Current collector, method for manufacturing the same, positive electrode sheet, secondary battery, and electric device

Abstract

The application provides a current collector and a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The current collector comprises a substrate and a protective coating on at least one side of the substrate, and the protective coating comprises polydioxolane. The protective coating is uniform and dense, and has good mechanical flexibility. On the one hand, the protective coating can effectively protect the substrate under high pressure to reduce or even avoid the rupture of the oxide film on the surface of the substrate, and on the other hand, the protective coating can prevent the electrolyte from directly contacting the substrate and inhibit the corrosion of the electrolyte on the substrate, thereby improving the safety and service life of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a current collector and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Current collectors are key components in batteries, directly determining their cycle life and performance. An ideal current collector should first have sufficient electronic conductivity; in addition, it should possess stable chemical and electrochemical properties to adapt to various operating environments of different battery systems.

[0003] In related technologies, aluminum foil is often used as the positive electrode current collector. However, aluminum foil has poor stability in lithium-ion electrolytes, and the naturally formed Al2O3 surface is insufficient to resist electrolyte corrosion. Especially under high voltages exceeding 3.0V, lithium salts in the electrolyte, such as LiPF6, LiClO4, LiFSI, and LiTFSI, will corrode the aluminum foil and oxidize it into Al. 3+ Ions dissolve into the electrolyte, causing the aluminum foil to break and leading to battery safety issues. Summary of the Invention

[0004] Therefore, it is necessary to provide a current collector and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device to improve the corrosion of the current collector substrate by the electrolyte and enhance battery safety.

[0005] To achieve the above objectives, a first aspect of this application provides a current collector comprising:

[0006] Substrate; and

[0007] A protective coating is located on at least one side of the substrate, the protective coating comprising polydioxane.

[0008] The current collector of this application has a protective coating containing polydioxanone. The coating is uniform and dense and has good mechanical flexibility. On the one hand, the protective coating can effectively protect the substrate under high pressure to reduce or even avoid the rupture of the oxide film on the substrate surface. On the other hand, the protective coating can also prevent the electrolyte from directly contacting the substrate and inhibit the electrolyte from corroding the substrate. Through the above combined effects, the safety and life of the secondary battery are improved.

[0009] In some embodiments, the protective coating further comprises lithium ions and at least one of sulfonic acid groups and sulfonic acid-like groups, wherein the lithium ions form a lithium salt with at least one of the sulfonic acid groups and sulfonic acid-like groups;

[0010] Optionally, the lithium salt accounts for 0.5%-8% of the mass of the protective coating, and optionally 2%-5%.

[0011] Optionally, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide.

[0012] In some embodiments, the thickness of the protective coating is 50nm-800nm, and optionally 300nm-500nm.

[0013] In some embodiments, the polydioxolane comprises 92%-99.5% by mass in the protective coating, and optionally 95%-98%.

[0014] In some embodiments, aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is an electrostatic attraction between the aluminum ions and the protective coating on the side of the substrate adjacent to the substrate.

[0015] In some embodiments, the current collector further includes a pre-coating;

[0016] Optionally, the pre-coating includes at least one of the following features:

[0017] (1) The pre-coating layer is located between the substrate and the protective coating;

[0018] (2) The pre-coating layer is located between the substrate and the protective coating layer. Aluminum ions are adsorbed at the interface between the pre-coating layer and the protective coating layer. There is a charge adsorption effect between the aluminum ions and the surface of the protective coating layer adjacent to the pre-coating layer.

[0019] (3) The pre-coating layer is located on the side of the protective coating away from the substrate;

[0020] (4) The pre-coating is located on the side of the protective coating away from the substrate. Aluminum ions are adsorbed at the interface between the substrate and the protective coating. There is an electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0021] In some embodiments, the pre-coating includes a carbon coating;

[0022] Optionally, the material of the carbon coating has at least one of the following characteristics:

[0023] (1) The thickness of the carbon coating is 1μm-10μm, and can be selected as 1μm-5μm;

[0024] (2) The carbon coating comprises a first conductive agent and a first binder;

[0025] Optionally, the mass ratio of the first conductive agent to the first adhesive is (1-19):1;

[0026] Optionally, the first conductive agent includes one or more of superconducting carbon fibers, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0027] Optionally, the first adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0028] In some embodiments, the pre-coating includes an active particle coating;

[0029] Optionally, the active particle coating has at least one of the following characteristics:

[0030] (1) The thickness of the active particle coating is 2μm-20μm;

[0031] (2) The active particle coating comprises active material particles, a second conductive agent, and a second binder;

[0032] Optionally, the volume average particle size Dv50 of the active substance particles is 0.2 μm-4 μm;

[0033] Optionally, the mass ratio of the active material particles, the second conductive agent, and the second binder is (50-80):(10-30):(10-20);

[0034] Optionally, the second conductive agent includes one or more of superconducting carbon fibers, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0035] Optionally, the second adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0036] The second aspect of this application provides a method for preparing the current collector of the first aspect of this application, comprising the following steps:

[0037] Solution A containing an etchant and solution B containing 1,3-dioxolane are prepared separately; solution B further contains one or more of sulfonic acid groups and sulfonic acid-like groups.

[0038] The substrate is prepared by etching at least one side surface of the substrate precursor with solution A.

[0039] The current collector is prepared by coating solution B onto the surface of the etched substrate precursor.

[0040] In some embodiments, solution A includes at least one of the following conditions:

[0041] (1) The etching agent includes aluminum fluorosulfonate salt;

[0042] Optionally, the fluorosulfonate aluminum salt includes one or more of aluminum trifluoromethanesulfonate, aluminum perfluorobutanesulfonate, and aluminum bis(trifluoromethanesulfonyl)imide;

[0043] (2) The mass percentage of the aluminum fluoride sulfonate salt in solution A is 2%-5%;

[0044] (3) The solvent of solution A includes one or more of 1,2-dimethoxyethane, diethyl ether, acetone and acetonitrile.

[0045] In some embodiments, solution B further comprises lithium ions, which form a lithium salt with at least one of the sulfonic acid group and the sulfonic acid-like group;

[0046] Optionally, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide;

[0047] Optionally, the lithium salt accounts for 2%-5% of the mass of the solution B.

[0048] In some embodiments, the etching time is 5 min to 30 min.

[0049] The third aspect of this application provides a positive electrode sheet, including the current collector of the first aspect of this application or the current collector prepared by the method of the second aspect of this application.

[0050] The fourth aspect of this application provides a secondary battery, which includes the positive electrode sheet of the third aspect of this application.

[0051] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of a current collector according to one embodiment of this application.

[0053] Figure 2 This is a schematic diagram of a current collector according to one embodiment of this application.

[0054] Figure 3 This is a schematic diagram of a current collector according to one embodiment of this application.

