Composite current collector, secondary battery, and electric device

Abstract

The application provides a composite current collector, a secondary battery and a power consumption device. The composite current collector comprises an organic layer and a metal layer arranged on at least one surface of the organic layer; the metal layer has pores, at least part of the pores has a pore size of 10 nm to 200 nm, and the porosity of the metal layer is 3% to 20%; the composite current collector satisfies the following relationship: 0.5*σ1*T 有 / (T 有 +T 金 )≤σ s ≤0.8*σ1*T 有 / (T 有 +T 金 ); 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; and σ s is the yield strength of the composite current collector, in MPa. The composite current collector can improve the rate performance and stability of the secondary battery.

Description

TECHNICAL FIELD

[0001] 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

[0002] In recent years, with the application range of secondary batteries becoming more and more extensive, 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.

[0003] 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 current secondary batteries using composite current collectors also have the problems of poor rate performance and poor stability of the battery cell.

[0004] Therefore, it is one of the focuses of the person skilled in the art to seek secondary batteries using composite current collectors with good rate performance and good stability. SUMMARY

[0005] The present application is carried out 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.

[0006] 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;

[0007] 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%;

[0008] The composite current collector satisfies the following relationship:

[0009] 0.5*σ1*T 有 / (T 有 +T 金 )≤σ s ≤0.8*σ1*T 有 / (T 有 +T 金 );

[0010] 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.

[0011] 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, and the current collector is not prone to breaking, thereby improving the rate performance and stability of the secondary battery.

[0012] In any embodiment, the metal element in the metal layer includes one or more of copper, aluminum, nickel, titanium, platinum, iron, cobalt, chromium, tungsten, molybdenum, magnesium, lead, indium, and tin.

[0013] In any embodiment, the metal layer is a metal aluminum layer, and the composite current collector satisfies the following relationship:

[0014]

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 make up 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.

[0019] 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 is better, the direct current resistance DCR of the battery cell is reduced, and the rate performance of the battery is further improved.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In any embodiment, the thickness of a single layer of the metal layer is 0.8 μm to 1.5 μm.

[0025] 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 arranged on the surface of the organic layer and the porous layer arranged on the surface of the dense layer away from the organic layer can also improve the adhesion between the metal layer and the organic layer and improve the long-term electrolyte immersion performance of the composite current collector.

[0026] In any embodiment, the density p3 of the dense layer is 2.65 g / cm 3 ≤ p3 ≤ 2.70 g / cm 3 , and the density p4 of the porous layer is 2.00 g / cm 3 ≤ p4 < 2.65 g / cm 3 .

[0027] 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.

[0028] 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.

[0029] 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 the composite current collector is less likely to break even under large swelling forces or large deformations during use in a battery cell.

[0030] 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, polyazulphide, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives, cross-linked products, and copolymers thereof.

[0031] In any embodiment, the thickness of the organic layer is 1 μm to 20 μm.

[0032] In any embodiment, the thickness of the organic layer is 3 μm to 10 μm.

[0033] 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.

[0034] The third aspect of the present application provides an electrical device comprising the secondary battery of the second aspect of the present application.

[0035] The composite current collector of the present application controls the porosity of the metal layer within a certain range by providing pores with a certain pore size in the metal layer, and controls the yield strength of the composite current collector within a certain range; can reduce the brittleness of the metal layer in the composite current collector, make the composite current collector have moderate ductility, make the metal layer of the composite current collector not easy to produce cracks during processing and subsequent battery cycle, 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

[0036] 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.

[0037] Figure 1 is a structural schematic diagram of a composite current collector of an embodiment of the present application;

[0038] Figure 2 is a structural schematic diagram of a composite current collector of another embodiment of the present application;

[0039] Figure 3 is a structural schematic diagram of a composite current collector of another embodiment of the present application;

[0040] Figure 4 is a longitudinal (MD) tensile curve of a composite current collector of an embodiment of the present application and a composite current collector of D>2.65;

[0041] Figure 5 is a transverse (TD) tensile curve of a composite current collector of an embodiment of the present application and a composite current collector of D>2.65;

[0042] Figure 6 is a photograph of surface cracks of a metal layer of a composite current collector of D>2.65 after 30% longitudinal (MD) stretching;

[0043] Figure 7 is a photograph of surface cracks of a metal layer of a composite current collector of D>2.65 after 30% transverse (TD) stretching;

[0044] Figure 8 is a photograph of surface cracks of a metal layer of a composite current collector of an embodiment of the present application after 30% longitudinal (MD) stretching;

[0045] Figure 9 is a photograph of surface cracks of a metal layer of a composite current collector of an embodiment of the present application after 30% transverse (TD) stretching;

[0046] Figure 10 is a surface topography diagram of a porous layer in a composite current collector of an embodiment of the present application;

[0047] Figure 11 is a surface topography diagram of a dense layer in a composite current collector of an embodiment of the present application;

[0048] Figure 12 is a schematic diagram of a secondary battery of an embodiment of the present application;

[0049] Figure 13 is Figure 12Exploded view of a secondary battery according to an embodiment of the present application;

[0050] 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.

