Nothing Special   »   [go: up one dir, main page]

WO2023123088A1 - 一种水系正极极片及包含该极片的二次电池及用电装置 - Google Patents

一种水系正极极片及包含该极片的二次电池及用电装置 Download PDF

Info

Publication number
WO2023123088A1
WO2023123088A1 PCT/CN2021/142610 CN2021142610W WO2023123088A1 WO 2023123088 A1 WO2023123088 A1 WO 2023123088A1 CN 2021142610 W CN2021142610 W CN 2021142610W WO 2023123088 A1 WO2023123088 A1 WO 2023123088A1
Authority
WO
WIPO (PCT)
Prior art keywords
positive electrode
active material
electrode active
material layer
positive
Prior art date
Application number
PCT/CN2021/142610
Other languages
English (en)
French (fr)
Inventor
程丛
陈均桄
裴海乐
张盛武
王星会
王宁
Original Assignee
宁德时代新能源科技股份有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
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 PCT/CN2021/142610 priority Critical patent/WO2023123088A1/zh
Priority to CN202180092930.2A priority patent/CN116848665A/zh
Priority to EP21969456.9A priority patent/EP4273963A1/en
Priority to US18/202,487 priority patent/US20230307648A1/en
Publication of WO2023123088A1 publication Critical patent/WO2023123088A1/zh

