Secondary battery and preparation method therefor, electrode sheet, secondary battery, and electric device

Abstract

A secondary battery (5) and a preparation method therefor, an electrode sheet, and an electric device in which the secondary battery (5) is used. The secondary battery (5) comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on the surface of at least one side of the negative electrode current collector, wherein the gram capacity of a negative electrode active material in the negative electrode film layer is 800-1500 mAh / g; and the negative electrode current collector comprises a copper foil. The copper foil comprises copper grains having different particle sizes, and the copper grains comprise copper grains having a particle size less than or equal to 0.5 μm and copper grains having a particle size greater than 0.5 μm, wherein the proportion of the number of the copper grains having a particle size less than or equal to 0.5 μm in the total number of the copper grains is 70-95%, and the proportion of the number of the copper grains having a particle size greater than 0.5 μm in the total number of the copper grains is 5-30%.

Description

Secondary battery, preparation method thereof, electrode sheet, secondary battery, and electric device

[0001] Cross-reference to related applications

[0002] This application refers to the Chinese Patent Application No. 202411154807.0, filed on August 21, 2024, for “Secondary battery, preparation method thereof, and electric device”, which is incorporated by reference in its entirety.

[0003] This application refers to the Patent Application No. PCT / CN2025 / 115989, filed on August 20, 2025, for “Secondary battery, preparation method thereof, and electric device”, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0004] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, an electrode sheet, a secondary battery, and an electric device. BACKGROUND

[0005] With the secondary batteries being widely used in energy storage power supply systems such as hydroelectric, thermal, wind, and solar power stations, and in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., the market has increasingly high requirements for the energy density of secondary batteries.

[0006] The energy density can be increased by using a silicon-based negative electrode active material or increasing the amount of secondary battery active material, but the silicon-based material has a high thermal expansion coefficient, and the silicon-based battery has a serious volume expansion under heat; after the amount of secondary battery active material is increased, the volume of the battery cell also increases accordingly, which puts higher requirements on the performance of the negative electrode current collector. The negative electrode current collector copper foil is an important component of the secondary battery, which can constrain the expansion of the battery cell and prevent the anode of the secondary battery from breaking during use, and has a great influence on the electrical performance and safety performance of the secondary battery.

[0007] Therefore, there is an urgent need for a secondary battery with improved performance of the negative electrode current collector. SUMMARY

[0008] The present application provides a secondary battery with a negative electrode current collector having improved tensile properties, which can effectively constrain the expansion of the battery cell, delay or reduce the fracture of the electrode sheet, and prolong the service life of the secondary battery.

[0009] In a first aspect, the application provides a secondary battery, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side surface of the negative electrode current collector, the gram capacity of the negative electrode active material in the negative electrode film layer being 800 mAh / g-1500 mAh / g; the negative electrode current collector comprising a copper foil, the copper foil comprising copper grains with different particle sizes, the copper grains comprising copper grains with a particle size of less than or equal to 0.5 μm and copper grains with a particle size of greater than 0.5 μm, wherein the proportion of the number of the copper grains with a particle size of less than or equal to 0.5 μm in the total number of the copper grains is 70%-95%, and the proportion of the number of the copper grains with a particle size of greater than 0.5 μm in the total number of the copper grains is 5%-30%.

[0010] Increasing the amount of active material is one of the effective means to improve the energy density or capacity of the secondary battery, but this will cause the volume of the battery cell to increase; the applicant has found that using high-gram-capacity negative electrode active material can significantly improve the available lithium intercalation capacity of the negative electrode active material, improve the energy density or capacity of the secondary battery while reducing the impact on the volume of the battery cell, however, the high-gram-capacity negative electrode active material has a large particle volume expansion before and after the lithium ion intercalation / deintercalation, and the expansion stress acts on the copper foil of the current collector, increasing the probability of the copper foil being broken or cracked along the thickness direction after being subjected to the expansion stress, and deteriorating the safety and service life of the secondary battery. The copper foil comprising the copper grains with different particle sizes provided in the secondary battery of the application has excellent tensile strength and elongation at break, and has excellent plasticity while improving the mechanical strength, thereby improving the energy density, capacity and safety of the secondary battery.

[0011] In any embodiment, the gram capacity of the negative electrode active material in the negative electrode film layer is 800 mAh / g-1500 mAh / g.

[0012] The copper foil provided in the application is suitable for a secondary battery comprising a negative electrode active material with a gram capacity of 800 mAh / g-1500 mAh / g. High-gram-capacity negative electrode materials can intercalate more active ions, such as silicon-based negative electrodes, alkali metal negative electrodes, etc., and generally have high swelling properties, which will increase the probability of the copper foil being broken or cracked in the battery cell. The copper foil has excellent mechanical properties and plasticity, can reduce the risk of the copper foil being broken or cracked in a high-energy-density battery system or a high-swelling battery system, and can improve the energy density, capacity and safety of the secondary battery.

[0013] In any embodiment, the particle size of the copper grains with a particle size of greater than 0.5 μm is in the range of greater than 0.5 μm and less than or equal to 3 μm, which can adjust or optimize the tensile strength of the copper foil.

[0014] In any embodiment, the number of copper grains with a particle size greater than 0.5 μm and less than or equal to 3 μm accounts for 5%-30% of the total number of copper grains.

[0015] As previously described, the copper grain particle size satisfying greater than 0.5 μm and less than or equal to 3 μm can help reduce the average grain size of the copper foil, achieving further improvement of the mechanical strength of the copper foil; further controlling the number of copper grains with a particle size greater than 0.5 μm and less than or equal to 3 μm to satisfy 5%-30% can make the copper foil have good elongation at break, combining excellent mechanical properties and plasticity, which can reduce the risk of copper foil fracture or crack in high-energy density battery systems or high-expansion battery systems, achieving simultaneous improvement of the energy density and safety of secondary batteries.

[0016] In any embodiment, the short diameter of at least part of the copper grains with a particle size greater than 0.5 μm is arranged along the thickness direction of the current collector.

[0017] The short diameter of at least part of the copper grains with a particle size greater than 0.5 μm arranged along the thickness direction of the current collector indicates that the internal grain boundary of the copper foil has a high degree of tortuosity, and the energy required for the copper foil to fracture through the grain boundary (i.e., the thickness direction of the current collector) is also greater, which helps to reduce the probability of copper foil fracture along the thickness direction, improve the brittleness of the current collector, and further reduce the risk of copper foil fracture or crack, thereby improving the safety of secondary batteries.

[0018] In any embodiment, the number of copper grains with a particle size less than or equal to 0.5 μm accounts for 80%-95% of the total number of copper grains, which helps to further improve the tensile strength and improve the mechanical strength of the copper foil.

[0019] In any embodiment, the number of copper grains with a particle size greater than 0.5 μm accounts for 5%-20% of the total number of copper grains, which helps to further improve the elongation at break and improve the plasticity of the copper foil.

[0020] In any embodiment, the copper foil satisfies at least one of the following conditions:

[0021] (1) the average particle size of the copper grains is 0.3 μm-1.2 μm;

[0022] (2) the maximum particle size of the copper grains is 1 μm-2.5 μm;

[0023] (3) the minimum particle size of the copper grains is 0.1 μm-0.3 μm;

[0024] (4) the particle size span of the copper grains is 0.8 μm-2.5 μm.

[0025] The particle size distribution of the copper grains helps to adjust the proportion of the copper grains with a particle size less than or equal to 0.5 μm and the copper grains with a particle size greater than 0.5 μm, so as to adjust and improve the tensile strength and the elongation at break of the copper foil, and the copper foil has excellent mechanical properties and plastic properties.

[0026] In any embodiment, the copper foil satisfies at least one of the following conditions:

[0027] (1) the average particle size of the copper grains is 0.3 μm-0.6 μm;

[0028] (2) the maximum particle size of the copper grains is 1.2 μm-2.0 μm;

[0029] (3) the minimum particle size of the copper grains is 0.1 μm-0.3 μm;

[0030] (4) the particle size span of the copper grains is 1 μm-2 μm.

[0031] The particle size distribution of the copper grains helps to further adjust the tensile strength and the elongation at break of the copper foil, and improve the mechanical properties and plastic properties.

[0032] In any embodiment, under the test conditions of room temperature (20±10 ℃), sample length x width of (50±0.25 mm) x (15±0.25 mm), and tensile speed of 50±0.5 mm / min, the tensile strength of the copper foil is 600 MPa-1000 MPa, and / or the elongation at break of the copper foil is 4%-8%.

[0033] The copper foil has excellent tensile strength and elongation at break, has good mechanical properties and plastic properties, and can be applied to high-energy-density batteries or high-swelling batteries, and helps to improve the safety of secondary batteries.

[0034] In any embodiment, under the test conditions of room temperature (20±10 ℃), sample length x width of (50±0.25 mm) x (15±0.25 mm), and tensile speed of 50±0.5 mm / min, the tensile strength of the copper foil is 700 MPa-1000 MPa, and / or the elongation at break of the copper foil is 4%-7%.

[0035] In any embodiment, under the test conditions of room temperature (20±10 ℃), sample length x width of (50±0.25 mm) x (15±0.25 mm), and tensile speed of 50±0.5 mm / min, the tensile strength of the copper foil is 700 MPa-800 MPa, and / or the elongation at break of the copper foil is 5%-6%.

[0036] The copper foil has good tensile strength, which can meet the practical needs of the battery field for high-strength copper foil to some extent. In addition, the copper foil also has excellent elongation at break, showing good plasticity, which helps to reduce the brittle defects of the copper foil and reduce the risk of copper foil fracture or slight cracking in the battery cell.

[0037] In any embodiment, the hardness of the copper foil is 55HV-65HV. In any embodiment, the hardness of the copper foil is 55HV-60HV. The suitable hardness is conducive to the surface treatment of the copper foil and the cold pressing treatment of the secondary battery, reducing the surface damage of the copper foil and reducing the influence on the bonding performance of the negative electrode film layer and the copper foil.

[0038] In any embodiment, the thickness of the copper foil is 4-10 μm. The copper foil can reduce the thickness without affecting the strength, which helps to design the battery to be light, and further improves the energy density or specific capacity.

[0039] In any embodiment, the secondary battery further comprises a negative electrode film layer on at least one side of the copper foil, and the negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate and metal lithium. The secondary battery can be suitable for a variety of different battery negative systems, and has a wide range of applications.

[0040] In any embodiment, the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite and silicon alloy. The secondary battery using the silicon-based material as the negative electrode active material has higher energy density, and at the same time, the copper foil in the secondary battery can well bind the volume expansion of the negative electrode during the battery cycle.

[0041] In any embodiment, the mass percentage of the silicon-based material is 5%-100%, optionally 10%-60%, and more optionally 10%-30%, based on the total mass of the negative electrode film layer.

