Positive electrode composite current collector, positive electrode plate, secondary battery and electric device

Abstract

The invention provides a positive electrode composite current collector, a positive electrode plate, a secondary battery and an electric device. The positive electrode composite current collector comprises a polymer supporting layer, a conductive layer and a high-resistance layer, and the conductive layer is arranged on at least one surface of the polymer supporting layer; the high-resistance layer is arranged on the surface, away from the polymer supporting layer, of the conducting layer, the resistivity of the high-resistance layer is higher than that of the conducting layer, the total sheet resistance of the high-resistance layer and the conducting layer is R1, and R1 is larger than or equal to 50 m omega / -and smaller than or equal to 80 m omega / -. The positive electrode composite current collector disclosed by the invention can keep normal electrode conductivity, so that the DCR of the battery is in a proper range; therefore, the battery has a high nail penetrating test passing rate, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a positive composite current collector, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

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

[0003] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, and electric vehicles.

[0004] Currently, due to the great development of secondary batteries, higher requirements are also put forward for their safety performance. Secondary batteries with better safety performance have higher requirements for the current collector. For example, secondary batteries with better safety performance require that the current collector can better avoid the conduction between the positive and negative electrodes during the nail penetration test.

[0005] Therefore, seeking a current collector that can improve the safety performance of secondary batteries is one of the key concerns of those skilled in the art. Summary of the Invention

[0006] The present application is made in view of the above problems, and one of its purposes is to provide a positive composite current collector that can improve the safety performance of the battery while keeping the DCR of the battery at a relatively low level.

[0007] To achieve the above object, the first aspect of the present application provides a positive composite current collector, including:

[0008] A polymer support layer;

[0009] A conductive layer provided on at least one surface of the polymer support layer; and

[0010] A high-resistance layer provided on the surface of the conductive layer facing away from the polymer support layer, the resistivity of the high-resistance layer being higher than that of the conductive layer, and the total sheet resistance of the high-resistance layer and the conductive layer being R1, where 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □.

[0011] By providing a high-resistance layer on the surface of the conductive layer facing away from the polymer support layer, the resistivity of the high-resistance layer is higher than that of the conductive layer, and the total sheet resistance R1 of the high-resistance layer and the conductive layer satisfies 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □; through the above composite structure of the high-resistance layer and the conductive layer, while maintaining the normal electrode conductivity of the conductive layer and keeping the direct current internal resistance (DCR) of the battery within a suitable range, the battery can have a high passing rate in the nail penetration test, improving the safety performance of the battery.

[0012] In any embodiment, 58 mΩ / □ ≤ R1 ≤ 70 mΩ / □. In this way, the electrode conductivity and the passing rate of the nail penetration test can be better balanced, enabling the battery to not only meet the DCR requirements but also improve the safety performance of the battery.

[0013] In any embodiment, the sheet resistance of the conductive layer is R2, 25 mΩ / □ ≤ R2 ≤ 45 mΩ / □; optionally, 30 mΩ / □ ≤ R2 ≤ 40 mΩ / □. In this way, the conductive layer has an appropriate sheet resistance. When combined with the high-resistance layer, the total sheet resistance of the high-resistance layer and the conductive layer can be within a suitable range.

[0014] In any embodiment, the thickness ratio of the conductive layer to the high-resistance layer is A, 2 ≤ A ≤ 25; optionally, 2.5 ≤ A ≤ 20. In this way, the total sheet resistance of the conductive layer and the high-resistance layer can be within a suitable range, enabling the battery to pass the nail penetration test better and improving the safety performance of the battery.

[0015] In any embodiment, the thickness of the conductive layer is D1, 500 nm ≤ D1 ≤ 1500 nm; optionally, 600 nm ≤ D1 ≤ 1200 nm. In this way, in combination with the above thickness ratio of the conductive layer and the high-resistance layer, the total sheet resistance of the conductive layer and the high-resistance layer can be within a suitable range, enabling the battery to pass the nail penetration test better and improving the safety performance of the battery.

[0016] In any embodiment, the thickness of the high-resistance layer is D2, 30 nm ≤ D2 ≤ 500 nm; optionally, 35 nm ≤ D2 ≤ 400 nm. In this way, in combination with the thickness ratio of the conductive layer and the high-resistance layer and the thickness range of the conductive layer, the total sheet resistance of the conductive layer and the high-resistance layer can be within a suitable range, enabling the battery to pass the nail penetration test better and improving the safety performance of the battery.

[0017] In any embodiment, the total density of the conductive layer and the high-resistance layer is M1, 70% ≤ M1 ≤ 95%; optionally, 75% ≤ M1 ≤ 90%. In this way, by controlling the thickness and density of the conductive layer and the high-resistance layer, the total sheet resistance of the conductive layer and the high-resistance layer can be within a suitable range, enabling the battery to have a high passing rate in the nail penetration test and improving the safety performance of the battery; at the same time, controlling the total density of the conductive layer and the high-resistance layer within the above range can also make the composite current collector have appropriate elongation at break and breaking strength.

[0018] In any embodiment, the density of the conductive layer is M2, 50% ≤ M2 ≤ 75%; optionally, 55% ≤ M2 ≤ 70%. In this way, the combination of this conductive layer and the high-resistance layer can make the total sheet resistance within a suitable range, keep the DCR of the battery at a suitable level, and improve the passing rate of the nail penetration test and the safety performance of the battery.

[0019] In any embodiment, the material of the high-resistance layer includes one or more of aluminum oxide, silicon oxide, nickel-chromium alloy, and iron-chromium-aluminum alloy. Thus, the above-mentioned high-resistance layer material has a high resistivity, and when combined with the conductive layer, the high-resistance layer and the conductive layer can have an appropriate total sheet resistance.

[0020] In any embodiment, the material of the conductive layer includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0021] In any embodiment, the surface roughness Rz of the surface of the high-resistance layer facing away from the conductive layer is 0.1 μm to 2 μm. Thus, by controlling the surface roughness of the high-resistance layer within the above range, a good adhesion can be achieved between the positive electrode active material layer of the positive electrode sheet and the positive electrode composite current collector, enabling the positive electrode sheet to withstand a large shear force.

[0022] In any embodiment, the positive electrode composite current collector further includes an adhesive layer disposed between the polymer support layer and the conductive layer. Thus, by using the adhesive layer to bond the conductive layer to the polymer support layer, compared with the traditional method of evaporating or sputtering the conductive layer on the polymer support layer, it will not cause significant thermal damage to the polymer support layer and can improve the elongation at break of the positive electrode composite current collector.

[0023] In any embodiment, the adhesive layer includes an adhesive, and the adhesive includes a composition containing polyfunctional isocyanate and polyester polyol compound, polyurethane, epoxy resin, polyacrylate, polyvinyl acetate, unsaturated polyester, phenolic resin, urea-formaldehyde resin, modified polyolefin resin, silicone resin, ethylene-acrylic copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, acrylic resin, polycarbonate, and polyamide. Thus, using the above-mentioned adhesive can play a good bonding role between the polymer support layer and the conductive layer, resulting in a large peeling force between the conductive layer and the polymer support layer.

[0024] In any embodiment, the thickness of the adhesive layer is D3, where 200 nm ≤ D3 ≤ 1500 nm; optionally, 300 nm ≤ D3 ≤ 700 nm. Thus, it can not only ensure good bonding force between the polymer support layer and the conductive layer but also avoid the adhesive layer being too thick and affecting the battery energy density.

[0025] In any embodiment, the positive electrode composite current collector further includes a passivation layer disposed between the adhesive layer and the conductive layer. Thus, it can provide passivation protection to the interface where the conductive layer contacts the adhesive layer and reduce the micro-corrosion of the conductive layer by the electrolyte.

