-woven fabric separator was prepared in the preparation of the electrode body. Except for this, an electrochemical device B1 was produced in the same manner as in Example 1 and evaluated in the same manner.
  • the cellulose non-woven fabric separator had a thickness of 25 ⁇ m and an air resistance of 5 sec/100 mL.
  • Example 2 In the production of the negative electrode, a copper foil (negative electrode current collector) having a thickness of 10 ⁇ m was prepared, and a negative electrode material layer was formed in the same manner as in Example 1 to obtain a negative electrode.
  • a metallic lithium foil was attached to part of the negative electrode material layer.
  • the amount of metallic lithium foil was calculated so that the negative electrode potential in the non-aqueous electrolyte after completion of pre-doping was 0.2 V or less relative to metallic lithium.
  • a positive electrode and a negative electrode to which a metallic lithium foil was adhered were wound into a columnar shape with a cellulose nonwoven fabric separator interposed therebetween to form an electrode body.
  • the cellulose non-woven fabric separator had a thickness of 25 ⁇ m and an air resistance of 5 sec/100 mL.
  • An electrochemical device B2 was produced in the same manner as in Example 1, and evaluated in the same manner.
  • Table 1 shows the internal resistance (low temperature DCR) and reliability evaluation results of electrochemical devices A1 to A9, B1 and B2.
  • Table 1 shows the values of the internal resistance R1 and cumulative application time T of each device together with the characteristics of the separator (material, thickness, and air resistance).
  • the internal resistance R1 and the cumulative application time T are shown as relative values with the result of the electrochemical device A7 set to 100.
  • Electrochemical devices A1-A9 correspond to Examples 1-9, respectively, and electrochemical devices B1 and B2 correspond to Comparative Examples 1 and 2, respectively.
  • devices B1 and B2 using cellulose separators have high internal resistance R1.
  • the internal resistance R1 of electrochemical device B1 is lower than the internal resistance R1 of electrochemical device B2.
  • the surface layer of the coating region contains a large amount of lithium carbonate, so the SEI coating tends to collapse, whereas in the electrochemical device B1, the lithium carbonate content in the surface layer of the coating region This is probably because the surface layer of the coating region contains a large amount of lithium fluoride, forming an SEI coating that is stable against the electrolytic solution.
  • a low-resistance coating containing a large amount of lithium carbonate is formed inside the coating region, and a coating containing a large amount of lithium fluoride is formed so as to cover the low-resistance coating, thereby increasing the movement resistance of lithium ions. It is thought that this is because it was reduced.
  • the cumulative application time T is compared, the cumulative application time T of the electrochemical device B1 is longer than the cumulative application time T of the electrochemical device B2, and the reliability is lowered.
  • the reason for this is that in the electrochemical device B1, pre-doping of lithium ions is progressed in a state in which a film of metallic lithium is formed over the entire negative electrode material layer, whereby metallic lithium reacts with cellulose and the separator deteriorates. It is thought that this is because it is easy to proceed.
  • the deterioration of the separator was suppressed by using the olefin separator, the cumulative application time T was increased, and the reliability was improved. A further reduction in the internal resistance R1 was also observed.
  • FIG. 2 is a graph obtained by analyzing the C1s spectrum, O1s spectrum, and F1s spectrum by performing XPS analysis on the surface layer portion of the negative electrode material layer in which the second layer containing lithium carbonate and the first layer covering the second layer are formed. indicates FIG. 2 is an example of analysis results of a negative electrode taken out from an electrochemical device produced by the method shown in Comparative Example 1.
  • X-ray photoelectron spectrometer (trade name: PHI QuanteraSXM, manufactured by ULVAC-Phi, Inc.) was used. Measurement conditions are shown below.
  • X-ray source Al-mono (1486.6 eV) 15 kV/25 W
  • Measurement diameter 100 ⁇ m ⁇
  • Photoelectron extraction angle 45°