[0042] In any embodiment, the mass percentage of silicon element in the silicon-based material is 20%-50%.

[0043] In any embodiment, the mass percentage of silicon element is 4%-10%, based on the total mass of the negative electrode film layer.

[0044] The second aspect of the application provides a preparation method of a secondary battery, the preparation method comprising: using a copper foil as a current collector to prepare a pole piece, the copper foil being prepared by an electroplating method, the electroplating method comprising: applying a pulse current to an electroplating solution to reduce and deposit copper ions in the electroplating solution to form the copper foil, the peak value of the pulse current being 40,000 A-100,000 A, the valley value of the pulse current being 100 A-20,000 A, and the change period of the current being 50 ms-5,000 ms; and the preparation method further comprising: using a negative electrode active material with a specific capacity of 800 mAh / g-1,500 mAh / g to prepare the pole piece.

[0045] Compared with the calendering method, the electroplating method is mature and simple, has low requirements on equipment, and can prepare a copper foil with excellent tensile strength and elongation at break, and has excellent mechanical strength and good plasticity.

[0046] In the preparation method of the secondary battery provided in the application, the copper foil is prepared by the electroplating method, so that the copper foil with excellent tensile strength and elongation at break is obtained, the mechanical strength is improved while excellent plasticity is achieved, the probability of fracture or crack of the copper foil under the expansion stress of the high specific capacity negative electrode active material due to the change in volume of the particles before and after lithium ion intercalation / deintercalation is reduced, and the safety and service life of the secondary battery are further improved.

[0047] In any embodiment, the electroplating method satisfies one or more of the following conditions:

[0048] (1) the peak value of the pulse current is 40,000 A-80,000 A;

[0049] (2) the valley value of the pulse current is 1,000 A-10,000 A;

[0050] (3) the change period of the pulse current is 500 ms-5,000 ms;

[0051] (4) the distance between the cathode electrode and the anode electrode is 8 mm-20 mm;

[0052] (5) the temperature of the electroplating deposition is 45°C-60°C;

[0053] (6) the roller speed of the cathode roller is 2 m / min-5 m / min.

[0054] In any embodiment, the electroplating method satisfies one or more of the following conditions:

[0055] (1) the peak value of the pulse current is 50,000 A-70,000 A;

[0056] (2) the valley value of the pulse current is 2,000 A-5,500 A;

[0057] (3) the change period of the pulse current is 2000 ms-4000 ms;

[0058] (4) the distance between the cathode electrode and the anode electrode is 8 mm-12 mm;

[0059] (5) the temperature of the electroplating deposition is 50℃-60℃;

[0060] (6) the roller speed of the cathode roller is 2 m / min-3 m / min.

[0061] Compared with direct current deposition, applying pulse current to the electroplating solution can make copper ions reduce and deposit to form fine grains with small particle size under high current conditions, and form grains (for example, columnar grains) with large particle size under low current conditions. By adjusting the current size and change period, the formation and growth of copper ion crystal nucleus can be adjusted, so that the size and morphology of the grain size, and the proportion of the number of copper grains with a particle size less than or equal to 0.5 μm and the copper grains with a particle size greater than 0.5 μm can be adjusted, and the tensile strength and elongation at break of the copper foil can be improved.

[0062] In any embodiment, the pulse current includes one or more of a square wave pulse current, a sine wave pulse current, a triangular wave pulse current, and a sawtooth wave pulse current. In any embodiment, the pulse current includes a sine wave pulse current. The sine wave pulse current continuously and periodically changes, which is conducive to the continuous and variable growth of the grains.

[0063] In any embodiment, the electroplating solution includes a leveling agent, a wetting agent, and a brightener, the leveling agent includes one or more of collagen, sodium saccharin; the wetting agent includes one or more of hydroxyethyl cellulose, polyethylene glycol; and the brightener includes polydithiobispropyl sulfone sodium.

[0064] The leveling agent can improve the flatness of the copper foil, the wetting agent can improve the wettability of the electroplating solution and the substrate, increase the nucleation rate of the copper foil, and reduce the average particle size of the grains in the copper foil, and the brightener can make the grain size of the copper foil smaller and reduce the surface roughness of the copper foil and improve the smoothness of the surface.

[0065] In any embodiment, the electroplating solution includes collagen with a concentration of 60 mg / L-300 mg / L, sodium saccharin with a concentration of 0.5 g / L-10 g / L, polyethylene glycol with a concentration of 50 mg / L-200 mg / L, hydroxyethyl cellulose with a concentration of 30 mg / L-200 mg / L, polydithiobispropyl sulfone sodium with a concentration of 500 mg / L-2000 mg / L, and chloride ions (calculated as chlorine atoms) with a concentration of 20 mg / L-80 mg / L.

[0066] In any of the embodiments, the electroplating solution comprises: collagen with a concentration of 80 mg / L-150 mg / L, sodium saccharin with a concentration of 0.5 g / L-4 g / L, polyethylene glycol with a concentration of 60 mg / L-150 mg / L, hydroxyethyl cellulose with a concentration of 50 mg / L-150 mg / L, sodium polydithiobispropyl sulfone with a concentration of 500 mg / L-1000 mg / L, and chloride ions with a concentration of 40 mg / L-80 mg / L.

[0067] The collagen and sodium saccharin in the electroplating solution help to improve the surface pits and protrusions of the copper foil, improve the flatness of the copper foil, the hydroxyethyl cellulose and polyethylene glycol help to reduce the difference in the thickness direction of the copper foil, improve the uniformity of the copper foil, the polydithiobispropyl sulfone sodium can improve the electrochemical reduction rate of copper ions, adjust the grain size, and the prepared copper foil is bright and flat, the number ratio of copper grains with a particle size of less than or equal to 0.5 μm and copper grains with a particle size of greater than 0.5 μm is appropriate, and has good tensile strength and elongation at break.

[0068] In any of the embodiments, the pH of the electroplating solution is 2.5-4.5, which is conducive to the reduction of copper ions.

[0069] The third aspect of the application provides a pole piece, which comprises the copper foil in the secondary battery provided by the first aspect of the application or the copper foil prepared by the preparation method of the second aspect of the application.

[0070] In any of the embodiments, the pole piece further comprises a negative electrode film layer on at least one side of the copper foil, and the negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and metallic lithium.

[0071] In any of the embodiments, the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0072] In any of the embodiments, the mass percentage of the silicon-based material is 5%-100%, optionally 10%-60%, and more optionally 10%-30%, based on the total mass of the negative electrode film layer.

[0073] In any of the embodiments, the mass percentage of silicon elements in the silicon-based material is 20%-50%.

[0074] In any of the embodiments, the mass percentage of silicon elements is 4%-10%, based on the total mass of the negative electrode film layer.

[0075] The fourth aspect of the present application provides a wound type secondary battery comprising the secondary battery provided by the first aspect of the present application or the secondary battery prepared according to the preparation method provided by the second aspect of the present application or comprising the electrode tab provided by the third aspect of the present application.

[0076] The fifth aspect of the present application provides a stacked type secondary battery comprising the secondary battery provided by the first aspect of the present application or the secondary battery prepared according to the preparation method provided by the second aspect of the present application or comprising the electrode tab provided by the third aspect of the present application.

[0077] The sixth aspect of the present application provides an electric device comprising the secondary battery of the first aspect of the present application or the secondary battery prepared by the method of the second aspect of the present application or the wound type secondary battery of the fourth aspect of the present application or the stacked type secondary battery of the fifth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0078] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained according to the drawings without any creative labor for those skilled in the art.

[0079] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0080] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1.

[0081] FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0082] FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0083] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4.

[0084] FIG. 6 is a schematic diagram of an electric device using the secondary battery according to an embodiment of the present application as a power supply.

[0085] FIG. 7 shows the inverse pole figure distribution diagram of the cross section of the copper foil of Example 1 of the present application obtained by electron backscatter diffraction (EBSD) test.

[0086] FIG. 8 shows the tensile curve of the copper foil of Example 1 of the present application.

[0087] FIG. 9 shows the grain size distribution diagram of the cross section of the copper foil of Example 1 of the present application obtained by EBSD diffraction test.

[0088] FIG. 10 shows the inverse pole figure distribution diagram of the cross section of the copper foil of Example 2 of the present application obtained by EBSD test.

[0089] Fig. 11 shows the tensile curve of the copper foil of Example 2 of the present application.

[0090] Fig. 12 shows the grain size distribution diagram obtained by EBSD diffraction test of the cross section of the copper foil of Example 2 of the present application.

[0091] Fig. 13 shows the inverse pole figure distribution diagram obtained by EBSD test of the cross section of the copper foil of Example 3 of the present application.

[0092] Fig. 14 shows the tensile curve of the copper foil of Example 3 of the present application.

[0093] Fig. 15 shows the grain size distribution diagram obtained by EBSD diffraction test of the cross section of the copper foil of Example 3 of the present application.

[0094] Fig. 16 shows the tensile curve of the copper foil of Example 3 of the present application.

[0095] Fig. 17 shows the inverse pole figure distribution diagram obtained by EBSD test of the cross section of the copper foil of Comparative Example 2 of the present application.

[0096] Fig. 18 shows the tensile curve of the copper foil of Comparative Example 2 of the present application.

[0097] Fig. 19 shows the grain size distribution diagram obtained by EBSD diffraction test of the cross section of the copper foil of Comparative Example 2 of the present application.

[0098] Fig. 20 shows the schematic diagram of the electrode assembly of the wound secondary battery of an embodiment of the present application.

[0099] Explanation of Reference Numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate; T thickness direction; A inflection point of the wound cell; B bending point of the inner circle of the wound cell. DETAILED DESCRIPTION

[0100] Hereinafter, the embodiments of the secondary battery and the method for manufacturing the same, the electrode sheet, the wound secondary battery, and the electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are well known, repeated description of actually 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. In addition, the accompanying 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.

[0101] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, i.e., all combinations of any two of the range limits, unless otherwise indicated. For example, a range of "1 to 10" is intended to include any number from 1 to 10, including the integers 1 and 10. Unless otherwise indicated, the use of "or" in the disclosed aspects herein is the inclusive, and not the exclusive use. Only the context, and not the number of times an item is used, can determine that it is the exclusive use. For example, the phrase "A uses B or C" means that A can use B, or A can use C, or A can use both B and C. Also, the use of the term "one" or "a" or "the" is intended to be singular as well as plural, unless only the singular form is used. For example, the phrase "one or more of A, B, and C" means that A, B, or C can be used, individually or in combination, or combinations of A, B, and C can be used. The use of the terms "first," "second," "top," "bottom," "front," "back," "leading," "trailing," and the like, if any, are used for clarity and convenience in providing a comparative or relative spatial description of the components or steps illustrated in the figures. It is to be understood that no absolute spatial or positional relationship is intended or should be inferred or understood. In other words, the use of these terms is not intended to limit the position, location, and / or attachment of the illustrated components relative to one another.

