Copper foil and preparation method therefor, negative electrode sheet, battery, and electric device

Abstract

Disclosed in the present disclosure are a copper foil and a preparation method therefor, a negative electrode sheet, a battery, and an electric device. In the copper foil provided by the present disclosure, on the basis of the sum of the texture coefficient of the (111) crystal plane of the copper foil, the texture coefficient of the (200) crystal plane of the copper foil, the texture coefficient of the (220) crystal plane of the copper foil and the texture coefficient of the (311) crystal plane of the copper foil, the texture coefficient ratio of the (220) crystal plane is 75% to 98%.

Description

Copper foil and its preparation method, negative electrode sheet, battery and electrical equipment

[0001] Priority information

[0002] This disclosure requests priority and benefits to patent applications filed with the China National Intellectual Property Administration on April 18, 2025, with patent application numbers 2025207674297, 2025104946203 and 2025105001526, and patent application number 2025107836440 filed with the China National Intellectual Property Administration on June 11, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, specifically to copper foil and its preparation method, negative electrode sheet, battery and electrical equipment. Background Technology

[0004] Existing methods for preparing electrolytic copper foil are mainly based on electrochemical deposition processes. The core of these processes involves reducing copper ions in the electrolyte solution to metallic copper on the cathode surface to form the foil. Due to its high conductivity, flexibility, and mass production capabilities, electrolytic copper foil has become the mainstream material for the negative electrode current collector in batteries (such as lithium-ion batteries and lithium metal batteries), primarily used in power batteries (such as electric vehicles) and consumer batteries (such as mobile phones and laptops).

[0005] However, as an important negative electrode current collector, the properties of copper foil, such as its crystal structure, have a significant impact on the cycle performance of the battery. However, the effect of improving the cycle performance of the battery by improving the copper foil structure needs to be further improved. Summary of the Invention

[0006] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, one object of this disclosure is to provide electrolytic copper foil and its preparation method, a negative electrode, a battery, and an electrical device. The copper foil of this disclosure has a preferred crystal orientation, which can promote the decomposition of lithium salts to form an effective SEI, thereby better improving the cycle performance of the battery.

[0007] The first aspect of this disclosure provides a copper foil. According to embodiments of this disclosure, the proportion of the (220) crystal plane texture coefficient is 75% to 98%, based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil.

[0008] The copper foil proposed in this disclosure has a texture coefficient of over 75% on the (220) crystal plane, exhibiting high affinity for lithium salts (such as lithium trifluoromethanesulfonylimide (LiTFSI) and lithium bisfluorosulfonylimide (LiFSI)). This effectively catalyzes the decomposition of lithium salts and accelerates the decomposition to generate a large amount of effective SEI components (such as lithium fluoride (LiF), lithium oxide (Li2O), and lithium sulfide (Li2S)). A stable SEI can prevent the electrolyte from repeatedly decomposing on the negative electrode surface during cycling, avoiding irreversible loss of active lithium and thus slowing down the cycle capacity decay. Furthermore, the higher the lithium ion insertion / extraction efficiency in subsequent cycles, the better the coulombic efficiency of the battery. In addition, a dense and uniform SEI can guide lithium ions to diffuse uniformly on the electrode surface and inhibit lithium dendrite growth. SEI containing high ionic conductivity components (such as LiF) can reduce lithium ion migration resistance and impedance. These factors have a good effect on improving the cycle performance of the battery.

[0009] In embodiments of this disclosure, the proportion of the (220) crystal plane texture coefficient is 80% to 90%, based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil.

[0010] In embodiments of this disclosure, the ratio of the texture coefficient of the (220) crystal plane to the texture coefficient of the (200) crystal plane is 6.1 to 17.5.

[0011] In embodiments of this disclosure, the ratio of the texture coefficient of the (220) crystal plane to the texture coefficient of the (200) crystal plane is 8.1 to 17.5.

[0012] In embodiments of this disclosure, the tensile strength of the copper foil is 350 MPa to 600 MPa, and / or the elongation of the copper foil is 2% to 10%.

[0013] In embodiments of this disclosure, the thickness of the copper foil is 4 μm to 15 μm.

[0014] In embodiments of this disclosure, the roughness of the copper foil satisfies: 0 < Ra ≤ 0.5 μm, and / or, 0 < Rz ≤ 4 μm.

[0015] A second aspect of this disclosure provides a method for preparing copper foil, comprising:

[0016] Provide copper ion-containing electrolytic solutions;

[0017] A mixture is prepared by mixing a copper-ion electrolyte with an additive; the additive includes a lithium salt functional additive; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonylimide) and lithium bis(fluorosulfonylimide); the functional additive includes a grain refiner.

[0018] The mixture is electrolyzed to obtain copper foil.

[0019] In embodiments of this disclosure, the lithium salt content is 1 mg / L to 15 mg / L based on the mixture; preferably, the lithium salt content is 2 mg / L to 15 mg / L.

[0020] In embodiments of this disclosure, the grain refiner includes one or more of collagen, sodium 3-mercapto-1-propanesulfonate, and sodium dimethylformamide sulfonate; and / or, based on the mixture, the content of the grain refiner is 50 mg / L to 200 mg / L.

[0021] In embodiments of this disclosure, the functional additives further include one or more of leveling agents, wetting agents, and brightening agents.

[0022] In embodiments of this disclosure, the functional additive satisfies at least one of the following (a) to (c):

[0023] (a) The leveling agent includes one or more of hydroxyethyl cellulose, tetrahydrothiazolyl thiophene, and gelatin;

[0024] (b) The wetting agent includes one or more of polyethylene glycol, hydroxymethyl cellulose, and polypropylene glycol;

[0025] (c) Brighteners include one or more of sodium dithiopropane sulfonate, sodium thiopropane sulfonate, and thiourea.

[0026] In embodiments of this disclosure, the content of the additive is less than or equal to 350 mg / L, based on the mixture.

[0027] A third aspect of this disclosure provides a negative electrode sheet, including a negative electrode current collector, which includes the copper foil described in the first aspect above, or a copper foil prepared by the method described in the second aspect above.

[0028] The fourth aspect of this disclosure provides a battery comprising the negative electrode sheet described in the third aspect above.

[0029] In embodiments of this disclosure, at least one side of the negative electrode current collector is provided with a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material; the negative electrode active material comprises one or more of natural graphite, artificial graphite, and silicon-based materials, or the negative electrode active material comprises metallic lithium.

[0030] In embodiments of this disclosure, the battery further includes an electrolyte comprising an electrolyte salt comprising lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0031] In embodiments of this disclosure, the concentration of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide, based on the electrolyte, is 0.02 mol / L to 1 mol / L.

[0032] A fifth aspect of this invention provides an electrical device. According to embodiments of this disclosure, the electrical device includes the battery described in the fourth aspect above. Therefore, the electrical device of this disclosure has a better service life and safety performance.

[0033] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0035] Figure 1 shows the XRD pattern of the copper foil prepared in Example 6;

[0036] Figure 2 is a schematic diagram of the structure of a negative electrode current collector according to an embodiment of the present disclosure;

[0037] Figure 3 is a schematic diagram of the negative electrode current collector according to another embodiment of the present disclosure;

[0038] Figure 4 is a schematic diagram of the negative electrode current collector according to another embodiment of the present disclosure;

[0039] Figure 5 is a physical image of the negative electrode sheet in the empty state of a battery in the related technology;

[0040] Figure 6 is a physical diagram of the negative electrode sheet of a battery in an empty state according to an embodiment of the present disclosure;

[0041] Figure 7 is a side view of the negative electrode sheet according to an embodiment of the present disclosure;

[0042] Figure 8 is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of the present disclosure;

[0043] Figure 9 is a schematic diagram of the structure of the negative electrode sheet according to another embodiment of the present disclosure;

[0044] Figure 10 is a schematic diagram of the structure of a negative electrode sheet according to another embodiment of the present disclosure;

[0045] Figure 11 is a physical image of the negative electrode sheet in the empty state of a battery in the related technology;

[0046] Figure 12 is a physical diagram of the negative electrode sheet of a battery in an empty state according to an embodiment of the present disclosure;

[0047] Figure 13 is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of the present disclosure;

[0048] Figure 14 is a schematic diagram of the structure of the negative electrode sheet according to another embodiment of the present disclosure;

[0049] Figure 15 is a schematic diagram of the structure of a negative electrode sheet according to another embodiment of the present disclosure;

[0050] Figure 16 is a physical image of the negative electrode sheet in the empty state of a battery in the related technology;

[0051] Figure 17 is a physical diagram of the negative electrode sheet of a battery in an empty state according to an embodiment of the present disclosure.

[0052] Explanation of reference numerals in the attached figures: 100 - Negative electrode current collector; 110 - First region; 120 - Second region; 121 - First sub-region; 122 - Second sub-region; 100a - Negative electrode sheet; 101 - Negative electrode current collector; 101a - Main surface; 102 - Negative electrode active material layer; 110a - Third region; 120a - Fourth region; 121a - Third sub-region; 122a - Fourth sub-region; 100b - Negative electrode sheet; 110b - Fifth region; 120b - Sixth region; 121b - Fifth sub-region; 122b - Sixth sub-region; X - Width direction; Y - Length direction; Z - Thickness direction. Detailed Implementation

[0053] The embodiments of this disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure.

[0054] It should be noted that the endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0055] In this disclosure, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this disclosure but do not exclude other contents.

[0056] In lithium-ion batteries, the crystal structure of copper foil, used as the negative electrode current collector, affects the uniformity of lithium deposition, dendrite suppression, and battery cycle life. Existing methods for improving the crystal structure of copper foil mainly focus on surface modification, crystal plane control, and composite structure design. However, the effect of improving the crystal structure of copper foil on the cycle performance of batteries still needs further refinement.

[0057] Therefore, in one aspect of this disclosure, a copper foil is proposed, wherein the proportion of the (220) crystal plane texture coefficient is 75% to 98%, based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil.

[0058] The texture coefficient (TC) is a parameter used to quantify the degree of orientation concentration of a specific crystal plane in a polycrystalline material. It characterizes the intensity of the preferred orientation of a crystal plane by comparing the experimentally measured X-ray diffraction (XRD) intensity of a particular crystal plane (such as (220)) with the theoretical intensity of a randomly oriented sample. The texture coefficient ratio represents the proportion of the texture coefficient of a particular crystal plane in the total coefficients of all measured crystal planes. It is used to compare the contribution of different crystal plane orientations to the overall texture. In X-ray diffraction analysis, the texture coefficient can be calculated by comparing the integral intensity of each diffraction peak with the intensity ratio of a standard powder sample, and then normalized to obtain the coefficient ratio of each crystal plane.

[0059] As an example, based on the sum of the texture coefficients of the (111) crystal plane, (200) crystal plane, (220) crystal plane, and (311) crystal plane, the proportion of the texture coefficient of the (220) crystal plane is 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc.

[0060] Existing conventional copper foils have a significantly lower (220) crystal plane texture coefficient ratio than the present invention, and can only be used as conventional current collectors without showing any special effect on lithium salts. The copper foil proposed in the present invention has a (220) crystal plane texture coefficient of over 75%, exhibiting a high affinity for electrolyte salts (such as lithium trifluoromethanesulfonylimide (LiTFSI) and lithium bisfluorosulfonylimide (LiFSI)), effectively catalyzing the decomposition of LiTFSI or LiFSI salts, and accelerating the decomposition of electrolyte salts LiFSI or LiFSI to generate a large amount of effective SEI components (such as lithium fluoride (LiF), lithium oxide (Li2O), lithium sulfide (Li2S), etc.). The stable SEI can prevent the electrolyte from repeatedly decomposing on the negative electrode surface during cycling, avoiding irreversible loss of active lithium, thereby slowing down the cycle capacity decay; and the higher the lithium ion insertion / extraction efficiency in subsequent cycles, the better the coulombic efficiency of the battery. In addition, a dense and uniform SEI can guide lithium ions to diffuse uniformly on the electrode surface and suppress lithium dendrite growth. SEI containing high ionic conductivity components (such as LiF) can reduce lithium ion migration resistance and reduce impedance. These factors have a good effect on improving the cycle performance of the battery.

[0061] In some embodiments of this disclosure, the proportion of the (220) crystal plane texture coefficient is 80% to 90%, based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil.

[0062] In this embodiment, the proportion of the (220) crystal plane texture coefficient satisfies the above conditions, which is beneficial for better catalyzing the decomposition of electrolyte salts (such as LiTFSI or LiFSI) to form an effective SEI at the negative electrode, thereby reducing side reactions, stabilizing the electrode interface, optimizing ion transport, and other mechanisms, further improving the coulombic efficiency and cycle capacity retention of the battery. In addition, the preparation method for obtaining the above-mentioned proportion of the (220) crystal plane texture coefficient is relatively simple and has low difficulty.

[0063] In some embodiments of this disclosure, the ratio of the texture factor of the (220) crystal plane to the texture factor of the (200) crystal plane is 6.1 to 17.5.

[0064] In this embodiment, the ratio of the texture coefficient of the (220) crystal plane to that of the (200) crystal plane satisfies the above conditions. On the one hand, the higher proportion of the texture coefficient of the (220) crystal plane is beneficial for catalyzing the decomposition of electrolyte salts (such as LiTFSI or LiFSI) to form an effective SEI at the negative electrode, thereby reducing side reactions, stabilizing the electrode interface, optimizing ion transport, and further improving the coulombic efficiency and cycle capacity retention of the battery. On the other hand, the ratio of the texture coefficients of the two satisfies the above conditions, which is beneficial for better improving the mechanical properties of the copper foil. The obtained copper foil exhibits better elongation and tensile strength. During the charge and discharge cycle of the battery, the negative electrode active material will generate stress due to volume expansion and contraction. The copper foil with high elongation and tensile strength can better adapt to this stress change, play a buffering role, suppress the deformation and shedding of the active material, thereby reducing the battery capacity decay caused by the loss of active material, and thus improving the cycle life of the battery.

[0065] As an example, the ratio of the texture factor of the (220) crystal plane to that of the (200) crystal plane is 6.1, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, etc.

[0066] In some embodiments of this disclosure, the ratio of the texture factor of the (220) crystal plane to the texture factor of the (200) crystal plane is 8.1 to 17.5.

[0067] In this embodiment, the ratio of the texture coefficient of the (220) crystal plane to the texture coefficient of the (200) crystal plane satisfies the above conditions, which is conducive to better forming an effective SEI in the negative electrode. At the same time, the copper foil exhibits good mechanical properties, further improving the cycle performance of the battery.

[0068] In some embodiments of this disclosure, the tensile strength of the copper foil is 350 MPa to 600 MPa, and / or the elongation of the copper foil is 2% to 10%.

