Secondary battery, electric device, and current collector

Abstract

A secondary battery, an electric device, and a current collector. The secondary battery comprises electrode sheets; each electrode sheet comprises a current collector and a film layer arranged on at least one side of the current collector; the current collector comprises a metal current collector substrate and a primer layer arranged on at least one side of the metal current collector substrate; the primer layer comprises an inorganic oxide; and the film layer comprises an aqueous binder.

Description

CROSS-REFERENCE

[0001] The present application claims priority to Chinese Patent Application No. 202410437980.5, filed on April 11, 2024 and entitled “SECONDARY BATTERY AND ELECTRIC APPARATUS”, which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, and in particular, to a secondary battery, an electric apparatus, and a current collector. BACKGROUND

[0003] As energy and environmental issues become increasingly prominent, the new energy industry has received increasing attention. Due to characteristics such as high energy density and good cycle performance, secondary batteries have been widely used in recent years in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0004] The electrode plate is an important component of the secondary battery. How to improve the quality of the electrode plate to further improve the performance of the secondary battery is a technical problem that urgently needs to be solved in the art. SUMMARY

[0005] The present application is made in view of the above issues, and an objective of the present application is to provide a secondary battery with improved performance.

[0006] A first aspect of the present application provides a secondary battery. The secondary battery includes an electrode plate. The electrode plate includes a current collector and a film layer disposed on at least one side of the current collector. The current collector includes a current collector substrate and a primer layer disposed on at least one side of the current collector substrate. The primer layer includes an inorganic oxide. The film layer includes an aqueous binder.

[0007] The inorganic oxide has a high density and better affinity with a metal current collector substrate. Compared to an active material (such as soft carbon or hard carbon) or a conductive agent (such as conductive carbon) commonly used in the film layer, the inorganic oxide is less likely to shrink or displace under the action of the surface tension of the slurry and can effectively improve the coating quality of the primer layer, thereby achieving the successful coating of a liquid slurry, having a large difference in surface energy from the current collector substrate, on the surface of the current collector substrate. An aqueous slurry including an aqueous binder has a high surface tension and often has the problems of a large difference in surface energy and poor coating quality when coated on a current collector substrate. The inclusion of the inorganic oxide in the primer layer can particularly solve the problem of poor compatibility between the aqueous slurry and the current collector substrate and improve the coating quality of the aqueous slurry on the current collector substrate.

[0008] In any embodiment, the inorganic oxide includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide.

[0009] In any embodiment, based on a total mass of the primer layer, a mass proportion of the inorganic oxide is 30% to 60%.

[0010] The inclusion of the inorganic oxide within the above mass range in the primer layer can not only achieve the improvement in the coating quality of the electrode plate, but also improve the adhesion strength of the electrode plate and reduce the elongation of the electrode plate during cold pressing, and can further achieve the effective control over the resistance of the current collector, ensuring the electrochemical performance of the battery.

[0011] In any embodiment, the inorganic oxide has a volume distribution particle size Dv50 < 2 pm.

[0012] The inorganic oxide having a volume distribution particle size within the above range can closely adhere to the metal current collector substrate, thereby improving the forming quality of the primer layer and the electrode plate.

[0013] In any embodiment, the primer layer further includes a particulate binder, and the particulate binder includes one or more of styrene-butadiene rubber and acrylate rubber.

[0014] The particulate binder has water-oil amphiphilicity, and compared to a linear binder having strong affinity for an aqueous solvent, the particulate binder can exhibit better water resistance, thereby enabling the primer layer to remain stable during the coating process of an upper film layer containing an active substance, and further realizing the function of the primer layer in improving coating quality.

[0015] In any embodiment, based on a total mass of the primer layer, a mass proportion of the particulate binder is 10% to 40%.

[0016] The inclusion of the particulate binder within the above mass range in the primer layer can not only achieve the improvement in the coating quality of the electrode plate, but also improve the adhesion strength of the electrode plate, and can further achieve the effective control over the resistance of the current collector, ensuring the electrochemical performance of the battery.

[0017] In any embodiment, the primer layer further includes a dispersant, and the dispersant includes one or more of polyacrylic acid-based polymers.

[0018] The polyacrylic acid-based polymer is a linear polymer that can be fully dispersed in a solvent to achieve the coating of the inorganic oxide. The polyacrylic acid-based polymer can reduce the agglomeration of the inorganic oxide, function to effectively disperse the inorganic oxide, assist the inorganic oxide in fully delivering the performance thereof, further improve the forming quality of the primer layer, improve the coating quality and adhesion strength of the electrode plate, and reduce the elongation of the electrode plate during cold pressing.

[0019] In any embodiment, based on a total mass of the primer layer, a mass proportion of the dispersant is 1% to 8%.

[0020] In any embodiment, based on a total mass of the primer layer, a mass proportion of the dispersant is 1% to 5%.

[0021] The dispersant with a mass content falling within this range can not only effectively improve the adhesion strength between the film layer and the current collector, but also reduce the adverse effect of a decrease in water resistance of the primer layer caused by an excessively high content of acrylic acid, thereby comprehensively improving the forming quality of the electrode plate.

[0022] In any embodiment, the primer layer further includes one or more of a conductive agent, a thickener, and a wetting agent.

[0023] The conductive agent can minimize the negative impact of the primer layer on the conductivity of the current collector, while ensuring the electrochemical performance of the battery. The thickener is conducive to improving the dispersion of the conductive agent and can also reduce the sedimentation of the conductive agent and the inorganic oxide, thereby helping improve the stability of the primer layer slurry and expanding the process window. The wetting agent is conducive to improving the wetting of the film layer slurry on the current collector containing an oil film, thus facilitating the coating of the primer layer slurry on the metal current collector substrate.

[0024] In any embodiment, the conductive agent includes one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or the thickener includes one or more of sodium carboxymethylcellulose, sodium alginate, xanthan gum, and carrageenan; and / or the wetting agent includes one or more of a polyethoxy ether surfactant, a polyether silicone surfactant, a non-ionic fluorocarbon polymer surfactant, and an acetylenic surfactant.

[0025] In any embodiment, based on a total mass of the primer layer, a mass proportion of the conductive agent is 10% to 40%, a mass proportion of the thickener is 0.5% to 4%, and a mass proportion of the wetting agent is 0.2% to 1%.

[0026] In any embodiment, a thickness of the primer layer is 0.5 pm to 3 pm.

[0027] The primer layer, having a thickness within an appropriate range, can ensure both the forming quality and the electrochemical performance of the battery.