Links

Images

Classifications

    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of secondary batteries, in particular to a water-based positive electrode sheet with a non-uniform structure and a secondary battery including the positive electrode sheet, a battery pack and an electrical device thereof.
  • Lithium iron phosphate (LFP) cathode material lithium-ion batteries are extremely safe in terms of safety due to the stable structure and high-temperature decomposition characteristics of lithium iron phosphate materials. It has great advantages, and the lithium iron phosphate material does not contain heavy metals, and the cost is also low. It has developed rapidly in recent years.
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyridone
  • a conductive agent is added to form a slurry, and then the slurry is Coating on the surface of the current collector, drying and rolling to prepare the positive electrode sheet.
  • both PVDF and NMP are petroleum-derived chemical products, and their synthesis and post-treatment processes are complex and energy-intensive. Therefore, the cost of making electrodes with the oily system formed by PVDF and NMP organic solvents is relatively high.
  • NMP toxic gas will volatilize into the air, pollute the environment and cause harm to the human body, and a large amount of cost will be invested in recycling NMP.
  • the present application is made in view of the above problems, and its purpose is to provide a water-based positive electrode sheet to solve the technical problems of reducing the sheet resistance and further improving the kinetic performance of the battery.
  • the first aspect of the present application provides a water-based positive electrode sheet, which includes a current collector and a positive active material layer disposed on at least one surface of the current collector, and the positive active material layer includes a water-based binder ,
  • the porosity of the surface area of the positive active material layer is greater than that of the inner area, and the average particle size of the positive active material in the surface area is greater than the average particle size of the positive active material in the inner area.
  • the thickness of the positive electrode active material layer of the water-based positive electrode sheet is set as H.
  • H may be 0.05-5 mm, optionally 0.1-0.5 mm.
  • the surface area of the positive active material layer refers to the area within the range of 0 to H/3 from the surface of the positive active material layer; correspondingly, the inner area of the positive active material layer refers to A region within a range of 0 to H/3 from the current collector in the positive electrode active material layer.
  • the positive electrode active material layer has a non-uniform structure in the vertical direction .
  • the positive electrode sheet with the positive electrode active material layer having a non-uniform structure reduces the resistance and impedance of a secondary battery including the positive electrode sheet, and simultaneously improves rate performance and capacity retention.
  • the porosity in the region H/3 from the surface of the positive electrode active material layer is 10%-30%.
  • the porosity in the positive electrode active material layer is 5%-25% in the region H/3 from the current collector.
  • the ratio of the porosity in the area of H/3 from the surface of the positive active material layer to the porosity in the area of H/3 from the current collector in the positive active material layer is r1, r1 1.05-6.5, optionally 1.2-2.5. In the present application, when the ratio r1 of the porosity in the surface area and the inner area of the positive electrode active material layer is within the above range, the sheet resistance and battery impedance can be further reduced and the rate performance and capacity retention can be improved.
  • the average particle size of the positive active material in the positive active material layer in the region H/3 from the surface is 0.8-2.5 ⁇ m.
  • the average particle diameter of the positive electrode active material in the positive electrode active material layer in the region H/3 from the current collector is 0.5-1.5 ⁇ m.
  • the average particle diameter of the positive active material in the positive electrode active material layer from the surface H/3 area and the positive active material in the positive active material layer from the current collector H/3 area The ratio of the average particle size is r2, and r2 is 1.05-5, optionally 1.2-2.5.
  • the surface area of the positive electrode active material layer and the ratio r2 of the average particle diameter of the positive electrode active material in the inner region are located in the above range, the reduction of the sheet resistance and battery impedance and the rate performance and capacity retention can be realized. improvement.
  • the value of the product r1 ⁇ r2 of the ratio r1 of the porosity to the ratio r2 of the average particle diameter of the positive electrode active material is 1.2 to 50, optionally 1.5 to 10, and further optionally 1.5 to 6.
  • the performance of the secondary battery can be further improved.
  • the ratio r1/r2 between r1 and r2 is 0.3 to 1.5, optionally 0.5 to 1.0.
  • the range of the ratio of r1/r2 further reflects the adjustment of the structure of the positive electrode active material layer of the positive electrode sheet, thereby realizing further adjustment of battery performance.
  • the layer in the region of H/3 from the surface of the positive electrode active material layer contains 1 to 5 parts by weight of an aqueous binder and 1 to 5 parts by weight of a conductive agent, based on the total amount of the layer in this region.
  • the layer contains 2 to 4 parts by weight of the aqueous binder and 2 to 3 parts by weight of the conductive agent, based on the total weight of the layer in the region.
  • the layer within the region of H/3 from the current collector in the positive electrode active material layer contains 2 to 6 parts by weight of an aqueous binder and 1 to 5 parts by weight of a conductive agent, based on the The total weight of the layer; optionally, the layer contains 3 to 5 parts by weight of the aqueous binder and 2 to 3 parts by weight of the conductive agent, based on the total weight of the layer in the region.
  • the conductive agent includes one or more of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes.
  • the positive electrode active material comprises lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, One or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
  • the water-based adhesive comprises soluble polysaccharides and derivatives thereof, water-soluble or water-dispersible polymers, or mixtures thereof.
  • the aqueous binder is methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyethyleneimine and its salts, Polyacrylamide, acrylonitrile-acrylic acid copolymer and its derivatives, or mixtures thereof.
  • the water-based adhesive is a compound mixture of xanthan gum and polyethyleneimine, and the ratio of xanthan gum and polyethyleneimine can be 2:1-1:15, Optionally 1:2-1:14;
  • the average molecular weight Mn of the xanthan gum is 300,000-2,000,000 g/mol, and the average molecular weight Mn of the polyethyleneimine is 2,000-50,000 g/mol.
  • water-based adhesives are more environmentally friendly and safer to use.
  • the combination of specific aqueous binders can further improve the performance of the battery.
  • the sheet resistance of the aqueous positive electrode sheet is 0.3 to 2 ⁇ , optionally 0.3 to 1 ⁇ .
  • the water-based positive electrode sheet of the invention has relatively low sheet resistance, and effectively improves the kinetic performance of a battery using the electrode sheet.
  • the positive active material layer of the aqueous positive electrode sheet is formed by a multi-layer die extrusion coating process.
  • the positive electrode active material layer formed by this process can easily form a layer with an uneven structure without obvious delamination, and the polarization of the film layer is small, which helps to improve the kinetic performance of the battery.
  • the second aspect of the present application provides a secondary battery, which includes the aqueous positive electrode sheet selected from the first aspect of the present application.
  • a third aspect of the present application provides a battery pack including the secondary battery selected from the second aspect of the present application.
  • a fourth aspect of the present application provides an electric device, which includes the secondary battery selected from the second aspect of the present application or the battery pack of the third aspect of the present application.
  • FIG. 1 is a schematic side view of a water-based positive electrode sheet in an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a lithium ion secondary battery in one embodiment of the present application.
  • FIG. 3 is an exploded view of the lithium-ion secondary battery in one embodiment of the present application shown in FIG. 2 .
  • Fig. 4 is a schematic diagram of a battery pack in an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack shown in FIG. 4 in one embodiment of the present application.
  • Fig. 6 is a schematic diagram of a device in which a battery pack is used as a power source in an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or individual value may serve as a lower or upper limit by itself in combination with any other point or individual value or with other lower or upper limits to form an unexpressly recited range.
  • the binder binds the positive electrode material and the conductive agent to the metal current collector (such as aluminum foil) to prepare the battery pole piece, which can enhance the contact between the active material and the conductive agent and the active material and the current collector, and stabilize the structure of the pole piece , is the connection medium of electrode active materials, and its characteristics will directly affect the cycle performance, fast charge and discharge capability, high temperature performance, DCR and many other performances of lithium batteries.
  • the water-soluble binders for secondary batteries developed on the market such as styrene-butadiene emulsion (SBR), hydroxymethylcellulose (CMC), polyacrylic acid Polyester (PAA), polytetrafluoroethylene emulsion (PTFE), etc. generally have problems such as uneven dispersion of solid matter, poor consistency of water-based positive electrode slurry, low stability, prone to sedimentation, poor adhesion of electrode pieces, and high brittleness. , can not meet the requirements for the use of lithium-ion secondary batteries. Although there are reports in the industry that the brittleness of pole pieces can be improved by adding plasticizers, the improvement effect is limited.
  • the inventors have found through research that by setting the positive electrode active material layer of the water-based positive electrode sheet to an inhomogeneous structure so that it has different porosities and average particle diameters of the positive electrode active material in the surface area and the internal area, the positive electrode active material can be significantly reduced.
  • the sheet resistance of the positive pole piece can be improved and the kinetic performance of the secondary battery can be improved.
  • the inventors believe that due to the different pore structures of the pole pieces, the porosity of the film layer gradually increases from the side close to the current collector to the surface of the film layer, and at the same time, the positive electrode active material on the surface of the film layer from the side close to the current collector to the surface of the film layer The average particle size also increases gradually, resulting in different capillary tension in the vertical direction, which is more conducive to the removal of residual water in the pole piece.
  • the first aspect of the present application provides a water-based positive electrode sheet, which includes a current collector and a positive active material layer disposed on at least one surface of the current collector, and the positive active material layer includes a water-based binder, wherein The porosity of the surface area of the positive active material layer is larger than that of the inner area, and the average particle size of the positive active material in the surface area is larger than the average particle size of the positive active material in the inner area.
  • the thickness of the positive electrode active material layer of the water-based positive electrode sheet is set as H, as shown in FIG. 1 .
  • H may be 0.05-5 mm, optionally 0.1-0.5 mm.
  • the surface area of the positive active material layer refers to the area from 0 to H/3 from the surface of the positive active material layer; correspondingly, the inner area of the positive active material layer refers to the A region of 0 to H/3 from the current collector in the positive electrode active material layer.
  • the positive current collector can be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the positive electrode current collector and the positive electrode active material layer are bonded by a water-based adhesive, which can effectively reduce environmental pollution, reduce hazards to production and users, and reduce manufacturing costs compared with oily adhesives.
  • a water-based adhesive which can effectively reduce environmental pollution, reduce hazards to production and users, and reduce manufacturing costs compared with oily adhesives.
  • the use of water-based adhesives and the use of a positive active material layer with an uneven structure as defined above can significantly reduce the sheet resistance of the positive electrode sheet and the impedance of the battery, while improving the rate performance and capacity retention of the secondary battery including the positive pole piece.
  • the porosity in the positive electrode active material layer is 10%-30% in a region H/3 from the surface.
  • the porosity in the positive electrode active material layer is 5%-25% in the region H/3 from the current collector.
  • the ratio of the porosity in the positive electrode active material layer in the area H/3 from the surface to the porosity in the positive active material layer in the area H/3 from the current collector is r1, r1 1.05-6.5, optionally 1.2-2.5.
  • r1 is a value greater than 1.
  • r1 is too small, the degree of structural unevenness of the positive electrode active material layer is small, and it is difficult to fully realize its effect. If r1 is too large, the sheet resistance tends to increase instead. Therefore, in order to further improve the performance of the positive electrode sheet and the battery, it is advantageous to set r1 in an appropriate range, which can reduce the resistance and impedance of the battery and improve the rate performance and capacity retention.
  • the average particle size of the positive active material in the positive active material layer in a region H/3 from the surface is 0.8-2.5 ⁇ m.
  • the average particle diameter of the positive electrode active material in the positive electrode active material layer in the region H/3 from the current collector is 0.5-1.5 ⁇ m.
  • the average particle diameter of the positive active material in the positive electrode active material layer from the surface H/3 area and the positive active material in the positive active material layer from the current collector H/3 area The ratio of the average particle size is r2, and r2 is 1.05-5, optionally 1.2-2.5.
  • r2 is a value greater than 1. If r2 is too small, the degree of structural unevenness of the positive electrode active material layer will be small, and it will be difficult to fully realize its effect. If r2 is too large, the sheet resistance tends to increase instead. Therefore, in order to further improve the performance of the positive electrode sheet and the battery, it is advantageous to set r2 in an appropriate range, which can reduce the resistance and impedance of the battery and improve the rate performance and capacity retention.
  • the value of the product r1 ⁇ r2 of the ratio r1 of the porosity to the ratio r2 of the average particle size of the positive electrode active material is 1.2 to 50, optionally 1.5 to 10, and further optionally 1.5 to 6.
  • the value of the product r1 ⁇ r2 of r1 and r2 reflects the degree of overall structural inhomogeneity in the positive electrode active material layer.
  • the value of the product r1 ⁇ r2 is also advantageously set within a specific range, and within this range the resistance of the positive electrode sheet is reduced more significantly, The capacity retention rate of the battery has also been significantly improved.
  • the ratio r1/r2 between the ratios r1 and r2 is 0.3 to 1.5, optionally 0.5 to 1.0.
  • the range of the ratio of r1/r2 further reflects the adjustment of the structure of the positive electrode active material layer of the positive electrode sheet, thereby realizing further adjustment of battery performance.
  • the layer within the region H/3 from the surface of the positive electrode active material layer contains 1 to 5 parts by weight of an aqueous binder and 1 to 5 parts by weight of a conductive agent, based on the total weight of the layers in this region.
