Positive electrode composite current collector, positive electrode sheet, secondary battery, and electrical apparatus

Abstract

A positive electrode composite current collector, a positive electrode sheet, a secondary battery, and an electrical apparatus. The positive electrode composite current collector comprises a polymer support layer, a conductive layer, and a high-resistance layer; the conductive layer is arranged on at least one surface of the polymer support layer; the high-resistance layer is arranged on the surface of the conductive layer away from the polymer support layer, the electrical resistivity of the high-resistance layer is higher than the electrical resistivity of the conductive layer, the total sheet resistance of the high-resistance layer and the conductive layer is R1, and 50 mΩ / □≤R1≤80 mΩ / □. The positive electrode composite current collector can maintain normal electrode conductivity, so that the DCR of a battery is within a proper range, and the battery has a high nail penetration test pass rate, thereby improving the safety performance of the battery.

Description

Positive electrode composite current collector, positive electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202311606664.8 filed on November 27, 2023, entitled “Positive electrode composite current collector, positive electrode sheet, secondary battery and electrical device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode composite current collector, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, as the application scope of secondary batteries has become increasingly wider, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0006] Currently, due to the rapid development of secondary batteries, higher safety performance requirements have been put forward. Secondary batteries with better safety performance have higher requirements for current collectors. For example, secondary batteries with better safety performance must effectively prevent the positive and negative electrodes from conducting during the nail penetration test.

[0007] Therefore, seeking a current collector that can improve the safety performance of secondary batteries is one of the key areas of focus for those skilled in the art.

[0008] Summary of the Invention

[0009] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a positive electrode composite current collector that can improve the safety performance of the battery while maintaining the DCR of the battery at a low level.

[0010] In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode composite current collector, comprising:

[0011] a polymer support layer;

[0012] a conductive layer disposed on at least one surface of the polymer support layer; and

[0013] The high resistance layer is arranged on the surface of the conductive layer away from the polymer support layer. The resistivity of the high resistance layer is higher than that of the conductive layer. The total square resistance of the high resistance layer and the conductive layer is R1, 50mΩ / □≤R1≤80mΩ / □.

[0014] 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 square resistance R1 of the high-resistance layer and the conductive layer satisfies 50mΩ / □≤R1≤80mΩ / □; through the composite structure of the above-mentioned high-resistance layer and the conductive layer, while maintaining the normal electrode conductivity of the conductive layer and keeping the battery DC internal resistance (DCR) within an appropriate range, the battery can have a higher nail penetration test pass rate, thereby improving the safety performance of the battery.

[0015] In any embodiment, 58mΩ / □≤R1≤70mΩ / □. In this way, the electrode conductivity and the nail penetration test pass rate can be better balanced, so that the battery can not only meet the DCR requirements but also improve the battery safety performance.

[0016] In any embodiment, the sheet resistance of the conductive layer is R2, 25mΩ / □≤R2≤45mΩ / □; alternatively, 30mΩ / □≤R2≤40mΩ / □. Thus, the conductive layer has an appropriate sheet resistance, and when combined with the high-resistance layer, the combined sheet resistance of the high-resistance layer and the conductive layer can be within an appropriate range.

[0017] 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. This ensures that the total sheet resistance of the conductive layer and the high-resistance layer is within an appropriate range, enabling the battery to better pass the nail penetration test and improving battery safety.

[0018] In any embodiment, the thickness of the conductive layer is D1, 500nm≤D1≤1500nm; optionally, 600nm≤D1≤1200nm. This, combined with the aforementioned thickness ratio of the conductive layer to the high-resistance layer, ensures that the total sheet resistance of the conductive layer and the high-resistance layer is within an appropriate range, enabling the battery to successfully pass the nail penetration test and improving battery safety.

[0019] In any embodiment, the thickness of the high-resistance layer is D2, 30nm≤D2≤500nm; optionally, 35nm≤D2≤400nm. This, combined with the thickness ratio of the conductive layer to the high-resistance layer and the thickness range of the conductive layer, can ensure that the total sheet resistance of the conductive layer and the high-resistance layer is within an appropriate range, enabling the battery to better pass the nail penetration test and improving battery safety.

[0020] In any embodiment, the total density of the conductive layer and the high-resistance layer is M1, 70% ≤ M1 ≤ 95%; alternatively, 75% ≤ M1 ≤ 90%. Thus, by controlling the thickness and density of the conductive layer and the high-resistance layer, the total square resistance of the conductive layer and the high-resistance layer can be kept within an appropriate range, resulting in a higher nail penetration test pass rate and improved battery safety. Furthermore, controlling the total density of the conductive layer and the high-resistance layer within the above range can also ensure that the composite current collector has an appropriate elongation at break and fracture strength.

[0021] In any embodiment, the density of the conductive layer is M2, 50% ≤ M2 ≤ 75%; alternatively, 55% ≤ M2 ≤ 70%. In this way, the conductive layer and the high-resistance layer can be combined to keep the total square resistance within a suitable range, thereby maintaining the battery's DCR at an appropriate level and improving the battery's nail penetration test pass rate and safety performance.

[0022] 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 high-resistance layer material has a relatively high resistivity, and when combined with the conductive layer, the high-resistance layer and the conductive layer can have a suitable total square resistance.

[0023] 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.

[0024] In any embodiment, the surface roughness Rz of the high-resistance layer on the side facing away from the conductive layer is 0.1 μm to 2 μm. Controlling the surface roughness of the high-resistance layer within the above range can ensure good adhesion between the positive active material layer and the positive composite current collector of the positive electrode sheet, allowing the positive electrode sheet to withstand greater shear forces.

[0025] In any embodiment, the positive electrode composite current collector further includes a bonding layer disposed between the polymer support layer and the conductive layer. Thus, using the bonding layer to bond the conductive layer to the polymer support layer does not cause significant thermal damage to the polymer support layer, compared to conventional methods of vapor-depositing or sputtering the conductive layer on the polymer support layer, and can improve the elongation at break of the positive electrode composite current collector.