[0055] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0056] Figure 5 yes Figure 4 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0057] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0058] Explanation of reference numerals in the attached figures:

[0059] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0060] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0062] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0063] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0064] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 10-1000nm means that the units of the left endpoint "10" and the right endpoint "1000" are both nm (nanometer).

[0065] In this application, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "multiple" means two or more. This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0066] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way may include end values ​​or not.

[0067] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0068] In related technologies, when aluminum foil is used as the positive electrode current collector, the naturally formed Al2O3 surface is insufficient to resist electrolyte corrosion, especially under high voltages exceeding 3.0V, where lithium salts in the electrolyte will corrode the aluminum foil and oxidize it into Al. 3+ Ions dissolve into the electrolyte, causing the aluminum foil to break and leading to battery safety issues.

[0069] In addition, when aluminum foil is used as a positive current collector, it needs to have high electronic conductivity to allow a considerable current to flow through a high-load cathode.

[0070] Meanwhile, in order to meet energy density requirements, the compaction density of the positive electrode sheet is becoming increasingly higher, generally increasing to 3.5 g / cm³. 3 As mentioned above, under high pressure and dense roller pressing, the oxide film on the surface of the current collector is easily damaged and destroyed, resulting in the exposure of fresh aluminum and accelerating the corrosion of the aluminum foil.

[0071] To address the aforementioned issues, this application provides a current collector comprising a substrate and a protective coating. The protective coating is made of a polymer polydioxanone. The protective coating containing polydioxanone is uniform and dense, exhibiting good mechanical flexibility. On one hand, the protective coating can effectively protect the substrate under high pressure to reduce or even prevent the oxide film on the substrate surface from cracking. On the other hand, the protective coating can also prevent the electrolyte from directly contacting the substrate, inhibiting electrolyte corrosion of the substrate, thereby improving the safety and lifespan of the secondary battery.

[0072] A first aspect of this application provides a current collector including a substrate and a protective coating located on at least one side of the substrate, the protective coating comprising polydioxane.

[0073] It should be noted that the protective coating may be located on only one side of the substrate or on both sides of the substrate; preferably, the protective coating is located on both sides of the substrate.

[0074] The structural formula of polydioxolane is as follows:

[0075]

[0076] The value of n ranges from 100 to 5000.

[0077] Understandably, the preparation process of the protective coating first involves adding an etchant to etch the surface of the substrate. A large number of 1,3-dioxolane rings on the substrate surface undergo ring-opening polymerization under the catalysis of sulfonic acid groups or sulfonate-like groups. The ring-opened 1,3-dioxolane rings can then uniformly connect and polymerize into a film perpendicular to the substrate, exhibiting a macroscopically uniform and dense characteristic. The polydioxolane rings prepared after ring-opening polymerization have a long-chain structure. Ideally, the long chains of polydioxolane rings are perpendicular to the substrate surface; however, in reality, the long chains are not perpendicular to the substrate. Furthermore, the long-chain structure gives the internal molecules of the protective coating good flexibility, allowing it to withstand the mechanical stress under high pressure and density, thus providing a buffering protection for the substrate. The current collector of this application includes a protective coating, and the material of the protective coating includes polydioxolane rings. This protective coating is uniform and dense, possessing good mechanical flexibility. On the one hand, the protective coating can effectively protect the substrate under high pressure and density to reduce or even prevent the oxide film on the substrate surface from cracking; on the other hand, the protective coating can also prevent the electrolyte from directly contacting the substrate, inhibiting electrolyte corrosion of the substrate. Through these combined effects, the safety and lifespan of the secondary battery are improved.

[0078] As an example, the polymers contained in the aforementioned protective coatings can be qualitatively analyzed using detection methods such as infrared or Raman spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analysis.

[0079] Figure 1 A schematic diagram of the structure of the current collector improved according to one embodiment; Figure 2 In the process, the current collector includes a substrate 111 and a protective coating 112, with the protective coating 112 located on both sides of the substrate 111.

[0080] In some embodiments, the protective coating further includes lithium ions and at least one of sulfonic acid groups and sulfonic acid-like groups, wherein the lithium ions form a lithium salt with at least one of the sulfonic acid groups and sulfonic acid-like groups; due to the presence of the lithium salt, lithium ions can be slowly released during battery operation, thereby improving battery life; at the same time, during the preparation of the protective coating, the sulfonic acid groups and sulfonic acid-like groups can catalyze the ring-opening polymerization of 1,3-dioxolane.

[0081] In some optional embodiments, the lithium salt constitutes 0.5%-8% of the protective coating by mass. If the mass percentage of lithium salt in the protective coating is lower than this range, insufficient catalytic reaction may occur, making it difficult for 1,3-dioxolane to polymerize into chains. If the mass percentage of lithium salt in the protective coating is higher than this range, excessive lithium salt may exist in the protective coating as crystalline particles, affecting the overall flexibility of the protective coating. As an example, the mass percentage of lithium salt in the protective coating can be, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any two of the above values. Optionally, the mass percentage of lithium salt in the protective coating is 2%-5%.

[0082] It should be noted that when the current collector is used to fabricate a secondary battery, the mass percentage of lithium ions or lithium salt in the protective coating becomes variable as the secondary battery undergoes charge-discharge cycles because lithium salt slowly releases lithium ions during operation. The aforementioned mass percentage of lithium salt in the protective coating refers to the mass percentage of lithium salt contained within the current collector before it is used to fabricate the secondary battery.

[0083] As an example, the mass percentage of lithium salt in the protective coating mentioned above can be determined by the following method: the substrate with the protective coating is immersed in an appropriate amount of deionized water, and after being accelerated to dissolve by ultrasonication, stirring and other processes, the lithium salt content is determined by ion chromatography.

[0084] In some alternative embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide. It should be noted that the anion contained in the lithium salt, as a sulfonic acid-like group, can catalyze the ring-opening polymerization of 1,3-dioxolane.

[0085] As one possible implementation, the thickness of the protective coating is 50nm-800nm. When the thickness of the protective coating is less than this range, it is difficult to prepare and the uniformity is poor. When the thickness of the protective coating is greater than this range, the internal impedance of the battery cell may increase due to insufficient conductivity of the protective coating, and it will occupy the limited space inside the battery cell, affecting the battery cell's electrical performance. As an example, the thickness of the protective coating can be, but is not limited to, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, or any two of the above values. Optionally, the thickness of the protective coating is 300nm-500nm.

[0086] It should be noted that the thickness of the protective coating mentioned above refers to the thickness of the protective coating on one side of the substrate; when the substrate has protective coatings on both sides, the total thickness of the protective coating is the sum of the thicknesses of the protective coatings on both sides.

[0087] As an example, the thickness of the protective coating mentioned above can be measured using a high-magnification scanning electron microscope.

