Composite current collector for positive electrode, positive electrode sheet, secondary battery, and electric device

Abstract

The invention provides a composite current collector for a positive electrode, which comprises a support layer and a conductive layer arranged on at least one side of the support layer, and the support layer is an organic support layer; the thickness of the supporting layer is d1, the tensile breaking strength is T1, the yield strength is Q1, and the elastic modulus is G1; the total thickness of the conductive layer is d2, the tensile breaking strength is T2, and the elastic modulus is G2; the composite current collector for the positive electrode satisfies (d1 * T1-(d2 * T2) * (1-alpha)-d1 * Q1 * alpha) > = 800 Pa.m, wherein alpha = G1 / (G1 + G2).

Description

Composite current collector for positive electrode, positive electrode sheet, secondary battery and electrical device Technical Field

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

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

[0003] With the gradual promotion of secondary battery technologies such as lithium-ion batteries in consumer electronics, electric vehicles, and energy storage power stations, the demand for secondary battery energy density is becoming increasingly higher. Composite current collectors, which incorporate a polymer-based support layer on a metal current collector, offer lower density at the same thickness and offer significant advantages in safety and cost. However, the poor processability of composite current collectors has seriously hampered their further application.

[0004] Therefore, it is necessary to further develop new products of composite current collectors.

[0005] Summary of the Invention

[0006] In view of the above problems, the present application provides a composite current collector for a positive electrode, a positive electrode sheet, a secondary battery, and an electrical device. The composite current collector for a positive electrode is suitable for a positive electrode and can have significantly improved processability while maintaining good energy density.

[0007] In a first aspect, the present application provides a composite current collector for a positive electrode, comprising a support layer and a conductive layer disposed on at least one side of the support layer, wherein the support layer is an organic support layer;

[0008] The thickness of the support layer is recorded as d1, the tensile strength is recorded as T1, the yield strength is recorded as Q1, and the elastic modulus is recorded as G1;

[0009] The total thickness of the conductive layer is recorded as d2, the tensile strength at break is recorded as T2, and the elastic modulus is recorded as G2;

[0010] The composite current collector for the positive electrode satisfies the following condition: (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800 Pa·m, wherein α=G1 / (G1+G2).

[0011] For a positive electrode composite current collector comprising an organic support layer and a conductive layer, by reasonably matching the thickness d1, tensile fracture strength T1, yield strength Q1 and elastic modulus G1 of the support layer and the thickness d2, tensile fracture strength T2 and elastic modulus G2 of the conductive layer, and also using the distribution coefficient α = G1 / (G1+G2) to finely adjust the distribution of the elastic modulus between the support layer and the conductive layer, (d1×T1-(d2×T2)×(1-α)-d1×Q1×α) can be defined as the ductility coefficient of the positive electrode composite current collector. The ductility coefficient can represent: under stress, when the positive electrode composite current collector undergoes elastic deformation and enters the yield deformation stage, the residual force that the unit width of the support layer can withstand. This "residual force" can roughly correspond to the residual force that the positive electrode composite current collector can withstand when it breaks after deducting the force that it can withstand at the elastic limit; the greater this residual force, based on the stress-strain relationship, the greater the elongation of the positive electrode composite current collector during the later plastic deformation. When the elongation coefficient of the composite current collector for the positive electrode is ≥800, the elongation at break of the composite current collector for the positive electrode is higher, and the processability in mass production is better, which is beneficial to reducing the fracture of the composite current collector for the positive electrode during the electrode processing process, improving the processing efficiency, and reducing or avoiding the increase in local interface side reactions caused by wrinkling of the electrode during the charge and discharge process, thereby improving the battery cycle performance; and at the cell level, it is beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the electrode in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0012] In some embodiments, the thickness d1 of the support layer is 4 μm-15 μm;

[0013] Optionally, the thickness d1 of the support layer is 4 μm-12 μm;

[0014] Further optionally, the thickness d1 of the support layer is 4 μm-6 μm.

[0015] The thicker the positive electrode composite current collector, the lower the battery cell energy density. However, if the positive electrode composite current collector is too thin, it can withstand less force and has low elongation, which is detrimental to processability. Adjusting the thickness of the support layer can indirectly adjust the thickness of the positive electrode composite current collector, allowing it to better balance high energy density and superior processability.

[0016] In some embodiments, the tensile strength at break of the support layer T1 is ≥ 200 MPa;

[0017] Optionally, the tensile fracture strength T1 of the support layer is ≥300 MPa.

[0018] The higher the tensile strength of the support layer, the greater the force it can withstand, the better the mechanical strength of the composite current collector for the positive electrode is, and the more favorable the processability of the composite current collector for the positive electrode is.

[0019] In some embodiments, the yield strength Q1 of the support layer is ≥90 MPa;

[0020] Optionally, the yield strength Q1 of the support layer is ≥150 MPa.

[0021] The higher the yield strength of the support layer, the better its ability to resist micro-plastic deformation, and the more conducive it is to the processing of the composite current collector for the positive electrode.

[0022] In some embodiments, the composite current collector for the positive electrode satisfies any one or more of the following characteristics:

[0023] The total thickness d2 of the conductive layer is 0.6 μm-3 μm; optionally, the total thickness d2 of the conductive layer is 1 μm-3 μm; further optionally, the total thickness d2 of the conductive layer is 1.4 μm-2.4 μm;

[0024] The single-side thickness d2 of the conductive layer s 0.3-1.5 μm; Optionally, the thickness d2 of the conductive layer on one side s 0.5 μm-1.5 μm; further optionally, the thickness d2 of the conductive layer on one side s 0.7μm-1.2μm;

[0025] The thickness D of the composite current collector for the positive electrode a 3μm-17μm; Optionally, the thickness D of the composite current collector for the positive electrode a 3μm-14μm; further optionally, the thickness D of the composite current collector for the positive electrode a 3.4μm-8.4μm.

[0026] By adjusting the thickness of the conductive layer or directly controlling the thickness of the composite current collector for the positive electrode so that the thickness of the composite current collector for the positive electrode is within a certain range, the composite current collector for the positive electrode can better have both better energy density and superior processability.

[0027] In some embodiments, the tensile strength T2 of the conductive layer is ≥ 150 MPa;

[0028] Optionally, the tensile strength T2 of the conductive layer is ≥200 MPa.

[0029] The higher the tensile strength of the conductive layer, the more favorable it is for the processability of the composite current collector for the positive electrode.

[0030] In some embodiments, the composite current collector for the positive electrode satisfies any one or more of the following characteristics:

[0031] The elastic modulus G1 of the support layer is ≥3 GPa; optionally, the elastic modulus G1 of the support layer is ≥4 GPa;

[0032] The elastic modulus G2 of the conductive layer is 25 GPa-40 GPa; optionally, the elastic modulus G2 of the conductive layer is 25 GPa-35 GPa;

[0033] The α is 0.024-0.43; optionally, the α is 0.095-0.300; further optionally, the α is 0.105-0.250.

[0034] By regulating the distribution of the elastic modulus between the support layer and the conductive layer, for example, by adjusting the value of α=G1 / (G1+G2), the magnitude of the force exerted on the support layer and the conductive layer in the composite current collector for the positive electrode under stress can be reasonably adjusted, thereby better improving the overall tolerance of the composite current collector for the positive electrode, and further improving the processability of the composite current collector for the positive electrode. Among them, when the current collector material composed of the support layer and the conductive layer is subjected to stress, during the elastic deformation stage, due to the different elastic moduli (stiffness) of the two material layers, the actual forces exerted on the support layer and the conductive layer are not consistent. The material with a large elastic modulus is often subjected to a greater force. Thus, by adjusting the distribution coefficient, the respective force proportions of the support layer and the conductive layer in the composite current collector for the positive electrode can be regulated.

[0035] In some embodiments, (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1000 Pa·m;

[0036] Optionally, (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1650 Pa·m.

[0037] The greater the ductility coefficient of the composite current collector for the positive electrode, the higher the elongation at break of the composite current collector for the positive electrode, the better the processability in mass production, and the more conducive to reducing the fracture of the composite current collector for the positive electrode during the electrode processing process and improving the processing quality rate; at the battery cell level, it is also more conducive to reducing the cracking problem that may be caused by the gradual increase in the electrode expansion force in the later stage of the battery cell cycle, and is more conducive to improving the cycle performance and safety and reliability of the battery cell.

[0038] In some embodiments, the support layer is made of a polymer-based material or a polymer-based composite material;

[0039] Optionally, the polymer component in the supporting layer includes polyimide, polyamide, 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 one or more of the derivatives of the above materials, the cross-linked products of the above materials and the copolymers of the above materials.

[0040] When polymer materials are selected as the main material of the support layer, polymers have a lighter density and better ductility than conductive metals, which can reduce the surface density of the composite current collector for the positive electrode, thereby helping to improve the energy density of the battery cell. It can also improve the overall ductility of the composite current collector for the positive electrode, which is beneficial to improving the processing efficiency of the electrode sheet.

[0041] The main material of the support layer may or may not contain other materials besides polymers, and may also form a composite material with other materials. When it is a polymer-based composite material, it can be appropriately selected based on performance requirements and in accordance with processing requirements to improve the processability of the positive electrode composite current collector, battery core performance, or a combination thereof, for example, to improve one or more of the properties of the positive electrode composite current collector, such as volume resistivity, elongation at break, and Young's modulus.

[0042] In some embodiments, the polymer component in the support layer includes polyimide, and the polyimide includes one or both of homophenyl polyimide and biphenyl polyimide;

[0043] Optionally, the polymer component in the support layer includes biphenyl polyimide;

[0044] Further optionally, the support layer comprises biphenyl polyimide in an amount of ≥50% by mass;

[0045] Further optionally, the support layer comprises biphenyl polyimide in an amount of ≥80% by mass;

[0046] Further optionally, the support layer is made of biphenyl polyimide.

[0047] Polyimide is an organic carbonyl polymer containing an imide ring in its main chain. It has excellent mechanical properties and heat resistance, high mechanical strength, and good high-temperature resistance. Using polyimide in the support layer can leverage its tensile strength, yield strength, and elastic modulus properties to better synergize with the tensile strength and elastic modulus of the conductive layer, thereby better adjusting the ductility coefficient of the positive electrode composite current collector. This is more conducive to achieving the dual requirements of good energy density and excellent processability for the positive electrode composite current collector.