[0026] In any embodiment, the material of the passivation layer includes chromate, dichromate, organic phosphonate, Al 2 O3 , SiO 2 , and Si 3 N 4 One or more of them. In this way, a passivation layer is formed at the interface where the conductive layer contacts the adhesive layer by using the above materials, which can play a good passivation protection role for the conductive layer and effectively alleviate the micro-corrosion of the conductive layer by the electrolyte.

[0027] In any implementation, the chromate includes one or more of sodium chromate, potassium chromate, magnesium chromate, and silver chromate; the dichromate includes one or more of sodium dichromate, potassium dichromate, magnesium dichromate, and silver dichromate; the organic phosphonate includes one or more of hydroxyethylidene diphosphonic acid, diethylenetriamine pentamethylenephosphonic acid, triethylenetetramine hexamethylenephosphonic acid, and ethylenediamine tetramethylenephosphonic acid.

[0028] In any implementation, the thickness of the passivation layer is D4, and 1 nm ≤ D4 ≤ 500 nm; optionally, 10 nm ≤ D4 ≤ 200 nm. In this way, the micro-corrosion of the conductive layer by the electrolyte can be effectively alleviated.

[0029] In any implementation, the material of the polymer support layer includes one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene styrene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, sulfur nitride polymer materials, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and their derivatives, crosslinked products, and copolymers. Using the above materials as the polymer support layer can effectively improve the safety and energy density of the battery and reduce the cost of the current collector compared with traditional metal foil current collectors such as aluminum foil.

[0030] In any implementation, the thickness of the polymer support layer is D5, and 2 μm ≤ D5 ≤ 40 μm; optionally, 3 μm ≤ D5 ≤ 8 μm. In this way, the battery using the positive electrode composite current collector can have a higher energy density and better safety.

[0031] The second aspect of the present application also provides a positive electrode plate, which includes a positive electrode active material layer and the positive electrode composite current collector of the first aspect of the present application, and the positive electrode active material layer is disposed on the surface of the high-resistance layer away from the conductive layer. In this way, while maintaining the normal electrode conductivity of the conductive layer and keeping the battery DCR within a suitable range, the positive electrode plate can enable the battery to have a higher passing rate in the nail penetration test and improve the safety performance of the battery.

[0032] The third aspect of the present application further provides a secondary battery, including the positive composite current collector of the first aspect of the present application or the positive electrode sheet of the second aspect of the present application. Thus, the secondary battery has a high passing rate in the nail penetration test, good safety performance, and low DCR.

[0033] The fourth aspect of the present application further provides an electrical device, including the secondary battery of the third aspect of the present application.

[0034] Details of one or more embodiments of the present application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present application will become apparent from the specification, the drawings, and the claims. Description of the Drawings

[0035] To better describe and illustrate the embodiments or examples provided by the present application, one or more drawings may be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed application, the currently described embodiments or examples, and the best mode currently understood of these applications. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0036] Figure 1 Schematic diagram of the positive composite current collector according to an embodiment of the present application;

[0037] Figure 2 Schematic diagram of the positive electrode sheet according to an embodiment of the present application;

[0038] Figure 3 Schematic diagram of a battery cell according to an embodiment of the present application;

[0039] Figure 4 is Figure 3 Exploded view of the battery cell shown in an embodiment of the present application;

[0040] Figure 5 Schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0041] Explanation of the Reference Numerals in the Drawings:

[0042] 1. Positive composite current collector; 11. Polymer support layer; 12. Conductive layer; 13. High-resistance layer; 14. Adhesive layer; 15. Passivation layer; 2. Positive electrode sheet; 21. Positive electrode active material layer; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Embodiments

[0043] Hereinafter, embodiments of the composite current collector, electrode sheet, secondary battery, and electrical device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0044] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or not include the end values, and any end value can be independently included or not included, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are also listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer greater than or equal to 2, it is equivalent to listing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a certain parameter is an integer selected from "2 to 10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] In the present application, when it comes to "a plurality of", "a variety of", etc., unless otherwise specified, it means greater than 2 or equal to 2 in quantity. For example, "one or more" means one or greater than or equal to two.

[0046] If there is no special description, all embodiments and alternative embodiments of the present application can be combined with each other to form a new technical solution.

[0047] References to "embodiments" in this document mean that the specific features, structures, or characteristics described in connection with the embodiments may be included in at least one embodiment or implementation of this application. The phrase does not necessarily refer to the same embodiment at every position in the specification, nor are they independent or alternative embodiments mutually exclusive of other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments. References to "implementations" in this document have a similar understanding.

[0048] Those skilled in the art can understand that in the methods of each implementation or embodiment, the written order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Without special instructions, all steps of this application can be carried out 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) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may also include steps (c), (a), and (b), etc.

[0049] In this application, in an open technical feature or technical solution described by words such as "containing", "comprising", "including", etc., without other instructions, additional members outside the listed members are not excluded. It can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that also includes additional members outside the listed members. For example, A includes a1, a2, and a3. Without other instructions, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A not only includes a1, a2, and a3, but also includes other members". In this application, without other instructions, A (such as B) means that B is a non-limiting example in A, and it can be understood that A is not limited to B.

[0050] In this application, "optionally", "optional", "option" mean that it is optional, that is, it refers to any one of two parallel options of "having" or "not having". If "optional" appears multiple times in a technical solution, without special instructions and without contradictions or mutual constraints, each "optional" is independent of each other.

[0051] The weights described in the specification of the embodiments of this application may be weight units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0052] At present, due to the great development of secondary batteries, higher requirements are also put forward for their safety performance. Secondary batteries with better safety performance have higher requirements for current collectors. For example, a secondary battery with better safety performance requires that the current collector can better avoid the conduction between the positive and negative electrodes of the battery during the nail penetration test, thereby increasing the passing rate of the nail penetration test of the battery. In this regard, the present application improves the passing rate of the nail penetration test of the battery using the positive composite current collector by improving the structure of the positive composite current collector, and improves the safety performance of the battery.

[0053] Please refer to Figure 1 , a first aspect of the present application provides a positive composite current collector 1, which includes a polymer support layer 11, a conductive layer 12, and a high-resistance layer 13. Among them, the conductive layer 12 is disposed on at least one surface of the polymer support layer 11, the high-resistance layer 13 is disposed on the surface of the conductive layer 12 facing away from the polymer support layer 11, the resistivity of the high-resistance layer 13 is higher than that of the conductive layer 12, and the total sheet resistance of the high-resistance layer 13 and the conductive layer 12 is R1, and 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □.

[0054] In the present application, a high-resistance layer 13 is disposed on the surface of the conductive layer 12 facing away from the polymer support layer 11. The resistivity of the high-resistance layer 13 is higher than that of the conductive layer 12, and the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 satisfies 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □; through the above composite structure setting of the high-resistance layer 13 and the conductive layer 12, while maintaining the normal electrode conductivity of the conductive layer 12 and the battery DCR within a suitable range, the sheet resistance of the conductive layer 12 is increased, so that the passing rate of the nail penetration test of the battery using the positive composite current collector 1 can be increased, and the safety performance of the battery can be improved.

[0055] It should be noted that resistivity is a physical quantity used to represent the magnitude of the resistance of a material to the flow of current. The magnitude of resistivity is related to the nature of the material itself. The resistivity of the high-resistance layer 13 being higher than that of the conductive layer 12 means that, under the same other conditions, the material of the high-resistance layer 13 has a greater resistance to the flow of current than the material of the conductive layer 12. Sheet resistance refers to the resistance of a film material with a certain thickness and the same length and width. The total sheet resistance of the high-resistance layer 13 and the conductive layer 12 refers to the sheet resistance measured by taking the high-resistance layer 13 and the conductive layer 12 as a whole film layer.