[0102] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0103] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0104] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises 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.

[0105] Unless otherwise specified, "including" and "including" mentioned in the present application means open, and can also be closed. For example, "including" and "including" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0106] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0107] 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 (e.g., lithium ions, sodium ions) are intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct the active ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and mainly functions to prevent short circuiting of the positive and negative electrodes while allowing the active ions to pass through. The negative electrode sheet includes a negative current collector, which functions to carry electrode active material and to collect output current, and can also bind the cell expansion to prevent the anode from breaking during cycling.

[0108] Increasing the capacity of the positive electrode and the negative electrode is one of the main means to improve the energy density of a secondary battery. However, the applicant has found that the use of silicon-based negative electrode materials, high-capacity graphite, lithium metal, and the like can significantly increase the capacity of the negative electrode. However, due to the large intercalation lithium capacity of the above-mentioned negative electrode materials, the volume expansion problem after intercalation of lithium is serious, increasing the probability of fracture of the electrode sheet and failure of the battery. The applicant has further found that, as the high-capacity negative electrode continuously intercalates lithium during battery operation, the volume of the negative electrode active material particles expands, which can cause the current collector in the electrode sheet to be squeezed. For both stacked cells and wound cells, when the active material expands, the expansion force in the direction perpendicular to the current collector (i.e., the thickness direction) is transferred to the in-plane direction parallel to the current collector due to the blockage of the expansion force by external objects, thereby generating a local stress overload caused by the lateral tensile force, which can easily cause the weak points to break, leading to fracture of the current collector. When the current collector fails, it usually first undergoes elastic deformation under the action of external force, and as the volume continuously expands, the current collector is continuously subjected to tensile force, transitioning from elastic deformation to plastic deformation (i.e., irreversible deformation). When the irreversible deformation exceeds the maximum deformation of the current collector, the current collector is torn, further causing the electrode sheet to fracture and the battery performance to plummet.

[0109] [Secondary battery]

[0110] Based on this, the application provides a secondary battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side surface of the negative electrode current collector, the gram capacity of the negative electrode active material in the negative electrode film layer being 800 mAh / g-1500 mAh / g; the negative electrode current collector comprising a copper foil, the copper foil comprising copper grains with different particle sizes, the copper grains comprising copper grains with a particle size of less than or equal to 0.5 μm and copper grains with a particle size of greater than 0.5 μm, wherein the proportion of the number of the copper grains with a particle size of less than or equal to 0.5 μm in the total number of the copper grains is 70%-95%, and the proportion of the number of the copper grains with a particle size of greater than 0.5 μm in the total number of the copper grains is 5%-30%.

[0111] The copper grains with a particle size of greater than 0.5 μm tend to be columnar grains or columnar-like grains, which are also referred to as "large grains" herein, and the copper grains with a particle size of less than or equal to 0.5 μm are fine grains close to particles, forming a fine-grain region around the columnar grains. Therefore, in the application, the copper foil substrate forms a grain morphology mainly composed of fine grains and mixedly distributed large grains, which is a heterogeneous grain morphology with a small amount of large grains doped in the fine grains. The main reason for the difference in the heterogeneous morphology of grains of different sizes is the adjustment of the grain size in the process of foil production. Specifically, as an embodiment, the size of the grain size can be controlled by adjusting the change of the current during the production of the copper foil. After the current is reduced, the grains tend to form grains with a larger size, and after the current is increased, the grains tend to form grains with a smaller size.

[0112] The copper grains with a particle size of less than or equal to 0.5 μm help to improve the tensile strength of the copper foil and improve the mechanical properties; the particle size of the copper grains with a particle size of greater than 0.5 μm helps to improve the elongation at break and improve the plasticity of the copper foil. The proportion of the number of the copper grains with a particle size of less than or equal to 0.5 μm and the copper grains with a particle size of greater than 0.5 μm in the copper grains can affect the mechanical properties and plasticity of the copper foil to different degrees, so that the copper foil exhibits different degrees of excellent mechanical properties and plasticity. In the copper foil provided by the application, the proportion of the number of the copper grains with a particle size of less than or equal to 0.5 μm in the total number of the copper grains is 70%-95%, which can significantly improve the tensile strength of the copper foil, and the proportion of the number of the copper grains with a particle size of greater than 0.5 μm in the total number of the copper grains is 5%-30%, which can make the copper foil have good elongation at break, providing a material basis for improving the energy density and safety of the secondary battery.

[0113] Take the wound core as an example, please refer to FIG. 20. In the wound core, due to the large deformation process such as winding and pressure setting of the current collector during the manufacturing process, the positive electrode expansion causes the top shell to form a local stress overload of the current collector. The outer ring tab of the wound core receives high expansion force from the shell extrusion, which is prone to fracture at the inflection point (e.g., point A) of the cell. The applicant found that reducing the grain size of the tab helps to improve the tensile strength of the battery, reduce the deformation rate of the tab under the action of expansion force, and delay the time of crack generation of the tab during the battery cycle. When the number of copper grains with a particle size less than or equal to 0.5 μm is greater than 95% of the total number of copper grains, the tensile strength of the tab is significantly improved, but the bending resistance is significantly sacrificed, which makes the B point with high bending degree in the wound core prone to brittle fracture, which also causes the cell to fail.

[0114] The copper foil provided by the present application is used in the secondary battery and includes copper grains with different particle sizes, which has excellent tensile strength and elongation at break, improves the mechanical strength while having excellent plasticity, forms a good match with high-capacity negative electrode active materials, improves the energy density and capacity of the secondary battery, and improves the safety and service life of the secondary battery.

[0115] In some embodiments, the gram capacity of the negative electrode active material in the negative electrode film layer is 800 mAh / g-1500 mAh / g.

[0116] The copper foil provided by the present application is especially suitable for a negative electrode active material system with a gram capacity of 800 mAh / g-1500 mAh / g. High-capacity negative materials can embed more active ions, such as silicon-based negative electrodes, alkali metal negative electrodes, etc., which usually have high expansion, which increases the probability of fracture or crack of the copper foil in the cell. The copper foil has excellent mechanical properties and plasticity, which can reduce the risk of fracture or crack of the copper foil in the high-energy-density battery system or the high-expansion battery system.

[0117] Without wishing to be bound by any theory, the difference in work hardening ability between the coarse grains and the fine grains is large, and the heterogeneous grain morphology of doping a small amount of coarse grains in the fine grains makes the strain partition in the initial plastic deformation of the copper foil more obvious. This can be due to the fact that the moderate doping of coarse grains produces a higher density of geometrically necessary dislocations (GND) than the case where all the grains are fine grains. During the process of inhomogeneous plastic deformation, the bending of the crystal plane of the copper foil can produce dislocations, which are called geometrically necessary dislocations (GND). Geometrically necessary dislocations (GND) can coordinate the plastic strain caused by deformation and maintain the continuity of the material, which helps to reduce the occurrence of concentrated stress during the deformation process of the copper foil, so that the copper foil exhibits stronger ability to inhibit strain localization, and the plasticity of the copper foil is improved. In addition, in the copper crystal, the contact interface between the grains is called the grain boundary. It can be understood that in the same area, the smaller the grain size of the grain, the higher the total area of the grain boundary, and the higher the grain boundary stress that the copper foil needs to overcome during the deformation process, that is, the higher the mechanical strength. At the same time, the generation of a higher density of geometrically necessary dislocations (GND) during the deformation process of the copper foil helps to reduce the concentrated stress, which can improve the mechanical strength.

[0118] In some embodiments, the number of copper grains with a particle size of less than or equal to 0.5 μm accounts for 75%-95%, 80%-95%, 85%-95%, 83%-93%, 85%-93%, or 87%-93% of the total number of copper grains, which helps to further improve the tensile strength and optimize the mechanical properties of the copper foil.

[0119] In some embodiments, the number of copper grains with a particle size of less than or equal to 0.5 μm accounts for 75%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any value within the range between any two of the above values.

[0120] In this paper, the particle size of the copper grains with a particle size of less than or equal to 0.5 μm is in the range of greater than or equal to 0.1 μm and less than or equal to 0.5 μm.

[0121] In some embodiments, the number of copper grains with a particle size of greater than 0.5 μm accounts for 5%-20%, 2%-20%, 2%-15%, 5%-15%, 5%-13%, 6%-12%, or 7%-10% of the total number of copper grains, which helps to further improve the elongation at break and optimize the plasticity of the copper foil.

[0122] In some embodiments, the number of copper grains having a particle size greater than 0.5 μm accounts for 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 18%, 20%, 25%, 30%, or a range between any two of the above values or any value within the range, of the total number of copper grains.

[0123] In this context, the particle size of the copper grains having a particle size greater than 0.5 μm ranges from greater than 0.5 μm to less than or equal to 3 μm, which helps to reduce or optimize the average particle size of the copper foil and improve the tensile strength of the copper foil.

[0124] The number and particle size of the grains in the copper foil can be tested by methods known in the art. For example, the cross section of the copper foil can be measured by an electron backscatter diffraction instrument (EBSD) and a scanning electron microscope, a pole figure distribution map with a magnification of 3000 can be obtained, the number and particle size of the grains can be counted by the imageJ analysis software of the Oxford C-Nano+ electron backscatter diffraction instrument, the equivalent circle diameter of the grains can be taken as the particle size of the grains, a number distribution map can be made, a skew distribution can be used for fitting, and the particle size and number of the grains in different particle size intervals can be obtained.

[0125] In some embodiments, the number of copper grains having a particle size greater than 0.5 μm and less than or equal to 3 μm accounts for 5%-30% of the total number of the copper grains.

[0126] As mentioned before, the copper grain particle size meeting the condition of greater than 0.5 μm and less than or equal to 3 μm can help to reduce the average grain size of the copper foil and further improve the mechanical strength of the copper foil. Further controlling the number of the copper grains having a particle size greater than 0.5 μm and less than or equal to 3 μm to meet the condition of 5%-30% can make the copper foil have a good elongation at break, have excellent mechanical properties and plasticity, and reduce the risk of fracture or crack of the copper foil in a high-energy-density battery system or a high-expansion battery system, thereby achieving a simultaneous improvement in the energy density and safety of the secondary battery.

[0127] In some embodiments, the specific capacity of the negative active material can be selected as 800 mAh / g, 820 mAh / g, 850 mAh / g, 880 mAh / g, 900 mAh / g, 920 mAh / g, 950 mAh / g, 980 mAh / g, 1000 mAh / g, 1020 mAh / g, 1050 mAh / g, 1080 mAh / g, 1100 mAh / g, 1120 mAh / g, 1150 mAh / g, 1180 mAh / g, 1200 mAh / g, 1250 mAh / g, 1300 mAh / g, 1350 mAh / g, 1400 mAh / g, 1450 mAh / g, 1500 mAh / g, or a range between any two of the above values or any value within the range.