[0051] Explanation of Reference Numerals:

[0052] 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

[0053] 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.

[0054] 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 are listed, and if a maximum range value of 3, 4 and 5 is also listed, 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.

[0055] In the present application, "a plurality of", "a plurality of kinds", and the like, if not specifically limited, refer to more than two or equal to two in number. For example, "one or more" means one or more than two.

[0056] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0057] In the present application, the phrase "embodiments" is mentioned, which means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment or embodiment of the present application. The appearance of this phrase 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.

[0058] 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.

[0059] 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 both a closed feature or solution composed of listed members, and 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 the feature or solution that "A is composed of a1, a2 and a3", and also providing the 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.

[0060] In the present application, "optionally", "optional", "option" means optional, that is, selected from "yes" or "no" two parallel schemes. If there are multiple "options" in a technical solution, if there is no special description, and there is no contradiction or mutual restriction relationship, each "option" is independent.

[0061] The weight described in the specification of the present application can be μg, mg, g, kg, etc. weight units known in the chemical industry.

[0062] 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.

[0063] 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:

[0064] 0.5*σ1*T 有 / (T 有 +T 金 )≤σ s ≤0.8*σ1*T 有 / (T 有 +T 金 );

[0065] Wherein, σ1 is the breaking strength of the organic layer 11, unit: MPa; T 有 is the thickness of the organic layer 11, unit: μm; T 金 is the total thickness of the metal layer 12, unit: μm; σ s is the yield strength of the composite current collector 10, unit: MPa.

[0066] 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 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 DCR of the secondary battery gradually increases during long-term use, and the rate performance and long-term stability are reduced.

[0067] 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.

[0068] 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 composite current collector 10 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 composite current collector slowly increases after the yield strength, so that the composite current collector is not prone to breaking, and the composite current collector has uniform ductility and higher breaking elongation. In addition, the slowly increasing 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 composite 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 cold pressing process does not cause the composite current collector to deform, the interface performance of the battery to decrease, the DCR to increase, and the rate performance to decrease.

[0069] 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 composite current collector 10 is not prone to breaking, 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.

[0070] 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.

[0071] 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 ).

[0072] 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.

[0073] In some embodiments, the metal layer 12 is a metal aluminum layer, and the composite current collector 10 satisfies the following relationship:

[0074] 2.00≤D<2.65;

[0075] wherein ρ1 is the average density of the composite current collector 10, in g / cm 3 ; 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 .

[0080] 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.

[0081] 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.

[0082] As shown in FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 after 30% longitudinal stretch and 30% transverse stretch respectively, the surface of which produces a lot of cracks. Figure 6 As shown in FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 after 30% longitudinal stretch and 30% transverse stretch respectively, the surface of which produces a lot of cracks. Figure 7 As shown in FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 after 30% longitudinal stretch and 30% transverse stretch respectively, the surface of which produces a lot of cracks. Figure 8 As shown in FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 after 30% longitudinal stretch and 30% transverse stretch respectively, the surface of which produces a lot of cracks. Figure 9 As shown in FIG. 6 and FIG. 7, the composite current collector 10 with D>2.65 after 30% longitudinal stretch and 30% transverse stretch respectively, the surface of which produces a lot of cracks.

[0083] 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.

[0084] In some embodiments, the yield strength of the composite current collector 10 is 120 MPa to 180 MPa. The breaking 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 applicable to 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] It should be noted that the size of the primary single crystal particles is determined by XRD diffraction peaks, and the size of the primary single crystal particles can be calculated using the Scherer formula based on the full width at half maximum (FWHM). The size of the secondary particles is determined by surface SEM measurement, and the average value is taken after measuring the size of more than 50 secondary particles.

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

[0091] In some embodiments, the surface roughness of the composite current collector 10 is ≥0.2μm. A larger surface roughness of the composite current collector 10 allows for better contact between the composite current collector 10 and the active material, resulting in a lower DC resistance (DCR) of the battery cell and further improving the rate performance of the battery.

