WO2024197768A1 - 二次电池和电子装置 - Google Patents

二次电池和电子装置 Download PDF

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Publication number
WO2024197768A1
WO2024197768A1 PCT/CN2023/085340 CN2023085340W WO2024197768A1 WO 2024197768 A1 WO2024197768 A1 WO 2024197768A1 CN 2023085340 W CN2023085340 W CN 2023085340W WO 2024197768 A1 WO2024197768 A1 WO 2024197768A1
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Prior art keywords
secondary battery
positive electrode
layer
material layer
battery according
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PCT/CN2023/085340
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English (en)
French (fr)
Inventor
胡克文
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宁德新能源科技有限公司
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Priority to CN202380079865.9A priority Critical patent/CN120239909A/zh
Priority to PCT/CN2023/085340 priority patent/WO2024197768A1/zh
Publication of WO2024197768A1 publication Critical patent/WO2024197768A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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 application relates to the field of energy storage, and in particular to a secondary battery and an electronic device.
  • the existing technology often uses a positive electrode current collector such as aluminum foil coated with a high-adhesion safety coating to reduce short-circuit points, thereby reducing the heat generation power during short circuit.
  • a positive electrode current collector such as aluminum foil coated with a high-adhesion safety coating
  • the internal resistance of lithium-ion batteries with a high-adhesion safety coating is generally large, and after high-temperature storage, high temperature and high humidity, thermal shock and other tests, the internal resistance growth rate is much higher than that of lithium-ion batteries without a high-adhesion safety coating. Therefore, it is necessary to develop and design a new type of pole piece to solve the problem of large internal resistance growth of lithium-ion batteries coated with a high-adhesion safety coating under high temperature conditions.
  • the present application provides a secondary battery and an electronic device to reduce the internal resistance and internal resistance growth rate of the secondary battery, thereby improving the electrical performance and life of the secondary battery.
  • the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector, a first material layer and a second material layer stacked, the positive electrode current collector comprising a metal layer, the first material layer being disposed between the positive electrode current collector and the second material layer; the first material layer comprising first material particles, the first material particles comprising a matrix and a carbon coating layer located on the surface of the matrix, and the second material layer comprising a positive electrode active material.
  • the Dv10 of the first material particles is D 1 ⁇ m, 0.3 ⁇ D 1 ⁇ 2.0
  • the matrix comprises at least one of LiFe k M( 1-k )PO 4 , wherein 0 ⁇ k ⁇ 1, and the M element is selected from at least one of manganese, cobalt, magnesium, calcium, zinc, chromium or lead.
  • the internal resistance of secondary batteries with the first material layer is relatively large, and after high-temperature storage, high-temperature and high-humidity, thermal shock and other tests, the internal resistance growth rate is much higher than that of secondary batteries without safety coatings. Excessive internal resistance growth rate will have a serious impact on the performance and life of secondary batteries.
  • the inventors of this application have found through research that when secondary batteries with safety coatings are stored at high temperatures, the positive electrode current collector is affected by the first material particles in the first material layer, and the gas will be in the first material layer.
  • the first material layer and the metal layer gather at the interface, corroding the metal layer, increasing the interface resistance between the first material layer and the metal layer; in addition, the carbon coating layer on the surface of the substrate increases the side reactions at high temperatures, causing the side reaction products to accumulate on the surface of the substrate and in the first material layer, obstructing the electron channel, and thus causing the internal resistance of the secondary battery to continue to increase.
  • the present application reasonably controls the particle size of the first material particles in the first material layer, so that the first material layer and the metal layer have a higher peeling strength, reducing the risk of the metal layer being exposed when the secondary battery is subjected to external force, and the above-mentioned substrate has a larger short-circuit resistance, which can reduce the short-circuit current and improve safety performance; at the same time, it can also effectively reduce the gas enriched in the first material layer and reduce the occurrence of side reactions of the carbon coating layer, thereby reducing the internal resistance and internal resistance growth rate of the secondary battery during charging and discharging.
  • 0.7 ⁇ D 1 ⁇ 1.5 0.7 ⁇ D 1 ⁇ 1.5.
  • the Dv10 value of the first material particles is too small, the gas accumulated at the interface between the first material layer and the metal layer will increase, causing the carbon coating layer to have more side reactions at high temperatures, thereby causing the internal resistance of the secondary battery to continue to increase.
  • the Dv10 value of the first material particles is too large, although large particles can reduce the occurrence of interface side reactions to a certain extent, the number of large particles in the particle distribution is not easy to control, which will increase the number of bad points of the electrode and reduce the yield rate.
  • the Dv90 of the first material particles is D 2 ⁇ m, 5.0 ⁇ D 2 ⁇ 10.0.
  • the Dv90 value of the first material particles is too small, the number of small particles in the particle distribution is too large, and the number of small particles is difficult to control, which will lead to gas enrichment in the cross section of the metal layer and the first material layer under high temperature conditions and the intensification of the side reaction of the carbon coating layer, which will cause the internal resistance growth rate of the secondary battery to increase.
  • the Dv90 value of the first material particles is too large, the number of large particles in the particle distribution is not easy to control, which will increase the number of bad points of the electrode.
  • 6.0 ⁇ D 2 ⁇ 8.0 which can further reduce the internal resistance growth rate and improve the yield rate.
  • the mass content of the carbon coating is C%, 0.1 ⁇ C ⁇ 3.0.
  • the carbon coating can increase the conductivity of the substrate and hinder the aggregation and growth of the substrate; but when the carbon coating content is too large, after high-temperature storage, due to the different thermal expansion coefficients of the carbon coating and the substrate, and the high-temperature electrolyte will cause part of the carbon coating to decompose, resulting in an uneven layer of sediment attached to the surface of the substrate, and the contact between the first material particles becomes worse, thereby increasing the resistance of the secondary battery.
  • the synergistic effect of the appropriate carbon coating content and particle size can further significantly reduce its internal resistance and internal resistance growth rate on the basis of improving the safety performance of the secondary battery.
  • 0.5 ⁇ C ⁇ 2.0 which can further reduce the internal resistance growth rate.
  • the Dv90 of the first material particles is D 2 ⁇ m, based on the mass of the first material particles, the mass content of the carbon coating layer is C%, 3.0 ⁇ D 1 ⁇ D 2 /C ⁇ 12.0, 0.7 ⁇ D 1 ⁇ 1.5, 6.0 ⁇ D 2 ⁇ 8.0, 0.5 ⁇ C ⁇ 2.0.
  • the particle size of the first material particles and the carbon coating amount satisfy the above relationship, the internal resistance growth rate of the secondary battery can be further reduced.
  • 4.7 ⁇ D1 ⁇ D2/C ⁇ 12.0 which can further reduce the internal resistance growth rate, and have lower internal resistance and higher yield.
  • the matrix includes at least one of lithium iron phosphate or lithium iron manganese phosphate.
  • Lithium iron phosphate and lithium iron manganese phosphate have low conductivity, which can increase short-circuit resistance, reduce short-circuit current, and improve safety when the secondary battery is short-circuited due to external force.
  • the first material layer further comprises at least one of inorganic particles, a conductive agent and a binder.