[0088] In some embodiments, the mass percentage of polydioxolane in the protective coating is 92%-99.5%; for example, it can be, but is not limited to, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, or any range between two of the above values. When the mass percentage of polydioxolane in the protective coating is lower than the above range, it may result in a relatively high mass percentage of lithium salt in the protective coating, affecting the overall flexibility of the protective coating; when the mass percentage of polydioxolane in the protective coating is higher than the above range, it may result in a relatively low mass percentage of lithium salt in the protective coating, insufficient catalytic reaction, and difficulty in polymerizing 1,3-dioxolane into chains. Optionally, the mass percentage of polydioxolane in the protective coating is 95%-98%.

[0089] As an example, the mass percentage of polydioxolane mentioned above in the protective coating can be quantitatively analyzed using detection methods such as infrared or Raman spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analysis.

[0090] In some embodiments, aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is an electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0091] It should be noted that the aluminum ions adsorbed on the substrate are residues obtained after etching the substrate with an etchant containing aluminum ions. After etching, the aluminum ions can be evenly distributed on the substrate. There is an electrostatic attraction between the aluminum ions and the protective coating on the side of the substrate adjacent to the substrate. The aluminum ions can electrostatically connect the substrate and the protective coating, improving the bonding strength between them. Simultaneously, the etching process creates an uneven, pitted surface on the substrate, significantly reducing its smoothness. This results in strong surface interactions between the substrate and the protective coating, further enhancing the bonding strength between them. This strong bond between the protective coating and the substrate serves two purposes: firstly, it prevents the positive electrode material from breaking or peeling off, reducing impedance increases during cycling; secondly, it provides support to prevent the positive electrode active material layer from breaking during processing.

[0092] As one possible implementation, the substrate material includes one of aluminum foil, nickel foil, and titanium-nickel alloy, or Eucommia ulmoides.

[0093] In some possible implementations, the current collector may also include a pre-coating. The relative positions of the pre-coating and the protective coating are not limited; the pre-coating can further reduce or even prevent damage to the substrate by positive electrode active particles under high pressure and density, thereby enhancing the substrate's corrosion protection.

[0094] In some alternative embodiments, the pre-coating is located between the substrate and the protective coating; the pre-coating also prevents the etchant from excessively etching the Al2O3 surface of the aluminum foil itself. It should be noted that in practical applications, when preparing the protective coating on the surface of the pre-coating, the raw material solution of the protective coating can penetrate into the pores of the pre-coating, enhancing the protective effect on the substrate.

[0095] In some alternative embodiments, the pre-coating layer is located between the substrate and the protective coating, and aluminum ions are adsorbed at the interface between the pre-coating layer and the protective coating. There is a charge adsorption between the aluminum ions and the surface of the protective coating adjacent to the pre-coating layer.

[0096] It should be noted that aluminum ions are adsorbed on the pre-coating layer. These aluminum ions are obtained by etching the pre-coating layer with an aluminum-ion-containing etchant, leaving residues. After etching, the aluminum ions are evenly distributed on the pre-coating layer. Due to the electrostatic attraction between the aluminum ions and the protective coating on the side adjacent to the pre-coating layer, the aluminum ions can electrostatically connect the pre-coating and protective coatings, improving the bonding strength between them. Simultaneously, the etching process creates an uneven, pitted surface on the pre-coating layer, significantly reducing its smoothness. This results in strong surface interactions between the pre-coating and protective coatings, further enhancing their bonding strength. This strong bond between the protective and pre-coating layers serves two purposes: firstly, it prevents the positive electrode active material from breaking or peeling off, reducing impedance increases during cycling; secondly, it provides support to prevent the positive electrode active material layer from breaking during processing.

[0097] In some alternative implementations, the pre-coating is located on the side of the protective coating away from the substrate.

[0098] In some alternative embodiments, the pre-coating is located on the side of the protective coating away from the substrate, aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is an electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0099] It should be noted that the aluminum ions adsorbed on the substrate are residues obtained after etching the substrate with an aluminum-ion-containing etchant. After etching, the aluminum ions can be evenly distributed on the substrate. Due to the electrostatic attraction between the aluminum ions and the side of the protective coating adjacent to the substrate, the aluminum ions can electrostatically connect the substrate and the protective coating, improving the bonding strength between them. Simultaneously, the etching process creates an uneven, pitted surface on the substrate, significantly reducing its smoothness. This results in strong surface interactions between the substrate and the protective coating, further enhancing the bonding strength between them. This strong bond between the protective coating and the substrate serves two purposes: firstly, it prevents the positive electrode material from breaking or peeling off, reducing impedance increases during cycling; secondly, it provides support to prevent the positive electrode active material layer from breaking during processing.

[0100] As one possible implementation, the pre-coating includes a carbon coating; on the one hand, using a carbon coating as a pre-coating can further improve the conductivity of the current collector; on the other hand, the particle size of the solid phase particles in the carbon coating is much smaller than the particle size of the solid phase in the negative electrode film layer of the negative electrode sheet. The carbon coating is located between the substrate and the negative electrode film layer, which can reduce the pressure damage to the substrate surface caused by large particles in the negative electrode film layer during cold pressing.

[0101] Figure 2 A schematic diagram of the current collector structure provided in one embodiment; Figure 2 In the current collector, there are a substrate 211, a carbon coating 212 located on both sides of the substrate 211, and a protective coating 213 located on both sides of the substrate 211; for the carbon coating 212 and the protective coating 213 on the same side of the substrate 211, the carbon coating 212 is located between the substrate 211 and the protective coating 213.

[0102] It should be noted that, Figure 2 This is merely a schematic diagram of a current collector and should not be interpreted as a limitation on the relative positional relationship between the carbon coating and the protective coating in the current collector.

[0103] In some optional embodiments, the thickness of the carbon coating is 1 μm-10 μm. If the thickness of the carbon coating is less than this range, it is difficult to prepare and cannot be coated evenly; if the thickness of the carbon coating is greater than this range, it will occupy the limited space inside the battery, resulting in a loss of battery energy density. As an example, the thickness of the carbon coating can be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any two of the above values. Optionally, the thickness of the carbon coating is 1 μm-5 μm.

[0104] It should be noted that the thickness of the carbon coating mentioned above refers to the thickness of the carbon coating on one side of the substrate; when the substrate has carbon coatings on both sides, the total thickness of the carbon coating is the sum of the thicknesses of the carbon coatings on both sides.

[0105] As an example, the thickness of the aforementioned carbon coating can be measured using a scanning electron microscope.

[0106] In some alternative embodiments, the carbon coating comprises a first conductive agent and a first binder; it should be noted that the terms "first conductive agent" and "first binder" mentioned in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0107] In some optional embodiments, the mass ratio of the first conductive agent to the first binder in the carbon coating is (1-19):1; for example, it can be, but is not limited to, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or any range between two of the above values. When the mass ratio of the first conductive agent to the first binder in the carbon coating is within the above range, both the conductivity and adhesion of the carbon coating can be considered.