[0092] In some embodiments, the specific surface area of ​​the composite current collector 10 is ≥0.188 m². 2 / g. The composite current collector 10 has a larger specific surface area, which can also improve the contact between the composite current collector 10 and the active material, thereby further reducing the DC resistance DCR of the cell and further improving the rate performance of the battery.

[0093] In some embodiments, the sheet resistance growth rate of the composite current collector 10 after 10% stretching and springback is ≤5%. Thus, the stretching and springback sheet resistance of the composite current collector 10 shows almost no growth, further ensuring that the current collector will hardly generate macroscopic cracks during processing, such as cold pressing, thereby ensuring the conductivity of the metal layer 12; and ensuring that the current collector will hardly generate macroscopic cracks during use inside the battery cell, thereby ensuring the battery cell performance and long-term stability.

[0094] 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 macro-cracks during processing, even in more severe conditions, thereby further ensuring the conductivity of the metal layer 12; and ensuring that the current collector has little or no macro-cracks during use in more severe conditions inside the battery cell (e.g. high silicon and high expansion, high stress, high deformation systems), thereby further ensuring the performance and long-term stability of the battery cell.

[0095] 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 thickness of the single layer metal layer 12 is not too thin nor too thick, allowing the current collector to have good conductivity while avoiding safety issues due to the metal layer 12 being too thick. It is understood that the thickness of the single layer metal layer 12 can be, 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.

[0096] In some embodiments, the composite current collector 10 includes two metal layers 12, 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.

[0097] 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 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, and can ensure that the metal layer 12 almost does not produce macroscopic cracks when being extended, and the conductivity almost does not decrease; and can ensure that the yield strength is not too low, the cold rolling extension is not too large, and 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 improve the adhesion between the metal layer 12 and the organic layer 11, and improve 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. 3. Figure 10 The surface morphology of the dense layer 122 in the composite current collector 10 is shown in FIG. 4. Figure 11

[0098] 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 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).

[0099] 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 .

[0100] 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.

[0101] 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%, 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%, 90% of the thickness of the corresponding single-layer metal layer 12.

[0102] In some embodiments, the thickness of the dense layer 122 is 100 nm to 500 nm; 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; 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.

[0103] In some embodiments, the longitudinal (MD) and transverse (TD) breaking elongation of the composite current collector 10 are both ≥ 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 swelling force or large deformation during use in the battery cell.

[0104] 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, polyazolium, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and derivatives, cross-linked products and copolymers of the above polymers.

[0105] In some embodiments, the thickness of the organic layer 11 is 1 μm to 20 μm. It can be understood 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.

[0106] In some embodiments, the thickness of the organic layer 11 is 3 μm to 10 μm.

[0107] 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.

[0108] A third aspect of the present application provides an electric device including the secondary battery of the second aspect of the present application.

[0109] The secondary battery and the electric device of the present application are described below with appropriate reference to the accompanying drawings.

[0110] 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.

[0111] In one embodiment of the present application, a secondary battery is provided.

[0112] 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 and extracted between 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 functions to prevent short circuiting between the positive and negative electrodes, while allowing ions to pass through.

[0113] Positive electrode sheet

[0114] 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.

[0115] 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.

[0116] In some embodiments, the positive electrode current collector can employ the composite current collector of the first aspect of the present application.

[0117] In some embodiments, the positive electrode active material can include a positive electrode active material for a battery known in the art.

[0118] As an example, the positive electrode active material of the lithium ion secondary battery can include at least one of a lithium-containing phosphate having 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 battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination. 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(also referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of the lithium-containing phosphate having an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4(also 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.

[0119] It can be understood that the battery will be accompanied by lithium (Li) deintercalation and consumption during charging and discharging, and the content of Li in the positive plate is different when the battery is discharged to different states. In the enumeration of the positive electrode material in this application, the content of Li is the initial state of the material unless otherwise stated. The positive electrode material is applied to the positive plate in the battery system, and after charging and discharging cycle, the content of Li in the positive electrode material contained in the plate will usually change. Among them, the content of Li can be quantified by molar content, but not limited to this. As for "the content of Li is the initial state of the material", the initial state of the material refers to the state before being put into the positive electrode slurry. It can be understood that the new material obtained by properly modifying the listed positive electrode material is also within the scope of the positive electrode material, and the foregoing proper modification refers to acceptable modification of the positive electrode material, and non-limiting examples include coating modification.

[0120] In the enumeration of the positive electrode material in this application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will appear to be floating. Among them, the content of O can be quantified by molar content, but not limited to this.

