Composite current collector and preparation method thereof, pole piece, secondary battery and electric device

Abstract

The invention provides a composite current collector and a preparation method thereof, a pole piece, a secondary battery and an electric device. The composite current collector comprises a current collector base material and a current collector metal oxide film arranged on at least one side of the current collector base material, and the thickness of the metal oxide film is 0.5-2 microns. The composite current collector has high sheet resistance, and the safety performance of the battery can be improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a composite current collector and a preparation method thereof, a pole piece, a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] However, the safety of secondary batteries limits their application and popularity. How to effectively improve the safety performance of secondary batteries is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] The purpose of the present application is to provide a composite current collector capable of improving the safety performance of a secondary battery.

[0005] A first aspect of the present application provides a composite current collector, which includes a current collector substrate and a metal oxide film disposed on at least one side of the current collector substrate, wherein the thickness of the metal oxide film is 0.5 μm-2 μm.

[0006] The method of depositing a certain thickness of metal oxide film on at least one side of the current collector substrate effectively controls the square resistance of the composite current collector within a certain range, thereby increasing the short-circuit resistance when a short circuit occurs in an abnormal battery situation, greatly reducing the short-circuit current, reducing the heat released by the short circuit in the battery, reducing the risk of thermal runaway, and greatly improving the safety performance of the battery. Compared with the current collector in the prior art, the composite current collector structure has a high tolerance for the thickness difference of the metal conductive layer therein, so that the current collector substrate with poor precision and large square resistance deviation can also be used in the manufacture of batteries, greatly reducing the entry threshold of the current collector substrate that can be used for batteries, and significantly reducing the production cost of the battery.

[0007] In any embodiment, the thickness of the metal conductive layer may be 0.8 um to 2 um, or even greater.

[0008] In any embodiment, the thickness range of the metal oxide film is less than or equal to 400 nm.

[0009] The metal oxide film provided in the embodiments of the present application has good thickness uniformity, which is beneficial to improving the uniformity and consistency of the composite current collector and improving its electrochemical performance in the battery.

[0010] In any embodiment, the current collector substrate includes a support layer and a metal conductive layer disposed on two opposite surfaces of the support layer.

[0011] In any embodiment, the current collector substrate includes a metal conductive layer and a support layer, the support layer includes an insulating layer, and the metal conductive layer is disposed on two opposite surfaces of the insulating layer.

[0012] In any embodiment, the current collector substrate includes a metal conductive layer and a support layer, the support layer includes a metal layer or an alloy layer, and the metal conductive layer is disposed on two opposite surfaces of the metal layer or the alloy layer.

[0013] When a short circuit occurs under abnormal conditions of the battery, the insulating layer will fuse and block current conduction, which greatly reduces the short-circuit current and the temperature rise is small, ultimately reducing the risk of battery cell combustion and thermal runaway, greatly improving the safety performance of the battery. At the same time, the insulating layer is conducive to improving the elongation at break of the composite current collector, which can compensate for the negative impact of the metal oxide film on the processing performance of the composite current collector and meet the battery's requirements for the processing performance of the current collector. The metal conductive layer has conductive properties and is used to provide electrons for the electrode active material layer loaded on the composite current collector, playing the role of conductivity and current collection.

[0014] In any embodiment, the metal conductive layer includes at least one of aluminum, copper, titanium, silver, nickel, aluminum alloy, nickel alloy, titanium alloy, and silver alloy.

[0015] In any embodiment, the metal conductive layer includes a composite material of any one of metals or alloys and a two-dimensional material; the two-dimensional material includes at least one of a graphene material, a graphene-like material or a carbon fiber material.

[0016] In any embodiment, the thickness of the metal conductive layer is 0.8 um to 2 um.

[0017] The metal conductive layer has a conductive property and is used to provide electrons for the electrode active material layer loaded on the composite current collector, playing the role of conduction and current collection. In the prior art, the sheet resistance of the current collector is usually increased by controlling the thickness of the metal conductive layer. As the sheet resistance value increases, the metal conductive layer needs to be thinned to a certain extent. The embodiment of the present application adjusts the sheet resistance of the composite current collector through a metal oxide film, so that the composite current collector can tolerate a higher thickness of the metal conductive layer, broaden the formation path of the metal conductive layer, reduce the manufacturing cost of the composite current collector, and effectively achieve a significant reduction in battery cost.

[0018] In any embodiment, the thickness range of the metal conductive layer is less than or equal to 1.2 μm.

[0019] In any embodiment, the thickness range of the metal conductive layer is less than or equal to 0.6 μm.

[0020] The composite current collector provided in the embodiment of the present application is different from the current collector in the prior art, and is compatible with metal conductive layers with large thickness deviations, greatly expanding the production method of metal conductive layers, so that the manufacturing cost of the composite current collector is significantly reduced, thereby achieving a reduction in battery costs.

[0021] In any embodiment, the insulating layer comprises a polymer.

[0022] In any embodiment, the metal oxide film includes aluminum oxide or copper oxide.

[0023] The aluminum oxide film is non-conductive and has high chemical and thermal stability, which can steadily increase the square resistance of the composite current collector during the cycle life of the battery, thereby improving the safety performance of the battery.

[0024] In any embodiment, at room temperature, the sheet resistance of the composite current collector on one side of the metal oxide film is 25 mΩ / □-35 mΩ / □.

