Secondary battery and preparation method thereof, electrode plate and power-using device

Abstract

The present application relates to a secondary battery and a preparation method thereof, an electrode plate and an electric device. The secondary battery includes an electrode plate, which includes a current collector and an electrode active layer disposed on at least one surface of the current collector, wherein the electrode active layer contains an electrode active material and a polymer binder; the polymer binder includes a core and a shell covering at least part of the surface of the core, wherein at least one of the shell and the core includes a polymer, and both the shell and the core have a pore structure, wherein the number of pores in the shell is greater than the number of pores in the core. Such a design can improve the fast charging performance of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and a preparation method thereof, an electrode plate and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of secondary batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. The great development of secondary batteries has made the consumer market put forward higher requirements for their fast charging performance. Therefore, how to improve the fast charging performance of secondary batteries is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a secondary battery and a preparation method thereof, an electrode plate and an electrical device, aiming to improve the fast charging performance of the secondary battery.

[0005] In a first aspect of the present application, a secondary battery is provided, the secondary battery comprising an electrode plate, the electrode plate comprising a current collector and an electrode active layer disposed on at least one surface of the current collector, the electrode active layer comprising an electrode active material and a polymer binder;

[0006] The polymer binder includes a core and a shell covering at least a portion of the surface of the core, at least one of the shell and the core includes a polymer, both the shell and the core have a pore structure, and the number of pores in the shell is greater than the number of pores in the core.

[0007] In the above-mentioned secondary battery, the number of pores in the shell of the polymer binder is greater than the number of pores in the core, which can improve the transfer rate of active ions between the electrode active material and the electrolyte, reduce the transmission resistance of the active ions, and increase the electrolyte storage capacity, improve the average liquid absorption rate of the electrode plate, and improve the interface of the electrode plate. Therefore, during the high-current charge and discharge cycle of the secondary battery, the active ions can be quickly embedded in the electrode active material or released from the electrode active material, thereby improving the fast charging performance of the secondary battery.

[0008] In some embodiments, the average pore size of the core is 0.5 nm to 3 nm. When the average pore size of the core is within the above range, active ions can migrate quickly in the polymer binder, which is beneficial to further improve the fast charging performance of the secondary battery. Furthermore, the average pore size of the core is 0.5 nm to 1.5 nm.

[0009] In some embodiments, the average pore size of the shell is 0.5 nm to 3 nm. When the average pore size of the shell is within the above range, active ions can migrate quickly in the polymer binder, which is beneficial to further improve the fast charging performance of the secondary battery. Furthermore, the average pore size of the shell is 0.5 nm to 1.5 nm.

[0010] In some embodiments, the outer shell and the inner core both comprise a polymer, and the polymer in the inner core is different from the polymer in the outer shell.

[0011] In some embodiments, the polymer in the inner core includes one or more of polybutadiene, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polybutyl acrylate, and a graft copolymer of polyvinyl alcohol and isooctyl acrylate.

[0012] In some embodiments, the polymer in the shell includes one or more of a polymer containing an acrylate structural unit and a polymer containing an olefin structural unit.

[0013] In some embodiments, the polymer containing acrylic acid ester structural units includes one or more of styrene-methyl methacrylate copolymer, polymethyl methacrylate, styrene-methyl methacrylate copolymer, and methyl methacrylate-isobornyl methacrylate copolymer.

[0014] In some embodiments, the polymer containing olefin structural units includes one or more of polystyrene and styrene-methyl methacrylate copolymer.

[0015] By designing the polymer in the core to be different from the polymer in the shell, or selecting the above-mentioned types of materials for the polymer in the core and / or the polymer in the shell, the adhesion between the polymer binder and the electrode active material can be improved, and the fast charging performance of the secondary battery can be further improved.

[0016] In some embodiments, the volume average particle size Dv50 of the polymer binder is 100 nm to 500 nm.

[0017] In some embodiments, the average liquid absorption rate of the electrode plate is 1 mL / s to 4.5 mL / s. With such a design, the active ions have a suitable migration path, which is more conducive to improving the fast charging performance of the secondary battery.

[0018] In some embodiments, the electrode plate is a negative electrode plate, the current collector is a negative electrode current collector, the electrode active layer is a negative electrode active layer, and the electrode active material is a negative electrode active material. When the electrode plate is a negative electrode plate, introducing the above polymer binder into the negative electrode plate can reduce the transmission resistance of active ions and the risk of lithium plating of the negative electrode plate.

[0019] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

[0020] In some embodiments, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence along a surface direction away from the negative electrode current collector, the first negative electrode active layer and the second negative electrode active layer both contain the polymer binder, and the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer. With such a design, the second negative electrode active layer can retain certain pores and active ion transmission channels, which is conducive to improving the infiltration rate of the electrolyte from the first negative electrode active layer to the second negative electrode active layer, thereby improving the transmission rate of active ions and further improving the fast charging performance of the secondary battery.

[0021] In some embodiments, the mass percentage of the polymer binder in the first negative electrode active layer is 0.8% to 1.8%, thereby improving the adhesion between the polymer binder and the negative electrode active material in the first negative electrode active layer and further improving the fast charging performance of the secondary battery.

[0022] In some embodiments, the mass percentage of the polymer binder in the second negative electrode active layer is 0.6% to 1.8%, thereby improving the adhesion between the polymer binder and the negative electrode active material in the second negative electrode active layer and further improving the fast charging performance of the secondary battery.

[0023] In some embodiments, the first negative electrode active layer and the second negative electrode active layer both contain the negative electrode active material, and the mass percentage of the negative electrode active material in the first negative electrode active layer is less than or equal to the mass percentage of the negative electrode active material in the second negative electrode active layer.

[0024] In some embodiments, the mass percentage of the negative electrode active material in the first negative electrode active layer is 96% to 97%.

[0025] In some embodiments, the mass percentage of the negative electrode active material in the second negative electrode active layer is 97% to 98%.

[0026] In some embodiments, the electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material.

[0027] In a second aspect of the present application, a method for preparing a secondary battery is provided, comprising the steps of preparing an electrode sheet; the steps of preparing the electrode sheet include:

[0028] emulsion polymerizing a first solution containing a first pore-forming template and a first monomer to form an emulsion containing a core;

[0029] A second solution containing a second pore-forming template agent and a second monomer is mixed with the solution containing the inner core, and a shell is formed on at least a portion of the surface of the inner core through emulsion polymerization to obtain a polymer binder intermediate; the mass fraction of the second pore-forming template agent in the second solution is higher than the mass fraction of the first pore-forming template agent in the first solution;

[0030] Removing the first pore-forming template agent and the second pore-forming template agent from the polymer binder intermediate, so that both the core and the shell form a pore structure, and the number of pores in the shell is greater than the number of pores in the core, to obtain a polymer binder;

[0031] The electrode slurry containing the electrode active material and the polymer binder is coated on at least one surface of the current collector, and an electrode active layer is formed through drying to obtain the electrode plate.