  • the inorganic particles comprise at least one of aluminum oxide, magnesium oxide, calcium oxide, magnesium hydroxide, boehmite, silicon oxide or calcium oxide. The inorganic particles can further reduce the short-circuit current when the secondary battery is short-circuited, thereby improving safety.
  • the mass content of the first material particles is 70% to 85% based on the mass of the first material layer.
  • the mass ratio of the conductive agent to the binder is 10:1 to 3:1.
  • the thickness of the first material layer is 1 ⁇ m to 6 ⁇ m.
  • the secondary battery has both high energy density and safety performance.
  • the second material layer includes a positive electrode active material
  • the positive electrode active material includes lithium cobalt oxide and/or lithium nickel cobalt manganese oxide.
  • the Dv50 of the positive electrode active material is greater than the Dv50 of the first material particles. In some embodiments, the Dv50 of the positive electrode active material is D 3 ⁇ m, 4 ⁇ D 3 ⁇ 15.
  • the Dv50 value of the positive electrode active material is greater than the Dv50 value of the first material particles, which is beneficial to improving the conduction rate of lithium ions in the positive electrode active material and improving the rate performance of the secondary battery. At the same time, when D 3 is in the range of 4 to 15, it is beneficial to the coating of the pole piece and can reduce the number of bad points of the pole piece.
  • the metal layer is an aluminum layer.
  • the secondary battery further includes a negative electrode plate, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes graphite.
  • the first material layer is in direct contact with the metal layer, which is helpful in simplifying the process, reducing the manufacturing cost, and facilitating the conduction of electrons between the first material layer and the metal layer.
  • the present application provides an electronic device comprising the secondary battery of the first aspect.
  • 1 is a schematic diagram of the structure of a positive electrode sheet in a secondary battery in some embodiments of the present application, wherein 1 is a positive electrode current collector, 2 is a first material layer, and 3 is a second material layer.
  • FIG2 is a schematic diagram of the high temperature storage mechanism of the positive electrode sheet in the secondary battery in the prior art, wherein A is a schematic diagram before storage, B is a schematic diagram after storage, 1 is the positive electrode current collector, 2 is the first material layer, 3 is the second material layer, 4 is the separator Off-film, 5a is the first material particles before storage, 5b is the first material particles after storage, 6a is the by-product before storage, and 6b is the by-product after storage.
  • a list of items connected by the terms “at least one of,” “at least one of,” “at least one of,” or other similar terms may mean any combination of the listed items.
  • the phrase “at least one of A and B” means only A; only B; or A and B.
  • the phrase “at least one of A, B, and C” means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.
  • Item A may include a single element or multiple elements.
  • Item B may include a single element or multiple elements.
  • Item C may include a single element or multiple elements.
  • the secondary battery provided in the present application includes a positive electrode plate, which includes a stacked positive electrode collector, a first material layer and a second material layer, the positive electrode collector includes a metal layer, and the first material layer is arranged between the positive electrode collector and the second material layer; the first material layer includes first material particles, the first material particles include a matrix and a carbon coating layer located on the surface of the matrix, wherein the Dv10 of the first material particles is D 1 ⁇ m, 0.3 ⁇ D 1 ⁇ 2.0, the matrix includes at least one of LiFe k M( 1-k )PO 4 , wherein 0 ⁇ k ⁇ 1, and the M element is selected from at least one of manganese, cobalt, magnesium, calcium, zinc, chromium or lead.
  • some embodiments of the present application provide a secondary battery, which includes a positive electrode sheet, which includes a positive electrode collector 1 (surface metal layer is not shown), a first material layer 2, and a second material layer 3.
  • a positive electrode sheet which includes a positive electrode collector 1 (surface metal layer is not shown), a first material layer 2, and a second material layer 3.
  • first material layer is shown as being located on both sides of the positive electrode collector in FIG1 , this is only exemplary, and the first material layer 2 and the second material layer 3 may also be located on one side of the positive electrode collector.
  • the first material layer contains a small amount of byproduct 6a, and the battery performance is not greatly affected.
  • the positive electrode current collector 1 is affected by the first material particles 5 in the first material layer 2, and the gas will gather at the interface between the first material layer 2 and the positive electrode current collector 1, corroding the metal layer, so that the interface resistance between the first material layer and the metal layer increases; in addition, the carbon coating layer on the surface of the substrate is The side reactions increase, causing the side reaction products 6b to accumulate on the substrate surface and in the first material layer, obstructing the electron channel, and thus causing the internal resistance of the secondary battery to continue to increase.
  • the present application reasonably controls the particle size of the first material particles in the first material layer, so that the first material layer and the metal layer have a higher peel strength, reducing the risk of the metal layer being exposed when the secondary battery is subjected to external force, and has a higher short-circuit current, improving safety performance; at the same time, it can also effectively reduce the gas enriched in the first material layer and reduce the occurrence of side reactions in the carbon coating layer, thereby reducing the internal resistance and internal resistance growth rate of the secondary battery.
  • the first material layer is in direct contact with the metal layer, which is helpful in simplifying the process, reducing the manufacturing cost, and facilitating the conduction of electrons between the first material layer and the metal layer.
  • D1 is 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 ⁇ m, 1.7, 1.8, 1.9 or a range consisting of any two of these values. In some embodiments, 0.7 ⁇ D1 ⁇ 1.5 .
  • the Dv10 value of the first material particles is too small, the gas gathered at the interface between the first material layer and the metal layer will increase, causing the carbon coating layer to have more side reactions at high temperatures, thereby causing the internal resistance of the secondary battery to continue to increase.
  • the Dv10 value of the first material particles is too large, although large particles can reduce the occurrence of interface side reactions to a certain extent, the number of large particles in the particle distribution is not easy to control, which will increase the number of bad points of the pole piece.
  • the Dv90 of the first material particles is D 2 ⁇ m, 5.0 ⁇ D 2 ⁇ 10.0.
  • D 2 is 5.3, 5.5, 5.7, 6.0, 6.3, 6.5, 6.7, 7.0, 7.3, 7.5, 7.7, 8.0, 8.3, 8.5, 8.7, 9.0, 9.3, 9.5, 9.7 or a range consisting of any two of these values.
  • the Dv90 value of the first material particles is too small, the number of small particles in the particle distribution is too large, and the number of small particles is difficult to control, which will cause the internal resistance growth rate of the secondary battery to increase.
  • the Dv90 value of the first material particles is too large, the number of large particles in the particle distribution is not easy to control, which will increase the number of bad points of the pole piece.
  • Dv50 means that in the volume-based particle size distribution of the material, 50% of the particles have a particle size smaller than this value.
  • Dv10 means that in the volume-based particle size distribution of the material, 10% of the particles have a particle size smaller than this value.
  • Dv90 means that in the volume-based particle size distribution of the material, 90% of the particles have a particle size smaller than this value.
  • the mass content of the carbon coating is C%, 0.1 ⁇ C ⁇ 3.0.
  • C is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or a range consisting of any two of these values.
  • the carbon coating can increase the conductivity of the matrix and hinder the aggregation and growth of the matrix; however, when the content of the carbon coating is too large, after high-temperature storage, due to the different thermal expansion coefficients of the carbon coating and the matrix, and the high-temperature electrolyte will cause part of the carbon coating to decompose, making the surface of the first material particles not A layer of sediment is evenly attached, and the contact between the first material particles becomes poor, thereby increasing the resistance of the secondary battery.