[0026] In any embodiment, the adhesive layer includes an adhesive, and the adhesive includes one or more of a composition containing a multifunctional isocyanate and a 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. Thus, the use of the above-mentioned adhesive can achieve good bonding between the polymer support layer and the conductive layer, thereby achieving a strong peeling force between the conductive layer and the polymer support layer.

[0027] In any embodiment, the thickness of the adhesive layer is D3, 200nm≤D3≤1500nm; alternatively, 300nm≤D3≤700nm. This ensures good adhesion between the polymer support layer and the conductive layer while preventing the adhesive layer from being too thick and affecting the battery energy density.

[0028] In any embodiment, the positive electrode composite current collector further includes a passivation layer disposed between the adhesive layer and the conductive layer, thereby providing passivation protection at the interface between the conductive layer and the adhesive layer and reducing micro-corrosion of the conductive layer by the electrolyte.

[0029] In any embodiment, the material of the passivation layer includes one or more of chromate, dichromate, organic phosphonate, Al2O3, SiO2, and Si3N4. Thus, using the above materials to form a passivation layer at the interface between the conductive layer and the adhesive layer can provide good passivation protection for the conductive layer and effectively alleviate micro-corrosion of the conductive layer by the electrolyte.

[0030] In any embodiment, 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 penta (methylene phosphonic acid), triethylenetetraamine hexa (methylene phosphonic acid) and ethylenediamine tetra (methylene phosphonic acid).

[0031] In any embodiment, the thickness of the passivation layer is D4, 1 nm ≤ D4 ≤ 500 nm; alternatively, 10 nm ≤ D4 ≤ 200 nm. In this way, micro-corrosion of the conductive layer by the electrolyte can be effectively alleviated.

[0032] In any embodiment, the material of the polymer support layer includes one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene oxide, polyphenylene sulfide, polyethylene glycol, polysulfur 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 compared to traditional metal foil current collectors such as aluminum foil, and can reduce the cost of the current collector.

[0033] In any embodiment, the thickness of the polymer support layer is D5, 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 higher energy density and better safety.

[0034] The second aspect of the present application further provides a positive electrode plate, comprising a positive electrode active material layer and the positive electrode composite current collector of the first aspect of the present application, wherein the positive electrode active material layer is disposed on a surface of the high-resistance layer facing away from the conductive layer. Thus, while maintaining normal electrode conductivity of the conductive layer and keeping the battery DCR within an appropriate range, the positive electrode plate can enable the battery to achieve a high nail penetration test pass rate, thereby improving the battery's safety performance.

[0035] The third aspect of the present application further provides a secondary battery comprising the positive electrode 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 nail penetration test pass rate, good safety performance, and a low DCR.

[0036] The fourth aspect of the present application further provides an electrical device comprising the secondary battery of the third aspect of the present application.

[0037] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0039] FIG1 is a schematic diagram of a positive electrode composite current collector according to one embodiment of the present application;

[0040] FIG2 is a schematic diagram of a positive electrode sheet according to an embodiment of the present application;

[0041] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0042] FIG4 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG3 ;

[0043] FIG5 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0044] Description of reference numerals:

[0045] 1. Positive electrode 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 DESCRIPTION

[0046] Below, the embodiments of the composite current collector, electrode plate, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same 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 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 described in the claims.

[0047] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, 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 particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0048] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0051] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0053] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0054] The weights described in the examples of this application may be weight units known in the chemical industry, such as μg, mg, g, and kg.

[0055] Currently, due to the great development of secondary batteries, higher requirements have been placed on their safety performance. Secondary batteries with better safety performance have higher requirements for current collectors. For example, secondary batteries with better safety performance require that the current collector can effectively prevent the positive and negative electrodes of the battery from conducting during the nail penetration test, thereby improving the battery's nail penetration test pass rate. In response to this, the present application improves the structure of the positive electrode composite current collector, thereby improving the nail penetration test pass rate of batteries using this positive electrode composite current collector and improving the battery's safety performance.

[0056] Referring to FIG1 , a first aspect of the present application provides a positive electrode composite current collector 1, comprising a polymer support layer 11, a conductive layer 12, and a high-resistance layer 13. The conductive layer 12 is disposed on at least one surface of the polymer support layer 11, and the high-resistance layer 13 is disposed on a 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. The total square resistance of the high-resistance layer 13 and the conductive layer 12 is R1, and 50 mΩ / □ ≤ R1 ≤ 80 mΩ / □.

[0057] The present application provides a high-resistance layer 13 on the surface of the conductive layer 12 facing away from the polymer support layer 11, wherein the resistivity of the high-resistance layer 13 is higher than the resistivity of the conductive layer 12, and the total square resistance R1 of the high-resistance layer 13 and the conductive layer 12 satisfies 50mΩ / □≤R1≤80mΩ / □; through the composite structure 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 an appropriate range, the square resistance of the conductive layer 12 is improved, thereby improving the nail penetration test pass rate of the battery using the positive electrode composite current collector 1 and improving the safety performance of the battery.

[0058] It should be noted that resistivity is a physical quantity used to indicate the magnitude of a material's resistance to electric current. The magnitude of resistivity is related to the properties of the material itself. The resistivity of the high-resistance layer 13 is higher than that of the conductive layer 12, which means that under the same conditions, the material of the high-resistance layer 13 has a greater resistance to electric current than the material of the conductive layer 12. Sheet resistance refers to the electrical resistance of a film material with a certain thickness, length, and width. The total sheet resistance of the high-resistance layer 13 and the conductive layer 12 refers to the sheet resistance measured when the high-resistance layer 13 and the conductive layer 12 are considered as a whole film layer.

[0059] It is understandable that the conductive layer 12 and the high resistance layer 13 may be provided on one surface of the polymer support layer 11 , or may be provided on two opposite surfaces of the polymer support layer 11 . It can be understood that the total square resistance R1 of the high-resistance layer 13 and the conductive layer 12 in the present application can be but is not limited to 50mΩ / □, 51mΩ / □, 52mΩ / □, 53mΩ / □, 54mΩ / □, 55mΩ / □, 56mΩ / □, 57mΩ / □, 58mΩ / □, 59mΩ / □, 60mΩ / □, 61mΩ / □, 62mΩ / □, 63mΩ / □, 64mΩ / □, 65mΩ / □, 66mΩ / □, 67mΩ / □, 68mΩ / □, 69mΩ / □, 70mΩ / □, 71mΩ / □, 72mΩ / □, 73mΩ / □, 74mΩ / □, 75mΩ / □, 76mΩ / □, 77mΩ / □, 78mΩ / □, 79mΩ / □, and 80mΩ / □.