[0121] As an example, the positive active material of the sodium-ion secondary battery can include at least one of at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive active materials for sodium-ion batteries can also be used.

[0122] As an optional technical solution of the present application, the transition metal in the sodium transition metal oxide can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0

[0123] As an optional technical solution of the present application, the polyanion compound can be a compound having sodium ions, transition metal ions, and tetrahedral (YO4) n- anion 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; and n represents the valence state of (YO4) n- .

[0124] The polyanion compound can also be a compound having sodium ions, transition metal ions, tetrahedral (YO4) 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.

[0125] 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.

[0126] 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(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0127] Prussian blue compounds can contain 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 are, 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.

[0128] 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.

[0129] In some embodiments, the positive electrode film layer further optionally comprises a binder. As an example, the binder can comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin. The weight ratio of the binder in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0130] In some embodiments, the positive electrode film layer further optionally comprises a conductive agent. As an example, the conductive agent can comprise at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0131] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the 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 mass percent (wt%) to 80 wt%, the viscosity at room temperature is adjusted to 5000 millipascal-seconds (mPa-s) to 25000 mPa-s, the positive electrode slurry is coated on the surface of the positive electrode current collector, and the positive electrode tab is formed after drying and cold pressing by a cold rolling mill; the unit area surface density of the positive electrode powder coating is 150 milligrams per square meter (mg / m 2 ) to 350 mg / m 2 , and the positive electrode tab has a compacted density of 3.0 grams per cubic centimeter (g / cm 3 ) to 3.6 g / cm 3 , which can be optionally 3.3 g / cm 3 to 3.5 g / cm 3 .

[0132] The formula for calculating the compacted density is:

[0133] Compacted density = coating surface density / (thickness of the tab after extrusion - thickness of the current collector).

[0134] The mass M of the positive electrode active material per unit area of the positive electrode film can be measured using a standard balance.

[0135] The thickness T of the positive electrode film can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film as described herein refers to the thickness of the positive electrode film in the positive electrode tab after cold pressing and compaction and used for assembling the battery.

[0136] Negative electrode tab

[0137] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0138] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0139] In some embodiments, the negative electrode current collector can employ the composite current collector of the first aspect of the present application.

[0140] In some embodiments, the negative electrode active material can employ a negative electrode active material for a battery known in the art.

[0141] As an example, the negative electrode active material of the lithium ion secondary battery can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0142] As an example, the negative electrode active material of the sodium ion secondary battery is typically a hard carbon material, a two-dimensional metal carbide, or a two-dimensional metal nitride. Preferably, the negative electrode active material of the sodium ion secondary battery is typically a hard carbon material.

[0143] The weight ratio of the negative electrode active material in the negative electrode film layer is 70 to 100% by weight, based on the total weight of the negative electrode film layer.

[0144] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can 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 weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

[0145] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight, based on the total weight of the negative electrode film layer.

[0146] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like. The weight ratio of the other auxiliary agents in the negative electrode film layer is 0-15% by weight, based on the total weight of the negative electrode film layer.

[0147] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the 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 2000mPa·s-10000mPa·s; coating the obtained negative electrode slurry on a negative electrode current collector, and performing a drying process, cold pressing (e.g., against a roller), to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 75mg / m 2 -220mg / m 2 , and the negative electrode sheet compaction density is 1.2g / m 3 -2.0g / m 3 .

[0148] The mass M of the negative electrode active material per unit area of the negative electrode film can be measured using a standard balance.

[0149] The thickness T of the negative electrode film can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and a precision of 0.1μm. It should be noted that the thickness of the negative electrode film as described in the present application refers to the thickness of the negative electrode film in the negative electrode sheet after cold pressing and compaction and used for assembling the battery.

[0150] Electrolyte

[0151] The electrolyte serves the function of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not specifically limited in the present application and can be selected according to the needs. For example, the electrolyte can be in a liquid state, a gel state or a full solid state.

[0152] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0153] In some embodiments, the electrolyte salt of the lithium ion secondary battery can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0154] The electrolyte salt of the sodium ion secondary battery can be selected from one or more of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, sodium chloride.

[0155] The concentration of the electrolyte salt is typically 0.5 mol / L to 5 mol / L.

[0156] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0157] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0158] Separator film

[0159] In some embodiments, a separator film is also included in the secondary battery. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0160] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0161] In some embodiments, the thickness of the separator film is 6 μm to 40 μm, and can be selected from 12 μm to 20 μm.

[0162] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly through a winding process or a stacking process.

[0163] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0164] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0165] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 12 is a square structure of the secondary battery 5 as an example.