[0069] In this embodiment of the present disclosure, during the charge and discharge cycle of the battery, the negative electrode active material will generate stress due to volume expansion and contraction. The copper foil with high tensile strength and elongation can better adapt to this stress change, play a buffering role, suppress the deformation and shedding of the active material, thereby reducing the battery capacity decay caused by the loss of active material, and thus helping to improve the cycle life of the battery.

[0070] For example, the tensile strength of copper foil is 350MPa, 370MPa, 390MPa, 410MPa, 430MPa, 450MPa, 470MPa, 490MPa, 510MPa, 530MPa, 550MPa, 570MPa, 590MPa, 600MPa, etc.

[0071] In some embodiments of this disclosure, the thickness of the copper foil is 4 μm to 15 μm.

[0072] In this embodiment of the present disclosure, the thickness of the copper foil meets the above conditions, which can exhibit relatively high strength and toughness. During the charge and discharge cycle of the battery, it can better withstand the volume expansion and contraction of the active material, thereby reducing the detachment phenomenon between the current collector and the active material, which helps to improve the cycle stability of the battery and extend the cycle life of the battery.

[0073] For example, the thickness of the copper foil is 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc.

[0074] Furthermore, the thickness of the copper foil is 4μm to 12μm.

[0075] In some embodiments of this disclosure, the roughness of the copper foil satisfies: 0 < Ra ≤ 0.5 μm, and / or, 0 < Rz ≤ 4 μm.

[0076] Where Ra represents the average absolute height of the profile, used to evaluate the overall roughness of the copper foil surface; Rz represents the average or extreme value of the maximum peak-valley height of the profile, used to evaluate the local extreme height difference of the copper foil.

[0077] In this embodiment, the roughness of the copper foil meets the above-mentioned conditions. When applied to a battery, it helps to improve the adhesion between the copper foil and the active film layer on the surface, mitigating phenomena such as active material detachment during battery charge-discharge cycles. Furthermore, as the negative electrode current collector, the copper foil has a relatively short effective conductive path for surface current, resulting in relatively low impedance. In summary, this promotes improved battery cycle performance.

[0078] Furthermore, the roughness of the copper foil satisfies: 0.15≤Ra≤0.5μm, 1.8≤Rz≤4μm.

[0079] A second aspect of this disclosure provides a method for preparing copper foil, comprising:

[0080] Provide copper ion-containing electrolytic solutions;

[0081] A copper-ion-containing electrolyte solution is mixed with additives to obtain a mixture; the additives include lithium salts and functional additives; the lithium salts include at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, and the functional additives include grain refiners.

[0082] The mixture is electrolyzed to obtain copper foil.

[0083] In the process of electrolytic copper foil, the addition of a grain refiner promotes uniform growth of the copper foil crystal surface, refines the grains, and enables the copper foil to obtain better electrochemical performance. During the research on the preparation of electrolytic copper foil, the inventors discovered that adding lithium bis(fluorosulfonyl)imide (LiFSI) and / or lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to a copper ion-containing electrolytic solution allows the anions to autonomously bond with the Cu(220) crystal surface, thereby promoting Cu… 2+ Ions aggregate on the Cu(220) crystal plane, achieving preferential growth of the Cu(220) crystal plane during electrolysis, forming a copper foil with a high proportion of (220) crystal plane texture system. Due to the induction of the above lithium salt, Cu(220) has a good adsorption effect on the electrolyte salt of the corresponding battery cell, which will catalyze and promote the more efficient decomposition of the electrolyte salt during its cycle. For battery cells containing this LiFSI or LiTFSI electrolyte salt, it will promote the full decomposition of these electrolyte salts into inorganic matter of the SEI film, improve the interfacial ion transport efficiency and stability, and thus improve the cycle performance of the battery cell.

[0084] Furthermore, the proportion of the (220) crystal plane texture coefficient of the obtained copper foil is significantly improved. Based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil, the proportion of the (220) crystal plane texture coefficient is 75% to 98%.

[0085] The copper foil prepared according to the present invention has a texture coefficient of over 75% on the (220) crystal plane, exhibiting high affinity for electrolyte salts (such as LiTFSI and LiFSI), effectively catalyzing the decomposition of electrolyte salts, and accelerating the decomposition of LiTFSI / LiFSI to generate a large amount of effective SEI components (such as lithium fluoride (LiF), lithium oxide (Li2O), lithium sulfide (Li2S), etc.). The stable SEI can prevent the electrolyte from repeatedly decomposing on the negative electrode surface during cycling, avoiding irreversible loss of active lithium, thereby slowing down the cycle capacity decay; and the higher the lithium ion insertion / extraction efficiency in subsequent cycles, the better the coulombic efficiency of the battery. In addition, the dense and uniform SEI can guide lithium ions to diffuse uniformly on the electrode surface and inhibit lithium dendrite growth, while the SEI containing high ionic conductivity components (such as LiF) can reduce lithium ion migration resistance and reduce impedance. These factors have a good effect on improving the cycle performance of the battery.

[0086] The copper-containing electrolytic solution used in this embodiment of the invention provides copper ions for depositing copper foil and can be a mixed solution of copper salt (such as copper sulfate) and acidic medium (such as sulfuric acid).

[0087] Furthermore, in the copper ion electrolytic solution, the concentration of copper sulfate (CuSO4·5H2O) is (85±5) g / L, and the concentration of sulfuric acid (H2SO4) is (100±10) g / L.

[0088] In some embodiments of this disclosure, the lithium salt content is 1 mg / L to 15 mg / L based on the mixture; specifically, the lithium salt content is 2 mg / L to 10 mg / L.

[0089] In this embodiment of the present disclosure, the content of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide added to the mixture meets the above conditions, and copper foil with a significantly increased proportion of (220) crystal plane texture system can be obtained. Based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of copper foil, the proportion of (220) crystal plane texture coefficient can reach more than 75%, which is conducive to better improving the coulombic efficiency and cycle capacity retention of the battery.

[0090] The content of LiFSI / LiTFSI in the mixture can be determined qualitatively by identifying functional groups using Fourier Transmission Infrared Spectroscopy (FTIR) and quantitatively by using ion chromatography. For example, the lithium salt content can be 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, 11 mg / L, 12 mg / L, 13 mg / L, 14 mg / L, and 15 mg / L.

[0091] In this embodiment, the contents of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) meet the above conditions. On the one hand, this is beneficial to obtain copper foil with a higher proportion of (220) crystal plane texture system. On the other hand, it is beneficial to reduce the residual amount of lithium bis(trifluoromethanesulfonyl)imide on the copper foil, and better improve the surface roughness of the copper foil, so as to promote the overall improvement of the cycle performance of the battery.

[0092] In some embodiments of this disclosure, the grain refiner includes one or more of collagen, sodium 3-mercapto-1-propanesulfonate, and sodium dimethylformamide sulfonate; and / or, based on the mixture, the content of the grain refiner is 50 mg / L to 200 mg / L.

[0093] In this embodiment of the invention, by adding one or more of collagen, sodium 3-mercapto-1-propanesulfonate, and sodium dimethylformamide sulfonate to the copper ion-containing electrolyte solution, it is beneficial to refine the grain size, allow copper atoms to grow in a planar shape, make the copper grains more densely arranged, reduce the grain size, reduce the occurrence of pores, and improve the mechanical properties of the copper foil, such as increasing the tensile strength of the copper foil.

[0094] As the content of grain refiner increases, the electrolyte viscosity tends to increase, the deposition rate tends to decrease, and the grain refinement is enhanced. This may lead to an increase in the brittleness of the copper foil and the formation of organic film residues, affecting surface cleanliness. Conversely, as the content of grain refiner decreases, grain coarsening tends to increase, surface roughness (Ra) tends to increase, and tensile strength tends to decrease. In the embodiments of this disclosure, the content of grain refiner satisfies the above conditions, which is beneficial for obtaining copper foil with better overall performance.

[0095] As an example, based on the mixture, the content of the grain refiner is 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 110 mg / L, 120 mg / L, 130 mg / L, 140 mg / L, 150 mg / L, 160 mg / L, 170 mg / L, 180 mg / L, 190 mg / L, 200 mg / L, etc.

[0096] In some embodiments of this disclosure, the functional additives also include one or more of leveling agents, wetting agents, and brightening agents.

[0097] In this embodiment, by adding a leveling agent, it can be adsorbed onto the surface of the cathode roller to form an interface barrier layer to prevent copper ions from depositing too quickly in a localized manner, thereby promoting uniform deposition of copper atoms. Hydroxyethyl cellulose (HEC) is the most common, but it usually has multiple effects, acting as a leveling agent, grain refiner, and wetting agent, and its function is not singular. By adding a wetting agent, the surface tension of the cathode can be reduced, promoting the rapid escape of hydrogen bubbles that occur during the production process and reducing the generation of pinholes in the copper foil. By adding a brightener, it can be used to improve the surface morphology of the copper foil, enhance its brightness and smoothness, and may also affect its microstructure.

[0098] In some embodiments of this disclosure, the functional additive satisfies at least one of the following (a) to (c):

[0099] (a) The leveling agent includes one or more of tetrahydrothiazolyl thiophene, hydroxyethyl cellulose, and gelatin;

[0100] (b) The wetting agent includes one or more of polyethylene glycol, hydroxymethyl cellulose, and polypropylene glycol;

[0101] (c) Brighteners include one or more of sodium dithiopropane sulfonate, sodium thiopropane sulfonate, and thiourea.

[0102] In this embodiment, by adding a leveling agent such as tetrahydrothiazolyl thiophene, the reduction of copper ions is hindered, the peak height is reduced, the contour undulation of the copper foil surface is slowed down, and the surface roughness is reduced. Alternatives can also be hydroxyethyl cellulose, gelatin, etc. Taking hydroxyethyl cellulose as an example, its concentration range can be 50 mg / L to 200 mg / L.

[0103] In this embodiment, by adding wetting agents such as polyethylene glycol, hydroxymethyl cellulose, and polypropylene glycol, the surface tension of the cathode can be reduced, promoting the rapid escape of hydrogen bubbles generated during the production process and reducing the generation of pinholes in the copper foil. Taking polyethylene glycol as an example, its concentration range can be 20 mg / L to 200 mg / L.

[0104] In this embodiment, by adding brighteners such as sodium dithiopropane sulfonate, sodium thiopropane sulfonate, and thiourea, sodium dithiopropane sulfonate (SPS) cannot directly participate in the reduction of copper atoms during electrodeposition. Besides its grain-refining effect, it also improves the surface gloss of the copper foil. When SPS is added to an electrolyte solution system containing collagen and HEC, the degree of electrolyte and additive consumption is judged by observing the gloss of the raw foil. Adjustments and replenishments are made accordingly. The synergistic effect makes the copper foil surface smoother and improves the gloss of the rough surface. For example, the concentration range of sodium dithiopropane sulfonate can be 0.5 mg / L to 5 mg / L.

[0105] In some embodiments of this disclosure, the content of the additive is less than or equal to 350 mg / L, based on the mixture.

[0106] In this embodiment of the present disclosure, the total amount of additives added to the mixture satisfies the above conditions in order to better improve the performance of copper foil, such as the characteristics of crystal structure, surface properties, and mechanical properties, enhance the electrochemical performance of copper foil as a negative electrode current collector, and better improve the cycle performance of the battery.

[0107] For example, the additive content is 350 mg / L, 300 mg / L, 250 mg / L, 220 mg / L, 200 mg / L, 180 mg / L, 150 mg / L, 120 mg / L, 100 mg / L, 80 mg / L, 50 mg / L, etc.

[0108] In some embodiments of this disclosure, the structural parameters of the copper foil are controlled by adjusting the preparation parameters during the electrolytic treatment step. The structural parameters include one or more of the following: (220) crystal texture coefficient ratio, tensile strength, elongation, thickness, roughness, etc.; the preparation parameters include one or more of the following: current density, electrolysis temperature, electrolysis pressure.

[0109] In some embodiments of this disclosure, the preparation parameters controlled during the electrolysis process include at least one of the following (a) to (c):

[0110] (a) Current density is 30 A / dm 2 ~70A / dm 2 As an example, the current density is 30 A / dm. 2 35A / dm 2 40A / dm 2 45A / dm 2 50A / dm 2 55A / dm 2 60A / dm 2 65A / dm 2 70A / dm 2 wait.

[0111] (b) The electrolysis temperature is 50℃~60℃; for example, the electrolysis temperatures are 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, etc.

[0112] (c) The electrolysis voltage is 3V to 5V; for example, the electrolysis voltages are 3V, 3.2V, 3.4V, 3.6V, 3.8V, 4V, 4.2V, 4.4V, 4.6V, 4.8V, 5V, etc.

[0113] Currently, a key factor limiting fast charging of lithium-ion batteries is the tendency for lithium metal to deposit on the negative electrode surface during fast charging, a phenomenon known as lithium plating. When lithium plating occurs, on the one hand, the deposited lithium metal reacts with the electrolyte, consuming the active lithium at the positive electrode and causing a rapid decline in battery capacity; on the other hand, continued lithium metal growth can easily puncture the separator, leading to serious safety issues.

[0114] To address the issue of lithium plating, related technologies employ self-heating to raise the battery cell to a higher temperature (45-60°C) to improve lithium-ion charge-discharge kinetics and reduce the risk of lithium plating. However, the inventors discovered that high temperatures can easily lead to increased side reactions in lithium-ion batteries. For example, higher temperatures can promote chemical reactions between the electrolyte and active lithium, causing the active lithium to be consumed. This results in decreased battery energy, increased internal resistance, reduced power, and decreased range.

[0115] Based on the aforementioned technical problems, the inventors discovered through research on the mechanism of lithium plating that it first occurs in the edge region of the non-overhang area on the negative electrode sheet, near the overhang region. The overhang region, also known as the supercapacitor region or suspended region in the battery field, refers to the area of ​​the active material layer of the negative electrode sheet that exceeds the corresponding area of ​​the positive electrode sheet. During charging and discharging, lithium ions are extracted from the positive electrode and inserted into the negative electrode. If the area of ​​the negative electrode is smaller than that of the positive electrode, the positive electrode active material at the edge may not be able to find a corresponding negative electrode receiving site, leading to lithium plating at the edge of the negative electrode, which can cause short circuits or thermal runaway risks. Therefore, by designing an overhang region on the negative electrode sheet, sufficient space can be ensured to receive lithium ions.

[0116] However, during charging, lithium on the edge of the non-overhang region near the overhang region on the negative electrode diffuses into the overhang region. During discharging, lithium in the overhang region moves towards the edge region. As a result, during the next charge, the edge of the non-overhang region near the overhang region does not have enough space to receive lithium from the positive electrode, leading to lithium plating at the edge of the non-overhang region near the overhang region.

[0117] Therefore, the inventors discovered that by reducing the migration rate between the edge of the non-overhang region near the overhang region and the overhang region, the amount of lithium migration during charging and discharging can be reduced, thereby reducing the difference in the state of charge (SOC) between the edge of the non-overhang region near the overhang region and the overhang region, and effectively reducing the occurrence of lithium plating during fast charging.