[0056] It is understandable that the above-mentioned conductive layer 12 and high-resistance layer 13 can be provided on one of the surfaces of the polymer support layer 11, or the above-mentioned conductive layer 12 and high-resistance layer 13 can be provided on both opposite surfaces of the polymer support layer 11. It is understandable that the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 in this application can be, but is not limited to, 50 mΩ / sq, 51 mΩ / sq, 52 mΩ / sq, 53 mΩ / sq, 54 mΩ / sq, 55 mΩ / sq, 56 mΩ / sq, 57 mΩ / sq, 58 mΩ / sq, 59 mΩ / sq, 60 mΩ / sq, 61 mΩ / sq, 62 mΩ / sq, 63 mΩ / sq, 64 mΩ / sq, 65 mΩ / sq, 66 mΩ / sq, 67 mΩ / sq, 68 mΩ / sq, 69 mΩ / sq, 70 mΩ / sq, 71 mΩ / sq, 72 mΩ / sq, 73 mΩ / sq, 74 mΩ / sq, 75 mΩ / sq, 76 mΩ / sq, 77 mΩ / sq, 78 mΩ / sq, 79 mΩ / sq, 80 mΩ / sq.

[0057] In some embodiments, 58 mΩ / sq ≤ R1 ≤ 70 mΩ / sq. Controlling the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 in the positive composite current collector 1 within the range of 58 mΩ / sq to 70 mΩ / sq can better balance the electrode conductivity and the passing rate of the nail penetration test, enabling the battery to not only meet the DCR requirements but also improve the safety performance of the battery.

[0058] In some embodiments, the sheet resistance of the conductive layer 12 is R2, and 25 mΩ / sq ≤ R2 ≤ 45 mΩ / sq; optionally, 30 mΩ / sq ≤ R2 ≤ 40 mΩ / sq. In this way, the conductive layer 12 has an appropriate sheet resistance. When combined with the high-resistance layer 13, the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 can be within an appropriate range. It is understandable that R2 can be, but is not limited to, 25 mΩ / sq, 26 mΩ / sq, 27 mΩ / sq, 28 mΩ / sq, 29 mΩ / sq, 30 mΩ / sq, 31 mΩ / sq, 32 mΩ / sq, 33 mΩ / sq, 34 mΩ / sq, 35 mΩ / sq, 36 mΩ / sq, 37 mΩ / sq, 38 mΩ / sq, 39 mΩ / sq, 40 mΩ / sq, 41 mΩ / sq, 42 mΩ / sq, 43 mΩ / sq, 44 mΩ / sq, 45 mΩ / sq.

[0059] In some embodiments, the thickness ratio of the conductive layer 12 to the high-resistance layer 13 is A, and 2 ≤ A ≤ 25; the thickness of the conductive layer 12 is D1, and 500 nm ≤ D1 ≤ 1500 nm; the thickness of the high-resistance layer 13 is D2, and 30 nm ≤ D2 ≤ 500 nm. Controlling the thickness of the conductive layer 12, the thickness of the high-resistance layer 13, and the thickness ratio of the conductive layer 12 to the high-resistance layer 13 within the above ranges can keep the total sheet resistance of the conductive layer 12 and the high-resistance layer 13 within an appropriate range, enabling the battery to pass the nail penetration test better and improving the safety performance of the battery.

[0060] It can be understood that A can be, but is not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25; D1 can be, but is not limited to, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1100 nm, 1150 nm, 1200 nm, 1250 nm, 1300 nm, 1350 nm, 1400 nm, 1450 nm, 1500 nm; D2 can be, but is not limited to, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm.

[0061] In some embodiments, the thickness ratio of the conductive layer 12 to the high-resistance layer 13 is A, where 2.5 ≤ A ≤ 20; the thickness of the conductive layer 12 is D1, where 600 nm ≤ D1 ≤ 1200 nm; and the thickness of the high-resistance layer 13 is D2, where 35 nm ≤ D2 ≤ 400 nm. Controlling the thickness of the conductive layer 12, the thickness of the high-resistance layer 13, and the thickness ratio of the conductive layer 12 to the high-resistance layer 13 within the above ranges can make the total sheet resistance of the conductive layer 12 and the high-resistance layer 13 fall within a more appropriate range, further improving the passing rate of the battery nail penetration test and enhancing the safety performance of the battery; at the same time, it enables the battery to have a better DCR level, better balancing the DCR requirements and safety performance of the battery.

[0062] In some embodiments, the total density of the conductive layer 12 and the high-resistance layer 13 is M1, where 70% ≤ M1 ≤ 95%; optionally, 75% ≤ M1 ≤ 90%. The density of the conductive layer 12 and the high-resistance layer 13 has a certain impact on their resistivity, which in turn affects the total sheet resistance of the conductive layer 12 and the high-resistance layer 13. When the thicknesses of the conductive layer 12 and the high-resistance layer 13 are within the scope of this application, controlling the total density M1 of the conductive layer 12 and the high-resistance layer 13 within the above ranges can keep the total sheet resistance of the conductive layer 12 and the high-resistance layer 13 within a suitable range, thereby enabling the battery to have a high passing rate in the nail penetration test and good safety performance. At the same time, the density also affects the elongation at break and breaking strength of the positive composite current collector 1. Controlling the total density M1 of the conductive layer 12 and the high-resistance layer 13 within the above ranges can enable the positive composite current collector 1 to have appropriate elongation at break and breaking strength.

[0063] It can be understood that the total density of the conductive layer 12 and the high-resistance layer 13 refers to the density measured by taking the conductive layer 12 and the high-resistance layer 13 as a whole. The total density M1 of the conductive layer 12 and the high-resistance layer 13 can be, but is not limited to, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%.

[0064] In some of these embodiments, the density of the conductive layer 12 is M2, where 50% ≤ M2 ≤ 75%; optionally, 55% ≤ M2 ≤ 70%. Controlling the density of the conductive layer 12 within the above range can make the conductive layer 12 have an appropriate resistivity, make the high-resistance layer 13 have an appropriate density, and cooperate with the high-resistance layer 13 to make the total sheet resistance within an appropriate range, make the DCR of the battery at an appropriate level, and make the battery have a high passing rate in the nail penetration test. At the same time, it can make the positive composite current collector 1 have an appropriate elongation at break and breaking strength.

[0065] It can be understood that the density of the conductive layer 12 can be, but is not limited to, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%.

[0066] In some of these embodiments, the material of the high-resistance layer 13 includes one or more of alumina, silica, nickel-chromium alloy, and iron-chromium aluminum alloy. The above-mentioned material of the high-resistance layer 13 has a higher resistivity than the conductive layer 12, and cooperating with the conductive layer 12 can make the high-resistance layer 13 and the conductive layer 12 have an appropriate total sheet resistance.

[0067] In some of these embodiments, the material of the conductive layer 12 includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. It can be understood that the type of material of the conductive layer 12 can be selected from the above materials according to the type of the positive composite current collector 1. As an example, when the positive composite current collector 1 is a positive current collector, the material of the conductive layer 12 can be aluminum; when the positive composite current collector 1 is a negative current collector, the material of the conductive layer 12 can be copper.

[0068] In some of these embodiments, the surface roughness Rz of the surface of the high-resistance layer 13 facing away from the conductive layer 12 is 0.1 μm to 2 μm. When preparing the electrode sheet using the positive composite current collector 1 of the present application, it is necessary to form a corresponding positive active material layer on the high-resistance layer 13, and the surface roughness of the high-resistance layer 13 has a certain influence on the adhesion between the positive active material layer and the positive composite current collector 1. By controlling the surface roughness of the high-resistance layer 13 within the above range, the positive active material layer of the positive electrode sheet and the positive composite current collector 1 can have good adhesion, enabling the positive electrode sheet to withstand a large shear force.

[0069] Among them, the surface roughness Rz refers to the sum of the average value of the five largest profile peak heights and the average value of the five largest profile valley depths within the sampling length. It can be understood that the surface roughness Rz of the high-resistance layer 13 can be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm.