[0025] The composite current collector having the above-mentioned square resistance can increase the short-circuit resistance when a short circuit occurs in an abnormal situation of the battery, significantly reduce the short-circuit current, reduce the heat released due to the short circuit in the battery, reduce the risk of thermal runaway, and greatly improve the safety performance of the battery.

[0026] The second aspect of the present application provides a method for preparing a composite current collector, comprising: providing a current collector substrate, preparing a metal oxide film on at least one side of the current collector substrate by anodization to obtain a composite current collector, wherein the thickness of the metal oxide film is 0.5 μm-2 μm.

[0027] The anodic oxidation process is adopted, and the current collector substrate is used as the anode. A metal oxide film of a certain thickness is generated on its surface through an electrochemical reaction to obtain a composite current collector. The composite current collector has a certain square resistance, so that when a short circuit occurs inside the battery under abnormal conditions, the short-circuit current can be greatly reduced, the heat released by the short circuit is reduced, the risk of thermal runaway is reduced, and the safety performance of the battery is greatly improved. Compared with the current collector in the prior art, the composite current collector allows the current collector substrate with poor precision and large square resistance deviation to be applied to the manufacture of batteries, greatly reducing the entry threshold of the current collector substrate that can be used for batteries, and significantly reducing the production cost of the battery. In addition, the oxide film generated by the anodic oxidation method has a high degree of density and good thickness uniformity, which is conducive to improving the uniformity and consistency of the composite current collector.

[0028] In any embodiment, the thickness range of the metal oxide film is less than or equal to 400 nm. In any embodiment, the electrolyte of the anodizing method is an acidic electrolyte, the acidic electrolyte includes at least one of sulfuric acid, hypochlorous acid, and hypochlorite, and the mass percentage concentration of the acidic electrolyte is 10%-40%.

[0029] When the concentration of the acidic electrolyte is within the above range, it is conducive to the formation of a metal oxide film on the surface of the current collector substrate, which can not only improve the preparation efficiency of the metal oxide film, but also prevent the metal oxide film from decomposing too quickly due to excessively high concentration of the acidic electrolyte, thereby achieving stable and efficient preparation of the metal oxide film.

[0030] In any embodiment, the temperature of the electrolyte is 0°C-40°C.

[0031] When the temperature of the electrolyte is within the above range, acid corrosion is not likely to occur, and the electrochemical reaction efficiency of anodization can be improved, thereby achieving stable and efficient preparation of the metal oxide film.

[0032] In any embodiment, the voltage of the anodization method is 5V-25V.

[0033] When the voltage of the anodic oxidation is within the above range, the surface of the current collector substrate will not be ablated due to the oxidation voltage being too high, nor will the oxide film be unable to be generated due to the oxidation voltage being too low, thereby achieving stable and efficient deposition of the metal oxide film.

[0034] In any embodiment, the preparation method is a continuous production method.

[0035] The above method improves the preparation efficiency of the composite current collector, which is beneficial to industrial promotion and application.

[0036] In any embodiment, at room temperature, the sheet resistance of the composite current collector on one side of the metal oxide film is 25 mΩ / □-35 mΩ / □.

[0037] The composite current collector with a certain square resistance can significantly reduce the short-circuit current when a short circuit occurs inside the battery under abnormal conditions, reduce the heat released by the short circuit, reduce the risk of thermal runaway, and greatly improve the safety performance of the battery. The third aspect of the present application provides a pole piece, the pole piece includes a current collector, and the current collector includes the composite current collector of the first aspect or the composite current collector prepared by the preparation method of the second aspect.

[0038] A fourth aspect of the present application provides a secondary battery, comprising the electrode sheet of the third aspect.

[0039] A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some implementation methods of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0041] Figure 1 is a schematic diagram of a cross section of a composite current collector according to one embodiment of the present application;

[0042] Figure 2 is a schematic diagram of a cross section of a composite current collector according to one embodiment of the present application;

[0043] Figure 3 is a scanning electron microscope image of the surface of a composite current collector according to one embodiment of the present application;

[0044] Figure 4 (a) is a scanning electron microscope image of a cross section of a composite current collector according to an embodiment of the present application; (b) is a scanning electron microscope image of a cross section of a current collector according to the prior art;

[0045] Figure 5 is a schematic diagram of an electroplating device according to one embodiment of the present application;

[0046] Figure 6 is a schematic diagram of an embodiment of a secondary battery of the present application;

[0047] Figure 7 is an exploded schematic diagram of an embodiment of a secondary battery of the present application;

[0048] Figure 8 is a schematic diagram of an embodiment of a battery module of the present application;

[0049] Fig. 9 is a schematic diagram of an embodiment of a battery pack of the present application;

[0050] Fig.10 yes Fig. 9 An exploded schematic diagram of an embodiment of a battery pack is shown.

[0051] Fig.11 It is a schematic diagram of one embodiment of an electric device including the secondary battery of the present application as a power source.

[0052] In the accompanying drawings, the drawings are not necessarily drawn according to the actual scale. The description of the accompanying drawings is as follows:

[0053] 1 battery pack, 2 upper box, 3 lower box, 4 battery module, 5 secondary battery, 51 shell, 52 electrode assembly, 53 cover plate, 6 composite current collector, 61 current collector substrate, 62 metal oxide film, 611 metal conductive layer, 612 support layer, 7 electroplating device, 71 conductive roller, 72 external power supply, 73 electrolytic cell, 74 roller, 75 cathode plate, 76 electrolyte, L1 thickness of metal oxide film, L2 thickness of metal conductive layer, L3 thickness of insulating layer. DETAILED DESCRIPTION

[0054] Hereinafter, the composite current collector and its preparation method, as well as the embodiments of the pole piece, secondary battery and electric device containing the composite current collector of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0057] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0058] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0060] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] If not specifically stated, the terms used in this application have the commonly known meanings generally understood by those skilled in the art.