[0060] In some embodiments, 58mΩ / □≤R1≤70mΩ / □. Controlling the total square resistance R1 of the high-resistance layer 13 and the conductive layer 12 in the positive electrode composite current collector 1 within the range of 58mΩ / □ to 70mΩ / □ can better balance the electrode conductivity and the nail penetration test pass rate, enabling the battery to not only meet the DCR requirements but also improve the battery safety performance.

[0061] In some embodiments, the sheet resistance R2 of the conductive layer 12 is 25 mΩ / □ ≤ R2 ≤ 45 mΩ / □; alternatively, 30 mΩ / □ ≤ R2 ≤ 40 mΩ / □. Thus, the conductive layer 12 has an appropriate sheet resistance, and when combined with the high-resistance layer 13, the total sheet resistance R1 of the high-resistance layer 13 and the conductive layer 12 is within an appropriate range. It can be understood that R2 can be but is not limited to 25mΩ / □, 26mΩ / □, 27mΩ / □, 28mΩ / □, 29mΩ / □, 30mΩ / □, 31mΩ / □, 32mΩ / □, 33mΩ / □, 34mΩ / □, 35mΩ / □, 36mΩ / □, 37mΩ / □, 38mΩ / □, 39mΩ / □, 40mΩ / □, 41mΩ / □, 42mΩ / □, 43mΩ / □, 44mΩ / □, and 45mΩ / □.

[0062] In some embodiments, the thickness ratio of the conductive layer 12 to the high-resistance layer 13 is A, 2≤A≤25; the thickness of the conductive layer 12 is D1, 500nm≤D1≤1500nm; and the thickness of the high-resistance layer 13 is D2, 30nm≤D2≤500nm. 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 aforementioned ranges can ensure that the total square resistance of the conductive layer 12 and the high-resistance layer 13 is within an appropriate range, enabling the battery to better pass the nail penetration test and improving the battery's safety performance.

[0063] It can be understood that A can be but 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 not limited to 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1250nm, 1300nm, 1350nm, 1400nm, 1450nm, 1500nm; D2 can be but not limited to 30nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm.

[0064] In some embodiments, the thickness ratio of the conductive layer 12 to the high-resistance layer 13 is A, 2.5≤A≤20; the thickness of the conductive layer 12 is D1, 600nm≤D1≤1200nm; and the thickness of the high-resistance layer 13 is D2, 35nm≤D2≤400nm. 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 aforementioned ranges can ensure that the total square resistance of the conductive layer 12 and the high-resistance layer 13 is within a more appropriate range, further improving the pass rate of the battery penetration test and enhancing the safety performance of the battery; at the same time, the battery has a better DCR level, better balancing the battery's DCR requirements and safety performance.

[0065] In some embodiments, the total density of the conductive layer 12 and the high-resistance layer 13 is M1, 70% ≤ M1 ≤ 95%; optionally, 75% ≤ M1 ≤ 90%. The density of the conductive layer 12 and the high-resistance layer 13 has a certain influence on their resistivity, which in turn affects the total square resistance of the conductive layer 12 and the high-resistance layer 13. When the thickness of the conductive layer 12 and the high-resistance layer 13 is 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 range can make the total square resistance of the conductive layer 12 and the high-resistance layer 13 within a suitable range, thereby making the battery have a higher nail penetration test pass rate and better safety performance. At the same time, the density will also affect the elongation at break and the fracture strength of the positive electrode composite current collector 1. Controlling the total density M1 of the conductive layer 12 and the high-resistance layer 13 within the above range can make the positive electrode composite current collector 1 have a suitable elongation at break and fracture strength.

[0066] It will be understood that the total density of the conductive layer 12 and the high-resistance layer 13 refers to the density measured for 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 may 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%, or 95%.

[0067] In some embodiments, the density of the conductive layer 12 is M2, 50% ≤ M2 ≤ 75%; alternatively, 55% ≤ M2 ≤ 70%. Controlling the density of the conductive layer 12 within the aforementioned range ensures that the conductive layer 12 has an appropriate resistivity and that the high-resistance layer 13 has an appropriate density. This, in combination with the high-resistance layer 13, ensures that the total square resistance falls within an appropriate range, the battery's DCR remains at an appropriate level, and the battery has a high nail penetration test pass rate. Furthermore, this ensures that the positive electrode composite current collector 1 has an appropriate elongation at break and fracture strength.

[0068] It will 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%.

[0069] In some embodiments, the material of the high-resistance layer 13 includes one or more of aluminum oxide, silicon oxide, nickel-chromium alloy, and iron-chromium-aluminum alloy. The above-mentioned high-resistance layer 13 materials have a higher resistivity than the conductive layer 12, and when combined with the conductive layer 12, the high-resistance layer 13 and the conductive layer 12 can have a suitable total square resistance.

[0070] In some 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 will be appreciated that the material of the conductive layer 12 can be selected from the aforementioned materials based on the type of positive composite current collector 1. For example, when the positive composite current collector 1 is a positive electrode current collector, the conductive layer 12 can be made of aluminum; when the positive composite current collector 1 is a negative electrode current collector, the conductive layer 12 can be made of copper.

[0071] In some embodiments, the surface roughness Rz of the high-resistance layer 13 on the side facing away from the conductive layer 12 is 0.1 μm to 2 μm. When using the positive composite current collector 1 of the present application to prepare an electrode sheet, it is necessary to form a corresponding positive electrode active material layer on the high-resistance layer 13. The surface roughness of the high-resistance layer 13 has a certain influence on the adhesion between the positive electrode 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 electrode active material layer of the positive electrode sheet can have good adhesion to the positive composite current collector 1, allowing the positive electrode sheet to withstand greater shear forces.

