WO2020237713A1 - 锂离子二次电池 - Google Patents

锂离子二次电池 Download PDF

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Publication number
WO2020237713A1
WO2020237713A1 PCT/CN2019/090407 CN2019090407W WO2020237713A1 WO 2020237713 A1 WO2020237713 A1 WO 2020237713A1 CN 2019090407 W CN2019090407 W CN 2019090407W WO 2020237713 A1 WO2020237713 A1 WO 2020237713A1
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Prior art keywords
current collector
layer
ion secondary
secondary battery
active material
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PCT/CN2019/090407
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English (en)
French (fr)
Inventor
刘欣
黄起森
王铈汶
刘向辉
彭佳
李铭领
盛长亮
Original Assignee
宁德时代新能源科技股份有限公司
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Application filed by 宁德时代新能源科技股份有限公司 filed Critical 宁德时代新能源科技股份有限公司
Priority to KR1020207034296A priority Critical patent/KR102600399B1/ko
Priority to EP19931444.4A priority patent/EP3796437B1/en
Priority to JP2020566300A priority patent/JP7130781B2/ja
Publication of WO2020237713A1 publication Critical patent/WO2020237713A1/zh
Priority to US17/123,268 priority patent/US11646424B2/en

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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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C317/00—Sulfones; Sulfoxides
    • C07C317/12—Sulfones; Sulfoxides having sulfone or sulfoxide groups bound to carbon atoms of rings other than six-membered aromatic rings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/651—Means for temperature control structurally associated with the cells characterised by parameters specified by a numeric value or mathematical formula, e.g. ratios, sizes or concentrations
    • 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
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/654—Means for temperature control structurally associated with the cells located inside the innermost case of the cells, e.g. mandrels, electrodes or electrolytes
    • 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
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/66—Heat-exchange relationships between the cells and other systems, e.g. central heating systems or fuel cells
    • H01M10/663—Heat-exchange relationships between the cells and other systems, e.g. central heating systems or fuel cells the system being an air-conditioner or an engine
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This application belongs to the technical field of electrochemical devices, and in particular relates to a lithium ion secondary battery.
  • Lithium-ion secondary batteries have high charge and discharge performance, no memory effect, and are environmentally friendly. They are widely used in electric vehicles and consumer electronic products. Lithium iron phosphate is currently one of the most commonly used positive electrode active materials for power batteries due to its high cycle life, good safety, and high temperature resistance. However, lithium-ion secondary batteries using lithium iron phosphate generally face the problem of poor low-temperature performance, and cannot meet the application requirements of the battery in a low-temperature environment.
  • the embodiments of the present application provide a lithium ion secondary battery, which aims to improve the low temperature performance of a lithium ion secondary battery using lithium iron phosphate.
  • the embodiments of the present application provide a lithium ion secondary battery.
  • the lithium ion secondary battery includes a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • the positive pole piece includes a positive electrode current collector and is arranged on the surface of the positive electrode current collector and includes a positive electrode.
  • the positive electrode active material layer of the active material, the negative electrode piece includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector and containing the negative electrode active material; wherein the positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes graphite;
  • the current collector and/or the negative electrode current collector are composite current collectors, and the composite current collector includes an organic support layer and a conductive layer provided on at least one surface of the organic support layer.
  • the positive electrode active material includes lithium iron phosphate
  • the negative electrode active material includes graphite
  • the positive electrode current collector and/or the negative electrode current collector are composite current collectors
  • the composite current collector includes an organic support layer and The conductive layer provided on at least one surface of the organic support layer. Since the organic support layer of the composite current collector is made of organic materials, compared with the traditional metal current collector, the composite current collector of the present application has a lower thermal conductivity and is thermally insulated. The heat preservation performance is better, so when the battery is working in a low temperature environment, it is less affected by the ambient temperature, and the heat generated by the battery itself will not quickly dissipate.
  • the suitable working temperature inside the core improves the shortcomings of the poor dynamic performance of the lithium iron phosphate battery at low temperature, so that the lithium iron phosphate battery has good low-temperature electrochemical performance and safety performance.
  • the composite current collector has a smaller weight than traditional metal current collectors, so the weight energy density of the battery can be increased at the same time.
  • Fig. 1 is a schematic structural diagram of a composite current collector according to an embodiment of the present application.
  • Fig. 2 is a schematic structural diagram of a composite current collector according to another embodiment of the present application.
  • Fig. 3 is a schematic structural diagram of a composite current collector according to another embodiment of the present application.
  • Fig. 4 is a schematic structural diagram of a composite current collector according to another embodiment of the present application.
  • Fig. 5 is a schematic structural diagram of a composite current collector according to another embodiment of the present application.
  • any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and any upper limit may be combined with any other upper limit to form an unspecified range.
  • every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit in combination with any other point or single numerical value or in combination with other lower or upper limits to form an unspecified range.
  • the embodiment of the present application provides a lithium ion secondary battery, which includes a battery cell and an electrolyte, and the battery core and the electrolyte may be packaged in a packaging shell.
  • the cell includes a positive pole piece, a separator and a negative pole piece.
  • the battery cell can be formed by stacking or winding the positive pole piece, the negative pole piece, and the separator together, wherein the separator is an insulator between the positive pole piece and the negative pole piece and can play a role of isolation.
  • the positive pole piece includes a positive current collector and a positive active material layer arranged on the positive current collector, and the positive active material layer includes a positive active material.
  • the negative pole piece includes a negative current collector and a negative active material layer disposed on the negative current collector, and the negative active material layer includes a negative active material.
  • the positive electrode active material includes lithium iron phosphate
  • the negative electrode active material includes graphite
  • the positive electrode current collector and/or the negative electrode current collector are the composite current collector 10.
  • FIG. 1 is a schematic structural diagram of a composite current collector 10 according to an embodiment of the present application. Please refer to FIG. 1, the composite current collector 10 includes an organic support layer 101 and a conductive layer 102 that are stacked.
  • the organic support layer 101 has a first surface 101 a and a second surface 101 b opposite in the thickness direction, and the conductive layer 102 is disposed on the first surface 101 a and the second surface 101 b of the organic support layer 101.
  • the conductive layer 102 may also be disposed on any one of the first surface 101a and the second surface 101b of the organic support layer 101.
  • the conductive layer 102 is disposed on the first surface 101a of the organic support layer 101.
  • the conductive layer 102 may also be disposed on the second surface 101b of the organic support layer 101.
  • the positive electrode active material includes lithium iron phosphate
  • the negative electrode active material includes graphite
  • the positive electrode current collector and/or the negative electrode current collector is a composite current collector 10
  • the composite current collector 10 includes an organic support layer 101 And the conductive layer 102 disposed on at least one surface of the organic support layer 101. Since the organic support layer 101 of the composite current collector 10 is made of organic materials, the thermal conductivity of the composite current collector 10 is smaller than that of the traditional metal current collector.
  • the composite current collector 10 has better heat insulation/heat preservation performance, so when the battery is working in a low temperature environment, it is less affected by the ambient temperature, and the heat generated by the battery itself will not quickly dissipate, which is conducive to the low temperature environment Lithium-ion secondary batteries can also maintain a suitable working temperature inside the cell, thereby improving the disadvantages of poor kinetic performance of lithium iron phosphate batteries at low temperatures, and making lithium iron phosphate batteries have good low-temperature electrochemical performance and safety performance.
  • the organic support layer 101 in the composite current collector 10 can also effectively support the conductive layer 102 and ensure the overall strength of the composite current collector 10. Therefore, compared with traditional metal current collectors, such as aluminum foil, copper foil, etc., conductive The thickness of the layer 102 can be significantly reduced, and it is not easy to break.
  • the thickness of the conductive layer 102 is significantly reduced, and the density of the organic support layer 101 is lower than that of metal, this ensures that the conductive layer 102 has good conductivity and current collecting performance. It is beneficial to reduce the weight of the battery cell and the lithium ion secondary battery, thereby increasing the energy density of the lithium ion secondary battery.
  • lithium iron phosphate and graphite have the characteristics of high cycle life, good safety, high temperature resistance, etc., it can make the battery cell and the lithium ion secondary battery using the battery have higher cycle performance, safety performance and good Low temperature performance and high temperature performance.
  • the thickness D 1 of the conductive layer 102 is preferably 30 nm ⁇ D 1 ⁇ 3 ⁇ m.
  • the thickness D 1 of the conductive layer 102 is within the above range, so that the conductive layer 102 has higher conductivity and current collecting performance, which is beneficial to make the lithium ion secondary battery have low impedance, reduce battery polarization, and improve the lithium ion secondary battery.
  • the thickness D 1 of the conductive layer 102 within the above range also makes the conductive layer 102 difficult to break during processing and use, so that the composite current collector 10 has higher mechanical stability and working stability, which is beneficial to improve the battery and The service life of lithium ion secondary batteries.
  • the thickness D 1 of the conductive layer 102 is 3 ⁇ m or less. In the case of abnormalities such as spikes in the lithium ion secondary battery, the conductive layer 102 generates less burrs, which can reduce the risk of metal burrs contacting the counter electrode, thereby improving Safety performance of lithium ion secondary batteries.
  • arranging the conductive layer 102 with a smaller thickness on the surface of the organic support layer 101 can significantly reduce the weight of the composite current collector 10, thereby helping to reduce the weight of the lithium-ion secondary battery and increase the energy density of the lithium-ion secondary battery. Significantly improved.
  • the upper limit of the thickness D 1 of the conductive layer 102 may be selected from 3 ⁇ m, 2.5 ⁇ m, 2 ⁇ m, 1.8 ⁇ m, 1.5 ⁇ m, 1.2 ⁇ m, 1 ⁇ m, 900 nm, 750 nm, 450 nm, 250 nm, 100 nm, and the lower limit It can be selected from 1.6 ⁇ m, 1 ⁇ m, 800nm, 600nm, 400nm, 300nm, 150nm, 100nm, 80nm, 30nm, and the range of the thickness D 1 of the conductive layer 102 can be formed by a combination of any upper limit and any lower limit mentioned above, or It may be formed by combining any of the foregoing upper limit values and any other upper limit values, or may be formed by combining any of the foregoing lower limit values and any other lower limit values.
  • the thickness D 1 of the conductive layer 102 is 300 nm ⁇ D 1 ⁇ 2 ⁇ m. More preferably, the thickness D 1 of the conductive layer 102 is 500 nm ⁇ D 1 ⁇ 1.5 ⁇ m. More preferably, the thickness D of the conductive layer 102 is 1 800nm ⁇ D 1 ⁇ 1.2 ⁇ m.
  • the aforementioned “thickness D 1 of the conductive layer 102 ” refers to the thickness of the conductive layer 102 on one side of the organic supporting layer 101.
  • the conductive layer 102 may include one or more of metal materials, carbon-based conductive materials, and conductive polymer materials.
  • the aforementioned metal material may include one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, silver and silver alloy, and for example, aluminum, copper , Nickel, iron, titanium, silver, nickel-copper alloy and aluminum-zirconium alloy one or more.
  • the aforementioned carbon-based conductive material may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the aforementioned conductive polymer material may include one or more of polysulfur nitrides, aliphatic conjugated polymers, aromatic ring conjugated polymers, and aromatic heterocyclic conjugated polymers.
  • the conductive polymer material may include one or more of polyacetylene, polyphenylene, polypyrrole, polyacetylene, polyaniline, polythiophene, and polypyridine.
  • doping can also increase the electron delocalization of the conductive polymer material and improve the conductivity.
  • the conductive layer 102 when the composite current collector 10 is used as a positive electrode current collector, the conductive layer 102 preferably includes aluminum or an aluminum alloy, wherein the weight percentage of aluminum in the aluminum alloy is preferably 80 wt% or more, more preferably 90 wt% the above.
  • the conductive layer 102 when the composite current collector 10 is used as a negative electrode current collector, the conductive layer 102 preferably includes copper or a copper alloy, wherein the weight percentage of the copper element in the copper alloy is preferably 80 wt% or more, more preferably 90 wt% or more.
  • the volume resistivity of the conductive layer 102 is preferably less than or equal to 8.0 ⁇ 10 -8 ⁇ m. This is beneficial for the conductive layer 102 to have better conductivity and current collection performance, thereby improving the rate performance and cycle performance of the lithium ion secondary battery.
  • the volume resistivity of the conductive layer 102 is preferably 3.2 ⁇ 10 -8 ⁇ m to 7.8 ⁇ 10 -8 ⁇ m; the composite current collector 10 is used as a negative electrode current collector In this case, the volume resistivity of the conductive layer 102 is preferably 1.65 ⁇ 10 -8 ⁇ m to 3.3 ⁇ 10 -8 ⁇ m. This is conducive to making the conductive layer 102 have better conductivity and current collecting performance, and it can also make the lithium ion secondary battery have a lower impedance and reduce the polarization of the negative electrode, so that the lithium ion secondary battery has better performance. High rate performance and cycle performance, especially under low temperature conditions, better improve the kinetic performance of lithium-ion secondary batteries, and ensure good low-temperature rate performance and other low-temperature electrochemical performance.
  • the thickness D 2 of the organic support layer 101 is preferably 1 ⁇ m ⁇ D 2 ⁇ 30 ⁇ m.
  • the thickness D 2 of the organic support layer 101 is within the above range, which can better exert the function of the organic support layer 101 to keep the cell and the lithium ion secondary battery in heat preservation, and improve the low temperature performance of the lithium ion secondary battery; It is ensured that the organic support layer 101 has high mechanical strength, is not easy to break during processing and use, plays a good support and protection role for the conductive layer 102, and improves the mechanical stability and working stability of the composite current collector 10.