[0062] If not otherwise specified, the values ​​of the parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in this application.

[0063] If not otherwise specified, in the present application, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0064] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0065] Secondary batteries are prone to fire and explosion when subjected to abnormal conditions such as squeezing, collision or puncture, thus causing serious harm. Research results show that when secondary batteries are subjected to abnormal conditions such as squeezing, collision or puncture, internal short circuits occur in the battery, resulting in intense heat generation, which is the root cause of safety hazards such as battery fires and explosions. In the prior art, the square resistance of the current collector is often controlled within a certain range to reduce the probability of instantaneous internal short circuits in secondary batteries when safety hazards occur. In order to keep the square resistance of the current collector within a certain range, it is necessary to strictly control the thickness and precision of the conductive metal in the current collector, which makes the cost of the current collector remain high.

[0066] Based on this, Figure 1 As shown, the present application proposes a composite current collector 6, which includes a current collector substrate 61 and a metal oxide film 62 disposed on at least one side of the current collector substrate 61, and a thickness L1 of the metal oxide film 62 is 0.5 μm-2 μm.

[0067] In this article, "metal oxide film" refers to a film layer mainly composed of metal oxide.

[0068] Herein, “current collector substrate” refers to a main component for collecting current during discharge or charge of a secondary battery. In some embodiments, the metal oxide film 62 is disposed on one surface of the current collector substrate 61 .

[0069] In some embodiments, the metal oxide film 62 is disposed on two opposite surfaces of the current collector substrate 61 .

[0070] The thickness of the metal oxide film 62 can be tested by methods known in the art, for example, Figure 4 As shown in a, the composite current collector is polished by argon ion polishing technology to obtain a flat polished cross-section of the composite current collector, the cross-section of the composite current collector is tested by a scanning electron microscope, and the thickness L1 of the metal oxide film is measured by software.

[0071] In some embodiments, the thickness L1 of the metal oxide film 62 is 0.5um, 0.6um, 0.7um, 0.8um, 0.9um, 1.0um, 1.1um, 1.2um, 1.3um, 1.4um, 1.5um, 1.6um, 1.7um, 1.8um, 1.9um, 2.0um, or any range therebetween. It is generally believed that naturally generated metal oxide films are less than 0.5um.

[0072] In the prior art, it is often believed that depositing a metal oxide film on one side of the current collector substrate is not conducive to the electrochemical level of the current collector substrate in the battery. The present application overcomes the technical prejudice in the prior art, and adopts the method of depositing a certain thickness of metal oxide film 62 on at least one side of the current collector substrate 61 to effectively control the square resistance of the composite current collector 6 within a certain range, thereby increasing the short-circuit resistance when a short circuit occurs under abnormal conditions of the battery, greatly reducing the short-circuit current, reducing the heat released due to the short circuit in the battery, reducing the risk of thermal runaway, and greatly improving the safety performance of the battery. Compared with the current collector in the prior art, the composite current collector enables the current collector substrate with poor precision and large square resistance deviation to be applied to the manufacture of batteries, greatly reducing the entry threshold of the current collector substrate that can be used for batteries, and significantly reducing the production cost of the battery.

[0073] In some embodiments, the thickness L1 of the metal oxide film 62 has a range of less than or equal to 400 nm.

[0074] The range of the thickness of the metal oxide film refers to the larger one of the difference between the maximum thickness of the metal oxide film and the average thickness of the metal oxide film and the difference between the average thickness of the metal oxide film and the minimum thickness of the metal oxide film.

[0075] The range of the thickness of the metal oxide film can be obtained by any known method in the art. As an example, the composite current collector is polished by argon ion polishing technology to obtain a flat polished cross section of the composite current collector, the cross section of the composite current collector is tested by a scanning electron microscope, the thickness of the metal oxide film is measured by software, at least five different samples are taken, each sample takes at least 10 sites, the average thickness of the metal oxide film is calculated, and the larger of the difference between the maximum thickness of the metal oxide film and the average thickness of the metal oxide film or the difference between the average thickness of the metal oxide film and the minimum thickness of the metal oxide film is used as the range of the thickness of the metal oxide film.

[0076] In some embodiments, the range of the thickness L1 of the metal oxide film may be 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, or any range therebetween.

[0077] The metal oxide film provided in the embodiments of the present application has good thickness uniformity, which is beneficial to improving the uniformity and consistency of the composite current collector and improving its electrochemical performance in the battery.

[0078] In some embodiments, Figure 2 As shown, the current collector substrate 61 includes a support layer 612 and a metal conductive layer 611 disposed on two opposite surfaces of the support layer 612 .

[0079] In some embodiments, the metal conductive layer 611 includes at least one of aluminum, copper, titanium, silver, nickel, aluminum alloy, nickel alloy, titanium alloy, and silver alloy. Alternatively, the nickel alloy may be a nickel-iron alloy or a nickel-copper alloy.