[0032] In the secondary battery prepared by the above preparation method, the number of holes in the shell of the polymer binder is greater than the number of holes in the core, which can improve the transfer rate of active ions between the electrode active material and the electrolyte, reduce the transmission resistance of active ions, and increase the electrolyte storage capacity, improve the average liquid absorption rate of the electrode plate, and improve the interface of the electrode plate. Therefore, during the high-current charge and discharge cycle of the secondary battery, the active ions can be quickly embedded in the electrode active material or released from the electrode active material, thereby improving the fast charging performance of the secondary battery. In addition, the above preparation method is relatively simple and suitable for large-scale production.

[0033] In some embodiments, the current collector is a negative electrode current collector, the electrode active material is a negative electrode active material, the electrode slurry is a negative electrode slurry, the electrode active layer is a negative electrode active layer, and the electrode plate is a negative electrode plate.

[0034] In some embodiments, the electrode slurry comprising an electrode active material and the polymer binder is coated on at least one surface of a current collector, and an electrode active layer is formed by drying. The step of obtaining the electrode sheet comprises:

[0035] Applying a first negative electrode slurry comprising the negative electrode active material and the polymer binder on at least one surface of the negative electrode current collector to prepare a first negative electrode active layer to obtain a negative electrode sheet intermediate;

[0036] The second negative electrode slurry containing the negative electrode active material is coated on the surface of the negative electrode plate intermediate away from the negative electrode current collector, and a second negative electrode active layer is formed after drying to obtain the electrode plate, and the electrode plate is the negative electrode plate; the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer. With such a design, the second negative electrode active layer can retain certain pores and active ion transmission channels, which is conducive to improving the infiltration rate of the electrolyte from the first negative electrode active layer to the second negative electrode active layer, thereby improving the transmission rate of active ions and further improving the fast charging performance of the secondary battery.

[0037] In some embodiments, the second negative electrode slurry further includes the polymer binder.

[0038] In some embodiments, the electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material.

[0039] In some embodiments, the first monomer includes one or more of an olefin compound, an acrylate compound, and an enol compound.

[0040] In some embodiments, the second monomer includes one or more of an olefin compound and an acrylate compound.

[0041] In some embodiments, the first pore-forming template agent and the second pore-forming template agent each independently include an inorganic salt, and the inorganic salt includes one or more of ammonium phosphate, ammonium sulfate and ammonium chloride.

[0042] In some embodiments, the first solution further comprises one or more of a first initiator, a first emulsifier, and a first molecular weight regulator.

[0043] In some embodiments, the second solution further comprises one or more of a second initiator, a second emulsifier, and a second molecular weight regulator.

[0044] In some embodiments, the first initiator and the second initiator each independently include one or more of a persulfate and an azo compound.

[0045] In some embodiments, the first emulsifier and the second emulsifier each independently include one or more of anionic emulsifiers, nonionic emulsifiers, and amphoteric emulsifiers.

[0046] In some embodiments, the first molecular weight regulator and the second molecular weight regulator each independently include one or more of a thiol compound, a halogenated compound, and a nitroxide free radical compound.

[0047] In a third aspect of the present application, an electrode plate is provided, the electrode plate comprising a current collector and an electrode active layer disposed on at least one surface of the current collector, the electrode active layer comprising an electrode active material and a polymer binder;

[0048] The polymer binder comprises a core and a shell covering at least a portion of the surface of the core, the shell and the core both have pore structures, and the number of pores in the shell is greater than the number of pores in the core.

[0049] The above-mentioned electrode plate has the same advantages as the electrode plate in the secondary battery of the present application.

[0050] The fourth aspect of the present application provides an electrical device, comprising at least one of the secondary battery described in the first aspect of the present application, the secondary battery prepared by the preparation method described in the second aspect of the present application, and the electrode plate described in the third aspect of the present application.

[0051] The electrical device of the present application includes at least one of the above-mentioned secondary battery of the present application, the secondary battery manufactured by the above-mentioned preparation method of the present application, and the above-mentioned electrode plate of the present application, and thus has at least the same advantages as the secondary battery, the secondary battery manufactured by the above-mentioned preparation method, or the electrode plate.

[0052] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0054] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0055] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0056] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0057] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

[0058] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0059] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0060] Description of reference numerals:

[0061] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0062] Below, some embodiments of the secondary battery and its preparation method, electrode plate and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0063] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0064] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0066] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0067] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0068] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0069] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0070] The fast charging performance of secondary batteries is related to the charging and discharging current. In the case of high current charging and discharging, the electrode plates may be limited by the lithium insertion speed, which may cause lithium deposition on the electrode plates, thereby greatly limiting the fast charging capability of secondary batteries.

[0071] Based on this, an embodiment of the present application provides a secondary battery, which includes an electrode plate, the electrode plate includes a current collector and an electrode active layer disposed on at least one surface of the current collector, and the electrode active layer contains an electrode active material and a polymer binder;

[0072] The polymer binder comprises a core and a shell covering at least a portion of the surface of the core, at least one of the shell and the core comprises a polymer, both the shell and the core have a pore structure, and the number of pores in the shell is greater than the number of pores in the core.

[0073] In the above-mentioned secondary battery, the number of pores in the shell of the polymer binder is greater than the number of pores in the core, which can improve the transfer rate of active ions between the electrode active material and the electrolyte, reduce the transmission resistance of the active ions, and increase the electrolyte storage capacity, improve the average liquid absorption rate of the electrode plate, and improve the interface of the electrode plate. Therefore, during the high-current charge and discharge cycle of the secondary battery, the active ions can be quickly embedded in the electrode active material or released from the electrode active material, thereby improving the fast charging performance of the secondary battery.

[0074] As a non-limiting example, the current collector has two surfaces opposite to each other in its thickness direction, and the electrode active layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0075] In some embodiments, the average pore size of the kernel is 0.5nm~3nm. When the average pore size of the kernel is within the above range, the active ions can migrate quickly in the polymer binder, which is beneficial to further improve the fast charging performance of the secondary battery. Specifically, the average pore size of the kernel includes but is not limited to: 0.5nm, 0.8nm, 1nm, 1.2nm, 1.5nm, 1.8nm, 2nm, 2.3nm, 2.5nm, 2.8nm, 3nm or a range between any two of the foregoing. Further, the average pore size of the kernel is 0.5nm~1.5nm.