[0166] In some embodiments, referring to Figure 13 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0167] 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, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0168] In the battery module, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0169] Optionally, the battery module can further include a housing having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

[0170] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0171] In the battery pack, a battery case and a plurality of battery modules disposed in the battery case can be included. The battery case includes an upper case and a lower case, and the upper case can be disposed on the lower case to form an enclosed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery case in any manner.

[0172] In addition, the present application also provides a power consuming device including at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0173] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0174] Figure 14 The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the power consuming device for the secondary battery, the battery pack or the battery module can be used.

[0175] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power source.

[0176] The following are some embodiments.

[0177] 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.

[0178] 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.

[0179] I. Implementation Examples

[0180] Example 1

[0181] 1) Positive electrode plate

[0182] 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 to serve 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.

[0183] 2) Negative electrode plate

[0184] 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.

[0185] 3) Separating membrane

[0186] A polyethylene film (PE) with a thickness of 9 μm was used as the base film of the separator. Alumina, sodium carboxymethyl cellulose (CMC) and acrylate in a weight ratio of 93:3:4 were added to deionized water and stirred uniformly under the action of a vacuum stirrer to obtain a slurry, the solid content of the slurry being 55%. The obtained slurry was uniformly coated on the base film at a thickness of 2 μm on one side, and then PVDF was coated on both sides to obtain the separator.

[0187] 4) Cell assembly

[0188] The above positive electrode sheet, separator and negative electrode sheet were stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain a bare cell. The bare cell was welded into a square aluminum shell and laser-welded with a top cover.

[0189] 5) Cell liquid injection

[0190] After vacuum baking at 100°C to remove water, electrolyte was injected and sealed. Subsequently, after standing at 45°C, formation (0.02C constant current charging to 3.3V, and then 0.1C constant current charging to 3.6V), shaping and capacity test, a finished hard-shell lithium ion battery was obtained

[0191] In Example 1, the positive electrode current collector was a composite current collector, the porosity of the metal layer was 3%, the proportion of the pore size in the range of 10 nm to 200 nm was 50%, the breaking strength of the organic layer was 305 MPa, the thickness of the metal layer was 1 μm, the metal element was aluminum, the aluminum metal layer was deposited by vacuum plating, the vacuum degree was about 1*10 -2 Pa, one-pass plating forming mode, and some detailed current collector parameters are shown in Table 1.

[0192] Example 2

[0193] This example is basically the same as Example 1, the main difference being that the porosity, roughness and specific surface area of the metal layer in the positive electrode current collector are different, and the yield strength of the current collector is different accordingly. In this example, the porosity of the metal layer is 7%, the roughness is 0.23 μm, and the specific surface area is 0.192 g / m 2 . The yield strength of the current collector is 161 MPa. Some detailed current collector parameters are shown in Table 1.

[0194] Example 3

[0195] This example is basically the same as Example 1, the main difference being that the porosity, roughness and specific surface area of the metal layer in the positive electrode current collector are different, and the yield strength of the current collector is different accordingly. In this example, the porosity of the metal layer is 11%, the roughness is 0.25 μm, and the specific surface area is 0.195 g / m 2 . The yield strength of the current collector is 150 MPa. Some detailed current collector parameters are shown in Table 1.

[0196] Example 4

[0197] This example is basically the same as Example 1, the main difference being that the porosity, roughness and specific surface area of the metal layer in the positive electrode current collector are different, and accordingly the yield strength of the current collector is different. In this example, the porosity of the metal layer is 15%, the roughness is 0.27 μm, and the specific surface area is 0.201 g / m 2 . The yield strength of the current collector is 141 MPa. Some detailed current collector parameters are shown in Table 1.

[0198] Example 5

[0199] This example is basically the same as Example 1, the main difference being that the porosity, roughness and specific surface area of the metal layer in the positive electrode current collector are different, and accordingly the yield strength of the current collector is different. In this example, the porosity of the metal layer is 20%, the roughness is 0.29 μm, and the specific surface area is 0.21 g / m 2 . The yield strength of the current collector is 120 MPa. Some detailed current collector parameters are shown in Table 1.

[0200] Example 6

[0201] This example is basically the same as Example 1, the main difference being that the metal layer of the positive electrode current collector is composed of two structures (dense layer + porous layer). The specific preparation method is to first deposit a thin metal layer as a dense layer using a slow deposition method, with a single deposition amount of about 30 nm, and the thickness of the dense layer is 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 / m 2 , and the yield strength of the current collector is 169 MPa. Some detailed current collector parameters are shown in Table 1.