  • the thickness D 2 of the organic support layer 101 is 30 ⁇ m or less, which is beneficial to make the lithium ion secondary battery have a smaller volume and a lower weight, thereby increasing the volume energy density and weight energy density of the lithium ion secondary battery.
  • the upper limit of the thickness D 2 of the organic support layer 101 can be selected from 30 ⁇ m, 25 ⁇ m, 20 ⁇ m, 18 ⁇ m, 15 ⁇ m, 12 ⁇ m, 10 ⁇ m, 8 ⁇ m, and the lower limit can be selected from 1 ⁇ m, 1.5 ⁇ m. , 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 9 ⁇ m, 16 ⁇ m.
  • the range of the thickness D 2 of the organic support layer 101 can be formed by a combination of any of the foregoing upper limit and any lower limit, or can be formed by a combination of any of the foregoing upper limit and any other upper limit, or can be formed by any combination of the foregoing.
  • the lower limit is combined with any other lower limit.
  • the thickness D 2 of the organic support layer 101 is 1 nm ⁇ D 1 ⁇ 20 ⁇ m. More preferably, the thickness D 2 of the organic support layer 101 is 1 ⁇ m ⁇ D 2 ⁇ 15 ⁇ m. More preferably, the thickness D 2 of the organic support layer 101 is 1 ⁇ m ⁇ D 2 ⁇ 10 ⁇ m. More preferably, the thickness D 2 of the organic support layer 101 is 1 ⁇ m ⁇ D 2 ⁇ 8 ⁇ m, preferably 2 ⁇ m ⁇ D 2 ⁇ 8 ⁇ m.
  • the Young's modulus E of the organic support layer 101 is preferably E ⁇ 2GPa, which makes the organic support layer 101 rigid, which not only satisfies the higher support effect of the organic support layer 101 on the conductive layer 102 , To ensure the overall strength of the composite current collector 10, and to prevent the organic support layer 101 from being excessively stretched or deformed during the processing of the composite current collector 10, which more effectively prevents the organic support layer 101 and the conductive layer 102 from breaking.
  • the bonding strength between the organic support layer 101 and the conductive layer 102 is higher, so that the conductive layer 102 is not easily peeled off, and the mechanical stability and working stability of the composite current collector 10 are improved, so that the lithium ion secondary battery Performance is improved.
  • the Young's modulus E of the organic support layer 101 is preferably 2GPa ⁇ E ⁇ 20GPa; for example, 2GPa, 3GPa, 4GPa, 5GPa, 6GPa, 7GPa, 8GPa, 9GPa, 10GPa, 11GPa, 12GPa, 13GPa, 14GPa, 15GPa , 16GPa, 17GPa, 18GPa, 19GPa, 20GPa.
  • This allows the organic support layer 101 to have rigidity and at the same time suitable toughness, and to ensure the flexibility of the organic support layer 101 and the composite current collector 10 using the same for winding during processing.
  • the organic support layer 101 adopts one or more of polymer materials and polymer-based composite materials.
  • polystyrene resin for example, polyamides, polyimides, polyesters, polyolefins, polyacetylenes, siloxane polymers, polyethers, polyols, polysulfones, Polysaccharide polymers, amino acid polymers, polysulfur nitrides, aromatic ring polymers, aromatic heterocyclic polymers, epoxy resins, phenolic resins, their derivatives, their cross-linked products and their copolymers One or more of.
  • the polymer material can be, for example, polycaprolactam (commonly known as nylon 6), polyhexamethylene adipamide (commonly known as nylon 66), polyparaphenylene terephthalamide (PPTA), polyisophthalamide M-phenylenediamine (PMIA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycarbonate ( PC), polyethylene (PE), polypropylene (PP), polypropylene (PPE), polyvinyl alcohol (PVA), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTEE), polystyrene sulfonate (PSS), polyacetylene (PA), silicone rubber, polyoxymethylene (POM), polyphenylene oxide (PPO), polyphenylene sulfide Ether (PPS), polyethylene glycol (PO
  • the above-mentioned polymer-based composite material for example, the above-mentioned polymer material and additives may be included, and the additives may be one or more of metal materials and inorganic non-metal materials.
  • the aforementioned metal material additives are, for example, one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, iron, iron alloy, silver, and silver alloy.
  • the above-mentioned inorganic non-metallic material additives are, for example, one or more of carbon-based materials, alumina, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicate, and titanium oxide, and for example, glass materials, One or more of ceramic materials and ceramic composite materials.
  • the carbon-based material additives are, for example, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • additives it may also be a carbon-based material coated with a metal material, such as one or more of nickel-coated graphite powder and nickel-coated carbon fiber.
  • the organic support layer 101 adopts one or more of insulating polymer materials and insulating polymer-based composite materials.
  • the organic support layer 101 has a relatively high volume resistivity, which is beneficial to improve the safety performance of the lithium ion secondary battery.
  • the organic support layer 101 includes polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polystyrene sulfonate One or more of sodium (PSS) and polyimide (PI).
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PEN polyethylene naphthalate
  • PSS polystyrene sulfonate
  • PSS polystyrene sulfonate
  • PSS polystyrene sulfonate
  • PSS polystyrene sulfonate
  • PI polyimide
  • the organic support layer 101 may be a single-layer structure or a composite layer structure of more than two layers, such as two layers, three layers, four layers, and so on.
  • FIG. 2 is a schematic structural diagram of another composite current collector 10 according to an embodiment of the present application.
  • the organic support layer 101 is composed of a first sublayer 1011, a second sublayer 1012, and a third sublayer 1013.
  • the organic support layer 101 of the composite layer structure has a first surface 101 a and a second surface 101 b opposite to each other, and the conductive layer 102 is stacked on the first surface 101 a and the second surface 101 b of the organic support layer 101.
  • the conductive layer 102 may be provided only on the first surface 101a of the organic support layer 101, or only on the second surface 101b of the organic support layer 101.
  • the materials of each sublayer may be the same or different.
  • the thermal conductivity of the composite current collector 10 is preferably 0.01 W/(m ⁇ K) to 10 W/(m ⁇ K).
  • the thermal conductivity of the composite current collector 10 is higher than 10W/(m ⁇ K), which is insufficient to improve the low-temperature electrochemical performance of the entire battery and the effect of low-temperature lithium evolution; the thermal conductivity of the composite current collector 10 is lower than 0.01W/( m ⁇ K), the thickness of the organic support layer 101 is generally larger, which will affect the volume energy density and weight energy density of the battery.
  • the thermal conductivity of the composite current collector 10 is 0.1 W/(m ⁇ K) to 2 W/(m ⁇ K).
  • the thermal conductivity of the composite current collector 10 will be affected by the following factors: the thickness D 1 of the conductive layer 102, the material of the conductive layer 102, the thickness D 2 of the organic support layer 101, the material of the organic support layer 101, and the preparation process of the conductive layer 102 Conditions (for example, deposition rate, deposition temperature, cooling rate, etc. when the conductive layer 102 is prepared by a deposition process), the bonding force between the conductive layer 102 and the organic support layer 101, and the like. By adjusting one or more of the aforementioned factors, the thermal conductivity of the composite current collector 10 can be improved.
  • the composite current collector 10 of the embodiment of the present application further optionally includes a protective layer 103.
  • the conductive layer 102 includes two opposite surfaces in its thickness direction, and the protective layer 103 is stacked on either or both of the two surfaces of the conductive layer 102 to protect the conductive layer 102. Prevent damages such as chemical corrosion or mechanical damage to the conductive layer 102, and ensure the working stability and service life of the composite current collector 10, so that the lithium ion secondary battery has higher safety performance and electrochemical performance.
  • the protective layer 103 can also enhance the strength of the composite current collector 10.
  • FIGS. 3 to 5 show that there is a conductive layer 102 on one side of the organic support layer 101, on one or both of the two opposite surfaces in the thickness direction of the conductive layer 102 itself It has a protective layer 103, but in other embodiments, it is also possible to have conductive layers 102 on the two opposite surfaces of the organic support layer 101, which can be on the two opposite surfaces of any conductive layer 102 in the thickness direction.
  • One or both of the protective layer 103 may be provided, or the protective layer 103 may be provided on one or both of the two opposite surfaces of the two conductive layers 102 in the thickness direction.
  • the protective layer 103 includes one or more of metal, metal oxide, and conductive carbon. Among them, the protective layer 103 of metal material is a metal protective layer, and the protective layer 103 of metal oxide material is a metal oxide protective layer.
  • the aforementioned metals are, for example, one or more of nickel, chromium, nickel-based alloys, and copper-based alloys.
  • the aforementioned nickel-based alloy is an alloy formed by adding one or more other elements to pure nickel as a matrix, preferably a nickel-chromium alloy.
  • the nickel-chromium alloy is an alloy formed of metallic nickel and metallic chromium.
  • the weight ratio of nickel to chromium in the nickel-chromium alloy is 1:99 to 99:1, such as 9:1.
  • the aforementioned copper-based alloy is an alloy formed by adding one or more other elements to pure copper as a matrix, preferably a nickel-copper alloy.
  • the weight ratio of nickel to copper in the nickel-copper alloy is 1:99-99:1, such as 9:1.
  • the aforementioned metal oxide is, for example, one or more of alumina, cobalt oxide, chromium oxide, and nickel oxide.
  • the aforementioned conductive carbon is, for example, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and further is carbon black, carbon nano One or more of tube, acetylene black and graphene.
  • the composite current collector 10 includes an organic support layer 101, a conductive layer 102, and a protective layer 103 that are stacked.
  • the organic support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction
  • the conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the organic support layer 101
  • the protective layer 103 is stacked on the surface of the conductive layer 102 facing away from the organic support layer 101.
  • a protective layer 103 (referred to as the upper protective layer for short) is provided on the surface of the conductive layer 102 facing away from the organic support layer 101 to protect the conductive layer 102 from chemical corrosion and mechanical damage, and can also improve the composite current collector 10
  • the interface with the active material layer improves the bonding force between the composite current collector 10 and the active material layer.
  • the upper protective layer of the composite current collector 10 is preferably at least one of a metal protective layer and a metal oxide protective layer.
  • the metal oxide protective layer and the metal protective layer have high mechanical strength and high corrosion resistance. With a large specific surface area, the conductive layer 102 can be better prevented from chemical corrosion or mechanical damage, and at the same time, the interface bonding force between the conductive layer 102 and the positive electrode active material layer can be further improved, and the performance of the lithium ion secondary battery can be improved.
  • the upper protective layer of the composite current collector 10 is preferably a metal oxide protective layer, such as aluminum oxide, cobalt oxide, nickel oxide, chromium oxide, etc., the metal oxide protective layer It has high hardness and mechanical strength, a larger specific surface area, better corrosion resistance, and can better protect the conductive layer 102; in addition, it is also beneficial to improve the battery's nail penetration safety performance.
  • a metal oxide protective layer such as aluminum oxide, cobalt oxide, nickel oxide, chromium oxide, etc.
  • the upper protective layer is preferably a metal protective layer.
  • the metal protective layer can improve the conductivity of the composite current collector 10, reduce battery polarization, and reduce the lithium evolution of the negative electrode. Risk, improve the cycle performance and safety performance of lithium ion secondary batteries; more preferably a double protective layer, that is, a composite layer of a metal protective layer and a metal oxide protective layer, wherein preferably, the metal protective layer
  • the conductive layer 102 faces away from the surface of the organic supporting layer 101, and the metal oxide protective layer is disposed on the surface of the metal protective layer facing away from the organic supporting layer 101. This can improve the conductivity, corrosion resistance, and conductive layer 102 of the negative electrode current collector at the same time.
  • the interface with the negative electrode active material layer, etc. can obtain a negative electrode current collector with better overall performance.
  • the composite current collector 10 includes an organic support layer 101, a conductive layer 102 and a protective layer 103 that are stacked.
  • the organic support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction
  • the conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the organic support layer 101
  • the protective layer 103 is stacked on the surface of the conductive layer 102 facing the organic support layer 101.
  • a protective layer 103 (referred to as the lower protective layer for short) is provided on the surface of the conductive layer 102 facing the organic support layer 101.
  • the lower protective layer protects the conductive layer 102 from chemical corrosion and mechanical damage, and can also improve The bonding force between the conductive layer 102 and the organic support layer 101 prevents the conductive layer 102 from being separated from the organic support layer 101, and improves the support and protection effect of the conductive layer 102.
  • the lower protective layer is a metal oxide protective layer or a metal protective layer, and the metal protective layer and the metal oxide protective layer have high corrosion resistance, and their specific surface area is large, which can further improve the conductive layer 102 and the organic support layer The interface bonding force between 101, so that the lower protective layer can better protect the conductive layer 102 and improve the performance of the lithium ion secondary battery.
  • the metal oxide protective layer has higher hardness and better mechanical strength, which is more conducive to improving the strength of the composite current collector 10.
  • the lower protective layer is preferably a metal oxide protective layer.
  • the lower protective layer is preferably a metal protective layer, which can protect the conductive layer 102 from chemical corrosion and mechanical damage while also improving the conductivity of the composite current collector 10 Performance can reduce battery polarization, reduce the risk of lithium precipitation in the negative electrode, and improve the cycle performance and safety performance of the lithium ion secondary battery.
  • the composite current collector 10 includes an organic support layer 101, a conductive layer 102 and a protective layer 103 that are stacked.
  • the organic support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction
  • the conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the organic support layer 101
  • the protective layer 103 is stacked on the surface of the conductive layer 102 facing away from the organic supporting layer 101 and on the surface facing the organic supporting layer 101.