[0118] The negative electrode current collector 100, negative electrode sheet, battery, battery assembly, and electrical equipment provided in this disclosure are described below with reference to the accompanying drawings and specific embodiments.

[0119] Referring to Figures 2 to 4, the negative electrode current collector 100 of this embodiment can be used as the negative electrode sheet of a battery. The negative electrode current collector 100 may include a metal foil and a carbon coating layer.

[0120] The metal foil includes two main surfaces disposed opposite each other in the thickness direction of the metal foil. A carbon coating layer is located on at least one main surface of the metal foil. Along a first direction, at least one carbon coating layer includes a first region 110 and a second region 120. The first direction is perpendicular to the thickness direction of the metal foil. The thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110.

[0121] In this disclosure, when the thickness of the carbon coating layer is not uniform, the thickness of the carbon coating layer in the first region 110 and the second region 120 can be understood as the average thickness.

[0122] It is readily understood that the negative electrode sheet has an overhang region. Along the thickness direction of the negative electrode current collector 100, the orthogonal projection of the overhang region onto the main surface can lie on the second region 120. Therefore, lithium plating is prone to occur in the second region 120 of the negative electrode sheet. In particular, lithium plating tends to occur at the edge of the non-overhang region near the overhang region. In this embodiment, the thickness of the carbon coating layer in the second region 120 can be less than the thickness of the carbon coating layer in the first region 110, thereby making lithium plating less likely to occur in the second region 120, and thus making lithium plating less likely to occur at the edge of the non-overhang region near the overhang region and in the overhang region itself.

[0123] Specifically, the carbon coating layer can be used to enhance the conductivity between the negative electrode current collector 100 and the negative electrode active material, thereby reducing internal resistance and improving charging and discharging efficiency. Therefore, when the thickness of the carbon coating layer is small, it will affect the conductivity between the negative electrode current collector 100 and the negative electrode active material, leading to an increase in the interfacial impedance between them, which in turn affects the lithium migration rate.

[0124] Therefore, in this embodiment, by setting the thickness of the carbon coating layer in the second region 120 to be less than the thickness of the carbon coating layer in the first region 110, the migration rate of lithium flowing in the second region 120 can be reduced, thereby effectively reducing the possibility of lithium plating occurring in the second region 120. Thus, the possibility of lithium plating affecting battery energy density can be reduced, improving battery performance.

[0125] In summary, by setting the thickness of the carbon coating layer in the second region 120 to be less than the thickness of the carbon coating layer in the first region 110, the occurrence of lithium plating during fast charging can be reduced from aspects such as the mechanism of lithium plating. Therefore, this embodiment of the invention, while solving the lithium plating problem, does not require high-temperature heating of the battery, which helps to reduce the impact of high temperature on battery performance and lifespan.

[0126] Referring to Figures 2 to 4, the dashed line can be used to enclose and form a first region 110. A second region 120 can be formed between the dashed line and the outermost solid line of the negative electrode current collector 100.

[0127] In some examples, the carbon coating layer may be disposed on one of the main surfaces of the metal foil. However, the carbon coating layer may be disposed on either main surface, and this is not limited in the embodiments of this disclosure. Alternatively, the carbon coating layer may be disposed on both main surfaces of the metal foil.

[0128] It is readily understood that when the carbon coating layer is located on one of the main surfaces, the main surface may include a first region 110 and a second region 120. The main surface without the carbon coating layer does not have the first region 110 and the second region 120. When the carbon coating layer is provided on both main surfaces, the first region 110 and the second region 120 are provided on each of the two main surfaces, or the first region 110 and the second region 120 are provided on one of the two main surfaces. This is not limited in the embodiments disclosed herein.

[0129] In some examples, the fact that the thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110 can mean that the thickness of the carbon coating layer in a portion of the second region 120 is less than the thickness of the carbon coating layer in the first region 110; or that the thickness of the carbon coating layer in all the second regions 120 is less than the thickness of the carbon coating layer in the first region 110. This is not limited in this embodiment.

[0130] In some possible implementations, the second region 120 of this disclosure embodiment is disposed on one or both edges of the negative electrode current collector 100 in the longitudinal direction Y.

[0131] The second region 120 can be located on one side edge of the negative electrode current collector 100 along the length direction Y, or the second region 120 can be located on both sides edge of the negative electrode current collector 100 along the length direction Y.

[0132] Referring to the direction shown in Figure 2, the length direction can refer to the Y direction. Therefore, the second region 120 can be located above the first region 110. Alternatively, the second region 120 can be located below the first region 110. Or, the second region 120 can be located both above and below the first region 110.

[0133] Since the thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110, the possibility of lithium plating in the second region 120 is reduced by decreasing the lithium migration rate in the second region 120. Therefore, when the second region 120 is provided on at least one side edge in the length direction Y of the negative electrode current collector 100, lithium plating can be less likely to occur on that side edge where the second region 120 is provided.

[0134] In some possible implementations, the second region 120 of this disclosure embodiment is disposed on one or both edges of the negative electrode current collector 100 in the width direction X.

[0135] The second region 120 can be located on one side edge of the negative electrode current collector 100 in the width direction X, or the second region 120 can be located on both sides edge of the negative electrode current collector 100 in the width direction X.

[0136] Referring to the direction shown in Figure 2, the width direction can refer to the X-direction. Therefore, the second region 120 can be located to the left of the first region 110. Alternatively, the second region 120 can be located to the right of the first region 110. Or, the second region 120 can be located to the left and right of the first region 110.

[0137] Since the thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110, the possibility of lithium plating in the second region 120 is reduced by decreasing the mobility of lithium in the second region 120. Therefore, when the second region 120 is provided on at least one side edge in the width direction X of the negative electrode current collector 100, lithium plating can be less likely to occur on that side edge where the second region 120 is provided.

[0138] In some possible implementations, the second region 120 of the present disclosure embodiment may be disposed on one or both edges of the negative electrode current collector 100 in the length direction Y, and the second region 120 may be disposed on one or both edges of the negative electrode current collector 100 in the width direction X.

[0139] The second region 120 can be disposed on one edge in the length direction Y and one edge in the width direction X of the negative electrode current collector 100. Alternatively, the second region 120 can be disposed on both edges in the length direction Y and one edge in the width direction X of the negative electrode current collector 100. Alternatively, the second region 120 can be disposed on one edge in the length direction Y and both edges in the width direction X of the negative electrode current collector 100. Alternatively, the second region 120 can be disposed on both edges in the length direction Y and both edges in the width direction X of the negative electrode current collector 100. No specific limitation is made in this disclosure.

[0140] When the negative electrode current collector 100 has a rectangular structure, the second region 120 is disposed on both sides of the length direction Y and the two sides of the width direction X of the negative electrode current collector 100, which can mean that the second region 120 is arranged around the first region 110.

[0141] Referring to the direction shown in Figure 2, the second region 120 can be located above and below the first region 110, and to the left and right of the first region 110.

[0142] Since the thickness of the carbon coating layer in the second region 120 is less than that in the first region 110, the possibility of lithium plating in the second region 120 is reduced by decreasing the lithium migration rate in the second region 120. Therefore, when the second region 120 is arranged around the first region 110, lithium plating can be less likely to occur in the edge region of the negative electrode.

[0143] In summary, since the thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110, making lithium plating less likely to occur in the second region 120, it is easy to understand that when the negative electrode current collector 100 is rectangular, the effect of setting the second region 120 on both sides of the length direction Y and width direction X of the negative electrode current collector 100 to solve the lithium plating problem is better than setting the second region 120 on both sides of the width direction X of the negative electrode current collector 100 to solve the lithium plating problem, which is better than setting the second region 120 on both sides of the length direction Y of the negative electrode current collector 100 to solve the lithium plating problem.

[0144] In some examples, when the negative electrode current collector 100 has multiple edges, when the negative electrode current collector 100 with the second region 120 is applied to the negative electrode sheet, the edges of the negative electrode sheet are less prone to lithium plating. Therefore, the more edges with the second region 120, the more edges on the negative electrode sheet are less prone to lithium plating. Thus, when the second region 120 is arranged around the outer periphery of the first region 110, the possibility of lithium plating can be reduced more effectively, thereby improving the battery's lifespan.

[0145] In some possible implementations, referring to Figures 2 to 4, the negative electrode current collector 100 of this disclosure is used to be stacked with the positive electrode sheet of the battery. The second region 120 may include a first sub-region 121 and a second sub-region 122. The first sub-region 121 is located on the side of the first region 110 near the edge of the carbon coating layer. The second sub-region 122 is located at the edge of the first sub-region 121 away from the first region 110.

[0146] In this configuration, the orthographic projection of the edge of the first sub-region 121 away from the first region 110 onto the main surface coincides with the edge of the orthographic projection of the positive electrode sheet onto the main surface. Similarly, the orthographic projection of the edge of the second sub-region 122 near the first region 110 onto the main surface coincides with the edge of the orthographic projection of the positive electrode sheet onto the main surface.

[0147] Referring to Figures 2 to 4, the first sub-region 121 can refer to the area enclosed by the dotted line and the dashed line. The second sub-region 122 can refer to the area enclosed by the dashed line and the outermost solid line of the negative electrode current collector 100.

[0148] It is easy to understand that, along the thickness direction of the metal foil, the orthogonal projection of the second sub-region 122 onto the main surface can coincide with the overhang region of the negative electrode. The orthogonal projection of the first sub-region 121 onto the main surface can correspond to the region on the negative electrode where lithium plating is prone to occur.

[0149] It should be noted that, since the thickness of the carbon coating layer in the second region 120 is less than the thickness of the carbon coating layer in the first region 110, the thickness of the carbon coating layer in at least one of the first sub-region 121 and the second sub-region 122 can be less than the thickness of the carbon coating layer in the first region 110.

[0150] For example, the thickness of the carbon coating layer in the first sub-region 121 may be less than the thickness of the carbon coating layer in the first region 110, while the thickness of the carbon coating layer in the second sub-region 122 may be the same as the thickness of the carbon coating layer in the first region 110. Alternatively, the thickness of the carbon coating layer in the second sub-region 122 may be less than the thickness of the carbon coating layer in the first region 110, while the thickness of the carbon coating layer in the first sub-region 121 may be the same as the thickness of the carbon coating layer in the first region 110. Alternatively, the thickness of the carbon coating layer in both the first sub-region 121 and the second sub-region 122 may be less than the thickness of the carbon coating layer in the first region 110. In other words, the thickness of the carbon coating layer in all second regions 120 is less than the thickness of the carbon coating layer in the first region 110.

[0151] Specifically, when the thickness of the carbon coating layer in the first sub-region 121 is less than the thickness of the carbon coating layer in the first region 110, the resistance to charge transport within the first sub-region 121 can be increased. Therefore, during charging, the mobility and proportion of lithium entering the second sub-region 122 from the first sub-region 121 can be reduced. Consequently, during discharging, the mobility and proportion of lithium entering the first sub-region 121 from the second sub-region 122 also decrease. This reduces the space occupied by lithium in the first sub-region 121 for receiving lithium from the positive electrode. Consequently, when recharging, the first sub-region 121 can have space to receive lithium from the positive electrode, which helps reduce the possibility of lithium plating in the first sub-region 121.

[0152] When the thickness of the carbon coating layer in the second sub-region 122 is less than the thickness of the carbon coating layer in the first region 110, the resistance to charge transport within the second sub-region 122 can be increased. Therefore, during discharge, the mobility and proportion of lithium entering the first sub-region 121 from the second sub-region 122 can be reduced, thus reducing the space occupied by lithium in the first sub-region 121 for receiving lithium from the positive electrode. Consequently, when recharged, the first sub-region 121 can have sufficient space to receive lithium from the positive electrode, which helps to reduce the possibility of lithium plating in the first sub-region 121.

[0153] When the thickness of the carbon coating layer in both the first sub-region 121 and the second sub-region 122 is less than the thickness of the carbon coating layer in the first region 110, the impedance to charge transport within the entire second region 120 can be increased. Therefore, during charging, the mobility and proportion of lithium entering the second sub-region 122 from the first sub-region 121 can be reduced. Furthermore, during discharging, the mobility and proportion of lithium entering the first sub-region 121 from the second sub-region 122 can also be reduced. This reduces the space occupied by lithium in the first sub-region 121 for receiving lithium from the positive electrode, thus ensuring sufficient space for the first sub-region 121 to receive lithium from the positive electrode during recharging, thereby reducing the likelihood of lithium plating in the first sub-region 121.

[0154] In summary, in this embodiment of the present disclosure, by making the thickness of the carbon coating layer in the second region 120 less than the thickness of the carbon coating layer in the first region 110, the negative electrode current collector 100 can be improved from the mechanism of lithium plating, thereby reducing the occurrence of lithium plating. Therefore, this embodiment of the present disclosure, while solving the lithium plating problem, does not require high-temperature heating of the battery, which helps to reduce the impact of high temperature on battery performance and lifespan.

[0155] In some feasible ways, the carbon coating layer may include one or a mixture of materials such as carbon black, carbon nanotubes, graphene, and graphite sheets.

[0156] In this disclosure, "multiple" refers to two or more.

[0157] In some feasible ways, the width of the second region 120 can be greater than or equal to 0.5 mm and less than or equal to 10 mm.

[0158] It should be noted that the width of the second region 120 can refer to the dimension of the second region 120 from its edge near the first region 110 to its edge away from the first region 110, in the direction outward from the center of the first region 110. For example, when the negative electrode is rectangular, referring to the direction shown in FIG2, along the X direction, the dimension of the second region 120 from its edge near the first region 110 to its edge away from the first region 110 is the width of the second region 120. Furthermore, along the Y direction, the dimension of the second region 120 from its edge near the first region 110 to its edge away from the first region 110 is also the width of the second region 120.

[0159] Because the thickness of the carbon coating layer in the second region 120 is less than that in the first region 110, and the thinner carbon coating layer easily affects conductivity and lithium insertion / extraction activity, it increases charge transport impedance and reduces lithium mobility and proportion. Therefore, when the width of the second region 120 is too large (greater than 10 mm), the charge transport impedance is significantly increased, restricting electron transport within the negative electrode, thus affecting the battery's charge / discharge performance and requiring a longer time to complete charge transfer during charging and discharging. Furthermore, it also restricts electron transport between active materials within the negative electrode active material layer, preventing full utilization of the active materials and reducing battery capacity and energy density.

[0160] When the width of the second region 120 is too small (less than 0.5 mm), the area of ​​the second region 120 with a smaller carbon coating thickness is smaller, which has a smaller impact on charge transport impedance, a smaller effect on reducing conductivity and lithium insertion / extraction activity, and an insignificant effect on solving the lithium plating problem, thus resulting in poor improvement of the battery.