[0202] Example 7

[0203] This example is basically the same as Example 6, the main difference being that 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 / m 2 , and the yield strength of the current collector is 157 MPa. Some detailed current collector parameters are shown in Table 1.

[0204] Example 8

[0205] This example is substantially the same as Example 7, except that 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 metal layer has a porosity of 10%, a roughness of 0.24 μm, and a specific surface area of 0.194 m 2 / g. The yield strength of the current collector is 152 MPa. Some detailed current collector parameters are shown in Table 1.

[0206] Example 9

[0207] This example is substantially the same as Example 3, except that the material of the organic layer of the positive electrode current collector is different. In Example 9, the organic layer is a PI (polyimide) film. Some detailed current collector parameters are shown in Table 1.

[0208] Examples 10-13

[0209] This example is substantially the same as Example 3, except that the primary single crystal particle size, the secondary single crystal particle size, and the resistivity of the positive electrode current collector are different. Some detailed current collector parameters are shown in Table 2.

[0210] Comparative Examples

[0211] Comparative Example 1

[0212] This comparative example is substantially the same as Example 1, except that the positive electrode current collector is different. In Comparative Example 1, the positive electrode current collector is a composite current collector of the present application, which has a metal layer with a porosity of 0.5%, a roughness of 0.15 μm, and a specific surface area of 0.167 m 2 / g. The yield strength σ s of the composite current collector is 200 MPa. Some detailed current collector parameters are shown in Table 2.

[0213] Comparative Example 2

[0214] This comparative example is substantially the same as Example 1, except that the positive electrode current collector is different. In Comparative Example 2, the positive electrode current collector is a composite current collector of the present application, which has a metal layer with a porosity of 30%, a roughness of 0.35 μm, and a specific surface area of 0.246 m 2 / g. The yield strength σ s of the composite current collector is 105 MPa. Some detailed current collector parameters are shown in Table 2.

[0215] Comparative Example 3

[0216] This comparative example is substantially the same as Example 13, except that the positive electrode current collector is different. In Comparative Example 3, the positive electrode current collector is a composite current collector of the present application, which has a porosity of 0.5%, a roughness of 0.15 μm, and a specific surface area of 0.103 m 2The yield strength is 165 MPa. Some detailed current collector parameters are shown in Table 2.

[0217] III. Test Methods

[0218] 1) Pore size test

[0219] Take surface samples, measure the diameter of surface pores under SEM, measure multiple diameters and take the average.

[0220] 2) Porosity test

[0221] Take a fixed area S (for example, 100 cm 2 ) sample, use a true density tester (Acco pyc II 1340), use the formula PV = nRT to obtain the true volume V1 of the current collector sample. Since the micropores inside the metal layer are wrapped by the surface metal, gas cannot penetrate, so the true volume is larger than the theoretical volume of the tightly packed metal. The true volume V1 includes two parts, one part is the volume V 有 of the organic layer (V 有 = S*T 有 , T 有 is the thickness of the organic layer), and the other part is the volume V 金1 of the metal layer (V 金1 = V1-V 有 ); using the theoretical density of the tightly packed metal layer p 金 , the weight of the current collector m 集 , and the density of the organic layer p 有 , the thickness of the organic layer T 有 , the theoretical volume of the metal layer is calculated as V 金2 (V 金2 = (m 集 -m 有 ) / p 金 ), wherein m 有 = p 有 *T 有 *S, the porosity = (V 金1 -V 金2 ) / V 金1 .

[0222] 3) Composite current collector yield strength test

[0223] Use a tensile testing machine to perform tensile testing, use an initial distance of 50 mm, use a speed of 50 mm / min for stretching, and read the inflection point on the tensile curve as the yield strength.

[0224] 4) Organic layer breaking strength test

[0225] Tensile test is performed by using a tensile machine, using 50mm initial distance, using 50mm / min speed for stretching, and recording the elongation rate corresponding to the breaking position.

[0226] 5) Resistivity test

[0227] Sample is taken for sheet resistance test, then cross-section sample preparation is performed by using a cross-section sample preparation machine, then single surface metal layer thickness is observed under SEM, and resistivity = sheet resistance * single surface metal layer thickness.

[0228] 6) Grain size test

[0229] XRD is used for test, then Scherrer formula is used to calculate primary single crystal grain size.

[0230] 7) Surface roughness test

[0231] Surface roughness test is performed by using a roughness meter, and Ra value.

[0232] 8) Specific surface area test

[0233] BET method is used for test.