  • the protective layer 103 is provided on both surfaces of the conductive layer 102 to more fully protect the conductive layer 102, so that the composite current collector 10 has a higher comprehensive performance.
  • the materials of the protective layers 103 on the two surfaces of the conductive layer 102 may be the same or different, and the thicknesses may be the same or different.
  • the thickness D 3 of the protective layer 103 is 1 nm ⁇ D 3 ⁇ 200 nm, and D 3 ⁇ 0.1D 1 . If the protective layer 103 is too thin, it is not enough to protect the conductive layer 102; if it is too thick, the energy density of the lithium ion secondary battery will be reduced.
  • the upper limit value of the thickness D 3 of the protective layer 103 may be 200 nm, 180 nm, 150 nm, 120 nm, 100 nm, 80 nm, 60 nm, 55 nm, 50 nm, 45 nm, 40 nm, 30 nm, 20 nm, and the lower limit value may be 1nm, 2nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm.
  • the range of the thickness D 3 of the protective layer 103 can be formed by a combination of any of the aforementioned upper limit and any lower limit, or can be formed by a combination of any of the aforementioned upper limits and any other upper limit, or can be formed by any of the aforementioned lower limits.
  • the limit is combined with any other lower limit.
  • the aforementioned “thickness D 3 of the protective layer 103 ” refers to the thickness of the protective layer 103 on one side of the conductive layer 102. That is, the protective layer has a thickness of 1nm ⁇ D a ⁇ 200nm D a and D a ⁇ 0.1D 1; further, 5nm ⁇ D a ⁇ 200nm; Furthermore, 10nm ⁇ D a ⁇ 200nm.
  • the thickness of the protective layer D b is 1nm ⁇ D b ⁇ 200nm, and D b ⁇ 0.1D 1; further, 5nm ⁇ D b ⁇ 200nm; Furthermore, 10nm ⁇ D b ⁇ 200nm.
  • both surfaces of the conductive layer 102 are provided with protective layers 103, that is, when the composite current collector 10 includes an upper protective layer and a lower protective layer, preferably, D a > D b , which is beneficial to the coordination of the upper protective layer and the lower protective layer
  • the conductive layer 102 has a good protective effect against chemical corrosion and mechanical damage, and at the same time enables the lithium ion secondary battery to have a higher energy density. More preferably, 0.5D a ⁇ D b ⁇ 0.8D a , which can better exert the cooperative protection effect of the upper protective layer and the lower protective layer.
  • the bonding force F between the organic support layer 101 and the conductive layer 102 is preferably F ⁇ 100 N/m, more preferably F ⁇ 400 N/m. This can effectively prevent peeling between the organic support layer 101 and the conductive layer 102, improve the overall strength and reliability, and thereby help improve the performance of the lithium ion secondary battery.
  • the conductive layer 102 when the conductive layer 102 is made of a metal material, it can be formed on the organic support layer 101 by at least one of mechanical rolling, bonding, vapor deposition, electroless plating, and electroplating Among them, vapor deposition and electroplating are preferred.
  • the conductive layer 102 is formed on the organic support layer 101 by a vapor deposition method or an electroplating method, which is beneficial to make the bonding between the conductive layer 102 and the organic support layer 101 stronger.
  • the above-mentioned vapor deposition method is preferably a physical vapor deposition method.
  • the physical vapor deposition method is preferably at least one of an evaporation method and a sputtering method, wherein the evaporation method is preferably at least one of a vacuum evaporation method, a thermal evaporation method, and an electron beam evaporation method, and the sputtering method is preferably a magnetron sputtering method.
  • the conditions for forming the conductive layer 102 by mechanical rolling are as follows: a metal foil is placed in a mechanical roller, rolled to a predetermined thickness by applying a pressure of 20t to 40t, and then placed to undergo surface cleaning The surface of the organic support layer 101 is treated, and then the two are placed in a mechanical roller, and the two are tightly combined by applying a pressure of 30t-50t.
  • the conditions for forming the conductive layer 102 by bonding above are as follows: the metal foil is placed in a mechanical roller, and it is rolled to a predetermined thickness by applying a pressure of 20t to 40t; and then on the surface of the organic support layer 101 that has been cleaned. The surface is coated with a mixed solution of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP); finally, the conductive layer 102 of the predetermined thickness is bonded to the surface of the organic support layer 101, and dried to make the two tight Combine.
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the conditions for forming the conductive layer by the vacuum evaporation method are as follows: the organic support layer 101 with the surface cleaning treatment is placed in the vacuum coating chamber, and the high-purity metal wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1300°C ⁇ 2000°C. The latter metal passes through the cooling system in the vacuum coating chamber and is finally deposited on the surface of the organic support layer 101 to form the conductive layer 102.
  • a carbon-based conductive material When a carbon-based conductive material is used for the conductive layer 102, it may be formed on the organic support layer 101 by at least one of mechanical rolling, bonding, vapor deposition, in-situ formation, and coating.
  • the conductive layer 102 When the conductive layer 102 is made of a conductive polymer material, it may be formed on the organic support layer 101 by at least one of mechanical rolling, bonding, in-situ formation method, and coating method.
  • the protective layer 103 may be formed on the conductive layer 102 by at least one of a vapor deposition method, an in-situ formation method, and a coating method.
  • the vapor deposition method may be the vapor deposition method as described above.
  • the in-situ formation method is preferably an in-situ passivation method, that is, a method of forming a metal oxide passivation layer in situ on the metal surface.
  • the coating method is preferably at least one of roll coating, extrusion coating, knife coating, and gravure coating.
  • the protective layer 103 is formed on the conductive layer 102 by at least one of a vapor deposition method and an in-situ formation method, which is conducive to making the conductive layer 102 and the protective layer 103 have a higher bonding force, which is better.
  • the protective layer 102 protects the composite current collector 10 and ensures the working performance of the composite current collector 10.
  • the composite current collector 10 of any of the foregoing embodiments can be used as either or both of the positive electrode current collector and the negative electrode current collector.
  • the positive electrode current collector is a metal current collector (for example, an aluminum foil or aluminum alloy current collector) or a composite current collector 10
  • the negative electrode current collector is a composite current collector 10. Due to the high density of copper, replacing the traditional copper foil anode current collector with the composite current collector 10 can greatly improve the weight energy density of the lithium ion secondary battery and at the same time improve the low temperature performance of the lithium ion secondary battery .
  • the use of the composite current collector 10 at the negative pole piece can improve the low-temperature performance of the lithium-ion secondary battery, and at the same time, better prevent the low-temperature lithium evolution of the negative electrode, and better improve the dynamic performance of the lithium-ion secondary battery. Rate performance and safety performance.
  • both the positive electrode current collector and the negative electrode current collector are the composite current collector 10
  • the low temperature performance of the lithium ion secondary battery can be better improved.
  • the thickness of the conductive layer thickness D 102 D 1 and 2, the organic support layer 101 known in the art may be employed in the apparatus and method be measured, for example with very feet.
  • the thermal conductivity of the composite current collector 10 can be measured using instruments and methods known in the art.
  • a thermal conductivity meter is used, including: cutting the composite current collector 10 into a sample of 5 cm ⁇ 5 cm, and measuring the sample with a TC3000 thermal conductivity meter The thermal conductivity.
  • the four-probe method is used to test the sheet resistance R S of the conductive layer 102.
  • the method includes: using the RTS-9 double-electric four-probe tester, the test environment is: normal temperature 23 ⁇ 2°C, 0.1MPa, relative humidity ⁇ 65% During the test, clean the surface of the positive electrode collector 10 sample, then place it horizontally on the test bench, put down the four probes, make the probes make good contact with the surface of the conductive layer 102 of the sample, and then adjust the current of the automatic test mode to calibrate the sample Measuring range, measure the square resistance under the appropriate current range, and collect 8 to 10 data points of the same sample as the data measurement accuracy and error analysis. Finally, the average value is taken and recorded as the sheet resistance of the conductive layer 102.
  • the Young's modulus E of the organic support layer 101 can be measured by a method known in the art. As an example, cut the organic support layer 101 into a 15mm ⁇ 200mm sample, measure the thickness h ( ⁇ m) of the sample with a micrometer, and perform a tensile test using a high-speed rail tensile machine at normal temperature and pressure (25°C, 0.1MPa).
  • the bonding force F between the organic support layer 101 and the conductive layer 102 can be tested by methods known in the art.
  • the composite current collector 10 sample to be tested with the conductive layer 102 disposed on one side of the organic support layer 101 is selected, and the width d is 0.02 m.
  • the embodiments of the present application provide a positive pole piece used in a lithium ion secondary battery.
  • the positive electrode piece includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector.
  • the positive electrode current collector includes two opposite surfaces in its thickness direction, and the positive electrode active material layer is stacked on the two surfaces of the positive electrode current collector.
  • the positive electrode active material layer can also be laminated on any one of the two surfaces of the positive electrode current collector.
  • the positive electrode current collector is the composite current collector 10 described above. If the negative electrode current collector is the aforementioned composite current collector 10, the positive electrode current collector can be the aforementioned composite current collector 10, or it can be a metal current collector, such as aluminum foil or aluminum alloy.
  • the positive electrode current collector is the composite current collector 10 described above, it not only has the corresponding beneficial effects described above, but also can improve the safety performance of the lithium ion secondary battery.
  • the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate.
  • the positive electrode active material layer may also optionally include other positive electrode active materials known in the art that can perform reversible intercalation/deintercalation of lithium ions.
  • positive electrode active materials can be, for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium vanadium phosphate, lithium cobalt phosphate, One or more of lithium manganese phosphate, lithium iron manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, and lithium titanate.
  • other positive electrode active materials are LiMn 2 O 4 , LiNiO 2 , LiCoO 2 , LiNi 1-y Co y O 2 (0 ⁇ y ⁇ 1), LiNi a Co b Al 1-ab O 2 (0 ⁇ a ⁇ 1 , 0 ⁇ b ⁇ 1, 0 ⁇ a+b ⁇ 1), LiMn 1-mn Ni m Co n O 2 (0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m+n ⁇ 1), LiMPO 4 (M may be one or more of Mn, Co, and Fe) and one or more of Li 3 V 2 (PO 4 ) 3 .
  • the mass percentage of lithium iron phosphate in the positive electrode active material is more than 50% by weight, further more than 60% by weight, and still further more than 80% by weight. At this time, the low-temperature performance of the lithium ion secondary battery in the embodiments of the present application can be more significantly improved.
  • the positive active material layer may also optionally include a binder, and the application does not limit the type of the binder.
  • the binder is styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE)
  • SBR styrene butadiene rubber
  • CMC carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive active material layer may also optionally include a conductive agent, and the type of the conductive agent is not limited in this application.
  • the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the thickness T 1 of the positive electrode active material layer is preferably 50 ⁇ m to 100 ⁇ m. If the thickness T 1 of the positive electrode active material layer is within the above range, the effect of improving the low-temperature performance of the lithium ion secondary battery is better, and at the same time, it can ensure that the positive electrode has good dynamic performance and improve the electrochemical performance of the lithium ion secondary battery. More preferably, the thickness T 1 of the positive electrode active material layer is 60 ⁇ m to 90 ⁇ m, which can further improve the low temperature performance of the lithium ion secondary battery, and obtain a positive electrode piece and a lithium ion secondary battery with better overall performance.
  • the aforementioned "thickness T 1 of the positive electrode active material layer” refers to the thickness of the positive electrode active material layer on one side of the positive electrode current collector.
  • the positive pole piece can be prepared according to a conventional method in the art, such as a coating method.
  • a coating method As an example, disperse the positive electrode active material and the optional conductive agent and binder in a solvent.
  • the solvent can be N-methylpyrrolidone (NMP) to form a uniform positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the positive electrode slurry is coated on the positive electrode collector. On the fluid, after drying and other processes, the positive pole piece is obtained.
  • the embodiments of the present application provide a negative pole piece used in a lithium ion secondary battery.
  • the negative pole piece includes a negative current collector and a negative active material layer arranged on the negative current collector.
  • the negative electrode current collector includes two opposite surfaces in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is stacked on the two surfaces of the negative electrode current collector.
  • the negative electrode active material layer may also be laminated on any one of the two surfaces of the negative electrode current collector.
  • the negative electrode current collector is the composite current collector 10 described above. If the positive electrode current collector is the aforementioned composite current collector 10, the negative electrode current collector can be the aforementioned composite current collector 10, or it can be a metal current collector, such as copper foil or copper alloy.
  • the negative electrode current collector is the composite current collector 10 described above, it also has the corresponding beneficial effects described above, which will not be repeated here.
  • the negative active material layer includes a negative active material, and the negative active material includes graphite, such as at least one of natural graphite and artificial graphite.
  • the negative active material may also optionally include other negative active materials known in the art that can perform reversible ion intercalation/deintercalation.
  • negative electrode active materials can be, for example, metallic lithium, mesophase micro-carbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn , SnO, SnO 2 , spinel structure lithium titanate and one or more of Li-Al alloy.
  • MCMB mesophase micro-carbon spheres
  • the mass percentage of graphite in the negative electrode active material is 50 wt% or more, further 60 wt% or more, and still more 80 wt% or more. At this time, the low-temperature performance of the lithium ion secondary battery of the embodiment of the present application can be more significantly improved.
  • the negative active material layer may also optionally include a conductive agent, and the type of the conductive agent is not limited in this application.
  • the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the negative active material layer may also optionally include a binder, and the type of binder is not limited in this application.