[0128] As used herein, the gram capacity of the negative active material can be determined using instruments and methods known in the art, for example, by following the method: the negative active material is mixed with the conductive agent carbon black, polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent NMP to form a uniform negative electrode slurry; the negative electrode slurry is uniformly coated on the surface of the negative electrode current collector copper foil and dried and cold-pressed; then a lithium metal sheet is used as the counter electrode, a polypropylene (PP) film is used as the separator film, and an electrolyte is injected, wherein the electrolyte formulation used is as follows: dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 type button cell is assembled in an argon glove box. At 25°C, charge to the upper limit cutoff voltage of 3.8V at a rate of 0.1C, and then charge at constant voltage until the current is less than 0.05C; after standing for 30 min, discharge to the lower limit cutoff voltage of 2.0V at a rate of 0.1C, and record the first discharge capacity as Cm, then the gram capacity of the negative active material = discharge capacity Cm / mass of the negative active material.

[0129] It can be understood that the gram capacity of the negative active material can also be obtained by disassembling the battery, obtaining the negative electrode sheet, and then testing after assembling the button cell according to the method described above.

[0130] In some embodiments, the short diameter of at least part of the copper grains with a particle size greater than 0.5 μm is arranged along the thickness direction of the current collector.

[0131] The short diameter of at least part of the copper grains with a particle size greater than 0.5 μm is arranged along the thickness direction of the current collector, which indicates that the internal grain boundary of the copper foil is highly tortuous, and the energy required for the copper foil to break through the grain boundary (i.e., the thickness direction of the current collector) is also greater, which helps to reduce the probability of breaking the copper foil along the thickness direction, improve the brittleness of the current collector, further reduce the risk of copper foil breaking or cracking, and improve the safety of the secondary battery.

[0132] It can be understood that the arrangement direction of the short diameter of at least part of the copper grains with a particle size greater than 0.5 μm can be determined by referring to the EBSD and scanning electron microscopy described above for characterization of the short diameter of the copper grains and the arrangement direction.

[0133] In some embodiments, the average grain size of the copper grains is 0.3 pm to 1.2 pm. In some embodiments, the average grain size of the copper grains is 0.3 pm to 0.6 pm. In some embodiments, the average grain size of the copper grains is 0.3 pm to 0.5 pm. In some embodiments, the average grain size of the copper grains is 0.3 pm, 0.35 pm, 0.4 pm, 0.45 pm, 0.5 pm, 0.55 pm, 0.6 pm, 0.65 pm, 0.7 pm, 0.75 pm, 0.8 pm, 0.85 pm, 0.9 pm, 1.0 pm, 1.1 pm, 1.2 pm, or any range between any of the two of the aforementioned values or any value within the aforementioned range.

[0134] The suitable grain size range is theoretically favorable for the copper foil to obtain suitable grain boundaries, which can make the copper foil have suitable resistance to grain dislocation movement and deformation resistance, and thus can optimize the mechanical strength of the copper foil.

[0135] The average grain size of the grains can be tested by methods known in the art. For example, the cross section of the copper foil is measured by an electron backscatter diffraction instrument (EBSD) and a scanning electron microscope, a pole figure distribution map is obtained, the number and size of the grains are counted by the imageJ analysis software matched with the Oxford C-Nano+ electron backscatter diffraction instrument, the equivalent circle diameter of the grains is taken as the grain size, a number distribution map is made, a skewness distribution is used for fitting, and the average grain size of the grains is obtained.

[0136] In some embodiments, the maximum grain size of the copper grains is 1 pm to 2.5 pm. In some embodiments, the maximum grain size of the copper grains is 1.2 pm to 1.8 pm or 1.2 pm to 2.0 pm. In some embodiments, the maximum grain size of the copper grains is 1 pm, 1.2 pm, 1.4 pm, 1.6 pm, 1.8 pm, 2 pm, or any range between any of the two of the aforementioned values or any value within the aforementioned range.

[0137] The maximum grain size of the copper grains can be tested by methods known in the art. For example, the cross section of the copper foil is measured by an electron backscatter diffraction instrument (EBSD) and a scanning electron microscope, a pole figure distribution map is obtained, the number and size of the grains are counted by the imageJ analysis software matched with the Oxford C-Nano+ electron backscatter diffraction instrument, the equivalent circle diameter of the grains is taken as the grain size, a number distribution map is made, and a skewness distribution is used for fitting. The maximum grain size of the copper grains is the maximum grain size in the statistical results.

[0138] In some embodiments, the minimum grain size of the copper grains is 0.1 pm to 0.3 pm. In some embodiments, the minimum grain size of the copper grains is 0.1 pm to 0.3 pm. In some embodiments, the minimum grain size of the copper grains is 0.1 pm, 0.15 pm, 0.2 pm, 0.25 pm, 0.3 pm, or any value between any two of the above values or any value within the range of the above values.

[0139] The minimum grain size of the copper grains can be tested by methods known in the art, for example, by measuring the cross section of the copper foil using an electron backscatter diffraction instrument (EBSD) and a scanning electron microscope, obtaining a pole figure distribution map, counting the number and size of the grains using the imageJ analysis software provided with the Oxford C-Nano+ electron backscatter diffraction instrument, taking the equivalent circle diameter of the grains as the grain size, making a number distribution map, and fitting the skewness distribution. The smallest grain size in the statistical results is the minimum grain size of the copper grains.

[0140] The grain size span of the copper grains is the difference between the maximum grain size and the minimum grain size in the grain size distribution of the copper foil. In some embodiments, the grain size span of the copper grains is 0.8 pm to 2.5 pm. In some embodiments, the grain size span of the copper grains is 0.8 pm to 2 pm. In some embodiments, the grain size span of the copper grains is 1 pm to 2 pm. In some embodiments, the grain size span of the copper grains is 0.8 pm, 1 pm, 1.2 pm, 1.4 pm, 1.6 pm, 1.8 pm, 2.0 pm, 2.2 pm, 2.4 pm, 2.5 pm, or any value between any two of the above values or any value within the range of the above values.

[0141] The grain size span of the copper grains within the range can make the dispersion degree of the grain size distribution of the copper grains within a suitable range, which can help to balance the grain boundary area and the geometrically necessary dislocation density of the copper grains, improve the grain dislocation movement resistance, and reduce the occurrence of concentrated stress during the deformation of the copper foil, which is beneficial to the copper foil to have excellent plasticity while improving the mechanical strength.

[0142] In some embodiments, the tensile strength of the copper foil is 600 MPa to 1000 MPa under the test conditions of room temperature (20±10°C), a sample length x width of (50±0.25 mm) x (15±0.25 mm), and a tensile speed of 50±0.5 mm / min. In some embodiments, the tensile strength of the copper foil is 700 MPa to 1000 MPa. In some embodiments, the tensile strength of the copper foil is 700 MPa to 800 MPa.

[0143] In some embodiments, the copper foil has an elongation at break of 4-8% under the test condition of room temperature (20±10°C), sample length x width of (50±0.25mm) x (15±0.25mm), and a tensile speed of 50±0.5mm / min. In some embodiments, the copper foil has an elongation at break of 4-7%. In some embodiments, the copper foil has an elongation at break of 5-6%.

[0144] In the present context, the term "tensile strength" refers to the maximum load-bearing strength per unit area of a test sample when the sample is continuously loaded until it breaks.

[0145] In the present context, the term "elongation at break" refers to the ratio of the length change of a material after being stressed until it breaks due to plastic deformation, usually expressed in percentage, and is an important parameter for measuring the deformation ability of a material under stress during stretching.

[0146] In the present application, the tensile strength and elongation at break of the copper foil can be tested by methods known in the art, such as according to the standard GB / T 5230-1995 "Electrolytic Copper Foil". As an example, at least 4 test samples with a length of 50±0.25mm and a width of 15±0.25mm are cut, and the test samples are continuously loaded until they break at room temperature (20±10°C) with a tensile speed of 50±0.5mm / min. The tensile strength of the test sample is calculated by dividing the maximum load by the cross-sectional area of the test sample. The cross-sectional area of the test sample can be calculated by dividing the mass of the test sample by the product of the length of the test sample and the density. The elongation at break can be calculated according to the displacement method after the above test. The test area refers to the detection area during instrument testing. Considering that the test sample may need to be fixed by a clamp during testing, the length and width of the test sample can be greater than the length and width of the test area.

[0147] In some embodiments, the copper foil has a tensile strength of 600MPa, 650MPa, 700MPa, 750MPa, 800MPa, 850MPa, 900MPa, 950MPa, 1000MPa, or a range between any two of the above values or any value within the range, under the test condition of room temperature (20±10°C), sample length x width of (50±0.25mm) x (15±0.25mm), and a tensile speed of 50±0.5mm / min.

[0148] In some embodiments, the copper foil has an elongation at break of 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, or a range between any two of the above values or any value within the range, under the test conditions of room temperature (20±10℃), sample length x width of (50±0.25mm) x (15±0.25mm), and a tensile speed of 50±0.5mm / min.

[0149] The copper foil with the elongation at break has excellent mechanical strength and plasticity, and can be suitable for high-energy-density batteries or high-swelling batteries, and helps to improve the safety of secondary batteries.

[0150] In some embodiments, the copper foil has a hardness of 55HV-65HV. In some embodiments, the copper foil has a hardness of 55HV-60HV. In some embodiments, the copper foil has a hardness of 55HV, 56HV, 57HV, 58HV, 59HV, 60HV, 61HV, 62HV, 63HV, 64HV, 65HV, or a range between any two of the above values or any value within the range.

[0151] The hardness can reflect the pressure deformation or puncture resistance of the copper foil. In the preparation process of the secondary battery, the surface quality of the copper foil can affect the bonding performance of the negative electrode film layer and the copper foil, especially in the cold pressing process step of the secondary battery, the negative active material particles press the copper foil under external pressure, and appropriate hardness is conducive to reducing the surface damage of the copper foil and reducing the influence on the bonding performance of the negative electrode film layer and the copper foil.

[0152] In some embodiments, the copper foil has a thickness of 4μm-10μm. In some embodiments, the copper foil has a thickness of 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or a range between any two of the above values or any value within the range.

[0153] In this application, the thickness of the copper foil can be tested by methods known in the art. As an example, a 20x15cm 2 sample is cut, the cut sample is placed on an electronic balance to weigh, the weight of the sample is obtained, and the volume of the sample is calculated according to the density p of the copper foil of 8.96g / cm 3 The length and width of the sample are known, and thus the thickness of the sample can be calculated.