[0234] 9) 10% elongation tensile resilience after resistance growth rate test

[0235] Current collector is cut into 15mm*150mm strip, initial surface sheet resistance is measured, then 10% elongation tensile is performed, surface sheet resistance of the first tensile area after tensile is tested, and growth rate = (resistance after tensile - resistance before tensile) / resistance before tensile.

[0236] 10) 30% elongation tensile resilience after resistance growth rate test

[0237] Current collector is cut into 15mm*150mm strip, initial surface sheet resistance is measured, then 30% elongation tensile is performed, surface sheet resistance of the first tensile area after tensile is tested, and growth rate = (resistance after tensile - resistance before tensile) / resistance before tensile.

[0238] 11) Breaking elongation test

[0239] Current collector is cut into 15mm*150mm strip, tensile test is performed by using a universal tensile machine, 50mm gauge length, 50mm / min tensile speed, until test breaking, 10 strips are tested and average value is taken.

[0240] 12) Cell DCR test

[0241] Adjust the battery monomer to 50% SOC, discharge at 4C rate (corresponding discharge current is I) for 30s, record the voltage difference ΔV before and after 30s discharge. Calculate the DCR corresponding to 50% SOC according to the following formula: DCR = ΔV / I, get the DCR data of each battery monomer.

[0242] 13) Rate performance test

[0243] Discharge the fresh battery at 0.33C rate at room temperature 25℃ after full charge, and the discharge capacity at this time is recorded as initial capacity CO. Then, discharge the battery at 2C rate at room temperature 25℃ environment, and the discharge capacity at this time is recorded as C1. Calculate the capacity retention rate according to the following formula:

[0244] Capacity retention rate = C1 / C0 x 100%.

[0245] 14) Long-term stability test

[0246] Charge and discharge the fresh battery monomer at 60℃ high temperature condition at 1C rate until the capacity attenuation is 80% of the initial capacity, and record the corresponding cycle number at this time. Get the cycle number data of each battery monomer.

[0247] The parameters and performance test results of the above examples and comparative examples are shown in Table 1 and Table 2.

[0248] Table 1

[0249]

[0250]

[0251]

[0252]

[0253] Table 2

[0254]

[0255]

[0256] Description

[0257]

[0258] It can be seen from the comparison of examples 1-5 and comparative example 1 that when the porosity is between 3% and 20%, the yield strength of the current collector is between 120MPa and 180MPa, which is less than the fracture strength of the organic layer 305MPa; 0.5*σ1*T 有 / (T 有 +T金 ) corresponds to 114 MPa, 0.8*σ1*T 有 / (T 有 +T 金 ) corresponds to 183 MPa; the yield strength is between the two, so that the tensile stress of the current collector presents a slow increasing trend, thus the breaking elongation is high, greater than 50%; Comparative Example 1 has a too low porosity of only 0.5%, which leads to a high yield strength (200 MPa) of the current collector, exceeding 0.8*σ1*T 有 / (T 有 +T 金 ) corresponds to a range of 183 MPa, so that the stress of the current collector increases rapidly with the increase of the elongation during the stretching, thus the breaking elongation is reduced (~35%); at the same time, since the breaking elongation of Examples 1-5 is significantly higher than that of Comparative Example 1, the square resistance growth rate corresponding to 10% stretching and 30% stretching of Examples 1-5 is lower than that of Comparative Example 1 (under the same elongation, Examples 1-5 are subjected to less force than Comparative Example 1), so that the performance of the battery cell of Examples 1-5 is better than that of Comparative Example 1, especially the long-term cycle performance. In the long-term cycle, the sample with a large tensile rebound square resistance growth rate has more surface cracks, and the metal layer is more easily corroded by the electrolyte during the use of the battery cell, thus the cycle performance of the battery cell is deteriorated.

[0259] As can be seen from the comparison between Comparative Example 2 and Examples 1-5, the porosity of Comparative Example 2 reaches 30%, which is too high, leading to a decrease in the modulus of the metal layer and a decrease in the yield strength of the current collector (only 105 MPa). At this time, the decrease in the yield strength has no obvious improvement on the breaking elongation, but the too low yield strength leads to an increase in the elongation or other deformation of the current collector during cold pressing and other processing of the pole piece, resulting in deformation of the pole piece, deterioration of the interface performance of the battery cell, and thus deterioration of the DCR and rate performance of the battery cell, and the deterioration of the kinetics also leads to deterioration of the long-term cycle performance.