  • the binder is styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE)
  • SBR styrene butadiene rubber
  • CMC carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the thickness T 2 of the anode active material layer is 30 ⁇ m to 70 ⁇ m. If the thickness T 2 of the negative electrode active material layer is within the above range, the effect of improving the low temperature performance of the lithium ion secondary battery is better, and at the same time, it can ensure that the negative electrode has good kinetic performance and improve the electrochemical performance of the lithium ion secondary battery. More preferably, the thickness T 2 of the negative electrode active material layer is 40 ⁇ m to 60 ⁇ m, which can further improve the low temperature performance of the lithium ion secondary battery, and obtain a positive electrode piece and a lithium ion secondary battery with better overall performance.
  • the aforementioned "thickness T 2 of the negative electrode active material layer” refers to the thickness of the negative electrode active material layer on one side of the negative electrode current collector.
  • the negative pole piece can be prepared according to a conventional method in the art, such as a coating method.
  • a coating method As an example, disperse the negative electrode active material and the optional conductive agent and binder in a solvent.
  • the solvent can be deionized water to form a uniform negative electrode slurry.
  • the negative electrode slurry is coated on the negative electrode current collector and dried. After the drying process, the negative pole piece is obtained.
  • the embodiment of the present application provides an electrolyte for use in a lithium ion secondary battery.
  • the electrolyte includes an organic solvent and an electrolyte lithium salt dispersed in the organic solvent.
  • the organic solvent may be, for example, ethylene carbonate (EC), propylene carbonate (PC), pentenyl carbonate, 1,2-butanediol carbonate (1,2-BC), 2,3-butanediol carbonate (2,3-BC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene carbonate Propyl ester (EPC), butene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), ethyl formate (EM), methyl acetate (MA), ethyl acetate (EA) , Propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1, One or more of 4-butyrolactone
  • the organic solvent is a mixed solvent including cyclic carbonate and chain carbonate.
  • Such organic solvents are conducive to the preparation of electrolytes with good comprehensive properties such as electrical conductivity and viscosity.
  • the 25°C conductivity of the electrolyte may be 8 mS/cm to 11 mS/cm. If the conductivity is too low, the electrolyte dynamic performance is relatively reduced, and the polarization of the lithium iron phosphate battery is relatively large, which affects the normal temperature cycle performance and low temperature performance; if the conductivity is too large, the electrolyte thermal stability is relatively reduced, which affects the lithium iron phosphate battery. High temperature cycle performance of the battery.
  • the electrolyte lithium salt can be, for example, LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide) , LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bisoxalate borate), LiPO 2 F 2 (lithium difluorophosphate ), one or more of LiDFOP (lithium difluorobisoxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • the electrolyte may also optionally include additives.
  • the additives may include, for example, negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance of the battery, such as additives that improve battery overcharge performance, and improve battery Additives for high temperature performance, additives for improving low temperature performance of batteries, etc.
  • the additives include cyclic carbonates containing unsaturated bonds, for example, cyclic carbonates containing double bonds. Including unsaturated bond-containing cyclic carbonates in the electrolyte can improve the capacity retention rate of lithium ion secondary batteries using lithium iron phosphate as the positive electrode active material in high-temperature environments, and improve the capacity retention of lithium ion secondary batteries. High temperature performance.
  • the mass percentage of the unsaturated bond-containing cyclic carbonate in the electrolyte is preferably 0.1% to 4%, more preferably 0.5% to 4%, and even more preferably 0.5% to 3%.
  • the content of the unsaturated bond-containing cyclic carbonate in the electrolyte is within the above range, and a solid electrolyte interface with good density and stability (Solid Electrolyte Interphase (SEI) film, and the SEI film has good ion conductivity, which can improve the high-temperature cycle performance of the battery, prevent the risk of lithium deposition from the negative electrode during the cycle, and improve the safety performance of the battery.
  • SEI Solid Electrolyte Interphase
  • the upper limit of the mass percentage of the unsaturated bond-containing cyclic carbonate in the electrolyte may be 4%, 3.8%, 3.5%, 3.2%, 3%, 2.8%, 2.5%, 2.2%, 2.0%
  • the lower limit can be 0.1%, 0.5%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.7%, 1.8%.
  • the range of the mass percentage of the unsaturated bond-containing cyclic carbonate in the electrolyte can be formed by a combination of any of the foregoing upper limit and any lower limit, or can be formed by any of the foregoing upper limit and any other upper limit. The combination may also be formed by combining any of the aforementioned lower limit values and any other lower limit values.
  • the above-mentioned unsaturated bond-containing cyclic carbonate may be selected from one or two of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).
  • the additive includes a cyclic sulfonate, preferably a cyclic disulfonate represented by Formula I.
  • a and B are each independently selected from alkylene groups having 1 to 3 carbon atoms.
  • Including the cyclic disulfonate in the electrolyte can reduce the SEI film formation resistance. Therefore, the low-temperature performance, normal temperature performance and high-temperature cycle performance of the lithium ion secondary battery using the lithium iron phosphate positive electrode active material can be improved, and the battery life can be effectively extended.
  • the mass percentage of the cyclic disulfonate in the electrolyte is preferably 0.1% to 2%, more preferably 0.2% to 2%, and even more preferably 0.2% to 1%.
  • the content of the cyclic disulfonate in the electrolyte is within the above range, which can effectively reduce the film formation resistance of the SEI film, thereby effectively improving the use of lithium iron phosphate as the positive electrode active material Low temperature performance, room temperature performance and high temperature cycle performance of the lithium ion secondary battery.
  • the upper limit of the mass percentage of the cyclic disulfonate in the electrolyte may be 2%, 1.8%, 1.6%, 1.5%, 1.3%, 1.2%, 1.1%, 1.0%, 0.95%, 0.9%, and the lower limit can be 0.1%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.8%, 0.85%.
  • the range of the mass percentage of the cyclic disulfonate in the electrolyte can be formed by a combination of any of the foregoing upper limit and any lower limit, or can be formed by a combination of any of the foregoing upper limit and any other upper limit, It may also be formed by combining any of the aforementioned lower limit values and any other lower limit values.
  • cyclic disulfonate may be selected from one of methylene disulfonate (MMDS), ethylene disulfonate (EEDS) and propylene methane disulfonate (MPDS) Or multiple.
  • MMDS methylene disulfonate
  • EEDS ethylene disulfonate
  • MPDS propylene methane disulfonate
  • isolation membranes any well-known porous structure isolation membrane with good chemical and mechanical stability can be selected, such as glass fiber, non-woven fabric, polyethylene, polypropylene and poly One or more of vinylidene fluoride.
  • the isolation film can be a single-layer film or a multilayer composite film. When the isolation film is a multilayer composite film, the materials of each layer may be the same or different.
  • the isolation film may also be a composite isolation film, for example, a composite isolation film provided with an inorganic coating on the surface of the organic isolation film.
  • the porosity of the isolation membrane is 30% to 50%, which can further improve the dynamic performance of the lithium ion secondary battery, which is beneficial to improve the low temperature performance of the lithium ion secondary battery.
  • the battery cell is placed in the packaging shell, the electrolyte is injected and sealed to obtain a lithium ion secondary battery.
  • the positive active material lithium iron phosphate (LFP), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a mass ratio of 98:1:1, and the solvent N-methylpyrrolidone (NMP) is added. Stir it under the action of a mixer until it is stable and uniform to obtain a positive electrode slurry.
  • the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, a conventional positive electrode piece is obtained.
  • the compaction density of the positive electrode piece is 2.4g/cm 3 .
  • the positive electrode current collector is a composite current collector, which is prepared by a vacuum evaporation method, including: selecting a predetermined thickness of an organic support layer and performing surface cleaning treatment.
  • the organic support layer is placed in the vacuum coating chamber, and the high-purity aluminum wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1300°C to 2000°C.
  • the evaporated metal passes through the cooling system in the vacuum coating chamber and is finally deposited on the two organic support layers. On the surface, a conductive layer is formed.
  • the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and after drying and cold pressing, a conventional negative electrode piece is obtained, and the compaction density of the negative electrode piece is 1.7 g/cm 3 .
  • the negative electrode current collector is a composite current collector, which is prepared by vacuum evaporation, including: selecting an organic support layer of a predetermined thickness and performing surface cleaning treatment, and the The organic support layer is placed in the vacuum coating chamber, and the high-purity copper wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1300°C ⁇ 2000°C. The evaporated metal passes through the cooling system in the vacuum coating chamber and is finally deposited on the two organic support layers. On the surface, a conductive layer is formed.
  • the organic solvent is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl propionate (MP).
  • the electrolyte lithium salt is LiPF 6 .
  • the mass percentage of LiPF 6 in the electrolyte is 12.5% by weight.
  • the positive pole piece, the negative pole piece and the separator are wound to obtain the battery cell.
  • the electrolyte is injected and sealed, and the lithium ion is obtained by standing, compacting, forming, and exhausting. Secondary battery.
  • the ratio of the discharge capacity CD to the charge capacity CC is the discharge capacity retention rate of the lithium ion secondary battery at -10°C.
  • Lithium ion secondary battery discharge capacity retention rate at -10°C (%) CD/CC ⁇ 100%
  • the discharge capacity this time is the discharge capacity of the lithium-ion secondary battery for the first cycle at 60°C.
  • the capacity retention rate (%) of the lithium ion secondary battery after 500 cycles at 60°C the discharge capacity at the 500th cycle/the discharge capacity at the first cycle ⁇ 100%.
  • the positive electrode current collector is a composite current collector, its role in improving the weight energy density of the electrochemical device
  • the weight percentage of the positive electrode current collector refers to the percentage of the weight of the positive electrode current collector per unit area divided by the weight of the conventional positive electrode current collector per unit area.
  • the weight of the positive current collector using the composite current collector is reduced to varying degrees, thereby increasing the weight and energy density of the battery.
  • the negative electrode current collector is a composite current collector, its role in improving the weight energy density of the electrochemical device
  • the weight percentage of the negative electrode current collector is the weight of the negative electrode current collector per unit area divided by the weight of the conventional negative electrode current collector per unit area.
  • the weight of the negative electrode current collector using the composite current collector is reduced to varying degrees, thereby increasing the weight and energy density of the battery.
  • the thickness of the negative electrode active material layer is 52 ⁇ m, and the thickness of the positive electrode active material layer is 74 ⁇ m.
  • the thickness of the negative electrode active material layer is 52 ⁇ m, and the thickness of the positive electrode active material layer is 74 ⁇ m.
  • the thermal conductivity of the composite current collector is 0.01W/(m ⁇ K) ⁇ 10W/(m ⁇ K), which can improve the low-temperature performance of lithium iron phosphate batteries.
  • the positive electrode current collectors are all conventional positive current collectors, the positive active material of the positive active material layer is all LFP, and the thickness of the positive active material layer is 74 ⁇ m; the negative active material of the negative active material layer is graphite, The thickness of the negative active material layer is 52 ⁇ m; the content of the electrolyte additive refers to the mass percentage of the additive in the electrolyte.
  • the positive electrode active material of the positive electrode active material layer is all LFP, and the negative electrode active material of the negative electrode active material layer is all graphite.
  • the present application has a better effect on improving the low-temperature performance of the lithium ion secondary battery; further, the thickness T 1 of the positive active material layer is 60 ⁇ m When it is ⁇ 90 ⁇ m, the low temperature performance of the lithium ion secondary battery is further improved.
  • the thickness T 2 of the negative electrode active material layer is 30 ⁇ m to 70 ⁇ m, the present application has a better effect on improving the low-temperature performance of the lithium ion secondary battery; further, when the thickness T 2 of the negative electrode active material layer is 40 ⁇ m to 60 ⁇ m, it can be further improved Low temperature performance of lithium ion secondary batteries.
  • a protective layer is provided on the basis of the positive electrode current collector 33.
  • the thickness of the negative electrode active material layer is 52 ⁇ m, and the thickness of the positive electrode active material layer is 74 ⁇ m.
  • the protective layer when the positive electrode current collector is a composite current collector, the protective layer can further improve the capacity retention rate of the battery after 500 cycles at 60°C and 1C/1C, and the battery reliability is better.
  • a protective layer is provided on the basis of the negative electrode current collector 35.
  • the nickel-based alloy in Table 6-3 contains: nickel, 90wt%; chromium, 10wt%.
  • the double-layer protective layer includes a nickel protective layer arranged on the surface of the conductive layer facing away from the organic support layer, with a thickness of 30nm; and a nickel oxide protective layer arranged on the surface of the nickel protective layer facing away from the organic support layer, with a thickness of It is 30nm.
  • the thickness of the negative active material layer is 52 ⁇ m, and the thickness of the positive active material layer is 74 ⁇ m.
  • the protective layer can further improve the capacity retention rate of the battery after 500 cycles at 60°C and 1C/1C, and the battery reliability is better.