[0070] In some of these embodiments, the positive composite current collector 1 further includes an adhesive layer 14, and the adhesive layer 14 is disposed between the polymer support layer 11 and the conductive layer 12. The traditional positive composite current collector 1 usually forms the conductive layer 12 on the polymer support layer 11 by evaporation or sputtering. Since the temperature is relatively high when forming the conductive layer 12, it will cause relatively large thermal damage to the polymer support layer 11, and the positive composite current collector 1 is prone to deformation, resulting in a low elongation at break of the positive composite current collector 1. The present application uses the adhesive layer 14 to bond the conductive layer 12 to the polymer support layer 11, which will not cause significant thermal damage to the polymer support layer 11 and can improve the elongation at break of the positive composite current collector 1.

[0071] It can be understood that the adhesive layer 14 can be formed by coating and then curing. In some specific examples, an adhesive slurry can be first coated on the polymer support layer 11 and / or the conductive layer 12, the surfaces of the polymer support layer 11 and the conductive layer 12 coated with the adhesive slurry are compounded, and then the adhesive slurry is cured to form the adhesive layer 14, thereby bonding the polymer support layer 11 and the conductive layer 12 into one body. Among them, the conductive layer 12 can use a conductive metal foil with a certain thickness. After the conductive metal foil is compounded on the polymer support layer 11 through the adhesive layer 14, the conductive metal foil can be thinned to the required thickness of the conductive layer 12 by means of corrosion or the like. After forming the conductive layer 12, the high-resistance layer 13 can be formed on the conductive layer 12 by evaporation or the like.

[0072] In some of these embodiments, the adhesive layer 14 includes an adhesive, and the adhesive includes one or more of a composition containing polyfunctional isocyanate and polyester polyol compounds, polyurethane, epoxy resin, polyacrylate, polyvinyl acetate, unsaturated polyester, phenolic resin, urea-formaldehyde resin, modified polyolefin resin, silicone resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, acrylic resin, polycarbonate, and polyamide. Optionally, the adhesive includes one or more of a composition containing polyfunctional isocyanate and polyester polyol compounds and polyurethane. In some specific examples, the polyurethane includes one or more of thermoplastic polyurethane and reactive polyurethane. Using the above adhesives can play a good bonding role between the polymer support layer 11 and the conductive layer 12, so that there is a large peeling force between the conductive layer 12 and the polymer support layer 11.

[0073] In some of these embodiments, the thickness of the adhesive layer 14 is D3, where 200 nm ≤ D3 ≤ 1500 nm; optionally, 300 nm ≤ D3 ≤ 700 nm. Controlling the thickness of the adhesive layer 14 within the above range can not only enable good bonding force between the polymer support layer 11 and the conductive layer 12, but also avoid the adhesive layer 14 being too thick and affecting the battery energy density. It can be understood that the thickness D3 of the adhesive layer 14 can be, but is not limited to, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1100 nm, 1150 nm, 1200 nm, 1250 nm, 1300 nm, 1350 nm, 1400 nm, 1450 nm, 1500 nm.

[0074] In some of these embodiments, the positive composite current collector 1 further includes a passivation layer 15, and the passivation layer 15 is disposed between the adhesive layer 14 and the conductive layer 12. The conductive layer 12 of the positive composite current collector 1 and the polymer support layer 11 are bonded together through the adhesive layer 14 containing an adhesive. When the positive composite current collector 1 is used in a battery, the electrolyte may penetrate between the adhesive layer 14 and the conductive layer 12, thereby causing micro-corrosion to the conductive layer 12. By providing the passivation layer 15 between the adhesive layer 14 and the conductive layer 12 in this application, it can play a passivation protection role at the interface where the conductive layer 12 contacts the adhesive layer 14 and reduce the micro-corrosion of the conductive layer 12 by the electrolyte.

[0075] In some of these embodiments, the material of the passivation layer 15 includes chromate, dichromate, organic phosphonate, Al 2 O 3 、SiO 2 and Si3 N 4 One or more of them. Among them, the chromates include one or more of sodium chromate, potassium chromate, magnesium chromate, and silver chromate; the dichromates include one or more of sodium dichromate, potassium dichromate, magnesium dichromate, and silver dichromate; the organic phosphonates include one or more of hydroxyethane diphosphonic acid (HEDP), diethylenetriamine pentamethylenephosphonic acid (DETPMP), triethylenetetramine hexamethylenephosphonic acid (TETHMP), and ethylenediamine tetramethylenephosphonic acid (EDTMP). Using the above materials to form the passivation layer 15 at the interface where the conductive layer 12 contacts the adhesive layer 14 can play a good passivation and protection role on the conductive layer 12 and effectively relieve the micro-corrosion of the electrolyte on the conductive layer 12.

[0076] In some of these embodiments, the thickness of the passivation layer 15 is D4, 1 nm ≤ D4 ≤ 500 nm; optionally, 10 nm ≤ D4 ≤ 200 nm. Controlling the thickness of the passivation layer 15 within the above range can effectively relieve the micro-corrosion of the electrolyte on the conductive layer 12. It can be understood that the thickness of the passivation layer 15 can be, but is not limited to, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 250 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 350 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 450 nm, 460 nm, 480 nm, 500 nm.

[0077] In some of these embodiments, the material of the polymer support layer 11 includes one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene styrene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, sulfur nitride polymer materials, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and their derivatives, crosslinked products, and copolymers. Using the above materials as the polymer support layer 11 of the positive electrode composite current collector 1 can effectively improve the safety and energy density of the battery and reduce the cost of the current collector compared with traditional metal foil current collectors such as copper-aluminum and aluminum foil.

[0078] In some of these embodiments, the material of the polymer support layer 11 may further include one or more of a metal material and an inorganic insulating material. Among them, the inorganic insulating material may include one or more of alumina, silicon carbide, and silica. By adding the above-mentioned inorganic insulating material to the material of the polymer support layer 11, the strength of the positive electrode composite current collector 1 can be further improved.

[0079] In some of these embodiments, the thickness of the polymer support layer 11 is D5, where 2 μm ≤ D5 ≤ 40 μm; optionally, 3 μm ≤ D5 ≤ 8 μm. Controlling the thickness of the polymer support layer 11 within the above range can enable the battery using the positive electrode composite current collector 1 to have a higher energy density and better safety. It can be understood that the thickness of the polymer support layer 11 can be, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm.

[0080] In some of these embodiments, the positive electrode composite current collector 1 of the first aspect of the present application can be prepared by the following method: providing a polymer support layer 11 and a conductive layer 12; laminating the polymer support layer 11 and the conductive layer 12 through an adhesive paste; curing the adhesive paste to form an adhesive layer between the polymer support layer 11 and the conductive layer 12, and the adhesive paste includes an adhesive; whether to perform etching and thinning treatment on the conductive layer 12 can be selected according to the thickness requirement of the conductive layer 12; then a high-resistance layer 13 is formed on the conductive layer 12 by evaporation coating. During the preparation process of the positive electrode composite current collector 1, by controlling the thickness and density of the conductive layer 12 and the high-resistance layer 13, the total sheet resistance R1 of the conductive layer 12 and the high-resistance layer 13 is within the range of 50 mΩ / sq to 80 mΩ / sq.

[0081] By providing a high-resistance layer 13 on the surface of the conductive layer 12 facing away from the polymer support layer 11, and making the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 satisfy 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □; while maintaining the normal electrode conductivity of the conductive layer 12 and the battery DCR within a suitable range, the sheet resistance of the conductive layer 12 is increased, so that the passing rate of the nail penetration test of the battery using the positive composite current collector 1 can be improved, and the safety performance of the battery can be enhanced. Moreover, the conductive layer 12 and the polymer support layer 11 are compounded through the adhesive layer 14. Compared with the positive composite current collector 1 formed by the traditional methods of evaporation coating or magnetron sputtering to form the conductive layer 12, the positive composite current collector 1 prepared by the above method will not cause great thermal damage to the polymer support layer 11, and the positive composite current collector 1 can have a high elongation at break.