[0080] In some embodiments, the metal conductive layer 611 includes a composite material of any one of metals or alloys and a two-dimensional material. Optionally, the two-dimensional material includes at least one of a graphene material, a graphene-like material, or a carbon fiber material. Optionally, the composite material can be a physical mixture of different materials in a single layer, or a composite structure of multiple layers stacked.

[0081] In this article, “graphene material” refers to the allotrope of carbon, with carbon atoms in the form of sp 2 Hybrid bonding forms a single-layer hexagonal honeycomb lattice graphene.

[0082] In this article, "graphene-like materials" refers to a general term for materials with a two-dimensional single-layer or few-layer structure, including but not limited to layered van der Waals solid materials, layered ionic solid materials, Group IV graphene-like materials, Group IV compounds, and Group III-V compounds. In this article, "carbon fiber materials" refers to high-strength and high-modulus fibers with a carbon content of more than 90%. In some embodiments, the metal conductive layer 611 includes at least one of aluminum and aluminum alloy.

[0083] In some embodiments, the metal conductive layer 611 is prepared by at least one of mechanical rolling, bonding, vapor deposition, and chemical plating, and the vapor deposition method includes at least one of vacuum evaporation, thermal evaporation, electron beam evaporation, and magnetron sputtering.

[0084] In some embodiments, the metal conductive layer 611 is prepared by a mechanical rolling method.

[0085] The metal conductive layer prepared by the mechanical rolling method is often thicker and has a large deviation value, which makes the square resistance of the current collector substrate smaller and the square resistance measured at different positions vary greatly. By providing a metal oxide film on at least one side of the metal conductive layer, the composite current collector has a suitable square resistance, which can significantly improve battery safety while reducing battery manufacturing costs.

[0086] In some embodiments, Figure 2 and Figure 4 As shown in a, the thickness L2 of the metal conductive layer 611 is 0.8 um to 2 um.

[0087] In some embodiments, the thickness L2 of the metal conductive layer 611 may be 0.8 um, 1 um, 1.2 um, 1.4 um, 1.6 um, 1.8 um, 2 um, or any range of values ​​therebetween.

[0088] The thickness L2 of the metal conductive layer can be tested by methods known in the art. As an example, the composite current collector is polished using argon ion polishing technology to obtain a smooth polished cross-section of the composite current collector, the cross-section of the composite current collector is tested using a scanning electron microscope, and the thickness of the metal conductive layer is measured using software.

[0089] The metal conductive layer has a conductive property and is used to provide electrons for the electrode active material layer loaded on the composite current collector, playing the role of conducting and collecting current. In the prior art, the sheet resistance of the current collector is often controlled by limiting the thickness of the metal conductive layer. The embodiment of the present application adjusts the sheet resistance of the composite current collector through the metal oxide film, so that the composite current collector can have a higher metal conductive layer thickness, broaden the formation path of the metal conductive layer, reduce the manufacturing cost of the composite current collector, and effectively achieve a significant reduction in battery cost.

[0090] In some embodiments, the thickness L2 of the metal conductive layer 611 has a range of less than or equal to 0.6 μm.

[0091] The extreme difference in thickness of the metal conductive layer refers to the larger one of the difference between the maximum thickness of the metal conductive layer and the average thickness of the metal conductive layer and the difference between the average thickness of the metal conductive layer and the minimum thickness of the metal conductive layer.

[0092] In some embodiments, the thickness L2 of the metal conductive layer 611 may have a range of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, or any range therebetween.

[0093] The range of the thickness L2 of the metal conductive layer can be obtained by any known method in the art. As an example, the composite current collector is polished by argon ion polishing technology to obtain a flat polished cross section of the composite current collector, the cross section of the composite current collector is tested by a scanning electron microscope, the thickness of the metal conductive layer is measured by software, at least five different samples are taken, each sample takes at least 10 sites, the average thickness of the metal conductive layer is calculated, and the larger of the difference between the maximum thickness of the metal conductive layer and the average thickness of the metal conductive layer or the difference between the average thickness of the metal conductive layer and the minimum thickness of the metal conductive layer is used as the range of the thickness of the metal conductive layer.

[0094] Figure 4 (b) is a current collector in the prior art, which only includes a support 612 and a metal conductive layer 611 disposed on both surfaces of the support layer 612. Figure 4 (a) and Figure 4From the comparison of (b), it can be seen that the composite current collector provided in the embodiment of the present application is different from the composite current collector in the prior art. By setting a metal oxide film to adjust the overall square resistance, it is compatible with the metal conductive layer 611 with large thickness deviation, greatly expanding the production method of the metal conductive layer 611, and significantly reducing the manufacturing cost of the composite current collector, thereby achieving a reduction in battery cost.

[0095] In some embodiments, the support layer 612 is an insulating layer.

[0096] In some embodiments, the support layer 612 is a metal layer or an alloy layer.

[0097] In some embodiments, the thickness L3 of the insulating layer is 4 um to 8 um.

[0098] In some embodiments, the thickness L3 of the insulating layer can be selected to be 4um, 5um, 6um, 7um, 8um or any range of values ​​therebetween. In some embodiments, the insulating layer includes an intermediate layer and an adhesive layer disposed on both sides of the intermediate layer. The adhesive layer facilitates the bonding and mechanical bonding of the conductive layer and the intermediate layer, which helps to further reduce the production cost.

[0099] In some embodiments, the insulating layer includes a polymer.