  • the layer contains 2 to 4 parts by weight of the aqueous binder and 2 to 3 parts by weight of the conductive agent, based on the total weight of the layer in the region.
  • the layer in the region of H/3 from the current collector in the positive electrode active material layer contains 2 to 6 parts by weight of an aqueous binder and 1 to 5 parts by weight of a conductive agent, based on the weight of the layer in this region Based on the total weight; optionally, the layer contains 3 to 5 parts by weight of the aqueous binder and 2 to 3 parts by weight of the conductive agent, based on the total weight of the layer in the region.
  • the adjustment of the structure of the positive electrode active material layer and the adjustment of battery performance can be realized by setting the weight parts of the aqueous binder and the conductive agent in the surface area and the inner area of the positive electrode active material layer.
  • the conductive agent includes one or more of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes.
  • the positive electrode active material comprises lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, One or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
  • the water-based adhesive comprises soluble polysaccharides and derivatives thereof, water-soluble or water-dispersible polymers or mixtures thereof.
  • the aqueous binder is methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyethyleneimine and its salts, Polyacrylamide, acrylonitrile-acrylic acid copolymer and its derivatives, or mixtures thereof.
  • the water-based adhesive is a compound mixture of xanthan gum and polyethyleneimine, and the ratio of xanthan gum and polyethyleneimine can be 2:1-1:15, Optionally 1:2-1:14;
  • the average molecular weight Mn of the xanthan gum is 300,000-2,000,000 g/mol, and the average molecular weight Mn of the polyethyleneimine is 2,000-50,000 g/mol.
  • water-based adhesives are more environmentally friendly and safer to use, while improving battery performance.
  • the water-based positive electrode sheet can be formed by coating an aqueous positive electrode slurry on a positive electrode current collector.
  • the aqueous positive electrode slurry may contain 88-98 parts of positive electrode active material, 0.2-3 parts of thickener, 1-10 parts of water-based binder, 0.5-8 parts of conductive agent, and deionized water for the balance Adjusted to a solid content of 40-100%.
  • the water-based positive electrode slurry may contain 80-96 parts of positive electrode active material, 0.2-1 part of thickener, 2-6 parts of water-based binder, 1-5 parts of conductive agent, and the balance is adjusted to The solid content is 50-100%.
  • the coating method of the aqueous cathode slurry may be extrusion coating.
  • the aqueous positive electrode sheet is formed by coating the aqueous positive electrode slurry on the positive electrode current collector by means of multi-layer die extrusion coating.
  • the aqueous positive electrode slurry is extrusion-coated simultaneously using a plurality of dies to form a plurality of extrusion-coated layers, the number of which corresponds to the number of dies used.
  • two-layer, three-layer, four-layer or more layer die coating can be used.
  • extrusion coating is performed using a three-layer die.
  • the water-based cathode slurry is divided into three layers of 1/2/3, corresponding to the upper, middle and lower layers of the die respectively.
  • Each layer of the extrusion die corresponds to a corresponding channel, and different channels can correspond to water-based cathode slurries composed of different formulations.
  • the type, ratio or addition order of the positive electrode active material, conductive agent and water-based binder in the formula can be freely adjusted to realize the structure design of the electrode plate with uneven thickness direction.
  • the positive electrode active material layer prepared by the multi-layer die extrusion coating process has an uneven structural design in the thickness direction, it has no obvious layering, and the polarization of the film layer is small, which helps Improvement of battery dynamic performance.
  • the sheet resistance of the aqueous positive electrode sheet is 0.3 to 2 ⁇ , optionally 0.3 to 1 ⁇ .
  • the water-based positive electrode sheet of the invention has relatively low sheet resistance, which effectively improves the performance of the battery using the electrode sheet.
  • the second aspect of the present application provides a secondary battery, which includes the water-based positive electrode sheet of the first aspect of the present application.
  • the secondary battery is a lithium ion secondary battery.
  • the lithium ion secondary battery has a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes a positive electrode current collector and a positive active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode The active material layer contains a positive electrode active material and a conductive agent.
  • the battery cells of the secondary battery will be described in detail below.
  • a lithium-ion secondary battery typically includes a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolytic solution includes electrolyte salts and solvents.
  • the electrolyte salt can be a common electrolyte salt in lithium ion secondary batteries, such as lithium salt, including lithium salt that can be the above-mentioned lithium salt as a high thermal stability salt, lithium salt as a low impedance additive, or lithium salt that inhibits aluminum foil corrosion. Salt.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI (bistrifluoromethane Lithium sulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodifluorooxalate phosphate), LiSO 3 F (lithium fluorosulfonate), NDFOP (difluorodioxalate), Li 2 F(SO 2 N) 2 SO 2 F, KFSI, CsFSI, Ba(FSI) 2 and LiFSO 2 NSO 2 CH 2 CH 2 CF 3 more than one of them
  • the solvent is not particularly limited, and can be selected according to actual needs.
  • the solvent is a non-aqueous solvent.
  • the solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylates.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB) , e
  • the electrolyte may optionally include other additives.
  • additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc.
  • the additive is selected from cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate ester compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds , aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic acid anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.
  • the positive pole piece includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, and the positive active material layer includes a positive active material and a conductive agent.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by metal materials (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the positive electrode active material layer provided on the surface of the positive electrode current collector includes a positive electrode active material.
  • the cathode active material used in the present application may have any conventional cathode active material used in secondary batteries.
  • the positive electrode active material may contain one or more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, lithium manganese iron phosphate One or more of the composite materials with carbon and their modified compounds. These materials are all commercially available. Carbon may be coated on the surface of the positive electrode active material.
  • the positive active material layer optionally includes a conductive agent.
  • a conductive agent there is no specific limitation on the type of conductive agent, which can be selected by those skilled in the art according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive active material layer may also optionally include a binder.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid ( One or more of PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • a positive electrode active material coated with carbon, a conductive agent and a binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode On the current collector, after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material.
  • Composite current collectors can be formed by metal materials (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode material layer usually includes negative electrode active material and optional binder, optional conductive agent and other optional additives, usually formed by coating and drying negative electrode slurry into.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring them evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, simple silicon, silicon oxide compounds, silicon-carbon composites, and lithium titanate. kind.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • a separator is also included in a lithium ion secondary battery using an electrolytic solution.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the present application has no special limitation on the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from more than one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • a lithium ion secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer package of the lithium-ion secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the lithium-ion secondary battery may also be a soft bag, such as a pouch-type soft bag.
  • the material of the soft bag may be plastic, and examples of plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 2 shows a lithium-ion secondary battery 5 having a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the lithium-ion secondary battery can be assembled into a battery module 4, and the number of lithium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be determined by those skilled in the art according to the application of the battery module 4 and capacity selection.
  • a plurality of lithium ion secondary batteries 5 can be arranged in sequence along the length direction of the battery module. Of course, it can also be arranged in any other manner. Furthermore, the plurality of lithium-ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing with a containing space in which a plurality of lithium-ion secondary batteries 5 are housed.
  • the above-mentioned lithium-ion secondary batteries 5 or battery modules 4 can be assembled into a battery pack 1, and the number of lithium-ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 can be determined by those skilled in the art according to the battery pack 1 Choose from your application and capacity.
  • the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating battery cells.
  • the present application also provides a device, which includes the battery pack provided in the present application.
  • the battery pack can be used as a power source for the device and also as an energy storage unit for the device.
  • the device can be, but not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a battery pack can be selected according to its usage requirements.
  • Figure 6 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be employed.
  • lithium iron phosphate cathode active material LPF, conductive agent conductive carbon black, and water-based binder at a weight ratio of 96:1:3, wherein the water-based binder uses xanthan gum (molecular weight is about 1,000,000 g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and polyethyleneimine (molecular weight is about 10000g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), the compounding weight ratio is 1:1; the balance is solvent
  • the deionized water was stirred and mixed evenly to obtain a positive electrode slurry with a solid content of 50%; then the positive electrode slurry was uniformly coated on the aluminum foil positive electrode current collector.
  • the coating die adopts a three-layer co-extrusion die, and then combines the drying process conditions to obtain a film layer (ie, a positive electrode active material layer).
  • the thickness H of the film layer is 0.2 mm.
  • the average particle diameter D50 value of the positive electrode active material in the surface area (i.e. in the area of H/3 from the surface in the film layer) and the inner area (i.e. in the area of H/3 from the current collector in the film layer) in the film layer is respectively 0.8 ⁇ m and 0.5 ⁇ m, and the porosity of the surface area and the inner area of the film layer are 10.3% and 5.1%, respectively.
  • cold pressing and slitting are performed to obtain the positive electrode sheet.
  • a 2 ⁇ m thick ceramic coating was coated with a PE porous film as a separator.
  • NMP was used as a solvent to prepare the slurry for the positive electrode sheet, and the other steps were the same as in Comparative Example 1.
  • Example 1 Stack the positive electrode sheet, separator, and negative electrode sheet of Example 1 in order, so that the separator is between the positive and negative electrode sheets to play the role of isolation, and then wind up to obtain a bare cell, and weld the tabs to the bare cell, And put the bare battery into the aluminum case, and bake it at 80°C to remove water, then inject the electrolyte and seal it to get an uncharged battery.
  • the uncharged battery is then subjected to standing, hot and cold pressing, formation, shaping, capacity testing and other processes in sequence to obtain the lithium ion secondary battery product of Example 1.
  • the lithium ion secondary battery products of Examples 2-16 and Comparative Examples 1-4 were also prepared according to the above steps.
  • test methods for the parameters of the positive pole piece and the battery are as follows:
  • Porosity The film layer of the pole piece is peeled off by tape, and the porosity of the pole piece is converted by testing the volume and weight of the pole piece. Tested according to GB/T 24586-2009 True Density Method Porosity Analysis General Rules.
  • the DC impedance test process of the battery is as follows: at 25°C, charge the corresponding battery in the example with a constant current of 1/3C to 3.65V, then charge it with a constant voltage of 3.65V to a current of 0.05C, and record the voltage after leaving it for 5 minutes V1. Then discharge at 1/3C for 30s, record the voltage V2, then (V2-V1)/1/3C, get the internal resistance DCR of the battery.
  • 2C rate performance test At 25°C, charge the secondary batteries of each example and comparative example at a constant current rate of 0.33C to 4.20V, and then charge at a constant voltage to a current of 0.05C, let stand for 5min, and record this The charging capacity at that time is the first charging capacity; stand still for 5 minutes, then discharge to 2.8V at a constant current rate of 0.33C, and stand still for 30 minutes. Then charge the secondary battery at a rate of 2C to 4.20V at a constant current, then charge at a constant voltage to a current of 0.05C, let it stand for 5 minutes, and record the charging capacity at this time.
  • the capacity retention rate (%) of the battery at the 2C charging rate 2C charging capacity/0.33C charging capacity ⁇ 100%.
  • the battery capacity retention data corresponding to Example 1 in Table 1 is the data measured after 800 cycles under the above test conditions, that is, the value of P800.
  • the test process of other embodiments and comparative examples is the same as above.
  • the porosity of the surface area is smaller than that of the inner area, and the average particle size of the positive active material in the surface area is smaller than that of the inner area. If the average particle size of the positive electrode active material is increased, the sheet resistance and DC resistance increase significantly, while the rate performance and battery capacity retention decrease significantly.
  • the average particle size of the positive electrode active material in the surface area is greater than the average particle size of the positive electrode active material in the inner area, but the porosity of the surface area is still smaller than that in the inner area. The porosity of the region, the results show that its sheet resistance and DC resistance are still significantly higher than those of Examples 1-16 of the present invention, while the rate performance and battery capacity retention are still significantly lower than those of Examples 1-16 of the present invention.
  • Comparative Example 3 has adopted the same porosity and the average particle diameter of the positive electrode active material for the surface area and the internal area, and the results show that it is still better than the embodiment of the present invention in terms of sheet resistance, DC resistance, rate performance and battery capacity retention performance. Significantly worse.
  • Comparative Example 4 the structure of the positive electrode active material layer of the positive electrode sheet is basically the same as that of Comparative Example 3, but the solvent uses NMP instead of deionized water, and its performance is degraded to a certain extent compared with Comparative Example 3. .
  • the obtained battery can achieve better results in terms of sheet resistance, DC resistance, rate performance and battery capacity retention performance.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