[0028] In any embodiment, the current collector substrate is a metal current collector substrate, and the metal current collector substrate is prepared by a calendering method.

[0029] The metal current collector substrate prepared by a calendering method has a low cost, which can further reduce the overall cost of the battery. However, after calendering, an oil film inevitably remains on the surface of the metal current collector substrate. The present application is particularly applicable to such a metal current collector substrate, thereby comprehensively reducing the cost of the secondary battery.

[0030] In any embodiment, a dyne value of the current collector substrate is 20 mN / m to 35 mN / m.

[0031] The dyne value of water is greater than 70 mN / m, and the large difference in dyne value between an aqueous slurry and the metal current collector substrate makes uniform coating on the surface of the metal current collector substrate difficult to achieve. The embodiments of the present application can effectively improve the coating quality of the aqueous slurry on the metal current collector substrate, which is conducive to broadening the selectable range of the current collector substrate and further realizing the reduction of battery costs.

[0032] In any embodiment, the current collector substrate includes a metal current collector substrate, and the metal current collector substrate includes at least one of a copper foil, an aluminum foil, a stainless steel foil, a titanium foil, and a nickel foil.

[0033] In any embodiment, the film layer further includes a negative electrode active material, and the negative electrode active material includes one or more of hard carbon, soft carbon, graphite, and silicon; and / or the aqueous binder includes one or more of styrene-butadiene rubber (SBR) and acrylate rubber.

[0034] In any embodiment, the secondary battery includes one or more of a sodium secondary battery and a lithium secondary battery.

[0035] In any embodiment, the secondary battery includes a sodium-ion battery; a cell of the sodium-ion battery includes: a battery housing, where an upper portion of the battery housing is provided with an opening; a top cover assembly, where the top cover assembly is disposed at the opening of the battery housing, and the top cover assembly is sealed and electrically connected to the battery housing; and an electrode assembly, where the electrode assembly is configured for an electrical connection, and the electrode assembly is disposed on the top cover assembly. The top cover assembly includes a top cover plate, and the electrode assembly and the top cover plate are configured as a single integral member made of aluminum metal or aluminum alloy.

[0036] The sodium-ion battery features an optimized design of the battery top cover assembly while maintaining battery performance. By integrating the electrode assembly into the top cover assembly to configure the electrode assembly and the top cover assembly as a single integral member made of aluminum metal or aluminum alloy, the number of structural members can be reduced, and the manufacturing cost can be further lowered. Meanwhile, the electrical connection between the battery housing and the electrode assembly can be realized, thereby reducing the possibility of corrosion of the battery housing.

[0037] A second aspect of the present application provides an electric apparatus. The electric apparatus includes the secondary battery according to any embodiment.

[0038] A third aspect of the present application provides a current collector. The current collector includes a current collector substrate and a primer layer disposed on at least one side of the current collector substrate, and the primer layer includes an inorganic oxide.

[0039] In any embodiment, the inorganic oxide includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide.

[0040] In any embodiment, the primer layer further includes a particulate binder, and the particulate binder includes one or more of a styrene-butadiene emulsion and an acrylate-based emulsion.

[0041] In any embodiment, the primer layer further includes a dispersant, and the dispersant includes one or more of polyacrylic acid-based polymers.

[0042] In any embodiment, the current collector substrate is a metal current collector substrate, and a dyne value of the metal current collector substrate is 20 mN / m to 35 mN / m.

[0043] In any embodiment, the current collector substrate is a metal current collector substrate, and the metal current collector substrate includes an aluminum foil. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a schematic view of a secondary battery according to an embodiment of the present application.

[0045] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1.

[0046] FIG. 3 is a schematic view of a battery module according to an embodiment of the present application.

[0047] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present application.

[0048] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4.

[0049] FIG. 6 is a schematic view of an electric apparatus using a secondary battery as a power source according to an embodiment of the present application.

[0050] Description of the reference numerals:

[0051] 1: battery pack; 2: upper case body; 3: lower case body; 4: battery module; 5: secondary battery; 51: housing; 52: electrode assembly; 53: top cover assembly. DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of the secondary battery, the electric apparatus, and the current collector of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessary lengthiness of the following descriptions and to facilitate understanding by those skilled in the art. Additionally, the drawings and the following descriptions are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0053] The “ranges” disclosed in the present application are defined by lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that delineate the boundaries of a particular range. Ranges defined in this manner are typically inclusive of endpoints and may be arbitrarily combined; that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also anticipated. Additionally, if the minimum range values listed are 1 and 2, and the maximum range values listed are 3, 4, and 5, then the following ranges can all be anticipated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise specified, the numerical range “a to b” represents an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range “0 to 5” indicates that all real numbers “between 0 and 5” are listed herein, and “0 to 5” is merely an abbreviated representation of a combination of these numerical values. Additionally, when stating that a parameter is an integer > 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with one another to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with one another to form new technical solutions.

[0056] Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it indicates that the method may include steps (a) and (b) performed sequentially or steps (b) and (a) performed sequentially. For example, if the mentioned method may further include step (c), it indicates that step (c) may 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), or the like.

[0057] Unless otherwise specified, the terms “include / comprise” and “contain” mentioned in the present application are open-ended or closed-ended. For example, the terms “include / comprise” and “contain” may mean that other unlisted components may also be included / comprised or contained, or that only the listed components are included / comprised or contained.

[0058] Unless otherwise specified, the term “or” in the present application is inclusive. For example, the phrase “A or B” means “A, B, or both A and B”. More specifically, any one of the following conditions satisfies the condition “A or B”: A is true (or present) and B is false (or absent); A is false (or absent) and B is true (or present); or both A and B are true (or present).

[0059] With the increasing demand for cost reduction of batteries, the urgency of using lowcost current collector substrates continues to increase. However, low-cost current collector substrates are often produced using low-cost production processes, such as a calendering method, during which an oil film is coated on the surface of the current collector substrate in the rolling process to reduce surface damage to the substrate. However, the oil film on the surface of the current collector substrate is difficult to remove, such that when an aqueous slurry is coated on the surface of the current collector substrate, the aqueous slurry cannot sufficiently wet the surface of the current collector substrate, making it difficult to coat the aqueous slurry onto the current collector substrate. Taking a sodium secondary battery as an example, since sodium ions do not undergo an alloying reaction with aluminum metal like lithium ions, there is a wider variety of options for the negative electrode current collector material. For example, a low-cost foil material, such as an aluminum foil, may be used for the negative electrode of a sodium-ion battery to replace the copper foil widely used in the prior art, thereby achieving further cost reduction. As an example, if an aluminum foil is prepared by the calendering method, a layer of oil film will remain on the surface of the aluminum foil, making it difficult for the negative electrode aqueous slurry to be coated on the surface of the aluminum foil, and thus the aluminum foil cannot be applied to the negative electrode plate.