[0108] As an example, the mass ratio of the first conductive agent to the first binder in the aforementioned carbon coating can be determined using thermogravimetric analysis.

[0109] In some optional embodiments, the first conductive agent includes one or more of superconducting carbon fibers, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. When the above substances are used as the first conductive agent in the carbon coating, the solid phase component in the carbon coating is in the form of small particles or microspheres, and the binder is more uniformly dispersed in the carbon coating, resulting in more sufficient contact between the binder and the substrate or protective coating. This can further prevent the positive electrode active material from breaking or peeling off; it can also further provide support to prevent the positive electrode active material layer from breaking during processing.

[0110] In some alternative embodiments, the first binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0111] As one possible implementation, the pre-coating includes an active particle coating; on the one hand, the active particle coating contains active material particles, which can simultaneously exert capacity and alleviate the excessive decrease in battery capacity caused by the setting of protective coating and pre-coating; on the other hand, the particle size of the solid phase small particles in the active particle coating is much smaller than the particle size of the solid phase in the negative electrode film layer in the negative electrode sheet, and the active particle coating is located between the substrate and the negative electrode film layer, which can reduce the pressure damage to the substrate surface caused by large particles in the negative electrode film layer during cold pressing.

[0112] Figure 3 A schematic diagram of the current collector structure provided in one embodiment; Figure 3 In the current collector, there are a substrate 311, an active particle coating 312 located on both sides of the substrate 311, and a protective coating 313 located on both sides of the substrate 311; for the active particle coating 312 and the protective coating 313 on the same side of the substrate 311, the active particle coating 312 is located between the substrate 311 and the protective coating 313.

[0113] It should be noted that, Figure 3 This is merely a schematic diagram of a current collector and should not be interpreted as a limitation on the relative positional relationship between the active particle coating and the protective coating in the current collector.

[0114] In some optional embodiments, the thickness of the active particle coating is 2μm-20μm; for example, it can be, but is not limited to, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or any two of the above values. When the thickness of the active particle coating is less than the above range, it is difficult to prepare and cannot be uniformly coated; when the thickness of the active particle coating is greater than the above range, it will occupy the limited space inside the battery, resulting in a loss of battery energy density.

[0115] It should be noted that the thickness of the active particle coating mentioned above refers to the thickness of the active particle coating on one side of the substrate; when there are active particle coatings on both sides of the substrate, the total thickness of the active particle coating is the sum of the thicknesses of the carbon coatings on both sides.

[0116] As an example, the thickness of the aforementioned active particle coating can be measured using a scanning electron microscope.

[0117] In some alternative embodiments, the active particle coating comprises active material particles, a second conductive agent, and a second binder. It should be noted that the terms "second conductive agent" and "second binder" mentioned in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0118] In some optional embodiments, the volume average particle size Dv50 of the active material particles in the active particle coating is 0.2 μm-4 μm. When the volume average particle size Dv50 of the active material particles is lower than the above range, the slurry processing during the preparation of the active particle coating is difficult and it is prone to gelation. When the volume average particle size Dv50 of the active material particles is higher than the above range, it is easy to cause pressure damage to the substrate and cannot play a protective role. As an example, the volume average particle size Dv50 of the active material particles can be, but is not limited to, 0.2 μm, 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.7 μm, 4 μm or any two of the above values.

[0119] As an example, the volume average particle size Dv50 of the active material particles mentioned above can be determined by the following method: the coating of the active particles is wiped off and collected, the conductive agent and binder are burned off at high temperature, and the particle size distribution and volume average particle size Dv50 of the active material particles are obtained by using a laser particle size analyzer.

[0120] In some optional embodiments, the mass ratio of active material particles, the second conductive agent, and the second binder in the active particle coating is (50-80):(10-30):(10-20); for example, it can be, but is not limited to, (55-80):(10-25):(10-18), (60-80):(10-20):(10-15), (65-80):(15-20):(10-15), (70-80):(15-20):(10-13), or any range between the above two ratios. When the mass ratio of active material particles, the second conductive agent, and the second binder is within the above range, the adhesion and conductivity of the active particle coating, as well as the processability of the slurry during coating preparation, can be balanced; at the same time, the active particle coating contains an appropriate amount of active material particles, which can prevent excessive degradation of the cell energy density due to the coating.

[0121] As an example, the mass ratio of active material particles, the second conductive agent, and the second binder in the aforementioned active particle coating can be determined by the following method: First, the type of active material particles is determined by elemental scanning, and the mass percentage of active material particles is roughly determined based on the current collector capacity; then, thermogravimetric analysis is used to roughly quantify the second binder, and the remaining part is the mass percentage of the conductive agent; finally, the mass ratio of the three components in the active particle coating is calculated.

[0122] In some alternative embodiments, the second conductive agent includes one or more of superconducting carbon fibers, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some alternative embodiments, the second binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0124] In some optional embodiments, the active material particles may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0125] It should be noted that, in some embodiments, the pre-coating layer may include both a carbon coating and an active particle coating, and the relative positions of the pre-coating layer, the active particle coating, and the protective coating are not limited.

[0126] In some implementations, the current collector includes:

[0127] Substrate; the substrate material includes one or more of aluminum foil, nickel foil, and titanium-nickel alloy; and

[0128] A protective coating is located on at least one side of the substrate. The protective coating comprises polydioxolane and lithium salt. The lithium salt accounts for 0.5%-8% of the mass of the protective coating. The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide. The thickness of the protective coating is 50nm-800nm. The polydioxolane accounts for 92%-99.5% of the mass of the protective coating. Aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is a charge attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0129] In some implementations, the current collector includes:

[0130] Substrate; the material of the substrate includes one or more of aluminum foil, nickel foil, and titanium-nickel alloy;

[0131] A protective coating is located on at least one side of the substrate. The protective coating comprises polydioxolane and a lithium salt. The lithium salt accounts for 0.5%-8% of the mass of the protective coating. The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide. The thickness of the protective coating is 50 nm-800 nm. The polydioxolane accounts for 92%-99.5% of the mass of the protective coating. Aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is a charge attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0132] A carbon coating is located between a substrate and a protective coating. Aluminum ions are adsorbed at the interface between the carbon coating and the protective coating, and there is a charge adsorption between the aluminum ions and the surface of the protective coating adjacent to the carbon coating. Alternatively, the carbon coating is located on the side of the protective coating away from the substrate, and aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is a charge attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate. The thickness of the carbon coating is 1 μm-10 μm. The carbon coating contains a first conductive agent and a first binder, with a mass ratio of (1-19):1. The first conductive agent includes one or more of superconducting carbon fibers, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The first binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0133] In some implementations, the current collector includes:

[0134] Substrate; the material of the substrate includes one or more of aluminum foil, nickel foil, and titanium-nickel alloy;