  • Etching conditions acceleration voltage 2 kV, etching rate about 7.05 nm/min (in terms of SiO2 ), raster area 2 mm x 2 mm
  • the peak intensity A at the top of the peak appearing in the binding energy range of 530 to 534 eV was obtained from the O1s spectrum as the intensity of the peak attributed to the lithium carbonate bond.
  • the peak intensity B at the top of the peak appearing in the binding energy range of 684.8 to 685.3 eV was obtained as the intensity of the peak attributed to the lithium fluoride bond. While etching the surface layer of the negative electrode material layer, changes in the peak intensity A, the peak intensity B, and the peak intensity ratio A/B in the depth direction (thickness direction of the surface layer) were measured.
  • the peak intensity A (marked ⁇ (black triangle) in FIG. 2) attributed to the lithium carbonate bond in the O1s spectrum material side), and after reaching a maximum value at a depth of 10 nm in terms of SiO 2 , it decreases.
  • the peak intensity B (marked ⁇ (black square) in FIG. 2) attributed to the lithium fluoride bond in the F1s spectrum decreases from the surface layer toward the inner side (negative electrode active material side) of the coating region. This means that the SEI coating is formed such that the coating containing a large amount of lithium fluoride (first layer) covers the coating containing a large amount of lithium carbonate (second layer).
  • the peak intensity ratio A/B (marked ⁇ (black circle) in FIG. 2) is approximately 1.55 at a depth of approximately 20 nm in terms of SiO 2 , which is the maximum value.
  • the thickness of the SEI coating was estimated to be 50 nm in terms of SiO 2 by observing the peak derived from the carbon material, which is the negative electrode active material, in the C1s spectrum.
  • FIG. 3 shows a graph obtained by performing XPS analysis on the surface layer portion of the negative electrode material layer in which the second layer containing lithium carbonate is not covered with the first layer, and analyzing the C1s spectrum, O1s spectrum, and F1s spectrum.
  • FIG. 3 is an example of analysis results of a negative electrode taken out from an electrochemical device produced by the method shown in Comparative Example 2.
  • FIG. 3 shows changes in the depth direction of peak intensity A, peak intensity B, and peak intensity ratio A/B.
  • the peak intensity A ( ⁇ mark (white triangle) in FIG. 3 ) attributed to the lithium carbonate bond in the O1s spectrum material side).
  • the peak intensity B ( ⁇ mark (white square) in FIG. 3) attributed to the lithium fluoride bond in the F1s spectrum increased from the surface of the coating region toward the inside (negative electrode active material side) and then decreased. .
  • No maximum value was observed in the peak intensity ratio A/B (o mark (white circle) in FIG. 3) due to the change in the depth direction.
  • the thickness of the SEI coating was estimated to be 20 nm in terms of SiO 2 by observing the peak derived from the carbon material, which is the negative electrode active material, in the C1s spectrum.
  • the electrochemical device according to the present invention is suitable, for example, for in-vehicle use.
  • Electrode body 10 Positive electrode 11x: Positive electrode core exposed part 13: Positive electrode current collector 15: Tab lead 20: Negative electrode 21x: Negative electrode core exposed part 23: Negative electrode current collector 30: Separator 200: Electrochemical device 210: Cell Case 220: Sealing plate 221: Gasket

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  • Electric Double-Layer Capacitors Or The Like (AREA)
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WO2024202996A1 (ja) * 2023-03-28 2024-10-03 パナソニックＩｐマネジメント株式会社 電気化学キャパシタ

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Publication number Priority date Publication date Assignee Title
JP2009272585A (ja) * 2008-05-12 2009-11-19 Panasonic Corp 電気化学キャパシタ
WO2011058748A1 (ja) * 2009-11-13 2011-05-19 パナソニック株式会社 電気化学キャパシタおよびそれに用いられる電極
JP2013258422A (ja) * 2013-08-12 2013-12-26 Fuji Heavy Ind Ltd 蓄電デバイスおよびその製造方法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009272585A (ja) * 2008-05-12 2009-11-19 Panasonic Corp 電気化学キャパシタ
WO2011058748A1 (ja) * 2009-11-13 2011-05-19 パナソニック株式会社 電気化学キャパシタおよびそれに用いられる電極
JP2013258422A (ja) * 2013-08-12 2013-12-26 Fuji Heavy Ind Ltd 蓄電デバイスおよびその製造方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024202996A1 (ja) * 2023-03-28 2024-10-03 パナソニックＩｐマネジメント株式会社 電気化学キャパシタ

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