[0260] Examples 6-8 contain both dense layer and porous layer, the proportion of dense layer is between 10% and 50%, the thicker the dense layer, the higher the yield strength of the current collector, the lower the elongation at break of the current collector, and due to the presence of the porous layer, the yield strength of the current collector is not too high, and the dense layer and the porous layer coexist, the dense layer can effectively prevent the electrolyte from penetrating to the surface of the metal layer and the organic layer, preventing the occurrence of delamination, thus helping to improve the long-term cycle stability of the battery (the cycle number is higher than that of Examples 1-5 which only contain the porous layer). At the same time, compared with Comparative Example 1 (only the dense layer), the yield strength is too high, which can effectively avoid the decrease of elongation, the increase of tensile spring resistance growth rate, and the deterioration of the performance of the battery. The presence of the dense layer and the porous layer can make the yield strength, elongation and electrical performance all at a good level.

[0261] Example 9 uses a different organic layer, and still can achieve a higher elongation, better DCR, rate and cycle performance.

[0262] Examples 3, 10-12, the porosity is kept at 11%, the difference is the primary single crystal particle size and the secondary particle size (primary single crystal particle size 35-80 nm, secondary particle size 90-300 nm), the yield strength is all in the moderate position, and all obtain good ductility, tensile spring performance and battery performance; the larger the primary crystal size, the better the performance is obtained.

[0263] Example 13 and Comparative Example 3 show that when the metal layer is a copper layer, the porosity is in the appropriate range (5%), which can significantly improve the elongation at break of the copper composite current collector, thereby improving the performance of the battery; when the copper is close to a completely dense state (porosity 0.5%), due to the high yield strength, the elongation at break is significantly reduced, making the stretching process prone to cracking, the tensile spring resistance growth rate is increased, and the risk of cracking and breaking of the electrode during long-term cycling is increased, resulting in deterioration of the performance of the battery (including DCR, rate and cycle performance).

[0264] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments, combination of part of the components in the embodiments to construct other ways can also be included in the scope of the present application.

Claims

1. A composite current collector, characterized by, comprise an organic layer and a metal layer disposed on at least one surface of the organic layer; the metal layer has pores, at least part of the pores have a pore size of 10 nm to 200 nm, and the metal layer has a porosity of 3% to 20%; the composite current collector satisfies the following relationship: 0.5*σ1*T 有 / (T 有 + T 金 ) < σ s ≤ 0.8*σ1*T 有 / (T 有 + T 金 ) 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; the yield strength of the composite current collector is 120 MPa to 180 MPa, the thickness of a single layer of the 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 of claim 1, wherein 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.

3. The composite current collector of claim 1, wherein the metal layer is a metal aluminum layer, and the composite current collector satisfies the following relationship: wherein p1 is the average density of the composite current collector, in g / cm 3 ; p2 is the density of the organic layer, in g / cm 3 .

4. The composite current collector of claim 1, wherein the composite current collector satisfies at least one of the following: (1) the composite current collector has a resistivity of < 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 m 2 / g; (4) the sheet resistance of the composite current collector increases by ≤5% after 10% tensile elongation and recovery; (5) the sheet resistance of the composite current collector increases by ≤10% after 30% tensile elongation and recovery; (6) the longitudinal breaking elongation of the composite current collector is ≥40%; (7) the transverse breaking elongation of the composite current collector is ≥40%.

5. The composite current collector of claim 1, wherein the size of a primary single-crystal particle of the metal layer is 35 nm to 80 nm, and the size of a secondary particle in the metal layer is 90 nm to 300 nm.

6. The composite current collector of claim 1, wherein the thickness of a single layer of the metal layer is 0.8 μm to 1.5 μm.

7. The composite current collector of any one of claims 1-6, wherein, 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 disposed on the surface of the organic layer, and the porous layer is disposed on the surface of the dense layer away from 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 away from the organic layer.

8. The composite current collector of claim 7, wherein, the density p3 of the compact layer is 2.65 g / cm 3 ≤ p3 < 2.70 g / cm 3 ; the density p4 of the porous layer is 2.00 g / cm 3 ≤ p4 < 2.65 g / cm 3 .

9. The composite current collector of claim 7, wherein, the composite current collector satisfies at least one of the following: (8) 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; (9) 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.

10. The composite current collector of any one of claims 1-6, 8, or 9, wherein, the organic layer comprises an organic polymer, and the organic polymer comprises 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, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polyazolium, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, and phenolic resin.

11. The composite current collector of any one of claims 1-6, 8, or 9, wherein, the thickness of the organic layer is 3 μm to 10 μm.

12. A secondary battery comprising the composite current collector according to any one of claims 1 to 11.

13. An electric device comprising the secondary battery according to claim 12.

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