[0100] In some embodiments, the polymer includes at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate.

[0101] In some embodiments, the insulating layer further includes an inorganic filler.

[0102] In some embodiments, the inorganic filler includes at least one of alumina, silicon carbide, silicon dioxide, and glass fiber.

[0103] When a short circuit occurs in an abnormal battery situation, the insulating layer will melt and stop conducting current, which greatly reduces the short-circuit current. When an abnormal situation occurs, the heat released and the temperature rise will be reduced, which will ultimately reduce the risk of battery cell combustion and thermal runaway, greatly improving the safety performance of the battery. At the same time, the insulating layer is conducive to improving the elongation at break of the composite current collector, which can compensate for the negative impact of the metal oxide film on the processing performance of the composite current collector and meet the battery's requirements for the processing performance of the current collector.

[0104] In some embodiments, the metal oxide film 62 includes aluminum oxide or copper oxide.

[0105] In some embodiments, metal oxide film 62 includes aluminum oxide.

[0106] The surface of the metal oxide film can be tested by scanning electron microscopy, such as Figure 3 As shown. The aluminum oxide film is non-conductive and has high density, chemical stability and thermal stability. It can play a role in stably improving the square resistance of the composite current collector during the cycle life of the battery and improve the safety performance of the battery.

[0107] In some embodiments, Figure 1 As shown, under normal temperature conditions, the sheet resistance of the composite current collector 6 on the side of the metal oxide film 62 is 25 mΩ / □-35 mΩ / □.

[0108] In this article, "normal temperature" refers to 20±10℃.

[0109] In this article, "sheet resistance" refers to the voltage drop caused by the current density per unit area (i.e. the amount of current per unit area) in the thickness direction of the material at a certain temperature.

[0110] For conventional three-dimensional conductors, the resistance is calculated as:

[0111]

[0112] Where ρ represents resistivity, A represents cross-sectional area, and L represents length. The cross-sectional area can be decomposed into width W and film thickness t, that is, the resistance can be written as:

[0113]

[0114] Where Rs is the square resistance. When the diaphragm is in a square shape, L = W, and the measured resistance R is the square resistance R S , and R S Regardless of the size of L or W, R S is the resistance of the unit square, so R S The unit can be expressed as ohm per square (Ω / □).

[0115] The square resistance of the composite current collector on the metal oxide film side can be tested by methods known in the art. As an example, a four-terminal probe test instrument is used under room temperature conditions, and four smooth copper probes A, B, C, and D with a diameter of 2.0 mm are pressed in parallel on the metal oxide film of the composite current collector in sequence along the length direction of the composite current collector. A wire is welded on the copper rod and connected to the milliohmmeter so that the distance L between the copper rod B and the copper rod C is equal to the width W of the composite current collector. The distance between the copper rod A and the copper rod B, and the distance between the copper rod C and the copper rod D is not specifically limited, and can be selected as 10 mm-20 mm. After the milliohmmeter is turned on, the resistance value displayed by the milliohmmeter is the square resistance value of the composite current collector on the metal oxide film side.

[0116] In some embodiments, at room temperature, the square resistance of the composite current collector on one side of the metal oxide film is 25mΩ / □, 26mΩ / □, 27mΩ / □, 28mΩ / □, 29mΩ / □, 30mΩ / □, 31mΩ / □, 32mΩ / □, 33mΩ / □, 34mΩ / □, 35mΩ / □ or any range of values ​​therebetween.

[0117] The composite current collector having the above-mentioned square resistance can increase the short-circuit resistance when a short circuit occurs in an abnormal situation of the battery, significantly reduce the short-circuit current, reduce the heat released due to the short circuit in the battery, reduce the risk of thermal runaway, and greatly improve the safety performance of the battery.

[0118] In some embodiments, the elongation at break of the composite current collector is 15% to 30%.

[0119] In this article, the term "elongation at break" refers to the ratio of the length change of a material when it undergoes plastic deformation until it breaks after being subjected to force to its original length. It is usually expressed as a percentage and is an important parameter for measuring the deformation ability of a material under stress during stretching.

[0120] In the present application, the elongation at break of the composite current collector can be tested by methods known in the art. As an example, referring to GB / T 5230-1995 standard, at least 4 samples with a length of 200±0.5mm and a width of 15±0.25mm are cut, and the samples are continuously loaded at a tensile speed of 50mm / min at room temperature until they break. The maximum load divided by the cross-sectional area of ​​the sample is taken as the tensile strength of the sample.

[0121] In some embodiments, the elongation at break of the composite current collector may be 15%, 20%, 25%, 30% or any range therebetween.

[0122] When the elongation at break of the composite current collector is within the above range, the composite current collector also has good plasticity, which can reduce the probability of brittle fracture of the pole piece and further improve the safety of the battery.

[0123] The second aspect of the present application provides a method for preparing a composite current collector, comprising: providing a current collector substrate, preparing a metal oxide film on at least one side of the current collector substrate by anodization to obtain a composite current collector, wherein the thickness of the metal oxide film is 0.5 μm-2 μm.

[0124] In this article, the term "anodization method" refers to a process in which a metal oxide film is formed on the surface of a metal or its alloy in an electrolyte under specific process conditions and under the action of an applied current.