本申请涉及一种水系正极极片，其包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，其中所述正极活性物质层的表面区域的孔隙率大于内部区域的孔隙率，并且所述表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径。本申请还涉及包含所述水系正极极片的二次电池、包含所述二次电池的电池包以及包含所述电池包的用电装置。

Description

一种水系正极极片及包含该极片的二次电池及用电装置 技术领域
本申请涉及二次电池领域，尤其涉及一种具有不均匀结构的水系正极极片以及包含该正极极片的二次电池、电池包及其用电装置。
背景技术
二次电池因其成本低、寿命长，安全性好等特点成为最受欢迎的能量存储系统，现已被广泛应用于纯电动汽车、混合电动汽车以及智能电网等领域。高安全性与低成本是动力/储能电池市场技术持续发展的重点方向，磷酸铁锂(LFP)正极材料锂离子电池因磷酸铁锂材料稳定的结构与耐高温分解特性在安全性上具有极大优势，且磷酸铁锂材料不含重金属，成本亦较低，近年来发展愈发迅猛。
目前，二次电池正极极片制备大多采用聚偏氟乙烯(PVDF)作为粘结剂，N-甲基吡烷酮(NMP)作为溶剂搭配使用，同时加入导电剂形成浆料，再将浆料涂覆于集流体表面，烘干辊压，制备正极极片。然而PVDF和NMP均为石油衍生化学产品,其合成及后处理过程复杂，能耗高，因此PVDF与NMP有机溶剂形成的油性体系制作电极的成本较高。另外，在制作电池极片时，大量NMP毒性气体会挥发到空气中，污染环境并对人体产生危害，且NMP使用时也需投入大量成本进行回收。
基于此，电池行业也在尝试开发水系正极体系，但目前的水系正极极片在降低膜片电阻以及改善电池动力学性能方面仍不太令人满意。本领域中仍然需要对水系正极极片的膜片电阻及其电池动力学性能进一步改善。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种水系正极极片，以解决降低膜片电阻以及进一步改善电池动力学性能的技术问题。
为了达到上述目的，本申请第一方面提供一种水系正极极片，其包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，
其中所述正极活性物质层的表面区域的孔隙率大于内部区域的孔隙率，并且所述表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径。
在本申请中，所述水系正极极片的正极活性物质层的厚度设定为H。在任意实施方式中，H可为0.05-5mm，可选地为0.1-0.5mm。在本申请中，所述正极活性物质层的表面区域是指所述正极活性物质层中距离表面0至H/3范围内的区域；相对应的，所述正极活性物质层的内部区域是指所述正极活性物质层中距离所述集流体0至H/3范围内的区域。通过设定所述正极活性物质层的表面区域与内部区域具有不同的孔隙率以及各区域内正极活性材料具有不同的平均粒径，使得所述正极活性物质层在垂直方向上具有不均匀的结构。这种具有不均匀结构的正极活性物质层的正极极片降低了包含所述正极极片的二次电池的电阻和阻抗，同时提高了倍率性能以及容量保持率。
在任意实施方式中，所述正极活性物质层中距离表面H/3区域内的孔隙率为10％-30％。所述正极活性物质层中距离集流体H/3区域内的孔隙率为5％-25％。在任意实施方式中，所述正极活性物质层中距离表面H/3区域内的孔隙率和所述正极活性物质层中距离所述集流体H/3区域内的孔隙率的比值为r1，r1为1.05-6.5，可选地为1.2-2.5。本申请中，当正极活性物质层的表面区域和内部区域中的孔隙率的比值r1位于上述范围内时，可 进一步降低膜片电阻和电池阻抗以及提高倍率性能和容量保持率。
在任意实施方式中，所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径为0.8-2.5μm。所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径为0.5-1.5μm。在任意实施方式中，所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径和所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径的比值为r2，r2为1.05-5，可选地为1.2-2.5。本申请中，当正极活性物质层的表面区域和内部区域中的正极活性材料的平均粒径的比值r2位于上述范围内时，可实现膜片电阻和电池阻抗的降低以及倍率性能和容量保持率的提高。
在任意实施方式中，所述孔隙率的比值r1与所述正极活性材料的平均粒径的比值r2的乘积r1×r2的值为1.2至50，可选地为1.5至10，进一步可选地为1.5至6。在本申请中，当所述乘积位于上述范围内时，二次电池的性能可以得到进一步的改善。另外，所述r1与r2二者的比值r1/r2为0.3至1.5，可选地为0.5至1.0。r1/r2的比值的范围进一步体现了对正极极片的正极活性物质层结构的调节，从而实现对于电池性能的进一步调节。
在任意实施方式中，所述正极活性物质层中距离表面H/3区域内的层含有1至5重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有2至4重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。在任意实施方式中，所述正极活性物质层中距离集流体H/3区域内的所述层含有2至6重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有3至5重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。通过设定所述正极活性物质层中表面区域和内部区域中各自的水性粘结剂和导电剂的重量份数，可实现对于所述 正极活性物质层结构的调节以及电池性能的调节。
在任意实施方式中，所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。在任意实施方式中，所述正极活性材料包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、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、锂镍钴铝氧化物中的一种或多种。通过选择合适的导电剂和正极活性材料，可进一步改善正极极片以及锂离子二次电池的性能。
在任意实施方式中，所述水性粘接剂包含可溶性多糖类及其衍生物、水溶性或水分散液高分子聚合物或其混合物。在进一步的实施方式中，所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或其混合物。在任意实施方式中，所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，所述黄原胶和所述聚乙烯亚胺的比例可为2:1-1:15，可选地为1:2-1:14；可选地，所述黄原胶的平均分子量Mn为300000-2000000g/mol，所述聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。水性粘接剂相比于油系粘接剂，对环境更加友好且使用更安全。另外，特定的水性粘接剂的组合可进一步改善电池的性能。
在任意实施方式中，所述水系正极极片的膜片电阻为0.3至2Ω，可选地为0.3至1Ω。本发明的水系正极极片具有相对较低的膜片电阻，有效改善了使用该极片的电池的动力学性能。
在任意实施方式中，所述水系正极极片的正极活性物质层由多层模头挤压涂布工艺形成。通过该工艺形成的正极活性物质层可以简便的方式形成具有不均匀结构的层而不发生明显分层，膜层极化小，有助于电池动力学性能的提升。
本申请的第二方面提供一种二次电池，其包括选自本申请的第一方面 的水系正极极片。
本申请的第三方面提供一种电池包，其包括选自本申请的第二方面的二次电池。
本申请的第四方面提供一种用电装置，其包括选自本申请的第二方面的二次电池或者本申请的第三方面的电池包。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施例，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，还可以根据附图获得其他的附图。
图1是本申请的一个实施方式中的水系正极极片的侧视结构示意图。
图2是本申请一个实施方式中的锂离子二次电池的示意图。
图3是图2所示的本申请一个实施方式中的锂离子二次电池的分解图。
图4是本申请一个实施方式中的电池包的示意图。
图5是图4所示的本申请一个实施方式中的电池包的分解图。
图6是本申请一个实施方式中的电池包用作电源的装置的示意图。
附图标记说明
1电池包
2上箱体
3下箱体
4电池模块
5锂离子二次电池
51壳体
52电极组件
53盖板
具体实施方式
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以与任意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，每个单独公开的点或单个数值自身可以作为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。
目前，基于油性体系的制造成本问题、回收成本问题。电池行业已开始尝试开发水系正极体系，一方面可避免有机溶剂NMP的使用，减少对环境及人类的危害，另一方面不涉及氟聚合物PVDF的大量使用及NMP溶剂的复杂回收，其电池制作成本低，可实现规模化降低成本应用。
其中，水系粘接剂的开发应用至关重要。粘结剂将正极材料和导电剂粘接于金属集流体(如铝箔)上，从而制备电池极片，其能够增强活性材料与导电剂以及活性材料与集流体之间的接触，稳定极片结构，是电极活性材料的连接媒介，其特性将直接影响锂电池循环性能、快速充放电能力、高温性能、DCR等诸多性能。虽然在水性粘接剂体系中可以使用去离子水代替溶剂NMP使用，但市面上开发的二次电池用水溶性粘结剂如丁苯乳液(SBR)、羟甲基纤维素(CMC)、聚丙烯酸酯(PAA)、聚四氟乙烯乳液(PTFE)等普遍存在固体物质分散不均匀，水性正极浆料一致性较差，稳定性不高，易发生沉降、极片粘接力差和脆性高等问题，不能满足锂离子二次电池的使用要求。虽然行业内有报道可通过增塑剂的添加来改善极片脆性，但改善效果有限。
与此同时，在二次电池领域，随着科技的发展，对电池能量密度要求越来越高。想要提高电池的能量密度，虽可对材料、电解液以及隔膜进行优化提升，但电池极片的设计和制作工艺也是提高电池能量密度必不可少的一部分。其中，提高极片单位面积的涂布量或提高活性材料在配方中的占比都是有效提升电池能量密度的办法。然而，随着正极极片厚度或活性材料占比的增加，在较高倍率或较低温度下，锂离子扩散动力学受限，电极活性物质利用率随之下降，电池能量密度受损。尤其是在水系正极技术中，溶剂水分的残留会进一步恶化电池动力学性能。
本发明人经研究发现，通过将水系正极极片的正极活性物质层设定为不均匀的结构，使其在表面区域以及内部区域具有不同的孔隙率和正极活性材料平均粒径，可以显著降低正极极片的膜片电阻并改善二次电池的动力学性能。不囿于任何理论，本发明人认为由于极片孔隙结构不同，膜层沿靠近集流体一侧至膜层表面孔隙率逐渐增加，同时膜层沿靠近集流体一侧至膜层表面正极活性材料的平均粒径也逐渐增加，导致其毛细张力在垂直方向不同，更加利于极片中残余水分的去除。