[0060] A first aspect of the present application provides a secondary battery. The secondary battery includes an electrode plate. The electrode plate includes a current collector and a film layer disposed on at least one side of the current collector. The current collector includes a current collector substrate and a primer layer disposed on at least one side of the current collector substrate. The primer layer includes an inorganic oxide. The film layer includes an aqueous binder.

[0061] The inorganic oxide refers to an inorganic compound composed of oxygen atoms and one or more metal or non-metal elements.

[0062] The inorganic oxide in the primer layer may be tested by using any known test method. As an example, a phase analysis is performed on the decomposition products in the film layer by using a test instrument such as a Raman spectrometer, an X-ray diffractometer, and a transmission electron microscope; or a component analysis is performed in combination with an energy dispersive spectrometer.

[0063] The aqueous binder refers to a binder using an aqueous medium as a dispersant. Therefore, the film layer including the aqueous binder is often prepared by an aqueous slurry. Aqueous binders are classified into linear binders and particulate binders according to the dispersion morphology of the binders in a solvent. The linear binder presents a linear morphology in the solvent and can achieve polymer chain extension in a solvent, thus presenting a coating state for the active material in the film layer. As an example, the linear binder includes, but is not limited to, polyacrylic acid and polymethyl acrylate. The particulate binder refers to a binder exhibiting a dot-like morphology in a solvent and mostly consists of latex particles. As an example, the particulate binder includes, but is not limited to, styrenebutadiene rubber and styrene-acrylic rubber.

[0064] The inorganic oxide has a high density and better affinity with the current collector substrate. Compared to an active material (such as soft carbon or hard carbon) or a conductive agent (such as conductive carbon) commonly used in the film layer, the inorganic oxide is less likely to shrink or displace under the action of the surface tension of the slurry and can effectively improve the coating quality of the primer layer.

[0065] An aqueous slurry including an aqueous binder has a high surface tension and often has the problems of a large difference in surface energy and poor coating quality when coated on a current collector substrate. The inclusion of the inorganic oxide in the primer layer can particularly solve the problem of poor compatibility between the aqueous slurry and the current collector substrate and improve the coating quality of the aqueous slurry on the current collector substrate. Understandably, the electrode plate herein may be a positive electrode plate or a negative electrode plate, and the embodiments of the present application can achieve corresponding technical effects for different battery systems. As an example, for a positive electrode plate adopting an aqueous film layer slurry, the current collector provided according to the embodiments of the present application can also provide the improved coating quality of the electrode plate. It should be noted that the secondary battery herein is not limited to a sodium secondary battery, and also includes a lithium secondary battery.

[0066] Understandably, the material of the current collector is not particularly limited, as long as the material does not cause chemical changes in the secondary battery and has conductivity. The current collector includes a metal foil with a pure metal content of 95% or more, such as at least one of a copper foil, an aluminum foil, a stainless steel foil, a titanium foil, and a nickel foil. The current collector also includes an alloy foil of at least two main metals. For example, the current collector may be made of an alloy foil of at least two main elements among copper, aluminum, nickel, titanium, and iron. The current collector may further include copper, aluminum-cadmium alloy, iron, or stainless steel surface-treated with carbon, nickel, titanium, silver, copper, or the like. In addition, the binding force with a negative electrode active substance can be enhanced by forming fine concavities and convexities on the surface, and the current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0067] In some embodiments, the inorganic oxide includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide.

[0068] In some embodiments, the inorganic oxide includes one or more of aluminum oxide and boehmite.

[0069] The two inorganic oxides described above exhibit better adhesion on an aluminum foil and can further improve the forming quality and adhesion strength of the electrode plate.

[0070] In some embodiments, based on a total mass of the primer layer, a mass proportion of the inorganic oxide is 30% to 60%.

[0071] In some embodiments, based on the total mass of the primer layer, the mass proportion of the inorganic oxide is optionally 30%, 35%, 40%, 45%, 50%, 55%, or 60%, or within a range defined by any two of the numerical values.

[0072] The inclusion of the inorganic oxide within the above mass range in the primer layer can not only achieve the improvement in the coating quality of the electrode plate, but also improve the adhesion strength of the electrode plate and reduce the elongation of the electrode plate during cold pressing, and can further achieve the effective control over the resistance of the current collector, ensuring the electrochemical performance of the battery.

[0073] In some embodiments, the inorganic oxide has a volume distribution particle size Dv50 < 2 microns (pm).

[0074] The volume distribution particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, calculated from the small-particle-size side in a volume-based particle size distribution diagram of particles.

[0075] The volume distribution particle size Dv50 may be tested by any known method in the art. As an example, referring to GB / T 19077-2016 Particle size distribution laser diffraction method, the volume distribution particle size Dv50 is determined by using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0076] The inorganic oxide having a volume distribution particle size within the above range can closely adhere to the metal current collector substrate, thereby improving the forming quality of the primer layer and the electrode plate.

[0077] In some embodiments, the primer layer further includes a particulate binder, and the particulate binder includes one or more of styrene-butadiene rubber and acrylate rubber.

[0078] The particulate binder refers to a binder exhibiting a dot-like morphology in the primer layer. Such a binder generally exhibits a particulate distribution in a solvent and mostly consists of latex particles.

[0079] Styrene-butadiene rubber (SBR) is also referred to as a polystyrene-butadiene copolymer.

[0080] Acrylate rubber is an elastomer obtained by copolymerization using acrylate as a main monomer, where the main monomer mainly includes methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like. In some embodiments, the acrylate rubber includes styrene-acrylate rubber (SAR). Styrene-acrylate rubber (SAR) is also referred to as a styreneacrylate copolymer.

[0081] The particulate binder has water-oil amphiphilicity, and compared to a linear binder having strong affinity for an aqueous solvent, the particulate binder can exhibit better water resistance, thereby enabling the primer layer to remain stable during the coating process of an upper film layer containing an active substance, and further realizing the function of the primer layer in improving coating quality.

[0082] In some embodiments, the particulate binder includes acrylate rubber.

[0083] Compared with other particulate binders, acrylate rubber exhibits stronger adhesiveness to a metal current collector substrate and can further improve the coating quality and adhesion strength of the electrode plate.