  • the synergistic effect of the appropriate carbon coating content and particle size can further significantly reduce the internal resistance and internal resistance growth rate on the basis of improving the safety performance of the secondary battery.
  • the Dv90 of the first material particles is D 2 ⁇ m, and based on the mass of the first material particles, the mass content of the carbon coating layer is C%, 3.0 ⁇ D 1 ⁇ D 2 /C ⁇ 12.0, 0.7 ⁇ D 1 ⁇ 1.5, 6.0 ⁇ D 2 ⁇ 8.0, 0.5 ⁇ C ⁇ 2.0.
  • the internal resistance growth rate of the secondary battery can be further reduced.
  • D 1 ⁇ D 2 /C is 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5 or a range consisting of any two of these values.
  • 4.7 ⁇ D1 ⁇ D2/C ⁇ 12.0 is 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5 or a range consisting of any two of these values.
  • the matrix includes at least one of lithium iron phosphate or lithium iron manganese phosphate.
  • Lithium iron phosphate and lithium iron manganese phosphate have low conductivity, which can increase short-circuit resistance, reduce short-circuit current, and improve safety when the secondary battery is short-circuited due to external force.
  • the first material layer further comprises at least one of inorganic particles, a conductive agent and a binder.
  • the inorganic particles comprise at least one of aluminum oxide, magnesium oxide, calcium oxide, magnesium hydroxide, boehmite, silicon oxide or calcium oxide. The addition of inorganic particles can increase short-circuit resistance and improve safety performance.
  • the mass content of the first material particles is 70% to 85%, for example, 72%, 75%, 77%, 80% or 83%.
  • the mass ratio of the conductive agent to the binder is 10:1 to 3:1, for example, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1.
  • the thickness of the first material layer is 1 ⁇ m to 6 ⁇ m, for example 2 ⁇ m, 3 ⁇ m, 4 ⁇ m or 5 ⁇ m.
  • the secondary battery has both high energy density and safety performance.
  • the second material layer includes a positive electrode active material
  • the positive electrode active material includes lithium cobalt oxide and/or lithium nickel cobalt manganese oxide.
  • the Dv50 of the positive electrode active material is greater than the Dv50 of the first material particles.
  • the Dv50 of the positive electrode active material is D 3 ⁇ m, 4 ⁇ D 3 ⁇ 15, and D 3 is, for example, 6, 8, 10, 12 or 14.
  • the Dv50 value of the positive electrode active material is greater than the Dv50 value of the first material particles, which is beneficial to improving the conduction rate of lithium ions in the positive electrode active material and improving the rate performance of the secondary battery.
  • D 3 is in the range of 4 to 15, it is beneficial to the coating of the pole piece and can reduce the number of bad points of the pole piece.
  • the metal layer is an aluminum layer.
  • the secondary battery further comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises graphite.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used.
  • the composite current collector may be formed by compounding a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.
  • the second material layer also includes a binder and a conductive agent.
  • the binder includes an adhesive polymer, such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane.
  • the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.
  • the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.
  • a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber
  • a metal-based material such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.
  • a conductive polymer such as a polyphenylene derivative
  • the secondary battery further comprises a negative electrode
  • the negative electrode comprises a negative electrode active material layer
  • the negative electrode active material layer comprises a negative electrode active material
  • the negative electrode active material comprises graphite.
  • the negative electrode active material layer further comprises a binder and an optional conductive agent.
  • the binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylic acid salt, polyimide, polyamide-imide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, water-based acrylic resin, polyvinyl formal or styrene-acrylic copolymer resin.
  • any conductive material can be used as the conductive material as long as it does not cause chemical changes.
  • the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black or graphene.
  • the negative electrode further includes a negative electrode current collector
  • the negative electrode current collector includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.
  • the secondary battery of the present application also includes a separator.
  • the material and shape of the separator used in the secondary battery of the present application are not particularly limited, and it can be any technology disclosed in the prior art.
  • the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.
  • the isolation film may include a substrate layer and a surface treatment layer.
  • the substrate layer is a non-woven fabric, a film or a composite film having a porous structure
  • the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected.
  • a surface treatment layer is disposed on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic layer.
  • the inorganic layer includes inorganic particles and a binder.
  • the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium oxide, nickel oxide, At least one of zinc, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is selected from at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
  • the secondary of the present application also includes an electrolyte.
  • the electrolyte that can be used in the present application can be an electrolyte known in the prior art.
  • the electrolyte includes an organic solvent, a lithium salt and an optional additive.
  • the organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte.
  • the electrolyte used in the electrolyte according to the present application is not limited, and it can be any electrolyte known in the prior art.
  • the additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive.
  • the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.
  • the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME).
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bis(trifluoromethanesulfonyl)imide LiN(CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium bis(oxalatoborate) LiB(C 2 O 4 ) 2 (LiBOB), or lithium di(oxalatoborate) LiBF 2 (C 2 O 4 )(LiDFOB).
  • the additive includes at least one of fluoroethylene carbonate and adiponitrile.
  • the secondary battery of the present application includes, but is not limited to: a lithium ion battery or a sodium ion battery. In some embodiments, the secondary battery includes a lithium ion battery.
  • the present application further provides an electronic device, which includes the secondary battery according to the first aspect of the present application.
  • the electronic device or device of the present application is not particularly limited.
  • the electronic device of the present application includes, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.
  • Lithium iron phosphate is prepared by solid phase method, and the process can be divided into three parts:
  • the raw materials are iron blocks, sulfuric acid, phosphoric acid, hydrogen peroxide, and sodium carbonate. After two reactions, washing and filtering, flash drying, and dehydration of dihydrate ferric phosphate at 500° C. to 900° C., anhydrous ferric phosphate is obtained.
  • Precursor iron phosphate is mixed with lithium carbonate or lithium hydroxide, deionized water is added, the mixture is fully mixed and stirred, and then protective gas such as nitrogen or argon is introduced, and the mixture is treated at a relatively low temperature for 1 to 5 hours.
  • Carbon black, glucose, urea, citric acid, etc. are used as carbon sources, and the reducing property of carbon sources under high temperature environment is used to reduce trivalent iron to divalent iron, and at the same time, the pyrolyzed carbon is coated on the surface of lithium iron phosphate.
  • This carbon coating can not only form a porous carbon film to enhance conductivity, but also prevent particles from aggregating and growing.
  • lithium iron phosphate with different particle sizes can be obtained by adjusting the pressure, flow rate and size of the spray hole of the spray dryer liquid pump.
  • the content of the carbon coating layer can be adjusted by adjusting the mass fraction of the carbon source.
  • the specific surface area of the lithium iron phosphate material can be adjusted by adjusting the particle size of the lithium iron phosphate.
  • the powder resistivity of the lithium iron phosphate material can be adjusted by adjusting the carbon coating amount.
  • Lithium iron phosphate, ceramic (boehmite), conductive agent (carbon nanotubes), binder (PAA) and dispersant (CMC-Li) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a weight ratio of 85:10:3:2, and evenly stirred to obtain a first material layer slurry.
  • NMP N-methylpyrrolidone
  • the slurry is coated on aluminum foil, vacuum dried at 80°C, and then cold pressed to a thickness of 6 ⁇ m as the first material layer (safety coating).