[0161] Therefore, by setting the width of the second region 120 to be greater than or equal to 0.5 mm and less than or equal to 10 mm, the aforementioned technical problems can be effectively solved. This reduces the thickness of the carbon coating layer, minimizing its impact on overall battery performance and improving battery life, while also addressing the issue of lithium plating.

[0162] For example, the width of the second region 120 can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, or any combination thereof.

[0163] Preferably, the width of the second region 120 can be greater than or equal to 2 mm and less than or equal to 5 mm.

[0164] In some feasible implementations, the width of the first sub-region 121 is greater than or equal to 0 mm and less than or equal to 9 mm.

[0165] It should be noted that the width of the first sub-region 121 can refer to the dimension of the first sub-region 121 from its edge near the first region 110 to its edge away from the first region 110 in the direction outward from the center of the first region 110. For example, when the negative electrode current collector 100 is rectangular, referring to the direction shown in FIG2, along the X direction, the dimension of the first sub-region 121 from its edge near the first region 110 to its edge away from the first region 110 is the width of the first sub-region 121. Furthermore, along the Y direction, the dimension of the first sub-region 121 from its edge near the first region 110 to its edge away from the first region 110 is also the width of the first sub-region 121.

[0166] Along the thickness direction of the negative electrode current collector 100, the orthographic projection of the edge of the first sub-region 121 away from the first region 110 on the main surface coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface. The orthographic projection of the edge of the second sub-region 122 near the first region 110 on the main surface coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface. Therefore, the orthographic projection of the first sub-region 121 on the main surface is located inside the orthographic projection of the positive electrode sheet on the main surface. There is no overlapping area between the orthographic projection of the second sub-region 122 on the main surface and the orthographic projection of the positive electrode sheet on the main surface. That is, the second sub-region 122 corresponds to the negative electrode overhang region.

[0167] Since there is no overlap between the orthographic projection of the second sub-region 122 onto the main surface and the orthographic projection of the positive electrode onto the main surface, the second sub-region 122 cannot fully embed lithium from the positive electrode during charging, which reduces the battery's charging efficiency and discharge capacity. Furthermore, although the second sub-region 122 does not participate in the battery's charging and discharging reactions, it occupies battery volume and mass. Therefore, for the same battery volume and mass, an excessively large width of the second sub-region 122 can negatively impact the battery's energy density. Therefore, the above technical problems are solved by setting the width of the second sub-region 122 to be less than or equal to 1 mm. In other words, the difference between the width of the second region 120 and the width of the first sub-region 121 can be less than or equal to 1 mm.

[0168] For example, the width of the first sub-region 121 can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or any combination thereof.

[0169] Preferably, the width of the first sub-region 121 can be greater than or equal to 1 mm and less than or equal to 4 mm.

[0170] In some feasible ways, the ratio of the thickness of the carbon coating layer in the second region 120 to the thickness of the carbon coating layer in the first region 110 is greater than or equal to 0 and less than or equal to 50%.

[0171] When the ratio of the thickness of the carbon coating layer in the second region 120 to the thickness of the carbon coating layer in the first region 110 is greater than 50%, the lithium in the second region 120 still has good conductivity and lithium insertion / extraction activity, and its effect on charge transport impedance is small. The reduction effect of the mobility and ratio of lithium between the first sub-region 121 and the second sub-region 122 in the second region 120 is not obvious, and there is still a possibility of lithium plating.

[0172] Therefore, by setting the ratio of the thickness of the carbon coating layer in the second region 120 to the thickness of the carbon coating layer in the first region 110 to be less than or equal to 50%, the above-mentioned technical problems can be effectively solved. On the basis of solving the lithium plating problem, the thickness of the carbon coating layer can be reduced to reduce the impact on battery capacity and energy density, thereby maintaining the normal operating performance of the battery.

[0173] In some examples, the ratio of the thickness of the carbon coating in the second region 120 to the thickness of the carbon coating in the first region 110 can be 0, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value between the two.

[0174] Wherein, when the ratio of the thickness of the carbon coating layer in the second region 120 to the thickness of the carbon coating layer in the first region 110 is 0, then the second region 120 may not have a carbon coating layer.

[0175] Preferably, the ratio of the thickness of the carbon coating layer in the second region 120 to the thickness of the carbon coating layer in the first region 110 is greater than or equal to 0% and less than or equal to 25%.

[0176] In some feasible ways, the thickness of the carbon coating layer in the first region 110 can be greater than or equal to 0.2 μm and less than or equal to 2 μm.

[0177] In some feasible ways, the metal foil in the negative current collector 100 can be the copper foil described above.

[0178] A third aspect of this disclosure provides a negative electrode sheet, including a negative electrode current collector, which includes the copper foil described in the first aspect above, or the copper foil prepared by the method described in the second aspect above.

[0179] The negative electrode sheet proposed in this embodiment uses copper foil obtained by the method proposed in the first aspect or the second aspect, and therefore has the above-mentioned beneficial effects, which will not be repeated here.

[0180] This disclosure also provides a negative electrode sheet, which may include the negative electrode current collector 100 and the negative electrode active material layer in any of the above embodiments.

[0181] The negative electrode active material layer may be located on the negative electrode current collector 100 along at least a portion of the surface of the negative electrode current collector 100.

[0182] In some embodiments of this disclosure, the negative electrode 100a can be used in a battery. The negative electrode 100a includes a negative current collector 101 and a negative active material layer 102.

[0183] Referring to Figures 7 to 10, the negative electrode current collector 101 includes two main surfaces 101a disposed opposite each other in the thickness direction Z of the negative electrode current collector 101. A negative electrode active material layer 102 is located on at least one main surface 101a of the negative electrode current collector 101. Along a first direction, at least one negative electrode active material layer 102 includes a third region 110a and a fourth region 120a. The first direction is perpendicular to the thickness direction Z of the negative electrode current collector 101. The mass content of the conductive agent in the fourth region 120a is lower than the mass content of the conductive agent in the third region 110a.

[0184] The negative electrode active material layer 102 includes a negative electrode active material, a conductive agent, a binder, etc. The mass content of the conductive agent can refer to the percentage of the mass content of the conductive agent in the negative electrode active material layer 102.

[0185] It is readily understood that the negative electrode 100a has an overhang region. Along the thickness direction Z of the negative electrode current collector 101, the orthogonal projection of the overhang region onto the main surface 101a can lie within the orthogonal projection of the fourth region 120a onto the main surface 101a. Therefore, lithium plating is prone to occur in the fourth region 120a on the negative electrode 100a. In particular, lithium plating tends to occur at the edge near the overhang region (not in the overhang region). In this embodiment, the mass content of the conductive agent in the fourth region 120a can be lower than the mass content of the conductive agent in the third region 110a, making lithium plating less likely in the fourth region 120a, thereby making lithium plating less likely to occur at the edge near the overhang region and in the overhang region itself.

[0186] Specifically, the main function of the conductive agent is to provide a channel for electron transport and reduce the charge transport impedance inside the negative electrode 100a. When the mass content of the conductive agent decreases, electron transport inside the negative electrode 100a will be restricted, leading to an increase in charge transport impedance. Therefore, in this embodiment, by reducing the mass content of the conductive agent in the fourth region 120a to increase the charge transport impedance of the fourth region 120a, the mobility and proportion of lithium flow in the fourth region 120a can be reduced. This effectively reduces the possibility of lithium plating in the fourth region 120a during fast charging, thereby reducing the possibility of lithium plating affecting the battery energy density, which is beneficial to improving the battery energy density and ensuring stable battery operation during fast charging.

[0187] Referring to Figures 8 to 10, the dashed line can be used to enclose and form a third region 110a. A fourth region 120a can be formed between the dashed line and the outermost solid line of the negative electrode 100a.

[0188] It should be noted that, referring to Figure 7, the thickness direction of the negative electrode current collector 101 is the Z-direction in the figure. The main surface 101a refers to the surface perpendicular to the thickness direction Z.

[0189] In some examples, the negative electrode active material layer 102 may be disposed on one of the main surfaces 101a of the negative electrode current collector 101. However, the negative electrode active material layer 102 may be disposed on either main surface 101a, and this is not limited in this embodiment. Alternatively, the negative electrode active material layer 102 may be disposed on both main surfaces 101a of the negative electrode current collector 101.

[0190] It is readily understood that when the negative electrode current collector 101 is located on one of the main surfaces 101a, the main surface 101a may include a third region 110a and a fourth region 120a. The main surface 101a without the negative electrode current collector 101 does not have the third region 110a and the fourth region 120a. When the negative electrode current collector 101 is located on both main surfaces 101a, the third region 110a and the fourth region 120a are located on both main surfaces 101a respectively, or one of the two main surfaces 101a may have the third region 110a and the fourth region 120a. This is not limited in the embodiments disclosed herein.

[0191] In some possible implementations, the fourth region 120a of this disclosure is disposed at least on one side edge of the negative electrode 100a in the longitudinal direction Y.

[0192] The fourth region 120a can be located on one side edge of the negative electrode 100a along the length Y direction, or the fourth region 120a can be located on both sides edge of the negative electrode 100a along the length Y direction.

[0193] Referring to the direction shown in Figure 8, the length direction can refer to the Y direction. Therefore, the fourth region 120a can be located above the third region 110a. Alternatively, the fourth region 120a can be located below the third region 110a. Or, the fourth region 120a can be located both above and below the third region 110a.

[0194] Since the mass content of the conductive agent in the fourth region 120a is lower than that in the third region 110a, the possibility of lithium plating in the fourth region 120a is reduced by decreasing the lithium migration rate in the fourth region 120a. Therefore, when the fourth region 120a is provided on at least one side edge in the length direction Y of the negative electrode 100a, lithium plating can be less likely to occur on that side edge where the fourth region 120a is provided.

[0195] In some possible implementations, the fourth region 120a of the present disclosure is disposed at least on one side edge of the negative electrode 100a in the width direction X.

[0196] The fourth region 120a can be located on one side edge of the negative electrode 100a in the width direction X, or the fourth region 120a can be located on both sides edge of the negative electrode 100a in the width direction X.

[0197] Referring to the direction shown in Figure 8, the width direction can refer to the X-direction. Therefore, the fourth region 120a can be located to the left of the third region 110a. Alternatively, the fourth region 120a can be located to the right of the third region 110a. Or, the fourth region 120a can be located to the left and right of the third region 110a.

[0198] Since the mass content of the conductive agent in the fourth region 120a is lower than that in the third region 110a, the possibility of lithium plating in the fourth region 120a is reduced by decreasing the lithium migration rate in the fourth region 120a. Therefore, when the fourth region 120a is provided on at least one side edge in the width direction X of the negative electrode 100a, lithium plating can be less likely to occur on that side edge where the fourth region 120a is provided.

[0199] In some possible implementations, the fourth region 120a of the present disclosure may be disposed on at least one side of the negative electrode 100a in the length direction Y, and the fourth region 120a may be disposed on at least one side edge of the negative electrode 100a in the width direction X.

[0200] The fourth region 120a can be disposed on one edge in the length direction Y and one edge in the width direction X of the negative electrode 100a. Alternatively, the fourth region 120a can be disposed on both edges in the length direction Y and one edge in the width direction X of the negative electrode 100a. Alternatively, the fourth region 120a can be disposed on one edge in the length direction Y and both edges in the width direction X of the negative electrode 100a. Alternatively, the fourth region 120a can be disposed on both edges in the length direction Y and both edges in the width direction X of the negative electrode 100a. No specific limitation is made in this application.

[0201] When the negative electrode 100a has a rectangular structure, the fourth region 120a is disposed on both sides of the length direction Y and the width direction X of the negative electrode 100a, which can mean that the fourth region 120a is arranged around the third region 110a.

[0202] Referring to the direction shown in Figure 8, the fourth region 120a can be located above and below the third region 110a, and to the left and right of the third region 110a.

[0203] Since the mass content of the conductive agent in the fourth region 120a is lower than that in the third region 110a, the possibility of lithium plating in the fourth region 120a is reduced by decreasing the lithium migration rate in the fourth region 120a. Therefore, when the fourth region 120a is arranged around the third region 110a, lithium plating is less likely to occur in the edge regions of the negative electrode active material layer 102.

[0204] In summary, since the mass content of the conductive agent in the fourth region 120a is lower than that in the third region 110a, lithium plating is less likely to occur in the fourth region 120a. Therefore, it is easy to understand that when the negative electrode 100a is rectangular, the effect of placing the fourth region 120a on both sides of the length direction Y and width direction X of the negative electrode 100a to solve the lithium plating problem is better than placing the fourth region 120a on both sides of the width direction X of the negative electrode 100a to solve the lithium plating problem.

[0205] In some examples, when the negative electrode 100a has multiple edges, during the fast charging process of the battery, the edges of the negative electrode 100a with the fourth region 120a are less prone to lithium plating. Therefore, the more edges with the fourth region 120a, the more edges on the negative electrode 100a are less prone to lithium plating. Thus, when the fourth region 120a is arranged around the outer periphery of the third region 110a, the possibility of lithium plating can be reduced more effectively, thereby improving the battery's lifespan.

[0206] In some possible implementations, referring to Figures 7 to 10, the negative electrode 100a of this disclosure embodiment is used to be stacked with the positive electrode of the battery. The fourth region 120a may include a third sub-region 121a and a fourth sub-region 122a. The third sub-region 121a is located on the side of the third region 110a near the edge of the negative electrode current collector 101. The fourth sub-region 122a is located at the edge of the third sub-region 121a away from the third region 110a.

[0207] In this case, the orthographic projection of the edge of the third sub-region 121a away from the third region 110a onto the main surface 101a coincides with the edge of the orthographic projection of the positive electrode onto the main surface 101a. The orthographic projection of the edge of the fourth sub-region 122a near the third region 110a onto the main surface 101a coincides with the edge of the orthographic projection of the positive electrode onto the main surface 101a.

[0208] Referring to Figures 8 to 10, the third sub-region 121a can refer to the area enclosed by the dotted line and the dashed line. The fourth sub-region 122a can refer to the area enclosed by the dashed line and the outermost edge of the negative electrode 100a.

[0209] It is easy to understand that the fourth sub-region 122a can refer to the overhang region. The third sub-region 121a is the region on the negative electrode 100a where lithium plating is prone to occur.

[0210] For example, the mass content of the conductive agent in the third sub-region 121a and the fourth sub-region 122a can both be lower than the mass content of the conductive agent in the third region 110a. In other words, the mass content of the conductive agent in the entire fourth region 120a is lower than the mass content of the conductive agent in the third region 110a.

[0211] Specifically, when the mass content of the conductive agent in the third sub-region 121a is lower than that in the third region 110a, the resistance to charge transport within the third sub-region 121a increases. Therefore, during charging, the migration rate and proportion of lithium from the third sub-region 121a into the fourth sub-region 122a can be reduced. Consequently, during discharging, the migration rate and proportion of lithium from the fourth sub-region 122a into the third sub-region 121a also decrease. This reduces the space occupied by lithium in the third sub-region 121a for receiving lithium from the positive electrode, thus allowing the third sub-region 121a to have space to receive lithium from the positive electrode during recharging, which helps reduce the likelihood of lithium plating in the third sub-region 121a.

[0212] When the mass content of the conductive agent in the fourth sub-region 122a is lower than that in the third sub-region 110a, the resistance to charge transport within the fourth sub-region 122a increases. Therefore, during discharge, the mobility and proportion of lithium entering the third sub-region 121a from the fourth sub-region 122a can be reduced, decreasing the space occupied by lithium in the third sub-region 121a for receiving lithium from the positive electrode. This ensures that during recharging, the third sub-region 121a has sufficient space to receive lithium from the positive electrode, thus reducing the likelihood of lithium plating in the third sub-region 121a.

[0213] When the mass content of the conductive agent in both the third sub-region 121a and the fourth sub-region 122a is lower than that in the third region 110a, the impedance to charge transport within the entire fourth region 120a can be significantly increased. Therefore, during charging, the migration rate and proportion of lithium from the third sub-region 121a into the fourth sub-region 122a can be reduced. Furthermore, during discharging, the migration rate and proportion of lithium from the fourth sub-region 122a into the third sub-region 121a can also be reduced. This decreases the space occupied by lithium in the third sub-region 121a for accepting lithium from the positive electrode, ensuring sufficient space for lithium to be accepted from the positive electrode during recharging, thus reducing the likelihood of lithium plating in the third sub-region 121a.

[0214] In summary, in this embodiment, by lowering the mass content of the conductive agent in the fourth region 120a compared to the mass content of the conductive agent in the third region 110a, the negative electrode 100a can be improved based on the mechanism of lithium plating, thereby reducing the occurrence of lithium plating. Therefore, this embodiment, while addressing the lithium plating phenomenon during rapid battery charging, eliminates the need for high-temperature heating of the battery, which helps reduce the impact of high temperatures on battery performance and lifespan.

[0215] In some feasible ways, the conductive agent may include one or a mixture of materials such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon black, and graphene.

[0216] It should be noted that the conductive agent can be a single material or a mixture of the above-mentioned materials. When the conductive agent includes multiple materials, the proportions of these materials are not limited in this embodiment.

[0217] In some feasible ways, the negative electrode active material within the negative electrode active material layer 102 may include one or a mixture of materials such as graphite, silicon, and titanium-based compounds (e.g., lithium titanate).

[0218] It should be noted that the negative electrode active material can be a single material or a mixture of the above-mentioned materials. When the negative electrode active material includes multiple materials, the proportions of these materials are not limited in this embodiment.

[0219] In some possible implementations, the width of the fourth region 120a in this disclosure embodiment may be greater than or equal to 0.5 mm and less than or equal to 10 mm.

[0220] It should be noted that the width of the fourth region 120a can refer to the dimension of the fourth region 120a from its edge near the third region 110a to its edge away from the third region 110a, extending outwards from the center of the third region 110a. For example, when the negative electrode 100a is rectangular, referring to the direction shown in Figure 2, along the X direction, the dimension of the fourth region 120a from its edge near the third region 110a to its edge away from the third region 110a is the width of the fourth region 120a. Furthermore, along the Y direction, the dimension of the fourth region 120a from its edge near the third region 110a to its edge away from the third region 110a is also the width of the fourth region 120a.

[0221] Because the mass content of the conductive agent in the fourth region 120a is lower than that in the third region 110a, and the low mass content of the conductive agent easily affects conductivity and lithium intercalation / deintercalation activity, it increases charge transport impedance and reduces lithium mobility and proportion. Therefore, when the width of the fourth region 120a is too large (greater than 10 mm), the charge transport impedance is easily significantly increased, which restricts electron transport within the negative electrode 100a, thus affecting the battery's charge and discharge performance and requiring a longer time to complete charge transfer during charging and discharging. Furthermore, it also restricts electron transport between active materials within the negative electrode active material layer 102, preventing the active materials from being fully utilized, thereby reducing the battery's capacity and energy density.

[0222] When the width of the fourth region 120a is too small (less than 0.5 mm), the area of ​​the fourth region 120a with a low mass content of conductive agent is small, which has a smaller effect on charge transport impedance, a smaller effect on reducing conductivity and lithium insertion / extraction activity, and an insignificant effect on solving the lithium plating problem, thus resulting in poor improvement of the battery.

[0223] Therefore, by setting the width of the fourth region 120a to be greater than or equal to 0.5 mm and less than or equal to 10 mm, the aforementioned technical problems can be effectively solved. This reduces the impact of the conductive agent content on the overall battery performance and improves battery lifespan, while also addressing the issue of lithium plating.

[0224] For example, the width of the fourth region 120a can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or any combination thereof.

[0225] Preferably, the width of the fourth region 120a can be greater than or equal to 2 mm and less than or equal to 6 mm.

[0226] In some feasible implementations, the width of the third sub-region 121a is greater than or equal to 0 mm and less than or equal to 9 mm.

[0227] It should be noted that the width of the third sub-region 121a can refer to the dimension of the third sub-region 121a from its edge near the edge of the third region 110a to its edge away from the edge of the third region 110a, extending outward from the center of the third region 110a. For example, when the negative electrode 100a is rectangular, referring to the direction shown in Figure 2, the dimension of the third sub-region 121a from its edge near the edge of the third region 110a to its edge away from the edge of the third region 110a along the X direction is the width of the third sub-region 121a. Furthermore, the dimension of the third sub-region 121a from its edge near the edge of the third region 110a to its edge away from the edge of the third region 110a along the Y direction is also the width of the third sub-region 121a.

[0228] Along the thickness direction Z of the negative electrode current collector 101, the orthographic projection of the edge of the third sub-region 121a away from the third region 110a on the main surface 101a coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface 101a. The orthographic projection of the edge of the fourth sub-region 122a near the third region 110a on the main surface 101a coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface 101a. Therefore, the orthographic projection of the third sub-region 121a on the main surface 101a is located inside the orthographic projection of the positive electrode sheet on the main surface 101a. There is no overlapping area between the orthographic projection of the fourth sub-region 122a on the main surface 101a and the orthographic projection of the positive electrode sheet on the main surface 101a. That is, the fourth sub-region 122a is the negative electrode overhang region.

[0229] Since there is no overlap between the orthographic projection of the fourth sub-region 122a onto the main surface 101a and the orthographic projection of the positive electrode onto the main surface 101a, the fourth sub-region 122a cannot fully embed lithium from the positive electrode during charging, which reduces the battery's charging efficiency and discharge capacity. Furthermore, although the fourth sub-region 122a does not participate in the battery's charging and discharging reactions, it occupies battery volume and mass. Therefore, for the same battery volume and mass, an excessively large width of the fourth sub-region 122a can negatively impact the battery's energy density. Therefore, the above technical problems are solved by setting the width of the fourth sub-region 122a to be less than or equal to 1 mm. In other words, the difference between the width of the fourth region 120a and the width of the third sub-region 121a can be less than or equal to 1 mm.

[0230] For example, the width of the third sub-region 121a can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or any combination thereof.

[0231] Preferably, the width of the third sub-region 121a can be greater than or equal to 1 mm and less than or equal to 5 mm.

[0232] In some feasible ways, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is greater than or equal to 5 wt% and less than or equal to 50 wt%.

[0233] In this embodiment of the present disclosure, when the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is less than 5 wt%, the mass content of the conductive agent in the fourth region 120a is too low. In particular, when the mass content of the conductive agent in the third sub-region 121a of the fourth region 120a is too low, it is easy to cause the charge transport impedance to be too high, thereby affecting the capacity and energy density of the battery.

[0234] When the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is higher than 50 wt%, the lithium in the fourth region 120a still has good conductivity and lithium insertion / extraction activity, and its effect on charge transport impedance is small. The reduction effect of lithium mobility and ratio between the third subregion 121a and the fourth subregion 122a in the fourth region 120a is not obvious, and there is still a possibility of lithium plating.

[0235] Therefore, by setting the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a to be greater than or equal to 5 wt% and less than or equal to 50 wt%, the above-mentioned technical problems can be effectively solved. On the basis of solving the lithium plating problem, the impact of the decrease in the mass content of the conductive agent on the battery capacity and energy density can be reduced, thereby maintaining the normal operating performance of the battery.

[0236] For example, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a can be a range of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50%, or any two of these.

[0237] Preferably, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a can be greater than or equal to 15 wt% and less than or equal to 30 wt%.

[0238] Referring to Figures 7 and 13 to 16, the negative electrode current collector 101 includes two main surfaces 101a disposed opposite each other in the thickness direction Z of the negative electrode current collector 101. A negative electrode active material layer 102 is located on at least one main surface 101a of the negative electrode current collector 101. Along a first direction, at least one negative electrode active material layer 102 includes a fifth region 110b and a sixth region 120b. The first direction is perpendicular to the thickness direction Z of the negative electrode current collector 101. The binder mass content of the sixth region 120b is higher than that of the fifth region 110b.

[0239] The negative electrode active material layer 102 includes a negative electrode active material, a conductive agent, and a binder. The mass content of the binder can refer to the percentage of the mass content of the binder in the negative electrode active material layer 102.

[0240] It is readily understood that the negative electrode 100a has an overhang region. Along the thickness direction Z of the negative electrode current collector 101, the orthogonal projection of the overhang region onto the main surface 101a can lie within the orthogonal projection of the sixth region 120b onto the main surface 101a. Therefore, lithium plating is prone to occur in the sixth region 120b on the negative electrode 100a. In particular, lithium plating tends to occur at the edge near the overhang region (not in the overhang region). In this embodiment, the binder content in the sixth region 120b can be higher than that in the fifth region 110b to reduce the likelihood of lithium plating in the sixth region 120b, thereby reducing the likelihood of lithium plating at the edge near the overhang region and within the overhang region itself.

[0241] Specifically, the main function of the binder is to firmly bond the negative electrode active material, conductive agent, and current collector together to form a stable negative electrode structure. The binding effect of the binder can improve the integrity and stability of the negative electrode during battery charge-discharge cycles. Furthermore, the binder has insulating properties. Therefore, when the binder mass content increases, the lithium insertion / extraction resistance of the sixth region 120b is easily increased. Therefore, in this embodiment of the present disclosure, by increasing the binder mass content of the sixth region 120b to improve the lithium insertion / extraction resistance of the sixth region 120b, the migration rate and proportion of lithium flowing in the sixth region 120b can be reduced. This effectively reduces the possibility of lithium plating in the sixth region 120b during fast charging, thereby reducing the possibility of lithium plating affecting the battery energy density, which is beneficial for improving the battery energy density and ensuring stable battery operation during fast charging.

[0242] Referring to Figures 7, 13 to 15, the dashed lines can be used to enclose and form a fifth region 110b. A sixth region 120b can be formed between the dashed lines and the outermost solid line of the negative electrode 100a.

[0243] It should be noted that, referring to Figure 7, the thickness direction of the negative electrode current collector 101 is the Z-direction in the figure. The main surface 101a refers to the surface perpendicular to the thickness direction Z.

[0244] In some examples, the negative electrode active material layer 102 may be disposed on one of the main surfaces 101a of the negative electrode current collector 101. However, the negative electrode active material layer 102 may be disposed on either main surface 101a, and this is not limited in this embodiment. Alternatively, the negative electrode active material layer 102 may be disposed on both main surfaces 101a of the negative electrode current collector 101.

[0245] It is readily understood that when the negative electrode current collector 101 is located on one of the main surfaces 101a, the main surface 101a may include a fifth region 110b and a sixth region 120b. The main surface 101a without the negative electrode current collector 101 does not have the fifth region 110b and the sixth region 120b. When the negative electrode current collector 101 is located on both main surfaces 101a, the fifth region 110b and the sixth region 120b are located on both main surfaces 101a respectively, or one of the two main surfaces 101a may have the fifth region 110b and the sixth region 120b. This is not limited in the embodiments disclosed herein.

[0246] In some possible implementations, the sixth region 120b of this disclosure is disposed at least on one side edge of the negative electrode 100a in the longitudinal direction Y.

[0247] The sixth region 120b can be located on one side edge of the negative electrode 100a along the length Y direction, or the sixth region 120b can be located on both sides edge of the negative electrode 100a along the length Y direction.

[0248] Referring to the direction shown in Figure 13, the length direction can refer to the Y direction. Therefore, the sixth region 120b can be located above the fifth region 110b. Alternatively, the sixth region 120b can be located below the fifth region 110b. Or, the sixth region 120b can be located both above and below the fifth region 110b.

[0249] Since the mass content of the binder in the sixth region 120b is higher than that in the fifth region 110b, the possibility of lithium plating in the sixth region 120b is reduced by decreasing the migration rate of lithium in the sixth region 120b. Therefore, when the sixth region 120b is provided on at least one side edge in the length direction Y of the negative electrode 100a, lithium plating can be less likely to occur on that side edge where the sixth region 120b is provided.

[0250] In some possible implementations, the sixth region 120b of this disclosure embodiment is disposed at least on one side edge of the negative electrode 100a in the width direction X.

[0251] The sixth region 120b can be located on one side edge of the negative electrode 100a in the width direction X, or the sixth region 120b can be located on both sides edge of the negative electrode 100a in the width direction X.

[0252] Referring to the direction shown in Figure 13, the width direction can refer to the X-direction. Therefore, the sixth region 120b can be located to the left of the fifth region 110b. Alternatively, the sixth region 120b can be located to the right of the fifth region 110b. Or, the sixth region 120b can be located to the left and right of the fifth region 110b.

[0253] Since the mass content of the binder in the sixth region 120b is higher than that in the fifth region 110b, the possibility of lithium plating in the sixth region 120b is reduced by decreasing the migration rate of lithium in the sixth region 120b. Therefore, when the sixth region 120b is provided on at least one side edge in the width direction X of the negative electrode 100a, lithium plating can be less likely to occur on that side edge where the sixth region 120b is provided.

[0254] In some possible implementations, the sixth region 120b of the present disclosure embodiment may be disposed on at least one side of the negative electrode 100a in the length direction Y, and the sixth region 120b may be disposed on at least one side edge of the negative electrode 100a in the width direction X.

[0255] The sixth region 120b can be disposed on one edge in the length direction Y and one edge in the width direction X of the negative electrode 100a. Alternatively, the sixth region 120b can be disposed on both edges in the length direction Y and one edge in the width direction X of the negative electrode 100a. Alternatively, the sixth region 120b can be disposed on one edge in the length direction Y and both edges in the width direction X of the negative electrode 100a. Alternatively, the sixth region 120b can be disposed on both edges in the length direction Y and both edges in the width direction X of the negative electrode 100a. No specific limitation is made in this disclosure.