[0076] In some embodiments, the average pore size of the shell is 0.5nm~3nm. When the average pore size of the shell is within the above range, the active ions can migrate quickly in the polymer binder, which is beneficial to further improve the fast charging performance of the secondary battery. Specifically, the average pore size of the shell includes but is not limited to: 0.5nm, 0.8nm, 1nm, 1.2nm, 1.5nm, 1.8nm, 2nm, 2.3nm, 2.5nm, 2.8nm, 3nm or a range between any two of the foregoing. Further, the average pore size of the shell is 0.5nm~1.5nm.

[0077] In some embodiments, the outer shell and the inner core both comprise a polymer, and the polymer in the inner core is different from the polymer in the outer shell.

[0078] In some embodiments, the polymer in the inner core includes one or more of polybutadiene, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polybutyl acrylate, and a graft copolymer of polyvinyl alcohol and isooctyl acrylate.

[0079] In some embodiments, the polymer in the shell includes one or more of a polymer containing an acrylate-based structural unit and a polymer containing an olefin-based structural unit.

[0080] By designing the polymer in the core to be different from the polymer in the shell, or selecting the above-mentioned types of materials for the polymer in the core and / or the polymer in the shell, the adhesion between the polymer binder and the electrode active material can be improved, and the fast charging performance of the secondary battery can be further improved.

[0081] In some embodiments, the polymer containing acrylate structural units includes one or more of styrene-methyl methacrylate copolymer, polymethyl methacrylate, styrene-methyl methacrylate copolymer and methyl methacrylate-isobornyl methacrylate copolymer. The lone pair of electrons in the acrylate structural unit of the above polymer can provide an active ion transmission channel, and the polymer is more likely to react with the hydroxyl and carboxyl groups of the electrode active material to form an adhesion force. Therefore, the above polymer containing acrylate structural units can improve the adhesion between the polymer binder and the electrode active material, and further enhance the fast charging capability of the secondary battery.

[0082] In some embodiments, the polymer containing olefinic structural units includes one or more of polystyrene and styrene-methyl methacrylate copolymer.

[0083] In some embodiments, the volume average particle size Dv50 of the polymer binder is 100 nm to 500 nm. Specifically, the volume average particle size Dv50 of the polymer binder includes but is not limited to: 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or a range between any two of the foregoing.

[0084] In some embodiments, the average liquid absorption rate of the electrode plate is 1 mL / s to 4.5 mL / s. With this design, the active ions have a suitable migration path, which is more conducive to improving the fast charging performance of the secondary battery. Specifically, the average liquid absorption rate of the electrode plate includes but is not limited to: 1 mL / s, 1.5 mL / s, 2 mL / s, 2.5 mL / s, 3 mL / s, 3.5 mL / s, 4 mL / s, 4.5 mL / s.

[0085] In some embodiments, the electrode plate is a negative electrode plate, the current collector is a negative electrode current collector, the electrode active layer is a negative electrode active layer, and the electrode active material is a negative electrode active material. When the electrode plate is a negative electrode plate, introducing the above polymer binder into the negative electrode plate can reduce the transmission resistance of active ions and the risk of lithium plating of the negative electrode plate.

[0086] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite. As a non-limiting example, the graphite may include one or more of artificial graphite and natural graphite.

[0087] In some embodiments, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence along the surface direction away from the negative electrode current collector, the first negative electrode active layer and the second negative electrode active layer both contain a polymer binder, and the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer. With such a design, the second negative electrode active layer can retain certain pores and active ion transmission channels, which is conducive to improving the infiltration rate of the electrolyte from the first negative electrode active layer to the second negative electrode active layer, thereby improving the transmission rate of active ions and further improving the fast charging performance of the secondary battery.

[0088] In some embodiments, the mass percentage of the polymer binder in the first negative electrode active layer is 0.8% to 1.8%. As a result, the adhesion between the polymer binder and the negative electrode active material in the first negative electrode active layer can be improved, and the fast charging performance of the secondary battery can be further improved. Specifically, the above mass percentage includes but is not limited to: 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or a range between any two of the foregoing.

[0089] In some embodiments, the mass percentage of the polymer binder in the second negative electrode active layer is 0.6% to 1.8%. As a result, the adhesion between the polymer binder and the negative electrode active material in the second negative electrode active layer can be improved, and the fast charging performance of the secondary battery can be further improved. Specifically, the above mass percentage includes but is not limited to: 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or a range between any two of the foregoing.

[0090] In some embodiments, the first negative electrode active layer and the second negative electrode active layer both contain negative electrode active materials, and the mass percentage of the negative electrode active materials in the first negative electrode active layer is less than or equal to the mass percentage of the negative electrode active materials in the second negative electrode active layer. With such a design, the second negative electrode active layer can retain certain pores and active ion transmission channels, which is conducive to improving the infiltration rate of the electrolyte from the first negative electrode active layer to the second negative electrode active layer, thereby improving the transmission rate of active ions and further improving the fast charging performance of the secondary battery.

[0091] In some embodiments, the mass percentage of the negative electrode active material in the first negative electrode active layer is 96% to 97%. Specifically, the mass percentage includes but is not limited to: 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97% or a range between any two of the foregoing.

[0092] In some embodiments, the mass percentage of the negative electrode active material in the second negative electrode active layer is 97% to 98%. Specifically, the mass percentage includes but is not limited to: 97%, 97.2%, 97.4%, 97.6%, 97.8%, 98% or a range between any two of the foregoing.

[0093] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0094] In some embodiments, the negative electrode active layer may further include other binders. Other binders may include one or more 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).

[0095] In some embodiments, the negative electrode active layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0096] In some embodiments, the negative electrode active layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the first negative electrode active layer and the second negative electrode active layer further independently include other binders. The other binders may include one or more 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).

[0098] In some embodiments, the first negative electrode active layer and the second negative electrode active layer further independently include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)).

[0099] In some embodiments, the first negative electrode active layer and the second negative electrode active layer further independently include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material. When the electrode plate is a positive electrode plate, introducing the above polymer binder into the positive electrode plate can reduce the transmission resistance of active ions and improve the interface of the positive electrode plate.

[0101] In some embodiments, the positive electrode sheet contains a positive electrode active material, and the positive electrode active material includes one or more of an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.

