Electrode plate, electrode assembly and manufacturing method thereof

Abstract

The invention provides a pole piece, an electrode assembly and manufacturing methods of the pole piece and the electrode assembly, the pole piece comprises a current collector, an electrode active material arranged on at least one side of the current collector and a polymer film, and the polymer film has a cross-linked structure. The electrode assembly prepared by using the electrode plate can improve the energy density of the lithium ion battery and prevent the battery cell from being damaged, so that the stability and the safety of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to an electrode sheet, an electrode assembly and a manufacturing method thereof. Background Art

[0002] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of lithium-ion batteries, higher requirements are also put forward for their energy density, cycle performance and safety performance. In this regard, the electrode sheet of the electrode assembly has attracted attention because it does not require an additional separator film that contributes nothing to the energy density of the battery, and can improve the energy density of the battery. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to omit the separator film part in the preparation of traditional battery cells, and in addition, to avoid the loss caused by problems such as wrinkling and misalignment of the separator film during the preparation of battery cells, reduce the manufacturing cost of battery cells, and in addition, prevent the battery cells from being damaged.

[0004] To achieve the above object, the present application provides an electrode sheet, an electrode assembly having the electrode sheet and a manufacturing method thereof.

[0005] The first aspect of the present application provides an electrode sheet, which is characterized in that it includes a current collector, an electrode active material layer directly disposed on at least one side of the current collector, and a polymer film disposed on the surface of the electrode active material layer away from the current collector side, and the polymer film has a crosslinked structure.

[0006] Thus, a polymer film with a crosslinked structure is provided on the electrode sheet of the present application, and its thickness is smaller than that of the traditional separator film. By using the electrode sheet with the specific structure of the present application, the manufactured lithium-ion battery does not include a separator film, and can not only improve the energy density and cycle characteristics of the lithium-ion battery, but also prevent the damage of the electrode sheet based on the ductility of the polymer film, and can improve the stability and safety of the lithium-ion battery. In addition, by making the polymer film have a crosslinked structure, a three-dimensional network structure can be formed microscopically on the polymer film, which can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film. Furthermore, by providing a polymer film on the electrode sheet, since there is no need to additionally provide a separator film, the separator film part in the preparation of traditional battery cells is omitted, and in addition, the loss caused by problems such as wrinkling and misalignment of the separator film during the preparation of battery cells is avoided, and the manufacturing cost of battery cells is reduced.

[0007] In any embodiment, the polymer film is an insulating layer with an insulation resistance R ≥ 1 MΩ, optionally R ≥ 3000 MΩ, and its upper limit is not particularly limited. Usually, R ≤ 9000 MΩ, optionally R ≤ 6000 MΩ. By making the insulation resistance of the polymer film within the above range, the effect of insulating the positive and negative electrodes can be achieved better, and the transmission of lithium ions is not affected, ensuring good adhesion between the positive and negative electrodes, so that the battery cell can be used safely.

[0008] In any embodiment, the polymer includes at least one of polyester, polyether, polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, polyvinyl alcohol, etc.

[0009] In any embodiment, the monomer or prepolymer of the polyester includes at least one of (meth)acrylate and isocyanate; optionally methyl methacrylate, ethyl methacrylate or butyl methacrylate, and hexamethylene diisocyanate; the monomer or prepolymer of the polyether includes at least one of halogenated propylene oxide - polyol, ethylene oxide, and propylene oxide, optionally epichlorohydrin - glycerol, and the prepolymer refers to the product formed by preliminary polymerization of monomers.

[0010] By using specific polymers such as the above-mentioned polyester, polyether, polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, polyvinyl alcohol, etc. to form the polymer film, a polymer film with more excellent ductility and insulation can be obtained. As a result, the thickness of the polymer film can be made thinner, which can not only improve the energy density and cycle characteristics of the lithium-ion battery, but also prevent the electrode sheet from being damaged based on the ductility of the polymer film, and can improve the stability and safety of the lithium-ion battery.

[0011] In any embodiment, the thickness of the polymer film is 1 μm - 8 μm, optionally 1 μm - 5 μm, and further optionally 1 μm - 3 μm.

[0012] By making the thickness of the polymer film within the above range, the thickness of the polymer film can be significantly reduced compared to the thickness of the traditional separator, while improving the volumetric energy density and cycle characteristics of the battery and realizing the functions of the traditional separator.

[0013] In any embodiment, the ionic conductivity of the polymer film after absorbing the electrolyte is 10 -3 -10 -2 s / cm, optionally 5×10 -3 -10 -2 s / cm, and the electrolyte is a mixture in which 1 mol / L of LiPF 6 is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate with a volume ratio of 1∶1∶1.

[0014] By making the ionic conductivity of the polymer membrane within the above range after absorbing the electrolyte, ions can more easily pass through the polymer membrane layer, thus playing a role in improving battery kinetics.