[0072] The surface roughness Rz refers to the sum of the average of the five largest profile peak heights and the average of the five largest profile valley depths within the sampling length. It is 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, and 2.0 μm.

[0073] In some embodiments, the positive electrode composite current collector 1 further includes a bonding layer 14, which is disposed between the polymer support layer 11 and the conductive layer 12. Conventional positive electrode composite current collectors 1 typically form the conductive layer 12 on the polymer support layer 11 by evaporation or sputtering. Due to the high temperature at which the conductive layer 12 is formed, significant thermal damage is caused to the polymer support layer 11, and the positive electrode composite current collector 1 is prone to deformation, resulting in a low elongation at break of the positive electrode composite current collector 1. The present application utilizes a bonding layer 14 to bond the conductive layer 12 to the polymer support layer 11, which does not cause significant thermal damage to the polymer support layer 11 and can improve the elongation at break of the positive electrode composite current collector 1.

[0074] It is understandable that the bonding layer 14 can be formed by curing after coating. In some specific examples, a bonding slurry can be first applied on the polymer support layer 11 and / or the conductive layer 12, and the surfaces of the polymer support layer 11 and the conductive layer 12 coated with the bonding slurry are compounded, and then the bonding slurry is cured to form a bonding layer 14, thereby bonding the polymer support layer 11 and the conductive layer 12 into one. Among them, the conductive layer 12 can be a conductive metal foil of a certain thickness. After the conductive metal foil is compounded on the polymer support layer 11 through the bonding layer 14, the conductive metal foil can be thinned to the desired thickness of the conductive layer 12 by corrosion or the like. After the conductive layer 12 is formed, a high-resistance layer 13 can be formed on the conductive layer 12 by evaporation or the like.

[0075] In some embodiments, the bonding layer 14 includes a binder, and the binder includes one or more of a composition containing a multifunctional isocyanate and a 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. Optionally, the binder includes one or more of a composition containing a multifunctional isocyanate and a polyester polyol compound and polyurethane. In some specific examples, the polyurethane includes one or more of thermoplastic polyurethane and reactive polyurethane. The use of the above-mentioned binder can play a good bonding role between the polymer support layer 11 and the conductive layer 12, so that the conductive layer 12 and the polymer support layer 11 have a large peeling force.

[0076] In some embodiments, the thickness D3 of the adhesive layer 14 is 200 nm ≤ D3 ≤ 1500 nm; alternatively, 300 nm ≤ D3 ≤ 700 nm. Controlling the thickness of the adhesive layer 14 within this range ensures good adhesion between the polymer support layer 11 and the conductive layer 12 while preventing the adhesive layer 14 from being too thick and affecting the battery energy density. It can be understood that the thickness D3 of the bonding layer 14 can be but is not limited to 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1250nm, 1300nm, 1350nm, 1400nm, 1450nm, 1500nm.

[0077] In some embodiments, the positive electrode composite current collector 1 further includes a passivation layer 15, which is disposed between the bonding layer 14 and the conductive layer 12. The conductive layer 12 of the positive electrode composite current collector 1 and the polymer support layer 11 are bonded together by the bonding layer 14 containing a binder. When the positive electrode composite current collector 1 is used in a battery, the electrolyte may penetrate between the bonding layer 14 and the conductive layer 12, thereby causing micro-corrosion to the conductive layer 12. By disposing the passivation layer 15 between the bonding layer 14 and the conductive layer 12, the present application can provide a passivation protection at the interface where the conductive layer 12 contacts the bonding layer 14, thereby reducing micro-corrosion of the conductive layer 12 by the electrolyte.

[0078] In some embodiments, the material of the passivation layer 15 includes one or more of chromate, dichromate, organic phosphonate, Al2O3, SiO2 and Si3N4. Among them, chromate includes one or more of sodium chromate, potassium chromate, magnesium chromate and silver chromate; dichromate includes one or more of sodium dichromate, potassium dichromate, magnesium dichromate and silver dichromate; organic phosphonate includes one or more of hydroxyethylidene diphosphonic acid (HEDP), diethylenetriamine penta (methylene phosphonic acid) (DETPMP), triethylenetetramine hexa (methylene phosphonic acid) (TETHMP) and ethylenediamine tetra (methylene phosphonic acid) (EDTMP). The above-mentioned materials are used to form the passivation layer 15 at the interface where the conductive layer 12 contacts the bonding layer 14, which can provide good passivation protection for the conductive layer 12 and effectively alleviate the micro-corrosion of the conductive layer 12 by the electrolyte.

[0079] In some embodiments, the thickness of the passivation layer 15 is D4, 1nm≤D4≤500nm; alternatively, 10nm≤D4≤200nm. Controlling the thickness of the passivation layer 15 within the above range can effectively alleviate the micro-corrosion of the conductive layer 12 by the electrolyte. It is understood that the thickness of the passivation layer 15 can be, but is not limited to, 1nm, 5nm, 10nm, 20nm, 30nm, 50nm, 80nm, 100nm, 120nm, 140nm, 150nm, 160nm, 180nm, 200nm, 220nm, 240nm, 250nm, 260nm, 280nm, 300nm, 320nm, 340nm, 350nm, 360nm, 380nm, 400nm, 420nm, 440nm, 450nm, 460nm, 480nm, or 500nm.

[0080] In some 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, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene oxide, polyphenylene sulfide, polyethylene glycol, polysulfur 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 to traditional metal foil current collectors such as copper, aluminum, and aluminum foil.

[0081] In some embodiments, the material of the polymer support layer 11 may also include one or more of a metal material and an inorganic insulating material. The inorganic insulating material may include one or more of aluminum oxide, silicon carbide, and silicon dioxide. By adding the aforementioned inorganic insulating materials to the material of the polymer support layer 11, the strength of the positive electrode composite current collector 1 can be further improved.

[0082] In some embodiments, the thickness D5 of the polymer support layer 11 is 2 μm ≤ D5 ≤ 40 μm; alternatively, 3 μm ≤ D5 ≤ 8 μm. Controlling the thickness of the polymer support layer 11 within the aforementioned range can enable a battery employing 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 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm.