[0084] In some embodiments, based on the total mass of the primer layer, a mass proportion of the particulate binder is 10% to 40%.

[0085] In some embodiments, based on the total mass of the primer layer, the mass proportion of the particulate binder is optionally 10%, 15%, 20%, 25%, 30%, 35%, or 40%, or within a range defined by any two of the numerical values.

[0086] The inclusion of the particulate binder within the above mass range in the primer layer can not only achieve the improvement in the coating quality of the electrode plate, but also improve the adhesion strength of the electrode plate, and can further achieve the effective control over the resistance of the current collector, ensuring the electrochemical performance of the battery.

[0087] In some embodiments, the primer layer further includes a dispersant, and the dispersant includes one or more of polyacrylic acid-based polymers.

[0088] The polyacrylic acid-based polymer refers to a polymer prepared by polymerizing acrylic acid or an acrylic acid derivative as a monomer, or by copolymerizing predominantly acrylic acid or the acrylic acid derivative with other unsaturated compounds. Understandably, the polyacrylic acid-based polymer may include both a homopolymer and a copolymer.

[0089] In some embodiments, the polyacrylic acid-based polymer includes one or more of polyacrylic acid, polymethacrylic acid, polyacrylamide, poly(acrylic acid-acrylamide), poly(acrylic acid-acrylonitrile), and poly(acrylic acid-acrylonitrile-acrylamide).

[0090] The polyacrylic acid-based polymer is a linear polymer that can be fully dispersed in a solvent to achieve the coating of the inorganic oxide. The polyacrylic acid-based polymer can reduce the agglomeration of the inorganic oxide, function to effectively disperse the inorganic oxide, assist the inorganic oxide in fully delivering the performance thereof, further improve the forming quality of the primer layer, improve the coating quality and adhesion strength of the electrode plate, and reduce the elongation of the electrode plate during cold pressing.

[0091] In some embodiments, based on the total mass of the primer layer, a mass proportion of the dispersant is 1% to 8%.

[0092] In some embodiments, based on the total mass of the primer layer, the mass proportion of the dispersant is optionally 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, or within a range defined by any two of the numerical values.

[0093] The dispersant with a mass content falling within this range can not only effectively improve the adhesion strength between the film layer and the current collector, but also reduce the adverse effect of a decrease in water resistance of the primer layer caused by an excessively high content of acrylic acid, thereby comprehensively improving the forming quality of the electrode plate.

[0094] In some embodiments, the primer layer further includes one or more of a thickener, a conductive agent, and a wetting agent.

[0095] In some embodiments, the conductive agent includes one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] The conductive agent can minimize the negative impact of the primer layer on the conductivity of the current collector, while ensuring the electrochemical performance of the battery.

[0097] In some embodiments, the thickener includes one or more of sodium carboxymethylcellulose, sodium alginate, xanthan gum, and carrageenan.

[0098] The thickener is conducive to improving the dispersion of the conductive agent and can also reduce the sedimentation of the conductive agent and the inorganic oxide, thereby helping improve the stability of the primer layer slurry and expanding the process window.

[0099] In some embodiments, the wetting agent includes one or more of a polyethoxy ether surfactant, a polyether silicone surfactant, a non-ionic fluorocarbon polymer surfactant, and an acetylenic surfactant.

[0100] The wetting agent is conducive to improving the wetting of the film layer slurry on the current collector containing an oil film, thus facilitating the coating of the primer layer slurry on the metal current collector substrate.

[0101] In some embodiments, based on the total mass of the primer layer, a mass proportion of the conductive agent is 10% to 40%; a mass proportion of the thickener is 0.5% to 4%; and a mass proportion of the wetting agent is 0.2% to 1%.

[0102] In some embodiments, based on the total mass of the primer layer, the mass proportion of the conductive agent is optionally 10%, 20%, 30%, or 40%, or within a range defined by any two of the numerical values.

[0103] In some embodiments, based on the total mass of the primer layer, the mass proportion of the thickener is optionally 0.5%, 1%, 2%, 3%, or 4%, or within a range defined by any two of the numerical values.

[0104] In some embodiments, the mass proportion of the wetting agent is optionally 0.2%, 0.4%, 0.6%, 0.8%, or 1%, or within a range defined by any two of the numerical values.

[0105] In some embodiments, a thickness of the primer layer is 0.5 pm to 3 pm.

[0106] In some embodiments, the thickness of the primer layer is optionally 0.5 pm, 1 pm, 2 pm, or 3 pm, or within a range defined by any two of the numerical values.

[0107] The primer layer, having a thickness within an appropriate range, can ensure both the forming quality and the electrochemical performance of the battery.

[0108] In some embodiments, the primer layer may be prepared by: mixing an inorganic oxide and a dispersant in an aqueous solvent, adding a thickener after uniform stirring, and then successively adding a conductive agent, a binder, and a wetting agent to form a primer slurry; and coating the primer slurry on a metal current collector substrate, followed by drying, cold pressing, and other processes to obtain a current collector containing the primer layer.

[0109] In some embodiments, the film layer further includes a negative electrode active material, and the negative electrode active material includes one or more of hard carbon, soft carbon, graphite, and silicon.

[0110] In some embodiments, the aqueous binder includes one or more of styrene-butadiene rubber (SBR) and acrylate rubber.

[0111] The particulate binder described above is different from linear binders such as polyacrylic acid; the particulate binder can effectively alleviate the gelation of the film layer slurry and can mitigate the brittleness problem of the film layer, and the improvement effect on slurries including negative electrode active materials such as hard carbon, soft carbon, and graphite is particularly significant.

[0112] In some embodiments, the current collector substrate is a metal current collector substrate, and the metal current collector substrate is prepared by a calendering method.

[0113] The metal current collector substrate prepared by a calendering method has a low cost, which can further reduce the overall cost of the battery. However, after calendering, an oil film inevitably remains on the surface of the metal current collector substrate. The present application is particularly applicable to such a metal current collector substrate, thereby comprehensively reducing the cost of the secondary battery.

[0114] In some embodiments, a dyne value of the current collector substrate is 20 millinewtons per meter (mN / m) to 35 mN / m.

[0115] In some embodiments, the dyne value of the current collector substrate may be selected from 20 mN / m, 25 mN / m, 30 mN / m, 35 mN / m, or within a range defined by any two of the numerical values.