[0102] Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0103] It is understandable that the secondary battery will be accompanied by the deintercalation and consumption of lithium (Li) during the charge and discharge process, and the content of Li in the positive electrode plate is different when the secondary battery is discharged to different states. In the enumeration of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active material is applied to the positive electrode plate in the secondary battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode active materials is also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0104] In the list of positive electrode active materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0105] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0106] In some embodiments, the positive electrode active layer may further include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the polymer binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s-25000mPa·s.

[0108] In some embodiments, the secondary battery further includes an electrolyte. The electrolyte has the function of conducting ions between the positive electrode plate and the negative electrode plate. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid.

[0109] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0110] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0111] In some embodiments, the solvent may include 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 ( ), fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0112] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the secondary battery, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0113] In some embodiments, the additive in the electrolyte may include, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0114] In some embodiments, the secondary battery further comprises a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0115] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0116] In some embodiments, the thickness of the isolation film is 6 μm-40 μm, and optionally 12 μm-20 μm.

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0118] In some embodiments, the secondary battery is a lithium ion secondary battery.

[0119] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0120] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0121] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0122] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the charge and discharge process of the secondary battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0123] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0124] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0125] The secondary battery may be a battery module 4 or a battery pack 1 .

[0126] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0127] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0128] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0129] In some embodiments, the battery modules described above may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0130] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 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 the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0131] Another embodiment of the present application provides a method for preparing a secondary battery, including the step of preparing an electrode sheet; the step of preparing the electrode sheet includes:

[0132] emulsion polymerizing a first solution containing a first pore-forming template and a first monomer to form an emulsion containing a core;

[0133] A second solution containing a second pore-forming template agent and a second monomer is mixed with a solution containing an inner core, and an outer shell is formed on at least a portion of the surface of the inner core through emulsion polymerization to obtain a polymer binder intermediate; the mass fraction of the second pore-forming template agent in the second solution is higher than the mass fraction of the first pore-forming template agent in the first solution;

[0134] Removing the first pore-forming template agent and the second pore-forming template agent from the polymer binder intermediate, so that both the core and the shell form a pore structure, and the number of pores in the shell is greater than the number of pores in the core, to obtain a polymer binder;

[0135] An electrode slurry containing an electrode active material and a polymer binder is coated on at least one surface of a current collector, and an electrode active layer is formed through drying to obtain an electrode plate.

[0136] In the secondary battery prepared by the above preparation method, the number of holes in the shell of the polymer binder is greater than the number of holes in the core, which can improve the transfer rate of active ions between the electrode active material and the electrolyte, reduce the transmission resistance of active ions, and increase the electrolyte storage capacity, improve the average liquid absorption rate of the electrode plate, and improve the interface of the electrode plate. Therefore, during the high-current charge and discharge cycle of the secondary battery, the active ions can be quickly embedded in the electrode active material or released from the electrode active material, thereby improving the fast charging performance of the secondary battery. In addition, the above preparation method is relatively simple and suitable for large-scale production.

[0137] In some embodiments, the current collector is a negative electrode current collector, the electrode active material is a negative electrode active material, the electrode slurry is a negative electrode slurry, the electrode active layer is a negative electrode active layer, and the electrode plate is a negative electrode plate.

[0138] In some embodiments, the step of applying an electrode slurry comprising an electrode active material and a polymer binder to at least one surface of a current collector and drying the electrode slurry to form an electrode active layer to obtain an electrode sheet comprises:

[0139] Applying a first negative electrode slurry comprising a negative electrode active material and a polymer binder on at least one surface of a negative electrode current collector to prepare a first negative electrode active layer to obtain a negative electrode sheet intermediate;

[0140] A second negative electrode slurry containing a negative electrode active material is coated on the surface of the negative electrode plate intermediate away from the negative electrode current collector, and a second negative electrode active layer is formed after drying to obtain an electrode plate, which is a negative electrode plate; the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer.

[0141] In the above embodiment, the second negative electrode active layer can retain certain pores and active ion transmission channels, which is beneficial to improve the infiltration rate of the electrolyte from the first negative electrode active layer to the second negative electrode active layer, thereby improving the transmission rate of active ions and further improving the fast charging performance of the secondary battery.

[0142] In addition, since the solvent in the layer where the second negative electrode active layer is located evaporates first during the drying process, the solvent in the layer where the first negative electrode active layer is located rises rapidly. During the rising process, the solvent will carry part of the polymer binder, causing the polymer binder to float. Therefore, the mass percentage of the polymer binder in the first negative electrode slurry relative to the solid material in the slurry is less than the mass percentage of the polymer binder in the second negative electrode slurry relative to the solid material in the slurry. The mass of the solid material in the slurry is the mass of the slurry after the solvent is removed. Since the polymer binder will float, the second negative electrode slurry may or may not contain a polymer binder. The floating amount of the polymer binder = (the test value of the polymer binder content in the first negative electrode active layer - the design value of the polymer binder content in the first negative electrode active layer) / the design value of the polymer binder content in the second negative electrode active layer × 100%.

[0143] Possible reasons for the floating of the polymer binder are: (1) surface tension; (2) concentration gradient; (3) capillary action; (4) thermodynamic movement of solid particles; (5) particle sedimentation in the first negative electrode slurry and the second negative electrode slurry causes a density difference between the first negative electrode active layer and the second negative electrode active layer.

[0144] In some embodiments, the second negative electrode slurry further includes a polymer binder.

[0145] In some embodiments, the electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material.

[0146] In some embodiments, the first monomer includes one or more of an olefin compound, an acrylate compound, and an enol compound. Optionally, the olefin compound includes one or more of styrene, butadiene, ethylene, and vinyl acetate. Optionally, the acrylate compound includes one or more of butyl acrylate and isooctyl acrylate. Optionally, the enol compound includes one or more of vinyl alcohol and allyl alcohol.

[0147] In some embodiments, the second monomer includes one or more of an olefin compound and an acrylate compound. Optionally, the olefin compound includes one or more of styrene and styrene. Optionally, the acrylate compound includes one or more of methyl methacrylate and isobornyl methacrylate.

[0148] In some embodiments, the first pore-forming template agent and the second pore-forming template agent each independently include an inorganic salt, and the inorganic salt includes one or more of ammonium phosphate, ammonium sulfate, and ammonium chloride.

[0149] In some embodiments, the first solution further comprises one or more of a first initiator, a first emulsifier, and a first molecular weight regulator.

[0150] In some embodiments, the second solution further comprises one or more of a second initiator, a second emulsifier, and a second molecular weight regulator.