[0048] Both phenylene-type polyimide and biphenyl-type polyimide possess the aforementioned common advantages of polyimide. Furthermore, compared to phenylene-type polyimide as the main material for the support layer, when biphenyl-type polyimide is used as the main material for the support layer, the resulting composite current collector for the positive electrode can significantly improve one or more of the following properties: mechanical properties (such as tensile strength, elastic modulus, elongation at break), performance (such as coating efficiency, cold pressing elongation, cold pressing fracture frequency), and battery cell performance (such as cycle capacity retention).

[0049] In some embodiments, the conductive layer includes a metal material. Optionally, the metal material includes one or more of aluminum and an aluminum alloy.

[0050] When the conductive layer comprises a metal material, it is advantageous to provide better conductivity. Furthermore, when the metal material comprises one or more of aluminum and aluminum alloys, it is easier to control the ductility coefficient of the positive electrode composite current collector within an appropriate range. Furthermore, it is also easier to control parameters such as the tensile strength and elastic modulus of the conductive layer within a more suitable range, thereby better balancing the energy density of the battery cell and the processability of the positive electrode composite current collector.

[0051] In a second aspect, the present application provides a positive electrode plate, which includes the composite current collector for the positive electrode described in the first aspect of the present application.

[0052] In a third aspect, the present application provides a secondary battery comprising at least one of the composite current collector for the positive electrode described in the first aspect of the present application and the positive electrode sheet described in the second aspect of the present application.

[0053] When the positive electrode plate includes the composite current collector for the positive electrode of the first aspect of the present application, it can have both good energy density and high mechanical strength, and can reduce or avoid the increase of local interfacial side reactions caused by wrinkling of the plate during charging and discharging, thereby improving the battery cycle performance; further, for secondary batteries containing the aforementioned composite current collector for the positive electrode or the aforementioned positive electrode plate, it is also beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the plate in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0054] In a fourth aspect, the present application provides an electrical device comprising at least one of the composite current collector for the positive electrode described in the first aspect of the present application, the positive electrode sheet described in the second aspect of the present application, and the secondary battery described in the third aspect of the present application.

[0055] In a fifth aspect, the present application provides a method for preparing the composite current collector for the positive electrode described in the first aspect of the present application, which comprises the following steps: forming the conductive layer on at least one side of the support layer to prepare the composite current collector for the positive electrode.

[0056] A supporting layer with a specific thickness d1, a specific tensile fracture strength T1, a specific yield strength Q1 and a specific elastic modulus G1 is used to further form a conductive layer with a specific thickness d2, a specific tensile fracture strength T2 and a specific elastic modulus G2. The prepared composite current collector for the positive electrode has a high ductility coefficient, a high elongation at break, and better processability in mass production. It is beneficial to reduce the fracture of the positive electrode current collector during the electrode processing process, improve the processing quality rate, and reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the electrode during the charging and discharging process, thereby improving the battery cycle performance; and at the cell level, it is beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the electrode in the later stage of the cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0057] In a sixth aspect, the present application provides a method for preparing a positive electrode sheet, which comprises the following steps: coating a positive electrode slurry on at least one side of the composite current collector for the positive electrode described in the first aspect of the present application, drying, and cold pressing to prepare the positive electrode sheet.

[0058] When the positive electrode composite current collector provided in the first aspect of the present application is used to prepare the positive electrode pole piece, the prepared positive electrode pole piece can have both good energy density and high mechanical strength, which can reduce or avoid the increase of local interfacial side reactions caused by wrinkling of the pole piece during the charging and discharging process, thereby improving the battery cycle performance; further preparation of a secondary battery containing the aforementioned positive electrode composite current collector or the aforementioned positive electrode pole piece is also beneficial to reducing the cracking problem that may be caused by the gradual increase in the expansion force of the pole piece in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0059] 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

[0060] In order to better describe and illustrate the embodiments or examples of the applications disclosed herein, 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 to limit the scope of the disclosed applications, 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 drawings:

[0061] FIG1 is a schematic structural diagram of a composite current collector for a positive electrode in one embodiment of the present application, wherein the conductive layers are located on both sides of the support layer;

[0062] FIG2 is a schematic structural diagram of a composite current collector for a positive electrode in one embodiment of the present application, wherein the conductive layer is located on a single side of the support layer;

[0063] FIG3 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0064] FIG4 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG3 ;

[0065] FIG5 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0066] Explanation of reference numerals: 5, secondary battery; 51, housing; 52, electrode assembly; 53, cover plate; 6, power-consuming device; 100, composite current collector for positive electrode; 110, support layer; 120, conductive layer. DETAILED DESCRIPTION

[0067] Below, some embodiments of the composite current collector for the positive electrode, the positive electrode sheet, the secondary battery and the electric 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 structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following 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.

[0068] Numerical value " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special range. The scope that this mode limits can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, and promptly any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if also listing the maximum range value 3,4 and 5, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely 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.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0070] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and may preferably be performed sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0071] Unless otherwise specified, the terms "having," "including," "containing," and "comprising" used in this application may each independently represent open or closed forms. For example, "including" and "comprising" may also represent other components or temporal features not listed, or may only represent the listed components or temporal features. Examples of components include materials or components, structures, elements, and instruments; non-limiting examples of temporal features include actions, conditions for the occurrence of actions, timing, states, and steps.

[0072] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." Furthermore, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0073] 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.

[0074] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more relevant listed items, and also include any and all combinations of the relevant listed items, wherein the arbitrary and all combinations include any two relevant listed items, any more relevant listed items, or a combination of all relevant listed items. For example, "A and / or B" means a group consisting of A, B, and "a combination of A and B." Among them, "including A and / or B" can mean "including A, including B, and including A and B", and can also mean "including A, including B, or including A and B", which can be appropriately understood according to the sentence in which it is located.

[0075] In this application, references to "plurality," "multiple," and the like, unless otherwise specified, refer to a quantity greater than or equal to two. For example, "one or more" refers to one or greater than or equal to two. It is understood that references to "any number" of items refer to any suitable combination of multiple items, i.e., any combination of "any number" of items that is consistent with the present application and that allows for the implementation of the present application.

[0076] The terms "combination thereof", "any combination thereof", "any combination thereof" and the like used in this application include all suitable combinations of any two or more of the listed items.

[0077] In this application, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the technical solution that can implement this application.

[0078] Herein, the terms "preferred" and "better" are used solely to describe preferred implementations or examples and should not be construed as limiting the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, each "preferred" term is considered independent unless otherwise specified and there are no contradictions or mutual constraints.

[0079] In this application, the terms "optionally," "optional," and "optional" are optional, meaning they may be present or absent, i.e., they may be either of two parallel options: "present" or "absent." If a technical solution contains multiple "optional" clauses, each "optional" clause is considered independent unless otherwise specified and there are no conflicts or constraints.

[0080] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0081] In this application, the terms "first," "second," "third," "fourth," etc. in "the first aspect," "the second aspect," "the third aspect," "the fourth aspect," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implicitly indicating the importance or quantity of the indicated technical features. Furthermore, "first," "second," "third," "fourth," etc. serve only as non-exhaustive enumeration and description, and should be understood not to constitute a closed-ended limitation on quantity.

[0082] In this application, when referring to a data range, if the unit is only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 3~5h or 3-5h both mean that the units of the left endpoint "3" and the right endpoint "5" are both hours.

[0083] The weights of the relevant components mentioned in the examples of this application may not only refer to the content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Furthermore, the weights mentioned in the examples of this application may be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0084] With the gradual promotion of secondary battery technologies such as lithium-ion batteries in consumer electronics, electric vehicles, and energy storage power stations, the requirements for the energy density of secondary batteries are becoming increasingly higher. In terms of current collectors, the thickness of traditional aluminum foil positive electrode current collectors can be reduced to a relatively thin thickness (such as 10μm). However, in the process of preparing battery cells, there are common problems such as wrinkling during winding and unwinding, cracking during cold pressing, and broken belts. The improvement of processability has basically reached its limit. In order to further improve the energy density, a composite current collector with a "metal-polymer-metal" sandwich structure has a lighter density at the same thickness and has special advantages in safety and cost. Therefore, it has become a research hotspot in the current industry. However, the processability of the composite current collector is relatively poor, which seriously affects the further promotion and application of the composite current collector: during the production and processing, since the polymer layer has lower stiffness and temperature resistance than metal, the composite current collector may also have poor processability problems such as warping of the pole ear during coating and drying, and excessive cold pressing extension; in addition, based on the current composite current collector manufacturing process, defects such as pinholes are prone to appear on the surface of the composite current collector, which can easily lead to problems such as coating leakage, scraping off the belt and cracking of the cold pressed pole piece during use. Moreover, these problems are likely to be further aggravated when the thickness of the current collector is further reduced.

[0085] In a first aspect, the present application provides a composite current collector for a positive electrode, comprising a support layer and a conductive layer disposed on at least one side of the support layer, wherein the support layer is an organic support layer;

[0086] The thickness of the support layer is recorded as d1, the tensile strength is recorded as T1, the yield strength is recorded as Q1, and the elastic modulus is recorded as G1;

[0087] The total thickness of the conductive layer is recorded as d2, the tensile strength at break is recorded as T2, and the elastic modulus is recorded as G2;

[0088] The composite current collector for the positive electrode satisfies the following condition: (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800 Pa·m, wherein α=G1 / (G1+G2).

[0089] In the present application, the "composite current collector for a positive electrode" provided in the first aspect is a composite current collector suitable for a positive electrode, which can be directly used as a positive electrode current collector or used to prepare a positive electrode current collector. For example, while meeting the characteristics of the composite current collector for a positive electrode of the present application, other functional structural layers can be further laminated to produce a positive electrode current collector with more functions.

[0090] In this application, unless otherwise specified, "support layer" refers to the structural layer in the composite current collector for the positive electrode, which serves to support the conductive layer. Unless otherwise specified, the support layer is primarily made of organic materials, which can provide a lighter density than conductive metals to meet the energy density requirements of the battery cell.

[0091] Unless otherwise specified, the "organic support layer" used in this application is primarily made of organic materials, further primarily including polymer materials. Polymers can provide a certain degree of mechanical strength. Functional additives suitable for composite current collectors for positive electrodes may also be added to the organic support layer as needed.

