WO2023053849A1 - 電気化学デバイス - Google Patents

電気化学デバイス Download PDF

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WO2023053849A1
WO2023053849A1 PCT/JP2022/033203 JP2022033203W WO2023053849A1 WO 2023053849 A1 WO2023053849 A1 WO 2023053849A1 JP 2022033203 W JP2022033203 W JP 2022033203W WO 2023053849 A1 WO2023053849 A1 WO 2023053849A1
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negative electrode
layer
electrochemical device
mixture layer
lithium
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French (fr)
Japanese (ja)
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宣寛 島村
健一 永光
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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 US18/695,695 priority Critical patent/US20250046795A1/en
Priority to CN202280063905.6A priority patent/CN117981029A/zh
Priority to JP2023550493A priority patent/JPWO2023053849A1/ja
Publication of WO2023053849A1 publication Critical patent/WO2023053849A1/ja
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    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
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    • H01G11/04—Hybrid capacitors
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    • H01G11/54—Electrolytes
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    • 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
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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
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    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
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    • H01M2004/027—Negative electrodes
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    • 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.
  • electrochemical devices that combine the storage principle of lithium-ion secondary batteries and electric double-layer capacitors.
  • Such electrochemical devices typically use a polarizable electrode for the positive electrode and a non-polarizable electrode for the negative electrode.
  • electrochemical devices are expected to have both the high energy density of lithium ion secondary batteries and the high output characteristics of electric double layer capacitors.
  • Patent Document 1 an electricity storage device element in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween, and an electrolytic solution are housed inside an exterior body. and a negative electrode, the power storage device comprising a positive electrode terminal and a negative electrode terminal which are provided to protrude from the exterior body, wherein the power storage device element includes a positive electrode constituting the power storage device element,
  • An electricity storage device has been proposed that includes an insulating first fixing member that fixes a negative electrode and a separator and is unfixed at a temperature of 90° C. or more and 160° C. or less.
  • a cellulose-based nonwoven fabric (hereinafter also referred to as a cellulose-based separator) is used as a separator for electrochemical devices.
  • Cellulose-based separators are inexpensive, but on the other hand, they tend to contain moisture, which is likely to cause deterioration of the negative electrode, and the deterioration of the negative electrode tends to increase the internal resistance of the electrochemical device.
  • One aspect of the present invention includes a positive electrode, a negative electrode, a separator, and a lithium ion conductive electrolyte, wherein the positive electrode includes a positive active material reversibly doped with anions, the negative electrode comprises a negative current collector; and a negative electrode mixture layer supported on the negative electrode current collector, wherein the negative electrode mixture layer includes a negative electrode active material that reversibly dopes lithium ions, and the negative electrode active material is non-graphitizable carbon. wherein the negative electrode mixture layer has a specific surface area of 10 m 2 /g or more and 70 m 2 /g or less, and the separator contains an olefin resin.
  • 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.
  • An electrochemical device includes a positive electrode, a negative electrode, a separator, and a lithium ion conductive electrolyte.
  • the positive electrode includes a positive electrode active material reversibly doped with anions.
  • the negative electrode includes a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector.
  • the negative electrode mixture layer includes a negative electrode active material reversibly doped with lithium ions, and the negative electrode active material includes non-graphitizable carbon.
  • the specific surface area of the negative electrode mixture layer is 10 m 2 /g or more and 70 m 2 /g or less.
  • the separator contains an olefinic resin.
  • a separator containing an olefinic resin is also referred to as an "olefinic separator".
  • the olefin separator Since the olefin separator has a lower water content than the cellulose separator, the deterioration of the negative electrode due to the moisture in the separator is suppressed, and the increase in the internal resistance of the electrochemical device due to the deterioration of the negative electrode is suppressed.
  • the olefinic separator has superior stability to an electrolyte containing lithium ions (or metallic lithium attached to the surface of the negative electrode in the pre-doping step) and is less likely to deteriorate than a cellulose separator. Therefore, by using the olefinic separator, the state of low internal resistance is maintained over a long period of time. As a result, the reliability of the electrochemical device is improved.