[0083] In some 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 by means of a bonding slurry; curing the bonding slurry to form a bonding layer between the polymer support layer 11 and the conductive layer 12, wherein the bonding slurry includes a binder; whether or not to perform a etching thinning treatment on the conductive layer 12 is selected according to the thickness requirement of the conductive layer 12; and then forming a high-resistance layer 13 on the conductive layer 12 by evaporation. During the preparation of the positive electrode composite current collector 1, the thickness and density of the conductive layer 12 and the high-resistance layer 13 are controlled so that the total square resistance R1 of the conductive layer 12 and the high-resistance layer 13 is within the range of 50mΩ / □ to 80mΩ / □.

[0084] By providing a high-resistance layer 13 on the surface of the conductive layer 12 facing away from the polymer support layer 11, and ensuring that the total square resistance R1 of the high-resistance layer 13 and the conductive layer 12 satisfies 50mΩ / □≤R1≤80mΩ / □, while maintaining the normal electrode conductivity of the conductive layer 12 and the battery DCR within an appropriate range, the square resistance of the conductive layer 12 is increased, thereby improving the nail penetration test pass rate of batteries using this positive electrode composite current collector 1 and enhancing the battery's safety performance. Furthermore, the conductive layer 12 and the polymer support layer 11 are composited by an adhesive layer 14. Compared to traditional positive electrode composite current collectors 1 in which the conductive layer 12 is formed by evaporation or magnetron sputtering, the positive electrode composite current collector 1 prepared by this method does not cause significant thermal damage to the polymer support layer 11, and can thus provide the positive electrode composite current collector 1 with a higher elongation at break.

[0085] In some embodiments, the polymer support layer 11 and the conductive layer 12 can be composited by the following method: gravure coating of an adhesive slurry on a metal foil serving as the conductive layer 12, baking the metal foil coated with the adhesive slurry in an oven at 80°C to 110°C, and then thermally composite the baked metal foil with the adhesive slurry coated side with the polymer support layer 11. After the composite current collector is aged to allow the adhesive to fully adhere, the metal foil can then be thinned by a corrosion thinning process according to design requirements to obtain a conductive layer 12 of appropriate thickness. In addition, a metal layer can be formed as the conductive layer 12 on a thick carrier by evaporation or electrolysis before composite, the metal layer can be peeled off from the thick carrier, and then the metal layer can be composited with the polymer support layer 11 by coating with an adhesive slurry.

[0086] In some embodiments, before gravure coating the adhesive slurry on the conductive layer 12, the surface of the conductive layer 12 coated with the adhesive slurry may be passivated to form a passivation layer 15. Specifically, the passivation layer 15 may be formed by compositely coating the passivation material on the conductive layer 12 using gravure printing, evaporation, or magnetron sputtering; then, gravure coating the adhesive slurry on the passivation layer 15.

[0087] Referring to FIG. 2 , in some embodiments, the second aspect of the present application further provides a positive electrode plate 2, which includes a positive electrode active material layer 21 and a positive electrode composite current collector 1 according to the first aspect of the present application. 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. Thus, the positive electrode plate 2 employs the positive electrode composite current collector 1 according to the first aspect of the present application. Since the high-resistance layer 13 and the conductive layer 12 have a suitable total square 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 higher nail penetration test pass rate, thereby providing the battery with better safety performance.

[0088] In some embodiments, the third aspect of the present application further provides a secondary battery, which includes the positive electrode composite current collector 1 of the first aspect of the present application or the positive electrode plate 2 of the second aspect of the present application. In this way, the secondary battery has a high nail penetration test pass rate, has good safety performance, and the battery DCR is at an appropriate level.

[0089] In some embodiments, the fourth aspect of the present application further provides an electrical device, which includes the secondary battery of the third aspect of the present application.

[0090] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0091] Unless otherwise specified, the components, material types, or contents of the batteries mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0092] In one embodiment of the present application, a secondary battery is provided.

[0093] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0094] Positive electrode

[0095] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0096] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0097] In some embodiments, the positive electrode current collector may adopt the positive electrode composite current collector of the first aspect of the present application.

[0098] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery known in the art.

[0099] As a non-limiting example, the positive electrode active material of the lithium-ion secondary battery may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides 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 lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc.; Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.1 Al 0.05 O2.

[0100] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0101] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0102] As non-limiting examples, the positive electrode active material of a sodium ion secondary battery may include one or more of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0103] As an optional technical solution of the present 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. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0104] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. 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 (YO4) n- valence.

[0105] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n-A class of compounds containing anion 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 (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0106] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0107] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0108] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0109] 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.

[0110] 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 fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0% to 20% by weight, based on the total weight of the positive electrode film layer.

[0111] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As non-limiting examples, 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% to 20% by weight, based on the total weight of the positive electrode film layer.

[0112] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000mPa·s to 25000mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit area density is 150mg / m 2 ~350 mg / m 2 The compaction density of the positive electrode is 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0113] The calculation formula of the compacted density is:

[0114] Compaction density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0115] The mass M of the positive electrode active material per unit area of ​​the positive electrode membrane can be obtained by weighing using a standard balance.

[0116] The thickness T of the positive electrode film can be measured using a micrometer, for example, a Mitutoyo 293-100 with an accuracy of 0.1 μm. 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 sheet after cold pressing and used in battery assembly.

[0117] Negative electrode

[0118] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0119] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0120] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. Among them, in the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0121] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art.

[0122] As a non-limiting example, the negative electrode active material of the lithium-ion secondary battery may 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. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0123] As a non-limiting example, the negative active material of the sodium ion secondary battery is generally a hard carbon material, a two-dimensional metal carbide or a nitride. Preferably, the negative active material of the sodium ion secondary battery is generally a hard carbon material.

[0124] 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).

[0125] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0127] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0128] electrolytes

[0129] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt of the lithium ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0132] 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).

[0133] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0134] 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), trifluoromethylethylene carbonate (TFPC), and the like.

[0135] Isolation film

[0136] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0139] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0140] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0141] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0142] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0143] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0144] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 with a square structure as an example.

[0145] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0146] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0147] In the battery module, the plurality of battery cells 5 can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the plurality of battery cells 5 can be fixed by fasteners.