  • the positive electrode active material ( LiCoO2 ), the conductive agent (conductive carbon black), and the binder (PVDF) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.5:1:1.5 to obtain a second material layer slurry, and the second material layer slurry is coated on the upper surface of the first material layer to form a second material layer (active material layer).
  • NMP N-methylpyrrolidone
  • the positive electrode sheets are made by cold pressing, die cutting and striping.
  • the negative electrode active material graphite
  • conductive carbon black binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are mixed in a weight ratio of 95.7:1.5:1.8:1, and then fully stirred and mixed in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry; the slurry is coated on the current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.
  • SBR binder styrene-butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • EC ethylene carbonate
  • PC propylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the mass percentage of LiPF 6 was 12.5%
  • the mass percentage of fluoroethylene carbonate was 2%
  • the mass percentage of 1,3-propane sultone was 2%
  • the mass percentage of each substance was calculated based on the mass of the electrolyte.
  • a polyethylene (PE) porous polymer film is selected as the isolation film, and the negative electrode sheet and the positive electrode sheet are taken and rolled together with the isolation film, placed in an aluminum-plastic film, and then injected with liquid, left to stand, and formed to make a lithium-ion secondary battery.
  • PE polyethylene
  • Examples 2 to 23 and Comparative Examples 1 to 2 are achieved on the basis of Example 1 by adjusting the pressure, flow rate, size of the spray hole, mass fraction of the carbon source, particle size of the lithium iron phosphate, etc. of the spray dryer liquid pump.
  • Example 9 is achieved by adjusting the base material based on Example 1.
  • the obtained lithium iron phosphate material was tested as follows:
  • the particle size test method refers to GB/T 19077-2016.
  • the specific process is to weigh 1g of the sample and mix it evenly with 20mL of deionized water and a trace amount of dispersant. After placing it in an ultrasonic device for 5 minutes, the solution is poured into the sampling system Hydro2000SM for testing.
  • the test equipment used is the Mastersizer 3000 produced by Malvern.
  • the particle size measurement is completed by measuring the intensity of the scattered light.
  • the data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum.
  • the refractive index of the particles used in the test is 1.8. One sample is tested three times, and the particle size is finally taken as the average of the three tests.
  • the carbon coating amount is tested by boiling and drying a dilute hydrochloric acid solution.
  • the IMP growth rate of a lithium-ion battery placed at 85°C for 6 hours is (IMP6h-IMP0)/IMP0 ⁇ 100%.
  • Table 1 shows the effect of the particle size of the lithium iron phosphate material on the battery performance, wherein the Dv10 of the lithium iron phosphate material is D 1 ⁇ m, the Dv90 of the lithium iron phosphate material is D 2 ⁇ m, and the mass content of the carbon coating layer is C% based on the mass of the lithium iron phosphate material.
  • the Dv10 value of lithium iron phosphate will affect the internal resistance growth rate of lithium-ion batteries and the number of bad points of the pole piece.