[0082] In some embodiments, the polymer support layer 11 and the conductive layer 12 can be compounded by the following method: gravure coating an adhesive paste on the metal foil serving as the conductive layer 12, baking the metal foil coated with the adhesive paste in an oven at 80°C to 110°C, and then thermally compounding the side of the baked metal foil coated with the adhesive paste with the polymer support layer 11. After the compounded current collector is cured, the binder is fully adhered. Then, according to the design requirements, the metal foil can be thinned by an etching thinning process to obtain a conductive layer 12 with a suitable thickness. In addition, a metal layer can also be formed as the conductive layer 12 on a thick carrier by evaporation coating or electrolysis before compounding, the metal layer is peeled off from the thick carrier, and then an adhesive paste is coated to compound the metal layer with the polymer support layer 11.

[0083] In some embodiments, before gravure coating the adhesive paste on the conductive layer 12, the surface of the side of the conductive layer 12 to be coated with the adhesive paste can be passivated to form a passivation layer 15. Specifically, the passivation layer 15 can be formed by compounding a passivation material on the conductive layer 12 by gravure printing, evaporation coating or magnetron sputtering, so as to form the passivation layer 15; then the adhesive paste is gravure coated on the passivation layer 15.

[0084] Please refer to Figure 2 , in some embodiments, the second aspect of the present application further provides a positive electrode sheet 2, which includes a positive electrode active material layer 21 and the positive composite current collector 1 of the first aspect of the present application. Among them, the positive electrode active material layer 21 is disposed on the surface of the high-resistance layer 13 facing away from the conductive layer 12. In this way, the positive electrode sheet 2 adopts the positive composite current collector 1 of the first aspect of the present application. Since the high-resistance layer 13 and the conductive layer 12 have a suitable total sheet resistance, while maintaining the normal electrode conductivity of the conductive layer 12 and keeping the battery DCR within a suitable range, the battery can have a high passing rate of the nail penetration test and good safety performance.

[0085] In some embodiments, a third aspect of the present application further provides a secondary battery, which includes the positive composite current collector 1 of the first aspect of the present application or includes the positive electrode sheet 2 of the second aspect of the present application. Thus, the secondary battery has a high passing rate in the nail penetration test, good safety performance, and the DCR of the battery is at an appropriate level.

[0086] In some embodiments, a fourth aspect of the present application further provides an electrical device, which includes the secondary battery of the third aspect of the present application.

[0087] The secondary battery and the electrical device of the present application will be described below with appropriate reference to the accompanying drawings.

[0088] Unless otherwise specified, the components, material types or contents of the battery mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0089] In one embodiment of the present application, a secondary battery is provided.

[0090] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0091] Positive electrode sheet

[0092] The positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector.

[0093] As a non-limiting example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive current collector.

[0094] In some embodiments, the positive current collector may adopt the positive composite current collector of the first aspect of the present application.

[0095] In some embodiments, the positive active material may include positive active materials known in the art for batteries.

[0096] As a non-limiting example, the positive electrode active material of a lithium-ion secondary battery may include one or more of the following materials: lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of a battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, 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, and their modified compounds. Non-limiting examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. A non-limiting example of lithium cobalt oxide may include LiCoO 2 ; a non-limiting example of lithium nickel oxide may include LiNiO 2 ; a non-limiting example of lithium manganese oxide may include LiMnO 2 , LiMn 2 O 4 and so on; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which may also be abbreviated as NCM 811 ) and so on; non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.1 Al 0.05 O 2 .

[0097] Understandably, during the charge and discharge process of the battery, the insertion and extraction of lithium (Li) and its consumption will occur, and the content of Li in the positive electrode plate varies when the battery is discharged to different states. In the enumeration of the positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. When the positive electrode material is applied to the positive electrode plate in the battery system, after charge and discharge cycles, the content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but it is not limited thereto. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before being fed into the positive electrode slurry. It can be understood that the new materials obtained by appropriate modification based on the listed positive electrode materials are also within the scope of the positive electrode materials. The aforementioned appropriate modification refers to the acceptable modification methods for the positive electrode materials, and non-limiting examples include coating modification.

[0098] In the enumeration of the positive electrode materials in this application, the content of oxygen (O) is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will show fluctuations. Among them, the content of O can be measured by molar content, but it is not limited thereto.

[0099] As a non-limiting example, the positive electrode active material of the sodium-ion secondary battery can include one or more of the following materials: one or more of sodium transition metal oxides, polyanion-type compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as the positive electrode active material of the sodium-ion battery can also be used.

[0100] As an alternative technical solution of this application, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO 2 , where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0101] As an alternative technical solution of this application, the polyanion-type compound can be a type of compound having sodium ions, transition metal ions, and a tetrahedral (YO 4 ) n- anion unit. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; n represents the valence state of (YO 4 ) n- .

[0102] The polyanion-type compound can also be a compound having sodium ions, transition metal ions, and a tetrahedral (YO 4 )n- A class of compounds containing anionic units and halogen anions. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, and n represents the valence state of (YO 4 ) n- . The halogen can be one or more of F, Cl, and Br.

[0103] The polyanionic compound can also be a class of compounds having sodium ions, tetrahedral (YO 4 ) n- anionic units, polyhedral units (ZO y ) m+ , and optionally halogen anions. Y can be one or more of P, S, and Si, and n represents the valence state of (YO 4 ) n- . Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence state of (ZO y ) m+ . The halogen can be one or more of F, Cl, and Br.

[0104] Examples of polyanionic compounds are NaFePO 4 , Na 3 V 2 (PO 4 ) 3 (sodium vanadium phosphate, abbreviated as NVP), Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), NaM’PO 4 F (M’ is one or more of V, Fe, Mn, and Ni) and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ≤ y ≤ 1), and the like.

[0105] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds are Na a Me b Me’ c (CN)6 , where Me and Me’ are each independently one or more of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0106] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 wt% to 100 wt%, based on the total weight of the positive electrode film layer.

[0107] In some embodiments, the positive electrode film layer may further optionally include a binder. As a non-limiting example, the binder 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 fluorinated acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 wt% to 20 wt%, based on the total weight of the positive electrode film layer.

[0108] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 wt% to 20 wt%, based on the total weight of the positive electrode film layer.

[0109] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, where the solid content of the positive electrode slurry is 40 wt% to 80 wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s to 25000 mPa·s. Coating the positive electrode slurry on the surface of the positive electrode current collector, and after drying, cold pressing through a cold rolling mill to form a positive electrode plate; the unit surface density of the positive electrode powder coating is 150 mg / m 2 ~350 mg / m 2 , and the compaction density of the positive electrode plate is 3.0 g / cm 3 ~3.6 g / cm 3 , optionally 3.3 g / cm 3 ~3.5 g / cm 3 .

[0110] The calculation formula for the compaction density is:

[0111] Compaction density = coating surface density / (thickness of the extruded electrode plate - thickness of the current collector).

[0112] The mass M of the positive electrode active substance per unit area of the positive electrode film can be obtained by weighing with a standard balance.

[0113] The thickness T of the positive electrode film can be measured using a micrometer. For example, a micrometer with the model Mitutoyo 293-100 and an accuracy of 0.1 μm can be used for measurement. It should be noted that the thickness of the positive electrode film described in this application refers to the thickness of the positive electrode film in the positive electrode plate that has been cold-pressed and compacted and is used for assembling the battery.

[0114] Negative electrode plate

[0115] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0116] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0117] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Among them, in the negative electrode current collector, non-limiting examples of the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the negative electrode current collector, non-limiting examples of the polymer material substrate can include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0118] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for use in batteries.

[0119] As a non-limiting example, the negative electrode active material of a lithium-ion secondary battery can include one or more 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 materials can include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials can include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0120] As a non-limiting example, the negative electrode active material of a sodium-ion secondary battery is generally hard carbon material, two-dimensional metal carbides or nitrides. Preferably, the negative electrode active material of a sodium-ion secondary battery is generally hard carbon material.