[0154] The maximum load that can be carried by the ordinary strength copper foil after thinning is sharply attenuated, the thickness of the copper foil that can be used for plastic deformation is severely reduced, resulting in a substantial decrease in the tensile strength and elongation at break of the copper foil, and fatigue fracture is prone to occur in the later stage of the secondary battery cycle, which may cause safety accidents. The copper foil provided in the present application still has excellent tensile strength and elongation at break in the thickness range of 4-10 μm, and has good mechanical properties and plasticity. The copper foil can be thinned without affecting the strength, which is helpful for lightweight design of the battery and further improves the energy density or specific capacity of the secondary battery.

[0155] The present application provides a preparation method of a secondary battery, which comprises using a copper foil as a current collector to prepare a pole piece, the copper foil is prepared by an electroplating method, the electroplating method comprises applying a pulse current to an electroplating solution to reduce and deposit copper ions in the electroplating solution to form a copper foil, the peak value of the pulse current is 40,000-100,000 A, the valley value of the pulse current is 100-20,000 A, and the change cycle of the current is 50-5,000 ms; and the preparation method further comprises using a negative electrode active material with a specific capacity of 800-1,500 mAh / g to prepare the pole piece.

[0156] Compared with the calendering method in the prior art, the electroplating method is mature and simple, has low requirements for equipment, and has low manufacturing cost. The copper foil prepared by the electroplating method has excellent tensile strength and elongation at break, and not only has excellent mechanical strength and plasticity, but also helps to reduce the manufacturing cost of the secondary battery.

[0157] Some schemes use high direct current to prepare a copper foil by an electroplating method in order to improve the mechanical strength of the copper foil. However, because the difference in work hardening ability between the crystal grains is very small, the ability to inhibit strain localization is reduced, and the copper foil is prone to concentrated stress during deformation, which reduces the plasticity of the copper foil and easily causes brittle fracture. In the preparation method provided in the present application, a pulse current is used to continuously change the size of the current to adjust the nucleation and growth rate of copper grains, thereby adjusting the size and morphology of the copper grains, and adjusting the number ratio of copper grains with a particle size of less than or equal to 0.5 μm and copper grains with a particle size of greater than 0.5 μm, and improving the tensile strength and elongation at break of the copper foil, so that the copper foil has excellent mechanical properties and plasticity.

[0158] In the preparation method of the secondary battery provided in the present application, the copper foil is prepared by the above-mentioned electroplating method, and a copper foil with excellent tensile strength and elongation at break is obtained. The copper foil has excellent plasticity while improving the mechanical strength, and the probability of fracture or crack of the copper foil when subjected to the expansion stress of the high specific capacity negative electrode active material before and after the volume change of the particles caused by lithium ion intercalation / deintercalation is reduced, which is beneficial to further improve the safety and service life of the secondary battery.

[0159] In the present context, the term "electroplating method" refers to a method in which metal or alloy is deposited on the surface of a workpiece by means of electroplating principles to form a metal layer.

[0160] In the present context, the term "pulse current" refers to a current or voltage pulse that occurs repeatedly in cycles.

[0161] In some embodiments, the peak value of the pulse current is 40,000 A - 80,000 A. In some embodiments, the peak value of the pulse current is 50,000 A - 70,000 A. In some embodiments, the peak value of the pulse current is 55,000 A - 70,000 A, 50,000 A - 80,000 A, 55,000 A - 80,000 A, 50,000 A - 60,000 A.

[0162] In some embodiments, the peak value of the pulse current is 45,000 A, 50,000 A, 55,000 A, 60,000 A, 65,000 A, 70,000 A, 75,000 A, 80,000 A, 85,000 A, 90,000 A, 95,000 A, 100,000 A, or a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0163] In some embodiments, the valley value of the pulse current is 1,000 A - 10,000 A. In some embodiments, the valley value of the pulse current is 2,000 A - 5,500 A. In some embodiments, the valley value of the pulse current is 2,500 A - 5,000 A, 2,000 A - 8,000 A, 2,000 A - 5,000 A.

[0164] In some embodiments, the valley value of the pulse current is 1,000 A, 2,000 A, 2,500 A, 3,500 A, 4,000 A, 4,500 A, 5,000 A, 8,000 A, 10,000 A, 15,000 A, 20,000 A, or a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0165] In some embodiments, the variation period of the pulse current is 500 ms - 5,000 ms. In some embodiments, the variation period of the pulse current is 2,000 ms - 4,000 ms. In some embodiments, the variation period of the pulse current is 50 ms, 100 ms, 200 ms, 500 ms, 1,000 ms, 1,200 ms, 1,500 ms, 1,800 ms, 2,000 ms, 2,500 ms, 2,750 ms, 3,000 ms, 3,500 ms, 4,000 ms, 4,500 ms, 5,000 ms, or a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0166] In the present disclosure, the term "peak value" refers to the maximum current value of the pulse current, usually the value at the peak of the pulse current waveform. Similarly, the term "valley value" refers to the minimum current value of the pulse current, usually the value at the valley of the pulse current waveform.

[0167] In the present disclosure, the term "change period" refers to the time between two adjacent peaks or valleys in the pulse current waveform, in ms.

[0168] During the deposition of copper ions, increasing the current can accelerate the deposition rate of copper ions, which helps to form fine grains with small particle size; reducing the current can reduce the deposition rate of copper ions, which helps to form relatively regular and orderly grains with large particle size, such as columnar crystals. Adjusting the change parameters of the current, i.e. the peak value, the valley value and the change period, helps to adjust the formation of copper grain nuclei, the growth rate of grains and the deposition time of copper ions, to produce a heterogeneous grain morphology with mixed distribution of large and small grains, and to adjust the particle size and quantity ratio of the grains, thereby improving the tensile strength and elongation at break of the copper foil, so that the copper foil has excellent mechanical strength and plasticity.

[0169] In some embodiments, the pulse current comprises one or more of a square wave pulse current, a sinusoidal wave pulse current, a triangular wave pulse current, and a sawtooth wave pulse current.

[0170] In some embodiments, the pulse current comprises a sinusoidal wave pulse current. The sinusoidal wave pulse current continuously and periodically changes, which is conducive to the continuous and variable growth of the grains.

[0171] In some embodiments, the preparation method is a continuous production method.

[0172] In some embodiments, the preparation method is a roller deposition method. The working principle is that the cathode roller is connected to the negative electrode of the power supply, and the anode tank is connected to the positive electrode of the power supply. When the electroplating solution containing copper ions enters the anode tank, an electric field is formed between the positive and negative electrodes. Under the action of the electric field, copper ions migrate to the surface of the cathode roller and deposit. The deposited copper foil is peeled off from the cathode roller and wound on another roller. The electroplating solution is continuously added and circulated, and copper ions are continuously deposited on the cathode roller under the action of the electric field, continuously peeled off and wound on the winding shaft. This preparation method can realize the continuous production of large-scale copper foil and provide the possibility for industrial application.

[0173] In some embodiments, the cathode electrode is a titanium roller or a titanium plate.

[0174] In some embodiments, the anode electrode is a titanium substrate plate.

[0175] In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm to 20 mm. In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm to 12 mm. In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, or a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0176] In some embodiments, the temperature of the electroplating deposition is 45 °C to 60 °C. In some embodiments, the temperature of the electroplating deposition is 50 °C to 60 °C. In some embodiments, the temperature of the deposition can be selected from 45 °C, 50 °C, 55 °C, 60 °C, a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0177] In some embodiments, the speed of the cathode roller is 2 m / min to 5 m / min. In some embodiments, the speed of the cathode roller is 2 m / min to 3 m / min. In some embodiments, the speed of the cathode roller is 2 m / min, 2.5 m / min, 3 m / min, 3.5 m / min, 4 m / min, 4.5 m / min, 5 m / min, or a range between any two of the aforementioned values or any value between the aforementioned ranges.

[0178] The cathode roller can be any roller suitable for the preparation of copper foil in the art, for example, a titanium roller.

[0179] In some embodiments, the electroplating solution includes a leveler, a wetting agent, and a brightener.

[0180] In the present disclosure, the term "leveler" refers to a substance added to the electroplating solution to improve the flatness of the plated layer, which can adhere to the tip of the copper foil with a high deposition rate, inhibit the growth of the crystal grains, balance the growth rate of the pits and the tip, and improve the flatness of the copper foil.

[0181] In the present disclosure, the term "wetting agent" refers to a substance used to reduce the interfacial tension between the electroplating solution and the electrode, and to improve the adhesion of the plated layer to the substrate. The wetting agent can improve the wettability of the electroplating solution to the substrate, and the wetting of the electroplating solution on the cathode is sufficient to allow the use of a large current for fast electrodeposition, to improve the nucleation rate of the copper foil, and to reduce the grain size of the copper foil.

[0182] In the present disclosure, the term "brightener" refers to a substance that improves the smoothness of the plated layer and reduces the surface roughness. The brightener can make the grain size of the copper foil smaller, and reduce the surface roughness of the copper foil to improve the smoothness of the surface.

[0183] In some embodiments, the leveling agent comprises one or more of collagen, sodium saccharin. In some embodiments, the leveling agent comprises collagen and sodium saccharin.

[0184] Without being bound by any theory, collagen can inhibit the deposition of copper ions, balancing the growth rate of the pits and the tips. The introduction of sodium saccharin can attract the deposition of copper ions at the surface depressions of the copper foil, reducing the microscopic defects or unevenness inside the copper foil, reducing these warpage defects caused by defects. Two different leveling agents help to further improve the surface pits and protrusions of the copper foil, improving the flatness of the copper foil.

[0185] In some embodiments, the concentration of collagen in the electroplating solution is 60 mg / L-300 mg / L. In some embodiments, the concentration of collagen in the electroplating solution is 80 mg / L-150 mg / L. In some embodiments, the concentration of collagen in the electroplating solution is 60 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, or any range between any two of the aforementioned values or any value between the aforementioned ranges.

[0186] The collagen can be selected from proteins commonly used in the copper foil field with a molecular weight size, for example, collagen with a relative molecular weight of 8000-12000.

[0187] In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L-10 g / L. In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L-4 g / L. In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, 3.0 g / L, 3.5 g / L, 4.0 g / L, 4.5 g / L, 5.0 g / L, 5.5 g / L, 6.0 g / L, 6.5 g / L, 7.0 g / L, 7.5 g / L, 8.0 g / L, 8.5 g / L, 9.0 g / L, 9.5 g / L, 10 g / L, or any range between any two of the aforementioned values or any value between the aforementioned ranges. In some embodiments, the wetting agent comprises one or more of hydroxyethyl cellulose, polyethylene glycol. In some embodiments, the wetting agent comprises hydroxyethyl cellulose and polyethylene glycol.