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Abstract

本申请公开了一种锂离子二次电池，锂离子二次电池包括正极极片、负极极片、隔离膜和电解液，正极极片包括正极集流体以及设置于正极集流体表面且包含正极活性物质的正极活性物质层，负极极片包括负极集流体以及设置于负极集流体表面且包含负极活性物质的负极活性物质层；其中，正极活性物质包括磷酸铁锂，负极活性物质包括石墨；正极集流体和/或负极集流体为复合集流体，复合集流体包括有机支撑层及设置于有机支撑层的至少一个表面上的导电层。本申请提供的锂离子二次电池具有良好的低温性能。

Description

锂离子二次电池
相关申请的交叉引用
本申请要求享有于2019年05月31日提交的名称为“锂离子二次电池”的中国专利申请201910473216.2的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电化学装置技术领域，尤其涉及一种锂离子二次电池。
背景技术
锂离子二次电池，具备较高的充放电性能，且无记忆效应、环境友好，被广泛地应用于电动汽车以及消费类电子产品中。磷酸铁锂由于循环寿命高、安全性好、耐高温等特性，是目前动力电池最常用的正极活性材料之一。然而，采用磷酸铁锂的锂离子二次电池通常面临低温性能较差的问题，不能满足电池在低温环境中的应用需求。
发明内容
本申请实施例提供一种锂离子二次电池，旨在提高采用磷酸铁锂的锂离子二次电池的低温性能。
本申请实施例提供一种锂离子二次电池，锂离子二次电池包括正极极片、负极极片、隔离膜和电解液，正极极片包括正极集流体以及设置于正极集流体表面且包含正极活性物质的正极活性物质层，负极极片包括负极集流体以及设置于负极集流体表面且包含负极活性物质的负极活性物质层；其中，正极活性物质包括磷酸铁锂，负极活性物质包括石墨；正极集流体和/或负极集流体为复合集流体，复合集流体包括有机支撑层及设置于所述有机支撑层的至少一个表面上的导电层。
本申请实施例提供的锂离子二次电池，其正极活性物质包括磷酸铁锂，负极活性物质包括石墨，并且正极集流体和/或负极集流体为复合集流体，复合集流体包括有机支撑层及设置于有机支撑层的至少一个表面上的 导电层，由于复合集流体的有机支撑层采用有机材料，因此较传统的金属集流体而言，本申请的复合集流体的导热系数较小，隔热保温性能较好，因此电池在低温环境中工作时，受环境温度影响较小，且电池自身产生的热量不会快速散出，这有利于使低温环境下的锂离子二次电池也能够保持电芯内部适宜的工作温度，从而改善了磷酸铁锂电池在低温下动力学性能较差的缺点，使得磷酸铁锂电池具有良好的低温电化学性能和安全性能。此外，该复合集流体还较传统金属集流体的重量小，因此还可以同时提高电池的重量能量密度。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为根据本申请一个实施例的复合集流体的结构示意图。
图2为根据本申请另一个实施例的复合集流体的结构示意图。
图3为根据本申请另一个实施例的复合集流体的结构示意图。
图4为根据本申请另一个实施例的复合集流体的结构示意图。
图5为根据本申请另一个实施例的复合集流体的结构示意图。
标号说明：
10、复合集流体；
101、有机支撑层；
101a、第一表面；101b、第二表面；
1011、第一子层；1012、第二子层；1013、第三子层；
102、导电层；
103、保护层。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组 合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或多种”中“多种”的含义是两个以上。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
本申请实施例提供一种锂离子二次电池，其包括电芯和电解液，电芯和电解液可以是封装于包装外壳中。
电芯包括正极极片、隔离膜及负极极片。电芯可通过将正极极片、负极极片以及隔离膜一同堆叠或者卷绕而形成，其中，隔离膜是介于正极极片和负极极片之间的绝缘体，能够起到隔离的作用。
正极极片包括正极集流体以及设置于正极集流体上的正极活性物质层，正极活性物质层包括正极活性物质。负极极片包括负极集流体以及设置于负极集流体上的负极活性物质层，负极活性物质层包括负极活性物质。通过锂离子在正极活性物质和负极活性物质之间的往返嵌入和脱出，实现锂离子二次电池的充电和放电。
正极活性物质包括磷酸铁锂，负极活性物质包括石墨，并且，正极集流体和/或负极集流体为复合集流体10。
图1为根据本申请实施例的一种复合集流体10的结构示意图，请参照图1，复合集流体10包括层叠设置的有机支撑层101及导电层102。
其中，在有机支撑层101的厚度方向上具有相对的第一表面101a和第二表面101b，导电层102设置于有机支撑层101的第一表面101a和第二表面101b。
可以理解的是，导电层102还可以是设置于有机支撑层101的第一表面101a及第二表面101b中的任意一者上，例如，导电层102设置于有机支撑层101的第一表面101a，当然，导电层102也可以是设置于有机支撑层101的第二表面101b。
本申请实施例的锂离子二次电池，正极活性物质包括磷酸铁锂，负极活性物质包括石墨，并且正极集流体和/或负极集流体为复合集流体10，复合集流体10包括有机支撑层101及设置于有机支撑层101的至少一个表面上的导电层102，由于复合集流体10的有机支撑层101采用有机材料，因此较传统的金属集流体而言，复合集流体10的导热系数较小，复合集流体10的隔热/保温性能较好，因此电池在低温环境中工作时，受环境温度影响较小，且电池自身产生的热量不会快速散出，这有利于使低温环境下的锂离子二次电池也能够保持电芯内部适宜的工作温度，从而改善了磷酸铁锂电池在低温下动力学性能较差的缺点，使得磷酸铁锂电池具有良好的低温电化学性能和安全性能。
另外，复合集流体10中的有机支撑层101还可以对导电层102形成有效支撑，并保证复合集流体10的整体强度，因此，相较于传统金属集流体，如铝箔、铜箔等，导电层102的厚度能够明显减小，且不易断裂。
较传统的金属集流体而言，由于导电层102的厚度明显减小，且有机支撑层101的密度较金属的密度要小，这样，在保证导电层102具有良好的导电和集流性能的情况下，有利于降低电芯及锂离子二次电池的重量，从而使锂离子二次电池的能量密度得到提高。
另外，由于磷酸铁锂及石墨均具有循环寿命高、安全性好、耐高温等特性，因此能够使得电芯及采用该电芯的锂离子二次电池具有较高的循环性能、安全性能以及良好的低温性能和高温性能。
本申请实施例的复合集流体10中，导电层102的厚度D 1优选为30nm≤D 1≤3μm。导电层102的厚度D 1在上述范围内，使得导电层102具有较高的导电和集流的性能，有利于使锂离子二次电池具有低阻抗，减小电池极化，从而提高锂离子二次电池的电化学性能，其中锂离子二次电池具有较高的倍率性能及循环性能。导电层102的厚度D 1在上述范围内，还使得导电层102在加工及使用过程中不易发生断裂，使复合集流体10具有较高的机械稳定性和工作稳定性，有利于提高电芯及锂离子二次电池的使用寿命。
导电层102的厚度D 1为3μm以下，在锂离子二次电池发生穿钉等异常情况下，导电层102产生的毛刺较小，从而可降低产生的金属毛刺与对电极接触的风险，进而改善锂离子二次电池的安全性能。
另外，将厚度较小的导电层102设置于有机支撑层101的表面，能够 显著降低复合集流体10的重量，从而有利于降低锂离子二次电池的重量，使锂离子二次电池的能量密度得到显著提高。
在一些可选的实施例中，导电层102的厚度D 1的上限可以选自3μm、2.5μm、2μm、1.8μm、1.5μm、1.2μm、1μm、900nm、750nm、450nm、250nm、100nm，下限可以选自1.6μm、1μm、800nm、600nm、400nm、300nm、150nm、100nm、80nm、30nm，导电层102的厚度D 1的范围可以是由前述任意上限值和任意下限值组合形成，也可以是由前述任意上限值与任意其他上限值组合形成，还可以是由前述任意下限值与任意其他下限值组合形成。
进一步优选地，导电层102的厚度D 1为300nm≤D 1≤2μm。更优选地，导电层102的厚度D 1为500nm≤D 1≤1.5μm。更优选地，导电层102的厚度D 1为800nm≤D 1≤1.2μm。
上述“导电层102的厚度D 1”指的是有机支撑层101单侧导电层102的厚度。
本申请实施例的复合集流体10中，导电层102可以包括金属材料、碳基导电材料及导电高分子材料中的一种或多种。
作为上述金属材料，例如可以包括铝、铝合金、铜、铜合金、镍、镍合金、铁、铁合金、钛、钛合金、银及银合金中的一种或多种，再例如包括铝、铜、镍、铁、钛、银、镍铜合金及铝锆合金中的一种或多种。
作为上述碳基导电材料，例如可以包括石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种。
作为上述导电高分子材料，例如可以包括聚氮化硫类、脂肪族共轭聚合物、芳环共轭聚合物及芳杂环共轭聚合物中的一种或多种。作为示例，导电高分子材料可以包括聚乙炔、聚苯、聚吡咯、聚乙炔、聚苯胺、聚噻吩及聚吡啶中的一种或多种。此外，还可以通过掺杂使导电高分子材料的电子离域性增大，提高电导率。
在一些实施例中，复合集流体10用作正极集流体时，导电层102优选为包括铝或铝合金，其中铝合金中铝元素的重量百分含量优选为80wt％以上，更优选为90wt％以上。复合集流体10用作负极集流体时，导电层102优选为包括铜或铜合金，其中铜合金中铜元素的重量百分含量优选为80wt％以上，更优选为90wt％以上。
本申请实施例的复合集流体10，导电层102的体积电阻率优选为小于 或等于8.0×10 -8Ω·m。这有利于使导电层102具有较优的导电和集流性能，从而提高锂离子二次电池的倍率性能和循环性能。
进一步地，复合集流体10用作正极集流体时，导电层102的体积电阻率优选为3.2×10 -8Ω·m～7.8×10 -8Ω·m；复合集流体10用作负极集流体时，导电层102的体积电阻率优选为1.65×10 -8Ω·m～3.3×10 -8Ω·m。这有利于使导电层102具有较优的导电和集流性能的同时，还能够使锂离子二次电池进一步地具有低阻抗、并减小负极极化，从而使锂离子二次电池兼具较高的倍率性能及循环性能，尤其是在低温的条件下，更好地改善锂离子二次电池的动力学性能，保证良好的低温倍率性能等低温电化学性能。
本申请实施例的复合集流体10，有机支撑层101的厚度D 2优选为1μm≤D 2≤30μm。有机支撑层101的厚度D 2在上述范围内，能够较好地发挥有机支撑层101对电芯及锂离子二次电池的保温蓄热的功能，提高锂离子二次电池的低温性能；还能够保证有机支撑层101具有较高的机械强度，在加工及使用过程中不易发生断裂，对导电层102起到良好的支撑和保护作用，提高复合集流体10的机械稳定性和工作稳定性。
有机支撑层101的厚度D 2为30μm以下，有利于使锂离子二次电池具有较小的体积及较低的重量，从而提高锂离子二次电池的体积能量密度和重量能量密度。
在一些可选的实施例中，有机支撑层101的厚度D 2的上限值可以选自30μm、25μm、20μm、18μm、15μm、12μm、10μm、8μm，下限值可以选自1μm、1.5μm、2μm、3μm、4μm、5μm、6μm、7μm、9μm、16μm。有机支撑层101的厚度D 2的范围可以是由前述任意上限值和任意下限值组合形成，也可以是由前述任意上限值与任意其他上限值组合形成，还可以是由前述任意下限值与任意其他下限值组合形成。
进一步优选地，有机支撑层101的厚度D 2为1nm≤D 1≤20μm。更优选地，有机支撑层101的厚度D 2为1μm≤D 2≤15μm。更优选地，有机支撑层101的厚度D 2为1μm≤D 2≤10μm。更优选地，有机支撑层101的厚度D 2为1μm≤D 2≤8μm，优选2μm≤D 2≤8μm。
本申请实施例的复合集流体10，有机支撑层101的杨氏模量E优选为E≥2GPa，这使得有机支撑层101具有刚性，既满足有机支撑层101对导电层102较高的支撑作用，确保复合集流体10的整体强度，又能使有机支撑层101在复合集流体10的加工过程中不会发生过大的延展或变形， 更加有效地防止有机支撑层101及导电层102发生断带，同时有机支撑层101和导电层102之间的结合牢固度更高，使导电层102不易发生剥离，提高复合集流体10的机械稳定性和工作稳定性，从而使锂离子二次电池的性能得到提高。
进一步地，有机支撑层101的杨氏模量E优选为2GPa≤E≤20GPa；例如为2GPa、3GPa、4GPa、5GPa、6GPa、7GPa、8GPa、9GPa、10GPa、11GPa、12GPa、13GPa、14GPa、15GPa、16GPa、17GPa、18GPa、19GPa、20GPa。这使得有机支撑层101具有刚性的同时，还兼具适宜的韧性，保证有机支撑层101及采用其的复合集流体10在加工过程中进行卷绕的柔性。
本申请实施例的复合集流体10，有机支撑层101采用高分子材料及高分子基复合材料中的一种或多种。
作为上述高分子材料，例如可以是聚酰胺类、聚酰亚胺类、聚酯类、聚烯烃类、聚炔烃类、硅氧烷聚合物、聚醚类、聚醇类、聚砜类、多糖类聚合物、氨基酸类聚合物、聚氮化硫类、芳环聚合物、芳杂环聚合物、环氧树脂、酚醛树脂、它们的衍生物、它们的交联物及它们的共聚物中的一种或多种。