[0135] A protective coating is located on at least one side of the substrate. The protective coating comprises polydioxolane and a lithium salt. The lithium salt accounts for 0.5%-8% of the mass of the protective coating. The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide. The thickness of the protective coating is 50 nm-800 nm. The polydioxolane accounts for 92%-99.5% of the mass of the protective coating. Aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is a charge attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

[0136] An active particle coating is located between a substrate and a protective coating. Aluminum ions are adsorbed at the interface between the active particle coating and the protective coating, and there is electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the active particle coating. Alternatively, the active particle coating is located on the side of the protective coating away from the substrate, with aluminum ions adsorbed at the interface between the substrate and the protective coating, and there is electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate. The thickness of the active particle coating is 2μm-20μm. The active particle coating comprises active material particles, a second conductive agent, and a second binder. The volume average particle size D of the active material particles is... V50 is 0.2μm-4μm, and the mass ratio of active material particles, second conductive agent and second binder is (50-80):(10-30):(10-20). The second conductive agent includes one or more of superconducting carbon fiber, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The second binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorinated acrylate resin.

[0137] The second aspect of this application provides a method for preparing the current collector of the first aspect, comprising the following steps:

[0138] Solution A containing an etchant and solution B containing 1,3-dioxolane are prepared separately. Solution B also contains one or more of sulfonic acid groups and sulfonic acid-like groups. Solution A is coated on at least one side of the substrate precursor for etching to prepare a substrate. Solution B is coated on the surface of the etched substrate precursor to prepare a current collector.

[0139] In related technologies, aluminum foil is often used as the substrate for positive electrode current collectors. Taking aluminum foil as an example, the preparation mechanism of the current collector may be as follows: The surface of the aluminum foil has a naturally formed Al2O3 oxide layer. After coating the aluminum foil surface with solution A, the etchant can etch the aluminum foil surface. Then, solution B containing 1,3-dioxolane is coated on the etched aluminum foil surface. Under the catalysis of sulfonic acid groups and / or sulfonic acid-like groups, the 1,3-dioxolane molecules open rings and grow into chains, eventually forming a protective coating on a macroscopic scale, thus preparing the current collector.

[0140] In some embodiments, the etchant includes an aluminum fluorosulfonate salt; the etchant contains aluminum ions, which can be adsorbed onto the substrate surface and uniformly distributed when etching the substrate precursor. After the subsequent addition of a solution B containing 1,3-dioxolane, the aluminum ions distributed on the substrate can adsorb 1,3-dioxolane onto the substrate surface due to charge attraction. The large amount of adsorbed 1,3-dioxolane undergoes a ring-opening polymerization reaction under the catalysis of sulfonic acid groups or sulfonic acid-like groups; the etchant also contains sulfonic acid groups and / or sulfonic acid-like groups, which can play a synergistic role in catalyzing the ring-opening polymerization reaction of 1,3-dioxolane.

[0141] In some alternative embodiments, the fluorosulfonate aluminum salt includes one or more of aluminum trifluoromethanesulfonate, aluminum perfluorobutanesulfonate, and aluminum bis(trifluoromethanesulfonyl)imide.

[0142] In some optional embodiments, the mass percentage of the aluminum fluorosulfonate salt in solution A is 2%-5%; for example, but not limited to 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of the above values. When the mass percentage of the aluminum fluorosulfonate salt in solution A is lower than the above range, the substrate surface cannot be sufficiently etched, resulting in insufficient adhesion of the protective coating; when the mass percentage of the aluminum fluorosulfonate salt in solution A is higher than the above range, excessive sulfonic acid groups or sulfonic acid-like groups are introduced, which easily form lithium salt crystals after drying, affecting the polymer bonding.

[0143] In some alternative embodiments, the solvent of solution A includes one or more of 1,2-dimethoxyethane, diethyl ether, acetone, and acetonitrile.

[0144] In some embodiments, solution B also contains lithium ions, which form a lithium salt with at least one of sulfonic acid groups and sulfonic acid-like groups; by adding the lithium salt, the final protective coating also contains lithium ions, and after the current collector is prepared into a secondary battery, the lithium ions can be slowly released during the charging and discharging process of the secondary battery, thereby improving the cycle life of the secondary battery.

[0145] In some alternative embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide; the lithium salt contains both sulfonic acid groups and / or sulfonic acid-like groups, which can interact with the sulfonic acid groups and / or sulfonic acid-like groups in the etchant to catalyze the ring-opening polymerization of 1,3-dioxolane.

[0146] In some optional embodiments, the lithium salt constitutes 2%-5% of the mass of solution B; for example, it can be, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of the above values. When the mass percentage of lithium salt in solution B is lower than the above range, insufficient catalytic reaction may occur, making it difficult for 1,3-dioxolane to polymerize into chains; when the mass percentage of lithium salt in solution B is higher than the above range, excessive lithium salt will exist in the protective coating as crystalline particles, affecting the overall flexibility of the protective coating.

[0147] In some embodiments, the etching time is 5 min to 30 min; for example, it can be, but is not limited to, 5 min, 7 min, 10 min, 13 min, 15 min, 18 min, 20 min, 23 min, 25 min, 28 min, 30 min, or any two of the above values. When the etching time is controlled within the above range, effective etching of the substrate is ensured without affecting the substrate strength; when the etching time is below the above range, effective etching of the substrate cannot be achieved; when the etching time is above the above range, substrate damage is likely to occur, affecting the substrate strength.

[0148] It should be noted that in some embodiments, the steps of preparing a carbon coating and / or preparing an active particle coating are also included. When preparing the carbon coating and / or the active particle coating, conventional coating preparation methods in the art can be used. For example, a slurry can be prepared first, and then the slurry can be coated on a substrate or a protective coating and dried to obtain the carbon coating and / or the active particle coating.

[0149] In some embodiments, the method for preparing the current collector includes: preparing a solution A containing an etchant and a solution B containing 1,3-dioxolane; the etchant includes an aluminum fluorosulfonate salt, which includes one or more of aluminum trifluoromethanesulfonate, aluminum perfluorobutanesulfonate, and aluminum bis(trifluoromethanesulfonyl)imide, wherein the aluminum fluorosulfonate salt accounts for 2%-5% of the mass of the solution A; the solvent of solution A includes one or more of 1,2-dimethoxyethane, diethyl ether, acetone, and acetonitrile; solution B further includes a lithium salt, which includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide, wherein the lithium salt accounts for 2%-5% of the mass of the solution B;

[0150] Solution A is coated on at least one side of the substrate precursor and etched. After etching for 5-30 minutes, the substrate is dried to obtain the substrate.

[0151] Solution B was coated onto the surface of the etched substrate precursor, and dried after standing at room temperature for 24 hours to obtain the current collector.