[0121] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0122] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0124] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density in terms of dry weight (deducting the solvent) can be 75 g / m 2 ~220 g / m 2 . The compaction density of the negative electrode plate can be 1.0 g / cm 3 ~1.8 g / cm 3 .

[0125] Electrolyte

[0126] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The present application does not particularly limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0127] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0128] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4) Lithium perchlorate (LiClO 4 ) Lithium hexafluoroarsenate (LiAsF 6 ) One or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0129] In some embodiments, the solvent may include one or more of fluoroethylene carbonate (FEC), 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), 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0130] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0131] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl carbonate (TFPC), etc.

[0132] Separator

[0133] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0134] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0135] In some embodiments, the thickness of the separator membrane is 6 μm to 40 μm, and may be optionally 12 μm to 20 μm.

[0136] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0137] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0138] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. Further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0139] The secondary battery includes at least one battery cell. The secondary battery can include 1 or more battery cells.

[0140] In this application, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy into each other. Further, generally, it includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and de-embedded between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0141] This application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 is a battery cell 5 with a square structure as an example.

[0142] In some embodiments, referring to Figure 4 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator membrane can form an electrode assembly 52 through a winding process or a stacking 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 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0143] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0144] In the battery module, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple battery cells 5 can be fixed by fasteners.

[0145] Optionally, the battery module can further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0146] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0147] The battery pack can include a battery box and multiple battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body. The upper box body can cover the lower box body and form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in the battery box in any manner.

[0148] In addition, the present application also provides an electrical device, and the electrical device includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0149] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0150] Figure 5 Shown is an electrical device 6 as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0151] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinness and lightness, and a secondary battery can be used as the power source.

[0152] The following are some embodiments.

[0153] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will further elaborate on this application in combination with embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of them. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes any limitation to this application and its application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by this application.

[0154] For those not specifying specific techniques or conditions in the embodiments, follow the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0155] I. Embodiments and Comparative Examples

[0156] Example 1:

[0157] 1) Preparation of the positive electrode sheet

[0158] 1.1) Preparation of the positive composite current collector

[0159] Select metal aluminum foil as the material for the conductive layer, and evenly coat the passivation solution potassium dichromate on the surface of the metal aluminum foil by gravure printing for passivation treatment to form a passivation layer. The thickness D4 of the passivation layer is 100 nm; coat the polyurethane adhesive slurry on the passivated surface of the metal aluminum foil by gravure; bake the coated metal aluminum foil in an oven and then thermally compound it with a polymer support layer with a thickness D5 of 6 μm to complete single-sided lamination. The polymer support layer uses a polyamide support layer.

[0160] Use the same method to compound metal aluminum foil on the other side of the polymer support layer. After compounding the metal aluminum foil, carry out aging to make the binder fully adhere; then thin the metal aluminum foil through etching to obtain a conductive layer with a thickness D1 of 800 nm, a sheet resistance R2 of the conductive layer of 35 mΩ / □, a density M2 of the conductive layer of 60%, and a thickness D3 of the bonding layer of 500 nm.

[0161] Deposit aluminum oxide as a high-resistance layer on the conductive layers on both surfaces of the polymer support layer by evaporation. During evaporation, control the thickness of the high-resistance layer by controlling the wire feeding amount of aluminum wire and the amount of oxygen introduced, so that the thickness D2 of each high-resistance layer is 400 nm. The total density M1 of the high-resistance layer and the conductive layer is 95%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 80 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 2, and the surface roughness Rz of the high-resistance layer is 1.5 μm.

[0162] 1.2) Preparation of the positive active material layer

[0163] The cathode active material NCM811, the conductive agent conductive carbon black, and the binder SBR styrene-butadiene latex are mixed evenly in a mass ratio of 97:1.2:1.8 in the solvent N-methylpyrrolidone to obtain a cathode slurry. The above-mentioned cathode slurry is respectively coated on the high-resistance layers on both sides of the cathode composite current collector, and through processes such as drying, cold pressing, slitting, and cutting, a cathode electrode sheet is obtained. The tap density of the cathode electrode sheet is 3.4 g / cm 3 。

[0164] 2) Preparation of anode electrode sheet

[0165] The anode active material graphite, the conductive agent conductive carbon black, and the binder carboxymethyl cellulose CMC are mixed evenly in a mass ratio of 98:1:1 in an appropriate amount of solvent deionized water to obtain an anode slurry. The above-mentioned anode slurry is respectively coated on both sides of a 6-μm-thick anode current collector copper foil, and through processes such as drying, cold pressing, slitting, and cutting, an anode electrode sheet is obtained. The tap density of the anode electrode sheet is 1.6 g / cm 3 。

[0166] 3) Preparation of electrolyte

[0167] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7 to obtain an organic solvent, and fully dried LiPF 6 is dissolved in the above-mentioned organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0168] 4) Separator

[0169] A polypropylene / polyethylene / polypropylene (PP / PE / PP) composite separator is used as the separator.

[0170] 5) Preparation of battery cell

[0171] The above-mentioned cathode electrode sheet, separator, and anode electrode sheet are wound together to form a bare battery cell, with the separator located between the cathode electrode sheet and the anode electrode sheet to play an isolation role; a double-sided metal edge wrapping method is used for roll welding and butt welding to form tabs; the battery cell after welding the tabs is placed in a battery case, the above-mentioned electrolyte is injected, and processes such as sealing and formation are carried out to obtain a lithium-ion secondary battery.

[0172] Example 2:

[0173] This example is basically the same as Example 1, except that: the thickness D2 of the high-resistance layer in the cathode composite current collector is 320 nm, the total density M1 of the high-resistance layer and the conductive layer is 90%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 70 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 2.5, and the surface roughness Rz of the high-resistance layer is 1.2 μm.

[0174] Example 3:

[0175] This embodiment is basically the same as Embodiment 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 160 nm, the total density M1 of the high-resistance layer and the conductive layer is 85%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 68 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 5, and the surface roughness Rz of the high-resistance layer is 0.68 μm.

[0176] Embodiment 4:

[0177] This embodiment is basically the same as Embodiment 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 80 nm, the total density M1 of the high-resistance layer and the conductive layer is 78%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 65 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 10, and the surface roughness Rz of the high-resistance layer is 0.53 μm.

[0178] Embodiment 5:

[0179] This embodiment is basically the same as Embodiment 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 40 nm, the total density M1 of the high-resistance layer and the conductive layer is 75%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 58 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 20, and the surface roughness Rz of the high-resistance layer is 0.2 μm.

[0180] Embodiment 6:

[0181] This embodiment is basically the same as Embodiment 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 32 nm, the total density M1 of the high-resistance layer and the conductive layer is 70%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 50 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 25, and the surface roughness Rz of the high-resistance layer is 0.1 μm.

[0182] Embodiment 7:

[0183] This embodiment is basically the same as Embodiment 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 500 nm, the density M2 of the conductive layer is 50%, the sheet resistance R2 of the conductive layer is 45 mΩ / □, the thickness D2 of the high-resistance layer is 100 nm, the total density M1 of the high-resistance layer and the conductive layer is 75%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 60 mΩ / □, and the surface roughness Rz of the high-resistance layer is 0.55 μm.

[0184] Embodiment 8:

[0185] This embodiment is basically the same as Embodiment 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 600 nm, the density M2 of the conductive layer is 55%, the sheet resistance R2 of the conductive layer is 40 mΩ / □, the thickness D2 of the high-resistance layer is 120 nm, the total density M1 of the high-resistance layer and the conductive layer is 80%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 61 mΩ / □, and the surface roughness Rz of the high-resistance layer is 0.6 μm.

[0186] Example 9:

[0187] This embodiment is basically the same as Embodiment 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 1000 nm, the density M2 of the conductive layer is 65%, the sheet resistance R2 of the conductive layer is 30 mΩ / □, the thickness D2 of the high-resistance layer is 200 nm, the total density M1 of the high-resistance layer and the conductive layer is 87%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 66 mΩ / □, and the surface roughness Rz of the high-resistance layer is 0.8 μm.