[0015] In any embodiment, the swelling ratio of the polymer membrane is 100%-200%, optionally 130%-180%. The measurement conditions of the swelling ratio are as follows: After making the polymer into a film and completely drying it, cut it into a specimen with a weight of 0.5 g of 30 mm×30 mm×5 mm, immerse it in the following electrolyte, seal it and place it in an environment of 70°C. After 7 days, take it out, wipe the electrolyte on the surface, weigh it and record it. The swelling ratio is calculated by the following formula:

[0016] Swelling ratio (%) = (W1 - W0) / W0×100%, where W0 is the weight of the film before impregnation, and W1 is the weight of the film after impregnation. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1 dissolved with 1 mol / L of LiPF 6 mixture.

[0017] By making the swelling ratio of the polymer membrane within the above range, the polymer can easily achieve ionic conduction in the electrolyte.

[0018] The second aspect of the present application also provides a method for manufacturing a pole piece, which includes the following processes:

[0019] Directly dispose an electrode active material layer on at least one side of the current collector to obtain an electrode pole piece. The electrode active material layer includes an electrode active substance, a conductive agent and a binder;

[0020] Coat a mixed solution formed by a polymer monomer, an initiator and a crosslinking agent on the surface of the electrode active material layer on the side away from the current collector on at least one side of the electrode pole piece;

[0021] Polymerize the mixed solution to cure and form a polymer membrane on the surface of the electrode active substance to obtain a pole piece.

[0022] Through the manufacturing method of the electrode sheet of the present application, the electrode sheet with a polymer film of the present application can be obtained, and its thickness is smaller than that of the traditional separator film. By using the electrode sheet with the specific structure of the present application, the manufactured lithium-ion battery does not contain a separator film, which can not only improve the energy density and cycling characteristics of the lithium-ion battery, but also prevent the electrode sheet from being damaged based on the ductility of the polymer film, and can improve the stability and safety of the lithium-ion battery. In addition, by making the polymer film have a crosslinked structure, a three-dimensional network structure can be formed microscopically on the polymer film, which can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film. Furthermore, by setting the polymer film on the electrode sheet, since there is no need to additionally set a separator film, the separator film part in the preparation of the traditional battery cell is omitted. In addition, the loss caused by problems such as wrinkling and misalignment of the separator film during the preparation of the battery cell is avoided, and the manufacturing cost of the battery cell is reduced.

[0023] In any embodiment, the electrode active material is a positive electrode active material or a negative electrode active material; the positive electrode active material includes one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds; the negative electrode active material includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate; the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyamide, poly(acrylonitrile-acrylate), and poly(styrene-acrylate).

[0024] In any embodiment, the initiator is a thermal initiator or a photoinitiator, the thermal curing temperature of the thermal initiator is 25°C - 120°C, and the photocuring wavelength of the photoinitiator is 200nm - 400nm or 760nm - 1000nm.

[0025] In any embodiment, the thermal initiator includes at least one of azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, and azobisisoheptonitrile, and can be selected as azobisisobutyronitrile; the photoinitiator includes at least one of methyl benzoylformate, 2-hydroxy-2-methyl-1-phenylpropanone, or benzophenone, and can be selected as benzophenone.

[0026] By adopting the thermal initiator or the photoinitiator, the polymerization reaction can proceed more smoothly, and a polymer film with a thin thickness, excellent ductility, and insulation can be formed.

[0027] In any embodiment, the crosslinking agent is bisphenol A diallyl ether, divinylbenzene, and polyethylene glycol diacrylate, and can be selected as polyethylene glycol diacrylate.

[0028] By adopting the specific cross-linking agent, the cross-linking of the polymer can proceed more smoothly, forming a polymer film with a thin thickness, excellent ductility and insulation. In addition, by using the cross-linking agent to cross-link the polymer to form a polymer film with a cross-linked structure, it can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film.

[0029] In any embodiment, the content ratio of the polymer monomer, initiator and cross-linking agent in the mixture is (90-99.8):(0.1-5):(0.1-5), and can be optionally (98-99.4):(0.1-0.5):(0.5-1.5).

[0030] By setting the content ratio of the polymer monomer, initiator and cross-linking agent within the above range, it is possible to more easily form a polymer film with a thin thickness, excellent ductility and insulation, which helps to improve the energy density, cycle characteristics, battery stability and safety of the battery.

[0031] In any embodiment, the coating includes at least one of gravure coating, microgravure coating or spraying. The coating speed is 1 m / min - 150 m / min, and can be optionally 60 m / min - 90 m / min.

[0032] By adopting the above coating method and making the coating speed within the above range, the thickness of the polymer film can be made more uniform while taking into account the coating efficiency.