具体的，本申请第一方面提供一种水系正极极片，其包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，其中所述正极活性物质层的表面区域的孔隙率大于内部区域的孔隙率，并且所述表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径。
在本申请中，水系正极极片的正极活性物质层的厚度设定为H，如图1所示。在任意实施方式中，H可为0.05-5mm，可选地为0.1-0.5mm。在本申请中，所述正极活性物质层的表面区域是指所述正极活性物质层中距离表面0至H/3的区域；相对应的，所述正极活性物质层的内部区域是指所述正极活性物质层中距离所述集流体0至H/3的区域。所述正极集流体 可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。所述正极集流体与所述正极活性物质层通过水性粘接剂进行粘连，相比于油性粘接剂，可有效降低环境污染、降低对生产和使用人员的危害，并降低制造成本。尤其是对于较厚的正极极片，如厚度为3-10mm，采用水性粘接剂并采用如上所限定的具有不均匀结构的正极活性物质层，可显著降低所述正极极片的膜片电阻和电池的阻抗，同时提高了包含所述正极极片的二次电池的倍率性能以及容量保持率。
在一些实施方式中，所述正极活性物质层中距离表面H/3区域内的孔隙率为10％-30％。所述正极活性物质层中距离集流体H/3区域内的孔隙率为5％-25％。在一些实施方式中，所述正极活性物质层中距离表面H/3区域内的孔隙率和所述正极活性物质层中距离所述集流体H/3区域内的孔隙率的比值为r1，r1为1.05-6.5，可选地为1.2-2.5。在本申请的水系正极极片的正极活性物质层中，由于表面区域的孔隙率大于内部区域的孔隙率，r1为大于1的值。如果r1过小，则正极活性物质层的结构不均匀程度较小，难以充分实现其效果。如果r1过大，则膜片电阻反而有增大的趋势。因此，为进一步改善正极极片及电池性能，有利的是将r1设置在适宜的范围内，可实现对于电池的电阻和阻抗的降低以及倍率性能和容量保持率的提高。
在一些实施方式中，所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径为0.8-2.5μm。所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径为0.5-1.5μm。在一些实施方式中，所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径和所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径的比值为r2，r2为1.05-5，可选地为1.2-2.5。在本申请的水系正 极极片的正极活性物质层中，由于表面区域的正极活性材料的平均粒径大于内部区域的正极活性材料的平均粒径，r2为大于1的值。如果r2过小，则正极活性物质层的结构不均匀程度较小，难以充分实现其效果。如果r2过大，则膜片电阻反而有增大的趋势。因此，为进一步改善正极极片及电池性能，有利的是将r2设置在适宜的范围内，可实现对于电池的电阻和阻抗的降低以及倍率性能和容量保持率的提高。
在一些实施方式中，所述孔隙率的比值r1与所述正极活性材料的平均粒径的比值r2的乘积r1×r2的值为1.2至50，可选地为1.5至10，进一步可选地为1.5至6。r1与r2的乘积r1×r2的值反映的是所述正极活性物质层中总的结构不均匀的程度。为进一步降低膜片电阻以及改善二次电池的性能，所述乘积r1×r2的值也有利地设置在特定的范围之内，在该范围内正极极片的电阻得到了更为显著的降低，而电池的容量保持率也得到更为显著的提高。另外，所述比值r1与r2二者的比值r1/r2为0.3至1.5，可选地为0.5至1.0。r1/r2的比值的范围进一步体现了对正极极片的正极活性物质层结构的调节，从而实现对于电池性能的进一步调节。
在一些实施方式中，所述正极活性物质层中距离表面H/3区域内的层含有1至5重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有2至4重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。在任意实施方式中，所述正极活性物质层中距离集流体H/3区域内的层含有2至6重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有3至5重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。通过设定所述正极活性物质层中表面区域和内部区域中水性粘结剂和导电剂的重量份数，可实现对于所述正极活性物质层结构的调节以及电池性能的调节。
在一些实施方式中，所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。在任意实施方式中，所述正极活性材料包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、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、锂镍钴铝氧化物中的一种或多种。通过选择合适的导电剂和正极活性材料，可进一步改善正极极片以及锂离子二次电池的性能。
在一些实施方式中，所述水性粘接剂包含可溶性多糖类及其衍生物、水溶性或水分散液高分子聚合物或其混合物。在进一步的实施方式中，所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或其混合物。在一些实施方式中，所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，所述黄原胶和所述聚乙烯亚胺的比例可为2:1-1:15，可选地为1:2-1:14；可选地，所述黄原胶的平均分子量Mn为300000-2000000g/mol，所述聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。水性粘接剂相比于油系粘接剂，对环境更加友好且使用更安全，同时还能改善电池的性能。
所述水系正极极片可通过将水性正极浆料涂覆在正极集流体上而形成。在一些实施方式中，水性正极浆料可包含88-98份正极活性物质、0.2-3份增稠剂、1-10份水性粘结剂、0.5-8份导电剂，余量用去离子水调节成固含量为40-100％。可选地，水性正极浆料可包含80-96份正极活性物质、0.2-1份增稠剂、2-6份水性粘结剂、1-5份导电剂，余量用去离子水调节成固含量为50-100％。所述水性正极浆料涂覆的方式可为挤压涂布。在一些实施方式中，所述水系正极极片通过将水性正极浆料以多层模头挤压涂布的方式涂覆在正极集流体上而形成。在该方式中，使用多个模头同时挤压涂覆所述水性正极浆料，形成多个挤压涂布的层，所述层的数量对 应于使用的模头的数量。例如，可使用二层、三层、四层或更多层模头涂布。可选地，使用三层模头挤压涂布。在三层模头挤压涂布工艺中，水性正极浆料分成1/2/3三层，分别对应模头的上中下三层。各层挤压模头对应相应的通道，不同通道可对应不同配方组成的水性正极浆料。根据动力学性能需求，可自由调控配方中正极活性物质、导电剂和水性粘接剂的种类、配比或添加顺序，来实现厚度方向不均匀的极片结构设计。尤其在涂布过程中，由于其上层大孔隙、下层小孔隙(孔隙率多少及大小)的特殊结构设计，更利于水分的蒸发及电解液的浸润。更进一步的，多层模头挤压涂布工艺方式制备的正极活性物质层，虽在厚度方向上呈现不均匀的结构设计，但其没有明显的分层，膜层极化小，有助于电池动力学性能的提升。
在一些实施方式中，所述水系正极极片的膜片电阻为0.3至2Ω，可选地为0.3至1Ω。本发明的水系正极极片具有相对较低的膜片电阻，有效改善了使用该极片的电池的性能。
本申请第二方面提供一种二次电池，其包括本申请的第一方面的水系正极极片。在一些实施方案中，所述二次电池为锂离子二次电池。所述锂离子二次电池具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极活性物质层，所述正极活性物质层包含正极活性材料和导电剂。
下面对所述二次电池的电池单体进行详细阐述。
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[电解液]
电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为锂离子二次电池中的常用电解质盐，例如锂盐，包括可为上述作为高热稳定性盐的锂盐、作为低阻抗添加剂的锂盐或抑制铝箔腐蚀的锂盐。作为实例，电解质盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、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)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)、LiSO 3F(氟磺酸锂)、NDFOP(二氟二草酸盐)、Li 2F(SO 2N) 2SO 2F、KFSI、CsFSI、Ba(FSI) 2及LiFSO 2NSO 2CH 2CH 2CF 3中的一种以上。
所述溶剂的种类没有特别的限制，可根据实际需求进行选择。在一些实施方式中，所述溶剂为非水性溶剂。可选地，所述溶剂可包括链状碳酸酯、环状碳酸酯、羧酸酯中的一种或几种。在一些实施方式中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、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)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、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)、四氢呋喃、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种以上。
在一些实施方式中，所述电解液中还可选地包括其他添加剂。例如添加剂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、以及改善电池低温性能的添加剂等。作为示例，所述添加剂选自含有不饱和键的环状碳酸酯化合物、卤素取代的环状碳酸酯化合物、硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极活性物质层，所述正极活性物质层包括正极活性材料和导电剂。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性物质层设置在正极集流体相对的两个表面的其中任意一者或两者上。
本申请的锂离子二次电池中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(例如铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
设置于正极集流体的表面上的正极活性物质层包括正极活性材料。本申请中所用的正极活性材料可具有二次电池中使用的任意常规正极活性材料。在一些实施方式中，所述正极活性材料可包含选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸 盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。正极活性材料表面上可包覆有碳。