[0092] Unless otherwise specified, the terms "primarily composed of" or "primarily includes" as used herein mean that the weight percentage of the listed material is at least 50%, further 60%, further 70%, further 80%, further 90%, or any of the following weight percentages, or greater than or equal to any of the following weight percentages, or a range consisting of any two of the following weight percentages: 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc. Non-limiting examples of the range consisting of any two of the foregoing weight percentages include 50%-100%, 60%-100%, 70%-100%, 80%-100%, 90%-100%, etc. For example, "the main material of A is B" or "A primarily includes B" means that the weight percentage of B in A can meet any of the aforementioned appropriate conditions to preferably obtain a better ductility coefficient.

[0093] In this application, (d1×T1-(d2×T2)×(1-α)-d1×Q1×α) is defined as the ductility coefficient of the composite current collector for the positive electrode. The ductility coefficient can be expressed as follows: under stress, when the composite current collector for the positive electrode enters the yield deformation stage after elastic deformation, the residual force that the unit width of the support layer can withstand. This "residual force" can roughly correspond to the residual force that the composite current collector for the positive electrode can withstand when it breaks after deducting the force that it can withstand at the elastic limit; the greater this residual force, based on the stress-strain relationship, the greater the elongation of the composite current collector for the positive electrode during the later plastic deformation. The unit of the ductility coefficient is MPa·μm or Pa·m, which can also be converted to N / m. Physically, it can be considered as the force per unit width. The value of the ductility coefficient can be calculated by using micrometers (μm) as the unit of thickness and MPa as the unit of tensile fracture strength T1, T2 and yield strength Q1.

[0094] In this application, G1 / (G1+G2) is defined as the distribution coefficient α of the composite current collector for the positive electrode, which is equal to the ratio of the elastic modulus of the support layer to the sum of the elastic modulus of the support layer and the elastic modulus of the conductive layer. It can reflect the distribution ratio of the elastic modulus of the composite current collector for the positive electrode between the support layer and the conductive layer, and represents the proportion of the elastic modulus of the support layer in the elastic modulus of the composite system composed of the support layer and the conductive layer. The distribution coefficient α is a dimensionless value. When the composite current collector material composed of the support layer and the conductive layer is subjected to force, in the elastic deformation stage, due to the different elastic moduli (stiffness) of the two material layers, the actual forces exerted on the support layer and the conductive layer are inconsistent. Materials with large elastic modulus tend to be subjected to greater forces. Thus, by adjusting the distribution coefficient, the respective force proportions of the support layer and the conductive layer in the composite current collector for the positive electrode can be regulated.

[0095] For a composite current collector for a positive electrode comprising an organic support layer and a conductive layer, by reasonably matching the thickness d1, tensile fracture strength T1, yield strength Q1 and elastic modulus G1 of the support layer and the thickness d2, tensile fracture strength T2 and elastic modulus G2 of the conductive layer, and also using the distribution coefficient α to finely adjust the distribution of the elastic modulus between the support layer and the conductive layer, the ductility coefficient of the composite current collector for the positive electrode is regulated (d1×T1-(d2×T2)×(1-α)-d1×Q1×α); when the ductility coefficient of the composite current collector for the positive electrode is greater than or equal to 800, the elongation at break of the composite current collector for the positive electrode is higher, and the mass production processability is better, which is beneficial to reducing the fracture of the composite current collector for the positive electrode during the processing of the electrode sheet and improving the processing quality rate. It can also reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the electrode sheet during the charge and discharge process, thereby improving the battery cycle performance; and at the cell level, it is beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the electrode sheet in the later stage of the cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the cell.

[0096] If the elongation coefficient is less than 800 Pa·m, the elongation of the positive electrode composite current collector is low, which can easily lead to low yield during the processing of the positive electrode plate and poor cycling performance of the battery cell. The thickness d1, tensile fracture strength T1, yield strength Q1, elastic modulus G1 of the support layer, and the total thickness d2, tensile fracture strength T2, and elastic modulus G2 of the conductive layer synergistically affect the elongation coefficient of the positive electrode composite current collector. Some aspects of this synergy include, for example, excessive thickness that can affect energy density, while excessive thickness can not only lead to low processing yield, but also easily lead to poor electrode interface during cycling, large cycle expansion, and thus affect cycling performance. In addition, the elastic modulus and tensile fracture strength also affect the cycling performance of the battery cell.

[0097] In this application, unless otherwise specified, the test temperature of the thickness d1, tensile strength at break T1, yield strength Q1, elastic modulus G1 of the support layer, and the total thickness d2, tensile strength at break T2, and elastic modulus G2 of the conductive layer are all 15-35°C, for example, 20-30°C, and further such as 25°C.

[0098] In this application, unless otherwise specified, for the determination of tensile fracture strengths T1 and T2, yield strength Q1, and elastic moduli G1 and G2, tensile tests were performed on samples of the same material as the test object (the conductive layer or support layer of the composite current collector for the positive electrode). The sample width was 15 mm and the length was 150 mm. It is understood that the tensile test applied a tensile force along the length direction of the sample, which corresponds to the length direction of the current collector roll, which can be recorded as the MD direction. Unless otherwise specified, for the tensile fracture strengths T1 and T2, the tensile test was performed using the following parameters: a stretching distance of 50 mm and a stretching rate of 50 mm / min. Unless otherwise specified, the elastic moduli G1 and G2 were determined based on the tensile test results at an elongation of 1%. Elastic modulus = tensile strength in the elastic deformation stage / corresponding elongation = tensile strength in the elastic deformation stage / 1%. Elongation refers to the percentage of the increase in length (ΔL) of the sample in the stretched direction under the action of the tensile force relative to the initial length (L0) when not stretched, and is numerically equal to ΔL / L0 × 100%. It should be noted that for the tests of parameters such as tensile strength, yield strength, and elastic modulus, if the thickness of the conductive layer is relatively thin (e.g., ≤2μm) and it is difficult to conduct a tensile test directly, or it is difficult to prepare and test samples of the same thickness, the composition of the conductive layer can be detected first, and then samples of the same material with a measurable thickness (e.g., 10μm to 100μm) can be prepared for the corresponding tensile test.

[0099] In the present application, for composite current collector samples taken from secondary batteries or from positive electrode sheets, for testing parameters such as tensile fracture strength, yield strength, and elastic modulus, the support layer can be peeled off from the composite current collector sample for the positive electrode for tensile testing; for the conductive layer, the composition of the conductive layer can be first detected, and then a sample of the same material with a measurable thickness (such as 10μm to 100μm) can be prepared for corresponding tensile testing.

[0100] The composite current collector for the positive electrode provided in the present application meets the following conditions: (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800Pa·m, wherein α=G1 / (G1+G2). Furthermore, the test samples of T1, Q1, G1, T2 and G2 all meet the following conditions: width is 15mm, length is 150mm; further, the test parameters under the stretching mode include: stretching distance is 50mm, stretching rate is 50mm / min. Further, the test temperature of d1, T1, Q1, G1, d2, T2 and G2 is 15~35℃, for example, 20~30℃, further such as 25℃.

[0101] In some embodiments, at 15-35° C., the composite current collector for the positive electrode satisfies the following condition: (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800 Pa·m, wherein α=G1 / (G1+G2).

[0102] In this application, unless otherwise specified, the tensile strength T1, yield strength Q1 and elastic modulus G1 of the support layer, as well as the tensile strength T2 and elastic modulus G2 of the conductive layer can be obtained by testing and analysis using a tensile testing machine (as a non-limiting example, such as INSTRON3365 tensile testing machine).

[0103] As a non-limiting example, the sample width (which may be recorded as w0) is 15 mm, the sample length is 150 mm, the stretching distance (which may be recorded as s0) is 50 mm, and the stretching rate is 50 mm / min. Each parameter can be calculated by the following formula:

[0104] Yield strength = yield point tensile force / sample cross-sectional area; where sample cross-sectional area = w0 × sample thickness;

[0105] Tensile strength at break = tensile force at break / cross-sectional area of ​​sample; where cross-sectional area of ​​sample = w0 × sample thickness;

[0106] Elastic modulus = tensile strength corresponding to elongation δ / δ; where elongation δ is 1%;

[0107] Elongation at break = (length of sample stretched to break - s0) / s0 × 100%;

[0108] Elastic modulus = tensile strength in the elastic deformation stage / corresponding elongation. For the convenience of calculation, the tensile strength corresponding to 1% elongation (elastic deformation stage) / 1% is used for calculation;

[0109] In addition, for conductive layer samples with a thin thickness (such as ≤2μm), the composition of the conductive layer can be tested first, and then samples of the same material with a measurable thickness (such as 10μm to 100μm) can be prepared for corresponding tensile testing.

[0110] The conductive layer may be located on one side of the supporting layer or on both sides of the supporting layer.

[0111] FIG1 is a schematic structural diagram of a composite current collector 100 for a positive electrode in one embodiment of the present application, which includes a support layer 110 and conductive layers 120 located on both sides of the support layer.

[0112] FIG2 is a schematic structural diagram of a composite current collector 100 for a positive electrode in another embodiment of the present application, which includes a support layer 110 and a conductive layer 120 located on one side of the support layer.

[0113] In some embodiments, the thickness d1 of the support layer is 4 μm-15 μm; alternatively, the thickness d1 of the support layer is 4 μm-12 μm; further alternatively, the thickness d1 of the support layer is 4 μm-6 μm. The thickness of the support layer can also be any of the following thicknesses or a range consisting of any two of the following thicknesses: 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0114] The thicker the composite current collector for the positive electrode, the lower the energy density of the battery cell. If the thickness of the composite current collector for the positive electrode is too thin, it will result in a lower force it can withstand and a lower elongation, which is not conducive to processability. By adjusting the thickness of the support layer, the thickness of the composite current collector for the positive electrode can be indirectly adjusted, so that the composite current collector for the positive electrode can better combine better energy density and superior processability. If the support layer is too thin, it is easy to increase the difficulty of processing the composite current collector for the positive electrode, reduce the production efficiency, and be unfavorable for mass application; if the support layer is too thick, it is easy to lead to a decrease in advantages in terms of increased energy density and improved battery cell production efficiency, and it will also lead to higher costs and lower cost performance.