[0033] The third aspect of the present application further provides an electrode assembly, which is characterized in that it includes a positive electrode plate and a negative electrode plate, and at least one of the positive electrode plate and the negative electrode plate is the electrode plate of the present application, and optionally only the positive electrode plate is the electrode plate of the present application.

[0034] The fourth aspect of the present application further provides a manufacturing method of the electrode assembly, and the electrode assembly is prepared by laminating or winding the positive electrode plate and the negative electrode plate.

[0035] The fifth aspect of the present application further provides a secondary battery, which includes the electrode assembly of the present application.

[0036] The fifth aspect of the present application further provides an electrical device, which includes the secondary battery of the present application. Description of the Drawings

[0037] Figure 1 It is a schematic structural diagram of an electrode plate of the present application.

[0038] Description of the Reference Numerals:

[0039] 1: Current collector 2: Electrode active material layer 3: Polymer film Detailed implementation manners

[0040] Hereinafter, embodiments of the electrode sheet, electrode assembly, and manufacturing method thereof of the present application will be specifically described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following descriptions from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following descriptions are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0041] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application mean open-ended or may also be closed-ended. For example, the "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0046] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0047] In the preparation of traditional battery cells, a separator film part is provided. During the preparation of the battery cells, the separator film may be damaged due to problems such as wrinkling and misalignment, resulting in an increase in the manufacturing cost of the battery cells. In addition, the existing electrode assemblies use inorganic material films or insulating ceramic layers and adhesive layers coated on the electrode foils. However, inorganic solid materials are rigid and have no extensibility, and the coating elongation rate is low. Using such electrode foils to prepare battery cells may cause damage to the electrode foils, thereby causing safety problems of the battery cells.

[0048] However, the existing electrode foil preparation technology for electrode assemblies is: coating an inorganic material film or an insulating ceramic layer and an adhesive layer on the electrode foil. However, inorganic solid materials are rigid and have no extensibility, and the coating elongation rate is low. Using such electrode foils to prepare battery cells may cause damage to the electrode foils, thereby causing safety problems of the battery cells. Therefore, the existing electrode foils of electrode assemblies still need to be improved.

[0049] Based on this, this application provides an electrode foil, an electrode assembly having the electrode foil, and a manufacturing method thereof. The electrode foil, the electrode assembly having the electrode foil, and the manufacturing method thereof of this application are described in detail below.

[0050] [Electrode Foil]

[0051] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are inserted into and extracted from between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short - circuit between the positive and negative electrodes and allowing ions to pass through at the same time.

[0052] In an embodiment of the present application, a pole piece is provided, which is characterized by including a current collector, an electrode active material layer directly disposed on at least one side of the current collector, and a polymer film disposed on the surface of the electrode active material layer away from the current collector side, and the polymer has a cross - linked structure.

[0053] Specifically, the pole piece of the present application is obtained by forming a polymer film on the surface of the positive electrode film layer or the negative electrode film layer of the positive electrode plate or the negative electrode plate away from the current collector side. The pole piece of the present application can be a positive electrode plate or a negative electrode plate, and is preferably a positive electrode plate. When the pole piece of the present application is a positive electrode plate, the negative electrode plate is not particularly limited and can be any of the above - mentioned negative electrode plates.

[0054] [Positive electrode plate]

[0055] The positive electrode plate includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, and the positive electrode film layer includes positive electrode active materials.

[0056] As an example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on the two opposite surfaces of the positive current collector.

[0057] In any embodiment, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer disposed on at least one surface of the polymer material base layer. The composite current collector can be formed by disposing a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0058] In any embodiment, the positive electrode active material can be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of a battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and their modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure can include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0059] In any embodiment, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] In any embodiment, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0061] In any embodiment, the positive electrode plate can be prepared in the following manner: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0062] [Negative electrode plate]

[0063] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0064] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on the two surfaces of the negative electrode current collector.

[0065] In any embodiment, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer provided on at least one surface of the polymer material substrate. The composite current collector can be formed by setting a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0066] In any embodiment, the negative electrode active material can be the negative electrode active material for batteries known in the art. By way of example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone, or two or more of them can be used in combination.

[0067] In any embodiment, the negative electrode film layer may further optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0068] In any embodiment, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] In any embodiment, the negative electrode film layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0070] In any embodiment, the negative electrode plate can be prepared by the following method: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0071] [Electrolyte]

[0072] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application has no specific limitation on the type of electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0073] In any embodiment, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0074] In any embodiment, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0075] In any embodiment, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0076] In any embodiment, the electrolyte may further optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature or low-temperature performance, etc.

[0077] [Polymer film]

[0078] As described above, the electrode sheet of the present application has a polymer film disposed on the surface of the electrode active material layer away from the current collector. The polymer film of the present application has a cross-linked structure. By cross-linking the polymer to form a cross-linked structure, a three-dimensional network structure is formed microscopically in the polymer film, which can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film.