  • the secondary battery has a smaller internal resistance growth rate on the basis of ensuring a low number of bad points.
  • the Dv10 value is too low, although it is beneficial to the coating process and can reduce the number of bad points of the pole piece, it will enrich more gas at the interface and cause excessive carbon coating layer side reactions, thereby causing the internal resistance to grow too fast.
  • Table 2 further studies the effect of Dv90 of lithium iron phosphate material on battery performance based on Example 4.
  • the Dv10 value of lithium iron phosphate is in the range of 0.3 ⁇ m to 2.0 ⁇ m, and further controlling the Dv90 value in the range of 5 ⁇ m to 10 ⁇ m can make the lithium-ion battery have both low number of bad points in the pole piece and internal resistance growth rate. Furthermore, controlling the Dv90 value in the range of 6 ⁇ m to 8 ⁇ m can comprehensively balance the number of bad points in the pole piece and the internal resistance growth rate within a better range.
  • Table 3 further studies the effect of the carbon coating amount of the lithium iron phosphate material on the battery performance based on Example 12.

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Abstract

提供一种二次电池，其包括正极极片，该正极极片包括层叠设置的正极集流体、第一材料层和第二材料层，正极集流体包括金属层，第一材料层设置于正极集流体和第二材料层之间；第一材料层包括第一材料颗粒，第一材料颗粒包括基体和位于基体表面的碳包覆层，其中，第一材料颗粒的Dv10为D1μm，0.3≤D1≤2.0，基体包括LiFekM(1-k)PO4中的至少一种，其中，0≤k≤1，M元素选自锰、钴、镁、钙、锌、铬或铅中的至少一种。本申请的二次电池具有低的内阻及内阻增长率。还提供一种包括该二次电池的电子装置。

Description

二次电池和电子装置 技术领域
本申请涉及储能领域，具体涉及一种二次电池和电子装置。
背景技术
锂离子电池在受到外界异物刺穿时，会发生短路导致异常产热。如果锂离子电池内部产热速率大于散热速率，热累积使得其整体温度升高及副反应加速，可能造成锂离子电池热失控，极端情况下甚至出现着火或者爆炸现象。
目前，现有技术常采用正极集流体例如铝箔涂布高粘结安全涂层来减少短路点，进而降低短路时的产热功率。然而，具有高粘结安全涂层的锂离子电池的内阻一般较大，且在高温存储、高温高湿、热冲击等测试后，内阻增长率远高于不设置高粘结安全涂层的锂离子电池。因此，需要开发设计一种新型极片，以解决涂布有高粘结安全涂层的锂离子电池在高温条件下内阻增长偏大的问题。
发明内容
鉴于现有技术存在的上述问题，本申请提供一种二次电池及电子装置，以降低二次电池的内阻及内阻增长率，进而提升二次电池的电性能和寿命。
在第一方面，本申请提供一种二次电池，其包括正极极片，该正极极片包括层叠设置的正极集流体、第一材料层和第二材料层，正极集流体包括金属层，第一材料层设置于正极集流体和第二材料层之间；第一材料层包括第一材料颗粒，第一材料颗粒包括基体和位于基体表面的碳包覆层，第二材料层包括正极活性材料。其中，第一材料颗粒的Dv10为D1μm，0.3≤D1≤2.0，基体包括LiFekM(1-k)PO4中的至少一种，其中，0≤k≤1，M元素选自锰、钴、镁、钙、锌、铬或铅中的至少一种。
现有技术中具有第一材料层(安全涂层)的二次电池内阻偏大，且在高温存储、高温高湿、热冲击等测试后，内阻增长率远高于不设置安全涂层的二次电池，内阻增长率过大会对二次电池性能、寿命等造成严重影响。本申请的发明人通过研究发现，具有安全涂层的二次电池在高温存储时，正极集流体受第一材料层中第一材料颗粒的影响，气体会在第 一材料层和金属层的界面处聚集，腐蚀金属层，使得第一材料层和金属层之间的界面电阻增大；此外，基体表面的碳包覆层在高温下副反应增多，使得副反应产物堆积在基体表面以及第一材料层中，阻碍电子通道，进而导致二次电池的内阻不断增大。针对这一问题，本申请通过合理控制第一材料层中第一材料颗粒的粒径，能够使得第一材料层与金属层之间具有较高的剥离强度，降低二次电池在外力作用时金属层暴露的风险，且上述基体具有较大的短路电阻，可以降低短路电流，提高安全性能；同时还能够有效降低第一材料层中富集的气体以及减少碳包覆层副反应的发生，进而降低二次电池充放电的内阻和内阻增长率。
在一些实施方式中，0.7≤D1≤1.5。第一材料颗粒的Dv10值过小时，聚集在第一材料层和金属层的界面处的气体会增多，使得碳包覆层在高温下副反应增多，进而导致二次电池的内阻不断增大。第一材料颗粒的Dv10值过大时，大颗粒虽然可以一定程度上降低界面副反应的发生，但是颗粒分布中大颗粒数量不容易控制，会增大极片的坏点数量，降低良品率。
在一些实施方式中，第一材料颗粒的Dv90为D2μm，5.0≤D2≤10.0。第一材料颗粒的Dv90值过小时，颗粒分布中小颗粒的数量过多，小颗粒数量难以控制，会导致高温情况下金属层与第一材料层截面的气体富集以及碳包覆层的副反应的加剧，会引发二次电池的内阻增长率升高。第一材料颗粒的Dv90值过大时，颗粒分布中大颗粒数量不容易控制，会增大极片的坏点数量。
在一些实施方式中，6.0≤D2≤8.0。可以进一步降低内阻增长率，提高良品率。
在一些实施方式中，基于第一材料颗粒的质量，碳包覆层的质量含量为C％，0.1≤C≤3.0。碳包覆层可以增加基体导电性以及阻碍基体聚集成长；但碳包覆层含量过大时，高温存储后，由于碳包覆层与基体的热膨胀系数不同，且高温电解液会使得部分碳包覆层分解，使得基体表面不均匀附着一层沉积物，第一材料颗粒间接触变差，进而增加二次电池的电阻。合适碳包覆层含量与粒径协同作用，能够在提高二次电池安全性能的基础上，进一步显著降低其内阻及内阻增长率。
在一些实施方式中，0.5≤C≤2.0。可以进一步降低内阻增长率。
在一些实施方式中，第一材料颗粒的Dv90为D2μm，基于第一材料颗粒的质量，述碳包覆层的质量含量为C％，3.0≤D1×D2/C≤12.0，0.7≤D1≤1.5，6.0≤D2≤8.0，0.5≤C≤2.0。第一材料颗粒的粒径和碳包覆量满足上述关系式时，可以进一步降低二次电池的内阻增长率。
在一些实施方式中，4.7≤D1×D2/C≤12.0。可以进一步降低内阻增长率，以及具有较低的内阻和较高的良品率。
在一些实施方式中，基体包括磷酸铁锂或磷酸铁锰锂中的至少一种。磷酸铁锂和磷酸铁锰锂的电导率较低，在外力作用下导致二次电池短路时，可以增加短路电阻，降低短路电流，提高安全性。
在一些实施方式中，第一材料层还包括无机颗粒、导电剂和粘结剂中的至少一种。在一些实施方式中，无机颗粒包括氧化铝、氧化镁、氧化钙、氢氧化镁、勃姆石、氧化硅或氧化钙中的至少一种。无机颗粒可以进一步降低二次电池短路时的短路电流，提高安全性。