[0151] In some embodiments, the first initiator and the second initiator each independently include one or more of a persulfate and an azo compound.

[0152] In some embodiments, the first emulsifier and the second emulsifier each independently include one or more of anionic emulsifiers, nonionic emulsifiers and amphoteric emulsifiers. Optionally, the anionic emulsifier includes one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate. Optionally, the nonionic emulsifier includes polyoxyethylene alkyl ether. Optionally, the amphoteric emulsifier includes a betaine emulsifier.

[0153] In some embodiments, the first molecular weight regulator and the second molecular weight regulator each independently include one or more of a thiol compound, a halogenated compound, and a nitroxide free radical compound. Optionally, the thiol compound includes dodecyl mercaptan. Optionally, the halogenated compound includes one or more of carbon tetrachloride and tetrabromoethane. Optionally, the nitroxide free radical compound includes 2,2,6,6-tetramethylpiperidin-1-oxyl free radical.

[0154] In some embodiments, the step of removing the first pore-forming template agent and the second pore-forming template agent in the polymer binder intermediate comprises: mixing an acid solution or an alkali solution with the polymer binder intermediate to remove the first pore-forming template agent and the second pore-forming template agent through a neutralization reaction.

[0155] By adjusting the process parameters in the above-mentioned preparation method, a secondary battery provided in one embodiment of the present application can be obtained.

[0156] Another embodiment of the present application provides an electrode plate, the electrode plate comprising a current collector and an electrode active layer disposed on at least one surface of the current collector, wherein the electrode active layer comprises an electrode active material and a polymer binder;

[0157] The polymer binder comprises a core and a shell covering at least a portion of the surface of the core, at least one of the shell and the core comprises a polymer, both the shell and the core have a pore structure, and the number of pores in the shell is greater than the number of pores in the core.

[0158] In some embodiments, the electrode plate is the electrode plate in the secondary battery described above in the present application.

[0159] Another embodiment of the present application further provides an electrical device, comprising at least one of the secondary battery mentioned above in the present application, the secondary battery manufactured by the above manufacturing method of the present application, and the electrode plate mentioned above in the present application.

[0160] Secondary batteries can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0161] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0162] Figure 6 The power consumption device 6 is taken as an example. The power consumption device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0163] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0164] Hereinafter, the 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 limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0165] The test method involved in the embodiment:

[0166] (1) Test of average particle size Dv50 of polymer binder:

[0167] The dispersion medium used in the test is water, the refractive index of the dispersant is 1.33, the test instrument is Malvern 3000 of the United States, and the parameters of the test instrument are: refractive index is 1.42, absorbance is 0.005, and shading degree (scattering intensity) is 8%~12%.

[0168] Specifically, a disposable pipette is used to dip a polymer binder sample for injection. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics (shading degree: 8%~12%) can be obtained by receiving and measuring the energy distribution of the scattered light. A particle size volume distribution diagram is drawn based on the test data. From the distribution diagram, it is obtained that: 50% of the total volume of particles have a diameter greater than a certain Dv50 value, and another 50% of the total volume of particles have a diameter less than this Dv50 value, then this Dv50 value is the volume average particle size of the particles.

[0169] (2) Test on the mass percentage of polymer binder:

[0170] The mass percentage of the polymer binder in the first negative electrode active layer and the second negative electrode active layer was tested using STA449F3 differential scanning thermal gravimeter. The specific test process is as follows: take a double-sided tape and stick it on the surface of the negative electrode plate to be tested, then roll it three times in the same direction with a pressure roller, tear off the double-sided tape, and the powder stuck on the tape is the second negative electrode active layer powder; use a scraper to gently scrape off the powder left on the negative electrode plate, and be careful not to scrape the negative electrode collector. This part of the powder is the first negative electrode active layer powder. Using the first negative electrode active layer powder and the second negative electrode active layer powder, the content of the polymer binder in the first negative electrode active layer and the second negative electrode active layer was tested respectively according to the following steps, and the test steps were: weigh about 50 mg of the sample in an Al2O3 crucible and shake it flat; parameter setting: nitrogen atmosphere, purge gas flow rate of 60 mL / min, protective gas flow rate of 20 mL / min; temperature rise program: 10℃ / min, 35℃~600℃, to ensure that the sample is completely dispersed, and then draw the thermogravimetric and DTG-temperature change diagrams, and the heat flow-temperature change diagrams, and calculate the mass percentage of the polymer binder in the first negative electrode active layer and the second negative electrode active layer.

[0171] (3) Test on average liquid absorption rate of electrode plates:

[0172] 1) Dry the electrode plate at 80℃ / 4h; 2) Cut the electrode plate of appropriate size, test the thickness of the electrode plate, and fix it on the sample stage; 3) Select a capillary with an inner diameter of d=200μm, and polish it with 5000 mesh sandpaper until the end is neat; 4) Turn on the microscope, adjust the lens magnification 20~30 times, adjust the sample stage height and the angle between the lens and the sample stage until the image is clear; 5) The capillary absorbs the above electrolyte, controls the electrolyte height h=3mm, clamps the capillary on the clamp of the bracket, further adjusts the image clarity, lowers the capillary to make it contact with the electrode plate, and uses a stopwatch to time the capillary liquid level while it drops; 6) When the liquid level drops, read the liquid absorption time t and record the data; 7) Calculate the average liquid absorption rate v of the electrode according to the formula, v=π×(d / 2)^2×h×ρ / t, ρ is the density of the electrolyte.

[0173] (4) Lithium deposition test:

[0174] At 25°C, the battery was charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to a voltage of 2.8V. This charge and discharge cycle was repeated for 500 times. The battery was then charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage to a current ≤0.05C to reach a fully charged state. The fully charged battery was disassembled in a low-humidity room to observe whether lithium was deposited on the surface of the electrode.

[0175] (5) Fast charging performance test:

[0176] The battery was charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour), specifically including: at 35°C, the battery was charged at a constant current rate of 1C to a voltage of 3.65V, then charged at a constant voltage to a current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V, and its actual capacity was recorded as C0. Then the battery is charged with constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, 5C0 in sequence to the full battery charge cut-off voltage of 3.65V or 0V negative electrode cut-off potential (whichever is reached first). After each charge is completed, it is necessary to discharge with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the state of charge (State of Charge) at different charge rates to 10%, 20%, 30%, ..., 80% Charge, state of charge, when "SOC=0" means the battery is fully discharged, when "SOC=100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charging rate-negative electrode potential curve under different SOC states, and obtain the charging rate corresponding to the negative electrode potential of 0V under different SOC states after linear fitting. The charging rate is the charging window under the SOC state, which is recorded as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC, according to the formula (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%, the charging time T of the battery from 10%SOC to 80%SOC is calculated in min. The shorter the time, the better the fast charging performance of the battery.