  • the resistance of the negative electrode is significantly reduced, thereby significantly increasing the internal resistance of the electrochemical device. reduced. Further, in this case, the reactivity of the negative electrode is increased, and the deterioration of the negative electrode described above is likely to proceed, so that the use of the olefinic separator has a remarkable effect of suppressing the deterioration of the negative electrode.
  • the specific surface area of the negative electrode mixture layer is larger than 70 m 2 /g, the reactivity of the negative electrode is extremely high, and the deterioration of the negative electrode described above may not be suppressed.
  • the specific surface area of the negative electrode mixture layer is preferably 10 m 2 /g or more and 50 m 2 /g or less.
  • the Faraday reaction in which lithium ions are reversibly absorbed and released, develops capacity.
  • 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
  • the negative electrode potential is, for example, 0.2 V or less based on lithium (vs. Li/Li + ).
  • the above negative electrode potential is the negative electrode potential (25° C.) at the time of completion of pre-doping (or during charging), which will be described later.
  • the negative electrode mixture layer is pre-doped with lithium ions in advance. This lowers the potential of the negative electrode, increases the potential difference (that is, voltage) between the positive electrode and the negative electrode, and improves the energy density of the electrochemical device.
  • the amount of lithium to be pre-doped is set so that the negative electrode potential in the electrolyte after pre-doping is completed is 0.2 V or less with respect to metallic lithium.
  • 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 mixture layer.
  • the specific surface area of the negative 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 negative electrode is taken out. A half cell is assembled using this negative electrode as a working electrode and a Li metal foil as a counter electrode, and the Li in the negative electrode is dedoped until the potential of the negative electrode reaches 1.5V. Next, the Li-dedoped negative electrode is washed with dimethyl carbonate (DMC) and dried. Thereafter, the negative electrode mixture layer is peeled off from the negative electrode current collector, and about 0.5 g of a sample of the negative electrode mixture layer is collected.
  • a measuring device for example, Tristar II3020 manufactured by Shimadzu Corporation
  • 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 surface layer of the negative electrode mixture layer may have a first layer containing lithium carbonate as a component of the coating.
  • the first layer is mainly formed on the surface of the negative electrode active material.
  • the specific surface area of the negative electrode mixture layer increases, the negative electrode is more likely to deteriorate, but the formation of the first layer significantly suppresses the deterioration of the negative electrode.
  • the cellulose separator tends to deteriorate rapidly.
  • the olefin-based separator is resistant to deterioration even in an environment where lithium carbonate is generated on the surface of the negative electrode mixture layer, and a good first layer is formed, so the above effect of the first layer is maximized. be able to
  • the surface layer of the negative electrode may have a second layer containing a solid electrolyte as a component of the coating.
  • the second layer has a different composition than the first layer and the second layer is distinguishable from the first layer.
  • a solid electrolyte interfacial coating that is, an SEI coating
  • the second layer may be formed as an SEI coating.
  • the SEI coating plays an important role in the charge/discharge reaction, but if the SEI coating is excessively thick, the deterioration of the negative electrode increases.
  • the first layer containing lithium carbonate has the effect of promoting the formation of a good SEI film and maintaining the SEI film in a good state even when charging and discharging are repeated. Therefore, by forming the first layer on the surface layer of the negative electrode mixture layer, deterioration of the negative electrode can be significantly suppressed even when the specific surface area of the negative electrode mixture layer is increased in order to suppress an increase in the low-temperature DCR. become.
  • the coating has a first layer and a second layer
  • at least part of the second layer covers at least part of the surface of the negative electrode active material via the first layer. That is, at least part of the first layer is covered with the second layer.
  • the first layer is interposed between the surface of the negative electrode active material and the second layer, and serves as a base layer for the second layer.
  • the second layer is formed as an SEI coating in good condition by the first layer serving as the underlayer.
  • the second layer may also contain lithium carbonate.
  • the content of lithium carbonate contained in the second layer is less than the content of lithium carbonate contained in the first layer.