[0079] In any embodiment, the polymer film is an insulating layer, and its insulation resistance R≥1 MΩ, and may be selected as R≥3000 MΩ. There is no particular limitation on its upper limit. Usually, R≤9000 MΩ, and may be selected as R≤6000 MΩ.

[0080] In some embodiments, the insulation resistance R of the polymer film may be selected as 1 MΩ, 10 MΩ, 100 MΩ, 1000 MΩ, 2000 MΩ, 3000 MΩ, 4000 MΩ, 5000 MΩ, 6000 MΩ, 7000 MΩ, 8000 MΩ, or 9000 MΩ, or a range between any two of the above values.

[0081] By making the insulation resistance of the polymer film within the above range, the effect of insulating the positive and negative electrodes can be achieved better, and it does not affect the transmission of lithium ions, ensuring good adhesion between the positive and negative electrodes, so that the battery cell can be used safely.

[0082] In any embodiment, the polymer includes at least one of polyester, polyether, polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, polyvinyl alcohol, etc.

[0083] In any embodiment, the monomer or prepolymer of the polyester includes at least one of (meth)acrylate and isocyanate; optionally methyl methacrylate, ethyl methacrylate or butyl methacrylate, hexamethylene diisocyanate; the monomer or prepolymer of the polyether includes at least one of halogenated propylene oxide-polyol, ethylene oxide and propylene oxide, optionally epichlorohydrin-glycerol, and the prepolymer refers to the product formed by preliminary polymerization of monomers.

[0084] By using specific polymers such as the polyester, polyether, polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, polyvinyl alcohol, etc. to form a polymer film, a polymer film with more excellent ductility and insulation can be obtained. As a result, the thickness of the polymer film can be made thinner, which can not only improve the energy density and cycling characteristics of the lithium-ion battery, but also prevent the electrode sheet from being damaged based on the ductility of the polymer film, and can improve the stability and safety of the lithium-ion battery. In addition, by selecting the polymer, a three-dimensional network structure can be formed better during cross-linking, which can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film.

[0085] In any embodiment, the thickness of the polymer film is 1 μm - 8 μm, optionally 1 μm - 5 μm, and further optionally 1 μm - 3 μm.

[0086] In some embodiments, the thickness of the polymer film can be optionally 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm, or the range between any two of the above values.

[0087] By making the thickness of the polymer film within the above range, the thickness of the polymer film can be significantly reduced compared to the thickness of the traditional separator, while realizing the functions of the traditional separator while improving the volumetric energy density and cycling characteristics of the battery.

[0088] In any embodiment, the ionic conductivity of the polymer film after absorbing the electrolyte is 1×10 -3 -1×10 -2 s / cm, optionally 5×10 -3 -1×10 -2 s / cm, and the electrolyte is a mixture in which LiPF with a concentration of 1 mol / L is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate with a volume ratio of 1∶1∶1. 6 of the mixture.

[0089] In some embodiments, the ionic conductivity may be 1×10 -3 s / cm, 2×10- 3 s / cm, 3×10 -3 s / cm, 4×10 -3 s / cm, 5×10 -3 s / cm, 6×10 -3 s / cm, 7×10 -3 s / cm, 8×10 -3 s / cm, 9×10 -3 s / cm or 1×10 -2 s / cm, or a range between any two of the above values.

[0090] By making the ionic conductivity of the polymer membrane within the above range after absorbing the electrolyte, ions can more easily pass through the polymer membrane layer, thus improving the battery kinetics.

[0091] In any embodiment, the swelling ratio of the polymer membrane is 100%-200%, and may be 130%-180%. The measurement conditions for the swelling ratio are as follows: After making the polymer into a film and drying it completely, cut it into a specimen weighing 0.5 g with dimensions of 30 mm×30 mm×5 mm, immerse it in the following electrolyte, seal it and place it in an environment at 70°C. After 7 days, take it out, wipe the electrolyte on the surface dry, weigh it and record it. The swelling ratio is calculated by the following formula:

[0092] Swelling ratio (%) = (W1 - W0) / W0×100%, where W0 is the weight of the film before impregnation, and W1 is the weight of the film after impregnation. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1 and dissolved with 1 mol / L of LiPF 6 mixture.

[0093] In some embodiments, the swelling ratio of the polymer may be 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190% or 200%, or a range between any two of the above values.

[0094] By making the swelling ratio of the polymer membrane within the above range, the polymer can easily achieve ionic conduction in the electrolyte.

[0095] [Method for manufacturing a pole piece]

[0096] The method for manufacturing the pole piece of the present application includes the following steps:

[0097] An electrode active material layer is directly disposed on at least one side of the current collector to obtain an electrode sheet, and the electrode active material layer includes an electrode active substance, a conductive agent, and a binder;

[0098] A mixed solution formed by a polymer monomer, an initiator, and a crosslinking agent is coated on the surface of the electrode active material layer on the side away from the current collector on at least one side of the electrode sheet;

[0099] The mixed solution is polymerized to form a polymer film cured on the surface of the electrode active substance to obtain a sheet.