[0125] The anodic oxidation process is adopted, and the current collector substrate is used as the anode. A metal oxide film of a certain thickness is generated on its surface through an electrochemical reaction to obtain a composite current collector. The composite current collector has a certain square resistance, so that when a short circuit occurs inside the battery under abnormal conditions, the short-circuit current can be greatly reduced, the heat released by the short circuit is reduced, the risk of thermal runaway is reduced, and the safety performance of the battery is greatly improved. Compared with the current collector in the prior art, the composite current collector allows the current collector substrate with poor precision and large square resistance deviation to be applied to the manufacture of batteries, greatly reducing the entry threshold of the current collector substrate that can be used for batteries, and significantly reducing the production cost of the battery. In addition, the oxide film generated by the anodic oxidation method has a high degree of density and good thickness uniformity, which is conducive to improving the uniformity and consistency of the composite current collector.

[0126] In any embodiment, the thickness range of the metal oxide film is less than or equal to 400 nm. In some embodiments, at room temperature, the sheet resistance of the composite current collector on one side of the metal oxide film is 25 mΩ / □-35 mΩ / □.

[0127] In some embodiments, the electrolyte of the anodizing method is an acidic electrolyte, and the acidic electrolyte includes at least one of sulfuric acid, hypochlorous acid, and hypochlorite, and the mass percentage concentration of the acidic electrolyte is 10%-40%.

[0128] In some embodiments, the acidic electrolyte includes sulfuric acid.

[0129] In some embodiments, the mass percentage concentration of the acidic electrolyte is 10%, 15%, 20%, 25%, 30%, 35%, 40% or any range therebetween.

[0130] The mass percentage concentration refers to the percentage of the mass of the solute contained in the solution to the mass of the solution. When the concentration of the acidic electrolyte is within the above range, it is conducive to the formation of the metal oxide film on the surface of the current collector substrate, which can not only improve the preparation efficiency of the metal oxide film, but also prevent the metal oxide film from being decomposed too quickly due to the excessively high concentration of the acidic electrolyte, thereby realizing the stable and efficient preparation of the metal oxide film.

[0131] In some embodiments, the temperature of the electrolyte is 0°C-40°C.

[0132] In some embodiments, the temperature of the electrolyte is 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any range therebetween.

[0133] When the temperature of the electrolyte is within the above range, acid corrosion is not likely to occur, and the electrochemical reaction efficiency of anodization can be improved, thereby achieving stable and efficient preparation of the metal oxide film.

[0134] In some embodiments, the voltage of the anodization method is 5V-25V.

[0135] In some embodiments, the voltage of the anodization method is 5 V, 9 V, 13 V, 17 V, 21 V, 25 V, or any range therebetween.

[0136] When the voltage of the anodization method is within the above range, the surface of the current collector substrate will not be ablated due to the oxidation voltage being too high, nor will the oxide film be unable to be generated due to the oxidation voltage being too low, thereby achieving stable and efficient deposition of the metal oxide film.

[0137] In some embodiments, the preparation method is a continuous production method.

[0138] In some embodiments, the continuous production method uses a continuous belt conveyor to enable the current collector substrate to be continuously anodized. The above method improves the preparation efficiency of the composite current collector, which is conducive to industrial promotion and application.

[0139] In some embodiments, the continuous production method uses a continuous electroplating device. In some embodiments, the electroplating device 7 is as follows Figure 5 As shown, it includes a conductive roller 71, an external power source 72, an electrolytic cell 73, a roller 74, a cathode plate 75, and an electrolyte 76 contained in the electrolytic cell. The cathode plate 75 is immersed in the electrolyte 76 opposite to the surface of the current collector substrate 61.

[0140] In some embodiments, the conductive rollers 71 are disposed on two opposite surfaces of the current collector substrate 61 , respectively, so that both surfaces of the current collector substrate 61 can be positively charged.

[0141] In some embodiments, the continuous production method includes: connecting the conductive roller 71 of the electroplating device 7 to the positive electrode of the external power supply 72, and connecting the cathode plate 75 to the negative electrode of the external power supply 72; the current collector substrate 61 is transferred to the electrolytic cell 73 containing the electrolyte 76 via the conductive roller 71 for anodization and then moved out of the electrolytic cell 73 via the roller 74.

[0142] In some embodiments, the cathode plate is at least one of a copper plate and a lead plate.

[0143] In some embodiments, the conductive roller is a metal roller, and may be a stainless steel roller.

[0144] In some embodiments, the electroplating device includes at least two cathode plates, and the at least two cathode plates are disposed opposite to each other on two opposite surfaces of the current collector substrate.

[0145] This arrangement enables the upper and lower surfaces of the current collector substrate to be simultaneously anodic oxidized to form a metal oxide film when the current collector substrate is conveyed in the electrolytic cell, thereby improving production efficiency.

[0146] Pole piece

[0147] A third aspect of the embodiments of the present application provides a pole piece, the pole piece comprising a current collector, the current collector comprising a composite current collector of any embodiment or a composite current collector prepared by a preparation method of any embodiment.

[0148] In some embodiments, the electrode sheet is a positive electrode sheet, and the current collector is a composite current collector.

[0149] In some embodiments, the positive electrode sheet includes a composite current collector and a positive electrode film layer disposed on at least one surface of the composite current collector. For example, the composite current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the composite current collector.

[0150] The positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on a metal oxide film of a composite current collector, drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0151] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0152] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxide may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphate may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0153] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for a lithium ion battery may include one or more of lithium transition metal oxides and their modified compounds having the general formula Li a Ni b Co c M d O e A f where 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0154] In some embodiments, by way of example, the positive electrode active material for a lithium ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4.