[0148] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0149] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0150] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0151] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may 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 and satellites, energy storage systems, etc., but is not limited thereto.

[0152] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0153] FIG5 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0154] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0155] The following are some examples.

[0156] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0157] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0158] 1. Examples and Comparative Examples

[0159] Example 1:

[0160] 1) Preparation of positive electrode sheet

[0161] 1.1) Preparation of positive electrode composite current collector

[0162] Aluminum foil was selected as the conductive layer material. A passivation solution, potassium dichromate, was evenly applied to the surface of the aluminum foil via gravure printing to form a passivation layer with a thickness D4 of 100 nm. A polyurethane adhesive slurry was then gravure-coated on the passivated surface of the aluminum foil. The coated aluminum foil was then baked in an oven and thermally laminated to a polymer support layer with a thickness D5 of 6 μm, completing single-sided lamination. The polymer support layer was a polyamide support layer.

[0163] The same method was used to laminate a metal aluminum foil onto the other side of the polymer support layer. After lamination, the aluminum foil was aged to ensure sufficient adhesion of the adhesive. The aluminum foil was then thinned by etching to produce a conductive layer with a thickness D1 of 800 nm, a sheet resistance R2 of 35 mΩ / □, a density M2 of 60%, and an adhesive layer thickness D3 of 500 nm.

[0164] Aluminum oxide was vapor-deposited onto the conductive layers on both surfaces of the polymer support layer to form a high-resistance layer. The thickness of the high-resistance layer was controlled by adjusting the aluminum wire feed rate and the oxygen flow rate during vapor deposition, resulting in a thickness D2 of 400 nm for each high-resistance layer. The combined density M1 of the high-resistance and conductive layers was 95%, the total sheet resistance R1 of the high-resistance and conductive layers was 80 mΩ / □, the thickness ratio A of the conductive layer to the high-resistance layer was 2, and the surface roughness Rz of the high-resistance layer was 1.5 μm.

[0165] 1.2) Preparation of positive electrode active material layer

[0166] The positive electrode active material NCM811, the conductive agent conductive carbon black, and the binder SBR styrene butadiene latex were mixed uniformly in the solvent N-methylpyrrolidone at a mass ratio of 97:1.2:1.8 to obtain a positive electrode slurry. The above positive electrode slurry was coated on the high resistance layer on both sides of the positive electrode composite current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The compacted density of the positive electrode sheet is 3.4g / cm 3 .

[0167] 2) Preparation of negative electrode sheet

[0168] The negative electrode active material graphite, conductive agent conductive carbon black, and binder carboxymethyl cellulose (CMC) were mixed uniformly in an appropriate amount of deionized water at a mass ratio of 98:1:1 to obtain a negative electrode slurry. The negative electrode slurry was applied to both sides of a 6μm thick negative electrode current collector copper foil. The negative electrode sheet was obtained through drying, cold pressing, slitting, and cutting. The compacted density of the negative electrode sheet was 1.6g / cm 3 .

[0169] 3) Electrolyte preparation

[0170] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain an organic solvent, and fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0171] 4) Isolation film

[0172] Polypropylene / polyethylene / polypropylene (PP / PE / PP) composite diaphragm is used as the isolation membrane.

[0173] 5) Cell preparation

[0174] The above-mentioned positive electrode sheet, separator and negative electrode sheet are wound together into a bare battery cell, and the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role; double-sided metal edging is used for roller welding and transfer welding to form tabs; the battery cell with the tabs welded is placed in a battery casing, and the above-mentioned electrolyte is injected, and sealing, formation and other processes are carried out to obtain a lithium-ion secondary battery.

[0175] Example 2:

[0176] This embodiment is basically the same as Example 1, with the only difference being that the thickness D2 of the high-resistance layer in the positive composite current collector is 320 nm, the total density M1 of the high-resistance layer and the conductive layer is 90%, the total square 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.

[0177] Example 3:

[0178] This embodiment is basically the same as Example 1, with the only difference being that the thickness D2 of the high-resistance layer in the positive electrode composite current collector is 160 nm, the total density M1 of the high-resistance layer and the conductive layer is 85%, the total square 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.

[0179] Example 4:

[0180] This embodiment is basically the same as Example 1, with the only difference being that the thickness D2 of the high-resistance layer in the positive electrode composite current collector is 80 nm, the total density M1 of the high-resistance layer and the conductive layer is 78%, the total square 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.

[0181] Example 5:

[0182] This embodiment is basically the same as Example 1, with the only difference being 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 square 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.

[0183] Example 6:

[0184] This embodiment is basically the same as Example 1, with the only differences being 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 square 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.

[0185] Example 7:

[0186] This embodiment is basically the same as Example 3, with the only difference being that the thickness D1 of the conductive layer in the positive electrode composite current collector is 500 nm, the density M2 of the conductive layer is 50%, the square 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 square 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.

[0187] Example 8:

[0188] This embodiment is basically the same as Example 3, with the only difference being that the thickness D1 of the conductive layer in the positive electrode composite current collector is 600 nm, the density M2 of the conductive layer is 55%, the square 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 square 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.

[0189] Example 9:

[0190] This embodiment is basically the same as Example 3, except that: the thickness D1 of the conductive layer in the positive electrode composite current collector is 1000 nm, the density M2 of the conductive layer is 65%, the square 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 square 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.

[0191] Example 10:

[0192] This embodiment is basically the same as Example 3, with the only difference being that the thickness D1 of the conductive layer in the positive electrode composite current collector is 1200 nm, the density M2 of the conductive layer is 70%, the square 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 square 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.

[0193] Example 11:

[0194] This embodiment is basically the same as Example 3, with the only difference being that the thickness D1 of the conductive layer in the positive electrode composite current collector is 1500 nm, the density M2 of the conductive layer is 75%, the square 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 square 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.

[0195] Comparative Example 1:

[0196] This comparative example is basically the same as Example 1, with the only differences being that the thickness D2 of the high-resistance layer in the positive electrode composite current collector is 800 nm, the total density M1 of the high-resistance layer and the conductive layer is 100%, the total square 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.