[0100] Through the method for manufacturing the sheet of the present application, the sheet with a polymer film of the present application can be obtained, and its thickness is smaller than that of a traditional separator. By using the sheet with the specific structure of the present application, the manufactured lithium-ion battery does not include a separator, and can not only improve the energy density and cycle characteristics of the lithium-ion battery, but also prevent the sheet from being damaged based on the ductility of the polymer film, and can improve the stability and safety of the lithium-ion battery. In addition, by making the polymer film have a crosslinked structure, a three-dimensional network structure can be formed microscopically on the polymer film, which can not only ensure that the polymer film swells but does not dissolve in the electrolyte, but also significantly improve the mechanical properties of the polymer film. Furthermore, by disposing a polymer film on the sheet, since there is no need to additionally dispose a separator, the separator part in the preparation of a traditional battery cell is omitted, and in addition, the loss caused by problems such as wrinkling and misalignment of the separator during the preparation of the battery cell is avoided, reducing the manufacturing cost of the battery cell.

[0101] [Initiator]

[0102] The initiator used in the manufacturing method is a thermal initiator or a photoinitiator. The thermal curing temperature of the thermal initiator is 25°C - 120°C, and the photo-curing wavelength of the photoinitiator is 200nm - 400nm or 760nm - 1000nm. Specifically, the thermal initiator includes at least one of azobisisobutyronitrile, dibenzoyl peroxide, lauroyl peroxide, azobisisoheptonitrile, and can be selected as azobisisobutyronitrile; the photoinitiator includes at least one of methyl benzoylformate, 2-hydroxy-2-methyl-1-phenylpropanone, or benzophenone, and can be selected as benzophenone.

[0103] In some embodiments, the thermal curing temperature of the thermal initiator can be selected from 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, or the range between any two of the above values. In some embodiments, the photocuring wavelength of the photoinitiator can be selected from 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm or 400nm, or the range between any two of the above values.

[0104] By using the thermal initiator or photoinitiator, the polymerization reaction can proceed more smoothly to form a polymer film with a thin thickness, excellent ductility and insulation.

[0105] [Crosslinking agent]

[0106] The crosslinking agent used in the manufacturing method is a diene crosslinking agent, such as bisphenol A diallyl ether, divinylbenzene and polyethylene glycol diacrylate, and polyethylene glycol diacrylate can be selected.

[0107] The content ratio of the polymer monomer, initiator and crosslinking agent in the mixture is (90 - 99.8)∶(0.1 - 5)∶(0.1 - 5), and (98 - 99.4)∶(0.1 - 0.5)∶(0.5 - 1.5) can be selected.

[0108] By setting the content ratio of the polymer monomer, initiator and crosslinking agent within the above range, it is possible to more easily form a polymer film with a thin thickness, excellent ductility and insulation, which helps to improve the energy density, cycle characteristics, battery stability and safety of the battery.

[0109] [Coating]

[0110] The coating method used in the manufacturing method includes at least one of gravure coating, microgravure coating or spraying. The coating speed is 1m / min - 150m / min, and 60m / min - 90m / min can be selected.

[0111] In some embodiments, the coating speed can be selected from 1m / min, 10m / min, 20m / min, 30m / min, 40m / min, 50m / min, 60m / min, 70m / min, 80m / min, 90m / min, 100m / min, 110m / min, 120m / min, 130m / min, 140m / min or 150m / min, or the range between any two of the above values.

[0112] By adopting the coating method and making the coating speed within the above range, it is possible to make the thickness of the polymer film more uniform while taking into account the coating efficiency.

[0113] In one embodiment of the present application, an electrode assembly having the above-mentioned electrode sheet is provided.

[0114] [Electrode assembly]

[0115] The electrode assembly of the present application includes a positive electrode sheet and a negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet is the above-mentioned electrode sheet of the present application. Optionally, only the positive electrode sheet is the above-mentioned electrode sheet of the present application.

[0116] In one embodiment of the present application, a manufacturing method of an electrode assembly having the above-mentioned electrode sheet is provided.

[0117] [Manufacturing method of electrode assembly]

[0118] The electrode assembly of the present application is an electrode assembly prepared by laminating or winding a positive electrode sheet and a negative electrode sheet. The types of the positive and negative electrode sheets of the electrode assembly are not particularly limited as long as they have the above-mentioned electrode sheet of the present application. It can be made by laminating or winding the film-forming positive electrode sheet of the present application and the film-forming negative electrode sheet of the present application; it can also be made by laminating or winding the film-forming positive electrode sheet of the present application and a negative electrode sheet other than the film-forming negative electrode sheet of the present application; it can also be made by laminating or winding a positive electrode sheet other than the film-forming positive electrode sheet of the present application and the film-forming negative electrode sheet of the present application.