[0152] A third aspect of this application provides a positive electrode sheet, comprising the current collector of the first aspect or the current collector prepared by the method of the second aspect.

[0153] The positive electrode also includes a positive electrode film layer located on at least one side of the current collector; as an example, the current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the current collector.

[0154] In some embodiments, the lithium-ion cathode active material may comprise cathode active materials known in the art for use in batteries. As an example, the cathode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0155] It should be noted that during the charging and discharging process of the battery, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li at different discharge states. In the examples of positive electrode active materials in this application, the molar contents of Li refer to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li will change after charge-discharge cycles.

[0156] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0157] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0158] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0159] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is coated on both sides of the positive current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coated on one side is 12-20 mg / cm². 2The compaction density of the positive electrode sheet is 3.0-3.75 g / cm³. 3 The selectable value is 3.4-3.65 g / cm³. 3 The formula for calculating the compaction density is as follows:

[0160] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0161] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet of the third aspect of this application. The secondary battery containing the aforementioned current collector exhibits high safety and excellent cycle performance.

[0162] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0163] Negative electrode sheet

[0164] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0165] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0166] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0167] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0168] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0169] In some embodiments, the negative electrode film may optionally include 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. The conductive agent accounts for 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0170] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0171] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; the obtained negative electrode slurry is coated on both sides of the negative electrode current collector, and after a drying process, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coated on one side is 75-220 mg / m³. 2 The compacted density of the negative electrode sheet is 1.2-2.0 g / m³. 3 .

[0172] electrolytes

[0173] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0174] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0175] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0176] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0177] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0178] Separating membrane

[0179] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0180] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0181] In some embodiments, the thickness of the isolation membrane is 3-20 μm, optionally 5-12 μm.

[0182] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process; the electrode assembly and electrolyte are packaged using the battery cell packaging material of the first aspect of this application.

[0183] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 1.

[0184] In some embodiments, refer to Figure 5 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed on the opening to close the receiving cavity.

[0185] The positive electrode, negative electrode, and separator can be formed into electrode assembly 12 by a winding or stacking process. Electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in electrode assembly 12. The secondary battery 1 can contain one or more electrode assemblies 12, which can be adjusted according to requirements.

[0186] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0187] In a battery module, multiple secondary batteries can be arranged sequentially along the length of the module. Alternatively, they can be arranged in any other manner. Furthermore, these multiple secondary batteries can be secured using fasteners.

[0188] Optionally, the battery module may also include a housing with a receiving space in which multiple secondary batteries are housed.

[0189] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0190] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0191] Electrical appliances

[0192] This application provides a fifth aspect of an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in the fourth aspect of this application. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; wherein, mobile devices may include, but are not limited to, at least one of mobile phones, laptops, etc.; electric vehicles may include, but are not limited to, at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0193] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0194] Figure 6 This is an example of an electrical device 2. This electrical device 2 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0195] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0196] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0197] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0198] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0199] I. Preparation of Current Collectors

[0200] Example 1

[0201] Aluminum trifluoromethanesulfonate (as an etchant) was dissolved in 1,2-dimethoxyethane, with the mass percentage concentration controlled at 2%-5%, to obtain solution A;

[0202] Solution A is applied to the surface of aluminum foil, etched for 5-30 minutes, and then dried to obtain the substrate;

[0203] Lithium bis(trifluoromethanesulfonyl)imide (as a lithium salt) was dissolved in 1,3-dioxolane to obtain solution B with a mass percentage concentration of 2%-5%.

[0204] Solution B is coated onto the etched surface of the substrate, left to stand at room temperature for 24 hours, and then dried to form a protective coating, thus obtaining the current collector.

[0205] Example 2-39

[0206] The preparation methods of the current collectors in Examples 2-39 are basically similar to those in Example 1. The main differences are: the type of etchant and / or its mass percentage concentration in solution A, the etching time, the type of lithium salt and / or its mass percentage concentration in solution B, the type of substrate, and at least one of the raw materials of the pre-coating are different, as detailed in Table 1.

[0207] The current collectors prepared in the above embodiments were measured, including at least one of the following structural parameters: the mass percentage of lithium salt in the protective coating, the thickness of the protective coating, the mass percentage of polydioxopentane in the protective coating, the thickness of the carbon coating, the mass ratio of conductive agent to binder in the carbon coating, the thickness of the active particle coating, the volume average particle size Dv50 of the active material particles, and the mass ratio of active material particles, the second conductive agent, and the second binder in the active particle coating. The measurement results are shown in Table 1.

[0208] Comparative Example 1

[0209] In Comparative Example 1, only aluminum foil was used as the current collector, and no protective coating or pre-coating was prepared.

[0210] The preparation and structural parameters in the above embodiments and comparative examples are shown in Tables 1-1 and 1-2.

[0211] Table 1-1

[0212]

[0213] Table 1-2

[0214]

[0215] In Tables 1-1 and 1-2, W1 represents the mass percentage concentration of the etchant in solution A, T1 represents the etching time, W2 represents the mass percentage concentration of the lithium salt in solution B, W3 represents the mass ratio of the first conductive agent to the first binder added during the preparation of the carbon coating, or W3 represents the mass ratio of the active material particles, the second conductive agent, and the second binder added during the preparation of the active particle coating; d1 represents the volume average particle size Dv50 of the active material particles in the preparation of the active particle coating; SP represents carbon black; PVDF represents polyvinylidene fluoride; PTFE represents polytetrafluoroethylene; CNT represents carbon nanotubes; M1 represents the mass percentage of the lithium salt in the protective coating, L1 represents the thickness of the protective coating, M2 represents the mass percentage of polydioxane in the protective coating; L2 represents the thickness of the pre-coating when it is an active particle coating; L3 represents the thickness of the pre-coating when it is a carbon coating. LiTFSI represents lithium bis(trifluoromethanesulfonyl)imide, and LiFSI represents lithium bis(fluorosulfonyl)imide.

[0216] It should be noted that the mass percentage of lithium salt in the aforementioned protective coating was determined using the following method: the substrate with the protective coating was immersed in deionized water, dissolved by ultrasound and stirring, and the lithium salt content was determined by ion chromatography.

[0217] The mass percentage of polydioxolane in the aforementioned protective coating was determined using thermogravimetric analysis.

[0218] The thicknesses of the protective coating, carbon coating, and active particle coating mentioned above were measured using scanning electron microscopy.

[0219] II. Preparation of Secondary Batteries

[0220] 1. Preparation of positive electrode sheet

[0221] The positive electrode active material NCM955, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 96.5:1.5:2. After thorough stirring and mixing, a positive electrode slurry was obtained. The positive electrode slurry was then uniformly coated on both sides of the current collectors prepared in the above embodiments and comparative examples. After drying, cold pressing, and slitting, the positive electrode sheets were obtained.