在一些实施方式中，基于第一材料层的质量，第一材料颗粒的质量含量为70％至85％。
在一些实施方式中，第一材料层中，导电剂和粘结剂的质量比为10:1至3:1。
在一些实施方式中，第一材料层的厚度为1μm至6μm。第一材料层的厚度在上述范围内时，二次电池兼具高的能量密度和安全性能。
在一些实施方式中，第二材料层包括正极活性材料，正极活性材料包括钴酸锂和/或镍钴锰酸锂。
在一些实施方式中，正极活性材料的Dv50大于第一材料颗粒的Dv50。在一些实施方式中，正极活性材料的Dv50为D3μm，4≤D3≤15。正极活性材料的Dv50值大于第一材料颗粒的Dv50值，有利于提高锂离子在正极活性材料中的传导速率，提升二次电池倍率性能。同时D3在4至15范围内时，有利于极片涂布，能够减少极片坏点数量。
在一些实施方式中，金属层为铝层。
在一些实施方式中，二次电池还包括负极极片，负极极片包括负极活性物质，负极活性物质包括石墨。
在一些实施例方式中，所述第一材料层与所述金属层直接接触。如此有利于简化工艺，降低制造成本；且有利于电子在第一材料层和金属层之间的传导。
在第二方面，本申请提供了一种电子装置，其包括第一方面的二次电池。
附图说明
图1为本申请一些实施方式的二次电池中正极极片的结构示意图，其中，1为正极集流体，2为第一材料层，3为第二材料层。
图2为现有技术中的二次电池中正极极片的高温存储机理示意图，其中，A为存储前示意图，B为存储后示意图，1为正极集流体，2为第一材料层，3为第二材料层，4为隔 离膜，5a为存储前第一材料颗粒，5b为存储后第一材料颗粒，6a为存储前副产物，6b为存储后副产物。
具体实施方式
本申请的实施例将会被详细的描示在下文中。本申请的实施例不应该被解释为对本申请的限制。
另外，有时在本申请中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围。
在具体实施方式及权利要求书中，由术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
一、二次电池
本申请提供的二次电池包括正极极片，该正极极片包括层叠设置的正极集流体、第一材料层和第二材料层，正极集流体包括金属层，第一材料层设置于正极集流体和第二材料层之间；第一材料层包括第一材料颗粒，第一材料颗粒包括基体和位于基体表面的碳包覆层，其中，第一材料颗粒的Dv10为D1μm，0.3≤D1≤2.0，基体包括LiFekM(1-k)PO4中的至少一种，其中，0≤k≤1，M元素选自锰、钴、镁、钙、锌、铬或铅中的至少一种。
如图1所示，本申请的一些实施方式提供了一种二次电池，其包括正极极片，该正极极片包括正极集流体1(表面金属层未示意出)、第一材料层2和第二材料层3。应该理解，虽然图1中将第一材料层示出为位于正极集流体的两侧上，但是这仅是示例性的，第一材料层2和第二材料层3也可以位于正极集流体的一测上。
如图2所示，现有技术中的二次电池在高温存储前，第一材料层中含有较少量的副产物6a，电池性能未受到大的影响。但经过高温储存后，正极集流体1受第一材料层2中第一材料颗粒5的影响，气体会在第一材料层2和正极集流体1的界面处聚集，腐蚀金属层，使得第一材料层和金属层之间的界面电阻增大；此外，基体表面的碳包覆层在高温 下副反应增多，使得副反应产物6b堆积在基体表面以及第一材料层中，阻碍电子通道，进而导致二次电池的内阻不断增大。针对这一问题，本申请通过合理控制第一材料层中第一材料颗粒的粒径，能够使得第一材料层与金属层之间具有较高的剥离强度，降低二次电池在外力作用时金属层暴露的风险，且具有较高的短路电流，提高安全性能；同时还能够有效降低第一材料层中富集的气体以及减少碳包覆层副反应的发生，进而降低二次电池的内阻和内阻增长率。
在一些实施例方式中，所述第一材料层与所述金属层直接接触。如此有利于简化工艺，降低制造成本；且有利于电子在第一材料层和金属层之间的传导。
在一些实施方式中，D1为0.4、0.5、0.6、0.7、0.8、0.9、1.0、1.1、1.2、1.3、1.4、1.5、1.6μm、1.7、1.8、1.9或这些值中任意两者组成的范围。在一些实施方式中，0.7≤D1≤1.5。第一材料颗粒的Dv10值过小时，聚集在第一材料层和金属层的界面处的气体会增多，使得碳包覆层在高温下副反应增多，进而导致二次电池的内阻不断增大。第一材料颗粒的Dv10值过大时，大颗粒虽然可以一定程度上降低界面副反应的发生，但是颗粒分布中大颗粒数量不容易控制，会增大极片的坏点数量。
在一些实施方式中，第一材料颗粒的Dv90为D2μm，5.0≤D2≤10.0。在一些实施方式中，D2为5.3、5.5、5.7、6.0、6.3、6.5、6.7、7.0、7.3、7.5、7.7、8.0、8.3、8.5、8.7、9.0、9.3、9.5、9.7或这些值中任意两者组成的范围。第一材料颗粒的Dv90值过小时，颗粒分布中小颗粒的数量过多，小颗粒数量难以控制，会引发二次电池的内阻增长率升高。第一材料颗粒的Dv90值过大时，颗粒分布中大颗粒数量不容易控制，会增大极片的坏点数量。在一些实施方式中，6.0≤D2≤8.0。
在一些实施方式中，0.7≤D1≤1.5，6.0≤D2≤8.0。
本申请中，Dv50表示材料在体积基准的粒度分布中，50％的颗粒粒径小于该值。Dv10表示材料在体积基准的粒度分布中，10％的颗粒粒径小于该值。Dv90表示材料在体积基准的粒度分布中，90％的颗粒粒径小于该值。
在一些实施方式中，基于第一材料颗粒的质量，碳包覆层的质量含量为C％，0.1≤C≤3.0。在一些实施方式中，C为0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1.0、1.1、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.9、2.0、2.1、2.2、2.3、2.4、2.5、2.6、2.7、2.8、2.9或这些值中任意两者组成的范围。在一些实施方式中，0.5≤C≤2.0。碳包覆层可以增加基体导电性以及阻碍基体聚集成长；但碳包覆层含量过大时，高温存储后，由于碳包覆层与基体的热膨胀系数不同，且高温电解液会使得部分碳包覆层分解，使得第一材料颗粒表面不 均匀附着一层沉积物，第一材料颗粒间接触变差，进而增加二次电池的电阻。合适碳包覆层含量与粒径协同作用，能够在提高二次电池安全性能的基础上，进一步显著降低其内阻及内阻增长率。
在一些实施方式中，第一材料颗粒的Dv90为D2μm，基于第一材料颗粒的质量，述碳包覆层的质量含量为C％，3.0≤D1×D2/C≤12.0，0.7≤D1≤1.5，6.0≤D2≤8.0，0.5≤C≤2.0。第一材料颗粒的粒径和碳包覆量满足上述关系式时，可以进一步降低二次电池的内阻增长率。在一些实施方式中，D1×D2/C为3.5、4、4.5、5、5.5、6、6.5、7、7.5、8、8.5、9、9.5、10、10.5、11、11.5或这些值中任意两者组成的范围。在一些实施方式中，4.7≤D1×D2/C≤12.0。
在一些实施方式中，基体包括磷酸铁锂或磷酸铁锰锂中的至少一种。磷酸铁锂和磷酸铁锰锂的电导率较低，在外力作用下导致二次电池短路时，可以增加短路电阻，降低短路电流，提高安全性。
在一些实施方式中，第一材料层还包括无机颗粒、导电剂和粘结剂中的至少一种。在一些实施方式中，无机颗粒包括氧化铝、氧化镁、氧化钙、氢氧化镁、勃姆石、氧化硅或氧化钙中的至少一种。无机颗粒的加入可以增加短路电阻，提高安全性能。
在一些实施方式中，基于第一材料层的质量，第一材料颗粒的质量含量为70％至85％，例如为72％、75％、77％、80％或83％。
在一些实施方式中，第一材料层中，导电剂和粘结剂的质量比为10:1至3:1，例如为4:1、5:1、6:1、7:1、8:1或9:1。
在一些实施方式中，第一材料层的厚度为1μm至6μm，例如为2μm、3μm、4μm或5μm。第一材料层的厚度在上述范围内时，二次电池兼具高的能量密度和安全性能。
在一些实施方式中，第二材料层包括正极活性材料，正极活性材料包括钴酸锂和/或镍钴锰酸锂。
在一些实施方式中，正极活性材料的Dv50大于第一材料颗粒的Dv50。在一些实施方式中，正极活性材料的Dv50为D3μm，4≤D3≤15，D3例如为6、8、10、12或14。正极活性材料的Dv50值大于第一材料颗粒的Dv50值，有利于提高锂离子在正极活性材料中的传导速率，提升二次电池倍率性能。同时D3在4至15范围内时，有利于极片涂布，能够减少极片坏点数量。