[0188] Without being bound by any theory, hydroxyethyl cellulose has good water solubility and thickening performance, and can form a uniform solution in water, increase the viscosity of the electroplating solution, and adhere to the surface of the copper foil substrate. Polyethylene glycol, as a lubricant and wetting agent, can reduce the surface tension of the liquid and enhance the wetting ability of the liquid to the solid surface. The combination of the two can improve the adhesion performance of the electroplating solution, increase and assist the adhesion of copper ions to the substrate surface and deposition, improve the consistency of the crystal grains during the deposition process, reduce the difference in crystal grain size in the thickness direction, improve the uniformity of the copper foil, and thus improve the mechanical properties of the copper foil.

[0189] In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 50 mg / L-200 mg / L. In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 60 mg / L-150 mg / L. In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, or any range between any two of the above values or any value between the ranges.

[0190] The polyethylene glycol can be selected from commonly used molecular weights in the field of copper foil, for example, polyethylene glycol with a relative molecular weight of 4000.

[0191] In some embodiments, the concentration of hydroxyethyl cellulose in the electroplating solution is 30 mg / L-200 mg / L. In some embodiments, the concentration of hydroxyethyl cellulose in the electroplating solution is 50 mg / L-150 mg / L. In some embodiments, the concentration of hydroxyethyl cellulose in the electroplating solution is 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 120 mg / L, 140 mg / L, 160 mg / L, 180 mg / L, 200 mg / L, or any range between any two of the above values or any value between the ranges.

[0192] The polyethylene glycol can be selected from commonly used molecular weights in the field of copper foil, and in some embodiments, the relative molecular mass of the hydroxyethyl cellulose is 120000.

[0193] In some embodiments, the mass ratio of polyethylene glycol and hydroxyethyl cellulose in the electroplating solution is (1-1.5):1. In some embodiments, the mass ratio of polyethylene glycol and hydroxyethyl cellulose in the electroplating solution is (1.2-1.5):1. As an example, the mass ratio of polyethylene glycol and hydroxyethyl cellulose is 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any range between any two of the above values or any value between the ranges.

[0194] In some embodiments, the brightener comprises sodium poly(dithiopropyl sulfone).

[0195] Without being bound by any theory, sodium poly(dithiopropyl sulfone) adsorbs on the cathode copper surface through the thiol functional group or disulfide bond, the terminal sulfonate anion captures the hydrated copper ions in the plating solution to destroy its hydration, and interacts with the chloride ions adsorbed on the cathode surface to transfer electrons to the captured copper ions through the chloride ions, thereby greatly improving the electrochemical reduction rate of copper ions, refining the grain size and achieving material strengthening.

[0196] In some embodiments, the concentration of sodium poly(dithiopropyl sulfone) in the plating solution is 500 mg / L to 2000 mg / L. In some embodiments, the concentration of sodium poly(dithiopropyl sulfone) in the plating solution is 500 mg / L to 1000 mg / L. In some embodiments, the concentration of sodium poly(dithiopropyl sulfone) in the plating solution is 500 mg / L, 600 mg / L, 700 mg / L, 800 mg / L, 900 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, or any range between any two of the aforementioned values or any value between the aforementioned ranges.

[0197] In some embodiments, the plating solution comprises chloride ions, and the concentration of chloride ions (in terms of chlorine atoms) is 20 mg / L to 80 mg / L. In some embodiments, the concentration of sodium poly(dithiopropyl sulfone) in the plating solution is 40 mg / L to 80 mg / L. In some embodiments, the concentration of chloride ions (in terms of chlorine atoms) is 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, or any range between any two of the aforementioned values or any value between the aforementioned ranges. The use of chloride ions in combination with the wetting agent can further improve the electrodeposition process.

[0198] In some embodiments, the plating solution comprises: collagen with a concentration of 60 mg / L to 300 mg / L, sodium saccharin with a concentration of 0.5 g / L to 10 g / L, polyethylene glycol with a concentration of 50 mg / L to 200 mg / L, hydroxyethyl cellulose with a concentration of 30 mg / L to 200 mg / L, sodium poly(dithiopropyl sulfone) with a concentration of 500 mg / L to 2000 mg / L, and chloride ions with a concentration of 20 mg / L to 80 mg / L.

[0199] In some embodiments, the electroplating solution comprises: collagen with a concentration of 80 mg / L-150 mg / L, sodium saccharin with a concentration of 0.5 g / L-4 g / L, polyethylene glycol with a concentration of 60 mg / L-150 mg / L, hydroxyethyl cellulose with a concentration of 50 mg / L-150 mg / L, sodium polydithiobisphosphine sulfonate with a concentration of 500 mg / L-1000 mg / L, and chloride ions with a concentration of 40 mg / L-80 mg / L.

[0200] The electroplating solution also comprises a copper source to provide copper ions for the electroplating solution. The electroplating solution also comprises sulfuric acid to provide an acidic environment for the reduction of copper ions.

[0201] In some embodiments, the concentration of copper ions (in terms of copper atoms) is 60 g / L-100 g / L. In some embodiments, the concentration of copper ions (in terms of copper atoms) is 80 g / L-100 g / L. In some embodiments, the concentration of copper ions (in terms of copper atoms) is 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, a range between any two of the above values, or any value between the ranges.

[0202] In some embodiments, the concentration of sulfuric acid is 60 g / L-110 g / L. In some embodiments, the concentration of sulfuric acid is 80 g / L-110 g / L. In some embodiments, the concentration of sulfuric acid is 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, a range between any two of the above values, or any value between the ranges.

[0203] In some embodiments, the pH of the electroplating solution is 2.5-4.5, such as 2.5, 3.0, 3.5, 4.0, 4.5, or a range between any two of the above values, or any value between the ranges.

[0204] The synergistic effect of the electroplating solution and the electroplating parameters helps to form a copper foil with heterogeneous grain morphology with different grain sizes, which has excellent tensile strength and elongation at break, and is conducive to improving the safety performance of high-energy density or high-expansion batteries. At the same time, the preparation method can realize large-size manufacturing and has the prospect of industrial application.

[0205] [Negative electrode sheet]

[0206] As an example of the negative electrode sheet, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is provided on either one or both of the two opposite surfaces of the negative current collector.

[0207] In some embodiments, the negative current collector can be the current collector described in the first aspect of the present application, thereby providing a material basis for improving the energy density of the secondary battery and helping to improve the safety of the secondary battery.

[0208] In some embodiments, the other negative active material includes, but is not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and lithium metal. The tin-based material can include one or more of elemental tin, tin oxide, and tin alloy material.

[0209] In some embodiments, the negative active material includes a silicon-based material, and the silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0210] In some embodiments, the mass content of the silicon-based material is 5%-100% based on the total mass of the negative film layer.

[0211] In some embodiments, the mass content of the silicon-based material is 10%-80% based on the total mass of the negative film layer.

[0212] In some embodiments, the mass content of the silicon-based material is 10%-30% based on the total mass of the negative film layer.

[0213] In some embodiments, the mass content of the silicon-based material can be selected as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any numerical range between any two of them, based on the total mass of the negative film layer.

[0214] In some embodiments, the mass content of silicon in the silicon-based material is 20%-50%.

[0215] In some embodiments, the mass content of silicon in the silicon-based material is 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any numerical range between any two of them.

[0216] In some embodiments, the mass content of silicon is 4%-10% based on the total mass of the negative film layer.

[0217] In some embodiments, the mass content of silicon is 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any numerical range between any two of them, based on the total mass of the negative film layer.

[0218] In some embodiments, the negative electrode film layer further optionally comprises 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).

[0219] In some embodiments, the negative electrode tab further comprises a conductive agent. The conductive agent comprises one or more of super-p carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0220] In some embodiments, the conductive agent comprises carbon black. In some embodiments, the conductive agent comprises carbon nanotubes. In some embodiments, the conductive agent comprises carbon black and carbon nanotubes. The conductive agent is widely available and has excellent conductivity, which is conducive to controlling the manufacturing cost of the secondary battery and improving the conductivity of the negative electrode tab.

[0221] In some embodiments, the negative electrode film layer further optionally comprises other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0222] In some embodiments, the negative electrode tab can be prepared by dispersing the above-mentioned components for preparing the negative electrode tab, 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; coating the negative electrode slurry on a negative electrode current collector, and after drying, cold pressing, and the like, the negative electrode tab can be obtained.

[0223] [Positive electrode tab]

[0224] The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material.

[0225] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction of itself, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0226] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be adopted. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0227] In some embodiments, the positive active material can employ a positive active material for a battery known in the art. As an example, the positive active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone only one kind, or two or more kinds in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(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 a modified compound thereof, etc. Examples of the lithium-containing phosphate of 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.

[0228] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluorotetrafluoroethylene-propylene terpolymer, a vinylidene-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0229] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0230] 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; coating the positive electrode slurry on a positive electrode current collector; and drying, cold-pressing, or the like, to obtain the positive electrode tab.

[0231] [Electrolyte]

[0232] The electrolyte serves to conduct ions between the positive electrode tab and the negative electrode tab. The type of electrolyte is not particularly limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0233] In some embodiments, the electrolyte is an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0234] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0235] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanedisulfone, methyl ethyl sulfone, and diethyl sulfone.

[0236] In some embodiments, the electrolytic 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 that can improve certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high-temperature or low-temperature performance of the battery, and the like.

[0237] [Separator]

[0238] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0239] 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.

[0240] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly by a winding process or a stacking process.

[0241] 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.

[0242] 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 plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0243] In some embodiments, the secondary battery includes a winding-type secondary battery, and the positive electrode tab, the negative electrode tab, and the separator film are formed into an electrode assembly by a winding process.

[0244] In some embodiments, the secondary battery includes a stacking-type secondary battery, and the positive electrode tab, the negative electrode tab, and the separator film are formed into an electrode assembly by a stacking process.

[0245] In addition, the secondary battery, the battery module, the battery pack, and the power consuming device of the present application are described below with appropriate reference to the accompanying drawings.

[0246] In one embodiment of the present application, a secondary battery is provided.

[0247] The shape of the secondary battery of the present application is not particularly limited, and can be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 is a secondary battery 5 of a square structure as an example.

[0248] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a cover plate 53. The housing 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 housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly 52 by 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 can be selected by a person skilled in the art according to specific actual needs.

[0249] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module 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 module.

[0250] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0251] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0252] In some embodiments, the above-mentioned battery module can also 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.

[0253] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0254] In addition, the present application also provides a power utilization device, which includes 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 supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization 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.

[0255] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0256] FIG. 6 is a power utilization device as an example. The power utilization 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 secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0257] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a secondary battery can be used as a power supply.

