Composite current collector, preparation method thereof, secondary battery and device

Abstract

The invention relates to a composite current collector, a preparation method thereof, a secondary battery and a device. The composite current collector of the present application comprises: a first polymer layer; the second polymer layer is arranged on the first polymer layer, and the second polymer layer comprises a heat conduction material; and the conductive layer is arranged on the second polymer layer. Therefore, the composite current collector has excellent thermal conductivity, electrical conductivity and tear resistance, the DCR of the battery using the composite current collector is reduced, and the cycle performance and needling safety performance are greatly improved.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a composite current collector and a preparation method thereof, a secondary battery and a device. Background Art

[0002] Lithium-ion batteries are currently widely used in automotive power batteries due to their long service life and high energy density. However, with the popularity of electric vehicles in recent years, safety accidents caused by lithium-ion batteries have also occurred frequently. Safety tests such as hot box, puncture, external short circuit and overcharging are important test methods to characterize the safety level of a battery cell. Among the above safety tests, puncture safety is the most difficult to pass, because when puncture occurs, the burrs of the positive electrode current collector aluminum foil will contact the fully charged negative electrode plate, the internal short circuit resistance is very small, and the ohmic heat generated instantly is huge, which in turn triggers the positive electrode active material (such as ternary positive electrode material) to release oxygen, undergo redox reactions with the electrolyte, generate uncontrollable heat, and cause thermal runaway of the battery. The use of a composite current collector can reduce the harm of aluminum foil burrs and is an effective means to improve battery safety.

[0003] However, current composite current collectors and preparation methods thereof, secondary batteries and devices still need to be improved. Summary of the invention

[0004] The inventors found that although the composite current collector can reduce the harm of aluminum foil burrs and improve the safety of the battery cell, its internal resistance during use is relatively large, higher than that of conventional current collectors, such as aluminum foil, which increases the overall impedance (DCR) of the battery cell and generates more heat. The composite current collector is a poor conductor of heat. The heat generated during the operation of the battery cell cannot be dissipated in time through the composite current collector, resulting in heat accumulation inside the battery cell, affecting the cycle, safety and other performance of the battery cell. In order to solve or alleviate at least one of the above problems, the present application provides a composite current collector and a preparation method thereof, a secondary battery and a device. By providing a thermally conductive polymer layer containing a thermally conductive material between the polymer core layer and the conductive layer of the composite current collector, the composite current collector has excellent thermal conductivity, electrical conductivity and tear resistance, and the battery using the composite current collector has a small DCR, and the cycle performance and acupuncture safety are greatly improved.

[0005] One aspect of the present application provides a composite current collector, which includes: a first polymer layer; a second polymer layer, which is arranged on the first polymer layer, and the second polymer layer includes a thermally conductive material; and a conductive layer, which is arranged on the second polymer layer.

[0006] Another aspect of the present application provides a method for preparing a composite current collector, the method comprising: forming a second polymer layer, a first polymer layer and a third polymer layer stacked in sequence through a three-layer co-extrusion composite process; wherein the first polymer layer comprises a first polymer, the second polymer layer comprises a second polymer and a thermally conductive material, and the third polymer layer comprises a second polymer and a thermally conductive material; and forming conductive layers on a side of the second polymer layer away from the first polymer layer and a side of the third polymer layer away from the first polymer layer, respectively, to obtain the composite current collector.

[0007] Another aspect of the present application provides a secondary battery, which includes the composite current collector described above or the composite current collector formed by the preparation method described above.

[0008] Another aspect of the present application provides a device, which includes the secondary battery described above.

[0009] The beneficial effects of this application are:

[0010] The present application improves the thermal conductivity of the composite current collector by setting a thermally conductive modified polymer layer containing a thermally conductive material between the polymer core layer and the conductive layer of the composite current collector; the setting of the thermally conductive modified polymer layer can make the contact between the composite current collector and the active material better, which is conducive to reducing the interface contact resistance, and the surface resistance of the composite current collector is reduced, thereby reducing the impedance (DCR) of the battery using the composite current collector; the composite current collector has a higher tensile modulus, greater tensile strength and elongation, which can reduce the deformation of the composite current collector during the coating process of the active material; the composite current collector can avoid the contact between the active material near the steel needle or the positive electrode current collector burr and the negative electrode active material during the acupuncture process, and improves the acupuncture safety performance of the battery using the composite current collector. Therefore, based on the above improvements, the composite current collector has excellent thermal conductivity, electrical conductivity and tear resistance, the DCR of the battery using the composite current collector is reduced, and the cycle performance and acupuncture safety performance are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to make the above-mentioned purpose, features and advantages of the present invention easier to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein, so the present invention is not limited to the specific embodiments disclosed below.

[0012] Figure 1 A schematic structural diagram of a composite current collector according to the present application is shown.

[0013] Description of reference numerals:

[0014] 1, 5: conductive layer; 2, 4: second polymer layer; 3: first polymer layer. DETAILED DESCRIPTION

[0015] For simplicity, this application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.

[0016] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0017] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0018] The selection range of the terms "and / or", "or / and", and "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, and the said any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution that is all connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the combination of four of A, B, C, and D (that is, the technical solution that is all connected by "logical AND").

[0019] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0020] 1. Composite current collector

[0021] One aspect of the present application provides a composite current collector, which includes: a first polymer layer, a second polymer layer and a conductive layer. The second polymer layer is disposed on the first polymer layer, and the second polymer layer includes a thermal conductive material; and the conductive layer is disposed on the second polymer layer.

[0022] The present application improves the thermal conductivity of the composite current collector by setting a thermally conductive modified polymer layer containing a thermally conductive material between the polymer core layer and the conductive layer of the composite current collector; the setting of the thermally conductive modified polymer layer can make the contact between the composite current collector and the active material better, which is conducive to reducing the interface contact resistance, and the surface resistance of the composite current collector is reduced, thereby reducing the impedance (DCR) of the battery using the composite current collector; the composite current collector has a higher tensile modulus, greater tensile strength and elongation, which can reduce the deformation of the composite current collector during the coating process of the active material; the composite current collector can avoid the contact between the active material near the steel needle or the positive electrode current collector burr and the negative electrode active material during the acupuncture process, and improves the acupuncture safety performance of the battery using the composite current collector. Therefore, based on the above improvements, the composite current collector has excellent thermal conductivity, electrical conductivity and tear resistance, the DCR of the battery using the composite current collector is reduced, and the cycle performance and acupuncture safety performance are greatly improved.

[0023] In some embodiments, the second polymer layer is disposed on the surfaces of the two opposite sides of the first polymer layer, and the conductive layer is disposed on the second polymer layer. Thus, the composite current collector includes a conductive layer, a second polymer layer, a first polymer layer, a second polymer layer and a conductive layer stacked in sequence.

[0024] In some embodiments, the first polymer layer includes a first polymer. In some embodiments, the first polymer includes at least one of polyethylene terephthalate, polybutylene terephthalate, and polypropylene.

[0025] In some embodiments, the first polymer layer has a thickness of 5 μm to 12 μm. In some embodiments, the first polymer layer has a thickness of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value therebetween.

[0026] In some embodiments, the transverse tensile strength and longitudinal tensile strength of the first polymer layer are both greater than or equal to 120 MPa. In some embodiments, the transverse tensile strength of the first polymer layer is 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 2000 MPa, or any value therebetween. In some embodiments, the longitudinal tensile strength of the first polymer layer is 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 2000 MPa, or any value therebetween.

[0027] In some embodiments, the second polymer layer includes a second polymer and a thermally conductive material. In some embodiments, the second polymer layer includes at least one of polyethylene terephthalate, polybutylene terephthalate and polypropylene. In some embodiments, the thermally conductive material includes at least one of carbon black, graphene, carbon nanotubes and boron nitride. Thus, the present application improves the thermal conductivity of the composite current collector by providing a thermally conductive modified polymer layer containing a thermally conductive material between the polymer core layer and the conductive layer of the composite current collector; the provision of the thermally conductive modified polymer layer can make the contact between the composite current collector and the active material better, which is conducive to reducing the interface contact resistance, and the surface resistance of the composite current collector is reduced, thereby reducing the impedance (DCR) of the battery using the composite current collector; the composite current collector has a higher tensile modulus, greater tensile strength and elongation, which can reduce the deformation of the composite current collector during the coating process of the active material; the composite current collector can avoid the contact between the active material near the steel needle or the positive current collector burr and the negative active material during the acupuncture process, thereby improving the acupuncture safety performance of the battery using the composite current collector.

[0028] In some embodiments, the average particle size of the thermally conductive material is 1 nm to 1 μm. In some embodiments, the average particle size of the thermally conductive material is 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1 μm, or any value therebetween. Thus, the thermal conductivity of the second polymer layer is further improved.

[0029] In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or any value therebetween, and the mass percentage of the thermal conductive material is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30% or any value therebetween. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 80% to 97%, and the mass percentage of the thermal conductive material is 3% to 20%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 90% to 97%, and the mass percentage of the thermal conductive material is 3% to 10%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 92% to 95%, and the mass percentage of the thermal conductive material is 5% to 8%. Thus, the thermal conductivity of the second polymer layer is further improved. Therefore, if the mass percentage of the thermal conductive material is too low, the thermal conductivity will be poor; if the mass percentage of the thermal conductive material is too high, the second polymer layer will have poor molding processability.

[0030] In some embodiments, the thickness of the second polymer layer is 0.5 μm to 3 μm. In some embodiments, the thickness of the second polymer layer is 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. In some embodiments, the thickness of the second polymer layer is 0.8 μm to 2 μm.

[0031] In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:(1-10). In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or any value therebetween. In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:(3-7).

[0032] In some embodiments, the thermal conductivity of the composite current collector is 30W / mK to 100W / mK. In some embodiments, the thermal conductivity of the composite current collector is 30W / mK, 35W / mK, 40W / mK, 45W / mK, 50W / mK, 55W / mK, 60W / mK, 70W / mK, 80W / mK, 90W / mK, 100W / mK or any value therebetween. In some embodiments, the thermal conductivity of the composite current collector is 35W / mK to 60W / mK.

[0033] In some embodiments, the conductive layer includes aluminum or copper. In some embodiments, the conductive layer includes aluminum (Al), for example, aluminum foil, whereby aluminum conductive layers are disposed on both sides of the composite current collector, and the composite current collector can be used in a positive electrode sheet as a positive electrode current collector. In some embodiments, the conductive layer includes copper (Cu), for example, copper foil, whereby copper conductive layers are disposed on both sides of the composite current collector, and the composite current collector can be used in a negative electrode sheet as a negative electrode current collector.

[0034] In some embodiments, the thickness of the conductive layer is 0.5 μm to 3 μm. In some embodiments, the thickness of the conductive layer is 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. In some embodiments, the thickness of the conductive layer is 0.8 μm to 2 μm.

[0035] In some embodiments, the composite current collector has a thickness of 6 μm to 16 μm. In some embodiments, the composite current collector has a thickness of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or any value therebetween.

[0036] In some embodiments, the side of the second polymer layer facing the conductive layer is a frosted surface, and the surface roughness Ra of the frosted surface is 0.1 μm to 2 μm. In some embodiments, the surface roughness Ra of the frosted surface is 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, or any value therebetween. Thus, the provision of the frosted surface improves the peeling force between the conductive layer and the second polymer layer.

[0037] In some embodiments, the composite current collector further includes: a carbon layer, and the carbon layer is disposed on the metal layer. In some embodiments, the carbon layer includes at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black and graphene. In some embodiments, the thickness of the carbon layer is 0.5 μm to 2 μm. In some embodiments, the thickness of the carbon layer is 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm or any value therebetween. It should be noted that the carbon layer also includes other components such as a binder, and those skilled in the art can select them according to their needs, which will not be repeated here.

[0038] 2. Preparation method of composite current collector

[0039] Another aspect of the present application provides a method for preparing a composite current collector. The composite current collector formed by the preparation method may be the composite current collector described above, and thus may have all the characteristics and advantages of the composite current collector described above, which will not be repeated here.

[0040] In some embodiments, the method comprises:

[0041] S100: performing a three-layer co-extrusion composite process to form a second polymer layer, a first polymer layer and a third polymer layer which are stacked in sequence; wherein the first polymer layer includes a first polymer, the second polymer layer includes a second polymer and a thermal conductive material, and the third polymer layer includes the second polymer and a thermal conductive material;

[0042] S200: forming a conductive layer on a side of the second polymer layer away from the first polymer layer and a side of the third polymer layer away from the first polymer layer, respectively, to obtain a composite current collector.

[0043] It should be noted that the first polymer layer prepared by the method can be the first polymer layer in the composite current collector described above, and thus can have all the characteristics and advantages of the first polymer layer described above. The second polymer layer and the third polymer layer prepared by the method can be the second polymer layer in the composite current collector described above, respectively, and thus can have all the characteristics and advantages of the second polymer layer described above.

[0044] The present application adopts a three-layer co-extrusion composite process to arrange a thermally conductive modified polymer layer (second polymer layer) containing a thermally conductive material between the polymer core layer (first polymer layer) of the composite current collector and the conductive layer, that is, the thermally conductive modified polymer layer is composited on both sides of the polymer core layer, and then a conductive layer is formed on the surface of the thermally conductive modified polymer layer by magnetron sputtering and / or evaporation.

[0045] In some embodiments, the three-layer co-extrusion composite process includes a co-extrusion casting process. Specifically, the co-extrusion casting process can be a film formed by co-extrusion, casting, and double drawing in sequence.

[0046] In some embodiments, the temperature of the three-layer coextrusion composite process is 180° C. to 300° C. In some embodiments, the temperature of the three-layer coextrusion composite process is 180° C., 200° C., 220° C., 240° C., 260° C., 280° C., 300° C. or any value therebetween.

[0047] In some embodiments, the first polymer layer includes a first polymer. In some embodiments, the first polymer includes at least one of polyethylene terephthalate, polybutylene terephthalate, and polypropylene.

[0048] In some embodiments, the first polymer layer has a thickness of 5 μm to 12 μm. In some embodiments, the first polymer layer has a thickness of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value therebetween.

[0049] In some embodiments, the transverse tensile strength and longitudinal tensile strength of the first polymer layer are both greater than or equal to 120 MPa. In some embodiments, the transverse tensile strength of the first polymer layer is 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 2000 MPa, or any value therebetween. In some embodiments, the longitudinal tensile strength of the first polymer layer is 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 2000 MPa, or any value therebetween.

[0050] In some embodiments, the second polymer layer includes a second polymer and a thermally conductive material. In some embodiments, the second polymer layer includes at least one of polyethylene terephthalate, polybutylene terephthalate and polypropylene. In some embodiments, the thermally conductive material includes at least one of carbon black, graphene, carbon nanotubes and boron nitride. Thus, the present application improves the thermal conductivity of the composite current collector by providing a thermally conductive modified polymer layer containing a thermally conductive material between the polymer core layer and the conductive layer of the composite current collector; the provision of the thermally conductive modified polymer layer can make the contact between the composite current collector and the active material better, which is conducive to reducing the interface contact resistance, and the surface resistance of the composite current collector is reduced, thereby reducing the impedance (DCR) of the battery using the composite current collector; the composite current collector has a higher tensile modulus, greater tensile strength and elongation, which can reduce the deformation of the composite current collector during the coating process of the active material; the composite current collector can avoid the contact between the active material near the steel needle or the positive current collector burr and the negative active material during the acupuncture process, thereby improving the acupuncture safety performance of the battery using the composite current collector.

[0051] In some embodiments, the average particle size of the thermally conductive material is 1 nm to 1 μm. In some embodiments, the average particle size of the thermally conductive material is 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1 μm, or any value therebetween. Thus, the thermal conductivity of the second polymer layer is further improved.

[0052] In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or any value therebetween, and the mass percentage of the thermal conductive material is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30% or any value therebetween. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 80% to 97%, and the mass percentage of the thermal conductive material is 3% to 20%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 90% to 97%, and the mass percentage of the thermal conductive material is 3% to 10%. In some embodiments, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 92% to 95%, and the mass percentage of the thermal conductive material is 5% to 8%. Thus, the thermal conductivity of the second polymer layer is further improved. Therefore, if the mass percentage of the thermal conductive material is too low, the thermal conductivity will be poor; if the mass percentage of the thermal conductive material is too high, the second polymer layer will have poor molding processability.

[0053] In some embodiments, the thickness of the second polymer layer is 0.5 μm to 3 μm. In some embodiments, the thickness of the second polymer layer is 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. In some embodiments, the thickness of the second polymer layer is 0.8 μm to 2 μm.

[0054] In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:(1-10). In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or any value therebetween. In some embodiments, the thickness ratio of the second polymer layer to the first polymer layer is 1:(3-7).

[0055] In some embodiments, the thermal conductivity of the composite current collector is 30W / mK to 100W / mK. In some embodiments, the thermal conductivity of the composite current collector is 30W / mK, 35W / mK, 40W / mK, 45W / mK, 50W / mK, 55W / mK, 60W / mK, 70W / mK, 80W / mK, 90W / mK, 100W / mK or any value therebetween. In some embodiments, the thermal conductivity of the composite current collector is 35W / mK to 60W / mK.

[0056] In some embodiments, the third polymer layer may have all the features and advantages of the second polymer layer described above.

[0057] In some embodiments, based on the total mass of the third polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%. In some embodiments, based on the total mass of the third polymer layer, the mass percentage of the second polymer is 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or any value therebetween, and the mass percentage of the thermal conductive material is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30% or any value therebetween. In some embodiments, based on the total mass of the third polymer layer, the mass percentage of the third polymer is 80% to 97%, and the mass percentage of the thermal conductive material is 3% to 20%. In some embodiments, based on the total mass of the third polymer layer, the mass percentage of the second polymer is 90% to 97%, and the mass percentage of the thermal conductive material is 3% to 10%. In some embodiments, based on the total mass of the third polymer layer, the mass percentage of the second polymer is 92% to 95%, and the mass percentage of the thermal conductive material is 5% to 8%. Thus, the thermal conductivity of the third polymer layer is further improved. Therefore, if the mass percentage of the thermal conductive material is too low, the thermal conductivity will be poor; if the mass percentage of the thermal conductive material is too high, the second polymer layer will have poor molding processability.

[0058] In some embodiments, the thickness ratio of the second polymer layer, the first polymer layer, and the third polymer layer is 1: (1 to 10): 1. In some embodiments, the thickness ratio of the second polymer layer, the first polymer layer, and the third polymer layer is 1: 1: 1, 1: 2: 1, 1: 3: 1, 1: 4: 1, 1: 5: 1, 1: 6: 1, 1: 7: 1, 1: 8: 1, 1: 9: 1, 1: 10: 1, or any value therebetween.

[0059] In some embodiments, the conductive layer may be the conductive layer described above, and thus has all the features and advantages of the conductive layer body described above, which will not be described in detail here.

[0060] In some embodiments, the conductive layer is formed by at least one of magnetron sputtering, evaporation and electroplating.

[0061] In some embodiments, the conductive layer includes Al, and the conductive layer is formed by magnetron sputtering Al2O3 and evaporating Al in sequence, thereby improving the bonding force between the Al conductive layer and the second polymer layer or the third polymer layer.

[0062] In some embodiments, the conductive layer includes Cu, and the conductive layer is formed by magnetron sputtering Al2O3, magnetron sputtering Cu, evaporating Cu, and electroplating CuSO4 solution in sequence, thereby improving the bonding force between the Cu conductive layer and the second polymer layer or the third polymer layer.

[0063] In some embodiments, the composite current collector has a thickness of 6 μm to 16 μm. In some embodiments, the composite current collector has a thickness of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or any value therebetween.

[0064] In some embodiments, the side of the second polymer layer facing the conductive layer is a frosted surface, and the surface roughness Ra of the frosted surface is 0.1 μm to 2 μm. In some embodiments, the surface roughness Ra of the frosted surface is 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, or any value therebetween. Thus, the provision of the frosted surface improves the peeling force between the conductive layer and the second polymer layer.

[0065] In some embodiments, the composite current collector further comprises: a carbon layer, the carbon layer being disposed on the metal layer. In some embodiments, the carbon layer comprises at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene. In some embodiments, the thickness of the carbon layer is 0.5 μm to 2 μm. In some embodiments, the thickness of the carbon layer is 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or any value therebetween.

[0066] 3. Secondary battery

[0067] Another aspect of the present application provides a secondary battery, which includes the composite current collector described above or the composite current collector formed by the preparation method described above. Thus, the secondary battery can have all the features and advantages of the composite current collector described above or the method described above, which will not be repeated here.

[0068] In some embodiments, the secondary battery includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode active material layer disposed on the positive current collector, and the negative electrode sheet includes a negative current collector and a negative electrode active material layer disposed on the negative current collector. In some embodiments, the conductive layer of the composite current collector includes aluminum, for example, aluminum foil, whereby aluminum conductive layers are disposed on both sides of the composite current collector, and the composite current collector can be used in the positive electrode sheet as a positive electrode collector. In some embodiments, the conductive layer of the composite current collector includes copper, for example, copper foil, whereby copper conductive layers are disposed on both sides of the composite current collector, and the composite current collector can be used in the negative electrode sheet as a negative electrode collector.

[0069] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a lithium nickel transition metal oxide and a phosphate. In some embodiments, the lithium nickel transition metal oxide includes LiNi x M 1-x O2, M is selected from at least one of cobalt, manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, yttrium, lanthanum, silver and niobium, 0.1≤x≤1. In some embodiments, x is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or any value therebetween. In some embodiments, the phosphate comprises LiMn k B (1-k) PO4, wherein 0≤k≤1, and the B element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead. In some embodiments, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or any value therebetween.

[0070] In some embodiments, the positive electrode active material layer further includes a binder and a conductive material. The types of the binder and the conductive material are not particularly limited, and those skilled in the art can select them as needed, which will not be described in detail here.

[0071] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. In some embodiments, the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide compound, and a silicon-carbon compound. In some embodiments, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments, the tin-based material includes at least one of tin, tin oxide, and a tin alloy. In some embodiments, the phosphorus-based material includes phosphorus and / or a phosphorus complex. In some embodiments, based on the mass of the negative electrode active material, the mass percentage z% of the silicon-based material satisfies: 1≤z≤100. In some embodiments, z is 1, 3, 5, 7, 9, 10, 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or any value therebetween.

[0072] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the positive electrode active material layer further includes a binder and a conductive material. The types of the binder and the conductive material are not particularly limited, and those skilled in the art can select them as needed, which will not be described in detail here.

[0073] The secondary battery of the present application also includes an electrolyte. The electrolyte of the present application may be an electrolyte known in the prior art. The electrolyte used in the electrolyte of the present application is not limited, and it may be any electrolyte known in the prior art.

[0074] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an optional additive. The organic solvent may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. The additive may be any additive known in the prior art that can be used as an electrolyte additive.

[0075] In some embodiments, the organic solvent includes at least one of a linear carbonate, a cyclic carbonate, and a carboxylic acid ester.

[0076] In some embodiments, the chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and fluorinated chain carbonate. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate. In some embodiments, the carboxylate is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone and fluorinated carboxylate. In some embodiments, based on the mass of the electrolyte, the mass percentage of the solvent is 40% to 80%. In some embodiments, the mass percentage of the solvent is 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or any value therebetween. In some embodiments, the mass percentage of the solvent is 50% to 70%.

[0077] In some embodiments, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), trifluorosulfonyl lithium (LiTf), bis(fluorosulfonyl)imide lithium (LiFSI), lithium trifluoromethanesulfonate, (trifluoromethylsulfonyl) (perfluorobutylsulfonyl) imide lithium (LiFNFSI), bis(trifluoromethylsulfonyl) imide lithium (LiTFSI), bis(pentafluoroethylsulfonyl) imide lithium (LiBETI), bis(fluoromalonate) borate lithium (LiBFMB), bis(oxalatoborate) lithium (LiBOB), difluorooxalatoborate lithium (LiDFOB) and difluorobis(oxalatophosphate) lithium and 4,5-dicyano-2-(trifluoromethyl) imidazole lithium (LiTDI) at least one. In some embodiments, based on the mass of the electrolyte, the mass percentage of the lithium salt is 4% to 25%. In some embodiments, the mass percentage of lithium salt is 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or any value therebetween. In some embodiments, the mass percentage of lithium salt is 6% to 18%.

[0078] In some embodiments, the additive includes at least one of a cyclic carbonate containing a carbon-carbon double bond, a silyl-containing phosphate, a silyl-containing borate, a nitrile compound, and a propanesulfonic acid pyridinium salt. In some embodiments, the additive is selected from at least one of vinylene carbonate (VC), vinyl ethylene carbonate, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), succinonitrile, adiponitrile, glutaronitrile, and hexanetrinitrile. In some embodiments, the additive further comprises at least one of methylene disulfonate (MMDS), ethylene disulfonate, 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST), 1,4-butane sultone (1,4-BS), vinyl sulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), propylene sulfate (TS), ethylene sulfite (DTO), dimethyl sulfite (DMS) and diethyl sulfite (DES). In some embodiments, the mass percentage of the additive is 0.05% to 10% based on the mass of the electrolyte. In some embodiments, the mass percentage of the additive is 0.05%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween. In some embodiments, the mass percentage of the additive is 0.1% to 5%.

[0079] In some embodiments, the preparation method of the secondary battery includes providing an electrode assembly, injecting, packaging and forming. In some embodiments, the temperature of the formation is 40°C to 50°C, for example, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C.

[0080] In some embodiments, the formation comprises: charging to 4.25V at 0.05C current and standing for 60 minutes at a temperature of 40°C to 50°C, such as 45°C, and a pressure of 150kgf to 250kgf, such as 210kgf, followed by charging to 4.25V at 0.1C, and then discharging to 3.0V at 0.2C.

[0081] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0082] In some embodiments, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0083] In some embodiments, the shape of the secondary battery is not particularly limited, and it may be cylindrical, square, or any other shape.

[0084] In some embodiments, the present application also provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0085] In some embodiments, the present application further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0086] 4. Device

[0087] Another aspect of the present application provides a device, which includes at least one of the secondary battery, battery module and battery pack described above. Therefore, the device can have all the features and advantages of the secondary battery, battery module or battery pack described above, which will not be repeated here.

[0088] In some embodiments, the device includes, but is not limited to: an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0089] In other embodiments, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0090] The following is further described in conjunction with specific embodiments and comparative examples. The raw materials involved in the following specific embodiments and comparative examples, unless otherwise specified, can all be commercially available, the instruments used, unless otherwise specified, can all be commercially available, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0091] Examples and Comparative Examples

[0092] Example 1

[0093] Positive electrode composite current collector: using (i) 97% polyethylene terephthalate (PET) and 3% carbon black, (ii) PET, (iii) 97% PET and 3% carbon black, three-layer co-extrusion casting and stretching to prepare a three-layer composite film layer of carbon black filled PET / PET / carbon black filled PET, wherein the carbon black filled PET layer (thickness of 2μm) is distributed on both sides of the PET layer (thickness of 2μm). Then, 30nm of Al2O3 is magnetron sputtered on both sides of the three-layer composite film layer (carbon black filled PET / PET / carbon black filled PET), and then a 1μm Al layer is continuously evaporated on the surface of Al2O3 to obtain the positive electrode composite current collector;

[0094] Positive electrode sheet: The positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2, Super-P (conductive carbon black), binder polyvinylidene fluoride (PVDF), by weight ratio LiNi 0.9 Co 0.05 Mn 0.05 O2: Super-P: PVDF = 97.5: 1.5: 1 in N-methylpyrrolidone (NMP), after being fully homogenized, is coated on the opposite sides of the positive electrode composite current collector prepared above, and then dried, rolled, hot pressed, etc. to obtain the positive electrode sheet;

[0095] Negative electrode sheet: negative electrode active material silicon oxide (SiOx, 0.5≤x≤1.5)-graphite composite (Si / C=30:70), conductive agent conductive carbon black, binder (styrene-butadiene rubber SBR, polyacrylic acid), thickener (sodium carboxymethyl cellulose CMCNa) are added into deionized water in a weight ratio of 96:1:2.4:0.6, and after being fully homogenized, they are coated on two opposite sides of a 12μm thick copper foil current collector, and then dried, rolled, hot pressed, etc. to obtain a negative electrode sheet;

[0096] Diaphragm: A polyethylene PE base film is used, and a ceramic layer is coated on the two opposite surfaces of the PE base film, that is, a double-sided ceramic layer is formed. The ceramic layer is aluminum oxide (Al2O3). The thickness of the PE base film is 9μm, the thickness of the ceramic layer is 2μm, and the total thickness of both sides is 4μm, thus obtaining a ceramic diaphragm body (Al2O3 / PE / Al2O3);

[0097] Electrolyte: In a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), fully dissolve the lithium salt LiPF6 in a mixed solution of EC / DEC / EMC (ethylene carbonate / diethyl carbonate / ethyl methyl carbonate) = 25 / 20 / 55 to prepare a 1 mol / L solution, and stir evenly to obtain an electrolyte.

[0098] Lithium-ion secondary battery: The positive electrode sheet, separator, and negative electrode sheet prepared above are overlapped in sequence, with the separator located between the positive electrode sheet and the negative electrode sheet, and are wound to obtain a bare battery cell, which is placed in a punched aluminum-plastic film soft-package shell, and injected with the above-prepared electrolyte after being fully dried. The battery is left at 45°C for 48h, formed in a high-temperature fixture (formation conditions are: temperature 45°C, pressure 210kgf, 0.05C current charged to 4.25V and allowed to stand for 60min, then 0.1C charged to 4.25V, then 0.2C discharged to 3.0V, and so on, repeated three times) and secondary sealed, and then conventional capacity division is carried out.

[0099] Embodiments 2 to 9

[0100] Examples 2 to 9 are implemented on the basis of Example 1 by adjusting the material and thickness of each layer structure in the composite current collector, the material type and content of the thermal conductive material, etc., and the specific adjustment measures and detailed data are shown in Table 1. The composite current collectors in Examples 2 to 6 and Examples 8 to 9 are all positive composite current collectors. The composite current collector in Example 7 is a negative composite current collector, and the positive current collector is a 12μm aluminum foil, wherein in Example 7, the Cu conductive layer in the composite current collector is formed by the following steps: 30nm Al2O3 is magnetron sputtered on both sides of the three-layer composite film layer (carbon black filled PET / PET / carbon black filled PET), and then a 1μm Cu layer is continuously evaporated on the surface of Al2O3, and then Cu is electroplated in a CuSO4 solution electrolytic cell to finally obtain the Cu conductive layer.

[0101] Comparative Example 1

[0102] The method is basically the same as Example 1, except that the positive electrode current collector is a commercially available 12 μm aluminum foil.

[0103] Comparative Example 2

[0104] It is basically the same as Example 1, except that the positive electrode current collector is a commercially available 8μm composite current collector, the polymer core layer is a 6μm PET single-layer film, and a 1μm Al layer is plated on both sides, with a total thickness of 8μm.

[0105] Comparative Example 3

[0106] The same as Example 7, except that the negative electrode uses a commercially available conventional 6 μm power copper foil.

[0107] Comparative Example 4

[0108] The same as Example 7, except that the negative electrode uses a commercially available 6 μm composite current collector, the core layer is a 4 μm PET single-layer film, and a 1 μm Cu layer is plated on both sides, with a total thickness of 6 μm.

[0109] Test Method

[0110] 1. Tensile test:

[0111] The tensile test was carried out according to GB / T1040 test standard. The tensile speed was 100 mm / min and the sample size was 200 mm long × 15 mm wide.

[0112] 2. Thermal conductivity test:

[0113] The thermal conductivity test was carried out according to the ASTM D5470 test standard. Ten samples were stacked to obtain a thickness of d.

[0114] 3. Composite current collector surface resistance test:

[0115] The surface resistance of the composite current collector was obtained by using a four-probe method and a test pressure of 0.2 KN.

[0116] 4. Battery impedance (DCR) test:

[0117] At 25°C, charge the secondary battery at 1 / 3C current to adjust it to 50% SOC, and record the voltage U1. Then discharge it at 2C current for 10 seconds, and record the voltage U2. The DCR of the battery at 50% SOC = (U1-U2) / 2C.

[0118] 5. Acupuncture test:

[0119] Use a 1mm diameter high temperature resistant steel needle with a taper of 30° to penetrate the center of the large surface perpendicular to the battery at a speed of 2mm / s until it penetrates the battery cell.

[0120] The above tests were performed on the composite current collectors or batteries obtained in Examples 1 to 9 and Comparative Examples 1 to 4, respectively. The test results are shown in Table 1, where the puncture performance test represents the number of times passed in 5 puncture tests, for example, 1 / 5 represents one pass in 5 puncture tests.

[0121] Test Results

[0122] Table 1

[0123]

[0124]

[0125] It can be seen from Examples 1 to 9 and Comparative Examples 1 to 4 that the thermal conductivity of the composite current collector is improved by providing a thermally conductive modified polymer layer (second polymer layer) containing a thermally conductive material between the polymer core layer (first polymer) and the conductive layer of the composite current collector; the provision of the thermally conductive modified polymer layer can make the contact between the composite current collector and the active material better, which is beneficial to reducing the interface contact resistance, and the surface resistance of the composite current collector is reduced, thereby reducing the impedance (DCR) of the battery using the composite current collector; the composite current collector has a higher tensile modulus, greater tensile strength and elongation, which can reduce the deformation of the composite current collector during the coating process of the active material; the composite current collector can avoid the contact between the active material near the steel needle or the positive electrode current collector burrs and the negative electrode active material during the acupuncture process, thereby improving the acupuncture safety performance of the battery using the composite current collector.

[0126] Comparison with Example 1 shows that the traditional aluminum foil as the positive current collector has poor puncture performance. When puncture occurs, the burrs of the aluminum foil of the positive current collector will contact the fully charged negative electrode plate, and the internal short-circuit resistance is very small. The ohmic heat generated instantly is huge, which then triggers the positive active material to release oxygen, and undergoes an oxidation-reduction reaction with the electrolyte, generating uncontrollable heat, leading to thermal runaway of the battery. Comparison with Example 2 shows that the conventional composite current collector is used as the positive current collector. Since a thermally conductive modified polymer layer containing a thermally conductive material is not provided between the polymer core layer and the conductive layer, the conductive layer is directly provided on the polymer core layer. Therefore, the tensile strength and tensile modulus of the current collector are poor, the surface resistance is high, and the thermal conductivity is poor, which in turn increases the DCR of the battery using the current collector, and the thermal conductivity, electrical conductivity and tear resistance are all poor, and the battery cycle performance is affected. Comparison with Example 3 shows that compared with Example 7, the traditional copper foil as the negative current collector has poor puncture performance, which also leads to thermal runaway of the battery. By comparing Comparative Example 4, it can be seen that compared with Example 7, the conventional composite current collector is used as the negative electrode current collector. Since no thermally conductive modified polymer layer containing a thermally conductive material is provided between the polymer core layer and the conductive layer, the conductive layer is directly provided on the polymer core layer. Therefore, the current collector has a poor tensile modulus, a high surface resistance, and a low thermal conductivity, which in turn increases the DCR of the battery using the current collector, and the thermal conductivity, electrical conductivity, and tear resistance are all poor, and the battery cycle performance is affected.

[0127] Figure 1 It is a schematic diagram of the structure of the composite current collector of Example 1, wherein the second polymer layer (2, 4) is arranged on both sides of the first polymer layer 3, and the surface of the second polymer layer (2, 4) is provided with a conductive layer (1, 5).

[0128] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A composite current collector, characterized in that: include: a first polymer layer; a second polymer layer, the second polymer layer being disposed on the first polymer layer, the second polymer layer comprising a thermally conductive material; A conductive layer is disposed on the second polymer layer.

2. The composite current collector according to claim 1, characterized in that: The second polymer layers are respectively disposed on surfaces of two opposite sides of the first polymer layer, and the conductive layer is disposed on the second polymer layer.

3. The composite current collector according to claim 1 or 2, characterized in that: The first polymer layer includes a first polymer, and the second polymer layer includes a second polymer; The first polymer and the second polymer respectively include at least one of polyethylene terephthalate, polybutylene terephthalate, and polypropylene.

4. The composite current collector according to claim 3, characterized in that: Based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%; and / or The thermally conductive material comprises at least one of carbon black, graphene, carbon nanotubes and boron nitride; and / or The conductive layer includes aluminum or copper.

5. The composite current collector according to claim 1 or 2, characterized in that: The thickness of the first polymer layer is 5 μm to 12 μm; and / or The thickness of the second polymer layer is 0.5 μm to 3 μm; and / or The thickness of the conductive layer is 0.5 μm to 3 μm; and / or The thickness ratio of the second polymer layer to the first polymer layer is 1:(1-10); and / or The thickness of the composite current collector is 6 μm to 16 μm; and / or The side of the second polymer layer facing the conductive layer is a frosted surface, and the surface roughness Ra of the frosted surface is 0.1 μm to 2 μm; and / or The transverse tensile strength and the longitudinal tensile strength of the first polymer layer are both greater than or equal to 120 MPa; and / or The average particle size of the thermally conductive material is 1 nm to 1 μm; and / or The thermal conductivity of the composite current collector is 30W / mK to 100W / mK.

6. The composite current collector according to claim 1 or 2, characterized in that: The composite current collector further comprises: A carbon layer is disposed on the metal layer; the carbon layer comprises at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black and graphene; and the thickness of the carbon layer is 0.5 μm to 2 μm.

7. A method for preparing a composite current collector, characterized in that: include: Through three-layer co-extrusion composite processing, a second polymer layer, a first polymer layer and a third polymer layer are stacked in sequence; wherein the first polymer layer includes a first polymer, the second polymer layer includes a second polymer and a thermal conductive material, and the third polymer layer includes a second polymer and a thermal conductive material; Conductive layers are formed on a side of the second polymer layer away from the first polymer layer and a side of the third polymer layer away from the first polymer layer, respectively, to obtain the composite current collector.

8. The preparation method according to claim 7, characterized in that: The three-layer co-extrusion composite process includes a co-extrusion casting process; and / or The temperature of the three-layer co-extrusion composite treatment is 180°C to 300°C; and / or The first polymer and the second polymer each include at least one of polyethylene terephthalate, polybutylene terephthalate and polypropylene; and / or The thermally conductive material comprises at least one of carbon black, graphene, carbon nanotubes and boron nitride; and / or In the second polymer layer, based on the total mass of the second polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%; and / or In the third polymer layer, based on the total mass of the third polymer layer, the mass percentage of the second polymer is 70% to 97%, and the mass percentage of the thermal conductive material is 3% to 30%; and / or The conductive layer is formed by at least one of magnetron sputtering, evaporation and electroplating; and / or The thickness ratio of the second polymer layer, the first polymer layer and the third polymer layer is 1:(1-10):1; and / or The thermal conductivity of the composite current collector is 30W / mK to 100W / mK.

9. A secondary battery, characterized in that: The invention comprises a composite current collector according to any one of claims 1 to 6 or a composite current collector formed by the preparation method according to any one of claims 7 to 8.

10. A device, characterized in that: A secondary battery comprising the secondary battery according to claim 9.

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