[0177] Example 1

[0178] (1) Preparation of positive electrode sheet

[0179] The positive electrode active material lithium iron phosphate (LiFePO4), the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the double-side surfaces of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0180] (2) Preparation of negative electrode sheet

[0181] (2.1) Preparation of polymer binder

[0182] (2.1.1) Evacuate the polymerization kettle, add 250g of deionized water, then add sodium dodecyl sulfate (first emulsifier), ammonium persulfate (first initiator) and ammonium phosphate (first pore-forming template agent), start stirring and heat to 70°C, then drop a mixed solution of 1,3-butadiene (first monomer), styrene (first monomer) and dodecyl mercaptan (first molecular weight regulator) for 3h, then heat to 90°C and keep warm for 0.5h, and form an emulsion containing a core through emulsion polymerization; wherein the mass ratio of 1,3-butadiene (first monomer), styrene (first monomer), ammonium phosphate (first pore-forming template agent), sodium dodecyl sulfate (first emulsifier), ammonium persulfate (first initiator) and dodecyl mercaptan (first molecular weight regulator) is 10:90:1.25:3.5:0.6:1, and the mass of styrene (first monomer) is 90g;

[0183] In step (2.1.1), the mass fraction of ammonium phosphate (first pore-forming template agent) in the first solution formed by 1,3-butadiene (first monomer), styrene (first monomer), ammonium phosphate (first pore-forming template agent), sodium dodecyl sulfate (first emulsifier), ammonium persulfate (first initiator) and dodecyl mercaptan (first molecular weight regulator) is recorded as W1;

[0184] (2.1.2) Add 170 g of deionized water, ammonium phosphate (second pore-forming template), sodium dodecylbenzene sulfonate (second emulsifier), and ammonium persulfate (second initiator) to the entire emulsion containing the core obtained in step (2.1.1), start stirring and heat to 70°C, then uniformly add a mixed solution of 1,3-butadiene (second monomer), styrene (second monomer), methacrylate (second monomer) and dodecyl mercaptan (second molecular weight regulator) dropwise for 3 hours, then heat to 90°C and keep warm for emulsion polymerization The reaction time is 3 hours, and a shell is formed on part of the surface of the inner core to obtain a polymer binder intermediate; wherein the mass ratio of 1,3-butadiene (second monomer), styrene (second monomer), methacrylate (second monomer), ammonium phosphate (second pore-forming template agent), sodium dodecylbenzene sulfonate (second emulsifier), ammonium persulfate (second initiator) and dodecyl mercaptan (second molecular weight regulator) is 90:90:5:1.25:3.5:0.6:1, and the mass of 1,3-butadiene (second monomer) is 90g;

[0185] In step (2.1.2), the mass fraction of ammonium phosphate (pore-forming template agent) in the second solution formed by 1,3-butadiene (second monomer), styrene (second monomer), methacrylate (second monomer), ammonium phosphate (second pore-forming template agent), sodium dodecylbenzene sulfonate (second emulsifier), ammonium persulfate (second initiator) and dodecyl mercaptan (second molecular weight regulator) is recorded as W2, W2>W1;

[0186] (2.1.3) Cooling the polymer binder intermediate, adjusting the pH value to 6-8 with ammonia (alkaline solution) after cooling, removing the first pore-forming template agent and the second pore-forming template agent in the core and the shell by neutralization reaction, so that both the core and the shell form a pore structure, and the number of pores in the shell is greater than the number of pores in the core, to obtain a polymer binder. The average pore size of the core is 1 nm, and the average pore size of the shell is 1 nm.

[0187] (2.2) Preparation of negative electrode active layer

[0188] (2.2.1) Weighing negative electrode active material graphite, sodium carboxymethyl cellulose (CMC-Na), conductive agent carbon black and the above-mentioned polymer binder in a mass ratio of 96.3:1.0:0.4:2.3, then mixing the negative electrode active material graphite, sodium carboxymethyl cellulose (CMC-Na) and conductive agent carbon black, stirring evenly, adding deionized water to stir and knead to obtain graphite agglomerates with good wettability; adding sodium carboxymethyl cellulose (CMC-Na) to the graphite agglomerates, stirring, adding deionized water to disperse, and then adding the above-mentioned polymer binder, stirring to obtain a first negative electrode slurry;

[0189] (2.2.2) Weighing the negative electrode active material graphite, sodium carboxymethyl cellulose (CMC-Na), conductive agent carbon black and the above-mentioned polymer binder in a mass ratio of 97.8:1.0:0.7:0.5, then mixing the negative electrode active material graphite, sodium carboxymethyl cellulose (CMC-Na) and conductive agent carbon black, stirring evenly, adding deionized water to stir and knead to obtain graphite agglomerates with good wettability; adding sodium carboxymethyl cellulose (CMC-Na) to the graphite agglomerates, stirring, adding deionized water to disperse, and then adding the above-mentioned polymer binder, stirring to obtain a second negative electrode slurry;

[0190] (2.2.3) Apply the first negative electrode slurry on both sides of the negative electrode current collector copper foil, and after drying, form a first negative electrode active layer; apply the second negative electrode slurry on the surface of the first negative electrode active layer away from the copper foil, and after drying, form a second negative electrode active layer to obtain a negative electrode sheet.

[0191] (3) Isolation film

[0192] A 12μm thick polypropylene isolation film was selected.

[0193] (4) Preparation of electrolyte

[0194] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent, LiFSI accounting for 3wt% of the entire electrolyte is dissolved in the mixed solvent, and fully dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0195] (5) Preparation of batteries

[0196] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound into an electrode assembly, loaded with an aluminum-plastic film, and then baked at 80°C to remove water, and then injected with the above-mentioned electrolyte and sealed. After standing, hot and cold pressing, formation, capacity division and other processes, a lithium-ion secondary battery is obtained.

[0197] The preparation of the lithium ion secondary battery of Comparative Examples 1-2 is basically the same as that of Example 1, except that the mass of the first pore-forming template agent in step (2.1.1) and the mass of the second pore-forming template agent in step (2.1.2) are changed, as shown in Table 1.

[0198] Table 1

[0199]

[0200] The preparation of the lithium ion secondary batteries of Examples 2 to 4 is basically the same as that of Example 1, except that the addition time of the mixed solution in step (2.1.1) is changed, as shown in Table 2.