[0188] Example 10:

[0189] This embodiment is basically the same as Embodiment 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 1200 nm, the density M2 of the conductive layer is 70%, the sheet resistance R2 of the conductive layer is 28 mΩ / □, the thickness D2 of the high-resistance layer is 240 nm, the total density M1 of the high-resistance layer and the conductive layer is 90%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 56 mΩ / □, and the surface roughness Rz of the high-resistance layer is 0.9 μm.

[0190] Example 11:

[0191] This embodiment is basically the same as Embodiment 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 1500 nm, the density M2 of the conductive layer is 75%, the sheet resistance R2 of the conductive layer is 25 mΩ / □, the thickness D2 of the high-resistance layer is 300 nm, the total density M1 of the high-resistance layer and the conductive layer is 95%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 50 mΩ / □, and the surface roughness Rz of the high-resistance layer is 1.1 μm.

[0192] Comparative Example 1:

[0193] This comparative example is basically the same as Example 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 800 nm, the total density M1 of the high-resistance layer and the conductive layer is 100%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 100 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 1, and the surface roughness Rz of the high-resistance layer is 2.2 μm.

[0194] Comparative Example 2:

[0195] This comparative example is basically the same as Example 1, except that: the thickness D2 of the high-resistance layer in the positive composite current collector is 27 nm, the total density M1 of the high-resistance layer and the conductive layer is 63%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 37 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer is 29.6, and the surface roughness Rz of the high-resistance layer is 0.08 μm.

[0196] Comparative Example 3:

[0197] This comparative example is basically the same as Example 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 1600 nm, the density M2 of the conductive layer is 95%, the sheet resistance R2 of the conductive layer is 18 mΩ / □, the thickness D2 of the high-resistance layer is 320 nm, the total density M1 of the high-resistance layer and the conductive layer is 100%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 32 mΩ / □, and the surface roughness Rz of the high-resistance layer is 1.2 μm.

[0198] Comparative Example 4:

[0199] This comparative example is basically the same as Example 3, except that: the thickness D1 of the conductive layer in the positive composite current collector is 400 nm, the density M2 of the conductive layer is 40%, the sheet resistance R2 of the conductive layer is 75 mΩ / □, the thickness D2 of the high-resistance layer is 80 nm, the total density M1 of the high-resistance layer and the conductive layer is 55%, the total sheet resistance R1 of the high-resistance layer and the conductive layer is 102 mΩ / □, and the surface roughness Rz of the high-resistance layer is 0.51 μm.

[0200] Comparative Example 5:

[0201] This comparative example is basically the same as Example 3, except that: no high-resistance layer is provided on the conductive layer of the positive composite current collector.

[0202] II. Test Methods

[0203] 1) Film layer thickness test

[0204] Use the liquid nitrogen quenching method or the argon ion etching method to prepare cross-sectional samples of the composite current collector. Observe the secondary electron phase morphology of the sample cross-section under a scanning electron microscope magnified (1000 - 30000 times), and measure the thickness of each layer such as the polymer support layer, conductive layer, high-resistance layer, adhesive layer, and passivation layer. Its minimum resolution can reach the nanometer level.

[0205] 2) High-resistance layer surface roughness Rz test

[0206] Use a roughness tester to test the surface roughness of the high-resistance layer and obtain the Rz value;

[0207] Rz average value = sum of Rz values at 10 test points / 10.

[0208] 3) Conductivity Layer / High-Resistance Layer Density Test

[0209] Take a flat test sample and place it on the operating table of the CCD optical microscope. Turn on the light source at the back of the operating table and turn off the light source of the microscope. Take photos of the sample in the dark field condition and photograph 3 areas; Use the Imagej image processing software for the 3 pictures. Select the pictures saved by the CCD and calculate the density percentage M value;

[0210] M average value = sum of M values of 3 test areas / 3.

[0211] 4) Sheet Resistance R Test of Conductivity Layer / Combined Layer of Conductivity Layer and High-Resistance Layer

[0212] Take a flat sample and measure the sheet resistance on the sample with a four-probe sheet resistance tester to obtain the R value;

[0213] R average value = sum of R values of 10 test points / 10.

[0214] 5) Tensile Strength and Elongation at Break Test of Positive Composite Current Collector

[0215] Use a standard sampler to cut the sample into 10 strips each with a width of 15 mm and a length of 15 cm along the MD (longitudinal) / TD (transverse) direction; Fix the sample on the fixture of the tensile testing machine, set the speed at 50 mm / min, and the gauge length between the clips at 50 mm, and test the corresponding strength and elongation at break.

[0216] Tensile strength = sum of tensile strengths of 10 test samples / 10;

[0217] Elongation at break = sum of elongations at break of 10 test samples / 10.

[0218] 6) Shearing Force Test of Positive Electrode Sheet

[0219] Stick the special shearing force tape on the steel plate with a width of 4 mm and a length of 5 mm. Stick the positive electrode sheet on the tape and use a high-speed tensile testing machine to measure the shearing force between the positive active material layer of the electrode sheet and the positive composite current collector.

[0220] Average shearing force = sum of shearing force values of 10 samples / 10. (Shearing force specification ≥ 0.3 MPa).

[0221] 7) U-Type Resistance Test of Welded Positive Electrode Sheet

[0222] Cut the welded positive electrode sheet into samples of the same size as the battery cell and measure the resistance between its two tabs with an internal resistance tester.

[0223] Average R value = sum of U-shaped resistance values of 10 samples / 10. (U-shaped resistance R specification: 70 mΩ to 130 mΩ, preferably 80 mΩ to 120 mΩ).

[0224] 8) Cell DCR Test

[0225] Adjust the cell capacity to 50% SOC and record the voltage V1; discharge at 4C current for 30s to obtain the voltage value V2;

[0226] DCR = (V1 - V2) / 4C;

[0227] Average DCR value = sum of DCR values of 10 samples / 10.

[0228] Generally speaking, the cell DCR should be less than 0.7 mΩ, preferably less than 0.6 mΩ.

[0229] 9) Cell Stud Penetration Test

[0230] First fully charge the cell to 100% SOC, connect the positive and negative electrodes of the cell to the power supply to test the voltage value, penetrate the large surface of the cell with a steel needle of 3 mm to 6 mm at a certain speed, and judge whether the cell fails by observing whether the cell smokes, catches fire, explodes, and whether the voltage drops suddenly, and calculate the stud penetration pass rate. Collect the stud penetration pass rate test data of 5 samples.

[0231] Stud penetration pass rate = (sum of the number of passes of 5 samples / 5) * 100%.

[0232] The battery parameters of each example and comparative example of this application are shown in Table 1, and the performance test data are shown in Table 2. " / " in Table 1 means non-existent.

[0233] Table 1

[0234]

[0235]

[0236] Table 2

[0237]

[0238] From the above data, it can be seen that the positive composite current collector of each example of this application can, while maintaining the normal electrode conductivity of the conductive layer and keeping the DC internal resistance of the battery within a suitable range, make the battery have a high stud penetration test pass rate by setting a high-resistance layer on the surface of the conductive layer facing away from the polymer support layer and making the total sheet resistance R1 of the high-resistance layer and the conductive layer 50 mΩ / sq to 80 mΩ / sq, thereby improving the safety performance of the battery. And the positive composite current collector has a high elongation at break and a large breaking strength; the positive electrode sheet can withstand a large shear force and has a low U-shaped resistance.

[0239] By comparing Examples 1 to 6, it can be seen that further controlling the total sheet resistance R1 of the high-resistance layer and the conductive layer within the range of 58 mΩ / sq to 70 mΩ / sq, controlling the thickness ratio A of the conductive layer to the high-resistance layer within the range of 2.5 to 20, and controlling the total density M1 of the conductive layer and the high-resistance layer within the range of 75% to 90% can enable the battery to have more excellent comprehensive performance, make the battery have both a lower DC internal resistance and a higher passing rate of the nail penetration test, and can better balance the electrode conductivity and safety performance.