[0115] In some embodiments, the tensile strength at break T1 of the support layer is ≥ 200 MPa; further, the tensile strength at break T1 of the support layer may be ≥ 300 MPa. The tensile strength at break T1 of the support layer may also be any of the following strengths, or may be greater than or equal to any of the following strengths, or may be selected from a range consisting of any two of the following strengths: 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 540 MPa, 550 MPa, 600 MPa, etc. The tensile strength at break T1 of the support layer may be selected from any of the following ranges: 200 MPa-600 MPa, 240 MPa-600 MPa, 250 MPa-600 MPa, 300 MPa-600 MPa, 200 MPa-550 MPa, 240 MPa-550 MPa, 250 MPa-550 MPa, 300 MPa-550 MPa, etc.

[0116] The higher the tensile strength of the support layer, the greater the force it can withstand, the better the mechanical strength of the composite current collector for the positive electrode is, and the more favorable the processability of the composite current collector for the positive electrode is.

[0117] In some embodiments, the yield strength Q1 of the support layer is ≥ 90 MPa; optionally, the yield strength Q1 of the support layer is ≥ 150 MPa. The yield strength Q1 of the support layer may also be any of the following strengths, or may be greater than or equal to any of the following strengths, or may be selected from a range consisting of any two of the following strengths: 90 MPa, 100 MPa, 120 MPa, 150 MPa, 160 MPa, 180 MPa, 200 MPa, 210 MPa, 220 MPa, 240 MPa, 250 MPa, etc. The yield strength Q1 of the support layer may be selected from any of the following ranges: 90 MPa to 250 MPa, 100 MPa to 250 MPa, 150 MPa to 250 MPa, 90 MPa to 220 MPa, 100 MPa to 220 MPa, 150 MPa to 220 MPa, etc.

[0118] The higher the yield strength of the support layer, the better its ability to resist micro-plastic deformation, and the more conducive it is to the processing of the composite current collector for the positive electrode.

[0119] In some embodiments, the total thickness d2 of the conductive layer is 0.6 μm-3 μm; alternatively, the total thickness d2 of the conductive layer is 1 μm-3 μm; further alternatively, the total thickness d2 of the conductive layer is 1.4 μm-2.4 μm. The total thickness d2 of the conductive layer can also be any of the following thicknesses or a range consisting of any two of the following thicknesses: 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, etc. The total thickness d2 of the conductive layer can also be selected from any of the following ranges: 1.5 μm-2 μm, 1.6 μm-2 μm, etc.

[0120] In this application, when the conductive layer is located on a single side of the support layer, the total thickness d2 of the conductive layer is numerically equal to the thickness of that single side; when the conductive layer is located on both sides of the support layer, the total thickness d2 of the conductive layer is numerically equal to the sum of the thicknesses of both sides. When the conductive layer is located on both sides of the support layer, the thicknesses of both sides can be the same or different. When the materials of the two conductive layers are different, the total thickness, average tensile strength at break, and average elastic modulus can be analyzed based on the test results of the two conductive layers, and used as d2, T2, and G2, respectively, to calculate the ductility coefficient of the positive electrode composite current collector.

[0121] In some embodiments, the thickness d2 of the conductive layer on one side is s 0.3 μm-1.5 μm; Optionally, the thickness d2 of the conductive layer on one side s 0.5 μm-1.5 μm; further optionally, the thickness d2 of the conductive layer on one side s The thickness of the conductive layer on one side is d2 s It can also be any of the following thicknesses or a range consisting of any two of the following thicknesses: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc. The thickness d2 of the conductive layer on one side s It can also be selected from any of the following ranges: 0.5 μm-1 μm, 0.8 μm-1.5 μm, 0.8 μm-1.2 μm, 0.5 μm-1.2 μm, etc.

[0122] In some embodiments, the thickness D of the composite current collector for the positive electrode is a 3μm-17μm; Optionally, the thickness D of the composite current collector for the positive electrode a 3μm-14μm; further optionally, the thickness D of the composite current collector for the positive electrode a The thickness D of the composite current collector for the positive electrode is 3.4 μm-8.4 μm. aIt can also be any of the following thicknesses or an interval consisting of any two of the following thicknesses: 3 μm, 3.4 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.4 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, etc. The thickness D of the composite current collector for the positive electrode is 2 μm, 3 μm, 5 μm, 6 μm, 7 μm, 8 μm, 8 μm, 9 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, etc. a It can also be selected from any of the following ranges: 4μm-17μm, 4μm-14μm, 4μm-10μm, 5μm-17μm, 5μm-14μm, 5μm-10μm, 6μm-17μm, 6μm-14μm, 6μm-10μm, 6μm-8μm, etc.

[0123] In some embodiments, the composite current collector for the positive electrode satisfies any one or more of the following characteristics:

[0124] The total thickness d2 of the conductive layer is 0.6 μm-3 μm; optionally, the total thickness d2 of the conductive layer is 1 μm-3 μm; further optionally, the total thickness d2 of the conductive layer is 1.4 μm-2.4 μm;

[0125] The single-side thickness d2 of the conductive layer s 0.3 μm-1.5 μm; Optionally, the thickness d2 of the conductive layer on one side s 0.5 μm-1.5 μm; further optionally, the thickness d2 of the conductive layer on one side s 0.7μm-1.2μm;

[0126] The thickness D of the composite current collector for the positive electrode a 3μm-17μm; Optionally, the thickness D of the composite current collector for the positive electrode a 3μm-14μm; further optionally, the thickness D of the composite current collector for the positive electrode a 3.4μm-8.4μm;

[0127] Among them, the total thickness of the conductive layer d2, the thickness of the conductive layer on one side d2 s , the thickness of the composite current collector for the positive electrode D a Any one of the parameters may also have the appropriate features of any of the aforementioned embodiments, and the three parameters may also be selected from a suitable combination of the aforementioned features in a suitable manner.

[0128] By adjusting the thickness of the conductive layer or directly controlling the thickness of the composite current collector for the positive electrode so that the thickness of the composite current collector for the positive electrode is within a certain range, the composite current collector for the positive electrode can better have both better energy density and superior processability.

[0129] If the composite current collector used for the positive electrode is too thick, the degree of improvement in the weight energy density and volume energy density of the battery cell may be reduced. If the composite current collector used for the positive electrode is too thin, it may become difficult to be compatible with the current battery cell preparation process, which may lead to a decrease in the quality rate and be unfavorable for industrial application.

[0130] If the conductive layer is too thin, the conductive current capacity of the positive electrode composite current collector may be weakened, which is not conducive to the rate performance of the battery cell; if the conductive layer is too thick, the unit area amount of the positive electrode composite current collector may be increased, thereby reducing the advantage of the positive electrode composite current collector in improving the energy density of the battery cell.

[0131] In some embodiments, the tensile strength at break of the conductive layer, T2, is ≥ 150 MPa; alternatively, the tensile strength at break of the conductive layer, T2, is ≥ 200 MPa. The tensile strength at break of the conductive layer, T2, can also be any of the following strengths, or can be greater than or equal to any of the following strengths, or can be selected from a range consisting of any two of the following strengths: 150 MPa, 160 MPa, 170 MPa, 180 MPa, 200 MPa, 210 MPa, 220 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 300 MPa, etc. The tensile strength at break of the conductive layer, T2, can be selected from any of the following ranges: 180 MPa to 300 MPa, 200 MPa to 300 MPa, 180 MPa to 250 MPa, 200 MPa to 250 MPa, etc.

[0132] The higher the tensile strength of the conductive layer, the more favorable it is for the processability of the composite current collector for the positive electrode.

[0133] In some embodiments, the elastic modulus G1 of the support layer is ≥ 3 GPa; optionally, the elastic modulus G1 of the support layer is ≥ 4 GPa. The elastic modulus G1 of the support layer may also be any of the following moduli, or may be greater than or equal to any of the following moduli, or may be selected from a range consisting of any two of the following moduli: 3 GPa, 3.5 GPa, 4 GPa, 4.2 GPa, 4.5 GPa, 4.6 GPa, 4.8 GPa, 5 GPa, 5.5 GPa, 6 GPa, 6.5 GPa, 7 GPa, 7.5 GPa, 8 GPa, 10 GPa, etc. The elastic modulus G1 of the support layer may also be selected from any of the following ranges: 3 GPa to 10 GPa, 4 GPa to 10 GPa, 3 GPa to 8 GPa, 4 GPa to 8 GPa, etc.

[0134] In some embodiments, the elastic modulus G2 of the conductive layer is 25 GPa-40 GPa; optionally, the elastic modulus G2 of the conductive layer is 25 GPa-35 GPa. The elastic modulus G2 of the conductive layer can also be any of the following moduli or a range consisting of any two of the following moduli: 30 GPa, 30.5 GPa, 31 GPa, 31.5 GPa, 32 GPa, 32.5 GPa, 33 GPa, 33.5 GPa, 34 GPa, 34.5 GPa, 35 GPa, 35.5 GPa, 36 GPa, 36.5 GPa, 37 GPa, 38 GPa, 39 GPa, 40 GPa, etc. The elastic modulus G2 of the conductive layer can also be selected from any of the following ranges: 30 GPa-37 GPa, 30 GPa-35 GPa, etc.

[0135] In some embodiments, the distribution coefficient α is 0.024-0.43; optionally, the distribution coefficient α is 0.095-0.300; further optionally, the distribution coefficient α is 0.105-0.250. The distribution coefficient α can also be any of the following values ​​or an interval consisting of any two of the following values: 0.024, 0.025, 0.030, 0.040, 0.050, 0.060, 0.080, 0.090, 0.095, 0.098, 0.100, 0.103, 0.105, 0.106, 0.108, 0.110, 0.115, 0.116, 0.118, 0.120, 0.125 , 0.130, 0.140, 0.145, 0.150, 0.155, 0.160, 0.165, 0.170, 0.180, 0.185, 0.190, 0.195, 0.200, 0.21, 0.22, 0.24, 0.25, 0.26, 0.28, 0.30, 0.32, 0.33, 0.34, 0.35, 0.36, 0.38, 0.40, 0.42, 0.43, etc. The distribution coefficient α can also be selected from any of the following ranges: 0.09-0.3, 0.09-0.25, 0.09-0.2, 0.095-0.25, 0.095-0.20, 0.103-0.195, 0.108-0.195, 0.1-0.2 (including 0.10-0.20), 0.10-0.25, etc.