[0119] The fifth aspect of the present application further provides a secondary battery, which includes the above-mentioned electrode assembly of the present application.

[0120] The present application has no particular limitation on the shape of the secondary battery, and it can be cylindrical, square or any other shape.

[0121] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries included in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0122] In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0123] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0124] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0125] As another example, the device can be a mobile phone, tablet computer, laptop, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0126] Embodiment

[0127] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those embodiments where specific technologies or conditions are not indicated, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0128] Embodiment 1

[0129] 1) Electrolyte

[0130] In an argon atmosphere glove box (H 2 O content < 10 ppm, O 2 content < 1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:1:1 and dissolved with LiPF 6 to a concentration of 1 mol / L, and stirred evenly to prepare the electrolyte.

[0131] 2) Preparation of the positive electrode sheet

[0132] The positive electrode active material lithium iron phosphate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed evenly at a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent system to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of a positive electrode current collector aluminum foil with a thickness of 13 μm, and the coating speed was 30 m / min; the temperature of the coating oven was 110 °C, and then it was cold-pressed and slit to obtain the positive electrode sheet.

[0133] 3) Preparation of Polymer Film

[0134] Methyl methacrylate, polyethylene glycol diacrylate, and azobisisobutyronitrile were stirred and mixed to obtain a mixed solution. The mass ratio of methyl methacrylate, polyethylene glycol diacrylate, and azobisisobutyronitrile in the coating slurry was 99.4∶0.5∶0.1. The mixed solution was respectively coated on both sides of the positive active material of the prepared positive electrode sheet using a microgravure coating method, and heated to 80 °C to initiate polymerization, forming a polymer film on the surface of the positive electrode sheet.

[0135] 4) Preparation of Negative Electrode Sheet

[0136] The negative active material graphite, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed evenly in a deionized water solvent system according to a mass ratio of 96∶2∶1∶1 to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on a negative current collector copper foil with a thickness of 13 μm, and the coating speed was 25 m / min, and the temperature of the coating oven was 110 °C; then it was cold-pressed and slit to obtain a negative electrode sheet.

[0137] 5) Preparation of Battery

[0138] The film-forming positive electrode sheet and the negative electrode sheet were stacked in sequence and wound to obtain a bare battery core, the electrode tabs were welded, the bare battery core was placed in an outer package, the prepared electrolyte was injected into the dried battery core, and then through processes such as encapsulation, standing, formation, shaping, and capacity testing, the lithium-ion secondary battery product of Example 1 was obtained.

[0139] Example 2

[0140] Except that the monomer used was butyl methacrylate, other parts were the same as in Example 1.

[0141] Example 3

[0142] Except that the monomer used was epichlorohydrin-glycerol, other parts were the same as in Example 1.

[0143] Examples 4-5

[0144] Except that benzophenone and dibenzoyl peroxide were used as initiators respectively, other parts were the same as in Example 1.

[0145] Examples 6-7

[0146] Except that bisphenol A diallyl ether and divinylbenzene were used as crosslinking agents respectively, other parts were the same as in Example 1.

[0147] Example 10

[0148] Except that the negative electrode sheet was used as the electrode sheet, other parts were the same as in Example 1.

[0149] 1) Preparation of negative electrode sheet

[0150] The negative electrode active material graphite, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were stirred and mixed evenly in a deionized water solvent system according to a mass ratio of 96:2:1:1 to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on a negative electrode current collector copper foil with a thickness of 13 μm, the coating speed was 25 m / min, and the temperature of the coating oven was 110 °C; then, after cold pressing and slitting, a negative electrode sheet was obtained.

[0151] 2) Preparation of polymer film

[0152] Methyl methacrylate, polyethylene glycol diacrylate, and azobisisobutyronitrile were stirred and mixed to obtain a mixed solution. The mass ratio of methyl methacrylate, polyethylene glycol diacrylate, and azobisisobutyronitrile in the coating slurry was 99.4:0.5:0.1. The mixed solution was coated on both sides of the positive electrode active material of the prepared negative electrode sheet using a microgravure coating method, and polymerization was initiated to form a polymer film on the surface of the positive electrode sheet.

[0153] Example 11

[0154] Except for using the stacking process, other parts are the same as in Example 1.

[0155] Example 12

[0156] Except for using the negative electrode sheet as the electrode sheet, other parts are the same as in Example 11.

[0157] Comparative Example 1

[0158] Except for not forming a polymer film on the positive electrode sheet and using a polyethylene (PE) porous polymer film with a thickness of 9 μm as the separator, other parts are the same as in Example 1.

[0159] Comparative Example 2

[0160] Except for not forming a polymer film on the positive electrode sheet and using a ceramic and polymer film layer as the separator, other parts are the same as in Example 1.