正极活性物质层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、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以上。
正极活性物质层还可选地包括粘结剂。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性材料、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，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、冷压等工序后，得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极材料层设置在负极集流体相对的两个表面中的任意一者或两者上。
本申请的锂离子二次电池中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体 可通过将金属材料(例如铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请的锂离子二次电池中，所述负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
所述负极活性物质的具体种类不做限制，可以采用本领域已知的能够用于锂离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或几种。
作为示例，导电剂可选自超导碳、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以上。
作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的锂离子二次电池中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请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。在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种以上。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，锂离子二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图2是作为一个示例的方形结构的锂离子二次电池5。
在一些实施方式中，参照图3，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。锂离子二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，锂离子二次电池可以组装成电池模块4，电池模块4所含锂离子二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块4的应用和容量进行选择。在电池模块4中，多个锂 离子二次电池5可以是沿电池模块的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
在一些实施方式中，上述锂离子二次电池5或者电池模块4可以组装成电池包1，电池包1所含锂离子二次电池5或者电池模块4的数量可由本领域技术人员根据电池包1的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，在电池包1中可以包括电池箱和设置于电池箱中的多个电池单体。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池单体的封闭空间。
另外，本申请还提供一种装置，所述装置包括本申请提供的电池包。所述电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
作为所述装置，可以根据其使用需求来选择电池包。
图6是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或 条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
正极极片的制备
将磷酸铁锂正极活性材料LPF、导电剂导电碳黑、水性粘结剂按重量比为96：1：3混合，其中水性粘接剂采用黄原胶(分子量约为1000000g/mol，购自上海阿拉丁生化科技股份有限公司)和聚乙烯亚胺(分子量约为10000g/mol，购自上海阿拉丁生化科技股份有限公司)的复配混合物，复配重量比例为1:1；余量用溶剂去离子水搅拌混合均匀，得到固含量为50％的正极浆料；之后将正极浆料均匀涂覆于铝箔正极集流体上。涂布模头采用三层共挤模头，然后结合干燥工艺条件，得到膜层(即正极活性物质层)。膜层的厚度H为0.2mm。所述膜层中表面区域(即膜层中距离表面H/3区域内)和内部区域(即膜层中距离集流体H/3区域内)的正极活性材料的平均粒径D50值分别为0.8μm和0.5μm，并且所述膜层中表面区域和内部区域的孔隙率分别为10.3％和5.1％。之后经过冷压、分切，得到正极极片。
负极极片的制备
将活性物质人造石墨、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照重量比为96.2：0.8：0.8：1.2溶于溶剂去离子水中，混合均匀后制备成负极浆料；将负极浆料多次均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
电解液的制备
在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5％LiPF6锂盐溶解于有机溶剂中，搅拌均匀，得到电解液。
隔离膜
以PE多孔薄膜涂布2μm厚的陶瓷涂层后作为隔离膜。
实施例2-16以及对比例1-3
除表面区域和内部区域的孔隙率和正极活性物质平均粒径存在差异外，其他步骤与实施例1相同。
对比例4
制备正极极片的浆料采用NMP作为溶剂，其他步骤与对比例1相同。
锂离子电池的制备
将实施例1的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电池，给裸电池焊接极耳，并将裸电池装入铝壳中，并在80℃下烘烤除水，随即注入电解液并封口，得到不带电的电池。不带电的电池再依次经过静置、热冷压、化成、整形、容量测试等工序，获得实施例1的锂离子二次电池产品。
实施例2-16以及对比例1-4的锂离子二次电池产品同样按照上述步骤制备。
实施例1-16以及对比例1-4的正极极片以及锂离子二次电池的制备参数均列于下表1中。
正极极片以及电池的各项参数的测试方法如下：
1)孔隙率：通过胶带剥离极片膜层，通过测试极片的体积和重量，换算极片的孔隙率。依据GB/T 24586-2009真密度法孔隙率分析通则测试。
2)正极活性物质平均粒径D50值测定：用设备型号马尔文2000(MasterSizer 2000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO 13320:2009，具体测试流程：取待测样品适量(样品浓度保证8-12％遮光度即可)，加入20ml去离子水，同时外超5min(53KHz/120W)，确保样品完全分散，之后按照GB/T19077-2016/ISO 13320:2009标准对样品进行测定。
3)正极极片的膜片电阻测试：
在室温下，使用CRM-01膜片电阻测试仪测试沿正极极片厚度方向的膜片电阻。每组测试5次，取平均值。
4)电池直流阻抗测试
电池直流阻抗测试过程如下：在25℃下，将实施例中对应的电池，以1/3C恒流充电至3.65V，再以3.65V恒定电压充电至电流为0.05C，搁置5min后，记录电压V1。然后再以1/3C放电30s，记录电压V2，则(V2-V1)/1/3C，得到电池的内阻DCR。
5)2C倍率性能测试：在25℃下，将各实施例和对比例的二次电池以0.33C倍率恒流充电至4.20V，再恒压充电至电流为0.05C，静置5min，记录此时的充电容量，即为首次充电容量；静置5min，再以0.33C倍率恒流放电至2.8V，静置30min。然后将二次电池以2C倍率恒流充电至4.20V，再恒压充电至电流为0.05C，静置5min，记录此时的充电容量。
电池在2C充电倍率下的容量保持率(％)＝2C充电容量/0.33C充电容量×100％。
6)电池容量保持率测试：电池容量保持率测试过程如下：在25℃下，将实施例中对应的电池，以1/3C恒流充电至3.65V，再以3.65V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.7V，所得容量记为初始容量C0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量Cn，则每次循环后电池容量保持率Pn＝Cn/C0*100％。该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第100次循环对应n＝100。表1中实施例1对应的电池容量保持率数据是在上述测试条件下循环800次之后测得的数据，即P800的值。其他实施例以及对比例的测试过程同上。
对各实施例中所制备的正极极片以及电池进行测试，测试结果显示于表1中。
表1：实施例1-16以及对比例1-4的正极极片以及电池的性能测试
Figure PCTCN2021142610-appb-000001
Figure PCTCN2021142610-appb-000002
由表1可见，对于本发明的实施例1-16的锂离子二次电池来说，当其正极极片的正极活性物质层的表面区域的孔隙率大于内部区域的孔隙率，并且表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径时，得到了具有较低的膜片电阻和直流阻抗以及较高的倍率性能和电池容量保持率。
与之相比，在对比例1的正极极片的正极活性物质层中，表面区域的孔隙率小于内部区域的孔隙率，并且表面区域中的正极活性材料的平均粒径小于所述内部区域中的正极活性材料的平均粒径，则膜片电阻和直流阻抗明显增大，而倍率性能和电池容量保持率显著降低。在对比例2的正极极片的正极活性物质层中，表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径，但是表面区域的孔隙率仍然小于内部区域的孔隙率，结果显示其膜片电阻和直流阻抗仍明显大于本发明实施例1-16，而倍率性能和电池容量保持率也仍然明显低于本发明实施例1-16。
对比例3对于表面区域和内部区域采用了相同的孔隙率和正极活性材料的平均粒径，结果表明其在膜片电阻、直流阻抗、倍率性能和电池容量保持率性能方面仍然比本发明实施例明显更差。至于对比例4，其正极极片的正极活性物质层的结构与对比例3基本相同，但是溶剂采用了NMP而不是去离子水，则其性能相比于对比例3又呈现出一定程度的劣化。
另外，对于表面区域和内部区域中的孔隙率的比值r1以及表面区域和内部区域中的正极活性材料的平均粒径的比值r2，当二者保持在一定范围内，尤其是二者的乘积r1×r2保持在1.8至8范围内时，所得电池在膜片电阻、直流阻抗、倍率性能和电池容量保持率性能方面可实现更好的效果。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤 其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (19)