[0258] Examples

[0259] Hereinafter, examples of the present application will be described. The examples described below are illustrative and are for the purpose of explanation only and are not to be taken as limiting the present application. In the examples, unless otherwise noted, techniques or conditions are performed according to those described in the literature or according to the product manual. Unless otherwise noted, the reagents or instruments used are all conventional products that can be obtained commercially.

[0260] I. Performance Test

[0261] (1) Grain characteristics test of copper foil

[0262] The cross section of the copper foil was observed by electron backscatter diffraction (EBSD) combined with scanning electron microscopy, wherein the electron backscatter diffraction instrument was Oxford C-Nano+. The inverse pole figure map (magnification 3000) was obtained, the particle size of each grain was measured, the diameter of the equivalent circle of the grain was taken as the particle size of the grain, the grain size distribution was statistically analyzed, the skewness distribution was fitted, and the total number of copper grains, the average particle size, the maximum particle size, the minimum particle size, the particle size span, the number ratio of copper grains with a particle size less than or equal to 0.5 μm, and the number ratio of copper grains with a particle size greater than 0.5 μm were obtained.

[0263] (2) Mechanical property test

[0264] According to GB / T 5230-1995 "Electrolytic Copper Foil", the copper foil prepared in the examples was cut into a tensile sample with a length L0 of 50 mm and a width of 15 mm. The tensile properties were tested by a universal testing machine at 25°C, and the tensile rate was set to 50 mm / min.

[0265] The cross-sectional area of the tensile sample is wherein ρ is 8.96 g / cm 3 , m is in grams, and L0 is in centimeters.

[0266] The sample was continuously loaded until it was pulled apart, the maximum load F was read from the force dial or the tensile curve, and the tensile strength σ was calculated according to Formula I. b

[0267] The distance between the two lines after the sample was pulled apart was L1, which was measured on the sample or read from the tensile curve. L1 can be measured by the straight line method or the displacement method, and the elongation at break δ was calculated according to Formula II.

[0268] (3) Hardness test

[0269] ​Put the copper foil sample into a metallographic hot-pressing machine, pour in wood powder, and heat at a rate of 150°C / 10 min, use a Vickers hardness tester to press into the copper foil sample (50 g weight), optically measure the lengths of two diagonal lines, and obtain the corresponding Vickers hardness according to the following Vickers hardness calculation formula.

[0270] HV represents Vickers hardness;

[0271] F represents the load of the indenter (Newton force);

[0272] α represents the included angle between the opposite faces of the indenter (136°);

[0273] d represents the average value of the lengths of the diagonal lines (mm).

[0274] (4) Crack failure corresponding to the state of health (SOH)

[0275] At 25°C, charge the battery at 1C constant current to a voltage of 3.8V, then charge at 3.8V constant voltage to a current ≤0.05C, then discharge the battery at 1C constant current to a voltage of 2.5V, which is one charge and discharge process, and such repeated cycle charging and discharging, the whole process is monitored to determine the SOH of the battery, then every 1% SOH, the battery is subjected to computer tomography (CT) to determine whether cracks are generated inside the battery. If cracks are generated, the battery after crack failure in the cycle process is disassembled to observe whether the negative electrode sheet is broken, and the SOH corresponding to the crack failure is obtained.

[0276] (5) Test method for gram capacity of negative active material

[0277] Take a freshly prepared negative electrode sheet or a negative electrode sheet disassembled from a battery monomer, then use a lithium metal sheet as a counter electrode, a polypropylene (PP) film as a separator, and inject an electrolyte, wherein the electrolyte formula used is as follows: mix dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) according to a weight ratio of 1:1:1 to obtain an organic solvent, then dissolve LiPF6 in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Assemble a CR2430 type button cell in an argon glove box. At 25°C, charge at a rate of 0.1C to an upper limit cutoff voltage of 3.8V, and then charge at a constant voltage to a current less than 0.05C; After standing for 30 min, discharge at a rate of 0.1C to a lower limit cutoff voltage of 2.0V, and record the first discharge capacity as Cm. The gram capacity of the negative active material = discharge capacity Cm / mass of the negative active material.

[0278] II. Preparation method

[0279] Example 1

[0280] (1) Preparation of copper foil

[0281] A copper plate or copper wire with a purity of 99.9% or more is dissolved in 98% mass content sulfuric acid to obtain a copper sulfate solution, which is used as a copper source to configure an electroplating solution by adding additives and hydrochloric acid at 55°C. Among them, the concentration of collagen (relative molecular weight 8000-12000) is 120 mg / L, the concentration of polyethylene glycol (relative molecular weight 4000) is 80 mg / L, the concentration of hydroxyethyl cellulose (relative molecular weight about 120000) is 60 mg / L, the concentration of chloride ion is 40 mg / L, the concentration of sodium polydithiobispropane sulfonate is 600 mg / L, the concentration of sodium saccharin is 2 g / L, the concentration of copper ions (in terms of copper atoms) is 90 g / L, and the rest is deionized water. The pH of the electroplating solution is 3.5.

[0282] A sinusoidal pulse current is used to periodically apply current to a cathode titanium roller that has been polished, and the anode electrode is a titanium base plate. The titanium roller has an area of 8.67 m 2 in the electroplating solution, the rotation speed of the titanium roller (roller speed) is 2.4 m / min, the sinusoidal pulse current is applied, the peak current is 55000 A, the peak-to-valley current is 2500 A, the period is 3000 ms, the distance between the cathode and the anode is 10 mm, the deposition temperature is 55°C, and the copper foil is deposited on the titanium roller with a thickness of 6 μm.

[0283] (2) Preparation of battery

[0284] The positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methyl pyrrolidone (NMP) in a weight ratio of 90:5:5, and after being thoroughly stirred and mixed uniformly, a positive electrode slurry is obtained; then the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0285] The negative active material silicon-carbon (silicon content 20wt%-50wt%), artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water in a weight ratio of 20:76:1:1.5:1.5, and after being uniformly mixed, a negative electrode slurry is prepared; then the negative electrode slurry is uniformly coated one or more times on the negative electrode current collector copper foil, and after drying, a negative electrode film is obtained, which is then cold-pressed and slitted to obtain a negative electrode sheet, wherein the gram capacity of the negative active material in the negative electrode film layer is 800 mAh / g-1500 mAh / g.

[0286] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, diethyl carbonate, dimethyl carbonate were mixed in a volume ratio of 1:1:1, and LiPF6 was dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 was 1 mol / L. Then, 2.0 wt% of fluoroethylene carbonate, 0.5 wt% of 1,3-propane sultone and 0.5 wt% of succinic anhydride were added as additives to the above organic solvent, and mixed and stirred uniformly to obtain an electrolyte.

[0287] A polypropylene film was used as a separator film.

[0288] The positive electrode sheet, the separator film and the negative electrode sheet were stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain an electrode assembly; the electrode assembly was placed in a battery shell, and after drying, an electrolyte was injected, and then a lithium ion battery was prepared through processes such as formation and standing.

[0289] Example 2-3

[0290] The preparation method of Example 2-3 was basically the same as that of Example 1, but the composition of the plating solution (see Table 1) and the sinusoidal pulse current parameters (see Table 2) were adjusted; the thickness of the deposited copper foil was 6 μm.

[0291] Comparative Example 1-2

[0292] The preparation method of Comparative Example 1 was basically the same as that of Example 1, but direct current was used for deposition, and the deposition current was 55,000 A. The thickness of the copper foil was 6 μm.

[0293] The preparation method of Comparative Example 2 was basically the same as that of Example 1, and the direct current deposition current was 30,000 A. The thickness of the copper foil was 6 μm.

[0294] Table 1: Composition of plating solution

[0295] Table 2: Sinusoidal pulse current parameters NA means not applicable.

[0296] The grain characteristics and mechanical characteristics of the copper foils prepared in Examples 1-3 and Comparative Examples 1-2, and the results of the secondary batteries were as shown in Table 3.

[0297] Table 3

[0298] FIG. 7, FIG. 10 and FIG. 13 show the inverse pole figure maps of the cross-section of the copper foils of Example 1-3, respectively, tested by EBSD, where T is along the thickness direction of the current collector, the cross-section of the copper foils presents a heterogeneous grain structure with a distribution of grains of different sizes. Compared with the inverse pole figure map of the copper foil of Comparative Example 2 (FIG. 17), it can be seen that there are more fine grains in the copper foils of Example 1-3, and the grain size is smaller in general.

[0299] FIG. 9, FIG. 12, FIG. 15 and FIG. 19 show the grain size distribution of the copper foils of Example 1-3, Comparative Example 2, respectively. It can be seen from Table 3 that in the copper foils of Example 1-3, the number of copper grains with a grain size of 0.5 pm or less accounts for 70%-95%, and is concentrated in the range of 80%-95%, while in Comparative Example 2, the number of copper grains with a grain size of 0.5 pm or less accounts for less than 50%, indicating that the copper grains of Example 1-3 are smaller in general, and the copper foils have higher mechanical strength. In addition, in the copper foils of Example 1-3, the number of copper grains with a grain size greater than 0.5 pm accounts for 5%-30%, while in Comparative Example 2, the number of copper grains with a grain size greater than 0.5 pm accounts for 50.5%, and the copper foils of Example 1-3 have a plasticity comparable to that of the copper foil of Comparative Example 2. This indicates that the preparation of copper foils by sinusoidal pulse current helps to adjust the grain size distribution of copper grains, thereby improving the mechanical properties and plasticity of the copper foils.

[0300] In the copper foils of Example 1-3, the average grain size is in the range of 0.3 pm-0.6 pm, the maximum grain size is in the range of 1 pm-2 pm, the minimum grain size is in the range of 0.1 pm-0.3 pm, and the grain size span is 0.8 pm-2 pm. In Comparative Example 2, the span of the copper grain size is larger, and the average grain size of the copper grains is larger. It can be understood that the copper foils of Example 1-3 have more cumulative crystal interface density, and have high mechanical strength; the copper foils of Comparative Example 2 have less cumulative crystal interface density, and have low mechanical strength. This also corresponds to the tensile strength of Example 1-3 and Comparative Example 2.

[0301] FIG. 8, FIG. 11 and FIG. 14 show the tensile curves of the copper foils of Example 1-3, respectively. It can be seen that the tensile strength of the prepared copper foils is in the range of 600 MPa-1000 MPa, and the elongation at break of the copper foils is in the range of 4%-8% (Table 3), indicating that the copper foils have excellent strength and plasticity. FIG. 16 shows the tensile curve of the copper foil of Comparative Example 1, which has a tensile strength similar to that of Example 1, but an elongation at break of only 2.7%, showing poor plasticity. FIG. 18 shows the tensile curve of the copper foil of Comparative Example 1, which has an elongation at break similar to that of Example 1, but a poor tensile strength.