[0197] Comparative Example 2:

[0198] This comparative example is basically the same as Example 1, with the only differences being that the thickness D2 of the high-resistance layer in the positive electrode composite current collector is 27 nm, the total density M1 of the high-resistance layer and the conductive layer is 63%, the total square 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.

[0199] Comparative Example 3:

[0200] This comparative example is basically the same as Example 3, except that: the thickness D1 of the conductive layer in the positive electrode composite current collector is 1600 nm, the density M2 of the conductive layer is 95%, the square 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 square 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.

[0201] Comparative Example 4:

[0202] This comparative example is basically the same as Example 3, with the only difference being that the thickness D1 of the conductive layer in the positive electrode composite current collector is 400 nm, the density M2 of the conductive layer is 40%, the square 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 square 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.

[0203] Comparative Example 5:

[0204] This comparative example is basically the same as Example 3, with the only difference being that no high-resistance layer is provided on the conductive layer of the positive electrode composite current collector.

[0205] 2. Test Method

[0206] 1) Film thickness test

[0207] Cross-sectional samples of the composite current collector are prepared using liquid nitrogen quenching or argon ion etching. The secondary electron phase morphology of the sample cross-section is observed using a scanning electron microscope at magnification (1,000 to 30,000 times), and the thickness of each layer, including the polymer support layer, conductive layer, high-resistance layer, adhesive layer, and passivation layer, is measured. The minimum resolution can reach the nanometer level.

[0208] 2) High resistance layer surface roughness Rz test

[0209] Use a roughness tester to test the surface roughness of the high-resistance layer and obtain the Rz value;

[0210] Rz mean = sum of Rz values ​​of 10 test points / 10.

[0211] 3) Conductive layer / high resistance layer density test

[0212] Place a flat test sample on the CCD optical microscope operating table, turn on the light source on the back of the operating table, turn off the light source of the microscope, and take dark field photos of the sample in three areas. Use Imagej image processing software to select the image saved by the CCD and calculate the density percentage M value.

[0213] M mean = sum of M values ​​of the three test areas / 3.

[0214] 4) Square resistance R test of conductive layer / conductive layer and high resistance layer combination layer

[0215] Take a flat sample and use a four-probe square resistance tester to measure the square resistance of the sample and take the R value;

[0216] R mean = sum of R values ​​of 10 test points / 10.

[0217] 5) Positive electrode composite current collector fracture strength and fracture elongation test

[0218] Use a standard sampler to cut the sample into 10 samples of 15 mm wide and 15 cm long along the MD (longitudinal) and TD (transverse) directions; fix the sample to the clamp of the tensile testing machine at a set speed of 50 mm / min and a gauge length of 50 mm between the clamps, and test the corresponding strength and elongation under fracture.

[0219] Breaking strength = sum of breaking strengths of 10 test samples / 10;

[0220] Elongation at break = sum of elongations at break of 10 test samples / 10.

[0221] 6) Positive electrode shear force test

[0222] A special shear force tape is attached to the steel plate with a width of 4 mm and a length of 5 mm. The positive electrode sheet is attached to the tape, and the shear force between the positive electrode active material layer of the sheet and the positive electrode composite current collector is measured using a high-speed rail tensile testing machine.

[0223] Average shear force = sum of shear force values ​​of 10 samples / 10. (Shear force specification ≥ 0.3 MPa).

[0224] 7) U-shaped resistance test of the positive electrode after welding

[0225] 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 meter.

[0226] Average R value = sum of the U-shaped resistance values ​​of 10 samples / 10. (U resistance R specification 70mΩ to 130mΩ, preferably 80mΩ to 120mΩ).

[0227] 8) Battery cell DCR test

[0228] Adjust the cell capacity to 50% SOC and record the voltage V1; discharge at 4C for 30s and obtain the voltage V2;

[0229] DCR = (V1-V2) / 4C;

[0230] DCR mean = sum of DCR values ​​of 10 samples / 10.

[0231] Generally speaking, the cell DCR should be less than 0.7mΩ, preferably less than 0.6mΩ.

[0232] 9) Battery cell nail penetration test

[0233] First, fully charge the battery cell to 100% SOC. Connect the positive and negative terminals of the battery cell to a power source to test the voltage. Use a 3mm to 6mm steel needle to penetrate the large surface of the battery cell at a constant speed. Determine if the battery cell has failed by observing whether it emits smoke, fire, or explosion, or whether the voltage drops suddenly. Calculate the nail penetration pass rate. Collect test data for five samples.

[0234] Nail penetration rate = (the sum of the number of nails passed for 5 samples / 5)*100%.

[0235] The battery parameters of the embodiments and comparative examples of the present application are shown in Table 1, and the performance test data are shown in Table 2. " / " in Table 1 indicates absence.

[0236] Table 1

[0237] Table 2

[0238] The above data demonstrates that the positive composite current collectors of the various embodiments of the present application, by providing a high-resistance layer on the surface of the conductive layer facing away from the polymer support layer, and ensuring that the total square resistance R1 of the high-resistance layer and the conductive layer is 50mΩ / □ to 80mΩ / □, can maintain the normal electrode conductivity of the conductive layer and keep the battery's DC internal resistance within an appropriate range, while achieving a high nail penetration test pass rate, thereby improving battery safety. Furthermore, the positive composite current collectors exhibit high elongation at break and high fracture strength; the positive electrode sheets can withstand high shear forces while exhibiting low U-shaped resistance.

[0239] By comparing Examples 1 to 6, it can be seen that further controlling the total square resistance R1 of the high-resistance layer and the conductive layer within the range of 58mΩ / □ to 70mΩ / □, 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, and enable the battery to have both lower DC internal resistance and higher nail penetration test pass rate, which can better take into account both 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 is increased so that 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%, and the total square resistance R1 of the high-resistance layer and the conductive layer is greater than 80mΩ / □. The overall conductivity of the positive electrode 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, the positive electrode composite current collector can no longer meet the use requirements of the positive electrode sheet and the battery cell. At the same time, due to the problem of cracking caused by the thick high-resistance layer material, the elongation at break of the positive electrode composite current collector cannot meet the requirements.