[0256] When the negative electrode 100a has a rectangular structure, the sixth region 120b is disposed on both sides of the length direction Y and the width direction X of the negative electrode 100a, which means that the sixth region 120b is arranged around the fifth region 110b.

[0257] Referring to the orientation shown in Figure 13, the sixth region 120b can be located above and below the fifth region 110b, and to the left and right of the fifth region 110b.

[0258] Since the mass content of the binder in the sixth region 120b is higher than that in the fifth region 110b, the possibility of lithium plating in the sixth region 120b is reduced by decreasing the migration rate of lithium in the sixth region 120b. Therefore, when the sixth region 120b is arranged around the fifth region 110b, lithium plating is less likely to occur in the edge regions of the negative electrode active material layer 102.

[0259] In summary, since the binder content in the sixth region 120b is higher than that in the fifth region 110b, making lithium plating less likely to occur in the sixth region 120b, it is easy to understand that when the negative electrode 100a is rectangular, the effect of the sixth region 120b being located on both sides of the negative electrode 100a in the length direction Y and width direction X to solve the lithium plating problem is better than the effect of the sixth region 120b being located on both sides of the negative electrode 100a in the width direction X to solve the lithium plating problem.

[0260] In some examples, when the negative electrode 100a has multiple edges, during the fast charging process of the battery, the edges of the negative electrode 100a with the sixth region 120b are less prone to lithium plating. Therefore, the more edges with the sixth region 120b, the more edges on the negative electrode 100a are less prone to lithium plating. Thus, when the sixth region 120b is arranged around the outer periphery of the fifth region 110b, the possibility of lithium plating can be reduced more effectively, thereby improving the battery's lifespan.

[0261] In some possible implementations, referring to Figures 7, 13 to 15, the negative electrode 100a of this disclosure embodiment is used to be stacked with the positive electrode of the battery. The sixth region 120b may include a fifth sub-region 121b and a sixth sub-region 122b. The fifth sub-region 121b is located on the side of the fifth region 110b near the edge of the negative electrode current collector 101. The sixth sub-region 122b is located on the edge of the fifth sub-region 121b away from the fifth region 110b.

[0262] In this case, the orthographic projection of the edge of the fifth sub-region 121b away from the fifth region 110b onto the main surface 101a coincides with the edge of the orthographic projection of the positive electrode onto the main surface 101a. The orthographic projection of the edge of the sixth sub-region 122b near the fifth region 110b onto the main surface 101a coincides with the edge of the orthographic projection of the positive electrode onto the main surface 101a.

[0263] Referring to Figures 13 to 15, the fifth sub-region 121b can refer to the area enclosed by the dotted line and the dashed line. The sixth sub-region 122b can refer to the area enclosed by the dashed line and the outermost edge of the negative electrode 100a.

[0264] It is easy to understand that the sixth sub-region 122b can refer to the overhang region. The fifth sub-region 121b is the region on the negative electrode 100a where lithium plating is prone to occur.

[0265] For example, the mass content of the adhesive in the fifth sub-region 121b and the mass content of the adhesive in the sixth sub-region 122b can both be higher than the mass content of the adhesive in the fifth region 110b. In other words, the mass content of the adhesive in all the sixth regions 120b is higher than the mass content of the adhesive in the fifth region 110b.

[0266] Specifically, when the mass content of the binder in the fifth sub-region 121b is higher than that in the fifth region 110b, the resistance to charge transport within the fifth sub-region 121b increases. Therefore, during charging, the migration rate and proportion of lithium from the fifth sub-region 121b to the sixth sub-region 122b can be reduced. Consequently, during discharging, the migration rate and proportion of lithium from the sixth sub-region 122b to the fifth sub-region 121b also decrease. This reduces the space occupied by lithium in the fifth sub-region 121b for receiving lithium from the positive electrode, thus allowing the fifth sub-region 121b to have space to receive lithium from the positive electrode during recharging, which helps reduce the likelihood of lithium plating in the fifth sub-region 121b.

[0267] When the mass content of the binder in the sixth sub-region 122b is higher than that in the fifth sub-region 110b, the resistance to charge transport within the sixth sub-region 122b increases. Therefore, during discharge, the migration rate and proportion of lithium from the sixth sub-region 122b into the fifth sub-region 121b can be reduced, decreasing the space occupied by lithium in the fifth sub-region 121b for accepting lithium from the positive electrode. This ensures that during recharging, the fifth sub-region 121b has sufficient space to accept lithium from the positive electrode, thus reducing the likelihood of lithium plating in the fifth sub-region 121b.

[0268] When the mass content of the binder in both the fifth sub-region 121b and the sixth sub-region 122b is higher than that in the fifth region 110b, the impedance to charge transport within the entire sixth region 120b can be increased. Therefore, during charging, the migration rate and proportion of lithium from the fifth sub-region 121b into the sixth sub-region 122b can be reduced. Furthermore, during discharging, the migration rate and proportion of lithium from the sixth sub-region 122b into the fifth sub-region 121b can also be reduced. This decreases the space occupied by lithium in the fifth sub-region 121b for accepting lithium from the positive electrode, thus ensuring sufficient space for lithium to accept from the positive electrode during recharging, which helps reduce the likelihood of lithium plating in the fifth sub-region 121b.

[0269] In summary, in this embodiment, by having a higher binder content in the sixth region 120b than in the fifth region 110b, the negative electrode 100a can be improved based on the mechanism of lithium plating, thereby reducing the occurrence of lithium plating. Therefore, this embodiment, while addressing the lithium plating problem, eliminates the need for high-temperature heating of the battery, which helps reduce the impact of high temperatures on battery performance and lifespan.

[0270] In some feasible ways, the binder may include one or a mixture of materials such as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0271] It should be noted that the adhesive can be a single material or a mixture of the above-mentioned materials. When the adhesive comprises multiple materials, the proportions of the materials are not limited in this embodiment.

[0272] In some examples, the negative electrode active material within the negative electrode active material layer may include one or a mixture of materials such as graphite, silicon, and titanium-based compounds (e.g., lithium titanate).

[0273] It should be noted that the negative electrode active material can be a single material or a mixture of the above-mentioned materials. When the negative electrode active material includes multiple materials, the proportions of these materials are not limited in this embodiment.

[0274] In some possible implementations, the width of the sixth region 120b in this disclosure embodiment may be greater than or equal to 0.5 mm and less than or equal to 10 mm.

[0275] It should be noted that the width of the sixth region 120b can refer to the dimension of the sixth region 120b from its edge near the fifth region 110b to its edge away from the fifth region 110b, extending outwards from the center of the fifth region 110b. For example, when the negative electrode 100a is rectangular, referring to the direction shown in Figure 13, along the X direction, the dimension of the sixth region 120b from its edge near the fifth region 110b to its edge away from the fifth region 110b is the width of the sixth region 120b. Furthermore, along the Y direction, the dimension of the sixth region 120b from its edge near the fifth region 110b to its edge away from the fifth region 110b is also the width of the sixth region 120b.

[0276] Because the binder content in the sixth region 120b is higher than that in the fifth region 110b, and a lower binder content can negatively impact conductivity and lithium intercalation / deintercalation activity, it increases charge transport impedance and reduces lithium mobility and proportion. Therefore, when the width of the sixth region 120b is too large (greater than 10 mm), the charge transport impedance can significantly increase, restricting electron transport within the negative electrode 100a. This affects the battery's charge / discharge performance, requiring a longer time to complete charge transfer during charging and discharging. Furthermore, it also restricts electron transport between active materials within the negative electrode active material layer 102, preventing full utilization of the active materials and reducing battery capacity and energy density.

[0277] When the width of the sixth region 120b is too small (less than 0.5 mm), the area of ​​the sixth region 120b with increased binder mass content is small, its influence on charge transport impedance is small, its effect on reducing conductivity and lithium insertion / extraction activity is small, and its effect on solving the lithium plating problem is not obvious, thus its effect on improving the battery is not good.

[0278] Therefore, by setting the width of the sixth region 120b to be greater than or equal to 0.5 mm and less than or equal to 10 mm, the aforementioned technical problems can be effectively solved. This can reduce the impact of increased binder content on overall battery performance and improve battery life while addressing the lithium plating phenomenon.

[0279] For example, the width of the sixth region 120b can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or any combination thereof.

[0280] Preferably, the width of the sixth region 120b can be greater than or equal to 2 mm and less than or equal to 5 mm.

[0281] In some feasible implementations, the width of the fifth sub-region 121b is greater than or equal to 0 mm and less than or equal to 9 mm.

[0282] It should be noted that the width of the fifth sub-region 121b can refer to the dimension of the fifth sub-region 121b from its edge near the edge of the fifth region 110b to its edge away from the edge of the fifth region 110b, extending outward from the center of the fifth region 110b. For example, when the negative electrode 100a is rectangular, referring to the direction shown in Figure 2, along the X direction, the dimension of the fifth sub-region 121b from its edge near the edge of the fifth region 110b to its edge away from the edge of the fifth region 110b is the width of the fifth sub-region 121b. Furthermore, along the Y direction, the dimension of the fifth sub-region 121b from its edge near the edge of the fifth region 110b to its edge away from the edge of the fifth region 110b is also the width of the fifth sub-region 121b.

[0283] Along the thickness direction Z of the negative electrode current collector 101, the orthographic projection of the edge of the fifth sub-region 121b away from the fifth region 110b on the main surface 101a coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface 101a. The orthographic projection of the edge of the sixth sub-region 122b near the fifth region 110b on the main surface 101a coincides with the edge of the orthographic projection of the positive electrode sheet on the main surface 101a. Therefore, the orthographic projection of the fifth sub-region 121b on the main surface 101a is located inside the orthographic projection of the positive electrode sheet on the main surface 101a. There is no overlapping area between the orthographic projection of the sixth sub-region 122b on the main surface 101a and the orthographic projection of the positive electrode sheet on the main surface 101a. That is, the sixth sub-region 122b is the negative electrode overhang region.

[0284] Since there is no overlap between the orthographic projection of the sixth sub-region 122b onto the main surface 101a and the orthographic projection of the positive electrode onto the main surface 101a, the sixth sub-region 122b cannot fully embed lithium from the positive electrode during charging, which reduces the battery's charging efficiency and discharge capacity. Furthermore, although the sixth sub-region 122b does not participate in the battery's charging and discharging reactions, it occupies battery volume and mass. Therefore, for the same battery volume and mass, an excessively large width of the sixth sub-region 122b can negatively impact the battery's energy density. Therefore, the above technical problems are solved by setting the width of the sixth sub-region 122b to be less than or equal to 1 mm. In other words, the difference between the width of the sixth region 120b and the width of the fifth sub-region 121b can be less than or equal to 1 mm.

[0285] For example, the width of the fifth sub-region 121b can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or any combination thereof.

[0286] Preferably, the width of the fifth sub-region 121b can be greater than or equal to 1 mm and less than or equal to 4 mm.

[0287] In some feasible ways, the ratio of the mass content of the adhesive in the sixth region 120b to the mass content of the adhesive in the fifth region 110b is greater than or equal to 105 wt% and less than or equal to 130 wt%.

[0288] In this embodiment of the present disclosure, when the mass content of the binder in the sixth region 120b and the mass content of the binder in the fifth region 110b are higher than 130 wt%, the mass content of the binder in the sixth region 120b is too high. In particular, when the mass content of the binder in the fifth sub-region 121b of the sixth region 120b is too high, it is easy to cause the charge transport impedance to be too large, thereby affecting the capacity and energy density of the battery.

[0289] When the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b is less than 105 wt%, the lithium in the sixth region 120b still has good conductivity and lithium insertion / extraction activity, and its effect on charge transport impedance is small. The reduction effect of lithium mobility and ratio between the fifth subregion 121b and the sixth subregion 122b in the sixth region 120b is not obvious, and there is still a possibility of lithium plating.

[0290] Therefore, by setting the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b to be greater than or equal to 105wt% and less than or equal to 130wt%, the above-mentioned technical problems can be effectively solved. On the basis of solving the lithium plating problem, the impact of the binder mass content reduction on battery capacity and energy density can be reduced, thereby maintaining the normal operating performance of the battery.

[0291] For example, the ratio of the mass content of the adhesive in the sixth region 120b to the mass content of the adhesive in the fifth region 110b can be a range of 105%, 110wt%, 115wt%, 120wt%, 125wt%, 130wt%, or any two of these.

[0292] Preferably, the ratio of the mass content of the adhesive in the sixth region 120b to the mass content of the adhesive in the fifth region 110b can be greater than or equal to 110wt% and less than or equal to 120wt%.

[0293] In some implementations, the third region 110a and the fifth region 110b may be the same region, and the fourth region 120a and the sixth region 120b may be the same region.

[0294] The fourth aspect of this disclosure provides a battery comprising the negative electrode sheet described in the third aspect above.

[0295] The battery proposed in this disclosure has the aforementioned beneficial effects, which will not be repeated here.

[0296] This disclosure also provides a battery, which may include the negative electrode sheet in any of the above embodiments.

[0297] A battery may also include a positive electrode and a separator. The separator is located between the positive and negative electrode.

[0298] In some feasible implementations, the positive electrode has an orthographic projection onto the main surface of the metal foil. The edge of the orthographic projection of the positive electrode can be within the orthographic projection of the second region 120 onto the main surface of the metal foil.

[0299] In some feasible ways, the edge of the orthographic projection of the positive electrode on the main surface 101a lies within the orthographic projection of the fourth region 120a on the main surface 101a.

[0300] In some feasible ways, the orthographic projection of the positive electrode on the main surface 101a lies within the orthographic projection of the sixth region 120b on the main surface 101a.

[0301] In some embodiments of this disclosure, a negative electrode film layer is provided on at least one side of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material; the negative electrode active material includes one or more of natural graphite, artificial graphite, and silicon-based materials, or the negative electrode active material includes metallic lithium.

[0302] The battery provided in this disclosure can be a lithium-ion battery. For example, a lithium-ion secondary battery, a lithium-sulfur battery, or a sodium-lithium-ion battery, etc. This application does not limit the type of battery. The negative electrode active material in the lithium-ion secondary battery can be a conventional negative electrode material in the art. For example, the negative electrode active material can be one or more of natural graphite, artificial graphite, and silicon-based materials.

[0303] The battery provided in this disclosure can be used in electrical equipment. This electrical equipment can be mobile devices such as vehicles, ships, and small aircraft. Taking a vehicle as an example, the vehicle can refer to a new energy electric vehicle. This new energy electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle.

[0304] Batteries can serve as a driving power source for vehicles, replacing or partially replacing fuel to provide propulsion. For example, a battery can provide electrical energy to a drive motor. The drive motor is connected to the wheels of the vehicle via a transmission mechanism, thereby propelling the vehicle forward.

[0305] The battery includes a cell. The cell includes two electrodes with opposite polarities and a separator. The electrodes with opposite polarities are a positive electrode and a negative electrode. The separator is located between the positive and negative electrodes to insulate them. The positive electrode, separator, and negative electrode can be formed into a wound cell using a winding process. Alternatively, the positive electrode, separator, and negative electrode can be stacked in a specific order to form a laminated cell, which is not limited in this embodiment.

[0306] A battery cell includes two tabs with opposite polarities: a positive tab and a negative tab. The positive tab can be led out from a positive electrode plate, and the negative tab can be led out from a negative electrode plate. The positive and negative tabs can be used to connect to external circuits.

[0307] During charging, lithium atoms in the positive electrode lose electrons and transform into lithium ions. These lithium ions migrate through the electrolyte to the negative electrode under the influence of an electric field. Taking graphite as the negative electrode active material as an example, lithium ions are captured by the micropores of the graphite layered structure and combine with electrons flowing in from the external circuit to form lithium intercalation compounds. In this process, the electrical energy provided by the external power source can be converted into chemical energy and stored in the battery.

[0308] During discharge, a lithium-ion battery can provide electrical energy to an external load. At this time, the lithium intercalation compound at the negative electrode decomposes, releasing lithium ions and electrons. Lithium ions migrate to the positive electrode through the electrolyte, while electrons flow to the positive electrode through the external circuit. Lithium ions and electrons recombine at the positive electrode to reform lithium atoms or lithium compounds, releasing electrical energy for the external load. In this process, the chemical energy stored in the battery is converted into electrical energy to provide power to the external load.

[0309] The battery proposed in this embodiment can be a metal battery, such as a lithium metal battery, in which case the negative electrode is lithium metal.

[0310] For lithium metal battery systems, the large volume change of lithium metal during deposition-dissolution can lead to cracks in the SEI film, resulting in side reactions and loss of active lithium. This disclosed embodiment uses the aforementioned copper foil, which, on the one hand, facilitates the formation of a large amount of effective SEI, improving the stability of the negative electrode interface; on the other hand, the copper foil with its (220) crystal plane preferentially formed allows for adjustment of the morphology of the lithium deposition particles, making the deposited lithium particles more even and uniform, promoting a more uniform and stable voltage distribution, and improving the battery's cycle stability. Compared to batteries assembled with traditional electrolytic copper foil, this results in better capacity retention and higher coulombic efficiency.

[0311] In some embodiments of this disclosure, an electrolyte is also included, comprising an electrolyte salt, which includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0312] In this embodiment of the disclosure, the electrolyte salt includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide. It can be that only one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide is used as the electrolyte salt, or one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide can be used in combination with other electrolyte salts, or a combination of both lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide can be used, or a combination of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide can be used. In the case of combined use, lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide can be used as the main salt or as the auxiliary salt, such as using lithium hexafluorophosphate as the main salt and lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide as the auxiliary salt.

[0313] Lithium bis(trifluoromethanesulfonyl)imide is added to the electrolyte of the battery, and the aforementioned copper foil is used as the negative electrode current collector. The texture coefficient of the copper foil (220) crystal plane is as high as 75% or more, which shows high affinity for lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). It effectively catalyzes the decomposition of LiTFSI and can accelerate the decomposition of lithium salt LiTFSI to generate a large number of effective SEI components (such as lithium fluoride (LiF), lithium oxide (Li2O), lithium sulfide (Li2S), etc.), which is beneficial to improve the cycle performance of the battery.

[0314] In some embodiments of this disclosure, the concentration of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide, based on the electrolyte, is 0.02 mol / L to 1 mol / L.

[0315] Based on the battery performance requirements, appropriate amounts of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide can be added to the electrolyte.

[0316] As an example, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide are 0.02 mol / L, 0.06 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.6 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.

[0317] Furthermore, based on the electrolyte, the concentration of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide is 0.1 mol / L to 0.5 mol / L.

[0318] In some embodiments of this disclosure, the electrolyte also includes a solvent.

[0319] According to embodiments of this disclosure, the solvent is a non-aqueous organic solvent, which is a major component of the electrolyte and should have high solubility of lithium salts to ensure high ionic conductivity of the electrolyte. The specific type is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the aforementioned non-aqueous organic solvent includes at least one of ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butenyl carbonate (BC), diethyl sulfite (DES), γ-butyrolactone (BL), dimethyl sulfoxide (DMSO), ethyl acetate, and methyl acetate. Preferably, at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) is selected. The solvent in the electrolyte acts as an important carrier for ion transport; after the electrolyte salt dissolves, it can have high electronic conductivity. Therefore, by selecting the aforementioned solvent, the cycle life, charge / discharge rate, high and low temperature performance, and energy density of the battery can be improved.

[0320] As an example, a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), etc., can be used as the solvent.

[0321] According to embodiments of this disclosure, the electrolyte salt may further include at least one of LiPF6, LiTNFSI, LiFNFSI, LiBF4, LiBOB, LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiCF3SO3, LiB(C2O4)2, or lithium tetrafluorooxalate phosphate. Therefore, this electrolyte can be used in lithium-ion batteries.

[0322] In some embodiments of this disclosure, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0323] In some embodiments of this disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including a positive active material.

[0324] For example, when the positive electrode is used in a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2) or its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, or lithium manganese iron phosphate and carbon composites.

[0325] As examples, positive electrode active materials include nickel cobalt manganese oxide (NCM), nickel cobalt aluminum oxide (NCA), or lithium iron phosphate (LFP).

[0326] In some embodiments of this disclosure, the positive current collector may include a metal foil or a composite positive current collector. For example, the metal foil may be aluminum foil. The composite positive current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. For example, the composite negative current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0327] In some embodiments of this disclosure, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0328] In some embodiments of this disclosure, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0329] In some embodiments of this disclosure, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet (e.g., positive electrode active material, conductive agent, binder) in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0330] In some embodiments of this disclosure, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0331] The negative electrode current collector can be the aforementioned copper foil or composite current collector. The composite current collector may include a polymer substrate and a copper foil layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0332] In some embodiments of this disclosure, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0333] In some embodiments of this disclosure, the negative electrode active material layer may optionally include a binder. The binder may include 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).

[0334] In some embodiments of this disclosure, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0335] In some embodiments of this disclosure, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0336] In some embodiments of this disclosure, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet (e.g., negative electrode active material, conductive agent, binder, and any other components) in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The coating thickness on one side is generally controlled between 50 μm and 150 μm.

[0337] This invention does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected. According to embodiments of this disclosure, the separator membrane material may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0338] In some embodiments of this disclosure, the battery may include an outer packaging. This outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0339] In some embodiments of this disclosure, the outer packaging may include a shell and a cover. The shell may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The shell has an opening communicating with the receiving cavity, and the cover plate is capable of covering the opening to close the receiving cavity.

[0340] In some embodiments of this disclosure, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0341] The outer packaging of the battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0342] The batteries disclosed herein may be in the form of individual battery cells, battery modules, and battery packs. In some embodiments, individual battery cells may be assembled into battery modules, and the number of battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into battery packs, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0343] This disclosure also provides a battery assembly, which includes one or two batteries as described in any of the above embodiments. The battery assembly can be a battery pack or a battery module, etc.

[0344] A fifth aspect of this disclosure provides an electrical device, wherein the electrical device may include the battery in any of the above embodiments. This electrical device has advantages corresponding to the electrode plates described above, which will not be elaborated further.

[0345] According to embodiments of this disclosure, the electrical device includes the battery described in the fourth aspect above. Therefore, the electrical device of this disclosure has a good service life.

[0346] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, digital cameras, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), wearable devices (such as watches, wristbands, VR glasses, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0347] As electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0348] As one example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device, a battery pack or battery module can be used.

[0349] Another example of the device could be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a single battery cell as its power source.

[0350] It should be noted that the features and advantages described above for the copper foil, negative electrode current collector, and negative electrode sheet of this disclosure are also applicable to the battery, battery module, and electrical equipment of this disclosure, and will not be repeated here.

[0351] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0352] Preparation of Electrolytic Copper Foil

[0353] Example A1

[0354] (1) Copper dissolution and solution preparation: The main chemical composition and content of the copper rod are: copper ≥ 99.9%; the copper rod is dissolved in 50wt% sulfuric acid water to prepare an electrolytic solution with a concentration of 85g / L copper sulfate (CuSO4·5H2O) and 100g / L sulfuric acid (H2SO4);

[0355] (2) Introduction of additives: Add the additive solution to the electrolyte solution provided in step (1), and use a heating and stirring device to mix the additive solution and the electrolyte solution evenly to form a mixture for use as green foil; and bring the mixture to the set electrolysis temperature of 50°C, and maintain this temperature throughout the electrolysis process. The mixture contains 205.5 mg / L of additives: lithium salt LiTFSI, grain refiner collagen, leveling agent hydroxyethyl cellulose (HEC), brightener sodium polydisulfide dipropane sulfonate (SPS), and wetting agent polyethylene glycol (PEG); wherein, the content of LiTFSI is 2 mg / L.

[0356] (3) Electrolytic treatment: The current density is constant and set to 50 A / dm³. 2 The electrolysis temperature is kept constant at 55°C; the voltage is kept constant at 3-5V; and electrolysis is performed for a set time until the target thickness of 6μm is achieved.

[0357] (4) After electrolysis, the copper foil surface is rinsed with running water to remove the attached copper sulfate solution, the surface is completely dried, and then washed with dilute hydrochloric acid and water in sequence. After passivation, it is dried to obtain copper foil.

[0358] Examples A2-A13

[0359] Examples A2-A13 were prepared using the same method as in Example A1, with the difference being that copper foils with different structural parameters were obtained by adjusting the amount of each additive. The specific differences are shown in Table 1.

[0360] Comparative Example A1

[0361] Copper foil was prepared using the method described in Example A1, except that LiTFSI or LiFSI was not added to the mixture. The specific differences are shown in Table 1.

[0362] Table 1

[0363] [Preparation of Lithium-ion Batteries]

[0364] Example B1

[0365] 1) Preparation of the positive electrode:

[0366] The positive electrode active material LiFePO4, conductive agent carbon black, binder PVDF, and conductive carbon nanotubes (CNTs) are thoroughly mixed in a mass ratio of 100:0.5:2:6.98. The solvent NMP is added, and the mixture is stirred under vacuum until the slurry is uniformly mixed to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of the current collector aluminum foil. After the electrode is completely dried, it is rolled and die-cut to obtain the positive electrode sheet.

[0367] 2) Preparation of the negative electrode:

[0368] The negative electrode active material graphite, conductive carbon black, binder CMC, emulsion SBR and pure water are mixed in a mass ratio of 100:1:1.5:3:100. Deionized water is added as a solvent and the mixture is stirred under vacuum until the slurry is homogeneous to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated on both surfaces of the current collector copper foil. After the electrode is completely dried, it is rolled and die-cut to obtain the negative electrode sheet.

[0369] 3) Preparation of electrolyte:

[0370] In an argon-filled glove box, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6) were then added to the mixed solvent to obtain the electrolyte. Based on the total mass of the electrolyte, the concentration of LiTFSI was 0.15 mol / L, and the concentration of LiPF6 was 1 mol / L.

[0371] 4) Separating membrane:

[0372] A polyethylene (PE) film with a thickness of 12 μm is used.

[0373] 5) Battery assembly:

[0374] The positive electrode, negative electrode, and separator are assembled into an electrode core in sequence. The electrode core is placed in an outer packaging shell, baked, and injected with electrolyte. After processes such as encapsulation, aging, formation, and capacity testing, a lithium-ion battery is obtained.

[0375] Examples B2-B13

[0376] The lithium-ion battery was prepared using the method of Example B1, except that the copper foil for the current collector of the negative electrode was prepared using the copper foil obtained in Examples A2-A13.

[0377] Comparative Example B1

[0378] The lithium-ion battery was prepared using the method of Example B1, except that the copper foil for the current collector of the negative electrode was prepared using the copper foil prepared in Comparative Example A1.

[0379] Parameter testing

[0380] I. Testing Methods

[0381] The structural parameters of the copper foils prepared in the examples and the performance parameters of the lithium-ion batteries were tested respectively, as follows:

[0382] 1. Calculation of crystal texture coefficient:

[0383] (1) XRD (short for "X-Ray Diffraction") characterization: An X-ray diffractometer (XRD) was used with a Cu target. The voltage and current were set to 40 kV and 40 mA, respectively. The trend changes of the grain size and texture coefficient of copper foil obtained under different conditions were analyzed. The scanning range was 30–100° and the scanning speed was 0.1°·s. -1 .

[0384] (2) Define the texture coefficient, which reflects preferred orientation, during crystal growth as:

[0385] Among them, TC (hkl) I is the texture coefficient of the (hkl) crystal plane. (hkl) The intensity (hkl) of the peak measured for the Cu coating, where n is the number of diffraction peaks measured, and I... 0(hkl) The diffraction intensity (hkl) of the standard peak is given. All the above data were obtained through XRD testing.

[0386] Taking the preferred orientation of the copper layer (220) in Example A6 as an example, the measured XRD diffraction intensity and standard data of the copper layer are shown in Table 2:

[0387] Table 2

[0388] Calculation process:

[0389] ① Calculate the intensity ratio of each crystal plane: I (hkl) / I 0(hkl) , to obtain I (111) / I 0(111) =85.31, I (200) / I 0(200) =99.43, I (220) / I 0(220) =607.8, I (311) / I 0(311) =14.11.

[0390] ② Calculate the average:

[0391] ③ Calculate the crystal texture coefficient: TC (220) =607.8 / 201.66=3.01.

[0392] (3) Calculate the proportion of crystal plane texture coefficient:

[0393] Specifically:

[0394] TC (220) \(TC (220) +TC (111) +TC (200) +TC (311) = 3.01 / (0.42+0.49+3.01+0.07)*100% = 75%.

[0395] 2. Testing of tensile strength and elongation:

[0396] Taking a 6μm thick copper foil as an example, cut copper foil strips with a width of 15mm and a length of 15cm. Tensile testing was performed using a universal testing machine with a gauge length of 50mm and a tensile speed of 50mm / min. Unit conversion: 0.1kgf / mm² 2 =0.98MPa. When the load drops to 80% of the peak load, it is considered a fracture, and the test is stopped. σ = F max / A;

[0397] σ represents tensile strength, with units of MPa.

[0398] F max This indicates the maximum load (N), which is read directly from the testing machine.

[0399] A represents the initial cross-sectional area (mm²). 2A = width × thickness.

[0400] Thickness measurement: using 100cm 2 The sample is taken using a sampler, and then the surface density of the copper foil is measured by weighing. According to the formula, the thickness = m / ρ (8.97 g / cm3).

[0401] 3. Calculation of elongation: △L=(L-L0) / L0*100% (where L0 is the initial length of the spline; L is the length after stretching).