[0201] Table 2

[0202]

[0203] The preparation of the lithium ion secondary batteries of Examples 5 to 7 is basically the same as that of Example 1, except that the dropping time of the mixed solution in step (2.1.2) is changed, as shown in Table 3.

[0204] Table 3

[0205]

[0206] The lithium ion secondary batteries of Examples 8 to 11 are basically the same as those of Example 1, except that the type of the second monomer in step (2.1.2) is changed, or the type of the first monomer in step (2.1.1) and the type of the second monomer in step (2.1.2) are changed, as described in Table 4;

[0207] In Example 8, 1,3-butadiene, styrene, and methacrylate in step (2.1.2) are replaced with styrene;

[0208] In Example 9, 1,3-butadiene, styrene, and methacrylate in step (2.1.2) are replaced with methyl methacrylate;

[0209] In Example 10, 1,3-butadiene and styrene in step (2.1.1) are replaced by butyl acrylate, and 1,3-butadiene, styrene and methacrylate in step (2.1.2) are replaced by styrene and methyl methacrylate. The mass ratio of styrene (second monomer), methyl methacrylate (second monomer), ammonium phosphate (second pore-forming template agent), sodium dodecylbenzene sulfonate (second emulsifier), ammonium persulfate (second initiator) and dodecyl mercaptan (second molecular weight regulator) in step (2.1.2) is 92.5:92.5:1.25:3.5:0.6:1, and the mass of styrene (second monomer) is 92.5 g.

[0210] In Example 11, 1,3-butadiene in step (2.1.1) is replaced by ethylene, and styrene in step (2.1.1) is replaced by ethyl acetate; 1,3-butadiene, styrene, and methacrylate in step (2.1.2) are replaced by methyl methacrylate and isobornyl methacrylate, and the mass ratio of methyl methacrylate (second monomer), isobornyl methacrylate (second monomer), ammonium phosphate (second pore-forming template agent), sodium dodecylbenzene sulfonate (second emulsifier), ammonium persulfate (second initiator) and dodecyl mercaptan (second molecular weight regulator) in step (2.1.2) is 92.5:92.5:1.25:3.5:0.6:1, and the mass of methyl methacrylate (second monomer) is 92.5g.

[0211] Table 4

[0212]

[0213] The preparation of the lithium ion secondary batteries of Examples 12 to 13 is basically the same as that of Example 1, except that the mass of the first emulsifier in step (2.1.1) and the mass of the second emulsifier in step (2.1.2) are changed, as described in Table 5.

[0214] Table 5

[0215]

[0216] The preparation of the lithium ion secondary batteries of Examples 14 to 15 is basically the same as that of Example 1, except that the mass ratios of graphite, sodium carboxymethyl cellulose, carbon black and polymer binder in step (2.2.1) and step (2.2.2) are changed, as described in Table 6.

[0217] Table 6

[0218]

[0219] The preparation of the lithium ion secondary batteries of Examples 16 to 17 is basically the same as that of Example 1, except that the types of the first pore-forming template agent and the second pore-forming template agent in step (2.1.1) and step (2.1.2) are changed, as described in Table 7.

[0220] Table 7

[0221]

[0222] The preparation of the lithium-ion secondary battery of Example 18 is basically the same as that of Example 1, except that: step (2.2.3) is different. In step (2.2.3), the first negative electrode slurry is coated on the double-side surfaces of the negative electrode collector copper foil, and after drying, a first negative electrode active layer is formed to obtain a negative electrode sheet, and the thickness of the first negative electrode active layer in this embodiment is the same as the total thickness of the first negative electrode active layer and the second negative electrode active layer in Example 1, as described in Table 8.

[0223] Table 8

[0224]

[0225] The preparation of the lithium ion secondary battery of Example 19 is basically the same as that of Example 1, except that: step (1) and step (2.2) are different;

[0226] In the preparation of the positive electrode sheet in step (1) of this embodiment, the positive electrode active material lithium iron phosphate (LiFePO4), the conductive agent carbon black (Super P), and the polymer binder prepared in step (2.1) of Example 1 are mixed uniformly in a solvent water at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the double-side surfaces of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0227] In the preparation of the negative electrode active layer in step (2.2) of this embodiment, the negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain a negative electrode sheet.

[0228] The preparation of the lithium ion secondary batteries of Comparative Examples 3-4 is basically the same as that of Example 19, except that the mass of the first pore-forming template agent in step (2.1.1) and the mass of the second pore-forming template agent in step (2.1.2) are changed, as described in Table 9.

[0229] Table 9

[0230]

[0231] It can be seen from Tables 1 to 8 that, compared with Comparative Examples 1 to 2, the polymer binder introduced into the negative electrode plates of the batteries of Examples 1 to 18 has a pore structure in both the outer shell and the core, and the number of pores in the outer shell is greater than the number of pores in the core, which can effectively improve the fast charging performance of the battery and reduce the risk of lithium plating of the negative electrode plates.

[0232] It can be seen from Table 9 that compared with Comparative Examples 3 to 4, the positive electrode plate of the battery of Example 19 introduces a polymer binder having a porous structure in both the outer shell and the core, and the number of holes in the outer shell is greater than the number of holes in the core, which can effectively improve the fast charging performance of the battery and improve the interface of the positive electrode plate.

[0233] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar parts can be referenced to each other, and for the sake of brevity, they will not be repeated in this article.

[0234] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises an electrode plate, wherein the electrode plate comprises a current collector and an electrode active layer disposed on at least one surface of the current collector, wherein the electrode active layer comprises an electrode active material and a polymer binder; The polymer binder includes a core and a shell covering at least a portion of the surface of the core, at least one of the shell and the core includes a polymer, both the shell and the core have a pore structure, and the number of pores in the shell is greater than the number of pores in the core.

2. The secondary battery according to claim 1, characterized in that: The secondary battery has at least one of the following features (1) to (2): (1) The average pore size of the core is 0.5 nm to 3 nm; (2) The average pore size of the shell is 0.5 nm to 3 nm.

3. The secondary battery according to claim 2, characterized in that: The secondary battery has at least one of the following features (1) to (2): (1) The average pore size of the core is 0.5 nm to 1.5 nm; (2) The average pore size of the shell is 0.5 nm to 1.5 nm.

4. The secondary battery according to claim 1, characterized in that: The outer shell and the inner core both include a polymer, the polymer in the inner core being different from the polymer in the outer shell.