[0302] The hardness of the copper foils of Example 1-3 is in the range of 55 HV-65 HV, indicating that the copper foils have good pressure deformation or puncture resistance.

[0303] Comparative Example 1 was prepared using the same direct current as the peak current of Example 1. Compared with Example 1, the copper foil of Comparative Example 1 had similar tensile strength and hardness to the copper foil of Example 1, but the elongation at break was significantly lower than that of Example 1. This shows that the grain size distribution of copper can be adjusted by the sinusoidal pulse current and current parameters, so that the copper foil has good mechanical strength and excellent plasticity.

[0304] Compared with Comparative Example 1-2, the crack failure of Example 1-3 corresponded to a significant decrease in SOH, which shows that the copper foil prepared in Example 1-3 significantly improves the service life of the secondary battery and improves the safety of the secondary battery. Although the copper foil of Comparative Example 2 has excellent elongation at break, the tensile strength is low, resulting in a relatively high SOH value corresponding to crack failure. In comparison, the copper foil prepared by using the sinusoidal pulse current with varying current size in Example 1-3 has significantly improved tensile strength and maintains good plasticity, and the SOH value corresponding to crack failure is significantly reduced, which can improve the service life of the battery by more than 25% SOH.

[0305] Further, from the comparison of Example 1-3 and Comparative Example 1-2, it can be seen that the secondary battery of Example 1-3 uses a copper foil that has excellent strength and plasticity, which can be well matched with a negative active material with a specific capacity of 800 mAh / g-1500 mAh / g, effectively prolonging the SOH value of the current collector in the secondary battery including the negative active material with high swelling, and the failure of the battery, thereby improving the energy density and capacity of the secondary battery while improving the safety and service life of the secondary battery.

[0306] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions 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 that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side surface of the negative electrode current collector, the gram capacity of the negative electrode active material in the negative electrode film layer is 800 mAh / g-1500 mAh / g; the negative electrode current collector comprises a copper foil, the copper foil comprises copper grains with different particle sizes, the copper grains comprise copper grains with a particle size less than or equal to 0.5 μm and copper grains with a particle size greater than 0.5 μm, wherein the number percentage of the copper grains with a particle size less than or equal to 0.5 μm in the total number of the copper grains is 70%-95%, and the number percentage of the copper grains with a particle size greater than 0.5 μm in the total number of the copper grains is 5%-30%.

2. The secondary battery according to claim 1, characterized by The particle size of the copper grains with a particle size greater than 0.5 μm is greater than 0.5 μm and less than or equal to 3 μm.

3. The secondary battery according to claim 1 or 2, characterized by The number percentage of the copper grains with a particle size greater than 0.5 μm and less than or equal to 3 μm in the total number of the copper grains is 5%-30%.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The short diameter of at least part of the copper grains with a particle size greater than 0.5 μm is arranged along the thickness direction of the current collector.

5. The secondary battery according to any one of claims 1 to 4, characterized by, The number percentage of the copper grains with a particle size less than or equal to 0.5 μm in the total number of the copper grains is 80%-95%, and / or the number percentage of the copper grains with a particle size greater than 0.5 μm in the total number of the copper grains is 5%-20%.

6. The secondary battery according to any one of claims 1 to 5, characterized by, The copper foil satisfies at least one of the following conditions: (1) the average particle size of the copper grains is 0.3 μm-1.2 μm; (2) the maximum particle size of the copper grains is 1 μm-2.5 μm; (3) the minimum particle size of the copper grains is 0.1 μm-0.3 μm; (4) the particle size span of the copper grains is 0.8 μm-2.5 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized by The copper foil satisfies at least one of the following conditions: (1) the average particle size of the copper grains is 0.3 μm-0.6 μm; (2) the maximum particle size of the copper grains is 1.2 μm-2.0 μm; (3) the minimum particle size of the copper grains is 0.1 μm-0.3 μm; (4) the particle size span of the copper grains is 1 μm-2 μm.

8. The secondary battery according to any one of claims 1 to 7, characterized by, Under the test conditions of room temperature (20±10 ℃), sample length×width (50±0.25 mm)×(15±0.25 mm), and tensile speed 50±0.5 mm / min, the tensile strength of the copper foil is 600 MPa-1000 MPa, and / or the breaking elongation of the copper foil is 4%-8%.

9. The secondary battery according to any one of claims 1 to 8, characterized by, Under the test conditions of room temperature (20±10 ℃), sample length×width (50±0.25 mm)×(15±0.25 mm), and tensile speed 50±0.5 mm / min, the tensile strength of the copper foil is 700 MPa-1000 MPa, and / or the breaking elongation of the copper foil is 4%-7%.

10. The secondary battery according to any one of claims 1 to 9, characterized by Under the test conditions of room temperature (20±10 ℃), sample length×width (50±0.25 mm)×(15±0.25 mm), and tensile speed 50±0.5 mm / min, the tensile strength of the copper foil is 700 MPa-800 MPa, and / or the breaking elongation of the copper foil is 5%-6%.

11. The secondary battery according to any one of claims 1 to 10, characterized by The hardness of the copper foil is 55HV-65HV.

12. The secondary battery according to any one of claims 1 to 11, characterized by The hardness of the copper foil is 55HV-60HV.

13. The secondary battery according to any one of claims 1 to 12, characterized by, The thickness of the copper foil is 4μm-10μm.

14. The secondary battery according to any one of claims 1 to 13, characterized by The secondary battery further comprises a negative electrode film layer on at least one side of the copper foil, and the negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate.

15. The secondary battery according to claim 14, characterized by The negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite and silicon alloy.

16. The secondary battery according to claim 14 or 15, characterized by The mass percentage of the silicon-based material is 5%-100% based on the total mass of the negative electrode film layer, which is optionally 10%-60%, and more optionally 10%-30%.

17. The secondary battery according to any one of claims 14 to 16, characterized by, The mass percentage of silicon element in the silicon-based material is 20%-50%.

18. The secondary battery according to any one of claims 14 to 17, characterized by, The mass percentage of silicon element is 4%-10% based on the total mass of the negative electrode film layer.

19. A method for producing a secondary battery, the method comprising producing an electrode sheet using a copper foil as a current collector, characterized by, The copper foil is prepared by an electroplating method, which comprises applying a periodic pulse current to an electroplating solution to reduce and deposit copper ions in the electroplating solution to form a copper foil; the peak value of the pulse current is 40000A-100000A, the valley value of the pulse current is 100A-20000A, and the change period of the current is 50ms-5000ms; and the preparation method further comprises using a negative electrode active material with a specific capacity of 800mAh / g-1500mAh / g to prepare an electrode sheet.

20. The method of claim 19, wherein, The electroplating method satisfies one or more of the following conditions: (1) the peak value of the pulse current is 40000A-80000A; (2) the valley value of the pulse current is 1000A-10000A; (3) the change period of the pulse current is 500ms-5000ms; (4) the distance between the cathode electrode and the anode electrode is 8mm-20mm; (5) the temperature of electroplating deposition is 45℃-60℃; (6) the speed of the cathode roller is 2m / min-5m / min.

21. The method of manufacturing according to claim 19 or 20, wherein, The electroplating method satisfies one or more of the following conditions: (1) the peak value of the pulse current is 50000A-70000A; (2) the valley value of the pulse current is 2000A-5500A; (3) the change period of the pulse current is 2000ms-4000ms; (4) the distance between the cathode electrode and the anode electrode is 8mm-12mm; (5) the temperature of electroplating deposition is 50℃-60℃; (6) the speed of the cathode roller is 2m / min-3m / min.

22. The production method according to any one of claims 19 to 21, characterized by, The pulse current comprises one or more of square wave pulse current, sinusoidal wave pulse current, triangular wave pulse current and sawtooth wave pulse current, and optionally, the pulse current comprises sinusoidal wave pulse current.

23. The production method according to any one of claims 19 to 22, characterized by, The electroplating solution comprises a leveling agent, a wetting agent and a brightener, The leveling agent comprises one or more of collagen and sodium saccharin; The wetting agent comprises one or more of hydroxyethyl cellulose and polyethylene glycol; The brightener comprises sodium polydithiopropyl sulfone.

24. The method of claim 23, wherein, The electroplating solution comprises: collagen with a concentration of 60 mg / L-300 mg / L, sodium saccharin with a concentration of 0.5 g / L-10 g / L, polyethylene glycol with a concentration of 50 mg / L-200 mg / L, hydroxyethyl cellulose with a concentration of 30 mg / L-200 mg / L, sodium poly(dithiobispropanesulfonate) with a concentration of 500 mg / L-2000 mg / L, and chloride ions (calculated as chlorine atoms) with a concentration of 20 mg / L-80 mg / L.

25. The method of manufacturing according to claim 23 or 24, wherein, The electroplating solution comprises: collagen with a concentration of 80 mg / L-150 mg / L, sodium saccharin with a concentration of 0.5 g / L-4 g / L, polyethylene glycol with a concentration of 60 mg / L-150 mg / L, hydroxyethyl cellulose with a concentration of 50 mg / L-150 mg / L, sodium poly(dithiobispropanesulfonate) with a concentration of 500 mg / L-1000 mg / L, and chloride ions with a concentration of 40 mg / L-80 mg / L.

26. The production method according to any one of claims 19 to 25, wherein, The pH of the electroplating solution is 2.5-4.

5.

27. A pole piece characterized by, The pole piece comprises the copper foil in the secondary battery of any one of claims 1 to 18 or the copper foil prepared by the preparation method of any one of claims 19 to 26.

28. The pole piece of claim 27, wherein, The pole piece further comprises a negative electrode film layer on at least one side of the copper foil, and the negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and metallic lithium.

29. The pole piece of claim 28, wherein, The negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

30. The pole piece of claim 28 or 29, wherein, The mass percentage of the silicon-based material is 5%-100%, optionally 10%-60%, and more optionally 10%-30%, based on the total mass of the negative electrode film layer.

31. The pole piece of any one of claims 28 to 30, wherein, The mass percentage of silicon element in the silicon-based material is 20%-50%.

32. The pole piece of any one of claims 28 to 31, wherein, The mass percentage of silicon element is 4%-10%, based on the total mass of the negative electrode film layer.

33. A wound secondary battery characterized by comprising: The secondary battery of any one of claims 1 to 18 or prepared by the preparation method of any one of claims 19 to 26 or the pole piece of any one of claims 27 to 32.

34. A stacked secondary battery characterized by comprising: The secondary battery of any one of claims 1 to 18 or prepared by the preparation method of any one of claims 19 to 26 or the pole piece of any one of claims 27 to 32.

35. An electrical device, comprising: The secondary battery of any one of claims 1 to 18 or prepared by the preparation method of any one of claims 19 to 26 or the wound-type secondary battery of claim 33 or the stacked-type secondary battery of claim 34.

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