  • the first layer is formed on the surface layer of the negative electrode mixture layer before assembling the electrochemical device.
  • a uniform second layer (SEI coating) having an appropriate thickness is formed on the surface of the negative electrode active material by subsequent charging and discharging.
  • the SEI coating is formed, for example, by reaction between an electrolyte and a negative electrode in an electrochemical device. Since the electrolyte can pass through the first layer as well as the second layer, the entire surface layer including the first and second layers may be referred to as the SEI coating. is called the SEI coating to distinguish it from the first layer.
  • a region containing lithium carbonate such as the first layer can be confirmed, for example, by analyzing the surface layer by X-ray photoelectron spectroscopy (XPS).
  • XPS X-ray photoelectron spectroscopy
  • the analysis method is not limited to XPS.
  • the thickness of the first layer may be, for example, 1 nm or more, 5 nm or more if a longer-term effect is expected, and 10 nm or more if a more reliable effect is expected. However, when the thickness of the first layer exceeds 50 nm, the first layer itself can become a resistance component. Therefore, the thickness of the first layer may be 50 nm or less, or 30 nm or less. The thickness of the first layer is, for example, 1 nm to 50 nm.
  • the thickness of the second layer 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 second layer exceeds 20 nm, the second layer itself can become a resistance component. Therefore, the thickness of the second layer may be 20 nm or less, or 10 nm or less.
  • the ratio of the thickness A of the first layer to the thickness B of the second layer: A/B is preferably 1 or less from the viewpoint of reducing the initial low-temperature DCR.
  • the thickness of the second layer is preferably 20 nm or less, and may be 10 nm or less.
  • A/B is preferably 0.1 or more, and for example, the A/B ratio may be 0.2 or more.
  • the thicknesses of the first layer and the second layer are measured by analyzing the surface layer portion of the negative electrode mixture layer at multiple locations (at least five locations) of the negative electrode mixture 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 mixture layer provided for the measurement sample may be peeled off from the negative electrode current collector. In this case, the film formed on the surface of the negative electrode active material forming the vicinity of the surface layer of the negative electrode mixture layer may be analyzed. Specifically, if the negative electrode active material covered with the film is sampled from the region of the negative electrode mixture layer that is arranged on the side opposite to the surface that was bonded to the negative electrode current collector and used for analysis, good.
  • XPS analysis of the surface layer of the negative electrode mixture layer is performed, for example, by irradiating the surface layer or the coating formed on the surface of the negative electrode active material with an argon beam in the chamber of an X-ray photoelectron spectrometer, and measuring the C1s and O1s 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 carbonate is stably observed corresponds to the thickness of the first layer.
  • the surface layer portion of the negative electrode mixture layer has an SEI coating (that is, the second layer) containing a solid electrolyte.
  • the thickness of the region where the peak attributed to the bond of the compound contained in the SEI coating is stably observed corresponds to the thickness of the SEI coating (that is, the thickness of the second layer).
  • a compound containing an element that can serve as a label for the second layer is selected.
  • an element (for example, F) that is contained in the electrolyte but not substantially contained in the first layer may be selected.
  • LiF for example, can be selected as the compound containing an element that can serve as a label for the second layer.
  • the second layer contains LiF
  • the second layer when the second layer is measured by X-ray photoelectron spectroscopy, a substantial F1s peak attributed to LiF bonds is observed.
  • the thickness of the region where peaks attributed to LiF bonds are stably observed corresponds to the thickness of the second layer.
  • the first layer usually does not contain LiF, and even if the first layer is measured by X-ray photoelectron spectroscopy, no substantial F1s peak attributed to LiF bonds is observed. Therefore, the thickness of the region in which peaks attributed to LiF bonds are not stably observed may be used as the thickness of the first layer.
  • An O1s peak attributed to lithium carbonate can also be observed in the SEI film.
  • the SEI coating produced in the electrochemical device has a different composition than the pre-formed first layer, so the two can be distinguished.
  • F1s peaks attributed to LiF bonds are observed, but no substantial F1s peaks attributed to LiF bonds are observed in the first layer.