在一些实施方式中，金属层为铝层。在一些实施方式中，二次电池还包括负极极片，负极极片包括负极活性物质，负极活性物质包括石墨。
在一些实施方式中，正极集流体可以采用金属箔片或复合集流体。例如，可以使用铝箔。复合集流体可以通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)复合在高分子基材上而形成。
在一些实施方式中，第二材料层还包括粘结剂和导电剂。在一些实施例中，粘结剂包括粘合剂聚合物，例如聚偏氟乙烯、聚四氟乙烯、聚烯烃类、羧甲基纤维素钠、羧甲基纤维素锂、改性聚偏氟乙烯、改性SBR橡胶或聚氨酯中的至少一种。在一些实施例中，聚烯烃类粘结剂包括聚乙烯、聚丙烯、聚烯酯、聚烯醇或聚丙烯酸中的至少一种。在一些实施例中，导电剂包括碳基材料，例如天然石墨、人造石墨、炭黑、乙炔黑、科琴黑或碳纤维；金属基材料，例如铜、镍、铝、银等的金属粉或金属纤维；导电聚合物，例如聚亚苯基衍生物；或它们的混合物。
在一些实施方式中，二次电池还包括负极，负极包括负极活性物质层，负极活性物质层包括负极活性物质，负极活性物质包括石墨。在一些实施方式中，负极活性材料层还包括粘结剂以及可选的导电剂。
在一些实施方式中，粘结剂包括丁苯橡胶、聚丙烯酸、聚丙烯酸盐、聚酰亚胺、聚酰胺酰亚胺、聚偏氟乙烯、聚二氟乙烯、聚四氟乙烯、水性丙烯酸树脂、聚乙烯醇缩甲醛或苯乙烯-丙烯酸共聚树脂中的至少一种。在一些实施方式中，可以使用任何导电的材料作为该导电材料，只要它不引起化学变化即可。在一些实施方式中，导电材料包括导电炭黑、乙炔黑、碳纳米管、科琴黑或石墨烯中的至少一种。
在一些实施方式中，负极还包括负极集流体，负极集流体包括：铜箔、铝箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、覆有导电金属的聚合物基底或其任意组合。
本申请的二次电池还包括隔离膜，本申请的二次电池中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化 锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本申请的二次还包括电解液。可用于本申请的电解液可以为现有技术中已知的电解液。
在一些实施方式中，电解液包括有机溶剂、锂盐和可选的添加剂。本申请的电解液中的有机溶剂可为现有技术中已知的任何可作为电解液的溶剂的有机溶剂。根据本申请的电解液中使用的电解质没有限制，其可为现有技术中已知的任何电解质。根据本申请的电解液的添加剂可为现有技术中已知的任何可作为电解液添加剂的添加剂。在一些实施例中，有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯或丙酸乙酯。在一些实施例中，有机溶剂包括醚类溶剂，例如包括1，3-二氧五环(DOL)和乙二醇二甲醚(DME)中的至少一种。在一些实施例中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，锂盐包括，但不限于：六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、二氟磷酸锂(LiPO2F2)、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(LiFSI)、双草酸硼酸锂LiB(C2O4)2(LiBOB)或二氟草酸硼酸锂LiBF2(C2O4)(LiDFOB)。在一些实施例中，添加剂包括氟代碳酸乙烯酯和己二腈中的至少一种。
在一些实施方式中，本申请的二次电池包括，但不限于：锂离子电池或钠离子电池。在一些实施例中，二次电池包括锂离子电池。
二、电子装置
本申请进一步提供了一种电子装置，其包括本申请第一方面的二次电池。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子设备包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
在下述实施例及对比例中，所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得。
实施例及对比例
磷酸铁锂材料制备
磷酸铁锂采用固相法制备，工艺可分为三部分：
1、前驱体磷酸铁锂的制备
原料为铁块、硫酸、磷酸、双氧水、碳酸钠，经过两次反应、洗涤压滤、闪蒸干燥，以及在500℃至900℃下，将二水磷酸铁脱水得到无水磷酸铁。
2、二次加工
①混料：将前驱体磷酸铁与碳酸锂或氢氧化锂进行配料，加入去离子水，充分混合搅拌，再通入保护气体如氮气或氩气等，在较低温度下处理1h至5h。
②喷雾干燥：将搅拌好的浆料通过压力喷出，经过喷雾干燥机后变成颗粒。按照工艺要求得到一定比例大小的球形颗粒。
③烧结：在550℃至750℃下，烧结处理5h至20h得到磷酸铁锂。
④粉碎：使用气流磨设备，对烧结后的磷酸铁锂进行粉碎处理。
⑤混合分级：对粉碎后的磷酸铁锂分体进行混合后，按照颗粒大小进行分级。
⑥烘烤：对合格的磷酸铁锂进行烘烤，去除水分。
3、碳包覆
以炭黑、葡萄糖、尿素、柠檬酸等作为碳源，利用碳源在高温环境下的还原性将三价铁还原为二价铁，同时使热解的碳包覆在磷酸铁锂表面。这种碳包覆不仅可以形成多孔碳膜，增强导电性，还可以防止颗粒聚集长大。
其中，通过调整喷雾干燥机液料泵的压力、流量、喷孔的大小可以获得不同粒径的磷酸铁锂。通过调整碳源的质量分数可以调整碳包覆层的含量。通过调整磷酸铁锂的颗粒度可以调整磷酸铁锂材料的比表面积。通过调整碳包覆量可以调整磷酸铁锂材料的粉末电阻率。
实施例1
正极极片的制备：
将磷酸铁锂、陶瓷(勃母石)、导电剂(碳纳米管)、粘结剂(PAA)和分散剂(CMC-Li)按照85:10:3:2的重量比例在适量的N-甲基吡咯烷酮(NMP)溶剂中充分搅拌混合，均匀搅拌得到第一材料层浆料，将该浆料在铝箔进行涂布，80℃真空烘干，然后冷压到第一材料层的厚度为6μm，作为第一材料层(安全涂层)。
其次，将正极活性材料(LiCoO2)、导电剂(导电炭黑)、粘结剂(PVDF)按照97.5:1:1.5的重量比例在适量的N-甲基吡咯烷酮(NMP)溶剂中充分搅拌混合，得到第二材料层浆料，将第二材料层浆料在第一材料层上表面进行涂布，形成第二材料层(活性材料层)。
80℃真空烘干后，进行冷压、模切、分条制成正极极片。
负极极片的制备
将负极活性材料(石墨)、导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比95.7∶1.5∶1.8∶1配比，再用适量的去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将此浆料涂覆于集流体Cu箔上，烘干、冷压，即可得到负极极片。
电解液的制备
在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC:PC:EMC:DEC＝1:3:3:3进行混合，接着加入氟代碳酸乙烯酯和1,3-丙烷磺内酯，溶解并充分搅拌后加入锂盐六氟磷酸锂(LiPF6)，混合均匀后得到电解液。其中，LiPF6的质量百分含量为12.5％，氟代碳酸乙烯酯的质量百分含量为2％，1,3-丙烷磺内酯的质量百分含量为2％，各物质的质量百分含量为基于电解液的质量计算得到。
锂离子电池的制备
选择聚乙烯(PE)多孔聚合物薄膜作为隔离膜，取上述负极极片和正极极片与隔离膜一起卷绕，放置于铝塑膜中，之后注液、静置、化成，制成锂离子二次电池。
实施例2至实施例8、实施例10至实施例24、对比例1至对比例2
实施例2至实施例23以及对比例1至对比例2是在实施例1的基础上通过调整喷雾干燥机液料泵的压力、流量、喷孔的大小、碳源的质量分数、磷酸铁锂的颗粒度等来实现的。
实施例9
实施例9是在实施例1的基础上调整基体材料实现。
测试方法
基体(磷酸铁锂、磷酸锰铁锂)相关参数测试
取完全放电的锂离子电池(电压<3V)，拆解后取出正极用DMC(乙烯碳酸酯)浸泡20min后，再依次用DMC、丙酮各淋洗一遍，以去除电解液，之后将其置于烘箱内，80℃烘烤12h，获得处理后的正极极片。随后用胶带剥离出第一材料层(安全涂层)，刮下材料。将刮下的材料进行如下处理：
①85℃浸泡NMP溶剂4h；
②超声清洗30min；
③25℃浸泡DI去离子水，超声30min；
④重复1～3步3次；
⑤80℃烘箱烘干，得到的磷酸铁锂粉末材料。
对所获得的磷酸铁锂材料进行如下测试
1、颗粒粒度测试
颗粒粒度测试方法参照GB/T 19077-2016。具体流程为称量样品1g与20mL去离子水和微量分散剂混合均匀，置于超声设备中超声5min后将溶液倒入进样系统Hydro2000SM中进行测试，所用测试设备为马尔文公司生产的Mastersizer 3000。测试过程中当激光束穿过分散的颗粒样品时，通过测量散射光的强度来完成粒度测量。然后数据用于分析计算形成该散射光谱图的颗粒粒度分布。测试所用颗粒折射率为1.8，一个样品测试三次，颗粒粒度最终取三次测试的平均值。
2、碳包覆层含量测试
稀盐酸溶液煮沸烘干测试碳包覆量，原理为碳不溶于盐酸，可以将磷酸铁锂和碳分开。程取M1g质量的磷酸铁锂，加入稀盐酸溶液。将上述混合溶液在加热炉上煮沸30分钟，使用循环泵抽滤并烘干固体，称量残留碳的质量M2g。碳包覆层含量＝M2/M1×100％。锂离子电池相关参数测试
3、锂离子电池内阻测试
使用电阻仪，采用正弦、1000Hz频率波测试锂离子电池的交流内阻。
4、锂离子电池内阻增长率测试
存储条件(85℃放置6h)：在25±3℃的环境中，将锂离子电池以0.2C恒流充电至4.45V，再以4.45V恒压充电至0.025C，测试锂离子电池初始内阻记为IMP0。将锂离子电池放入85±3℃的炉中6h(小时)后取出，待锂离子电池温度降至25±3℃后，测试其 内阻记为“IMP6h”。
记锂离子电池85℃放置6h IMP增长率为(IMP6h-IMP0)/IMP0×100％。
5、极片坏点数量测试
第一材料层烘干后冷压前，沿极片走带方向进行CCD拍照检测，拍照取样100个，统计极片表面凸点异常情况的取样数量。
测试结果
表1示出了磷酸铁锂材料的粒径对电池性能的影响，其中，磷酸铁锂材料的Dv10为D1μm，磷酸铁锂材料的Dv90为D2μm，基于磷酸铁锂材料的质量，碳包覆层的质量含量为C％。
表1
从表1的数据可以看出：磷酸铁锂的Dv10值会影响锂离子电池的内阻增长率及极片的坏点数，Dv10在0.3μm至2.0μm范围内时，二次电池在保证低的坏点数量的基础上，具有较小的内阻增长率。如对比例1的数据所示，Dv10值过低时，虽然有利于涂布工艺，能够降低极片的坏点数量，但会在界面处富集较多气体以及引发过度的碳包覆层副反应，进而导致内阻增长过快。如对比例2的数据所示，Dv10值过高时，大颗粒虽然可以一定程度上降低内阻增长率，但是磷酸铁锂的颗粒中大颗粒数量不容易控制，会增大极片的坏点数量。
表2在实施例4的基础进一步研究了磷酸铁锂材料的Dv90对电池性能的影响。
表2
从表2中的数据可以看出，磷酸铁锂的Dv10值在0.3μm至2.0μm范围内，进一步控制Dv90值在5μm至10μm范围内，可以使得锂离子电池兼具低的极片的坏点数量和内阻增长率。进一步地，控制Dv90值在6μm至8μm范围内，可以综合平衡极片的坏点数量和内阻增长率均在较优的范围内。
表3在实施例12的基础进一步研究了磷酸铁锂材料的碳包覆量对电池性能的影响。
表3
从表3中的数据可以看出，控制碳包覆层的质量含量在0.1％至3.0％范围内，锂离子电池具有较低的内阻和内阻增长率。如实施例17的数据所示，碳包覆量较低时，磷酸铁 锂材料的导电率改善不明显，锂离子电池的内阻较大。如实施例24的数据所示，碳包覆量较高时，界面副反应过多，锂离子电池的内阻增长率较高。进一步地，控制碳包覆层的质量含量在0.5％至2.0％范围内，可以综合平衡锂离子电池内阻和内阻增长率在较优的范围内。
综合表1至表3的实施例数据，可以得出，当满足3.0≤D1×D2/C≤12.0，0.7≤D1≤1.5，6.0≤D2≤8.0，0.5≤C≤2.0时，极片坏点数量较低，锂离子电池内阻较小，内阻增长率均在30％以下。进一步地，当满足4.7≤D1×D2/C≤12.0时，内阻增长率可以显著降低至25％以下。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的原理及范围的情况下对实施例进行改变，替代和修改。

Claims (14)

  1. 一种二次电池，包括正极极片，所述正极极片包括层叠设置的正极集流体、第一材料层和第二材料层，所述正极集流体包括金属层，所述第一材料层设置于所述正极集流体和所述第二材料层之间；所述第一材料层包括第一材料颗粒，所述第一材料颗粒包括基体和位于所述基体表面的碳包覆层，所述第二材料层包括正极活性材料；
    所述第一材料颗粒的Dv10为D1μm，0.3≤D1≤2.0；
    所述基体包括LiFekM(1-k)PO4中的至少一种，其中，0≤k≤1，M元素选自锰、钴、镁、钙、锌、铬或铅中的至少一种。
  2. 根据权利要求1所述的二次电池，其中，0.7≤D1≤1.5。
  3. 根据权利要求1所述的二次电池，其中，所述第一材料颗粒的Dv90为D2μm，5.0≤D2≤10.0。
  4. 根据权利要求3所述的二次电池，其中，6.0≤D2≤8.0。
  5. 根据权利要求1至4任一项所述的二次电池，其中，基于所述第一材料颗粒的质量，所述碳包覆层的质量含量为C％，0.1≤C≤3.0。
  6. 根据权利要求5所述的二次电池，其中，0.5≤C≤2.0。
  7. 根据权利要求1所述的二次电池，其中，所述第一材料颗粒的Dv90为D2μm，基于所述第一材料颗粒的质量，所述碳包覆层的质量含量为C％，3.0≤D1×D2/C≤12.0，0.7≤D1≤1.5，6.0≤D2≤8.0，0.5≤C≤2.0。
  8. 根据权利要求7所述的二次电池，其中，4.7≤D1×D2/C≤12.0。
  9. 根据权利要求1所述的二次电池，其中，所述基体包括磷酸铁锂或磷酸锰铁锂中的至少一种。
  10. 根据权利要求1所述的二次电池，其中，所述第一材料层还包括无机颗粒、导电剂和粘结剂中的至少一种；所述无机颗粒包括氧化铝、氧化镁、氧化钙、氢氧化镁、勃姆石、氧化硅或氧化钙中的至少一种；和/或
    所述正极活性材料包括钴酸锂和/或镍钴锰酸锂；和/或
    所述金属层为铝层。
  11. 根据权利要求1所述的二次电池，其中，所述第一材料层的厚度为1μm至6μm；和/或，
    所述正极活性材料的Dv50大于所述第一材料颗粒的Dv50，所述正极活性材料的Dv50为D3μm，4≤D3≤15。
  12. 根据权利要求1所述的二次电池，其还包括负极极片，所述负极极片包括负极活性物质，所述负极活性物质包括石墨。
  13. 根据权利要求1所述的二次电池，其中，所述第一材料层与所述金属层直接接触。
  14. 一种电子装置，包括权利要求1至13中任一项所述的二次电池。
PCT/CN2023/085340 2023-03-31 2023-03-31 二次电池和电子装置 WO2024197768A1 (zh)

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JP2018113235A (ja) * 2017-01-13 2018-07-19 三井化学株式会社 リチウムイオン二次電池用の正極の製造方法、およびリチウムイオン二次電池
CN111900392A (zh) * 2020-06-22 2020-11-06 珠海冠宇电池股份有限公司 一种正极片及含有该正极片的锂离子电池
CN113078282A (zh) * 2021-03-23 2021-07-06 珠海冠宇电池股份有限公司 一种正极片和锂离子电池
CN115066767A (zh) * 2021-03-23 2022-09-16 珠海冠宇电池股份有限公司 一种正极片和锂离子电池

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JP2018113235A (ja) * 2017-01-13 2018-07-19 三井化学株式会社 リチウムイオン二次電池用の正極の製造方法、およびリチウムイオン二次電池
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