[0241] Comparing Example 1 with Comparative Example 2 shows that when the thickness of the high-resistance layer is reduced, so that the thickness ratio A of the conductive layer to the high-resistance layer is greater than 25, the high-resistance layer does not significantly increase the sheet resistance of the conductive layer, and the total sheet resistance R1 of the high-resistance and conductive layers is less than 50 mΩ / □. Although the U-shaped resistance of the positive electrode sheet is small and the cell DCR meets the requirements, the pass rate of the cell's nail penetration test decreases significantly. Furthermore, due to the excessively thin high-resistance layer and its low surface roughness, the positive electrode sheet can withstand less shear force.

[0242] It can be seen from Comparative Example 3 that when the thickness of the conductive layer is too large, the square resistance of the conductive layer decreases, making the total square resistance of the high-resistance layer and the conductive layer too small; although the DCR of the battery cell can meet the requirements, the pass rate of the battery cell's nail penetration test is very low. It can be seen from Comparative Example 4 that when the thickness of the conductive layer is too small, the square resistance of the conductive layer increases, making the total square resistance of the high-resistance layer and the conductive layer too large; although the pass rate of the battery cell's nail penetration test is high, the U-shaped resistance of the positive electrode sheet is too large and the battery cell's DCR is too large, which cannot meet the use requirements. By comparing Example 1 and Comparative Example 5, it can be seen that when a high-resistance layer is not provided on the conductive layer of the positive composite current collector, the pass rate of the battery cell's nail penetration test is significantly reduced.

[0243] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0244] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode composite current collector, comprising: a polymer support layer; a conductive layer disposed on at least one surface of the polymer support layer; as well as The high resistance layer is arranged on the surface of the conductive layer away from the polymer support layer. The resistivity of the high resistance layer is higher than that of the conductive layer. The total square resistance of the high resistance layer and the conductive layer is R1, 50mΩ / □≤R1≤80mΩ / □.

2. The positive electrode composite current collector according to claim 1, wherein: 58mΩ / □≤R1≤70mΩ / □.

3. The positive electrode composite current collector according to claim 1 or 2, wherein: The square resistance of the conductive layer is R2, 25mΩ / □≤R2≤45mΩ / □.

4. The positive electrode composite current collector according to claim 3, wherein: 30mΩ / □≤R2≤40mΩ / □.

5. The positive electrode composite current collector according to any one of claims 1 to 4, wherein: The thickness ratio of the conductive layer to the high resistance layer is A, 2≤A≤25.

6. The positive electrode composite current collector according to claim 5, wherein: 2.5≤A≤20。 7. The positive electrode composite current collector according to any one of claims 1 to 6, wherein: The thickness of the conductive layer is D1, 500nm≤D1≤1500nm.

8. The positive electrode composite current collector according to claim 7, wherein: 600nm≤D1≤1200nm.

9. The positive electrode composite current collector according to any one of claims 1 to 8, wherein: The thickness of the high resistance layer is D2, 30nm≤D2≤500nm.

10. The positive electrode composite current collector according to claim 9, wherein: 35nm≤D2≤400nm.

11. The positive electrode composite current collector according to any one of claims 1 to 10, wherein: The total density of the conductive layer and the high resistance layer is M1, 70%≤M1≤95%.

12. The positive electrode composite current collector according to claim 11, wherein: 75％≤M1≤90％。 13. The positive electrode composite current collector according to any one of claims 1 to 12, wherein: The density of the conductive layer is M2, 50%≤M2≤75%.

14. The positive electrode composite current collector according to claim 13, wherein: 55％≤M2≤70％。 15. The positive electrode composite current collector according to any one of claims 1 to 14, wherein: The material of the high resistance layer includes one or more of aluminum oxide, silicon oxide, nickel-chromium alloy and iron-chromium-aluminum alloy.

16. The positive electrode composite current collector according to any one of claims 1 to 15, wherein: The material of the conductive layer includes one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

17. The positive electrode composite current collector according to any one of claims 1 to 16, wherein: The surface roughness Rz of the high resistance layer on a side away from the conductive layer is 0.1 μm to 2 μm.

18. The positive electrode composite current collector according to any one of claims 1 to 17, wherein: Also includes: A bonding layer is disposed between the polymer support layer and the conductive layer.

19. The positive electrode composite current collector according to claim 18, wherein: The bonding layer includes a bonding agent, and the bonding agent includes one or more of a composition containing a multifunctional isocyanate and a 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.

20. The positive electrode composite current collector according to claim 18 or 19, wherein: Also includes: A passivation layer is disposed between the bonding layer and the conductive layer.

21. The positive electrode composite current collector according to claim 20, wherein: The material of the passivation layer includes one or more of chromate, dichromate, organic phosphonate, Al2O3, SiO2 and Si3N4.

22. The positive electrode composite current collector according to claim 21, wherein: The chromate includes one or more of sodium chromate, potassium chromate, magnesium chromate and silver chromate.

23. The positive electrode composite current collector according to claim 21 or 22, wherein: The dichromate includes one or more of sodium dichromate, potassium dichromate, magnesium dichromate and silver dichromate.

24. The positive electrode composite current collector according to any one of claims 21 to 23, wherein: The organic phosphonate includes one or more of hydroxyethylidene diphosphonic acid, diethylene triamine penta methylene phosphonic acid, triethylene tetraamine hexa methylene phosphonic acid and ethylene diamine tetra methylene phosphonic acid.

25. The positive electrode composite current collector according to any one of claims 20 to 24, wherein: The thickness of the passivation layer is D4, 1nm≤D4≤500nm.

26. The positive electrode composite current collector according to claim 25, wherein: 10nm≤D4≤200nm.

27. The positive electrode composite current collector according to any one of claims 1 to 26, 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, 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, polysulfur nitride polymer materials, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin and their derivatives, crosslinked products and copolymers.

28. A positive electrode sheet, comprising a positive electrode active material layer and the positive electrode composite current collector according to any one of claims 1 to 27, wherein the positive electrode active material layer is arranged on a surface of the high resistance layer away from the conductive layer.

29. A secondary battery comprising the positive composite current collector according to any one of claims 1 to 27 or the positive electrode sheet according to claim 28.

30. An electrical device comprising the secondary battery according to claim 29.

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