[0222] 2. Preparation of negative electrode sheet

[0223] The active material graphite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose (CMC), and the binder are dissolved in deionized water in a weight ratio of 95:1:2:1. After being uniformly mixed with the deionized water, a negative electrode slurry is prepared. The negative electrode slurry is coated on both sides of a copper foil, dried, and then cold-pressed and slit to obtain the negative electrode sheet.

[0224] 3. Use PE film as the separator.

[0225] 4. Preparation of electrolyte

[0226] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte; the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0227] 5. Battery manufacturing

[0228] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes, including settling, hot and cold pressing, formation, shaping, and capacity testing, to obtain a lithium-ion battery product.

[0229] III. Secondary Battery Performance Testing

[0230] 1. Capacity test

[0231] At a normal temperature of 25℃, the battery capacity is tested according to the following procedure: discharge the battery at a rate of 0.33C to 2.8V, let it rest for 5 minutes, and then charge it at a rate of 0.33C to 4.25V. The charging capacity is the battery capacity.

[0232] 2. Cyclic life test

[0233] At 25°C, the battery was charged to 80% SOC at a constant current rate of 0.5C, and then charged to 4.25V at a constant current and constant voltage rate of 0.33C. After standing for 5 minutes, it was discharged to 2.8V at a rate of 0.5C to complete one charge-discharge cycle. The number of cycles when the battery capacity decayed to 80% SOC was recorded.

[0234] 3. Impedance test

[0235] The DC resistance of the battery was tested before cycling and when the battery capacity decayed to 80% SOC, and the increase in impedance before and after cycling was calculated. The test methods for DC resistance before cycling and when the capacity decayed to 80% SOC are as follows:

[0236] At 25°C, the battery was calibrated to 50% SOC by constant current discharge at 0.33C. After resting for 5 minutes, it was discharged at 4C for 30 seconds. The voltage difference before and after 4C discharge was recorded, and the ratio of the voltage difference to the 4C current was taken as the DC impedance. The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0237] Table 2

[0238]

[0239]

[0240] As can be seen from the comparison of the results of Examples 1-39 and Comparative Example 1 in Table 2, the current collector of this application can improve the safety and cycle life of the secondary battery and reduce the impedance of the secondary battery.

[0241] The difference between Examples 1-7 lies in the thickness of the protective coating. In Example 2, the protective coating thickness is the smallest, while in Example 7, the protective coating thickness is the largest. A comparison of the results from Examples 1-7 shows that Example 2 has the largest capacity, while Example 7 has the smallest. Furthermore, compared to Examples 2 and 7, Examples 1 and Examples 3-6 show a significant increase in the number of cycle times and a marked decrease in impedance increase. Technical personnel analyzed that the reason for this might be that: when the protective coating thickness is too small, it is beneficial for increasing battery capacity, but the electrolyte may easily corrode the aluminum foil, leading to a significant deterioration in battery cycle performance and impedance; when the protective coating thickness is too large, the electrolyte is less likely to corrode the aluminum foil, but the insufficient conductivity of the protective coating itself may lead to an increase in battery impedance, and an excessively thick protective coating will also deteriorate battery capacity. In addition, an excessively thick protective coating will also affect electron transport and worsen cycle life.

[0242] The difference between Examples 1 and Examples 8-13 lies in the different mass proportions of lithium salt in the protective coating. In Example 8, the mass proportion of lithium salt is the smallest, while in Example 13, the mass proportion of lithium salt is the largest. Compared with Examples 8 and 13, the number of cycle times in Examples 1 and Examples 9-12 is significantly increased, and the impedance increase is significantly reduced. The technicians analyzed that the reason may be that: when the mass proportion of lithium salt in the protective coating is too small, it indicates that too little lithium salt was added during the preparation of the protective coating, which leads to insufficient addition of sulfonic acid groups and / or sulfonic acid groups that catalyze the ring-opening polymerization of 1,3-dioxolane. This may result in the 1,3-dioxolane failing to fully polymerize to form a dense protective coating, thus deteriorating the protective effect. When the mass proportion of lithium salt in the protective coating is too large, excessive lithium salt may exist in the form of crystalline particles in the protective coating, resulting in insufficient flexibility of the protective coating and also deteriorating the protective effect.

[0243] The difference between Examples 14-19 lies in the thickness of the carbon coating. Example 15 has the thinnest carbon coating, while Example 19 has the thickest. Compared to Example 1, Examples 14-19 show an increase in the number of cycles and a decrease in impedance increase, indicating that adding a carbon coating can further improve the corrosion protection of the substrate and increase the conductivity of the current collector, thereby reducing the impedance of the secondary battery and improving its cycle performance. Compared to Examples 15 and 19, Examples 14 and 16-18 show a significant increase in the number of cycles and a decrease in impedance increase. Technical personnel analyzed that this may be because: when the carbon coating thickness is insufficient, the protective ability of the carbon coating against the substrate may be relatively limited; when the carbon coating is too thick, on the one hand, the carbon coating contains more conductive agents, which (e.g., carbon black) may adsorb the electrolyte, resulting in some electrolyte failing to function and thus a relatively poor cycle life; on the other hand, the carbon coating contains more conductive agents, resulting in a larger overall specific surface area of ​​the conductive agents. During cycling, under the influence of potential, byproducts may accumulate on the surface of the conductive agents, leading to a relative deterioration in impedance. The significant reduction in capacity in Example 15 may be due to the fact that an excessively thick carbon coating would occupy the limited internal space of the battery, significantly deteriorating the battery capacity.

[0244] The difference between Examples 14 and Examples 20-23 lies in the different mass ratios of conductive agent and binder in the carbon coating, with the lowest ratio in Example 20 and the highest ratio in Example 23. Compared with Examples 20 and 23, the number of cycles in Examples 14 and Examples 21-22 increased significantly, while the impedance increase decreased significantly. Technicians analyzed that the reason for this may be that: insufficient amount of conductive agent in the carbon coating may lead to poor conductivity of the carbon coating, thereby significantly deteriorating the impedance and cycle performance of the secondary battery; insufficient amount of binder in the carbon coating may lead to the carbon coating peeling off, thereby significantly deteriorating the cycle performance and impedance.

[0245] The difference between Examples 26-30 lies in the thickness of the active particle coating; Example 27 has the smallest thickness, while Example 30 has the largest. Compared to Example 1, Examples 26-30 show an increase in the number of cycles and a decrease in impedance increase, indicating that adding an active particle coating can further improve the anti-corrosion protection effect on the substrate and reduce the impedance increase. Compared to Examples 27 and 30, Examples 26 and 28-29 show a significant increase in the number of cycles and a decrease in impedance increase. This may be because: when the active particle coating thickness is insufficient, the protective ability of the active particle coating against the substrate may be relatively limited; when the active particle coating is too thick, on the one hand, the amount of non-conductive material in the active particle coating increases, which may worsen the situation where the impedance is relatively small compared to the thickness of the active particle coating; on the other hand, the active particle coating contains more active material particles, which have a large overall specific surface area, which may lead to an increase in side reactions, thereby resulting in a relative deterioration in cycle life. The reduced capacity in Example 30 may be due to the increased amount of inactive material in the coating when the active particle coating is too thick, leading to a decrease in capacity.