进一步地，高分子材料例如可以是聚己内酰胺(俗称尼龙6)、聚己二酰己二胺(俗称尼龙66)、聚对苯二甲酰对苯二胺(PPTA)、聚间苯二甲酰间苯二胺(PMIA)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚萘二甲酸乙二醇酯(PEN)、聚碳酸酯(PC)、聚乙烯(PE)、聚丙烯(PP)、聚丙乙烯(PPE)、聚乙烯醇(PVA)、聚苯乙烯(PS)、聚氯乙烯(PVC)、聚偏氟乙烯(PVDF)、聚四氟乙烯(PTEE)、聚苯乙烯磺酸钠(PSS)、聚乙炔(Polyacetylene，简称PA)、硅橡胶(Silicone rubber)、聚甲醛(POM)、聚苯醚(PPO)、聚苯硫醚(PPS)、聚乙二醇(PEG)、纤维素、淀粉、蛋白质、聚苯、聚吡咯(PPy)、聚苯胺(PAN)、聚噻吩(PT)、聚吡啶(PPY)、丙烯腈-丁二烯-苯乙烯共聚物(ABS)、它们的衍生物、它们的交联物及它们的共聚物中的一种或多种。
作为上述高分子基复合材料，例如可以是包括上述的高分子材料和添加剂，添加剂可以是金属材料及无机非金属材料中的一种或多种。
上述金属材料添加剂例如是铝、铝合金、铜、铜合金、镍、镍合金、 钛、钛合金、铁、铁合金、银及银合金中的一种或多种。
上述无机非金属材料添加剂例如是碳基材料、氧化铝、二氧化硅、氮化硅、碳化硅、氮化硼、硅酸盐及氧化钛中的一种或多种，再例如是玻璃材料、陶瓷材料及陶瓷复合材料中的一种或多种。其中碳基材料添加剂例如是石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种。
作为上述添加剂，还可以是金属材料包覆的碳基材料，例如镍包覆的石墨粉及镍包覆的碳纤维中的一种或多种。
优选地，有机支撑层101采用绝缘高分子材料及绝缘高分子基复合材料中的一种或多种。该种有机支撑层101的体积电阻率较高，有利于提高锂离子二次电池的安全性能。
进一步地，有机支撑层101包括聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚萘二甲酸乙二醇酯(PEN)、聚苯乙烯磺酸钠(PSS)及聚酰亚胺(PI)中的一种或多种。
本申请实施例的复合集流体10，有机支撑层101可以是单层结构，也可以是两层以上的复合层结构，如两层、三层、四层等。
图2为根据本申请实施例的另一种复合集流体10的结构示意图，请参照图2，有机支撑层101是由第一子层1011、第二子层1012及第三子层1013层叠设置形成的复合层结构。复合层结构的有机支撑层101具有相对的第一表面101a和第二表面101b，导电层102层叠设置在有机支撑层101的第一表面101a和第二表面101b。当然，导电层102可以是仅设置于有机支撑层101的第一表面101a，也可以是仅设置于有机支撑层101的第二表面101b。
当有机支撑层101为两层以上的复合层结构时，各子层的材料可以相同，也可以不同。
复合集流体10的导热系数优选为0.01W/(m·K)～10W/(m·K)。复合集流体10的导热系数高于10W/(m·K)，则不足以起到改善整个电池的低温电化学性能和低温析锂的作用；复合集流体10的导热系数低于0.01W/(m·K)，则通常有机支撑层101的厚度较大，则会影响电池的体积能量密度和重量能量密度。
更优选地，复合集流体10的导热系数为0.1W/(m·K)～2W/(m·K)。
复合集流体10的导热系数会受到以下因素的影响：导电层102的厚 度D 1、导电层102的材料、有机支撑层101的厚度D 2、有机支撑层101的材料、导电层102的制备工艺条件(例如采用沉积工艺制备导电层102时的沉积速率、沉积温度、冷却速率等)、导电层102与有机支撑层101之间的结合力等。通过调控前述因素中的一个或多个，可以改善复合集流体10的导热系数。
本申请实施例的复合集流体10进一步可选地包括保护层103。请参照图3至图5，导电层102在自身厚度方向上包括相对的两个表面，保护层103层叠设置于导电层102的两个表面中的任意一者或两者上，以保护导电层102，防止导电层102发生化学腐蚀或机械破坏等损害，保证复合集流体10的工作稳定性及使用寿命，从而有利于锂离子二次电池具有较高的安全性能及电化学性能。此外，保护层103还能够增强复合集流体10的强度。
可以理解的是，尽管图3至图5中是示出了在有机支撑层101的单面具有导电层102，在导电层102自身厚度方向上相对的两个表面中的一者或两者上具有保护层103，但在其他的实施例中，还可以在有机支撑层101相对的两个表面分别具有导电层102，可以是在任意一个导电层102自身厚度方向上相对的两个表面中的一者或两者上具有保护层103，也可以是在两个导电层102自身厚度方向上相对的两个表面中的一者或两者上具有保护层103。
保护层103包括金属、金属氧化物及导电碳中的一种或多种。其中，金属材料的保护层103即为金属保护层，金属氧化物材料的保护层103即为金属氧化物保护层。
上述金属例如是镍、铬、镍基合金及铜基合金中的一种或多种。前述镍基合金是以纯镍为基体加入一种或几种其他元素所构成的合金，优选为镍铬合金。镍铬合金是金属镍和金属铬形成的合金，可选的，镍铬合金中镍与铬的重量比为1:99～99:1，如9:1。前述铜基合金是以纯铜为基体加入一种或几种其他元素所构成的合金，优选为镍铜合金。可选的，镍铜合金中镍与铜的重量比为1:99～99:1，如9:1。
上述金属氧化物例如是氧化铝、氧化钴、氧化铬及氧化镍中的一种或多种。
上述导电碳例如是石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种，进一步地为炭黑、碳纳米 管、乙炔黑及石墨烯中的一种或多种。
作为一些示例，请参照图3，复合集流体10包括层叠设置的有机支撑层101、导电层102和保护层103。其中，在有机支撑层101的厚度方向上具有相对的第一表面101a和第二表面101b，导电层102层叠设置于有机支撑层101的第一表面101a及第二表面101b中的至少一者上，保护层103层叠设置于导电层102的背向有机支撑层101的表面。
在导电层102的背向有机支撑层101的表面上设置保护层103(简称为上保护层)，对导电层102起到防化学腐蚀、防机械破坏的保护作用，还能够改善复合集流体10与活性物质层之间的界面，提高复合集流体10与活性物质层之间的结合力。
在一些实施例中，复合集流体10的上保护层优选为金属保护层及金属氧化物保护层中的至少一种，金属氧化物保护层及金属保护层的机械强度高、耐腐蚀性能高、且比表面积大，能够更好地防止导电层102发生化学腐蚀或机械破坏等损害，同时能够更加提高导电层102与正极活性物质层之间的界面结合力，提高锂离子二次电池的性能。
进一步地，当复合集流体10用作正极集流体时，复合集流体10的上保护层优选为金属氧化物保护层，例如氧化铝、氧化钴、氧化镍、氧化铬等，金属氧化物保护层的硬度及机械强度高，比表面积更大，抗腐蚀性能更好，可以更好地保护导电层102；此外，还有利于改善电池的穿钉安全性能。
或进一步地，当复合集流体10用作负极集流体时，上保护层优选为金属保护层，金属保护层可以提高复合集流体10的导电性能，能够减小电池极化，降低负极析锂的风险，提高锂离子二次电池的循环性能及安全性能；更优选为双层保护层，即一层金属保护层和一层金属氧化物保护层的复合层，其中优选地，金属保护层设置于导电层102背向有机支撑层101的表面，金属氧化物保护层设置于金属保护层背向有机支撑层101的表面，这样可以同时改善负极集流体的导电性能、抗腐蚀性能、以及导电层102与负极活性物质层之间的界面等，能够得到综合性能更好的负极集流体。
作为另一些示例，请参照图4，复合集流体10包括层叠设置的有机支撑层101、导电层102和保护层103。其中，在有机支撑层101的厚度方向上具有相对的第一表面101a和第二表面101b，导电层102层叠设置于 有机支撑层101的第一表面101a及第二表面101b中的至少一者上，保护层103层叠设置于导电层102的朝向有机支撑层101的表面。
在导电层102的朝向有机支撑层101的表面上设置保护层103(简称为下保护层)，下保护层对导电层102起到防化学腐蚀、防机械损害的保护作用的同时，还能够提高导电层102与有机支撑层101的结合力，防止导电层102与有机支撑层101分离，提高对导电层102的支撑保护作用。
可选地，下保护层为金属氧化物保护层或金属保护层，金属保护层及金属氧化物保护层的耐腐蚀性能较高，且其比表面积大，能够更加提高导电层102与有机支撑层101之间的界面结合力，从而使下保护层更好的起到对导电层102的保护作用，提高锂离子二次电池的性能。其中金属氧化物保护层的硬度更高、机械强度更好，更加有利于提高复合集流体10的强度。当复合集流体10用作正极集流体时，下保护层优选为金属氧化物保护层。当复合集流体10用作负极集流体时，下保护层优选为金属保护层，在对导电层102起到防化学腐蚀、防机械损害的保护作用的同时，还能够提高复合集流体10的导电性能，能够减小电池极化，降低负极析锂的风险，提高锂离子二次电池的循环性能及安全性能。
作为又一些示例，请参照图5，复合集流体10包括层叠设置的有机支撑层101、导电层102和保护层103。其中，在有机支撑层101的厚度方向上具有相对的第一表面101a和第二表面101b，导电层102层叠设置于有机支撑层101的第一表面101a及第二表面101b中的至少一者上，保护层103层叠设置于导电层102的背向有机支撑层101的表面及朝向有机支撑层101的表面上。
在导电层102的两个表面上均设置保护层103，更加充分地保护导电层102，使复合集流体10具有较高的综合性能。
可以理解的是，导电层102的两个表面上的保护层103，其材料可以相同、也可以不同，其厚度可以相同、也可以不同。
优选地，保护层103的厚度D 3为1nm≤D 3≤200nm、且D 3≤0.1D 1。如果保护层103太薄，则不足以起到保护导电层102的作用；太厚，则会降低锂离子二次电池的能量密度。
在一些实施例中，保护层103的厚度D 3的上限值可以为200nm、180nm、150nm、120nm、100nm、80nm、60nm、55nm、50nm、45nm、40nm、30nm、20nm，下限值可以为1nm、2nm、5nm、8nm、10nm、 12nm、15nm、18nm。保护层103的厚度D 3的范围可以是由前述任意上限值和任意下限值组合形成，也可以是由前述任意上限值与任意其他上限值组合形成，还可以是由前述任意下限值与任意其他下限值组合形成。
更优选地，保护层103的厚度D 3为5nm≤D 3≤200nm，更优选地为10nm≤D 3≤200nm。
上述“保护层103的厚度D 3”指的是位于导电层102单侧的保护层103的厚度。也就是说，上保护层的厚度D a为1nm≤D a≤200nm且D a≤0.1D 1；进一步地，5nm≤D a≤200nm；更进一步地，10nm≤D a≤200nm。下保护层的厚度D b为1nm≤D b≤200nm，且D b≤0.1D 1；进一步地，5nm≤D b≤200nm；更进一步地，10nm≤D b≤200nm。
当导电层102的两个表面均设置有保护层103时，即复合集流体10包括上保护层和下保护层时，优选地，D a＞D b，有利于上保护层及下保护层协同对导电层102起到良好的防化学腐蚀、防机械损害的保护作用，同时使锂离子二次电池具有较高的能量密度。更优选地，0.5D a≤D b≤0.8D a，能够更好的发挥上保护层及下保护层的协同保护作用。
可以理解的是，保护层103的设置对复合集流体10的导热系数的影响可以忽略不计。
在一些实施例中，有机支撑层101与导电层102之间的结合力F优选为F≥100N/m，更优选为F≥400N/m。这能够有效防止有机支撑层101与导电层102之间发生剥离，提高整体强度及可靠性，从而有利于提高锂离子二次电池的性能。
本申请实施例的复合集流体10中，导电层102采用金属材料时，可以是通过机械辊轧、粘结、气相沉积法、化学镀、电镀中的至少一种手段形成于有机支撑层101上，其中优选气相沉积法、电镀法。通过气相沉积法或电镀法将导电层102形成于有机支撑层101上，有利于使得导电层102与有机支撑层101之间的结合更加牢固。
上述气相沉积法优选为物理气相沉积法。物理气相沉积法优选蒸发法及溅射法中的至少一种，其中蒸发法优选真空蒸镀法、热蒸发法及电子束蒸发法中的至少一种，溅射法优选磁控溅射法。
作为示例，上述通过机械辊轧形成导电层102的条件如下：将金属箔片置于机械辊中，通过施加20t～40t的压力将其碾压为预定的厚度，之后将其置于经过表面清洁处理的有机支撑层101的表面，然后将两者置于机 械辊中，通过施加30t～50t的压力使两者紧密结合。
上述通过粘结形成导电层102的条件如下：将金属箔片置于机械辊中，通过施加20t～40t的压力将其碾压为预定的厚度；然后在经过表面清洁处理的有机支撑层101的表面涂布聚偏氟乙烯(PVDF)与N-甲基吡咯烷酮(NMP)的混合溶液；最后将上述预定厚度的导电层102粘结于有机支撑层101的表面，并烘干，使两者紧密结合。
上述通过真空蒸镀法形成导电层的条件如下：将经过表面清洁处理的有机支撑层101置于真空镀室内，以1300℃～2000℃的高温将金属蒸发室内的高纯金属丝熔化蒸发，蒸发后的金属经过真空镀室内的冷却系统，最后沉积于有机支撑层101的表面，形成导电层102。
导电层102采用碳基导电材料时，可以是通过机械辊轧、粘结、气相沉积法、原位形成法及涂布法中的至少一种手段形成于有机支撑层101上。
导电层102采用导电高分子材料时，可以是通过机械辊轧、粘结、原位形成法及涂布法中的至少一种手段形成于有机支撑层101上。
当复合集流体10中具有保护层103时，保护层103可以是通过气相沉积法、原位形成法及涂布法中的至少一种手段形成于导电层102上。气相沉积法可以是如前文所述的气相沉积法。原位形成法优选原位钝化法，即在金属表面原位形成金属氧化物钝化层的方法。涂布法优选辊压涂布、挤压涂布、刮刀涂布及凹版涂布中的至少一种。