  1. 一种水系正极极片，包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，
    其中所述正极活性物质层的表面区域的孔隙率大于内部区域的孔隙率，并且所述表面区域中的正极活性材料的平均粒径大于所述内部区域中的正极活性材料的平均粒径。
  2. 根据权利要求1所述的正极极片，其中所述正极活性物质层厚度为H，所述正极活性物质层中距离表面H/3区域内的孔隙率和所述正极活性物质层中距离所述集流体H/3区域内的孔隙率的比值为r1，r1为1.05-6.5，可选地为1.2-2.5。
  3. 根据权利要求2中所述的正极极片，其中所述正极活性物质层中距离表面H/3区域内的孔隙率为10％-30％，和/或，
    所述正极活性物质层中距离集流体H/3区域内的孔隙率为5％-25％。
  4. 根据权利要求1至3中任一项所述的正极极片，其中所述正极活性物质层厚度为H，所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径和所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径的比值为r2，r2为1.05-5，可选地为1.2-2.5。
  5. 根据权利要求4中所述的正极极片，其中所述正极活性物质层中距离表面H/3区域内的正极活性材料的平均粒径为0.8-2.5μm，和/或
    所述正极活性物质层中距离所述集流体H/3区域内的正极活性材料的平均粒径为0.5-1.5μm。
  6. 根据权利要求4至5中任一项所述的正极极片，其中r1×r2的值为1.2至50，可选地为1.5至10，进一步可选地为1.5至6。
  7. 根据权利要求4至5中任一项所述的正极极片，其中r1/r2的比值为 0.3至1.5，可选地为0.5至1.0。
  8. 根据权利要求1至7中任一项所述的正极极片，其中所述正极活性物质层中含有导电剂，所述正极活性物质层中距离表面H/3区域内的所述层含有1至5重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有2至4重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。
  9. 根据权利要求1至7中任一项所述的正极极片，其中所述正极活性物质层中含有导电剂，所述正极活性物质层中距离集流体H/3区域内的所述层含有2至6重量份水性粘结剂以及1至5重量份导电剂，基于该区域内所述层的总重量计；可选地，所述层含有3至5重量份水性粘结剂以及2至3重量份导电剂，基于该区域内所述层的总重量计。
  10. 根据权利要求1至9中任一项所述的正极极片，其中所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。
  11. 根据权利要求1至10中任一项所述的正极极片，其中所述正极活性物质层中还含有正极活性材料，所述正极活性材料包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、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、锂镍钴铝氧化物中的一种或多种。
  12. 根据权利要求1至11中任一项所述的正极极片，其中所述水性粘接剂包含可溶性多糖类及其衍生物、水溶性或水分散液高分子聚合物或其混合物。
  13. 根据权利要求1至12中任一项所述的正极极片，其中所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或其混合物。
  14. 根据权利要求1至13中任一项所述的正极极片，其中所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，所述黄原胶和所述聚乙烯亚胺的比例为2:1-1:15，可选地为1:2-1:14；可选地，所述黄原胶的平均分子量Mn为300000-2000000g/mol，所述聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。
  15. 根据权利要求1至14中任一项所述的正极极片，其所述正极极片的膜片电阻为0.3至2Ω；可选的，所述膜片电阻为0.3至1Ω。
  16. 根据权利要求1至15中任一项所述的正极极片，其中所述正极活性物质层由多层模头挤压涂布工艺形成。
  17. 一种二次电池，其包括选自权利要求1-16中任一项所述的水系正极极片。
  18. 一种电池包，其包括权利要求17所述的二次电池。
  19. 一种用电装置，其包括权利要求17所述的二次电池或者权利要求18所述的电池包。
PCT/CN2021/142610 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置 WO2023123088A1 (zh)