[0116] The dyne value also refers to a surface tension coefficient, which mainly indicates the magnitude of surface tension, that is, a mutual pulling force per unit length between two adjacent portions of a liquid surface. The dyne value can be used to reflect the wettability of the current collector substrate, and a higher dyne value indicates better wettability of the current collector substrate. The dyne value can be obtained by testing using any method known in the art; for example, the dyne value of the current collector substrate is tested by stroking a dyne pen across the surface of the current collector substrate.

[0117] The dyne value of water is greater than 70 mN / m, and the large difference in dyne value between an aqueous slurry and the current collector substrate makes uniform coating on the surface of the current collector substrate difficult to achieve. The embodiments of the present application can effectively improve the coating quality of the aqueous slurry on the current collector substrate, which is conducive to broadening the selectable range of the current collector substrate and further realizing the reduction of battery costs. In some embodiments, the current collector substrate includes a metal current collector substrate, and the metal current collector substrate includes at least one of copper foil, aluminum foil, stainless steel foil, titanium foil, and nickel foil.

[0118] In some embodiments, the metal current collector substrate includes an aluminum foil.

[0119] The aluminum foil spontaneously forms an aluminum oxide film on its surface, such that the oxide of the primer layer in the embodiments of the present application has a higher affinity with the aluminum oxide film, and the coating quality and adhesion strength of the electrode plate can be further improved.

[0120] In some embodiments, the film layer optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the film layer optionally further includes other auxiliary agents, such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0122] In some embodiments, the electrode plate may be prepared by: dispersing the above components for preparing the electrode plate, such as the active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a film layer slurry; and coating the film layer slurry on the current collector, followed by drying, cold pressing, and other processes to obtain the electrode plate.

[0123] In some embodiments, the secondary battery includes one or more of a sodium secondary battery and a lithium secondary battery.

[0124] In some embodiments, the secondary battery is a sodium-ion battery, and the electrode plate is a negative electrode plate.

[0125] In some embodiments, the secondary battery is a negative electrode-free battery, and may optionally be a negative electrode-free sodium battery or a negative electrode-free lithium battery.

[0126] The negative electrode-free secondary battery refers to a battery formed without actively disposing a negative electrode active material layer on the negative electrode side during the manufacturing of the battery. For example, during the manufacturing of the battery, a metal or carbonaceous active material layer is not disposed on the negative electrode by a process such as coating or deposition to form a negative electrode active material layer. During the first charge, active ions gain electrons on the anode side and are deposited in a metal form on the surface of the current collector to form a metal phase. During discharge, the metal can be converted into active ions and return to the positive electrode, thus achieving cyclic charge and discharge. Therefore, the negative electrode-free battery is also a metal battery. Compared with other secondary batteries, the negative electrode-free secondary battery can achieve a higher energy density due to the absence of a pre-formed negative electrode active material layer.

[0127] Although a negative electrode-free secondary battery does not need to form a negative electrode active material layer by disposing a metal or carbonaceous active material layer through a process such as coating or deposition, the negative electrode-free secondary battery is often provided with a primer layer containing a conductive material to achieve the effect of inducing deposition. Due to an excessively large difference in surface tension, coating an aqueous primer layer of the negative electrode-free secondary battery onto a current collector substrate with a low dyne value also suffers from poor film formation. The primer layer provided according to the embodiments of the present application is also applicable to the negative electrode-free secondary battery, thereby improving the coating quality, and the inorganic oxide can further function to induce metal deposition, which is conducive to further improving the uniformity of the metal deposition.

[0128] In some embodiments, the secondary battery includes a sodium-ion battery; a cell of the sodium-ion battery includes: a battery housing, where an upper portion of the battery housing is provided with an opening; a top cover assembly, where the top cover assembly is disposed at the opening of the battery housing, and the top cover assembly is sealed and electrically connected to the battery housing; and an electrode assembly, where the electrode assembly is configured for an electrical connection, and the electrode assembly is disposed on the top cover assembly. The top cover assembly includes a top cover plate, and the electrode assembly and the top cover plate are configured as a single integral member made of aluminum metal or aluminum alloy.

[0129] The sodium-ion battery features an optimized design of the battery top cover assembly while maintaining battery performance. By integrating the electrode assembly into the top cover assembly to configure the electrode assembly and the top cover assembly as a single integral member made of aluminum metal or aluminum alloy, the number of structural members can be reduced, and the manufacturing cost can be further lowered. Meanwhile, the electrical connection between the battery housing and the electrode assembly can be realized, thereby reducing the possibility of corrosion of the battery housing.

[0130] In some embodiments, the secondary battery further includes a positive electrode plate; the positive electrode plate includes a positive electrode current collector and a positive electrode active substance layer formed on at least a portion of the surface of the positive electrode current collector. The positive electrode active substance layer includes a positive electrode active substance. The positive electrode active substance may include at least one of a layered transition metal oxide, a polyanionic compound, and a Prussian blue compound.

[0131] The transition metal in the layered transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide is, for example, NaxMO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x < 1.

[0132] The polyanionic compound may be a class of compounds having metal ions, transition metal ions, and tetrahedral (YO4)n- anion units. The metal ion is optionally one of a sodium ion, a lithium ion, a potassium ion, and a zinc ion; the transition metal is optionally at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ge, Ga, Sn, Hf, Ta, W, and Pb; Y is optionally at least one of P, S, and Si; and n represents the valence state of (YO4)n-.

[0133] As an optional embodiment of the present application, the general chemical formula of the polyanionic compound may be Nax-aAaVy-bMb(PO4)2-2c(DO4)2cFz.dQd, where the element A represents an alkali metal element doped to substitute the element Na, the element M represents a metal element substituting the element V, the element D represents a doping element substituting the element P, the element Q represents a doping element substituting the element F, the element D includes at least one of Si and S, and the element Q includes at least one of Cl and O; 3.5 < x < 4.5, 0 < a < 0.15x, 0.8 < y < 1.1, 0 < b < 0.3y, 0 < c < 0.15, 0.8 < z <1.1, and 0 < d < 0.2z. Optionally, the element A includes at least one of K and Li, and the element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0134] As an optional embodiment of the present application, the general chemical formula of the polyanionic compound may be NaxRy(PO4)2P2O7, where x = 3.5-4.5, y = 2.75-3.25, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0135] As an optional embodiment of the present application, the general chemical formula of the polyanionic compound may be Na4+xR3-yP4-mO15 / C, where 0 < x < 0.5, 0 < y < 0.5, 0 < m < 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0136] As an optional embodiment of the present application, the general chemical formula of the polyanionic compound may be NamFex(PO4)yP2O7 / C, where 3.6 < m < 4.4, 2.8 < x < 3, and 2 < y < 2.1. The Prussian blue compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, NaaMebMe’c(CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0<a<2,0<b<1, and 0 < c < 1.