优选地，保护层103通过气相沉积法及原位形成法中的至少一种手段形成于导电层102上，有利于使导电层102与保护层103之间具有较高的结合力，从而更好地发挥保护层102对复合集流体10的保护作用，并保证复合集流体10的工作性能。
前述任一实施例的复合集流体10，可以用作正极集流体及负极集流体中的任意一个或两个。
在一些实施例中，正极集流体为金属集流体(例如为铝箔或铝合金集流体)或复合集流体10，负极集流体为复合集流体10。由于铜的密度较高，因此将传统的铜箔负极集流体替换为复合集流体10，可以较大程度地改善锂离子二次电池的重量能量密度，且同时改善锂离子二次电池的低温性能。此外，在负极极片处采用复合集流体10，可以在改善锂离子二次电池低温性能的同时，更好地防止负极低温析锂现象，更好地改善锂离子二次电池的动力学性能、倍率性能和安全性能。
当正极集流体和负极集流体均为复合集流体10时，能够更好地改善锂离子二次电池的低温性能。
在本文中，导电层102的厚度D 1及有机支撑层101的厚度D 2可以采用本领域公知的仪器及方法进行测定，例如采用万分尺。
复合集流体10的导热系数可以采用本领域公知的仪器及方法进行测定，例如采用导热系数仪，包括：将复合集流体10裁切为5cm×5cm的样品，采用TC3000型导热系数仪测定该样品的导热系数。
导电层102的体积电阻率ρ为ρ＝R S×d，其中，ρ的单位为Ω·m；R S为导电层102的方块电阻，单位为Ω；d为导电层102以m为单位的厚度。采用四探针法测试导电层102的方块电阻R S，方法包括：使用RTS-9型双电测四探针测试仪，测试环境为：常温23±2℃，0.1MPa，相对湿度≤65％，测试时，将正极集流体10样品进行表面清洁，然后水平置于测试台上，将四探针放下，使探针与样品的导电层102表面良好接触，然后调节自动测试模式标定样品的电流量程，在合适的电流量程下进行方块电阻的测量，并采集相同样品的8至10个数据点作为数据测量准确性和误差分析。最后取平均值记录为导电层102的方块电阻。
有机支撑层101的杨氏模量E可以采用本领域已知的方法测定。作为示例，取有机支撑层101裁剪成15mm×200mm的样品，用万分尺量取样品的厚度h(μm)，在常温常压(25℃、0.1MPa)下使用高铁拉力机进行拉伸测试，设置初始位置使夹具之间样品为50mm长，拉伸速度为5mm/min，记录拉伸至断裂的载荷L(N)，设备位移y(mm)，则应力ε(GPa)＝L/(15×h)，应变η＝y/50，绘制应力应变曲线，取初始线性区曲线，该曲线的斜率即为杨氏模量E。
可以采用本领域已知的方法测试有机支撑层101与导电层102之间的结合力F，例如选用导电层102设置于有机支撑层101一面上的复合集流体10待测样品，宽度d为0.02m，在常温常压(25℃、0.1MPa)下，使用3M双面胶，均匀贴于不锈钢板上，再将待测样品均匀贴于双面胶上，使用高铁拉力机将待测样品的导电层102与有机支撑层101剥离，根据拉力和位移的数据图，读取最大拉力x(N)，根据F＝x/d计算得到导电层102与有机支撑层101之间的结合力F(N/m)。
正极极片
本申请实施例提供一种正极极片，用于锂离子二次电池。正极极片包 括正极集流体以及设置于正极集流体上的正极活性物质层。作为一个示例，正极集流体在自身厚度方向包括相对的两个表面，正极活性物质层层叠设置于正极集流体的两个表面上。当然，正极活性物质层还可以是层叠设置于正极集流体的两个表面中的任意一者上。
若负极集流体为金属集流体，正极集流体为前文所述的复合集流体10。若负极集流体为前文所述的复合集流体10，正极集流体可以为前文所述的复合集流体10，也可以为金属集流体，如铝箔或铝合金。
正极集流体为前文所述的复合集流体10时，不仅具有前文所述的相应有益效果，还能够提高锂离子二次电池的安全性能。
正极活性物质层包括正极活性物质，正极活性物质中包括磷酸铁锂。
正极活性物质层还可选的包括本领域已知的能够进行锂离子可逆嵌入/脱嵌的其他正极活性材料。
其他正极活性材料例如可以为锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂及钛酸锂中的一种或多种。例如，其他正极活性材料为LiMn 2O 4、LiNiO 2、LiCoO 2、LiNi 1-yCo yO 2(0<y<1)、LiNi aCo bAl 1-a-bO 2(0<a<1，0<b<1，0<a+b<1)、LiMn 1-m-nNi mCo nO 2(0<m<1，0<n<1，0<m+n<1)、LiMPO 4(M可以为Mn、Co及Fe中的一种或两种以上)及Li 3V 2(PO 4) 3中的一种或多种。
可选地，正极活性物质中磷酸铁锂的质量百分含量为50wt％以上，进一步地为60wt％以上，再进一步地为80wt％以上。此时，本申请实施例的锂离子二次电池的低温性能可以得到更加明显的改善。
正极活性物质层还可选地包括粘结剂，本申请对粘结剂的种类不做限制。作为示例，粘结剂为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或多种。
正极活性物质层还可选地包括导电剂，本申请对导电剂的种类不做限制。作为示例，导电剂为石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或多种。
正极活性物质层的厚度T 1优选为50μm～100μm。正极活性物质层的 厚度T 1在上述范围内，则对锂离子二次电池低温性能的改善效果更好，同时还能保证正极具有良好动力学性能，改善锂离子二次电池的电化学性能。更优选地，正极活性物质层的厚度T 1为60μm～90μm，可以进一步改善锂离子二次电池的低温性能，得到综合性能较好的正极极片和锂离子二次电池。
上述“正极活性物质层的厚度T 1”指的是正极集流体单侧的正极活性物质层的厚度。
正极极片可以按照本领域常规方法制备，例如涂布法。作为示例，将正极活性物质以及可选的导电剂和粘结剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)，形成均匀的正极浆料，将正极浆料涂覆在正极集流体上，经烘干等工序后，得到正极极片。
负极极片
本申请实施例提供一种负极极片，用于锂离子二次电池。负极极片包括负极集流体以及设置于负极集流体上的负极活性物质层。作为一个示例，负极集流体在自身厚度方向包括相对的两个表面，负极活性物质层层叠设置于负极集流体的两个表面上。当然，负极活性物质层还可以是层叠设置于负极集流体的两个表面中的任意一者上。
若正极集流体为金属集流体，负极集流体为前文所述的复合集流体10。若正极集流体为前文所述的复合集流体10，负极集流体可以为前文所述的复合集流体10，也可以为金属集流体，如铜箔或铜合金。
负极集流体为前文所述的复合集流体10时，也具有前文所述的相应有益效果，在此不再赘述。
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，如天然石墨、人造石墨中的至少一种。
负极活性物质还可选的包括本领域已知的能够进行离子可逆嵌入/脱嵌的其他负极活性材料。
其他负极活性材料例如可以为金属锂、中间相微碳球(简写为MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的钛酸锂及Li-Al合金中的一种或多种。
可选地，负极活性物质中石墨的质量百分含量为50wt％以上，进一步地为60wt％以上，再进一步地为80wt％以上。此时，本申请实施例的锂离 子二次电池的低温性能可以得到更加明显的改善。
负极活性物质层还可选地包括导电剂，本申请对导电剂的种类不做限制。作为示例，导电剂为石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或多种。
负极活性物质层还可选地包括粘结剂，本申请对粘结剂的种类不做限制。作为示例，粘结剂为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或多种。
优选地，负极活性物质层的厚度T 2为30μm～70μm。负极活性物质层的厚度T 2在上述范围内，则对锂离子二次电池低温性能的改善效果更好，同时还能保证负极具有良好动力学性能，改善锂离子二次电池的电化学性能。更优选地，负极活性物质层的厚度T 2为40μm～60μm，可以进一步改善锂离子二次电池的低温性能，得到综合性能较好的正极极片和锂离子二次电池。
上述“负极活性物质层的厚度T 2”指的是负极集流体单侧的负极活性物质层的厚度。
负极极片可以按照本领域常规方法制备，例如涂布法。作为示例，将负极活性物质以及可选的导电剂和粘结剂分散于溶剂中，溶剂可以是去离子水，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干等工序后，得到负极极片。
电解液
本申请实施例提供一种电解液，用于锂离子二次电池。电解液包括有机溶剂以及分散于有机溶剂中的电解质锂盐。
有机溶剂例如可以为碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸戊烯酯、1,2-丁二醇碳酸酯(1,2-BC)、2,3-丁二醇碳酸酯(2,3-BC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸丁烯酯(BC)、氟代碳酸乙烯酯(FEC)、甲酸甲酯(MF)、甲酸乙酯(EM)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、 甲乙砜(EMS)、二乙砜(ESE)中的一种或多种。
在一些优选的实施例中，有机溶剂为包括环状碳酸酯和链状碳酸酯的混合溶剂。这样的有机溶剂有利于制备电导率、粘度等综合性能良好的电解液。优选的，电解液的25℃电导率可为8mS/cm～11mS/cm。若电导率偏小，电解液动力学性能相对降低，磷酸铁锂电池极化相对较大，影响常温循环性能和低温性能；若电导率偏大，电解液热稳定性相对降低，影响磷酸铁锂电池的高温循环性能。
电解质锂盐例如可以为LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的一种或多种。
电解液中还可选地包括添加剂，添加剂例如可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
在一些优选的实施例中，添加剂包括含不饱和键的环状碳酸酯，例如含双键的环状碳酸酯。在电解液中包括含不饱和键的环状碳酸酯可以改善采用磷酸铁锂正极活性材料的锂离子二次电池在高温环境下存储及循环充放电的容量保持率，提高锂离子二次电池的高温性能。
进一步地，电解液中含不饱和键的环状碳酸酯的质量百分含量优选为0.1％～4％，更优选为0.5％～4％，更优选为0.5％～3％。
在根据本申请实施例的锂离子二次电池中，电解液中含不饱和键的环状碳酸酯的含量在上述范围内，能够在负极形成具有良好致密性及稳定性的固体电解质界面(Solid Electrolyte Interphase，SEI)膜，且该SEI膜具有良好的导离子性，从而能够提高电池的高温循环性能，并防止电池在循环过程中发生负极析锂的风险，提高电池的安全性能。
在一些实施例中，电解液中含不饱和键的环状碳酸酯的质量百分含量的上限值可以为4％、3.8％、3.5％、3.2％、3％、2.8％、2.5％、2.2％、2.0％，下限值可以为0.1％、0.5％、0.7％、0.8％、0.9％、1.0％、1.2％、1.4％、1.5％、1.7％、1.8％。电解液中含不饱和键的环状碳酸酯的质量百分 含量的范围可以是由前述任意上限值和任意下限值组合形成，也可以是由前述任意上限值与任意其他上限值组合形成，还可以是由前述任意下限值与任意其他下限值组合形成。
进一步地，上述含不饱和键的环状碳酸酯可以选自碳酸亚乙烯酯(VC)及碳酸乙烯亚乙酯(VEC)中的一种或两种。
在一些优选的实施例中，添加剂包括环状磺酸酯，优选为式I所示的环状二磺酸酯。
Figure PCTCN2019090407-appb-000001
上述式I中，A及B各自独立地选自碳原子数为1～3的亚烷基。
在电解液中包括环状二磺酸酯可以降低SEI膜成膜阻抗。从而可以使采用磷酸铁锂正极活性材料的锂离子二次电池的低温性能、常温性能及高温循环性能均得到改善，有效延长电池寿命。
进一步地，电解液中环状二磺酸酯的质量百分含量优选为0.1％～2％，更优选为0.2％～2％，更优选为0.2％～1％。
在根据本申请实施例的锂离子二次电池中，电解液中环状二磺酸酯的含量在上述范围内，能够有效降低SEI膜的成膜阻抗，从而有效提高采用磷酸铁锂正极活性材料的锂离子二次电池的低温性能、常温性能及高温循环性能。
在一些实施例中，电解液中环状二磺酸酯的质量百分含量的上限值可以为2％、1.8％、1.6％、1.5％、1.3％、1.2％、1.1％、1.0％、0.95％、0.9％，下限值可以为0.1％、0.2％、0.25％、0.3％、0.4％、0.5％、0.6％、0.7％、0.75％、0.8％、0.85％。电解液中环状二磺酸酯的质量百分含量的范围可以是由前述任意上限值和任意下限值组合形成，也可以是由前述任意上限值与任意其他上限值组合形成，还可以是由前述任意下限值与任意其他下限值组合形成。
进一步地，上述环状二磺酸酯可以选自甲烷二磺酸亚甲酯(MMDS)、乙烷二磺酸亚乙酯(EEDS)及甲烷二磺酸亚丙酯(MPDS)中的一种或多种。
隔离膜
本申请实施例对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜，例如玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种或多种。隔离膜可以是单层薄膜，也可以是多层复合薄膜。隔离膜为多层复合薄膜时，各层的材料可以相同，也可以不同。隔离膜也可以是复合隔离膜，例如是有机隔离膜的表面设置有无机涂层的复合隔离膜。