[0161] Preparation of ceramic and polymer film layer

[0162] Aluminum oxide, PVDF, and NMP were stirred and mixed according to a mass ratio of 4:6:90 to obtain a mixed solution. The mixed solution was coated on both sides of the positive electrode active material of the prepared positive electrode sheet using a microgravure coating method and dried at 120 °C to obtain a positive electrode sheet.

[0163] Comparative Example 3

[0164] When polymerizing the polymer, no crosslinking agent is used to form a polymer film with a non-crosslinked structure. Except for this, the other parts are the same as in Example 1.

[0165] Performance measurement

[0166] Film thickness measurement

[0167] Use a scanning electron microscope for the electrode sheet with the film layer to measure the thickness of its film layer.

[0168] Energy density calculation

[0169] Equipment: Battery performance test system of Shenghong Electric Co., Ltd. (equipment model: BTS05 / 10C8D-HP), test item: discharge capacity

[0170] Test conditions: temperature 25°C, voltage 2.5V - 3.65V, rate 1C

[0171] Calculation method: Calculate the energy density based on the discharge capacity and volume. Based on the energy density of Comparative Example 1 (9μm separator), calculate the energy density improvement ratio.

[0172] Cyclic capacity retention test:

[0173] Perform cyclic charge and discharge tests (charge rate: 1C, discharge rate: 1C) on the battery to be evaluated for a preset number of cycles (500 cycles), and record the discharge capacity of the 500th cycle and the initial cycle discharge capacity. The capacity retention rate is the ratio of the discharge capacity of the 500th cycle to the initial cycle discharge capacity.

[0174] Anti-breakage test:

[0175] Fold the electrode sheet with the film layer and roll it back and forth once with a pressure roller weighing 2 Kg, then flatten the electrode sheet. If there is no light leakage at the folded part, it is considered qualified. Measure 5 parallel samples in each group.

[0176] Tensile strength test:

[0177] After making the polymer into a 1mm thick film and completely drying it, cut it into samples with a width of 15mm and a length of 200mm. Fix the samples to the test fixture of a tensile testing machine made by High Tech. The test speed is 250mm / min, and the standard distance S0 between the two fixtures of the tensile testing machine is set to 50mm. Record the tensile strength and displacement. The maximum value of the tensile strength in the displacement curve is the tensile strength of the test specimen.

[0178] The relevant parameters of the positive electrode materials in Examples 1 - 12 and Comparative Examples 1 - 7 are shown in Table 1 below.

[0179] Table 1: Test Results of Examples 1-12 and Comparative Examples 1-3

[0180]

[0181] According to the above results, it can be seen that in Examples 1-12, by using the electrode sheet of the present application as the positive electrode sheet or the negative electrode sheet, the thickness of the formed polymer film is significantly smaller than that in the comparative examples, and the tensile strength of the polymer film is significantly enhanced. As a result, the energy density and the cycle capacity retention rate of the obtained battery are both significantly improved, and the evaluation of the anti-corner breakage of the electrodes in the battery is good.

[0182] In contrast, in Comparative Example 1, a traditional polyethylene separator was used, and as a result, its thickness was too large. In Comparative Example 2, a composite film layer of ceramic and polymer was formed on the electrode sheet. In Comparative Example 3, an uncrosslinked polymer film was used. As a result, the energy density in Comparative Example 1 was not improved at all; in Comparative Example 2, due to the formation of a rigid ceramic film layer, the electrode was damaged and cracked during winding, which in turn caused a short circuit between the positive and negative electrodes; in Comparative Example 3, the polymer forming the polymer film had a linear structure and was stabilized by intermolecular interactions. When immersed in the electrolyte, the smaller electrolyte molecules diffused between the polymer molecules, reducing the intermolecular binding of the polymer molecules. The polymer molecular chains obtained the ability to move, and thus diffused into the electrolyte, resulting in the dissolution of the polymer film and a short circuit between the positive and negative electrodes, so that the energy density and the cycle capacity retention rate could not be measured.

[0183] It should be noted that the present application is not limited to the above-described embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same function and effect as the technical idea within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A pole piece, characterized in that, it includes a current collector, an electrode active material layer directly disposed on at least one side of the current collector, and a polymer film disposed on the surface of the electrode active material layer away from the current collector side, and the polymer has a cross-linked structure.

2. The pole piece according to claim 1, characterized in that, the polymer film is an insulating layer, and the insulation resistance R≥1MΩ, and optionally 3000MΩ≤R≤9000MΩ.

3. The pole piece according to claim 1 or 2, characterized in that, the polymer includes at least one of polyester, polyether, polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, and polyvinyl alcohol.