[0155] In the present application, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0156] In some embodiments, the electrode sheet is a negative electrode sheet, and the current collector is a composite current collector.

[0157] In some embodiments, the negative electrode sheet includes a composite current collector and a negative electrode film layer provided on at least one surface of the composite current collector. For example, the composite current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the composite current collector.

[0158] In some embodiments, the negative electrode film layer includes a negative electrode active material. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy material.

[0159] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0160] In some embodiments, the negative electrode film layer may further include a negative electrode binder. The present application has no particular restrictions on the type of the negative electrode binder. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0161] In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0162] The negative electrode film layer is usually formed by coating the negative electrode slurry on the metal oxide film of the composite current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0163] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the composite current collector and the negative electrode film layer and disposed on the surface of the composite current collector; in some embodiments, the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.

[0164] Secondary battery

[0165] A fourth aspect of the embodiments of the present application provides a secondary battery.

[0166] The present application has no particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and removed back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present application has no particular restrictions on the type of the electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes may also include a separator, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0167] [Electrolytes]

[0168] In some embodiments, the electrolyte is an electrolyte solution, and the electrolyte solution includes an electrolyte salt and a solvent.

[0169] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0170] When the secondary battery of the present application is a lithium ion battery, as an example, the electrolyte salt may include 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 difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0171] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), 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), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

[0172] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high temperature performance of the secondary battery, and additives that improve the low temperature power performance of the secondary battery.

[0173] [Isolation film]

[0174] The present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0175] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0176] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly by a winding process or a lamination process.

[0177] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0178] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0179] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 6 The secondary battery 5 is a square structure as an example.

[0180] In some embodiments, Figure 7 As shown, the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0181] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying, and the secondary battery is obtained through vacuum packaging, standing, forming, shaping and other processes.

[0182] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0183] Figure 8 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 8 As shown, in the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0184] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0185] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0186] Fig. 9 and Fig.10 is a schematic diagram of a battery pack 1 as an example. Fig. 9 and Fig.10As shown, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0187] Electrical devices

[0188] The present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0189] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0190] Fig.11 Schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0191] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0192] Example

[0193] The following examples describe the disclosure of the present application in more detail, and these examples are only for illustrative purposes, as it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0194] Example 1

[0195] (1) Preparation of composite current collector

[0196] The structure of the current collector substrate is aluminum foil / polyvinyl fluoride / polypropylene / polyvinyl fluoride / aluminum foil, with polyvinyl fluoride / polypropylene / polyvinyl fluoride as the insulating layer, wherein the aluminum foil is deposited by mechanical calendering, and its single layer thickness is 1±0.2um, and the thickness of the insulating layer is 8um; the current collector substrate enters the electrolytic cell, passes through the conductive roller, and then enters the tank with the electrolyte, the electrolyte in the tank includes H2SO4, the electrolyte concentration is 15%, and the electrolyte temperature is 28°C,

[0197] The electrolytic cell is connected to an external power supply, the positive power supply is connected to a conductive roller, the conductive roller is a steel roller, after the current collector substrate passes through the conductive rollers arranged on the two opposite surfaces of the current collector, the two opposite surfaces of the current collector substrate are both positively charged, the negative power supply is connected to the cathode plate in the electrolytic cell, the cathode plate is negatively charged, the cathode plate is made of a copper plate, and the cathode plate area is 0.6m×2m, and a current loop is formed in the entire electrolytic cell; the electrolyte level is higher than the cathode plate, the cathode plate is immersed in the electrolyte as a whole, the current collector substrate passes between the upper and lower cathode plates in the electrolytic cell, the upper and lower cathode plates and the surfaces of the current collector substrate are basically parallel, the current collector substrate can realize the simultaneous anodization of the upper and lower surfaces during the belt walking process in the electrolytic cell, the belt walking speed is 4m / min, the anodization time is 3.0min, a metal oxide film is deposited on the current collector substrate, and a composite current collector is prepared. The thickness of the metal oxide film is 1.10±0.38um, and the elongation at break of the composite current collector is 18%.

[0198] (2) Preparation of batteries

[0199] The positive electrode active material NCM811, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are mixed evenly in an N-methylpyrrolidone (NMP) solution in a mass ratio of 97%:1%:2% to prepare a positive electrode slurry, which is then coated on the surface of the composite current collector using an extrusion coater and dried, and then the coated electrode is cold-pressed using a cold press to prepare the final positive electrode electrode.

[0200] The negative electrode active material artificial graphite, carbon nanotubes, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) are fully stirred and mixed in deionized water at a mass ratio of 97.1%:0.9%:1.1%:0.9% to form a uniform negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and a negative electrode film layer is obtained after drying and other processes.

[0201] A polyethylene film (PE membrane) is used as the isolation membrane.

[0202] Ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0203] The positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, and after drying, an electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, forming, shaping, and other processes.

[0204] Embodiment 2-4

[0205] The anodization parameters were adjusted, see Table 1 for details. The preparation method of the battery is basically the same as that of Example 1.

[0206] Comparative Example 1

[0207] A secondary battery was prepared using the current collector substrate before anodization in Example 1 as a positive electrode current collector.