5. The secondary battery according to claim 1, characterized in that: The secondary battery has one or more of the following features (1) to (2): (1) The polymer in the core includes one or more of polybutadiene, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polybutyl acrylate, and a graft copolymer of polyvinyl alcohol and isooctyl acrylate; (2) The polymer in the shell includes one or more of a polymer containing an acrylate structural unit and a polymer containing an olefin structural unit.

6. The secondary battery according to claim 5, characterized in that: The secondary battery has one or more of the following features (1) to (2): (1) The polymer containing acrylic acid ester structural units includes one or more of styrene-methyl methacrylate copolymer, polymethyl methacrylate, styrene-methyl methacrylate copolymer and methyl methacrylate-isobornyl methacrylate copolymer; (2) The polymer containing olefin structural units includes one or more of polystyrene and styrene-methyl methacrylate copolymer.

7. The secondary battery according to claim 1, characterized in that: The volume average particle size Dv50 of the polymer binder is 100nm~500nm.

8. The secondary battery according to claim 1, characterized in that: The average liquid absorption rate of the electrode plate is 1 mL / s to 4.5 mL / s.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The electrode plate is a negative electrode plate, the current collector is a negative electrode current collector, the electrode active layer is a negative electrode active layer, and the electrode active material is a negative electrode active material.

10. The secondary battery according to claim 9, characterized in that: The negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

11. The secondary battery according to claim 9, characterized in that: The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence along a surface direction away from the negative electrode current collector, the first negative electrode active layer and the second negative electrode active layer both contain the polymer binder, and the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer.

12. The secondary battery according to claim 11, characterized in that: The secondary battery has at least one of the following features (1) to (2): (1) The mass percentage of the polymer binder in the first negative electrode active layer is 0.8% to 1.8%; (2) The mass percentage of the polymer binder in the second negative electrode active layer is 0.6% to 1.8%.

13. The secondary battery according to claim 11, characterized in that: The first negative electrode active layer and the second negative electrode active layer both contain the negative electrode active material, and the mass percentage of the negative electrode active material in the first negative electrode active layer is less than or equal to the mass percentage of the negative electrode active material in the second negative electrode active layer.

14. The secondary battery according to claim 13, characterized in that: The secondary battery has at least one of the following features (1) to (2): (1) The mass percentage of the negative electrode active material in the first negative electrode active layer is 96% to 97%; (2) The mass percentage of the negative electrode active material in the second negative electrode active layer is 97% to 98%.

15. The secondary battery according to any one of claims 1 to 8, characterized in that: The electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material.

16. A method for preparing a secondary battery, characterized in that: The method comprises the steps of preparing an electrode sheet; The steps of preparing the electrode plate include: emulsion polymerizing a first solution containing a first pore-forming template and a first monomer to form an emulsion containing a core; A second solution containing a second pore-forming template agent and a second monomer is mixed with the emulsion containing the inner core, and a shell is formed on at least a portion of the surface of the inner core through emulsion polymerization to obtain a polymer binder intermediate; the mass fraction of the second pore-forming template agent in the second solution is higher than the mass fraction of the first pore-forming template agent in the first solution; Removing the first pore-forming template agent and the second pore-forming template agent from the polymer binder intermediate, so that both the core and the shell form a pore structure, and the number of pores in the shell is greater than the number of pores in the core, to obtain a polymer binder; The electrode slurry containing the electrode active material and the polymer binder is coated on at least one surface of the current collector, and an electrode active layer is formed through drying to obtain the electrode plate.

17. The preparation method according to claim 16, characterized in that: The current collector is a negative electrode current collector, the electrode active material is a negative electrode active material, the electrode slurry is a negative electrode slurry, the electrode active layer is a negative electrode active layer, and the electrode plate is a negative electrode plate.

18. The preparation method according to claim 17, characterized in that: The steps of coating an electrode slurry comprising an electrode active material and the polymer binder on at least one surface of a current collector, and forming an electrode active layer through drying, to obtain the electrode sheet include: Applying a first negative electrode slurry comprising the negative electrode active material and the polymer binder on at least one surface of the negative electrode current collector to prepare a first negative electrode active layer to obtain a negative electrode sheet intermediate; A second negative electrode slurry containing the negative electrode active material is coated on the surface of the negative electrode plate intermediate away from the negative electrode current collector, and a second negative electrode active layer is formed after drying to obtain the electrode plate, which is the negative electrode plate; the mass percentage of the polymer binder in the first negative electrode active layer is greater than or equal to the mass percentage of the polymer binder in the second negative electrode active layer.

19. The preparation method according to claim 18, characterized in that: The second negative electrode slurry further includes the polymer binder.

20. The preparation method according to claim 16, characterized in that: The electrode plate is a positive electrode plate, the current collector is a positive electrode current collector, the electrode active layer is a positive electrode active layer, and the electrode active material is a positive electrode active material.

21. The preparation method according to any one of claims 16 to 20, characterized in that The preparation method satisfies at least one of the following conditions (1) to (5): (1) the first monomer includes one or more of an olefin compound, an acrylate compound and an enol compound; (2) the second monomer includes one or more of an olefin compound and an acrylate compound; (3) the first pore-forming template agent and the second pore-forming template agent each independently include an inorganic salt, and the inorganic salt includes one or more of ammonium phosphate, ammonium sulfate and ammonium chloride; (4) the first solution further comprises one or more of a first initiator, a first emulsifier and a first molecular weight regulator; (5) The second solution further comprises one or more of a second initiator, a second emulsifier and a second molecular weight regulator.

22. The preparation method according to claim 21, characterized in that: The preparation method satisfies at least one of the following conditions (1) to (3): (1) The first initiator and the second initiator each independently include one or more of persulfate and azo compound; (2) the first emulsifier and the second emulsifier each independently include one or more of anionic emulsifiers, nonionic emulsifiers and amphoteric emulsifiers; (3) The first molecular weight regulator and the second molecular weight regulator each independently include one or more of a thiol compound, a halogenated compound and a nitroxide free radical compound.

23. An electrode plate, characterized in that: The electrode plate comprises a current collector and an electrode active layer disposed on at least one surface of the current collector, wherein the electrode active layer comprises an electrode active material and a polymer binder; The polymer binder comprises a core and a shell covering at least a portion of the surface of the core, the shell and the core both have pore structures, and the number of pores in the shell is greater than the number of pores in the core.

24. An electrical device, characterized in that: The invention comprises at least one of the secondary battery according to any one of claims 1 to 15, the secondary battery prepared by the preparation method according to any one of claims 16 to 22, and the electrode plate according to claim 23.

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