  • the amount of lithium carbonate contained in the SEI coating is very small.
  • the Li1s peak peaks derived from compounds such as ROCO 2 Li and ROLi can be detected.
  • a second peak of O1s attributed to Li—O bonds may be observed in addition to the first peak of O1s attributed to C ⁇ O bonds.
  • a region of the coating present near the surface of the negative electrode active material may contain a small amount of LiOH or Li2O .
  • the magnitude of the peak intensity can be judged by the height of the peak from the baseline.
  • the step of forming the first layer can be performed by, for example, a gas 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 adhered to the surface of the negative electrode mixture 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 mixture layer may be ⁇ 20 to ⁇ 20. 80°C is sufficient.
  • the first layer can be formed by coating a solution or dispersion containing lithium carbonate on 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 second layer containing a solid electrolyte so as to cover at least a portion of the first layer.
  • the surface layer portion of the obtained negative electrode mixture layer has a first layer and a second layer.
  • the second 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 through the first layer (that is, with the first layer as a base layer).
  • the step of forming the second layer is performed while the negative electrode mixture layer and the electrolyte are in contact with each other, it may also serve as at least a part of the step of pre-doping lithium ions into the negative electrode mixture layer.
  • 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 mixture layer.
  • a first 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 mixture 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 mixture 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.
  • metallic lithium may be formed in the form of a film on the surface of the negative electrode mixture 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 first layer thicker, it is efficient to increase the partial pressure of carbon dioxide to, for example, 0.5 atmospheres (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 first layer.
  • the thickness of the first 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 first 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 mixture 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. Then, the first layer may be formed on the surface layer of the negative electrode mixture layer.
  • the step of pre-doping lithium ions into the negative electrode mixture layer is, for example, further advanced by bringing the negative electrode mixture layer and the electrolyte into contact after that, and is completed by leaving for a predetermined period of time.
  • Such a step may be a step of forming a second layer to cover at least a portion of the first layer. For example, by charging and discharging the electrochemical device at least once, the second layer can be formed on the negative electrode mixture layer and pre-doping of the negative electrode with lithium ions can be completed.
  • a predetermined charging voltage eg, 3.4 to 4.0 V
  • a predetermined time eg, 1 to 75 hours
  • cellulose-based separators that are commonly used have many functional groups such as OH groups that readily react with lithium ions, and also contain relatively large amounts of water, so they are susceptible to damage due to side reactions. In addition, 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 electrochemical device uses an olefinic separator. Since the olefin-based separator has low reactivity with metallic lithium, the deterioration of the separator is suppressed and the reliability of the electrochemical device is improved. 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.
  • 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 are preferably used in electrochemical devices in which the first layer and the second layer are formed on the surface layer of the negative electrode mixture layer. can.
  • 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.
  • pre-doping can be performed without requiring a long period of time by bringing a negative electrode in which metallic lithium is pre-adhered to the entire surface of the negative electrode mixture layer into contact with the electrolyte.
  • the air resistance of the separator is preferably 70 sec/100 mL or more and 500 sec/100 mL or less. When the air resistance is within this range, both reduction in internal resistance and improvement in reliability of the electrochemical device can be achieved. More preferably, the air resistance of the separator is 70 sec/100 mL or more and 300 sec/100 mL or less, and still more preferably 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).
  • the degree of permeation resistance indicates the time (seconds) required for a predetermined volume (100 mL) of air to permeate per unit area of the separator when a predetermined pressure difference is applied between both surfaces 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.
  • 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.
  • the electrode body 100 is configured as a columnar wound body by winding a strip-shaped positive electrode 10 and a strip-shaped negative electrode 20 with a separator 30 interposed between the positive electrode 10 and the negative electrode 20 .
  • 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 one end of which is connected to the positive collector plate 13 , 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 electrochemical device is not limited to the wound electrochemical device shown in FIG.
  • it may be a laminated electrochemical device. That is, the electrode assembly may be configured as a laminate by laminating a sheet-like positive electrode and a negative electrode with a separator interposed between the positive and negative electrodes.