[0208] Performance Testing

[0209] (1) Square resistance test

[0210] At 25°C, a four-terminal probe test instrument is used, and four smooth round copper rod probes A, B, C, and D are pressed in parallel on the metal oxide film of the composite current collector in sequence along the length direction of the composite current collector. The probe diameter is 2.00 mm. Wires are welded on the copper rods and connected to the milliohmmeter, so that the distance L between the copper rods B and C is equal to the width W of the composite current collector. There is no specific limitation on the distance between the copper rods A and B, and between the copper rods C and D, which can be selected as 10 mm-20 mm. After the milliohmmeter is connected, the resistance value displayed by the milliohmmeter is the square resistance value of the composite current collector on the metal oxide film side.

[0211] (2) Thickness test

[0212] The composite current collector obtained after anodization is sampled, a flat polished cross section is obtained by cross-section polishing technology, and the cross section of the composite current collector is tested by a scanning electron microscope to measure the thickness of the metal oxide film.

[0213] (3) Acupuncture experiment

[0214] After the battery is fully charged, use a φ1mm high-temperature resistant steel needle to pierce the battery at a speed of 0.1mm / s to a depth of 4mm from a direction perpendicular to the battery electrode. The piercing position should be close to the geometric center of the pierced surface. The steel needle stays in the battery. After standing for 1 hour, observe the battery fire situation.

[0215] Test Results

[0216] The test results of the embodiments and comparative examples are shown in Table 1.

[0217] Table 1

[0218]

[0219]

[0220] From the comparison between the embodiment and the comparative example, it can be seen that the composite current collector provided in the embodiment of the present application includes a current collector substrate and a metal oxide film disposed on at least one side of the current collector substrate, and the thickness of the metal oxide film is 0.5 μm-2 μm. Under normal temperature conditions, the square resistance of the composite current collector at room temperature is 25 mΩ / □-35 mΩ / □. The composite current collector has a high square resistance and does not catch fire after a needle puncture test for 1 hour, which helps to improve the safety performance of the battery.

[0221] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A composite current collector, characterized in that: The composite current collector comprises a current collector substrate and a metal oxide film disposed on at least one side of the current collector substrate, and the thickness of the metal oxide film is 0.5 μm-2 μm.

2. The composite current collector according to claim 1, characterized in that: The thickness range of the metal oxide film is less than or equal to 400 nm.

3. The composite current collector according to claim 1 or 2, characterized in that: The current collector substrate comprises a support layer and a metal conductive layer disposed on two opposite surfaces of the support layer; the current collector substrate comprises one or more of the following features: (1) The support layer is an insulating layer, and the metal conductive layer is disposed on two opposite surfaces of the insulating layer; (2) The support layer is a metal layer or an alloy layer, and the metal conductive layer is arranged on two opposite surfaces of the metal layer or the alloy layer.

4. The composite current collector according to claim 3, characterized in that: The metal conductive layer includes one or more of the following features: (1) The metal conductive layer comprises at least one of aluminum, copper, titanium, silver, nickel, aluminum alloy, nickel alloy, titanium alloy, and silver alloy; (2) The metal conductive layer includes a composite material of any one of metals or alloys and a two-dimensional material; the two-dimensional material includes at least one of a graphene material, a graphene-like material or a carbon fiber material.

5. The composite current collector according to claim 3 or 4, characterized in that: The thickness of the metal conductive layer is 0.8 μm to 2 μm.

6. The composite current collector according to any one of claims 3 to 5, characterized in that: The thickness range of the metal conductive layer is less than or equal to 0.6 μm.

7. The composite current collector according to any one of claims 3 to 6, characterized in that: The insulating layer includes a polymer.

8. The composite current collector according to any one of claims 1 to 7, characterized in that: The metal oxide film includes aluminum oxide or copper oxide.

9. The composite current collector according to any one of claims 1 to 8, characterized in that: Under normal temperature conditions, the sheet resistance of the composite current collector on one side of the metal oxide film is 25 mΩ / □-35 mΩ / □.

10. A method for preparing a composite current collector, characterized in that: include: providing a current collector substrate, A metal oxide film is prepared on at least one side of the current collector substrate by an anodic oxidation method to obtain a composite current collector, wherein the thickness of the metal oxide film is 0.5 μm-2 μm.

11. The preparation method according to claim 10, characterized in that: The thickness range of the metal oxide film is less than or equal to 400 nm.

12. The preparation method according to claim 11, characterized in that: The electrolyte of the anodizing method is an acidic electrolyte, which includes at least one of sulfuric acid, hypochlorous acid and hypochlorite, and the mass percentage concentration of the acidic electrolyte is 10%-40%.

13. The preparation method according to claim 12, characterized in that: The temperature of the electrolyte is 0°C-40°C.

14. The preparation method according to any one of claims 10 to 13, characterized in that: The voltage of the anodizing method is 5V-25V.

15. The preparation method according to any one of claims 10 to 14, characterized in that: The preparation method is a continuous production method.

16. The preparation method according to any one of claims 10 to 15, characterized in that: Under normal temperature conditions, the sheet resistance of the composite current collector on one side of the metal oxide film is 25 mΩ / □-35 mΩ / □.

17. A pole piece, characterized in that: The pole piece includes a current collector, and the current collector includes the composite current collector according to any one of claims 1 to 9 or the composite current collector prepared by the preparation method according to any one of claims 10 to 16.

18. A secondary battery, characterized in that: Including the pole piece as claimed in claim 17.

19. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 18.

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