[0136] In some embodiments, the composite current collector for the positive electrode satisfies any one or more of the following characteristics:

[0137] The elastic modulus G1 of the support layer is ≥3 GPa; optionally, the elastic modulus G1 of the support layer is ≥4 GPa;

[0138] The elastic modulus G2 of the conductive layer is 25 GPa-40 GPa; optionally, the elastic modulus G2 of the conductive layer is 25 GPa-35 GPa;

[0139] The distribution coefficient α is 0.024-0.43; optionally, the distribution coefficient α is 0.095-0.300; further optionally, the distribution coefficient α is 0.105-0.250.

[0140] By regulating the distribution of the elastic modulus between the support layer and the conductive layer, for example, by adjusting the value of α=G1 / (G1+G2), the force magnitudes of the support layer and the conductive layer in the composite current collector for the positive electrode under stress can be reasonably adjusted, thereby better improving the overall tolerance of the composite current collector for the positive electrode, and further better improving the processability of the composite current collector for the positive electrode.

[0141] In some embodiments, the ductility coefficient (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800Pa·m; optionally, the ductility coefficient (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1000Pa·m; further optionally, the ductility coefficient (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1650Pa·m. The expansion coefficient may also be any of the following values, or may be greater than or equal to any of the following values, or may be selected from an interval consisting of any two of the following values: 800 Pa·m, 840 Pa·m, 850 Pa·m, 900 Pa·m, 1000 Pa·m, 1018 Pa·m, 1020 Pa·m, 1025 Pa·m, 1050 Pa·m, 1100 Pa·m, 1200 Pa·m, 1300 Pa·m, 1400 Pa·m, 145 0Pa·m, 1500Pa·m, 1550Pa·m, 1600Pa·m, 1650Pa·m, 1700Pa·m, 1800Pa·m, 2000Pa·m, 2200Pa·m, 2400Pa ·m, 2500Pa·m, 2600Pa·m, 2650Pa·m, 2660Pa·m, 2700Pa·m, 2800Pa·m, 3000Pa·m, 3500Pa·m, 4000Pa·m, etc. The expansion coefficient can also be selected from any of the following ranges: 840Pa·m-2660Pa·m, 1018Pa·m-2660Pa·m, 800Pa·m-3000Pa·m, 1000Pa·m-3000Pa·m, 800Pa·m-2800Pa·m, 1000Pa·m-2800Pa·m, etc.

[0142] The greater the ductility coefficient of the composite current collector for the positive electrode, the higher the elongation at break of the composite current collector for the positive electrode, the better the processability in mass production, and the more conducive to reducing the fracture of the composite current collector for the positive electrode during the electrode processing process and improving the processing quality rate; at the battery cell level, it is also more conducive to reducing the cracking problem that may be caused by the gradual increase in the electrode expansion force in the later stage of the battery cell cycle, and is more conducive to improving the cycle performance and safety and reliability of the battery cell.

[0143] In this application, the "processing quality rate" of a current collector is defined as the ratio of the number of qualified electrode sheets produced during the cell manufacturing process to the total current collector production input. It can also be defined as the ratio of the length of qualified electrode sheets produced during the cell manufacturing process to the total length of the current collector produced. For each cell process, it can also be expressed as the coating quality rate. Furthermore, parameters such as the frequency of cold press cracking can also reflect the processing quality rate. A higher processing quality rate indicates better processability of the current collector.

[0144] In the present application, the current collector includes a positive electrode current collector and a negative electrode current collector, which are used to prepare a positive electrode sheet and a negative electrode sheet respectively. The positive electrode current collector in the present application includes the composite current collector for the positive electrode described in the first aspect of the present application.

[0145] In this application, the "coating quality rate" of a current collector refers to the ratio of the length of qualified electrode sheets produced during the cell coating process to the length of the current collector input. The coating production quality rate can be calculated by recording the number of meters of qualified coated electrode sheets produced during the coating process for every 100,000 meters of current collector. The "coating quality rate" of a current collector reflects the processability of the current collector during the cell coating process. A higher coating quality rate indicates better processability of the current collector.

[0146] In this application, the "cold press fracture frequency" of the current collector refers to the number of times a unit length of the current collector fractures and fails during the cold pressing process of the battery cell, and the unit can be "times / km" or "km / time". The cold press cracking frequency of the current collector can be evaluated by recording the number of cracks in the cold pressing process of 100,000 meters of current collector coated pole pieces. The "cold press fracture frequency" of the current collector reflects the processability of the current collector in the cold pressing process of the battery cell. When the unit is "km / time", the higher the value of the cold press fracture frequency, the less likely it is to crack, reflecting that the processability of the current collector is better. When the unit is "times / km", the lower the value of the cold press fracture frequency, the less likely it is to crack, reflecting that the processability of the current collector is better. Wherein, 1km=1000m.

[0147] In some embodiments, the material of the support layer is a polymer-based material or a polymer-based composite material; optionally, the polymer component in the support layer includes polyimide, polyamide, 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 one or more of the derivatives of the above materials, the cross-linked products of the above materials and the copolymers of the above materials.

[0148] In the present application, unless otherwise specified, the “polymer-based material” is substantially composed of polymers. It is understood that the inevitable impurities introduced during the processing are not excluded.

[0149] In this application, unless otherwise specified, a "polymer-based composite material" includes a polymer having a weight percentage of ≥50%, and may also include one or more additives. Non-limiting examples of additives include one or more metallic materials, inorganic non-metallic materials, etc. In the "polymer-based composite material," the weight percentage of the polymer is at least 50%, and may further be 60%, 70%, 80%, 85%, or 90%. It may also be any of the following weight percentages, or may be greater than or equal to any of the following percentages and less than or equal to 100%. Alternatively, it may be selected from a range consisting of any two of the following weight percentages: 50%, 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc. Non-limiting examples of the range consisting of any two of the foregoing weight percentages include 50% to 100%, 60% to 100%, 70% to 100%, 80% to 100%, 90% to 100%, etc. The weight percentage of the polymer in the polymer-based composite material may meet any of the aforementioned appropriate conditions, preferably to obtain a preferred ductility coefficient.

[0150] The additives in the polymer-based composite material can be appropriately selected based on processing requirements and one or more of the performance requirements of the positive electrode composite current collector, the pole piece, and the battery cell.

[0151] The metal material additive may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, iron, iron alloy, silver, and silver alloy.

[0152] Inorganic non-metallic materials may include, but are not limited to, one or more of carbon-based materials, aluminum oxide, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicates, and titanium oxide, and may also include, but are not limited to, one or more of glass materials, ceramic materials, and ceramic composite materials. Carbon-based materials may include, but are not limited to, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] In some embodiments, the additive may include a carbon-based material coated with a metal material, such as one or more of nickel-coated graphite powder and nickel-coated carbon fiber.

[0154] When polymer materials are selected as the main material of the support layer, polymers have a lighter density and better ductility than conductive metals, which can reduce the surface density of the composite current collector for the positive electrode, thereby helping to improve the energy density of the battery cell. It can also improve the overall ductility of the composite current collector for the positive electrode, which is beneficial to improving the processing efficiency of the electrode sheet.

[0155] The main material of the support layer may or may not contain other materials besides polymers, and may also form a composite material with other materials. When it is a polymer-based composite material, it can be appropriately selected based on performance requirements and in accordance with processing requirements to improve the processability of the positive electrode composite current collector, battery core performance, or a combination thereof. For example, it can improve one or more of the properties of the positive electrode composite current collector, such as volume resistivity, elongation at break, and Young's modulus.

[0156] In some embodiments, the polymer component in the support layer includes polyimide. Further, the polyimide may include one or both of homophenyl polyimide and biphenyl polyimide.

[0157] In some embodiments, the polymer component of the support layer may include biphenyl polyimide.

[0158] In some embodiments, the support layer comprises biphenyl polyimide with a mass percentage of ≥50%; alternatively, the support layer comprises biphenyl polyimide with a mass percentage of ≥80%; further alternatively, the support layer is made of biphenyl polyimide. The mass percentage of biphenyl polyimide in the support layer can also be any of the following percentages: 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc., or can be greater than or equal to any of the aforementioned percentages and less than or equal to 100%, or can be selected from an interval consisting of any two of the aforementioned percentages, non-limiting examples of which include 50% to 100%, 60% to 100%, 70% to 100%, 80% to 100%, 90% to 100%, etc.

[0159] In some embodiments, the polymer component in the support layer is a combination of homophenyl polyimide and biphenyl polyimide. In some embodiments, the weight percentage of biphenyl polyimide can be any of the following percentages: 50%, 60%, 67%, 70%, 75%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc., and can also be greater than or equal to any of the aforementioned percentages and less than or equal to 100%, or can be selected from an interval consisting of any two of the aforementioned percentages, non-limiting examples of which include 50% to 100%, 60% to 100%, 70% to 100%, 80% to 100%, 90% to 100%, etc. In other embodiments, the weight ratio of biphenyl polyimide to homophenyl polyimide can be any of the following ratios or ratios, and can also be selected from an interval consisting of any two of the following ratios or ratios: 9:1, 8:2, 7:3, 6:4, etc.

[0160] Polyimide is an organic carbonyl polymer containing an imide ring in its main chain. It has excellent mechanical properties and heat resistance, high mechanical strength, and good high-temperature resistance. Using polyimide in the support layer can leverage its tensile strength, yield strength, and elastic modulus properties to better synergize with the tensile strength and elastic modulus of the conductive layer, thereby better adjusting the ductility coefficient of the positive electrode composite current collector. This is more conducive to achieving the dual requirements of good energy density and excellent processability for the positive electrode composite current collector.

[0161] Both benzene-type polyimide and biphenyl-type polyimide have the aforementioned common advantages of polyimide, among which biphenyl-type polyimide has more excellent high-temperature resistance and mechanical properties. By introducing biphenyl-type polyimide into the composite current collector for the positive electrode, for example as the main material (≥50 weight%), it is beneficial to improve the high-temperature tensile performance of the composite current collector for the positive electrode, and it is beneficial to maintain good flatness during the high-temperature battery preparation process such as coating, unwinding and drying. It can also avoid defective products caused by curling, wrinkling and even breakage caused by the volatilization of solvents, moisture, etc., and better improve the processing quality rate. As the operating speed of battery cell mass production equipment gradually increases, the drying temperature in the battery cell process also gradually increases. Improving the high-temperature mechanical properties of the composite current collector for the positive electrode is also more important for manufacturing quality rate. In addition, the improvement of the mechanical properties of the composite current collector for the positive electrode is also beneficial to reducing the shrinkage and expansion of the battery cell during the charging and discharging process, which is beneficial to the integrity of the positive and negative electrode interfaces of the battery cell. It can reduce or avoid the increase of local interface side reactions caused by wrinkling of the electrode during the charging and discharging process, and thus help improve the cycle performance of the battery cell.