  • the negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the negative electrode current collector.
  • the negative electrode mixture layer includes a negative electrode active material that reversibly dopes lithium ions. , contains non-graphitizable carbon (ie, hard carbon).
  • the thickness of the negative electrode mixture layer is, for example, 10 to 300 ⁇ m per side of 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 non-graphitizable carbon may have an interplanar spacing of (002) planes (that is, an interplanar spacing between carbon layers) d002 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 size means the volume-based median diameter (D50) in the particle size distribution obtained by laser diffraction particle size distribution measurement.
  • the negative electrode mixture layer contains a negative electrode active material as an essential component, and optionally contains a conductive agent, a binder, a thickener, and the like.
  • conductive agents include carbon black and carbon fibers.
  • carbon black include acetylene black (AB) and ketjen black (KB).
  • binders include fluorine resins, acrylic resins, and rubber materials. A cellulose derivative etc. are mentioned as a thickener.
  • the negative electrode mixture layer may contain a negative electrode active material and a conductive agent.
  • the specific surface area of the negative electrode mixture layer can reflect the specific surface areas of the negative electrode active material and the conductive agent.
  • the specific surface area of the negative electrode mixture layer may be adjusted by changing the amount of the conductive agent added.
  • the negative electrode mixture layer is formed, for example, by mixing a negative electrode active material, a conductive agent, etc. together with a dispersion medium to prepare a negative electrode mixture slurry, applying the negative electrode mixture slurry to a negative electrode current collector, and drying the slurry. Formed by
  • the negative electrode mixture 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 mixture layer.
  • the positive electrode includes a positive electrode active material reversibly doped with anions.
  • the positive electrode active material is, for example, a carbon material, a conductive polymer, or the like.
  • the positive electrode may include a positive electrode mixture layer containing a positive electrode active material, and a positive electrode current collector that supports the positive electrode mixture layer.
  • the thickness of the positive electrode mixture layer is, for example, 10 to 300 ⁇ m per side of 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 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 size of the activated carbon is not particularly limited, it is preferably 20 ⁇ m or less, more preferably 3 ⁇ m to 15 ⁇ m.
  • the specific surface area of the positive electrode mixture layer generally reflects the specific surface area of the positive electrode active material.
  • the specific surface area of the positive electrode mixture 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.
  • the specific surface area of the positive electrode material mixture layer is the BET specific surface area obtained using a measuring device conforming to JIS Z8830 (for example, Tristar II3020 manufactured by Shimadzu Corporation). Specifically, the electrochemical device is disassembled and the positive electrode is taken out. The positive electrode is then washed with DMC and dried.
  • 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.
  • the specific surface area of the collected sample is determined according to the method for measuring the specific surface area of the negative electrode mixture layer already described.
  • 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 mass % or more, further 70 mass % or more, furthermore 90 mass % or more of the positive electrode mixture layer.
  • the positive electrode mixture layer contains a positive electrode active material as an essential component, and optionally contains a conductive agent, a binder, a thickener, and the like.
  • conductive agents include carbon black and carbon fibers.
  • binders include fluorine resins, acrylic resins, and rubber materials. A cellulose derivative etc. are mentioned as a thickener.
  • the positive electrode mixture layer is formed, for example, by mixing a positive electrode active material, a conductive agent, etc. with a dispersion medium to prepare a positive electrode mixture slurry, applying the positive electrode mixture slurry to a positive electrode current collector, and then drying it. Formed by
  • 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-based 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 mixture layer by LiFSI contains a large amount of lithium fluoride and a small content of lithium carbonate. Thereby, a stable coating (second layer) mainly composed of lithium fluoride can be formed so as to cover the first 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.
  • 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 mixture 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.
  • a total of 90 parts by mass of the negative electrode active material and the conductive agent, 4 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and 6 parts by mass of styrene-butadiene rubber (SBR) as a binder are 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, the coating film was dried and rolled to form a negative electrode mixture layer, and a negative electrode was obtained.
  • Non-graphitizable carbon (average particle size: 5 ⁇ m) or graphite (average particle size: 5 ⁇ m) was used as the negative electrode active material.