优选地，隔离膜的孔隙率为30％～50％，可以进一步改善锂离子二次电池的动力学性能，有利于改善锂离子二次电池的低温性能。
锂离子二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠好，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯，也可以是经卷绕后得到电芯；将电芯置于包装外壳中，注入电解液并封口，得到锂离子二次电池。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
制备方法
常规正极极片的制备
将正极活性材料磷酸铁锂(LFP)、粘结剂聚偏二氟乙烯(PVDF)、导电剂乙炔黑按照质量比98:1:1混合，加入溶剂N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌至稳定均一，获得正极浆料，将正极浆料均匀涂覆于正极集流体铝箔上，经干燥、冷压、分切后，得到常规正极极片，正极极片压实密度为2.4g/cm 3。
正极极片的制备
与常规正极极片的制备不同的是，正极集流体为复合集流体，复合集流体采用真空蒸镀法制备，包括：选取预定厚度的有机支撑层并进行表面清洁处理，将经过表面清洁处理的有机支撑层置于真空镀室内，以1300℃～2000℃的高温将金属蒸发室内的高纯铝丝熔化蒸发，蒸发后的金属经过真空镀室内的冷却系统，最后沉积于有机支撑层的两个表面，形成导电 层。
常规负极极片的制备
将负极活性材料石墨、导电剂乙炔黑、增稠剂CMC、粘结剂SBR按照质量比97:1:1:1混合，加入溶剂去离子水，在真空搅拌机作用下搅拌至稳定均一，获得负极浆料，将负极浆料均匀涂覆于负极集流体铜箔上，经干燥、冷压后，得到常规负极极片，负极极片压实密度为1.7g/cm 3。
负极极片的制备
与常规负极极片的制备不同的是，负极集流体为复合集流体，复合集流体采用真空蒸镀法制备，包括：选取预定厚度的有机支撑层并进行表面清洁处理，将经过表面清洁处理的有机支撑层置于真空镀室内，以1300℃～2000℃的高温将金属蒸发室内的高纯铜丝熔化蒸发，蒸发后的金属经过真空镀室内的冷却系统，最后沉积于有机支撑层的两个表面，形成导电层。
电解液的制备
有机溶剂为碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、丙酸甲酯(MP)的混合溶剂。电解质锂盐为LiPF 6。电解液中LiPF 6的质量百分含量为12.5wt％。
锂离子二次电池的制备
将正极极片、负极极片以及隔离膜进行卷绕得到电芯，将电芯放入包装外壳后，注入电解液并封口，经静置、压实、化成、排气等工序，得到锂离子二次电池。
测试部分
(1)锂离子二次电池的低温性能测试
25℃下，将锂离子二次电池先以1C放电至2.0V；再在以1C恒流充电至3.6V，然后恒压充电至电流为0.05C，记充电容量为CC；然后将电池周围环境温度调节至-10℃，用1C恒流放电至2.0V，记放电容量为CD。放电容量CD与充电容量CC之比即为锂离子二次电池在-10℃下的放电容量保持率。
锂离子二次电池在-10℃下的放电容量保持率(％)＝CD/CC×100％
(2)锂离子二次电池的高温循环性能测试
25℃下，将锂离子二次电池先以1C放电至2.0V，之后锂离子二次电池周围环境温度升温至60℃，以1C恒流充电至3.6V，然后恒压充电至电 流为0.05C，然后以1C恒流放电至2.0V，此为一个充放电循环，此次的放电容量为锂离子二次电池60℃下首次循环的放电容量。按照上述方法进行500次循环测试，记录锂离子二次电池60℃下第500次循环的放电容量。
锂离子二次电池60℃循环500次后的容量保持率(％)＝第500次循环的放电容量/首次循环的放电容量×100％。
测试结果
1、复合集流体在改善电化学装置的重量能量密度方面的作用
1)正极集流体为复合集流体时，在改善电化学装置的重量能量密度方面的作用
表1-1
Figure PCTCN2019090407-appb-000002
表1中，正极集流体重量百分数是指单位面积正极集流体重量除以单位面积常规正极集流体重量的百分数。
相较于传统的铝箔正极集流体，采用复合集流体的正极集流体的重量都得到不同程度的减轻，从而可提升电池的重量能量密度。
2)负极集流体为复合集流体时，在改善电化学装置的重量能量密度方面的作用
表1-2
Figure PCTCN2019090407-appb-000003
Figure PCTCN2019090407-appb-000004
表2中，负极集流体重量百分数是单位面积负极集流体重量除以单位面积常规负极集流体重量的百分数。
相较于传统的铜箔负极集流体，采用复合集流体的负极集流体的重量都得到不同程度的减轻，从而可提升电池的重量能量密度。
2、复合集流体对于电化学装置的电化学性能的影响
表2
Figure PCTCN2019090407-appb-000005
表2的电池中，负极活性物质层的厚度均为52μm，正极活性物质层的厚度均为74μm。
表3的数据表明采用复合集流体可以改善磷酸铁锂锂离子二次电池的低温电化学性能。
3、复合集流体的导热系数及对电化学装置低温电化学性能的影响
表3-1
Figure PCTCN2019090407-appb-000006
表3-2
Figure PCTCN2019090407-appb-000007
表3-2的电池中，负极活性物质层的厚度均为52μm，正极活性物质层的厚度均为74μm。
由表3-2的数据可知，复合集流体的导热系数为0.01W/(m·K)～10W/(m·K)，可以改善磷酸铁锂电池的低温性能。
4、电解液添加剂等对于电化学装置的电化学性能的影响
表4
Figure PCTCN2019090407-appb-000008
表4的电池中，正极集流体均为常规正极集流体，正极活性物质层的正极活性物质均为LFP，正极活性物质层的厚度均为74μm；负极活性物质层的负极活性物质均为石墨，负极活性物质层的厚度均为52μm；电解液添加剂的含量指的是在添加剂在电解液中的质量百分含量。
由表4的数据可知，通过在电解液中添加含不饱和键的环状碳酸酯和/或环状二磺酸酯，锂离子二次电池的低温性能及高温循环性能均得到进一步的提升。
5、电极极片的活性物质层的厚度对于电化学装置的低温性能的影响
表5
Figure PCTCN2019090407-appb-000009
Figure PCTCN2019090407-appb-000010
表5的电池中，正极活性物质层的正极活性物质均为LFP，负极活性物质层的负极活性物质均为石墨。
由表5的数据可知，正极活性物质层的厚度T 1为50μm～100μm时，本申请对锂离子二次电池低温性能的改善效果更好；进一步地，正极活性物质层的厚度T 1为60μm～90μm时，进一步改善锂离子二次电池的低温性能。负极活性物质层的厚度T 2为30μm～70μm时，本申请对锂离子二次电池低温性能的改善效果更好；进一步地，负极活性物质层的厚度T 2为40μm～60μm时，可以进一步改善锂离子二次电池的低温性能。
6、保护层对于电化学装置的低温性能的影响
表6-1
Figure PCTCN2019090407-appb-000011
表6-1中是在正极集流体33的基础上设置保护层。
表6-2
Figure PCTCN2019090407-appb-000012
Figure PCTCN2019090407-appb-000013
表6-2的电池中，负极活性物质层的厚度均为52μm，正极活性物质层的厚度均为74μm。
由表6-2的数据可知，正极集流体为复合集流体时，设置保护层可以使电池在60℃、1C/1C循环500次后的容量保持率进一步获得提升，电池的可靠性更好。
表6-3
Figure PCTCN2019090407-appb-000014
表6-3中是在负极集流体35的基础上设置保护层。
表6-3中镍基合金中含有：镍，90wt％；铬，10wt％。
表6-3中双层保护层包括设置于导电层背向有机支撑层的表面的镍保护层，厚度为30nm；以及设置于镍保护层背向有机支撑层的表面的氧化镍保护层，厚度为30nm。
表6-4
Figure PCTCN2019090407-appb-000015
Figure PCTCN2019090407-appb-000016
表6-4的电池中，负极活性物质层的厚度均为52μm，正极活性物质层的厚度均为74μm。
由表6-4的数据可知，负极集流体为复合集流体时，设置保护层可以使电池在60℃、1C/1C循环500次后的容量保持率进一步获得提升，电池的可靠性更好。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (10)

  1. 一种锂离子二次电池，其中，包括正极极片、负极极片、隔离膜和电解液，所述正极极片包括正极集流体以及设置于所述正极集流体表面且包含正极活性物质的正极活性物质层，所述负极极片包括负极集流体以及设置于所述负极集流体表面且包含负极活性物质的负极活性物质层；
    所述正极活性物质包括磷酸铁锂，所述负极活性物质包括石墨；
    所述正极集流体和/或所述负极集流体为复合集流体，所述复合集流体包括有机支撑层及设置于所述有机支撑层的至少一个表面上的导电层。
  2. 根据权利要求1所述的锂离子二次电池，其中，所述复合集流体的导热系数为0.01W/(m·K)～10W/(m·K)，优选为0.1W/(m·K)～2W/(m·K)。
  3. 根据权利要求1或2所述的锂离子二次电池，其中，所述正极集流体为金属集流体或所述复合集流体，所述负极集流体为所述复合集流体。
  4. 根据权利要求1所述的锂离子二次电池，其中，
    所述导电层的厚度D 1为30nm≤D 1≤3μm，优选为300nm≤D 1≤2μm，优选为500nm≤D 1≤1.5μm，更优选为800nm≤D 1≤1.2μm；所述有机支撑层的厚度D 2为1μm≤D 2≤30μm，优选为1μm≤D 2≤15μm，优选为1μm≤D 2≤10μm，更优选为2μm≤D 2≤8μm；和/或，
    所述正极活性物质层的厚度T 1满足50μm≤T 1≤100μm，优选60μm≤T 1≤90μm，所述负极活性物质层的厚度T 2满足30μm≤T 2≤70μm，优选40μm≤T 2≤60μm；和/或，
    所述电解液的有机溶剂为包括环状碳酸酯和链状碳酸酯的混合溶剂，且所述电解液的25℃电导率为8mS/cm～11mS/cm；和/或，
    所述隔离膜的孔隙率为30％～50％。
  5. 根据权利要求1至4任一项所述的锂离子二次电池，其中，所述电解液中包括含不饱和键的环状碳酸酯，所述电解液中所述含不饱和键的环状碳酸酯的质量百分含量为0.5％～4％；
    优选地，所述含不饱和键的环状碳酸酯包括碳酸亚乙烯酯VC及碳酸乙烯亚乙酯VEC中的一种或两种。
  6. 根据权利要求1至5任一项所述的锂离子二次电池，其中，所述电解液中包括式I所示的环状二磺酸酯，所述电解液中所述环状二磺酸酯的质量百分含量为0.2％～2％；
    Figure PCTCN2019090407-appb-100001
    所述式I中，A及B各自独立地选自碳原子数为1～3的亚烷基；
    优选地，所述环状二磺酸酯包括甲烷二磺酸亚甲酯、乙烷二磺酸亚乙酯及甲烷二磺酸亚丙酯中的一种或多种。
  7. 根据权利要求1所述的锂离子二次电池，其中，
    所述有机支撑层的杨氏模量E为E≥2GPa，优选为2GPa≤E≤20GPa；和/或，
    所述有机支撑层与所述导电层之间的结合力F为F≥100N/m，优选为F≥400N/m；和/或，
    所述有机支撑层包括高分子材料及高分子基复合材料中的一种或多种；所述高分子材料为聚酰胺、聚酰亚胺、聚对苯二甲酸乙二醇酯、聚对苯二甲酸丁二醇酯、聚萘二甲酸乙二醇酯、聚碳酸酯、聚乙烯、聚丙烯、聚丙乙烯、丙烯腈-丁二烯-苯乙烯共聚物、聚乙烯醇、聚苯乙烯、聚氯乙烯、聚偏氟乙烯、聚四氟乙烯、聚苯乙烯磺酸钠、聚乙炔、硅橡胶、聚甲醛、聚苯醚、聚苯硫醚、聚乙二醇、聚氮化硫类、聚苯、聚吡咯、聚苯胺、聚噻吩、聚吡啶、纤维素、淀粉、蛋白质、环氧树脂、酚醛树脂、它们的衍生物、它们的交联物及它们的共聚物中的一种或多种；所述高分子基复合材料包括所述高分子材料和添加剂，所述添加剂包括金属材料及无机非金属材料中的一种或多种。
  8. 根据权利要求1所述的锂离子二次电池，其中，
    所述导电层包括金属材料、碳基导电材料及导电高分子材料中的一种 或多种；和/或，
    所述导电层的体积电阻率小于或等于8.0×10 -8Ω·m。
  9. 根据权利要求1至8任一项所述的锂离子二次电池，其中，所述复合集流体进一步包括保护层，所述保护层设置于所述导电层自身厚度方向上相对的两个表面中的至少一者上；
    所述保护层包括金属、金属氧化物及导电碳中的一种或多种，优选包括镍、铬、镍基合金、铜基合金、氧化铝、氧化钴、氧化铬、氧化镍、石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种；
    优选地，所述保护层的厚度D 3为1nm≤D 3≤200nm，且所述保护层的厚度D 3与所述导电层的厚度D 1之间满足D 3≤0.1D 1。
  10. 根据权利要求9所述的锂离子二次电池，其中，所述复合集流体为负极集流体时，所述复合集流体包括设置于所述导电层背向所述有机支撑层的表面的上保护层，所述上保护层包括：
    金属保护层，设置于所述导电层背向所述有机支撑层的表面；以及
    金属氧化物保护层，设置于所述金属保护层背向所述有机支撑层的表面。
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