[0162] Compared with using biphenyl polyimide as the main material of the support layer, when using biphenyl polyimide as the main material of the support layer, the prepared composite current collector for the positive electrode can significantly improve one or more of the mechanical properties (such as tensile strength, elastic modulus, elongation at break, etc.), usage performance (such as coating quality, cold pressing elongation, cold pressing fracture frequency, etc.), and battery cell performance (such as cycle capacity retention rate, etc.).

[0163] In this application, the “cold pressing elongation” of the current collector refers to the difference between the extended length of the cell electrode after cold pressing and the initial length (L 0C The cold pressing elongation rate of the electrode can be evaluated by measuring the extended length of the electrode after cold pressing of the 1m long current collector coated electrode. At this time, the cold pressing elongation rate = (length of the electrode after cold pressing - L 0C ) / L 0C ×100%,L 0C Take 1m. The "cold pressing elongation" of the current collector reflects the deformation of the current collector during the cold pressing process of the battery cell.

[0164] By using biphenyl polyimide as the supporting layer, the mechanical strength of the composite current collector for the positive electrode can be significantly improved, and further the process efficiency and performance of the battery cell can be improved; in addition, the pinhole defect rate can also be reduced.

[0165] In some embodiments, the biphenyl polyimide used in this application contains The structure is connected by two N atoms on the two imide rings. Furthermore, its infrared spectrum is at a wave number of 1618.65 cm -1 、1420.2cm -1 、1218.98cm -1 、888.9cm -1 、695.72cm -1 、673.08cm -1 There is a vibration peak in at least one of them.

[0166] In some embodiments, the conductive layer includes a metal material, and optionally, the metal material includes one or more of aluminum and an aluminum alloy. In addition to mainly containing aluminum, the aluminum alloy also contains doping elements. The types of doping elements may include one or more of metal elements and non-metal elements, wherein the doped metal elements may include but are not limited to one or more of nickel, nickel, titanium, titanium, silver, etc., and the doped non-metal elements may include but are not limited to one or more of N, O, C, Si, B, etc. The weight proportion of the doping element in the aluminum alloy may be ≤10%, and the weight proportion of the doping element in the aluminum alloy may further be any of the following percentages, or may be greater than 0 and less than or equal to any of the following percentages, or may be selected from the interval consisting of any two of the following percentages: 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0167] When the conductive layer comprises a metal material, it is advantageous to provide better conductivity. Furthermore, when the metal material comprises one or more of aluminum and aluminum alloys, it is easier to control the ductility coefficient of the positive electrode composite current collector within an appropriate range. Furthermore, it is also easier to control parameters such as the tensile strength and elastic modulus of the conductive layer within a more suitable range, thereby better balancing the energy density of the battery cell and the processability of the positive electrode composite current collector.

[0168] In some embodiments, the support layer can be a single-layer structure or a multi-layer structure, as long as it meets the requirements of the aforementioned ductility coefficient and related parameters. When the support layer has a multi-layer structure, the material composition and distribution of each structural layer can be the same or different.

[0169] In some embodiments, the thickness D of the composite current collector for the positive electrode is a It can be equal to d1+d2 or greater than d1+d2. a When the thickness is greater than d1+d2, the composite current collector for the positive electrode further includes other structural layers in addition to the aforementioned support layer and conductive layer.

[0170] The composite current collector provided in the first aspect is suitable for a positive electrode current collector, and can be used independently as a positive electrode current collector in a positive electrode sheet, or as a part of the positive electrode current collector in a positive electrode sheet.

[0171] In the field of secondary batteries (such as lithium-ion secondary batteries), generally speaking, the positive electrode tends to select oxidation-resistant materials (such as aluminum or its alloys) as the positive electrode current collector conductive material, and the negative electrode tends to select metal materials that are inert to lithium (such as copper or its alloys) as the negative electrode current collector conductive material, wherein exemplary aluminum and copper are both metal materials with high electrical conductivity. Therefore, the mechanical properties of the conductive layer metal materials of the positive electrode current collector and the negative electrode current collector may be different, corresponding to different ductility coefficients. When the composite current collector for the positive electrode described in the first aspect of the present application is used for the positive electrode current collector, it is more conducive to giving play to the advantages of the aforementioned embodiments.

[0172] In a second aspect, the present application provides a positive electrode plate, which includes the composite current collector for the positive electrode described in the first aspect of the present application.

[0173] The positive electrode sheet includes a positive electrode current collector, which at least includes the composite current collector for the positive electrode described in the first aspect of the present application.

[0174] In some embodiments, the positive electrode sheet includes the composite current collector for the positive electrode described in the first aspect of the present application and a positive electrode film layer arranged on at least one side of the composite current collector for the positive electrode, at least one of the positive electrode film layers includes a positive electrode active material layer, and any of the positive electrode active material layers independently contains a positive electrode active substance.

[0175] In some embodiments, the composite positive electrode current collector described in the first aspect of this application is independently used as the positive electrode current collector in the positive electrode sheet described in the second aspect. In other embodiments, the composite positive electrode current collector described in the first aspect of this application is used as part of the positive electrode current collector in the positive electrode sheet described in the second aspect.

[0176] When the positive electrode current collector of the positive electrode plate includes the composite current collector for the positive electrode as described in the first aspect of the present application (for example, when the positive electrode current collector of the positive electrode plate is the composite current collector for the positive electrode as described in the first aspect of the present application), it can have both good energy density and high mechanical strength, and can reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the positive electrode plate during charging and discharging, thereby improving the battery cycle performance; further, it is also beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the plate in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0177] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material 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 or substances that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, non-limiting examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as 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 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0178] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction. Furthermore, the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0179] In some embodiments, the positive electrode film layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0180] 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.

[0181] 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 to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, compaction (compaction can be performed by cold pressing) and other processes, the positive electrode sheet can be obtained. The type of solvent in the positive electrode slurry may include but is not limited to N-methylpyrrolidone (NMP), and NMP can be further used as a single solvent. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The compaction density of the positive electrode sheet can be 3.0 to 3.6g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0182] In this application, wt% means weight percentage.

[0183] In a third aspect, the present application provides a secondary battery comprising at least one of the composite current collector for the positive electrode described in the first aspect of the present application and the positive electrode sheet described in the second aspect of the present application.

[0184] For secondary batteries containing the aforementioned composite current collector for the positive electrode or the aforementioned positive electrode plate, they can have both good energy density and high mechanical strength, and can reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the plate during the charging and discharging process. Furthermore, it is also beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the plate in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0185] In some embodiments, the secondary battery includes the positive electrode sheet described in the second aspect of the present application, and also includes a negative electrode sheet and a separator; wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0186] In this application, unless otherwise specified, the electrode plate can be a positive electrode plate or a negative electrode plate, and the "active material" in the electrode plate refers to a substance that can reversibly embed and release active ions. Unless otherwise specified, "negative electrode active material" refers to a substance used for the negative electrode plate that can reversibly embed and release active ions; "positive electrode active material" refers to a substance used for the positive electrode plate that can reversibly release and embed active ions. When the secondary battery is charging, the active ions are released from the positive electrode and embedded in the negative electrode through the electrolyte; when the secondary battery is discharging, the active ions are released from the negative electrode and embedded in the positive electrode. The active ions are not particularly limited and can be lithium ions, in which case it corresponds to a lithium-ion secondary battery.

[0187] In this application, “active material” and “active substance” have the same meaning and can be used interchangeably; “positive electrode active substance” and “positive electrode active material” have the same meaning and can be used interchangeably; “negative electrode active substance” and “negative electrode active material” have the same meaning and can be used interchangeably.

[0188] In this application, unless otherwise specified, "active material layer" includes the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet. Depending on the specific circumstances, it can refer to either the positive electrode active material layer or the negative electrode active material layer. It is understood that the positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material.

[0189] Positive electrode

[0190] The positive electrode sheet in the third and fourth aspects of the present application includes the positive electrode sheet provided in the second aspect of the present application.

[0191] In some embodiments of the present application, the secondary battery is a lithium-ion secondary battery. Lithium-ion secondary batteries utilize the intercalation and deintercalation of lithium ions in electrodes and their transport in electrolytes to achieve charge and discharge. Generally speaking, the active ions in lithium-ion secondary batteries are lithium ions, but this is not limited to this.

[0192] Negative electrode

[0193] 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.

[0194] 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.

[0195] 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. 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.

[0196] In some embodiments, the negative electrode active material may adopt a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, 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.

[0197] 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).

[0198] 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.

[0199] In some embodiments, the negative electrode film layer may further include other auxiliary agents, such as a thickener, etc. Non-limiting examples of thickeners may include sodium carboxymethyl cellulose (CMC-Na), etc.

[0200] 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 current collector, and after drying, compacting (compacting can be performed by cold pressing) and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The compacted density of the negative electrode sheet can be 1.4g / cm 3 ~1.75g / cm 3 , further optional 1.5g / cm 3 ~1.7g / cm 3 .

[0201] electrolytes

[0202] The electrolyte conducts active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0203] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In a lithium-ion secondary battery, the electrolyte salt may include an electrolyte lithium salt.

[0204] In some embodiments, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0205] In some embodiments, the solvent is an organic solvent.

[0206] In some embodiments, the organic solvent comprises one or more of esters, carbonates and ethers. In some embodiments thereof, the organic solvent comprises esters. The carbonate solvent can comprise one or more of carbonate and halogenated carbonate. As the non-limiting example of organic solvent, for example 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), 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) and any one of the fluorochemicals described above.

[0207] In some embodiments, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0208] As non-limiting examples, the ether organic solvent may include one or more of tetrahydrofuran (THF), dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), diglyme (DG), and the like.

[0209] In some embodiments, the electrolyte may further include additives. For example, the additives may be used to improve the performance of the solid electrolyte interface (SEI) film, such as at least one of anode film-forming additives and cathode film-forming additives. The additives may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, additives that increase electrical conductivity, etc.