Priority Applications (4)

Application Number Priority Date Filing Date Title
PCT/CN2021/142610 WO2023123088A1 (zh) 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置
CN202180092930.2A CN116848665A (zh) 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置
EP21969456.9A EP4273963A1 (en) 2021-12-29 2021-12-29 Water-based positive electrode plate, secondary battery comprising same and electric device
US18/202,487 US20230307648A1 (en) 2021-12-29 2023-05-26 Aqueous positive electrode sheet, and secondary battery including the electrode sheet, and power consumption apparatus

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/CN2021/142610 WO2023123088A1 (zh) 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US18/202,487 Continuation US20230307648A1 (en) 2021-12-29 2023-05-26 Aqueous positive electrode sheet, and secondary battery including the electrode sheet, and power consumption apparatus

Publications (1)

Publication Number Publication Date
WO2023123088A1 true WO2023123088A1 (zh) 2023-07-06

Family

ID=86996902

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2021/142610 WO2023123088A1 (zh) 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置

Country Status (4)

Country Link
US (1) US20230307648A1 (zh)
EP (1) EP4273963A1 (zh)
CN (1) CN116848665A (zh)
WO (1) WO2023123088A1 (zh)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014143063A (ja) * 2013-01-23 2014-08-07 Toyota Motor Corp 二次電池
JP2016058187A (ja) * 2014-09-08 2016-04-21 トヨタ自動車株式会社 非水電解質二次電池
KR20190029187A (ko) * 2017-09-12 2019-03-20 현대자동차주식회사 파쇄강도가 서로 다른 2 이상의 전극 활물질을 포함하는 전극 조성물 및 이를 포함하는 리튬 이차전지
CN110660965A (zh) * 2019-08-29 2020-01-07 孚能科技(赣州)股份有限公司 负极片及其制备方法和锂离子电池及其制备方法和应用

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014143063A (ja) * 2013-01-23 2014-08-07 Toyota Motor Corp 二次電池
JP2016058187A (ja) * 2014-09-08 2016-04-21 トヨタ自動車株式会社 非水電解質二次電池
KR20190029187A (ko) * 2017-09-12 2019-03-20 현대자동차주식회사 파쇄강도가 서로 다른 2 이상의 전극 활물질을 포함하는 전극 조성물 및 이를 포함하는 리튬 이차전지
CN110660965A (zh) * 2019-08-29 2020-01-07 孚能科技(赣州)股份有限公司 负极片及其制备方法和锂离子电池及其制备方法和应用

Also Published As

Publication number Publication date
US20230307648A1 (en) 2023-09-28
EP4273963A1 (en) 2023-11-08
CN116848665A (zh) 2023-10-03

Similar Documents

Publication Publication Date Title
KR102502618B1 (ko) 이차 전지, 이차 전지를 포함하는 전지 모듈, 전지 팩 및 장치
WO2022032624A1 (zh) 二次电池及其制备方法与包含二次电池的电池模块、电池包及装置
WO2021008429A1 (zh) 二次电池及其相关的电池模块、电池包和装置
CN112467308B (zh) 一种隔膜及其制备方法、锂离子电池
WO2021189424A1 (zh) 二次电池和含有该二次电池的装置
CN115133020B (zh) 锰酸锂正极活性材料及包含其的正极极片、二次电池、电池模块、电池包和用电装置
CN112909220A (zh) 二次电池及含有它的装置
WO2023087213A1 (zh) 一种电池包及其用电装置
CN101110477B (zh) 一种电化学储能与能量转换装置
WO2023123087A1 (zh) 一种水系正极极片及包含该极片的二次电池及用电装置
CN117043983A (zh) 负极极片及其制备方法、二次电池、电池模块、电池包及用电装置
US20240079600A1 (en) Cathode plate, secondary battery, battery module, battery pack, and electric device
CN116826315B (zh) 隔离膜及其制备方法以及电池和用电设备
WO2021258275A1 (zh) 二次电池和包含该二次电池的装置
CN116526069B (zh) 隔离膜、电池单体、电池和用电装置
CN202839842U (zh) 一种倍率型锂离子电池
WO2023123088A1 (zh) 一种水系正极极片及包含该极片的二次电池及用电装置
CN118120072A (zh) 干法电极用底涂胶及其制备方法、复合集流体、电池极片、二次电池、电池模块、电池包和用电装置
CN112886050B (zh) 二次电池及含有该二次电池的装置
CN115842092A (zh) 多层涂布极片、二次电池、电池模块、电池包和用电装置
KR20220092577A (ko) 이차 전지 및 이차 전지를 포함하는 장치
CN116420259B (zh) 电解液、二次电池、电池模块、电池包和用电装置
WO2023193166A1 (zh) 电极组件以及包含其的二次电池、电池模块、电池包及用电装置
CN115832235B (zh) 负极浆料、负极极片、锂离子电池、电池模块、电池包和用电装置
WO2023087214A1 (zh) 一种电池包及其用电装置

Legal Events

Date Code Title Description
WWE Wipo information: entry into national phase

Ref document number: 202180092930.2

Country of ref document: CN

ENP Entry into the national phase

Ref document number: 2021969456

Country of ref document: EP

Effective date: 20230802

121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 21969456

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE