Composite current collector, secondary battery, and electric device

Abstract

The invention provides a composite current collector, a secondary battery and an electric device. The composite current collector comprises an organic layer and a metal layer arranged on at least one surface of the organic layer, pores are formed in the metal layer, the pore diameter of at least part of the pores is 10-200 nm, and the porosity of the metal layer is 3%-20%; the yield strength of the composite current collector ranges from 120 MPa to 180 MPa, the thickness of the single metal layer ranges from 0.5 micrometer to 5 micrometers, and the thickness of the organic layer ranges from 1 micrometer to 20 micrometers. The composite current collector can improve the rate capability and the stability of the secondary battery.

Description

[0001] This application is a divisional application of the invention patent application with the application number 202310792261.0 and the application date 2023 / 06 / 30, and the invention name "Composite current collector, secondary battery and electric device". TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a composite current collector, a secondary battery and an electric device. BACKGROUND

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

[0004] Due to the great development of secondary batteries, higher requirements are put forward for their performance. Secondary batteries using composite current collectors have great advantages in safety, energy density and cost. However, the secondary batteries using composite current collectors currently also have the problems of poor rate performance and poor stability of the battery cell.

[0005] Therefore, seeking a secondary battery using a composite current collector with good rate performance and good stability is one of the directions that the person skilled in the art focuses on. SUMMARY

[0006] The present application is made in view of the above-mentioned problems, and one of the purposes is to provide a composite current collector which can improve the rate performance and stability of a secondary battery.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a composite current collector, comprising an organic layer and a metal layer provided on at least one surface of the organic layer;

[0008] The metal layer has pores, at least part of the pores have a pore size of 10 nm to 200 nm, and the porosity of the metal layer is 3% to 20%;

[0009] The composite current collector satisfies the following relationship:

[0010] ;

[0011] Wherein, σ1 is the breaking strength of the organic layer, in MPa; T 有 is the thickness of the organic layer, in μm; T 金 is the total thickness of the metal layer, in μm; σ s is the yield strength of the composite current collector, in MPa.

[0012] The application forms a composite current collector by combining a metal layer and an organic layer, and sets a pore with a certain pore size in the metal layer, controls the porosity of the metal layer within a certain range, and controls the yield strength of the composite current collector within a certain range, so that the metal layer of the composite current collector is not prone to cracking during processing and subsequent battery cycling, the current collector is not prone to breaking, and the rate performance and stability of the secondary battery can be improved.

[0013] In any embodiment, the metal element in the metal layer comprises one or more of copper, aluminum, nickel, titanium, platinum, iron, cobalt, chromium, tungsten, molybdenum, magnesium, lead, indium, and tin.

[0014] In any embodiment, the metal layer is a metal aluminum layer, and the composite current collector satisfies the following relationship:

[0015] ;

[0016] wherein ρ1 is the average density of the composite current collector, in g / cm 3 ; and ρ2 is the density of the organic layer, in g / cm 3 . In this way, the direct current resistance DCR and the rate performance of the secondary battery can be further improved, and the long-term stability of the secondary battery can be improved.

[0017] In any embodiment, the yield strength of the composite current collector is 120 MPa to 180 MPa. In this way, the current collector is not prone to large cracks, and the cold rolling extension is not too large due to the too small yield strength, and the electrode sheet is not deformed.

[0018] In any embodiment, the resistivity of the composite current collector is ≤ 3.5*10 -8 Ωm. In this way, a thinner metal layer can be used to achieve the same conductive effect, and the energy density and safety of the battery cell can be improved.

[0019] In any embodiment, the size of the primary single crystal particles of the metal layer is 35 nm to 80 nm, the size of the secondary particles in the metal layer is 90 nm to 300 nm, and the particle size of the secondary particles is greater than the sum of the particle sizes of all the primary single crystal particles that constitute the secondary particles. In this way, the crystallinity and connectivity of the metal layer of the current collector can be ensured, the resistance of the battery cell can be reduced, and the micro-gaps in the secondary particles can also act as stress release points.

[0020] In any embodiment, the surface roughness of the composite current collector is ≥ 0.2 μm. In this way, the contact between the composite current collector and the active material can be better, the direct current resistance DCR of the battery cell can be reduced, and the rate performance of the battery can be further improved.

[0021] In any embodiment, the specific surface area of the composite current collector is ≥0.188 m 2 / g. In this way, the contact between the composite current collector and the active material is better, the direct current resistance DCR of the battery cell is further reduced, and the rate performance of the battery is further improved.

[0022] In any embodiment, the sheet resistance growth rate of the composite current collector after 10% ductile tensile stretch and rebound is ≤5%. In this way, the conductivity of the metal layer can be better ensured, and the performance and long-term stability of the battery cell can be ensured.

[0023] In any embodiment, the sheet resistance growth rate of the composite current collector after 30% ductile tensile stretch and rebound is ≤10%. In this way, the performance and long-term stability of the battery cell can be further ensured.

[0024] In any embodiment, the thickness of a single layer of the metal layer is 0.5 μm to 5 μm. In this way, the current collector has good conductivity, and the safety problem caused by the metal layer being too thick can be avoided.

[0025] In any embodiment, the thickness of a single layer of the metal layer is 0.8 μm to 1.5 μm.

[0026] In any embodiment, a single layer of the metal layer comprises a dense layer and a porous layer, the pores are located in the porous layer, the dense layer is arranged on the surface of the organic layer, and the porous layer is arranged on the surface of the dense layer away from the organic layer, or the porous layer is arranged on the surface of the organic layer, and the dense layer is arranged on the surface of the porous layer away from the organic layer. In this way, the battery cell has better interface performance, direct current resistance DCR and rate performance; and the dense layer is arranged on the surface of the organic layer, and the porous layer is arranged on the surface of the dense layer away from the organic layer, which can further improve the adhesion between the metal layer and the organic layer and improve the long-term electrolyte immersion performance of the composite current collector.

[0027] In any embodiment, the density ρ3 of the dense layer is 2.65 g / cm 3 ≤ ρ3 ≤ 2.70 g / cm 3 ; the density ρ4 of the porous layer is 2.00 g / cm 3 ≤ ρ4 < 2.65 g / cm 3 .

[0028] In any embodiment, the thickness of the dense layer is 10% to 50% of the thickness of a corresponding single layer of the metal layer; and the thickness of the porous layer is 50% to 90% of the thickness of a corresponding single layer of the metal layer.

[0029] In any embodiment, the thickness of the dense layer is 100 nm to 500 nm; and the thickness of the porous layer is 500 nm to 900 nm.

[0030] In any embodiment, the longitudinal and / or transverse breaking elongation of the composite current collector is ≥ 50%. In this way, the current collector is less likely to break during processing, improving manufacturing yield; and even if the composite current collector is subjected to a large expansion force or a large deformation during use in a battery cell, the electrode tab is less likely to break.

[0031] In any embodiment, the organic layer comprises an organic polymer film comprising one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene ethylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene sulfonate sodium, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polyazolium, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives, cross-linked products, and copolymers of the above polymers.

[0032] In any embodiment, the thickness of the organic layer is 1 μm to 20 μm.

[0033] In any embodiment, the thickness of the organic layer is 3 μm to 10 μm.

[0034] The second aspect of the present application provides a secondary battery comprising the composite current collector of the first aspect of the present application. In this way, the secondary battery has good rate performance and long-term stability.

[0035] The third aspect of the present application provides an electrical device comprising the secondary battery of the second aspect of the present application.

[0036] The composite current collector of the present application controls the porosity of the metal layer within a certain range and controls the yield strength of the composite current collector within a certain range by providing pores with a certain pore size in the metal layer. The brittleness of the metal layer in the composite current collector can be reduced, the composite current collector has moderate ductility, the metal layer is less likely to crack during processing and subsequent battery cycling, the current collector is less likely to break, and the rate performance and long-term stability of the secondary battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0037] For a better description and illustration of the embodiments and / or examples of the present application, reference can be made to one or more of the accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, presently described embodiments and / or examples, and the best mode presently contemplated of these applications.

[0038] Figure 1 is a structural schematic diagram of a composite current collector according to an embodiment of the present application;

[0039] Figure 2 is a structural schematic diagram of a composite current collector according to another embodiment of the present application;

[0040] Figure 3 is a structural schematic diagram of a composite current collector according to another embodiment of the present application;

[0041] Figure 4 is a longitudinal (MD) tensile curve of a composite current collector according to an embodiment of the present application and a composite current collector with D>2.65;

[0042] Figure 5 is a transverse (TD) tensile curve of a composite current collector according to an embodiment of the present application and a composite current collector with D>2.65;

[0043] Figure 6 is a photograph of surface cracks of a metal layer of a composite current collector with D>2.65 after 30% longitudinal (MD) stretching;

[0044] Figure 7 is a photograph of surface cracks of a metal layer of a composite current collector with D>2.65 after 30% transverse (TD) stretching;

[0045] Figure 8 is a photograph of surface cracks of a metal layer of a composite current collector according to an embodiment of the present application after 30% longitudinal (MD) stretching;

[0046] Figure 9 is a photograph of surface cracks of a metal layer of a composite current collector according to an embodiment of the present application after 30% transverse (TD) stretching;

[0047] Figure 10 is a surface topography diagram of a porous layer in a composite current collector according to an embodiment of the present application;

[0048] Figure 11 is a surface topography diagram of a dense layer in a composite current collector according to an embodiment of the present application;

[0049] Figure 12 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0050] Figure 13 is Figure 12Exploded view of a secondary battery according to an embodiment of the present application.

[0051] Figure 14 Fig. 6 is a schematic view of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0052] Explanation of Reference Numerals:

[0053] 10: composite current collector; 11: organic layer; 12: metal layer; 121: pore; 122: dense layer; 123: pore layer; 5: secondary battery; 51: case; 52: electrode assembly; 53: cover plate; 6: electric device. DETAILED DESCRIPTION

[0054] Hereinafter, some embodiments of the composite current collector, secondary battery, and electric device according to the present application are specifically disclosed with appropriate reference to the drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well and repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0055] The "ranges" disclosed in the present application can be defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this way can be inclusive or exclusive of the end values, either end value can be included or excluded independently, and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained within the range, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing those numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a parameter is an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0056] In the present application, "a plurality of", "a plurality of kinds", and the like, if not specifically limited, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or a number greater than or equal to two.

[0057] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0058] In the present application, the phrase "embodiments" is mentioned, which means that the specific features, structures or properties described in connection with the embodiments can be included in at least one embodiment or embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. Those skilled in the art understand explicitly and implicitly that the embodiments described herein can be combined with other embodiments. The phrase "embodiments" is mentioned in the present application, which has a similar understanding.

[0059] Those skilled in the art can understand that in the method of each embodiment or embodiment, the writing order of each step does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method comprises steps (a) and (b), which means that the method can comprise sequentially performed steps (a) and (b), or sequentially performed steps (b) and (a). For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0060] In the present application, the open technical features or technical solutions described by the words "contain", "include", "comprise" and the like, if not otherwise stated, do not exclude additional members from the listed members, which can be considered as providing a closed feature or solution composed of the listed members, and also providing an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, if not otherwise stated, it can also include other members, or it can not include additional members, which can be considered as providing a feature or solution that "A is composed of a1, a2 and a3", and also providing a feature or solution that "A includes a1, a2 and a3, and also includes other members". In the present application, if not otherwise stated, 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.

[0061] In the present application, "optionally", "optional" and "optional" mean optional, i.e. selected from "yes" or "no" two parallel schemes. If there are multiple "optional" in a technical solution, if there is no special description, and there is no contradiction or mutual restriction relationship, each "optional" is independent.

[0062] The weight described in the specification of the present application can be μg, mg, g, kg and other weight units known in the chemical industry.

[0063] At present, due to the great development of secondary batteries, higher requirements are put forward for the performance of secondary batteries. The secondary battery using composite current collector has great advantages in safety, energy density and cost. However, the secondary battery using composite current collector also has the problems of poor rate performance and poor long-term stability of the battery cell. Therefore, seeking a composite current collector that can improve the rate performance and long-term stability of the secondary battery is one of the directions that the skilled in the art focuses on. For this, the inventors have found a composite current collector which can improve the rate performance and long-term stability of the secondary battery using the composite current collector by setting the structure of the metal layer and the yield strength of the current collector.

[0064] In some embodiments, please refer to Figure 1 , Figure 2 and Figure 3 , the first aspect of the present application provides a composite current collector 10, comprising an organic layer 11 and a metal layer 12 arranged on at least one surface of the organic layer 11; the metal layer 12 has pores 121, at least part of the pores 121 have a pore size of 10 nm to 200 nm, and the porosity of the metal layer 12 is 3% to 20%; the composite current collector 10 satisfies the following relationship:

[0065] ;

[0066] Wherein, σ1 is the breaking strength of the organic layer 11, the unit is MPa; T 有 is the thickness of the organic layer 11, the unit is μm; T 金 is the total thickness of the metal layer 12, the unit is μm; σ s is the yield strength of the composite current collector 10, the unit is MPa.

[0067] The traditional composite current collector 10 is prone to cracks in the metal layer 12 during cold pressing, roll welding and other processes, resulting in a decrease in the conductivity of the metal layer 12 of the composite current collector 10, a large direct current resistance (DCR) of the secondary battery, and an impact on the rate performance and long-term stability of the battery; or the ductility of the composite current collector 10 during cold pressing is too large, the pole piece is prone to deformation, the interface performance is reduced, the direct current resistance of the secondary battery gradually increases during long-term use, and the rate performance and long-term stability are reduced.

[0068] The composite current collector 10 of the present application controls the porosity of the metal layer 12 within a certain range by providing pores 121 with a certain pore size in the metal layer 12, and controls the yield strength of the composite current collector 10 within a certain range; can reduce the brittleness of the metal layer 12 in the composite current collector 10, and make the ductility of the composite current collector 10 moderate during cold pressing, roll welding and other processes. The pores 121 inside the metal layer 12 of the composite current collector 10 during cold pressing, roll welding and other processes can provide stress release points, so that the metal layer 12 is not prone to cracking; the existence of the pores 121 can weaken the brittleness and reduce the elastic modulus of the metal layer 12, improve the ductility of the metal layer 12, reduce the yield strength of the composite current collector 10, so that the metal layer 12 can release stress through the pores 121 when subjected to stress (such as stretching, bending), without producing macroscopic cracks; thereby the composite current collector 10 will not produce macroscopic cracks during processing (such as welding, winding) and subsequent battery cycling, ensuring the conductivity of the composite current collector 10, thereby relieving the increase of DCR during the use of the secondary battery, and being beneficial to improve the rate performance and long-term stability of the secondary battery. The pore size and porosity of the pores 121 in the metal layer 12 are within the above range, which can ensure that the yield strength of the composite current collector 10 is within a suitable range.

[0069] During the stretching process of the composite current collector 10, the point of final fracture is strongly related to the breaking strength of the organic layer 11, and the breaking force of the organic layer 11 is basically close to the final breaking force of the composite current collector 10. Therefore, the breaking force and breaking strength of the current collector can be predicted by the breaking force of the organic layer 11, and the breaking strength of the current collector is approximately equal to the breaking strength of the organic layer σ1*T 有 / (T 有 + T 金), the yield strength of the current collector is controlled between 0.5 times the breaking strength and 0.8 times the breaking strength, so that the composite current collector 10 has a stretchable distance between the turning point of the tensile curve and the breaking strength during the stretching process, so that the strength of the current collector slowly increases after the yield strength, so that the current collector is not prone to breakage, and the current collector has uniform ductility and higher breaking elongation. In addition, the slow increase of the force makes the metal layer bear a smaller force under the same elongation, and the metal layer 12 itself has pores 121 to release stress, so that the metal layer 12 is not prone to macroscopic cracks, so that the conductivity of the current collector is guaranteed during processing and application in the battery. The lower limit of the yield strength of the composite current collector 10 is greater than 0.5 times the breaking strength, so that the yield strength is not too low, and the cold stretching of the current collector is not too large during cold pressing, so that the interface performance of the battery is not reduced, the DCR is not increased, and the rate performance is not reduced.

[0070] The present application controls the porosity of the metal layer 12 within a certain range and controls the yield strength of the composite current collector 10 within a certain range by providing pores 121 with a certain pore size in the metal layer 12 of the composite current collector 10. The brittleness of the metal layer 12 in the composite current collector 10 can be reduced, the composite current collector 10 has moderate ductility, the metal layer 12 in the composite current collector 10 is not prone to cracking during processing and subsequent battery cycling, and the current collector is not prone to breakage, which is beneficial to improve the rate performance and long-term stability of the secondary battery. In addition, the moderate ductility of the composite current collector 10 can also improve the processing yield of the composite current collector 10 and reduce the broken belt during processing.

[0071] It should be noted that the pores 121 in the metal layer 12 can be formed by controlling the single deposition rate to be greater than 500 nm during the deposition of the metal layer 12 on the organic layer 11, so that the metal layer 12 has not been filled with metal at some positions during high-speed production, thereby retaining a certain micro-pore 121. The presence of these pores 121 does not affect the conductivity of the current collector, and can provide a certain stress release point when the metal layer 12 is subjected to external force, so that the metal layer 12 does not produce macroscopic cracks.

[0072] It can be understood that only part of the apertures 121 in the metal layer 12 can have a pore size in the range of 10 nm to 200 nm, or all of the apertures 121 can have a pore size in the range of 10 nm to 200 nm. When the aperture 121 is a spherical hole, the pore size of the aperture 121 is the diameter of the spherical hole; when the aperture 121 is not a spherical hole, the pore size of the aperture 121 is the diameter of a spherical hole with the same volume as the aperture 121, i.e. the equivalent diameter. The porosity of the metal layer 12 can be, but is not limited to, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%. s may be, but is not limited to, 0.5 times, 0.55 times, 0.6 times, 0.65 times, 0.7 times, 0.75 times, 0.8 times of σ1*T 有 / (T 有 + T 金 ).

[0073] In some embodiments, the metal element in the metal layer 12 includes one or more of copper, aluminum, nickel, titanium, platinum, iron, cobalt, chromium, tungsten, molybdenum, magnesium, lead, indium, and tin. In other words, the metal layer 12 in the composite current collector 10 can be a metal copper layer, a metal aluminum layer, a metal nickel layer, a metal titanium layer, a metal platinum layer, a metal iron layer, a metal cobalt layer, a metal chromium layer, a metal tungsten layer, a metal molybdenum layer, a metal magnesium layer, a metal lead layer, a metal indium layer, and a metal tin layer, or an alloy metal layer formed by two or more of the above metal elements.

[0074] In some embodiments, the metal layer 12 is a metal aluminum layer, and the composite current collector 10 satisfies the following relationship:

[0075] 2.00≤D<2.65; ;

[0076] wherein ρ1 is the average density of the composite current collector 10, in g / cm 3 ; and ρ2 is the density of the organic layer 11, in g / cm 3 . It can be understood that, since the composite current collector 10 is a composite structure of the organic layer 11 and the metal layer 12, the densities at different positions of the composite current collector 10 can not be the same, and ρ1 represents the average density of the entire composite current collector 10.

[0077] When the metal layer 12 is a metal aluminum layer, the average density ρ1 of the composite current collector 10, the density ρ2 of the organic layer 11, the total thickness T 金 of the metal layer 12, and the thickness T 有When the above relationship is satisfied, the density of the metal aluminum layer can be within a proper range, the brittleness of the metal layer 12 in the composite current collector 10 can be reduced, better ductility can be obtained, the yield strength of the composite current collector 10 can be within a proper range, the force at the beginning of stretching of the current collector can not be too large, the force shows a slow growth trend during the stretching process of the current collector, and the metal layer 12 is not prone to macroscopic cracks during the stretching and ductility due to the reduced brittleness of the metal layer 12. With the increase of the ductility, the square resistance almost does not increase, and the conductivity is still very good. The composite current collector 10 can still maintain good conductivity at a higher ductility, can improve the DCR and rate performance of the secondary battery, and improve the long-term stability of the secondary battery.

[0078] When D < 2.00, the density of the metal aluminum layer is too poor, there are too many pores 121 or the size of the pores 121 is too large, the elastic modulus of the composite current collector 10 is too low, the yield strength is too low, the cold pressure ductility is too large during the cold pressing process, the pole piece is prone to deformation, the interface performance of the secondary battery is deteriorated, and the short-term and long-term performance of the secondary battery is deteriorated.

[0079] When D ≥ 2.65, the density of the metal aluminum layer is too high, the elastic modulus is very high, there is no good stress release point in the metal aluminum layer, the brittleness of the metal aluminum layer is relatively high, the metal aluminum layer is prone to cracks when subjected to external force (such as ductility, bending, compression, etc.), the conductivity of the metal aluminum layer is weakened, the square resistance is increased, and the rate performance and long-term stability of the secondary battery are deteriorated.

[0080] The longitudinal (MD) tensile curve of the composite current collector 10 with D > 2.65 and the composite current collector 10 with 2.00 ≤ D < 2.65 in the present application is shown in Figure 4 The transverse (TD) tensile curve is shown in Figure 5 .

[0081] The composite current collector 10 with D > 2.65 and the composite current collector 10 with 2.00 ≤ D < 2.65 in the present application are shown in Figure 4 and Figure 5It can be seen that when D < 2.00, the brittleness of the aluminum layer is too strong, resulting in too high yield strength of the current collector, the force reaches a very high value when stretching, thereby reducing the elongation at break of the current collector, and the aluminum layer is prone to crack under external force, thereby affecting the conductivity of the composite current collector 10 and the performance of the secondary battery. When D is in the range of 2.00≤D<2.65, the force borne by the current collector during stretching shows a slow rising state; the elongation at break of the current collector is significantly improved, and the elongation at break in the MD and TD directions is greater than 40%; and the current collector is not prone to crack when stressed, the conductivity is maintained well, the processing and tolerance window of the current collector are improved, thereby ensuring the conductivity of the current collector during processing and use, and ensuring the performance of the battery cell.

[0082] The surface crack picture of the composite current collector 10 with D>2.65 after 30% longitudinal stretch is shown in FIG. 6, and the surface crack picture of the composite current collector 10 after 30% transverse stretch is shown in FIG. 7. Figure 6 The surface crack picture of the composite current collector 10 with D>2.65 after 30% longitudinal stretch is shown in FIG. 6, and the surface crack picture of the composite current collector 10 after 30% transverse stretch is shown in FIG. 7. Figure 7 The surface crack picture of the composite current collector 10 with D>2.65 after 30% longitudinal stretch is shown in FIG. 6, and the surface crack picture of the composite current collector 10 after 30% transverse stretch is shown in FIG. 7. Figure 8 The surface crack picture of the composite current collector 10 with D>2.65 after 30% longitudinal stretch is shown in FIG. 6, and the surface crack picture of the composite current collector 10 after 30% transverse stretch is shown in FIG. 7. Figure 9 The surface crack picture of the composite current collector 10 with D>2.65 after 30% longitudinal stretch is shown in FIG. 6, and the surface crack picture of the composite current collector 10 after 30% transverse stretch is shown in FIG. 7.

[0083] As can be seen from FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 respectively after 30% longitudinal stretch and 30% transverse stretch, the surface thereof has many cracks. Figure 6 As can be seen from FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 respectively after 30% longitudinal stretch and 30% transverse stretch, the surface thereof has many cracks. Figure 7 As can be seen from FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 respectively after 30% longitudinal stretch and 30% transverse stretch, the surface thereof has many cracks. Figure 8 As can be seen from FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 respectively after 30% longitudinal stretch and 30% transverse stretch, the surface thereof has many cracks. Figure 9 As can be seen from FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 respectively after 30% longitudinal stretch and 30% transverse stretch, the surface thereof has many cracks.

[0084] It can be understood that the value of D can be, but is not limited to, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50, 2.55, 2.60.

[0085] In some embodiments, the yield strength of the composite current collector 10 is 120 MPa to 180 MPa. The fracture strength of the organic layer film currently used in the composite current collector 10 is generally 200 MPa to 300 MPa, and controlling the yield strength of the composite current collector 10 in the range of 120 MPa to 180 MPa can make the composite current collector 10 suitable for different types of organic layer films, so that the composite current collector 10 using different organic layers 11 can have higher elongation. Controlling the yield strength of the composite current collector 10 in the above range can prevent the current collector from generating large cracks, and can prevent the current collector from being deformed due to too small yield strength and too large cold rolling extension.

[0086] It can be understood that the yield strength of the composite current collector 10 can be, but is not limited to, 120 MPa, 125 MPa, 130 MPa, 135 MPa, 140 MPa, 145 MPa, 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 175 MPa, 180 MPa.

[0087] In some embodiments, the resistivity of the composite current collector 10 is ≤ 3.5*10 -8 Ωm. The low resistivity of the composite current collector 10 can make the current collector have better conductivity with the same thickness of the metal layer 12, and the same conductivity can be achieved with a thinner metal layer 12, which can improve the energy density of the battery cell. In addition, the thinner metal layer 12 can also improve the safety of the battery cell.

[0088] In some embodiments, the size of the primary single crystal particles of the metal layer 12 (i.e., the grain size) is 35 nm to 80 nm, the size of the secondary particles in the metal layer 12 is 90 nm to 300 nm, and the size of the secondary particles is greater than the sum of the sizes of all the primary particles that make up the secondary particles. Adjacent secondary particles in the metal layer 12 are spaced apart to form pores 121.

[0089] Controlling the size of the primary single crystal particles of the metal layer 12 of the composite current collector 10 to be 35 nm to 80 nm can ensure the crystallinity of the metal layer 12 of the current collector. Controlling the size of the secondary particles in the metal layer 12 to be 90 nm to 300 nm can ensure the connectivity of the current collector. In addition, the size of the secondary particles is slightly larger than the size of all the primary particles that make up the secondary particles, which means that there is a certain micro gap between the primary particles in the secondary particles. These micro gaps between the primary single crystal particles can have a similar effect to the pores 121 in the metal layer 12.

[0090] It should be noted that the primary single crystal particle of the metal layer 12 in the composite current collector 10 can have a size of, but is not limited to, 35 nm, 38 nm, 40 nm, 42 nm, 45 nm, 48 nm, 50 nm, 60 nm, 70 nm, 75 nm, 80 nm; and the size of the secondary particle in the metal layer 12 can be, but is not limited to, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm.

[0091] It can be understood that the size of the primary single crystal particle of the metal layer 12 in the composite current collector 10 can be, but is not limited to, 35 nm, 38 nm, 40 nm, 42 nm, 45 nm, 48 nm, 50 nm, 60 nm, 70 nm, 75 nm, 80 nm; and the size of the secondary particle in the metal layer 12 can be, but is not limited to, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm.

[0092] In some embodiments, the surface roughness of the composite current collector 10 is ≥ 0.2 μm. The larger surface roughness of the composite current collector 10 can make the contact between the composite current collector 10 and the active material better, so that the direct current resistance DCR of the battery cell is reduced, which is beneficial to further improve the rate performance of the battery.

[0093] In some embodiments, the specific surface area of the composite current collector 10 is ≥ 0.188 m 2 / g. The larger specific surface area of the composite current collector 10 can also make the contact between the composite current collector 10 and the active material better, so that the direct current resistance DCR of the battery cell is further reduced, which further improves the rate performance of the battery.

[0094] In some embodiments, the sheet resistance growth rate of the composite current collector 10 after 10% elongation stretching and rebound is ≤ 5%. In this way, the sheet resistance of the composite current collector 10 after stretching and rebound has little growth, which further ensures that the current collector will hardly produce macroscopic cracks in the process of processing, such as cold pressing, so as to ensure the conductivity of the metal layer 12; and ensures that the current collector will hardly produce macroscopic cracks in the use process in the battery cell, so as to ensure the performance and long-term stability of the battery cell.

[0095] In some embodiments, the composite current collector 10 has a sheet resistance growth rate of <10% after 30% tensile elongation and recovery. In this way, the composite current collector 10 has little or no sheet resistance growth after greater elongation, ensuring that the current collector has little or no macroscopic cracking during processing, even under more severe conditions, thereby further ensuring the conductivity of the metal layer 12; and ensuring that the current collector has little or no macroscopic cracking during use in more severe conditions within the battery cell (e.g., high silicon and high swelling, high stress, high deformation systems), thereby further ensuring the performance and long-term stability of the battery cell.

[0096] In some embodiments, the single layer metal layer 12 has a thickness of 0.5 μm to 5 μm, and further, the single layer metal layer 12 has a thickness of 0.8 μm to 1.5 μm. In this way, the single layer metal layer 12 has a thickness that is not too thin and not too thick, allowing the current collector to have good conductivity while avoiding safety issues that can arise from a metal layer 12 that is too thick. It is understood that the single layer metal layer 12 can have a thickness of, but is not limited to, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm.

[0097] In some embodiments, the composite current collector 10 includes two metal layers 12, an upper metal layer and a lower metal layer, with the organic layer 11 disposed between the two metal layers 12. It is understood that in other embodiments, the composite current collector 10 can include only one metal layer 12, i.e., the metal layer 12 is disposed on only one side of the organic layer 11.

[0098] In some embodiments, the single layer metal layer 12 includes a dense layer 122 and a porous layer 123, with the pores 121 disposed within the porous layer 123. Please refer to Figure 2 In some embodiments, the dense layer 122 is disposed on the surface of the organic layer 11, and the porous layer 123 is disposed on the surface of the dense layer 122 that is opposite the surface of the dense layer 122 that is disposed on the surface of the organic layer 11. Please refer to Figure 3In some embodiments, the porous layer 123 is disposed on the surface of the organic layer 11, and the dense layer 122 is disposed on the surface of the porous layer 123 away from the organic layer 11. In this way, the metal layer 12 is combined by the dense layer 122 and the porous layer 123, and the porous layer 123 can make the yield strength of the current collector within a suitable range, ensure the improvement of the fracture elongation of the current collector and the cold rolling extension not to be too large, so as to ensure that the metal layer 12 hardly produces macroscopic cracks during extension and the conductivity hardly decreases, and to ensure that the yield strength is not too low, the cold rolling extension is not too large, the electrode plate does not have too large deformation, and the interface performance, the direct current resistance DCR and the rate capability of the battery cell are ensured. In some embodiments, the dense layer 122 is disposed between the organic layer 11 and the porous layer 123, which is also beneficial to improving the adhesion between the metal layer 12 and the organic layer 11 and improving the long-term electrolyte immersion performance of the composite current collector 10. The surface morphology of the porous layer 123 in the composite current collector 10 is shown in FIG. 2. Figure 10 The surface morphology of the dense layer 122 in the composite current collector 10 is shown in FIG. 3. Figure 11

[0099] The dense layer 122 described above can be obtained by controlling the single deposition thickness of the metal to be 30 nm to 50 nm, controlling the vacuum degree of the deposition to be less than 1*10 -3 Pa, and controlling the deposition rate to be less than or equal to 10 μm*m / min during the preparation of the metal layer 12. The porous layer 123 described above can be obtained by controlling the single deposition thickness of the metal to be greater than or equal to 500 nm, controlling the deposition rate to be greater than or equal to 5 μm*m / min, and introducing inert gas or nitrogen to make the vacuum degree reach 5*10 -2 Pa (the flow rate of the inert gas or nitrogen can be 50 mL / min to 100 mL / min).

[0100] In some embodiments, the density p3 of the dense layer 122 is 2.65 g / cm 3 ≤p3≤2.70 g / cm 3 , and the density p4 of the porous layer 123 is 2.00 g / cm 3 ≤p4<2.65 g / cm 3 . It can be understood that the density of the dense layer 122 can be but is not limited to 2.66 g / cm 3 , 2.67 g / cm 3 , 2.68 g / cm 3 , 2.69 g / cm 3 , 2.70 g / cm 3 , and the density of the porous layer 123 can be but is not limited to 2.00 g / cm 3 , 2.05 g / cm 3 ​2.10 g / cm 3 2.15 g / cm 3 2.20 g / cm 3 2.25 g / cm 3 2.30 g / cm 3 2.35 g / cm 3 2.40 g / cm 3 2.45 g / cm 3 2.50 g / cm 3 2.55 g / cm 3 2.60 g / cm 3 .

[0101] In some embodiments, the thickness of the dense layer 122 is 10% to 50% of the thickness of the corresponding single-layer metal layer 12, and the thickness of the porous layer 123 is 50% to 90% of the thickness of the corresponding single-layer metal layer 12. That is, the thickness of the porous layer 123 in the single-layer metal layer 12 is thicker than the thickness of the dense layer 122. In this way, while effectively improving the adhesion between the metal layer 12 and the organic layer 11, improving the long-term electrolyte immersion performance of the composite current collector 10, and improving the interface performance, direct current resistance DCR, and rate performance of the battery cell.

[0102] It can be understood that the thickness of the dense layer 122 can be, but is not limited to, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50% of the thickness of the corresponding single-layer metal layer 12, and the thickness of the porous layer 123 can be, but is not limited to, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90% of the thickness of the corresponding single-layer metal layer 12.

[0103] In some embodiments, the thickness of the dense layer 122 is 100 nm to 500 nm; and the thickness of the porous layer 123 is 500 nm to 900 nm. It can be understood that the thickness of the dense layer 122 can be, but is not limited to, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm; and the thickness of the porous layer 123 can be, but is not limited to, 500 nm, 520 nm, 540 nm, 560 nm, 580 nm, 600 nm, 620 nm, 640 nm, 660 nm, 680 nm, 700 nm, 720 nm, 740 nm, 760 nm, 780 nm, 800 nm, 820 nm, 840 nm, 860 nm, 880 nm, 900 nm.

[0104] In some embodiments, the longitudinal (MD) and transverse (TD) breaking elongation of the composite current collector 10 is ≥ 40%. In this way, the breaking elongation of the composite current collector 10 is large, which can make the current collector not prone to belt breakage during processing, thereby improving the manufacturing yield; and can also make the composite current collector 10 not prone to tab breakage even under large expansion force or large deformation during use in the battery cell.

[0105] In some embodiments, the organic layer 11 comprises an organic polymer film comprising one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene ethylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene sulfonate sodium, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polythia sulfur, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives, cross-linked products and copolymers of the above polymers.

[0106] In some embodiments, the thickness of the organic layer 11 is 1 μm to 20 μm. It can be appreciated that the thickness of the organic layer 11 can be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm.

[0107] In some embodiments, the thickness of the organic layer 11 is 3 μm to 10 μm.

[0108] A second aspect of the present application provides a secondary battery including the composite current collector of the first aspect of the present application. The secondary battery of the present application employs the composite current collector 10 of the first aspect of the present application, and has good rate performance and long-term stability.

[0109] A third aspect of the present application provides an electric device including the secondary battery of the second aspect of the present application.

[0110] The secondary battery and the electric device of the present application are described below with appropriate reference to the accompanying drawings.

[0111] Unless otherwise specified, the components, material types or contents of the battery mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0112] In one embodiment of the present application, a secondary battery is provided.

[0113] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0114] Positive electrode sheet

[0115] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

[0116] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0117] In some embodiments, the positive electrode current collector can employ the composite current collector of the first aspect of the present application.

[0118] In some embodiments, the positive electrode active material can include a positive electrode active material for a battery known in the art.

[0119] As an example, the positive electrode active material of the lithium ion secondary battery can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery can also be used. These positive electrode active materials can be used alone only one or two or more of them can be used in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and a modified compound thereof. Examples of the lithium-containing phosphate of the olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which can also be referred to simply as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0120] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0121] In the examples of cathode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0122] As an example, the positive electrode active material of a sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0123] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0124] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0125] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0126] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0127] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0128] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0129] The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0130] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder accounts for 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0131] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0132] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40% to 80% by mass, and the viscosity at room temperature is adjusted to 5000 mPa·s to 25000 mPa·s. The positive electrode slurry is then coated onto the surface of the positive current collector, dried, and cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 150 mg / m². 2 ~350 mg / m 2 The compacted density of the positive electrode sheet is 3.0 g / cm³. 3 ~3.6 g / cm 3 3.3g / cm³ is an option. 3 ~3.5 g / cm 3 .

[0133] The formula for calculating the compaction density is:

[0134] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0135] The mass M of the positive electrode active material per unit area of ​​the positive electrode membrane can be obtained by weighing using a standard balance.

[0136] The thickness T of the positive electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film mentioned in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for battery assembly after cold pressing and compaction.

[0137] Negative electrode sheet

[0138] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0139] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0140] In some embodiments, the negative electrode current collector may be a composite current collector according to the first aspect of this application.

[0141] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0142] As an example, the negative electrode active material of a lithium-ion secondary battery may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0143] As an example, the negative electrode active material of a sodium-ion secondary battery is typically a hard carbon material, a two-dimensional metal carbide, or a nitride. Preferably, the negative electrode active material of a sodium-ion secondary battery is a hard carbon material.

[0144] The negative electrode active material accounts for 70-100% by weight in the negative electrode film, based on the total weight of the negative electrode film.

[0145] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one 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). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0146] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0 to 20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0147] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight percentage of the other additives in the negative electrode film is 0-15% by weight, based on the total weight of the negative electrode film.

[0148] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30wt%~70wt%, and the viscosity at room temperature is adjusted to 2000 mPa·s~10000 mPa·s; the obtained negative electrode slurry is coated onto a negative electrode current collector, and after a drying process, cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coating is 75 mg / m². 2 ~220 mg / m 2 The compacted density of the negative electrode sheet is 1.2 g / m³. 3 ~2.0 g / m 3 .

[0149] The mass M of the negative electrode active material per unit area of ​​the negative electrode membrane can be obtained by weighing using a standard balance.

[0150] The thickness T of the negative electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the negative electrode film mentioned in this application refers to the thickness of the negative electrode film in the negative electrode sheet used for battery assembly after cold pressing and compaction.

[0151] electrolytes

[0152] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0153] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0154] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0155] The electrolyte salt for sodium-ion secondary batteries can be selected from one or more of the following: sodium hexafluorophosphate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0156] The concentration of the electrolyte salt is typically 0.5 mol / L to 5 mol / L.

[0157] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0158] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0159] Separating membrane

[0160] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0161] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0162] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0163] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0164] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0165] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0166] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 12 This is an example of a square-structured secondary battery 5.

[0167] In some implementations, refer to Figure 13 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0168] In some embodiments, the secondary battery 5 can be assembled into a battery module, and the number of secondary batteries 5 contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0169] In the battery module, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be secured with fasteners.

[0170] Optionally, the battery module may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0171] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0172] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0173] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0174] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0175] Figure 14 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0176] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0177] The following are some examples.

[0178] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0179] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0180] I. Implementation Examples

[0181] Example 1

[0182] 1) Positive electrode plate

[0183] LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiNi 0.5 Co 0.2 Mn 0.3 O2 is mixed in a ratio of 17:3 as the positive electrode active material. The positive electrode active material, superconducting carbon black SP as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP) as a solvent at a mass ratio of 95:3:2 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on a composite current collector, and after drying, cold pressing, edge welding, die cutting, and slitting, a positive electrode sheet is obtained.

[0184] 2) Negative electrode plate

[0185] The negative electrode active material graphite, superconducting carbon black SP as a conductive agent, SBR as a binder, and CMC-Na as a thickener are dispersed in deionized water as a solvent at a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto a negative electrode current collector copper foil. After drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0186] 3) Separating membrane

[0187] Using a 9 μm thick polyethylene (PE) membrane as the base membrane, alumina, sodium carboxymethyl cellulose (CMC), and acrylate in a weight ratio of 93%:3%:4% were added to deionized water and stirred evenly under vacuum to obtain a slurry with a solid content of 55%. The obtained slurry was uniformly coated onto the base membrane with a thickness of 2 μm on one side, and then PVDF was coated on both sides to obtain the separator.

[0188] 4) Cell assembly

[0189] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as an isolation between the positive and negative electrode. The cells are then wound to obtain a bare cell, tabs are welded on, the bare cell is installed in a square aluminum shell, and the top cover is laser welded on.

[0190] 5) Cell electrolyte injection

[0191] After vacuum baking to remove moisture at 100 °C, electrolyte is injected and the battery is sealed. Subsequently, the battery undergoes a series of processes including standing at 45 °C, formation (0.02 C constant current charging to 3.3 V, then 0.1 C constant current charging to 3.6 V), shaping, and capacity testing to obtain the finished hard-shell lithium-ion battery.

[0192] Example 1: The positive electrode current collector is a composite current collector. The porosity of the metal layer is 3%, with 50% of the pores having a size between 10 nm and 200 nm. The tensile strength of the organic layer is 305 MPa, and the thickness of the metal layer is 1 μm. The metal element is aluminum, and the aluminum metal layer is deposited using a vacuum deposition method with a vacuum degree of approximately 1*10⁻⁶. -2 Pa, one-pass coating molding method, some detailed current collector parameters are shown in Table 1.

[0193] Example 2

[0194] This embodiment is basically the same as Embodiment 1, with the main difference being the porosity, roughness, and specific surface area of ​​the metal layer in the positive electrode current collector, resulting in different yield strengths of the current collector. In this embodiment, the porosity of the metal layer is 7%, the roughness is 0.23 μm, and the specific surface area is 0.192 g / m². 2 The yield strength of the current collector is 161 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0195] Example 3

[0196] This embodiment is basically the same as Embodiment 1, with the main difference being that the porosity, roughness, and specific surface area of ​​the metal layer in the positive electrode current collector are different, resulting in different yield strengths of the current collector. In this embodiment, the porosity of the metal layer is 11%, the roughness is 0.25 μm, and the specific surface area is 0.195 g / m². 2The yield strength of the current collector is 150 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0197] Example 4

[0198] This embodiment is basically the same as Embodiment 1, with the main difference being the porosity, roughness, and specific surface area of ​​the metal layer in the positive electrode current collector, resulting in different yield strengths of the current collector. In this embodiment, the porosity of the metal layer is 15%, the roughness is 0.27 μm, and the specific surface area is 0.201 g / m². 2 The yield strength of the current collector is 141 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0199] Example 5

[0200] This embodiment is basically the same as Embodiment 1, with the main difference being the porosity, roughness, and specific surface area of ​​the metal layer in the positive electrode current collector, resulting in different yield strengths of the current collector. In this embodiment, the porosity of the metal layer is 20%, the roughness is 0.29 μm, and the specific surface area is 0.21 g / m². 2 The yield strength of the current collector is 120 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0201] Example 6

[0202] This embodiment is basically the same as Embodiment 1, with the main difference being that the metal layer of the positive electrode current collector consists of two structures (a dense layer + a porous layer). Specifically, the preparation method involves first depositing a thin metal layer as the dense layer using a slow deposition method, with a single deposition depth of approximately 30 nm and a thickness of 0.5 μm; then, a porous layer with a thickness of 0.5 μm is deposited on the surface of the dense layer using a fast deposition method, with a single deposition thickness of 0.5 μm. The porosity of the metal layer is 5%, the roughness is 0.21 μm, and the specific surface area is 0.19 g / m². 2 The yield strength of the current collector is 169 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0203] Example 7

[0204] This embodiment is basically the same as Embodiment 6, with the main difference being: the thickness of the dense layer of the positive electrode current collector is 0.3 μm, and the thickness of the porous layer is 0.7 μm. The porosity of the metal layer is 8%, the roughness is 0.23 μm, and the specific surface area is 0.193 g / m². 2 The yield strength of the current collector is 157 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0205] Example 8

[0206] This embodiment is basically the same as Embodiment 7, with the main difference being: the thickness of the dense layer of the positive electrode current collector is 0.1 μm, and the thickness of the porous layer is 0.9 μm. The porosity of the metal layer is 10%, the roughness is 0.24 μm, and the specific surface area is 0.194 g / m². 2 The yield strength of the current collector is 152 MPa. Some detailed parameters of the current collector are shown in Table 1.

[0207] Example 9

[0208] This embodiment is basically the same as Embodiment 3, with the main difference being the material of the organic layer in the positive electrode current collector. In Embodiment 9, the organic layer is a PI (polyimide) film. Some detailed current collector parameters are shown in Table 1.

[0209] Examples 10-13

[0210] This embodiment is basically the same as Embodiment 3, with the main difference being the size of the primary single crystal particles, the size of the secondary single crystal particles, and the resistivity of the positive electrode current collector. Some detailed current collector parameters are shown in Table 2.

[0211] II. Comparative Example

[0212] Comparative Example 1

[0213] This comparative example is basically the same as Example 1, with the main difference being the different positive electrode current collector. In Comparative Example 1, the positive electrode current collector uses the composite current collector of this application, which has a metal layer porosity of 0.5%, a roughness of 0.15 μm, and a specific surface area of ​​0.167 m². 2 / g, yield strength σ of the composite current collector s The pressure is 200 MPa. Some detailed current collector parameters are shown in Table 2.

[0214] Comparative Example 2

[0215] This comparative example is basically the same as Example 1, with the main difference being the different positive electrode current collector. In Comparative Example 2, the positive electrode current collector uses the composite current collector of this application, which has a metal layer porosity of 30%, a roughness of 0.35 μm, and a specific surface area of ​​0.246 m². 2 / g, yield strength σ of the composite current collector s The pressure is 105 MPa. Some detailed current collector parameters are shown in Table 2.

[0216] Comparative Example 3

[0217] This comparative example is basically the same as Example 13, with the main difference being the different positive electrode current collector. In Comparative Example 3, the positive electrode current collector uses the composite current collector of this application, which has a porosity of 0.5%, a roughness of 0.15 μm, and a specific surface area of ​​0.103 m².2 / g, yield strength is 165 MPa. Some detailed current collector parameters are shown in Table 2.

[0218] III. Testing Methods

[0219] 1) Pore diameter testing

[0220] Take a surface sample and measure the diameter of the surface pores under SEM. Take the average value of multiple diameter measurements.

[0221] 2) Porosity test

[0222] Take a fixed area S (e.g., 100cm²) 2 The sample was analyzed using a true density meter (AccopycⅡ1340) and the formula PV=nRT. The true volume V1 of the current collector sample was obtained. Because the micropores inside the metal layer are wrapped by the surface metal, gas cannot permeate. Therefore, the true volume is larger than the theoretical volume of the closely packed metal. The true volume V1 includes two parts: one part is the volume V of the organic layer. 有 ( T 有 (where the organic layer thickness is one part is the volume V of the metal layer) 金1 , The theoretical density of tightly packed metal layers (k) 金 Current collector weight (m) 集 and the density of the organic layer 有 Organic layer thickness T 有 The theoretical volume of the metal layer was calculated to be V. 金2 ( ),in , .

[0223] 3) Composite current collector yield strength test

[0224] Tensile tests were performed using a tensile testing machine with an initial distance of 50 mm and a stretching speed of 50 mm / min. The inflection point of the tensile curve can be read from the tensile curve, which corresponds to the yield strength.

[0225] 4) Organic layer fracture strength test

[0226] Tensile tests were performed using a tensile testing machine. An initial distance of 50 mm was used, and the tensile test was performed at a speed of 50 mm / min. The elongation at the fracture location was recorded.

[0227] 5) Resistivity test

[0228] Samples were taken for sheet resistance testing, and then cross-sectional samples were prepared using a cross-section sample preparation machine. The thickness of the single-sided metal layer was then observed under SEM. Resistivity = sheet resistance * thickness of single-sided metal layer.

[0229] 6) Grain size testing

[0230] XRD was used for testing, and then the single crystal particle size was calculated using the Scherer formula.

[0231] 7) Surface roughness test

[0232] Surface roughness was tested using a roughness tester, and the Ra value was determined.

[0233] 8) Specific surface area test

[0234] The BET method was used for testing.

[0235] 9) 10% stretching and rebound resistance growth rate test

[0236] The current collector is cut into strips of 15 mm * 150 mm. Its initial surface sheet resistance is measured, and then it is stretched by 10%. The surface sheet resistance of the first stretched area is tested after stretching. The growth rate is calculated as (sheet resistance after stretching - sheet resistance before stretching) / sheet resistance before stretching.

[0237] 10) 30% stretching and rebound resistance growth rate test

[0238] The current collector is cut into strips of 15 mm * 150 mm. Its initial surface sheet resistance is measured, and then it is stretched by 30%. The surface sheet resistance of the first stretched area is tested after stretching. The growth rate is calculated as (sheet resistance after stretching - sheet resistance before stretching) / sheet resistance before stretching.

[0239] 11) Elongation at break test

[0240] Cut the current collector into strips of 15 mm * 150 mm and perform tensile testing using a universal tensile testing machine at a gauge length of 50 mm and a tensile speed of 50 mm / min until the test results in fracture. Test 10 strips and take the average value.

[0241] 12) Cell DCR Test

[0242] Adjust the individual battery cells to 50% SOC and discharge them at a 4C rate (corresponding to a discharge current of I) for 30 seconds. Record the voltage difference ΔV before and after the 30-second discharge. Calculate the DCR corresponding to 50% SOC using the following formula: DCR = ΔV / I, to obtain the DCR data for each battery cell.

[0243] 13) Ratio Performance Test

[0244] A fresh battery is fully charged at 0.33C at room temperature (25°C) and then discharged; the initial discharge capacity is recorded as C0. Then, the battery is discharged at 2C at room temperature (25°C); the discharge capacity at this point is recorded as C1. The capacity retention rate is calculated using the following formula:

[0245] Capacity retention rate = C1 / C0 × 100%.

[0246] 14) Long-term stability test

[0247] Fresh battery cells were cycled at 60°C using a 1C charge and 1C discharge rate until their capacity decreased to 80% of their initial capacity. The number of cycles at this point was recorded. This yielded the cycle count data for each battery cell.

[0248] The parameters and performance test results of the above embodiments and comparative examples are shown in Tables 1 and 2.

[0249] Table 1

[0250]

[0251]

[0252] Table 2

[0253]

[0254] A comparison of Examples 1-5 with Comparative Example 1 shows that when the porosity is between 3% and 20%, the yield strength of the current collector is between 120 MPa and 180 MPa, which is less than the fracture strength of the organic layer of 305 MPa. Corresponding to 114 MPa, The yield strength corresponds to 183 MPa; the yield strength is between the two, causing the tensile stress of the current collector to show a slow increasing trend, resulting in a higher elongation at break, greater than 50%; Comparative Example 1, due to its excessively low porosity of only 0.5%, results in a higher yield strength (200 MPa) for the current collector, exceeding... The range corresponds to 183 MPa, which causes the current collector to experience a rapid increase in stress with increasing elongation during stretching, thereby reducing the elongation at break (~35%). At the same time, since the elongation at break of Examples 1-5 is significantly higher than that of Comparative Example 1, the sheet resistance growth rate corresponding to 10% and 30% stretching of Examples 1-5 is lower than that of Comparative Example 1 (under the same elongation, Examples 1-5 experience less force than Comparative Example 1). As a result, the cell performance of Examples 1-5 is better than that of Comparative Example 1, especially in terms of long-term cycle performance. During long-term cycling, samples with a large increase in sheet resistance at stretching rebound have more surface cracks, and the metal layer is more susceptible to corrosion by the electrolyte during cell use, thus resulting in poorer cycle performance of the cell.

[0255] By comparing Comparative Example 2 with Examples 1-5, it can be seen that the porosity of Comparative Example 2 reaches 30%. Due to the excessive porosity, the modulus of the metal layer is reduced, which leads to a decrease in the yield strength of the current collector (only 105 MPa). At this point, the reduction in yield strength has no significant improvement on the elongation at break. However, the low yield strength leads to an increase in the extension or other deformation of the current collector during cold pressing and other electrode processing, resulting in electrode deformation and a deterioration in the interface performance of the cell. This leads to a deterioration in the DCR and rate performance of the cell, and the deterioration of the kinetics will also lead to a deterioration in the long-term cycle performance.

[0256] Examples 6-8 include a dense layer and a porous layer, with the dense layer comprising 10% to 50%. A thicker dense layer increases the yield strength of the current collector and relatively reduces its elongation at break. Simultaneously, the presence of the porous layer prevents the yield strength of the current collector from becoming excessively high. The coexistence of the dense and porous layers allows the dense layer to effectively prevent electrolyte penetration to the surfaces of the metal and organic layers, preventing delamination and thus contributing to improved long-term cycle stability of the cell (higher cycle count compared to Examples 1-5 with only a porous layer). Compared to Comparative Example 1 (with only a dense layer), it effectively avoids the decrease in elongation caused by excessively high yield strength, which leads to an increase in the rate of increase in tensile springback sheet resistance, thus preventing deterioration of cell performance. The presence of both the dense and porous layers ensures that yield strength, elongation, and electrical performance are all at a good level.

[0257] Example 9: Even with a different organic layer, a high elongation rate, good DCR, rate capability, and cycle performance can still be achieved.

[0258] In Examples 3 and 10-12, the porosity was maintained at 11%. The difference was the size of the primary single crystal particles and the size of the secondary particles (the primary single crystal particle size was 35-80 nm, and the secondary particle size was 90-300 nm). The yield strength was in a moderate position, and good ductility, tensile resilience and cell performance were obtained. The larger primary crystal size obtained better performance.

[0259] A comparison of Example 13 and Comparative Example 3 shows that when the metal layer is copper, the porosity is within a suitable range (5%), which can significantly improve the elongation at break of the copper composite current collector, thereby improving the performance of the battery cell. When the copper is close to a fully dense state (porosity 0.5%), the elongation at break is significantly reduced due to the excessively high yield strength, making it easy for cracks to form during the stretching process. The increase in the stretching springback sheet resistance growth rate increases the risk of electrode cracking and breakage during long-term cycling, thus deteriorating the performance of the battery cell (including DCR, rate capability, and cycle performance).

[0260] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite current collector, characterized in that, It includes an organic layer and a metal layer disposed on at least one surface of the organic layer; The metal layer has pores, at least a portion of which have a pore size of 10 nm to 200 nm, and the porosity of the metal layer is 3% to 20%. The composite current collector has a yield strength of 120 MPa to 180 MPa, the thickness of the single metal layer is 0.5 μm to 5 μm, and the thickness of the organic layer is 1 μm to 20 μm.

2. The composite current collector according to claim 1, characterized in that, The composite current collector satisfies the following relationship: ； Wherein, σ1 is the tensile strength of the organic layer, in MPa; T 有 T represents the thickness of the organic layer, in μm. 金 σ represents the total thickness of the metal layer, in μm; s The yield strength of the composite current collector is given in MPa.

3. The composite current collector according to any one of claims 1 to 2, characterized in that, The metallic elements in the metal layer include one or more of copper, aluminum, nickel, titanium, platinum, iron, cobalt, chromium, tungsten, molybdenum, magnesium, lead, indium, and tin.

4. The composite current collector according to any one of claims 1 to 3, characterized in that, The metal layer is an aluminum layer, and the composite current collector satisfies the following relationship: ； Wherein, ρ1 is the average density of the composite current collector, in g / cm³. 3 ρ2 is the density of the organic layer, in g / cm³. 3 .

5. The composite current collector according to any one of claims 1 to 4, characterized in that, The composite current collector satisfies at least one of the following: (1) The resistivity of the composite current collector is ≤3.5*10 -8 Ωm; (2) The surface roughness of the composite current collector is ≥0.2 μm; (3) The specific surface area of ​​the composite current collector is ≥0.188 m². 2 / g; (4) The sheet resistance growth rate of the composite current collector after 10% stretching and springback is ≤5%; (5) The sheet resistance growth rate of the composite current collector after 30% stretching and springback is ≤10%; (6) The longitudinal elongation at break of the composite current collector is ≥40%; (7) The transverse fracture elongation of the composite current collector is ≥40%.

6. The composite current collector according to any one of claims 1 to 5, characterized in that, The primary single-crystal particles in the metal layer have a size of 35 nm to 80 nm, and the secondary particles in the metal layer have a size of 90 nm to 300 nm.

7. The composite current collector according to any one of claims 1 to 6, characterized in that, The thickness of a single metal layer is 0.8 μm to 1.5 μm.

8. The composite current collector according to any one of claims 1 to 7, characterized in that, The single-layer metal layer includes a dense layer and a porous layer, with the pores located within the porous layer; the dense layer is disposed on the surface of the organic layer, and the porous layer is disposed on the surface of the dense layer opposite to the organic layer; or the porous layer is disposed on the surface of the organic layer, and the dense layer is disposed on the surface of the porous layer opposite to the organic layer.

9. The composite current collector according to claim 8, characterized in that, The density ρ3 of the dense layer is 2.65 g / cm³. 3 ≤ρ3≤2.70 g / cm 3 The density ρ4 of the porous layer is 2.00 g / cm³. 3 ≤ρ4<2.65 g / cm 3 .

10. The composite current collector according to claim 8, characterized in that, The composite current collector satisfies at least one of the following: (1) The thickness of the dense layer is 10% to 50% of the thickness of the corresponding single metal layer, and the thickness of the porous layer is 50% to 90% of the thickness of the corresponding single metal layer; (2) The thickness of the dense layer is 100 nm to 500 nm; the thickness of the porous layer is 500 nm to 900 nm.

11. The composite current collector according to any one of claims 1 to 10, characterized in that, The organic layer comprises an organic polymer, including one or more of the following: polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polysulfide, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives, crosslinks, and copolymers of the above polymers.

12. The composite current collector according to any one of claims 1 to 11, characterized in that, The thickness of the organic layer is 3 μm to 10 μm.

13. A secondary battery comprising the composite current collector as described in any one of claims 1 to 12.

14. An electrical device comprising the secondary battery of claim 13.

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