  • Ketjenblack (KB) was used as the conductive agent.
  • Table 1 shows the compounding ratio of the negative electrode active material and the conductive agent. The specific surface area of the negative electrode mixture layer was adjusted to the values shown in Table 1 by changing the compounding ratio of the negative electrode active material and the conductive agent.
  • a thin film of metallic lithium for pre-doping was formed on the entire surface of the negative electrode mixture 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 first layer containing lithium carbonate on the surface layer portion of the negative electrode mixture layer.
  • the dew point of the carbon dioxide gas atmosphere was ⁇ 40° C.
  • the molar 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 the carbon dioxide atmosphere of 1 atm was 25°C.
  • the time for exposing the negative electrode to the carbon dioxide atmosphere was 22 hours.
  • the first layer does not substantially contain F (or LiF).
  • a single-layer structure separator (thickness: 25 ⁇ m) made of polypropylene (PP) microporous membrane, which is an olefinic separator, or a cellulose non-woven fabric separator (thickness: 25 ⁇ m), which is a cellulose separator, was used.
  • the air permeation resistance of the separator was the value shown in Table 1.
  • 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 body.
  • 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.
  • a non-aqueous electrolyte was prepared by dissolving LiFSI as a lithium salt in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (volume ratio 3:5:2).
  • the concentration of LiFSI in the non-aqueous electrolyte was set to 1.2 mol/L.
  • the electrode assembly was housed in a bottomed cell case having an opening, the tab lead connected to the positive current collector was connected to the inner surface of the sealing plate, and the negative current collector was welded to the inner bottom surface of the cell 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 as shown in FIG.
  • A1 to A5 are electrochemical devices of Examples
  • B1 to B10 are electrochemical devices of Comparative Examples.
  • 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.
  • Table 1 shows the evaluation results.
  • HC indicates non-graphitizable carbon
  • the internal resistance R1 is indicated as an index when the internal resistance R1 of the electrochemical device A2 is 100.
  • the rate of change (R2/R1) is shown as an index when the rate of change (R2/R1) of the electrochemical device A2 is 100.
  • the electrochemical devices B1 to B10 had a small initial DCR and good reliability. Both the initial DCR and the rate of change were suppressed to be smaller when the negative electrode active material was HC than when the negative electrode active material was graphite (A2, B7).
  • the rate of change was small when the specific surface area of the negative electrode mixture layer was less than 10 m 2 /g, but when the specific surface area of the negative electrode mixture layer was 10 m 2 /g or more. increased the rate of change (B3, B5, B8, B9).
  • the rate of change is small when the specific surface area of the negative electrode mixture layer is less than 10 m 2 /g, and the specific surface area of the negative electrode mixture layer is 10 m 2 /g or more. Even in the case of , the rate of change was kept small (B4, A1 to A5).
  • the reliability was greatly improved by changing the cellulose separator to an olefin separator ( B5 ⁇ A1, B8 ⁇ A2, B9 ⁇ A4).
  • PP polypropylene
  • Electrochemical devices A4 and A7-A10 had a lower initial DCR.
  • X-ray source Al-mono (1486.6 eV) 14 kV/200 W Measurement diameter: 800 ⁇ m ⁇ Photoelectron extraction angle: 45° Etching conditions: acceleration voltage 3 kV, etching rate about 3.1 nm/min (in terms of SiO2 ), raster area 3.1 mm x 3.4 mm
  • the thickness of the first layer was approximately 18 nm. Specifically, peaks such as C—C bonds presumed to be impurity carbon were observed on the outermost surface, but sharply decreased near a depth of 1 to 2 nm in the first layer. On the other hand, a first peak attributed to C ⁇ O bonds was observed from the outermost surface of the surface layer to a depth of 18 nm. A peak attributed to Li—O bonds was also observed from around 18 nm depth. Furthermore, the presence of Li was confirmed constantly from the outermost surface of the surface layer to a depth of 18 nm. No peak attributed to LiF was observed.
  • 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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