[0210] In some embodiments, the additive may include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), methylene methanedisulfonate (MMDS), 1-propylene-1,3-sultone (PST), vinyl sulfite (ES), propylene sulfite (PS), vinyl sulfate (DTD), succinonitrile (SN), adiponitrile (AND), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB) and anisole.

[0211] Isolation film

[0212] 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.

[0213] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0214] Electrode assembly, electrochemical energy storage device, secondary battery, power device

[0215] 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.

[0216] In some embodiments, the electrochemical energy storage device may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0217] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0218] 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.

[0219] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG3 shows a secondary battery 5 having a square structure as an example.

[0220] 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 secondary battery 5 can be one or more, and those skilled in the art can select according to actual needs.

[0221] In a fourth aspect, the present application provides an electrical device comprising at least one of the composite current collector for the positive electrode described in the first aspect of the present application, the positive electrode sheet described in the second aspect of the present application, and the secondary battery described in the third aspect of the present application.

[0222] The secondary battery can be used as a power source or energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, and energy storage systems. Examples of mobile devices include, but are not limited to, mobile phones and laptops; and examples of electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0223] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0224] 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.

[0225] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0226] In a fifth aspect, the present application provides a method for preparing the composite current collector for the positive electrode described in the first aspect of the present application, which comprises the following steps: forming the conductive layer on at least one side of the support layer to prepare the composite current collector for the positive electrode.

[0227] A supporting layer with a specific thickness d1, a specific tensile fracture strength T1, a specific yield strength Q1 and a specific elastic modulus G1 is used to further form a conductive layer with a specific thickness d2, a specific tensile fracture strength T2 and a specific elastic modulus G2. The prepared composite current collector for the positive electrode has a high ductility coefficient, a high elongation at break, and better processability in mass production. It is beneficial to reduce the fracture of the composite current collector for the positive electrode during the processing of the electrode sheet, improve the processing quality rate, and reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the electrode sheet during the charging and discharging process, thereby improving the battery cycle performance; and at the cell level, it is beneficial to reduce the cracking problem that may be caused by the gradual increase in the expansion force of the electrode sheet in the later stage of the cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0228] The method of forming the conductive layer on at least one side of the support layer may include, but is not limited to, one or more of physical deposition (such as vapor deposition) technology, chemical deposition technology, electroplating, spraying, casting, hot pressing, etc.

[0229] It can be understood that the conductive layer can be formed on at least one side surface of the support layer, but is not limited thereto.

[0230] In a sixth aspect, the present application provides a method for preparing a positive electrode sheet, which comprises the following steps: coating a positive electrode slurry on at least one side of the composite current collector for the positive electrode described in the first aspect of the present application, drying, and cold pressing to prepare the positive electrode sheet.

[0231] The preparation method of the positive electrode sheet provided in this aspect can also refer to the second aspect of this application.

[0232] The drying step after coating the positive electrode slurry can be performed in a conventional manner in the art, for example, by drying at 90-120°C.

[0233] The cold pressing step after drying the coating layer can be performed using conventional methods in the art. A positive electrode sheet having a predetermined compaction density can be obtained by cold pressing. Non-limiting examples of the compaction density of the positive electrode sheet can be found in the context of this application.

[0234] When the positive electrode composite current collector provided in the first aspect of the present application is used to prepare the positive electrode plate, the prepared positive electrode plate can have both good energy density and high mechanical strength, which can reduce or avoid the increase in local interfacial side reactions caused by wrinkling of the plate during the charging and discharging process, thereby improving the battery cycle performance; further preparation of a secondary battery containing the aforementioned positive electrode composite current collector or the aforementioned positive electrode plate is also beneficial to reducing the cracking problem that may be caused by the gradual increase in the expansion force of the plate in the later stage of the battery cell cycle, which is beneficial to improving the cycle performance and safety and reliability of the battery cell.

[0235] Below, some embodiments of the present application are described. The embodiment described below is exemplary, is only used to explain the present application, and cannot be construed as limiting the present application. In the embodiment, if no technology or conditions are indicated, it is carried out according to the description above, or according to the technology or conditions described in the document in this area or according to the product specification. Reagents used or instruments that are not indicated by the manufacturer are conventional products that can be obtained commercially, or can be synthesized in a conventional manner by commercially available products.

[0236] Preparation of positive electrode current collector

[0237] 1.1. Preparation of positive electrode current collector

[0238] Refer to Table 1 and Table 2 to select the materials for the support layer and the conductive layer of Examples 1-21 and Comparative Examples 1-7 to prepare the positive electrode current collector; with respect to other parameters other than Table 1 and Table 2, Examples 1-21 and Comparative Examples 1-7 are basically the same and can be appropriately adjusted to meet the requirements of the preparation parameters in Table 1 and Table 2.

[0239] The preparation method of the positive electrode current collector using Example 1 as an example: a 12μm PET base film roll (as a support layer) was used, and a 2μm Al layer (as a conductive layer, 1μm thick on each side) was deposited on its front and back surfaces using vacuum vapor deposition technology to produce a 14μm aluminum composite current collector, named "14um AP". A vacuum evaporation equipment (Baofeng FZZ-1650) was used, and the vacuum degree was controlled at ≤1×10 -3 Pa, membrane speed 300m / min, aluminum wire feed rate 500mm / min, heating power 5-9kW, single deposition thickness of approximately 50nm, and 20 deposition passes in both directions to achieve an aluminum metal layer thickness of 1μm on each side. The prepared composite current collector was used as the positive electrode current collector in Example 1.

[0240] In Example 20, the positive electrode current collector is prepared using a method basically consistent with that in Example 1, except that the conductive layer is prepared using aluminum alloy (4043 type).

[0241] In Example 21, the positive electrode current collector was prepared using a method basically consistent with that in Example 1, except that the conductive layer was prepared using aluminum alloy (4032 type).

[0242] In Comparative Example 8, no support layer was provided, and an aluminum foil (Al foil) with a thickness of about 15 μm was used as the positive electrode current collector (denoted as “15 μm Al”), as shown in Table 1.

[0243] 1.2. Parameter Control

[0244] (1) Measurement of support layer thickness and conductive layer thickness

[0245] The thickness of the base film (support layer) and the metal layer (conductive layer) in the composite current collector for the positive electrode was measured by Ar ion polishing the cross section (JEOL IB19500CP) and then magnifying it to 10,000 times using a scanning electron microscope (JEOL IB-19500).

[0246] (2) Yield strength, tensile strength, elastic modulus and elongation at break tests

[0247] The tensile test was conducted using an INSTRON 3365 tensile testing machine to measure the tensile properties of the polymer base film, metal conductive layer, and composite current collector for the positive electrode. The sample width was 15 mm, the length was 150 mm, the stretching distance was 50 mm, and the stretching rate was 50 mm / min.

[0248] Yield strength = yield point tensile force / sample cross-sectional area; where sample cross-sectional area = 15 mm × sample thickness;

[0249] Tensile strength at break = tensile force at break / cross-sectional area of ​​sample; where cross-sectional area of ​​sample = 15 mm × sample thickness;

[0250] Elongation at break = (length of sample stretched to break - 50) / 50 × 100%; where the unit of the length of sample stretched to break is the same as the unit of the stretched distance, in mm;

[0251] Elastic modulus = tensile strength corresponding to 1% elongation / 1%.

[0252] Elastic modulus = tensile strength in the elastic deformation stage / corresponding elongation. For the convenience of calculation, the tensile strength corresponding to 1% elongation (elastic deformation stage) / 1% is used for calculation.

[0253] In addition, since the conductive layer is relatively thin, the conductive layer is prepared into samples with a uniform thickness (within the range of 10 μm to 100 μm) for tensile testing.

[0254] Secondary battery assembly:

[0255] Choose NCM 811 The positive electrode material / graphite negative electrode material chemical system 60Ah battery cell was evaluated. The composite current collector prepared in each embodiment was used to prepare the positive electrode sheet, wherein the active material coating weight of the positive electrode sheet was 20mg / cm 2 The positive electrode active material accounts for 97% by weight in the positive electrode slurry, and the compaction density is 3.5g / cm 3 The current collector of the negative electrode is 6μm Cu foil with a coating weight of 12mg / cm 2The weight proportion of negative electrode active material in negative electrode slurry is 96.5%, and the compaction density is 1.65g / cm 3 A 7μm polypropylene separator was used, and a 1M solution of lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate / ethyl methyl carbonate (EC / EMC) was used as the electrolyte.

[0256] Table 1. Positive electrode current collector

[0257] In Table 1, PET represents polyethylene terephthalate, PEN represents polyethylene naphthalate, PI-1 represents homphenyl polyimide, and PI-2 represents biphenyl polyimide.

[0258] Table 2. Positive electrode current collector

[0259] In Table 2, the extension coefficient is equal to (d1×T1-(d2×T2)×(1-α)-d1×Q1×α); the distribution coefficient α=G1 / (G1+G2).

[0260] Test methods and analysis:

[0261] 1. Processing performance characterization:

[0262] 1.1. Coating production rate, also known as coating rate or production rate

[0263] The coating production rate is calculated by recording the number of meters of qualified coated electrodes produced through the coating process for 100,000 meters of positive electrode current collector.

[0264] 1.2. Cold pressing cracking frequency, also recorded as cold pressing fracture frequency

[0265] The frequency of cold pressing cracking of the positive electrode collector is evaluated by recording the number of cracks on the positive electrode collector coated electrode during the cold pressing process for 100,000 meters of positive electrode collector; the unit is km / time, and the higher the value, the less likely it is to crack.

[0266] 1.3. Cold pressing elongation

[0267] The cold pressing elongation rate of the electrode was evaluated by measuring the extended length of a 1m long positive electrode current collector coated electrode after cold pressing, where the cold pressing elongation rate = (length of the electrode after cold pressing - 1) / 1 × 100%, where the unit of the length of the electrode after cold pressing is meter (m). The cold pressing elongation rate of each embodiment was determined by taking the average value of 5 measurements.

[0268] 2. Battery performance characterization

[0269] 2.1. Battery cell energy density

[0270] The battery cells prepared in each embodiment and comparative example were subjected to charge and discharge tests using a battery tester (Xinwei 5V100A) to evaluate the cycle performance of the battery. The test voltage range was 4.25-2.5V, and the charge and discharge current rate was 1C / 1C.