[0137] In some embodiments, the positive electrode active substance layer may further include a conductive agent to improve the conductive performance of the positive electrode. The conductive agent is optionally one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0138] In some embodiments, the positive electrode active substance layer may further include a binder to firmly bind the positive electrode active substance and the optional conductive agent to the positive electrode current collector. The binder is optionally at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0139] In some embodiments, the positive electrode current collector may be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet is optionally one or more of Super-P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metallic materials of the metal foil, the carbon-coated metal foil, and the porous metal plate are each independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector may be a composite current collector formed by combining a metal foil and a polymer base film.

[0140] In some embodiments, the positive electrode plate may be prepared by: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on the positive electrode current collector, followed by drying, cold pressing, and other processes to obtain the positive electrode plate.

[0141] [Electrolyte]

[0142] The electrolyte conducts ions between the positive electrode plate and the negative electrode plate. The present application does not specifically limit the type of the electrolyte, which may be selected based on requirements. For example, the electrolyte may be liquid, gel, or all-solid.

[0143] In some embodiments, the electrolyte is an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0144] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate,          sodium          bis(fluorosulfonyl)imide,          sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0145] In some embodiments, the electrolytic solution includes an ester solvent, and the ester solvent includes at least one selected from ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, and fluoroethylene carbonate.

[0146] In some embodiments, the electrolytic solution includes an ether solvent, and the ether solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0147] In some embodiments, the electrolytic solution includes an ether solvent, and the ether solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0148] In some embodiments, the electrolytic solution further optionally includes an additive. For example, the additive may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may further include an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery and an additive for improving the high- or low-temperature performance of the battery.

[0149] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any porous-structure separator known to have good chemical stability and mechanical stability may be selected.

[0150] In some embodiments, the separator may be made of a material selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, which is not specified. In the case where the separator is a multi-layer composite film, the materials of the layers may be the same or different, which is not specified.

[0151] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be manufactured into an electrode assembly through a winding process or a stacking process.

[0152] In some embodiments, the secondary battery may include an outer package. The outer package may be configured to enclose the electrode assembly and electrolyte described above.

[0153] In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer package of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The soft pack may be made of plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

[0154] The present application does not particularly limit the shape of the secondary battery, and it may have a cylindrical shape, a prismatic shape, or any other shape. For example, FIG. 1 shows a secondary battery 5 having a prismatic structure as one example.

[0155] In some embodiments, referring to FIG. 2, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates define, in an enclosing manner, an accommodating cavity. The housing 51 is provided with an opening in communication with the accommodating cavity, and the cover plate 53 is capable of covering the opening to close the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be subjected to a winding process or a stacking process to form an electrode assembly 52. The electrode assembly 52 is packaged in the accommodating cavity. The electrolytic solution wets the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select the number based on specific and actual needs.

[0156] In some embodiments, the secondary battery may be assembled into a battery module. The number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by those skilled in the art based on the use and capacity of the battery module.

[0157] FIG. 3 shows a battery module 4 as one example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 may be sequentially arranged along the length direction of the battery module 4. Certainly, the arrangement may also be in any other manner. Further, the plurality of secondary batteries 5 may be fixed by a fastener.

[0158] Optionally, the battery module 4 may further include a casing having an accommodating space in which the plurality of secondary batteries 5 are accommodated.

[0159] In some embodiments, the battery module described above may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number may be selected by those skilled in the art based on the use and capacity of the battery pack.

[0160] FIGs. 4 and 5 show a battery pack 1 as one example. Referring to FIGs. 4 and 5, the battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery case includes an upper case body 2 and a lower case body 3. The upper case body 2 is capable of covering the lower case body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in any manner in the battery case.

[0161] In addition, the present application further provides an electric apparatus. The electric apparatus includes at least one of the secondary battery, the battery module, or the battery pack provided in the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the electric apparatus, and they may also be used as an energy storage unit for the electric apparatus. The electric apparatus may include, but is not limited to, a mobile device (e.g., a mobile phone or a laptop computer), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, or an electric truck), an electric train, a ship, or a satellite, an energy storage system, or the like.

[0162] As the electric apparatus, a secondary battery, a battery module, or a battery pack may be selected based on its usage requirements.

[0163] FIG. 6 shows an electric apparatus as one example. The electric apparatus is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. To meet the requirements of the electric apparatus for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

[0164] As another example, the device may be a mobile phone, a tablet computer, a laptop computer, or the like. The device is generally required to be light and thin, and a secondary battery may thus be used as a power source.

[0165] Furthermore, the present application further provides a current collector; the current collector includes a metal current collector substrate and a primer layer disposed on at least one side of the metal current collector substrate, and the primer layer includes an inorganic oxide.

[0166] Understandably, the current collector includes the current collector features of the secondary battery in any of the embodiments.

[0167] Examples

[0168] Hereinafter, examples of the present application are described. The examples described below are illustrative and merely used to explain the present application, and they should not be construed as limiting the present application. The examples without techniques or conditions specified therein are implemented according to techniques or conditions described in the literature in the art or according to product instructions. Reagents or instruments used herein without specified manufacturers are all commercially available conventional products.

[0169] Example 1

[0170] 1) Preparation of current collector

[0171] Preparation of primer slurry: 40 parts of aluminum oxide and 5 parts of polyacrylic acid were mixed in an aqueous solution; after the mixture was stirred uniformly, 2 parts of thickener CMC-Na were added to form a uniform and stable aluminum oxide dispersion; after 29.7 parts of Super-P were added and the mixture was stirred and dispersed uniformly, 28 parts of styrene-butadiene emulsion as a dot-like binder were immediately added and dispersed for 30 min; finally, 0.3 parts of polyoxyethylene ether as a wetting agent were added and dispersed for 30 min, to form a primer slurry with a solid content of 18%.

[0172] Coating of the primer slurry: The above primer slurry was uniformly coated on an aluminum metal current collector substrate and dried to obtain a primer layer with a coating mass of 140 mg / 1540.25 mm2. The dyne value of the aluminum metal current collector substrate was in the range of 20 mN / m to 35 mN / m.

[0173] 2) Preparation of negative electrode plate

[0174] Hard carbon as a negative electrode active material, conductive carbon black, styrenebutadiene rubber (SBR) as an aqueous binder, and sodium carboxymethylcellulose (CMC-Na) as a thickener were fully stirred at a mass ratio of 96:2:1:1 in a solvent system of deionized water and mixed uniformly to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on the negative electrode current collector prepared in the previous step, followed by drying, cold pressing, and slitting to obtain a negative electrode plate.

[0175] The preparation methods of Examples 2 to 8 were substantially the same as that of Example 1, except that the specific components of the primer layer were adjusted, as shown in Table 1 specifically. The conductive agent in Example 4 was the carbon nanotube.

[0176] Comparative Example 1

[0177] Hard carbon as a negative electrode active material, conductive carbon black, styrenebutadiene rubber (SBR) as a binder, and sodium carboxymethylcellulose (CMC-Na) as a thickener were fully stirred at a mass ratio of 96:2:1:1 in a solvent system of deionized water and mixed uniformly to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on the surface of an aluminum foil, followed by drying, cold pressing, and slitting to obtain a negative electrode plate.

[0178] The preparation method of Comparative Example 2 was substantially the same as that of Example 1, except that the specific components of the primer layer were adjusted, as specifically shown in Table 1. Table 1 Serial number Inorganic oxide Dispersant Particulate binder Conductive agent Wetting agent Thickener Composition Mass proportion Mass proportion Mass proportion Mass proportion Mass proportion Mass proportion Example 1 Aluminum oxide 40% 3% 28% 26.7% 0.3% 2.0% Example 2 Boehmite 40% 5% 28% 24.7% 0.3% 2.0% Example 3 Aluminum oxide 30% 3% 28% 36.7% 0.3% 2.0% Example 4 Aluminum oxide 60% 3% 28% 6.7% 0.3% 2.0% Example 5 Aluminum oxide 40% 1% 28% 28.7% 0.3% 2.0% Example 6 Aluminum oxide 40% 8% 28% 21.7% 0.3% 2.0% Example 7 Aluminum oxide 40% 3% 10% 44.7% 0.3% 2.0% Example 8 Aluminum oxide 40% 3% 40% 14.7% 0.3% 2.0% Comparative Example 1 No primer Comparative Example 2 / / 60% / 40% / /

[0179] II. Battery Performance Test

[0180] 1. Test for water resistance of negative electrode current collector

[0181] The negative electrode current collector coated with the primer layer prepared above was punched with a punching machine to obtain a sample with an area of about 2 mm2. 0.2 g of water was uniformly dropped onto the surface of the primer layer side of the sample, and then the sample was baked at 120 °C for 5 min. The sample was observed using a CCD microscope. If an exposed current collector substrate existed in the sample, the sample was determined as unqualified; if film tearing existed in the sample or the primer layer migrated and diffused outward, but the substrate was not exposed, the sample was determined as qualified; if a film layer in the sample did not change significantly, the sample was determined as good.

[0182] 2. Test for coating quality of negative electrode plate

[0183] The coating quality of the prepared negative electrode plate was observed; if severe edge shrinkage and large-area missed coating occurred, the negative electrode plate was determined as unqualified; if slight jagged edge shrinkage and slight dot-like missed coating occurred, the negative electrode plate was determined as qualified; if there was no edge shrinkage or missed coating, and the surface of the film layer was flat and uniform, the negative electrode plate was determined as good.

[0184] 3. Test for adhesion strength

[0185] According to the test method in the national standard GB / T 2791-1995, the peel strength between the negative electrode film layer and the current collector provided with the primer layer was tested.

[0186] 4. Test for elongation of electrode plate

[0187] Anegative electrode plate was taken, and the tab region was removed; three mark points were made transversely at intervals of three meters along the direction of the electrode plate, with the distance between two mark points being accurate to 0.1 mm; the distance between two adjacent points was recorded as a; the left and right gaps and the pressure roller tonnage of a cold press were adjusted between 20 tons and 79 tons, and the cold pressing thickness was adjusted so that the electrode plate reached a desired compacted density; the length b between the marks on the cold-pressed electrode plate was measured when the compacted density of the electrode plate was 0.95 g / cm3. That is, cold pressing elongation p = (b / a -1) * 100%. Two segments were taken from each of three samples, and the average value of the six pieces of data obtained from the testing was taken as the elongation of the electrode plate.

[0188] 5. Test for resistance of current collector

[0189] The current collector provided with the primer was tested using an electrode plate resistance tester (IEST). Five samples were taken for parallel testing, and the measured average value was taken as the film resistance of the current collector.

[0190] III. Analysis of Test Results of Examples and Comparative Examples

[0191] The batteries of the examples and comparative examples were prepared according to the methods described above, and various performance parameters were measured. The results are shown in Table 2 below. Table 2 Serial number Electrode plate Water resistance Coating appearance Adhesion strength Elongation Example 1 Good Good 25N / m 0.40% Example 2 Good Good 22N / m 0.60% Example 3 Good Good 20N / m 0.65% Example 4 Good Good 28N / m 0.35% Example 5 Good Good 20N / m 0.50% Example 6 Qualified Qualified / / Example 7 Qualified Qualified / / Example 8 Good Good 28N / m 0.40% Comparative Example 1 / Unqualified / / Comparative Example 2 / Unqualified / /

[0192] As can be seen from the comparison between the examples and the comparative examples, the secondary battery provided according to the embodiments of the present application, in which the primer layer includes an inorganic oxide, can realize the coating of an aqueous film layer slurry on the surface of an aluminum foil, which is conducive to further reducing the cost of the sodium secondary battery. As can be seen from the comparison among Examples 1,3, and 4, when the mass proportion of the inorganic oxide in the primer layer is 30% to 60%, the primer layer not only can improve the coating quality of the aqueous slurry on the current collector substrate, but also can improve the mechanical interlocking force with the film layer by means of the riveting effect between the inorganic oxide and the negative electrode active material, thereby increasing the adhesion strength between the film layer and the current collector; the primer layer can reduce the driving effect of film layer extension on the current collector during a cold pressing process, and reduce the elongation of the current collector during the cold pressing process. Table 3 Serial number Current collector film resistance (mO) Example 1 20 Example 2 18 Example 3 12 Example 4 15 Example 5 19 Example 6 24 Example 7 10 Example 8 40

[0193] As can be seen from Table 3, the mass proportion of the inorganic oxide of 30% to 60% and the mass proportion of the particulate binder of 10% to 30% can ensure the resistance while improving the coating quality, adhesion strength, and elongation of the electrode plate, and can ensure the electrochemical performance of the secondary battery while reducing costs.

[0194] Although the coating quality of the electrode plate in Examples 6 and 7 is improved and upgraded to qualified, slight jagged edge shrinkage and slight dot-like missed coating appear in the coating, making the adhesion strength and elongation of the electrode plate impossible to be accurately measured; therefore, the performance of the electrode plate was not tested.

[0195] As can be seen from the comparison of Examples 1, 2, and 5 with Example 6, in the case where the mass proportion of the dispersant is 1% to 5% based on the total mass of the primer layer, the interaction force between water molecules in the aqueous negative electrode film layer slurry and the dispersant of polyacrylic acid in the primer layer is maintained at an appropriate level. This prevents water molecules from easily infiltrating the molecules of the primer layer, thereby imparting good water resistance to the primer layer and further improving the coating appearance of the electrode plate.

[0196] As can be seen from the comparison of Examples 1, 2, and 8 with Example 7, in the case where the mass proportion of the particulate binder is greater than 10% based on the total mass of the primer layer, the particulate binder can provide sufficient adhesion in the primer layer. This prevents water molecules from easily infiltrating the molecules of the primer layer, thereby imparting good water resistance to the primer layer and further improving the coating appearance of the electrode plate.

[0197] It should be noted that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments having a structure substantially identical to the technical concept and exerting the same functional effects within the scope of the technical solutions of the present application are all included within the technical scope of the present application. Furthermore, without departing from the spirit of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, as well as other embodiments formed by combining some of the constituent elements of the embodiments, are also included within the scope of the present application.

Claims

1. A secondary battery, wherein the secondary battery comprises an electrode plate, and the electrode plate comprises a current collector and a film layer disposed on at least one side of the current collector; the current collector comprises a current collector substrate and a primer layer disposed on at least one side of the current collector substrate, the primer layer comprises an inorganic oxide, and the film layer comprises an aqueous binder.

2. The secondary battery according to claim 1, wherein the inorganic oxide comprises one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide.

3. The secondary battery according to claim 1 or 2, wherein based on a total mass of the primer layer, a mass proportion of the inorganic oxide is 30% to 60%.

4. The secondary battery according to any one of claims 1 to 3, wherein the inorganic oxide has a volume distribution particle size Dv50 < 2 pm.

5. The secondary battery according to any one of claims 1 to 4, wherein the primer layer further comprises a particulate binder, and the particulate binder comprises one or more of styrene-butadiene rubber and acrylate rubber.

6. The secondary battery according to claim 5, wherein based on a total mass of the primer layer, a mass proportion of the particulate binder is 10% to 40%.

7. The secondary battery according to any one of claims 1 to 6, wherein the primer layer further comprises a dispersant, and the dispersant comprises one or more of polyacrylic acidbased polymers.

8. The secondary battery according to claim 7, wherein based on a total mass of the primer layer, a mass proportion of the dispersant is 1% to 8%.

9. The secondary battery according to any one of claims 1 to 8, wherein based on a total mass of the primer layer, a mass proportion of the dispersant is 1% to 5%.

10. The secondary battery according to claim 8, whereinthe primer layer further comprises one or more of a conductive agent, a thickener, and a wetting agent; the conductive agent comprises one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / orthe thickener comprises one or more of sodium carboxymethylcellulose, sodium alginate, xanthan gum, and carrageenan; and / orthe wetting agent comprises one or more of a polyethoxy ether surfactant, a polyether silicone surfactant, a non-ionic fluorocarbon polymer surfactant, and an acetylenic surfactant.

11. The secondary battery according to claim 10, wherein based on a total mass of the primer layer, a mass proportion of the conductive agent is 10% to 40%, a mass proportion of the thickener is 0.5% to 4%, and a mass proportion of the wetting agent is 0.2% to 1%.

12. The secondary battery according to any one of claims 1 to 11, wherein a thickness of the primer layer is 0.5 pm to 3 pm.

13. The secondary battery according to any one of claims 1 to 12, whereinthe current collector substrate is a metal current collector substrate, and the metal current collector substrate is prepared by a calendering method.

14. The secondary battery according to any one of claims 1 to 13, whereina dyne value of the current collector substrate is 20 mN / m to 35 mN / m.

15. The secondary battery according to any one of claims 1to14, whereinthe current collector substrate comprises a metal current collector substrate, and the metal current collector substrate comprises at least one of a copper foil, an aluminum foil, a stainless steel foil, a titanium foil, and a nickel foil.

16. The secondary battery according to any one of claims 1 to 15, wherein the film layer further comprises a negative electrode active material, and the negative electrode active material comprises one or more of hard carbon, soft carbon, graphite, and silicon; and / orthe aqueous binder comprises one or more of styrene-butadiene rubber (SBR) and acrylate rubber.

17. The secondary battery according to any one of claims 1 to 16, wherein the secondary battery comprises one or more of a sodium secondary battery and a lithium secondary battery.

18. The secondary battery according to any one of claims 1 to 17, wherein the secondary battery comprises a sodium-ion battery, and a cell of the sodium-ion battery comprises:a battery housing, wherein an upper portion of the battery housing is provided with an opening;a top cover assembly, wherein the top cover assembly is disposed at the opening of the battery housing, and the top cover assembly is sealed and electrically connected to the battery housing;andan electrode assembly, wherein the electrode assembly is configured for an electrical connection, and the electrode assembly is disposed on the top cover assembly;wherein the top cover assembly comprises a top cover plate, and the electrode assembly and the top cover plate are configured as a single integral member made of aluminum metal or aluminum alloy.

19. An electric apparatus, wherein the electric apparatus comprises the secondary battery according to any one of claims 1 to 18.

20. A current collector, wherein the current collector comprises a current collector substrate and a primer layer disposed on at least one side of the current collector substrate, and the primer layer comprises an inorganic oxide.

21. The current collector according to claim 20, wherein the inorganic oxide comprises one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide.

22. The current collector according to claim 20 or 21, wherein the primer layer further comprises a particulate binder, and the particulate binder comprises one or more of a styrenebutadiene emulsion and an acrylate-based emulsion.

23. The current collector according to any one of claims 20 to 22, wherein the primer layerfurther comprises a dispersant, and the dispersant comprises one or more of polyacrylic acidbased polymers.

24. The current collector according to any one of claims 20 to 23, wherein the current collector substrate is a metal current collector substrate, and a dyne value of the metal current collector substrate is 20 mN / m to 35 mN / m.

25. The current collector according to any one of claims 20 to 24, wherein the current collector substrate is a metal current collector substrate, and the metal current collector substrate comprises an aluminum foil.

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