[0240] By comparing Example 1 with Comparative Example 1, it can be seen that when the thickness of the high-resistance layer increases and the thickness ratio A of the conductive layer to the high-resistance layer is less than 2, the overall density of the high-resistance layer and the conductive layer is close to 100%, the total sheet resistance R1 of the high-resistance layer and the conductive layer > 80 mΩ / sq, the overall conductivity of the positive composite current collector decreases, resulting in a significant increase in the U-shaped resistance of the positive electrode sheet and a significant increase in the DCR of the battery cell. Although the battery cell can pass the nail penetration test, this positive composite current collector can no longer meet the usage requirements of the positive electrode sheet and the battery cell. At the same time, due to the thick high-resistance layer material, cracking is likely to occur, resulting in the elongation at break of the positive composite current collector not meeting the requirements.

[0241] By comparing Example 1 with Comparative Example 2, it can be seen that when the thickness of the high-resistance layer decreases and the thickness ratio A of the conductive layer to the high-resistance layer is greater than 25, the contribution of the high-resistance layer to the increase in the sheet resistance of the conductive layer is not significant, and the total sheet resistance R1 of the high-resistance layer and the conductive layer < 50 mΩ / sq; although the U-shaped resistance of the positive electrode sheet is small and the DCR of the battery cell can meet the requirements, the passing rate of the nail penetration test of the battery cell decreases significantly. Moreover, due to the too thin thickness of the high-resistance layer, the surface roughness of the high-resistance layer is low, and the shear force that the positive electrode sheet can withstand is small.

[0242] From Comparative Example 3, it can be seen that when the thickness of the conductive layer is too large, the sheet resistance of the conductive layer decreases, resulting in too small a total sheet resistance of the high-resistance layer and the conductive layer; although the DCR of the battery cell can meet the requirements, the passing rate of the nail penetration test of the battery cell is very low. From Comparative Example 4, it can be seen that when the thickness of the conductive layer is too small, the sheet resistance of the conductive layer increases, resulting in too large a total sheet resistance of the high-resistance layer and the conductive layer; although the passing rate of the nail penetration test of the battery cell is relatively high, the U-shaped resistance of the positive electrode sheet is too large and the DCR of the battery cell is too large, unable to meet the usage requirements. By comparing Example 1 and Comparative Example 5, it can be seen that when no high-resistance layer is provided on the conductive layer of the positive composite current collector, the passing rate of the nail penetration test of the battery cell decreases significantly.

[0243] The above descriptions of the various embodiments tend to emphasize the differences between the various embodiments. Their similarities can be referred to each other. For the sake of brevity, they will not be elaborated herein.

[0244] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A positive electrode composite current collector, characterized in that, it includes: a polymer support layer; a conductive layer provided on at least one surface of the polymer support layer; and a high-resistance layer provided on the surface of the conductive layer facing away from the polymer support layer, the resistivity of the high-resistance layer being higher than that of the conductive layer, and the total sheet resistance of the high-resistance layer and the conductive layer being R1, 50 mΩ / sq ≤ R1 ≤ 80 mΩ / sq.

2. The positive electrode composite current collector according to claim 1, characterized in that, 58 mΩ / sq ≤ R1 ≤ 70 mΩ / sq.

3. The positive electrode composite current collector according to claim 1 or 2, characterized in that, the sheet resistance of the conductive layer is R2, 25 mΩ / sq ≤ R2 ≤ 45 mΩ / sq; optionally, 30 mΩ / sq ≤ R2 ≤ 40 mΩ / sq.

4. The positive electrode composite current collector according to any one of claims 1 to 3, characterized in that, the thickness ratio of the conductive layer to the high-resistance layer is A, 2 ≤ A ≤ 25; optionally, 2.5 ≤ A ≤ 20.

5. The positive electrode composite current collector according to any one of claims 1 to 4, characterized in that, the thickness of the conductive layer is D1, 500 nm ≤ D1 ≤ 1500 nm; optionally, 600 nm ≤ D1 ≤ 1200 nm.

6. The positive electrode composite current collector according to any one of claims 1 to 5, characterized in that, the thickness of the high-resistance layer is D2, 30 nm ≤ D2 ≤ 500 nm; optionally, 35 nm ≤ D2 ≤ 400 nm.

7. The positive electrode composite current collector according to any one of claims 1 to 6, characterized in that, the total density of the conductive layer and the high-resistance layer is M1, 70% ≤ M1 ≤ 95%; optionally, 75% ≤ M1 ≤ 90%.

8. The positive electrode composite current collector according to any one of claims 1 to 7, characterized in that, the density of the conductive layer is M2, 50% ≤ M2 ≤ 75%; optionally, 55% ≤ M2 ≤ 70%.

9. The positive electrode composite current collector according to any one of claims 1 to 8, characterized in that, the material of the high-resistance layer includes one or more of alumina, silica, nickel-chromium alloy and iron-chromium aluminum alloy.

10. The positive electrode composite current collector according to any one of claims 1 to 9, characterized in that, the material of the conductive layer includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

11. The positive electrode composite current collector according to any one of claims 1 to 10, characterized in that, the surface roughness Rz of the surface of the high-resistance layer facing away from the conductive layer is 0.1 μm to 2 μm.

12. The positive electrode composite current collector according to any one of claims 1 to 11, characterized in that, it further includes: a bonding layer provided between the polymer support layer and the conductive layer.

13. The positive electrode composite current collector according to claim 12, characterized in that, The bonding layer includes a binder, and the binder includes one or more of a composition containing polyfunctional isocyanate and polyester polyol compound, polyurethane, epoxy resin, polyacrylate, polyvinyl acetate, unsaturated polyester, phenolic resin, urea-formaldehyde resin, modified polyolefin resin, silicone resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, acrylic resin, polycarbonate, and polyamide.

14. The positive electrode composite current collector according to claim 12 or 13, wherein, it further includes: a passivation layer disposed between the bonding layer and the conductive layer.

15. The positive electrode composite current collector according to claim 14, wherein, The materials of the passivation layer include chromate, dichromate, organic phosphonate, Al 2 O 3 , SiO 2 , and Si 3 N 4 or one or more of them.

16. The positive electrode composite current collector according to claim 15, wherein, it satisfies at least one of the following (1) to (3): (1) The chromate includes one or more of sodium chromate, potassium chromate, magnesium chromate, and silver chromate; (2) The dichromate includes one or more of sodium dichromate, potassium dichromate, magnesium dichromate, and silver dichromate; (3) The organic phosphonate includes one or more of hydroxyethylidene diphosphonic acid, diethylenetriamine pentamethylene phosphonic acid, triethylenetetramine hexamethylene phosphonic acid, and ethylenediamine tetramethylene phosphonic acid.

17. The positive electrode composite current collector according to any one of claims 14 to 16, wherein, the thickness of the passivation layer is D4, and 1 nm ≤ D4 ≤ 500 nm; optionally, 10 nm ≤ D4 ≤ 200 nm.

18. The positive electrode composite current collector according to any one of claims 1 to 17, wherein, the material of the polymer support layer includes one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene styrene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, sulfur nitride polymer materials, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and their derivatives, crosslinked products, and copolymers.

19. A positive electrode plate, wherein, it includes a positive electrode active material layer and the positive electrode composite current collector according to any one of claims 1 to 18, and the positive electrode active material layer is disposed on the surface of the high-resistance layer facing away from the conductive layer.

20. A secondary battery, wherein, it includes the positive electrode composite current collector according to any one of claims 1 to 18 or the positive electrode plate according to claim 19.

21. An electrical device, wherein, it includes the secondary battery according to claim 20.

Images