[0271] The energy density of the battery = the initial capacity of the battery at a current density of 1C × the voltage platform / the weight of the battery cell, where the capacity and voltage platform of the battery cell are directly read from the charge and discharge data, and the weight of the battery cell is obtained by weighing with a balance with three decimal places of accuracy.

[0272] 2.2. Battery cell cycle performance

[0273] The battery cell cycle number is the number of cycles corresponding to the cell capacity decaying to 80% of the capacity of the first cycle of the cell.

[0274] Test results and analysis:

[0275] The tensile strength and elongation at break of the positive electrode current collectors prepared in the above embodiments and comparative examples can be found in Table 3. The test results of the cell energy density and cell cycle performance of the secondary batteries prepared in the above embodiments and comparative examples can be found in Table 3.

[0276] The tensile strength and elongation at break of the positive electrode current collector in the positive electrode sheet have the following physical meanings: the tensile strength is the ratio of the maximum stress the positive electrode current collector can withstand before breaking to its cross-sectional area before stretching, and the elongation at break is the ratio of the elongation at break to its length before stretching. Higher tensile strength and elongation at break of the positive electrode current collector improve its processing performance and reduce the likelihood of breakage during battery cell fabrication.

[0277] The positive electrode composite current collectors prepared in Examples 1-18, 20-21 of the present application all have high tensile strength and elongation at break, good processability, and good energy density. The support layer of Example 19 is thicker than that of the other examples, and the positive electrode composite current collectors prepared therefrom all have high tensile strength and elongation at break, good processability, and a certain energy density. It should be noted that compared to the low energy density of the current collector without a support layer (traditional aluminum foil), Example 19 still has a certain energy density advantage. The test results of the traditional aluminum foil positive electrode current collector can be found in Comparative Example 8.

[0278] Examples 1-21 all exhibited excellent cell cycling performance, with the number of cycles to 80% capacity decay exceeding 900 cycles. Examples 1-17 and 19-21 all achieved cycle numbers exceeding 1200 cycles and even exceeding 1300 cycles. The conductive layer thickness of Example 18 was thinner than that of the other examples, and although the number of cycles to 80% capacity decay was lower than that of Examples 1-17 and 19-21, it still showed a certain degree of improvement compared to Comparative Example 1-7.

[0279] Examples 1-21 all have a higher coating production excellence rate, a higher cold pressing elongation rate and a higher cold pressing cracking frequency in the unit of "km / time" (that is, less prone to cracking); among them, the coating production excellence rates in Examples 1-21 are all above 70%, generally higher than 80%, and most are higher than 90%, and some can achieve ≥99%; the cold pressing elongation rates in Examples 1-21 are generally ≥0.8% (further generally ≥1.0%), among which, the cold pressing elongation rates of Examples 1-17 and 20-21 are ≥1.1%; the cold pressing cracking rate of Example 1-21 is ≥3km / time, and is not prone to cracking.

[0280] The ductility coefficients of the composite current collectors in the positive electrode sheets of Comparative Examples 1-7 are all lower than 800 Pa·m. At this time, the tensile fracture strength of the composite current collectors generally decreases, and the elongation at break is significantly reduced, resulting in poor overall mechanical properties. The processability of the composite current collectors is significantly poor, and the coating production rate is all lower than 60%, less than 10% for Comparative Example 2, and less than 30% for Comparative Example 1.

[0281] Although the supporting layer thickness d1, tensile fracture strength T1, yield strength Q1, elastic modulus G1, and the total thickness d2, tensile fracture strength T2, elastic modulus G2 of the conductive layer, and the distribution coefficient α of the composite current collector in Comparative Examples 1 and 6 are within the parameter ranges of Examples 1-21, since the ductility coefficient of the composite current collector is lower than 800 Pa·m, the overall mechanical properties of the composite current collector are significantly reduced, and the processability is significantly deteriorated, and the coating production rate and the frequency of cold pressing cracking are both low.

[0282] The support layer of Comparative Example 2 is thinner, the conductive layer of Comparative Example 4 is thicker, the tensile fracture strength T1 of the support layer of Comparative Example 5 is relatively low, and the elastic modulus G2 of the conductive layer of Comparative Example 7 is relatively high, all of which lead to the ductility coefficient of the composite current collector being lower than 800 Pa·m. The overall mechanical properties of the prepared composite current collector are significantly reduced, and the processability is significantly deteriorated. The coating production rate and the frequency of cold pressing cracking are both low.

[0283] Comparative Example 3 is based on Example 3, in which only the yield strength Q1 of the support layer is slightly adjusted from 100 MPa to 95 MPa, resulting in an ductility coefficient of the composite current collector being lower than 800 Pa·m. The overall mechanical properties of the prepared composite current collector are significantly reduced, and the processability is significantly deteriorated. The coating production rate and the frequency of cold pressing cracking are both low.

[0284] Table 3.

[0285] In Table 3, the number of cycles of the battery cell is the number of cycles corresponding to the battery cell capacity decaying to 80% of the capacity of the first cycle of the battery cell.

[0286] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0287] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same effect are all included in the technical scope of the present application. The above-mentioned embodiments only express several embodiments of the present application, and their descriptions are relatively detailed, but they cannot be understood as limiting the scope of the patent. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of constructing by combining some of the constituent elements in the embodiments are also included in the scope of the present application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be based on the attached claims, and the description and drawings may be used to explain the content of the claims.

Claims

1. A composite current collector for a positive electrode, comprising a support layer and a conductive layer disposed on at least one side of the support layer, wherein the support layer is an organic support layer; The thickness of the support layer is denoted as d1, the tensile strength is denoted as T1, the yield strength is denoted as Q1, and the elastic modulus is denoted as G1; The total thickness of the conductive layer is denoted as d2, the tensile strength at break is denoted as T2, and the elastic modulus is denoted as G2; The composite current collector for the positive electrode satisfies the following conditions: (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥800Pa·m, wherein: α=G1 / (G1+G2).

2. The composite current collector for positive electrode according to claim 1, wherein: The thickness d1 of the support layer is 4 μm-15 μm; Optionally, the thickness d1 of the support layer is 4 μm-12 μm; Further optionally, the thickness d1 of the support layer is 4 μm-6 μm.

3. The composite current collector for positive electrode according to claim 1 or 2, wherein: The tensile fracture strength T1 of the support layer is ≥200MPa; Optionally, the tensile fracture strength T1 of the support layer is ≥300 MPa.

4. The composite current collector for positive electrode according to any one of claims 1 to 3, wherein The yield strength Q1 of the support layer is ≥90MPa; Optionally, the yield strength Q1 of the support layer is ≥150 MPa.

5. The composite current collector for positive electrode according to any one of claims 1 to 4, wherein The composite current collector for the positive electrode satisfies any one or more of the following characteristics: The total thickness d2 of the conductive layer is 0.6 μm-3 μm; optionally, the total thickness d2 of the conductive layer is 1 μm-3 μm; further optionally, the total thickness d2 of the conductive layer is 1.4 μm-2.4 μm; The single-side thickness d2 of the conductive layer s 0.3 μm-1.5 μm; Optionally, the single-side thickness d2 of the conductive layer s 0.5 μm-1.5 μm; further optionally, the single-side thickness d2 of the conductive layer s 0.7μm-1.2μm; The thickness D of the composite current collector for the positive electrode a 3 μm-17 μm; Optionally, the thickness D of the composite current collector for the positive electrode a 3 μm-14 μm; further optionally, the thickness D of the composite current collector for the positive electrode a 3.4μm-8.4μm.

6. The composite current collector for positive electrode according to any one of claims 1 to 5, wherein The tensile strength of the conductive layer is T2≥150MPa; Optionally, the tensile fracture strength T2 of the conductive layer is ≥200 MPa.

7. The composite current collector for a positive electrode according to any one of claims 1 to 6, wherein The composite current collector for the positive electrode satisfies any one or more of the following characteristics: The elastic modulus G1 of the support layer is ≥3 GPa; optionally, the elastic modulus G1 of the support layer is ≥4 GPa; The elastic modulus G2 of the conductive layer is 25 GPa-40 GPa; optionally, the elastic modulus G2 of the conductive layer is 25 GPa-35 GPa; The α is 0.024-0.43; optionally, the α is 0.095-0.300; further optionally, the α is 0.105-0.

250.

8. The composite current collector for positive electrode according to any one of claims 1 to 7, wherein (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1000Pa·m; Optionally, (d1×T1-(d2×T2)×(1-α)-d1×Q1×α)≥1650Pa·m.

9. The composite current collector for a positive electrode according to any one of claims 1 to 8, wherein The material of the support layer is a polymer-based material or a polymer-based composite material; Optionally, the polymer component in the support layer includes polyimide, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, Olefins, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polysulfur nitride polymer materials, polyphenyl, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives of the above materials, crosslinked products of the above materials and copolymers of the above materials or one or more thereof.

10. The composite current collector for positive electrode according to any one of claims 1 to 9, wherein The polymer component in the support layer includes polyimide, and the polyimide includes one or both of homophenyl polyimide and biphenyl polyimide; Optionally, the polymer component in the support layer includes biphenyl polyimide; Further optionally, the support layer comprises biphenyl polyimide in an amount of ≥50% by mass; Further optionally, the support layer comprises biphenyl polyimide in an amount of ≥80% by mass; Further optionally, the material of the support layer is biphenyl polyimide.

11. The composite current collector for positive electrode according to any one of claims 1 to 10, wherein The conductive layer includes a metal material. Optionally, the metal material includes one or more of aluminum and an aluminum alloy. 12 . A positive electrode sheet, comprising the composite current collector for positive electrode according to claim 1 . 13 . A secondary battery comprising at least one of the composite current collector for a positive electrode according to claim 1 and the positive electrode sheet according to claim 12 . 14 . An electrical device comprising at least one of the composite current collector for a positive electrode according to claim 1 , the positive electrode sheet according to claim 12 , and the secondary battery according to claim 13 .

15. The method for preparing the composite current collector for positive electrode according to any one of claims 1 to 11, characterized in that: The method comprises the following steps: forming the conductive layer on at least one side of the support layer to prepare the composite current collector for the positive electrode.

16. A method for preparing a positive electrode sheet, characterized in that: The method comprises the following steps: coating the positive electrode slurry on at least one side of the surface of the positive electrode composite current collector according to any one of claims 1 to 11, drying, and cold pressing to prepare the positive electrode sheet.

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