[0246] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0247] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A current collector, characterized in that, include: Substrate; as well as A protective coating is located on at least one side of the substrate, the protective coating comprising polydioxolane; In the preparation process of the protective coating, an etchant is first added to etch the surface of the substrate. Then, 1,3-dioxolane on the surface of the substrate undergoes a ring-opening polymerization reaction under the catalysis of sulfonic acid groups or sulfonic acid-like groups. The etchant includes aluminum fluorinated sulfonate salts. The sulfonic acid-like groups include one or more of bis(trifluoromethanesulfonyl)imide groups, bis(fluorosulfonyl)imide groups, and bis(pentafluoroethanesulfonyl)imide groups.

2. The current collector as described in claim 1, characterized in that, The protective coating further comprises lithium ions and at least one of sulfonic acid groups and sulfonic acid-like groups, wherein the lithium ions form a lithium salt with at least one of the sulfonic acid groups and sulfonic acid-like groups.

3. The current collector as described in claim 2, characterized in that, The lithium salt accounts for 0.5%-8% of the mass of the protective coating.

4. The current collector as described in claim 3, characterized in that, The lithium salt accounts for 2%-5% of the mass of the protective coating.

5. The current collector as described in claim 2, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide.

6. The current collector as described in claim 1, characterized in that, The thickness of the protective coating is 50nm-800nm.

7. The current collector as described in claim 6, characterized in that, The thickness of the protective coating is 300nm-500nm.

8. The current collector as described in claim 1, characterized in that, The polydioxopentane comprises 92%-99.5% of the mass of the protective coating.

9. The current collector as described in claim 8, characterized in that, The polydioxopentane accounts for 95%-98% of the mass of the protective coating.

10. The current collector according to any one of claims 1 to 9, characterized in that, Aluminum ions are adsorbed at the interface between the substrate and the protective coating, and there is an electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

11. The current collector as described in claim 1, characterized in that, The current collector also includes a pre-coating.

12. The current collector as described in claim 11, characterized in that, The pre-coating includes at least one of the following features: (1) The pre-coating layer is located between the substrate and the protective coating; (2) The pre-coating is located on the side of the protective coating away from the substrate.

13. The current collector as described in claim 12, characterized in that, The pre-coating includes at least one of the following features: (1) The pre-coating layer is located between the substrate and the protective coating layer. Aluminum ions are adsorbed at the interface between the pre-coating layer and the protective coating layer. There is a charge adsorption effect between the aluminum ions and the surface of the protective coating layer adjacent to the pre-coating layer. (2) The pre-coating is located on the side of the protective coating away from the substrate. Aluminum ions are adsorbed at the interface between the substrate and the protective coating. There is an electrostatic attraction between the aluminum ions and the surface of the protective coating adjacent to the substrate.

14. The current collector as described in claim 11, characterized in that, The pre-coating includes a carbon coating.

15. The current collector as described in claim 14, characterized in that, The material of the carbon coating has at least one of the following characteristics: (1) The thickness of the carbon coating is 1μm-10μm; (2) The carbon coating comprises a first conductive agent and a first binder.

16. The current collector as described in claim 15, characterized in that, The thickness of the carbon coating is 1μm-5μm.

17. The current collector as described in claim 15, characterized in that, The mass ratio of the first conductive agent to the first adhesive is (1-19):

1.

18. The current collector as described in claim 15, characterized in that, The first conductive agent includes one or more of superconducting carbon fibers, carbon black, carbon dots, carbon nanotubes, and graphene.

19. The current collector as described in claim 15, characterized in that, The first conductive agent includes one or more of acetylene black, Ketjen black, and carbon nanofibers.

20. The current collector as described in claim 15, characterized in that, The first adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

21. The current collector according to any one of claims 11 to 20, characterized in that, The pre-coating includes an active particle coating.

22. The current collector as described in claim 21, characterized in that, The active particle coating has at least one of the following characteristics: (1) The thickness of the active particle coating is 2μm-20μm; (2) The active particle coating comprises active material particles, a second conductive agent and a second binder.

23. The current collector as described in claim 22, characterized in that, The volume average particle size Dv50 of the active substance particles is 0.2μm-4μm.

24. The current collector as described in claim 22, characterized in that, The mass ratio of the active material particles, the second conductive agent, and the second binder is (50-80):(10-30):(10-20).

25. The current collector as described in claim 22, characterized in that, The second conductive agent includes one or more of superconducting carbon fibers, carbon black, carbon dots, carbon nanotubes, and graphene.

26. The current collector as described in claim 22, characterized in that, The second conductive agent includes one or more of acetylene black, Ketjen black, and carbon nanofibers.

27. The current collector as described in claim 22, characterized in that, The second adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

28. A method for preparing a current collector as described in any one of claims 1 to 27, characterized in that, Includes the following steps: Solution A containing an etchant and solution B containing 1,3-dioxolane are prepared separately; solution B further contains one or more of sulfonic acid groups and sulfonic acid-like groups; the etchant includes aluminum fluorosulfonate. The substrate is prepared by etching at least one side surface of the substrate precursor with solution A. The current collector is prepared by coating solution B onto the surface of the etched substrate precursor.

29. The method for preparing a current collector as described in claim 28, characterized in that, Solution A includes at least one of the following conditions: (1) The fluorinated aluminum sulfonate salt includes one or more of aluminum trifluoromethanesulfonate, aluminum perfluorobutanesulfonate and aluminum bis(trifluoromethanesulfonyl)imide; (2) The mass percentage of the aluminum fluorosulfonate salt in solution A is 2%-5%; (3) The solvent of solution A includes one or more of 1,2-dimethoxyethane, diethyl ether, acetone and acetonitrile.

30. The method for preparing a current collector as described in claim 28, characterized in that, The solution B also contains lithium ions, which form a lithium salt with at least one of the sulfonic acid group and the sulfonic acid-like group.

31. The method for preparing a current collector as described in claim 30, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide.

32. The method for preparing a current collector as described in claim 30, characterized in that, The lithium salt accounts for 2%-5% of the mass of the solution B.

33. The method for preparing a current collector according to any one of claims 28 to 32, characterized in that, The etching time is 5 min to 30 min.

34. A positive electrode plate, characterized in that, Includes the current collector as described in any one of claims 1 to 27 or the current collector prepared by the method described in any one of claims 28 to 33.

35. A secondary battery, characterized in that, The secondary battery includes the positive electrode as described in claim 34.

36. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 35.

Images