4. The pole piece according to any one of claims 1 to 3, characterized in that, the monomer or prepolymer of the polyester includes at least one of (meth)acrylate and isocyanate; optionally includes at least one of methyl methacrylate, ethyl methacrylate or butyl methacrylate, and hexamethylene diisocyanate; the monomer or prepolymer of the polyether includes at least one of halogenated propylene oxide-polyol, ethylene oxide, and propylene oxide, and optionally epichlorohydrin-glycerol, the prepolymer refers to the product formed by the preliminary polymerization of monomers.

5. The pole piece according to any one of claims 1 to 4, characterized in that, the thickness of the polymer film is 1μm - 8μm, optionally 1μm - 5μm, and further optionally 1μm - 3μm.

6. The pole piece according to any one of claims 1 to 5, characterized in that, The ionic conductivity of the polymer membrane after absorbing the electrolyte is 10 -3 -10 -2 S / cm, optionally 5×10 -3 -10 -2 S / cm, The electrolyte is a mixture in which 1 mol / L of LiPF is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate with a volume ratio of 1:1:

1. 6 ​ 7. The pole piece according to any one of claims 1 to 6, characterized in that, the swelling ratio of the polymer film is 100% - 200%, optionally 130% - 180%, the measurement conditions of the swelling ratio are as follows: After the polymer is made into a film and completely dried, it is cut into a specimen weighing 0.5g with a size of 30mm×30mm×5mm, impregnated in the following electrolyte, sealed and placed in an environment of 70°C. After 7 days, it is taken out, wiped dry the surface electrolyte, weighed and recorded. The swelling ratio is calculated by the following formula: Swelling ratio (%) = (W1 - W0) / W0×100%, where W0 is the weight of the film before impregnation, and W1 is the weight of the film after impregnation. The electrolyte for measuring the swelling ratio is a mixture in which 1 mol / L of LiPF is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate with a volume ratio of 1:1:

1. 6 ​ 8. A manufacturing method of the pole piece according to any one of claims 1 to 7, characterized in that, it includes the following processes: Directly dispose an electrode active material layer on at least one side of the current collector to obtain an electrode pole piece, and the electrode active material layer includes an electrode active substance, a conductive agent, and a binder; Coat a mixed solution formed by a polymer monomer, an initiator, and a cross-linking agent on the surface of the electrode active material layer away from the current collector side on at least one side of the electrode pole piece; Cause the mixed solution to polymerize, and cure to form a polymer film on the surface of the electrode active substance to obtain a pole piece.

9. The manufacturing method of the pole piece according to claim 8, characterized in that, the electrode active substance is a positive electrode active substance or a negative electrode active substance; the positive electrode active substance includes one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds; The negative electrode active material includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate; The conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyamide, poly(acrylonitrile-acrylate), and poly(styrene-acrylate) as the negative electrode binder, and includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin as the positive electrode binder.

10. The method for manufacturing a pole piece according to claim 8 or 9, characterized in that, The initiator is a thermal initiator or a photoinitiator, The thermal curing temperature of the thermal initiator is 25°C - 120°C, and the photo-curing wavelength of the photoinitiator is 200nm - 400nm or 760nm - 1000nm.

11. The method for manufacturing a pole piece according to claim 10, characterized in that, The thermal initiator includes at least one of azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, and azobisisoheptonitrile, and may be azobisisobutyronitrile; The photoinitiator includes at least one of methyl benzoylformate, 2-hydroxy-2-methyl-1-phenylpropanone, or benzophenone, and may be benzophenone.

12. The method for manufacturing a pole piece according to any one of claims 8 to 11, characterized in that, The crosslinking agent is a diene crosslinking agent, and may be polyethylene glycol diacrylate.

13. The method for manufacturing a pole piece according to any one of claims 8 to 12, characterized in that, The content ratio of the polymer monomer, initiator, and crosslinking agent in the mixed solution is (90 - 99.8)∶(0.1 - 5)∶(0.1 - 5), and may be (98 - 99.4)∶(0.1 - 0.5)∶(0.5 - 1.5).

14. The method for manufacturing a pole piece according to any one of claims 8 to 13, characterized in that, The coating includes at least one of gravure coating, microgravure coating, or spraying.

15. The method for manufacturing a pole piece according to any one of claims 8 to 14, characterized in that, The coating speed is 1m / min - 150m / min, and may be 60m / min - 90m / min.

16. An electrode assembly, characterized in that, It includes a positive electrode pole piece and a negative electrode pole piece, At least one of the positive electrode pole piece and the negative electrode pole piece is the pole piece according to any one of claims 1 to 7, and optionally only the positive electrode pole piece is the pole piece according to any one of claims 1 to 7.

17. A method for manufacturing the electrode assembly according to claim 16, characterized in that, The positive electrode pole piece and the negative electrode pole piece are prepared into the electrode assembly through a stacking process or a winding process.

18. A secondary battery, characterized in that, It includes the electrode assembly according to claim 16.

19. An electrical device, It is characterized in that It includes the secondary battery described in claim 18

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