[0402] 4. Roughness inspection:

[0403] The copper foil is placed on a flat glass plate surface, and a portable roughness tester is used to test both sides of the copper foil. Ra represents the average value of the absolute height of the profile, which is used to evaluate the overall roughness of the copper foil surface, and Rz represents the average or extreme value of the maximum peak and valley height of the profile, which is used to evaluate the local extreme height difference of the copper foil.

[0404] 5. Coulomb efficiency testing:

[0405] ① Formation process: Before the first use of a new battery, it needs to undergo charge-discharge cycles (such as 1-3 times of 0.1C charge-discharge) to form a stable solid electrolyte interface (SEI film) and reduce interference from the first irreversible capacity.

[0406] ② Let it stand: After charging and discharging, let the battery stand for more than 30 minutes to allow the internal electrochemical reaction to reach equilibrium.

[0407] ③ Test conditions settings: Constant temperature chamber temperature 25±2℃, current selection 0.25C, voltage test range set to 2.5-3.8V. Charge-discharge cycle test: Charge at a constant current (0.25C) to the cutoff voltage of 3.8V, switch to constant voltage (CV) charging until the current drops to the set threshold (0.05C), and record the charging capacity Q. charge After charging is complete, let it stand for 10-30 minutes, then discharge it at the same rate to the cutoff voltage and record the discharge capacity Q. discharge Repeated cycles: Perform multiple charge-discharge cycles.

[0408] ④ Coulomb efficiency calculation: CE = Q charge / Q discharge ×100%.

[0409] 6. Testing of cyclic capacity retention:

[0410] Ambient temperature: 25℃, test started after 2 hours:

[0411] 1) Charging: Charge at 1C constant current to 3.8V, let stand for 5 minutes; then charge at 0.2C constant current to 3.8V, let stand for 10 minutes;

[0412] 2) Discharge: Discharge at a constant current of 1C to 2.0V; let stand for 10 minutes.

[0413] 3) The loop terminates after 100 iterations.

[0414] II. Test Results:

[0415] (a) The copper foils obtained in Examples A1-A13 and Comparative Example A1 were tested, and the test results are shown in Table 3.

[0416] Table 3

[0417] (ii) The batteries obtained in Examples B1-B13 and Comparative Example B1 were tested, and the test results are shown in Table 4.

[0418] Table 4

[0419] The test results of various parameters of the products obtained in each embodiment and comparative example are shown in Tables 3 and 4. The texture factor of the (220) crystal plane of the copper foil obtained in this embodiment is as high as 75% or more. Using this copper foil as the negative electrode current collector of the battery is beneficial to obtaining higher coulombic efficiency and cycle performance. In addition, by optimizing the design of parameters such as lithium salt concentration in the electrolyte and additives, the performance of the copper foil can be better improved, thereby enhancing the electrochemical performance of the copper foil and promoting the improvement of coulombic efficiency and cycle performance of the battery.

[0420] Example 1

[0421] This embodiment provides a negative electrode sheet and a battery, the preparation method of which is as follows:

[0422] 1. Preparation of negative electrode sheet

[0423] (1) Select high-quality negative electrode current collector material (copper foil) and perform corona cleaning;

[0424] Carbon powder (carbon black, 60g), binder (PVDF, 90g), and solvent (water, 2kg) are mixed evenly and coated onto two main surfaces of a copper foil arranged opposite each other in the thickness direction to form a carbon coating layer on the copper foil. The carbon coating layer includes a first region and a second region. The second region is located at both edges in the length direction and both edges in the width direction of the first region. The thickness of the carbon coating layer in the first region is 1μm, and the thickness of the carbon coating layer in the second region is 50% of the thickness of the carbon coating layer in the first region. The width of the second region is 1mm, the width of the carbon coating layer in the first sub-region is 1mm, and the width of the second sub-region is 0mm.

[0425] (2) Mix the negative electrode active material, binder, conductive agent, etc., and add solvent to make a uniform negative electrode slurry;

[0426] The negative electrode active material graphite, conductive agent carbon black, water-soluble thickener polyhydroxymethyl cellulose (CMC), and water-soluble binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 95:1:1:3. The solvents are water and NMP.

[0427] (3) The negative electrode slurry is coated on the two opposite surfaces of the negative electrode current collector material in the thickness direction;

[0428] The coated electrode material is dried, and then pressed into shape to form a negative electrode sheet.

[0429] 2. Preparation of the positive electrode sheet

[0430] The positive electrode active material, conductive agent, and binder were mixed, and a solvent was added to obtain a mixed slurry. The positive electrode active material (lithium iron phosphate), the conductive agent (carbon nanotubes), and the binder (PVDF) were mixed in a mass ratio of 91:6:3. The solvent was NMP.

[0431] The electrode material slurry is coated onto the positive current collector (e.g., aluminum foil).

[0432] The electrode material after coating is dried.

[0433] The dried electrode material is pressed into shape to form a negative electrode sheet.

[0434] 3. Preparation of lithium-ion batteries

[0435] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a barrier. The separator is mainly a polyolefin separator, primarily made of polyethylene (PE) and polypropylene (PP), as well as a separator derived from PE and PP by adding a ceramic layer to the surface of the polyolefin separator.

[0436] Example 2

[0437] The difference between this embodiment and Embodiment 1 is that the width of the carbon coating layer in the first sub-region is 5mm.

[0438] Example 3

[0439] The difference between this embodiment and Embodiment 1 is that the width of the carbon coating layer in the first sub-region is 10mm.

[0440] Example 4

[0441] The difference between this embodiment and embodiment 2 is that the thickness of the carbon coating layer in the first sub-region is 25% of the thickness of the carbon coating layer in the first region.

[0442] Example 5

[0443] The difference between this embodiment and embodiment 2 is that the thickness of the carbon coating layer in the first sub-region is 0% of the thickness of the carbon coating layer in the first region.

[0444] Example 6

[0445] The difference between this embodiment and Embodiment 1 is that the thickness of the carbon coating layer in the second sub-region is 50% of the thickness of the carbon coating layer in the first region. The width of the carbon coating layer in the second sub-region is 1 mm.

[0446] Example 7

[0447] The difference between this embodiment and Embodiment 6 is that the width of the carbon coating layer in the second sub-region is 5mm.

[0448] Example 8

[0449] The difference between this embodiment and Embodiment 6 is that the width of the carbon coating layer in the second sub-region is 10mm.

[0450] Example 9

[0451] The difference between this embodiment and embodiment 7 is that the thickness of the carbon coating layer in the second sub-region is 25% of the thickness of the carbon coating layer in the first region.

[0452] Example 10

[0453] The difference between this embodiment and embodiment 7 is that the thickness of the carbon coating layer in the second sub-region is 0% of the thickness of the carbon coating layer in the first region.

[0454] Example 11

[0455] The difference between this embodiment and Embodiment 1 is that the thickness of the carbon coating layer in the first sub-region is equal to the thickness of the carbon coating layer in the second sub-region, that is, the thickness of the carbon coating layer in the second region is uniform and is 50% of the thickness of the carbon coating layer in the first region, and the sum of the widths of the carbon coating layers in the second region is 1 mm.

[0456] Example 12

[0457] The difference between this embodiment and Embodiment 11 is that the width of the carbon coating layer in the second region is 5 mm.

[0458] Example 13

[0459] The difference between this embodiment and Embodiment 11 is that the width of the carbon coating layer in the second region is 10 mm.

[0460] Example 14

[0461] The difference between this embodiment and embodiment 12 is that the thickness of the carbon coating layer in the second region is 25% of the thickness of the carbon coating layer in the first region.

[0462] Example 15

[0463] The difference between this embodiment and embodiment 12 is that the thickness of the carbon coating layer in the second region is 0% of the thickness of the carbon coating layer in the first region.

[0464] Comparative Example 1

[0465] This comparative example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 1, except that the carbon coating layer is uniformly coated on the negative electrode current collector.

[0466] Comparative Example 2

[0467] This comparative example provides a negative electrode and a battery, the preparation method of which is basically the same as that of Example 1, except that the thickness of the carbon coating layer in the first sub-region exceeds 10% of the thickness of the carbon coating layer in the first region.

[0468] Comparative Example 3

[0469] This comparative example provides a negative electrode and a battery, the preparation method of which is basically the same as that of Example 1, except that the thickness of the carbon coating layer in the second sub-region exceeds the thickness of the carbon coating layer in the first region by 10%.

[0470] Comparative Example 4

[0471] This comparative example provides a negative electrode and a battery, the preparation method of which is basically the same as that of Example 1, except that the thickness of the carbon coating layer in the second region exceeds the thickness of the carbon coating layer in the first region by 10%.

[0472] Test case

[0473] The following tests were performed on the batteries of Example 1 and Comparative Example 1 above:

[0474] The charge / discharge cycles were set to 500, 1000, and 1500 cycles respectively. In each cycle, the battery was first charged to full capacity using a constant current and constant voltage method, and then discharged to a set cutoff voltage using a constant current method. The charging and discharging capacities for each cycle were recorded. After each cycle, the battery's capacity retention rate was calculated.

[0475] The testing methods for the 500-cycle, 1000-cycle, and 1500-cycle tests of lithium-ion batteries are the same. Specifically, the 500-cycle test at room temperature is described as an example. In a 25℃ environment, the lithium-ion battery is first discharged to 2.0V (2.5V for lithium iron phosphate and ternary materials) at 0.33C (i.e., the current value required to completely discharge the theoretical capacity within 3 hours), then left to stand for 5 minutes before starting the test. The test process is as follows: the lithium-ion battery is charged at a constant current of 1C to 3.8V (4.2V for lithium iron phosphate and ternary materials), then charged at a constant voltage of 3.8V until the current drops to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to 2.0V (2.5V for lithium iron phosphate and ternary materials). The discharge capacity at this point is taken as the discharge capacity of the first cycle. The lithium-ion battery is then subjected to 500 charge-discharge cycles using the above method. The same steps apply to cycles of 1000 and 1500.

[0476] The capacity retention rate of a lithium-ion battery after 500 cycles = (discharge capacity after 500 cycles / discharge capacity of the first cycle) × 100%.

[0477] Table 5

[0478] From Table 5 and Figures 5 and 6, the following conclusions can be drawn:

[0479] By setting the thickness of the carbon coating layer in the second region to be less than that in the first region, the performance of the battery can be effectively improved.

[0480] Figure 5 shows a negative electrode sheet in the related art, where the area within the black box represents lithium plating. Figure 6 shows a negative electrode sheet 100 according to an embodiment of this application. Combining Figures 5 and 6, it can be easily seen that no lithium plating is observed in the second region 120 of the negative electrode sheet in this embodiment, and no obvious lithium plating is observed on the negative electrode sheet itself. Therefore, it can effectively improve the capacity retention rate of the battery after multiple charge-discharge cycles.

[0481] Example 16

[0482] This embodiment provides a negative electrode 100a and a battery, the preparation method of which is as follows:

[0483] 1. Preparation of negative electrode 100a

[0484] The negative electrode active material, conductive agent, binder, etc., are mixed and a solvent is added to form a homogeneous slurry. In the slurry of region 110a, the negative electrode active material (graphite), conductive agent (carbon black), water-soluble thickener (polyhydroxymethyl cellulose (CMC), and water-soluble binder (styrene-butadiene rubber (SBR)) are mixed in a mass ratio of 95:1:1:3. The solvents are water and NMP.

[0485] The fourth region 120a is located at both sides of the length direction Y and the width direction X of the third region 110a. Since the mass content of the conductive agent in the fourth region 120a of this embodiment is lower than that in the third region 110a, two different mass contents of conductive agents are used in the early electrode material slurry preparation process to prepare two different slurries.

[0486] The two mixed electrode material slurries are coated onto the negative electrode current collector 101 (copper foil). A slurry with a lower conductive agent content is coated onto the fourth region 120a. Specifically, the mass ratio of the conductive agent in the fourth region 120a to that in the third region 110a is 5 wt%, meaning that the mass ratio of the negative electrode active material graphite, the conductive agent carbon black, the water-soluble thickener polyhydroxymethyl cellulose (CMC), and the water-soluble binder styrene-butadiene rubber (SBR) in the slurry of the fourth region 120a is 95:0.05:1:3. The width of the fourth region 120a is 1 mm, of which the width of the third sub-region 121a is 0 mm, and the width of the fourth sub-region 122a is 1 mm. Then, the electrode material is uniformly adhered to the negative electrode current collector 101 by methods such as scraping, rolling, or spraying.

[0487] The electrode material after coating is dried.

[0488] The dried electrode material is pressed into shape to form a negative electrode sheet 100a.

[0489] 2. Preparation of the positive electrode sheet

[0490] The positive electrode active material, conductive agent, and binder were mixed, and a solvent was added to obtain a mixed slurry. The positive electrode active material (lithium iron phosphate), the conductive agent (carbon nanotubes), and the binder (PVDF) were mixed in a mass ratio of 91:6:3. The solvent was NMP.

[0491] The electrode material slurry is coated onto the positive current collector (e.g., aluminum foil).

[0492] The electrode material after coating is dried.

[0493] The dried electrode material is pressed into shape to form a positive electrode sheet.

[0494] 3. Preparation of lithium-ion batteries

[0495] The prepared positive electrode, separator, and negative electrode 100a are stacked in sequence, with the separator positioned between the positive and negative electrode 100a to act as a separator. The separator is mainly a polyolefin separator, primarily composed of polyethylene (PE) and polypropylene (PP) membranes, as well as a separator derived from polyethylene (PE) and polypropylene (PP) membranes with a ceramic layer added to the surface of the polyolefin separator.

[0496] After the positive electrode, separator, and negative electrode 100a undergo a winding or stacking process, they are placed in an outer packaging foil (aluminum-plastic film). After drying, an electrolyte is injected into them, ultimately forming a lithium-ion battery. The electrolyte is a mixed solution of lithium electrolyte salt and carbonate organic solvent. The lithium electrolyte salt is lithium hexafluorophosphate (LPF6), and the solvent is a mixed solvent of chain and cyclic carbonates. The chain carbonates are at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or other chain organic esters containing unsaturated bonds. Propylene carbonate (PC), vinylene carbonate (VC), and other cyclic carbonates can be at least one of ethylene carbonate (EC) or unsaturated cyclic organic esters.

[0497] Example 17

[0498] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 1mm, wherein the width of the third sub-region 121a is 1mm and the width of the fourth sub-region 122a is 0mm.

[0499] Example 18

[0500] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 2mm, wherein the width of the third sub-region 121a is 1mm and the width of the fourth sub-region 122a is 1mm.

[0501] Example 19

[0502] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 3mm, wherein the width of the third sub-region 121a is 2mm and the width of the fourth sub-region 122a is 1mm.

[0503] Example 20

[0504] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 4mm, wherein the width of the third sub-region 121a is 3mm and the width of the fourth sub-region 122a is 1mm.

[0505] Example 21

[0506] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 5mm, wherein the width of the third sub-region 121a is 4mm and the width of the fourth sub-region 122a is 1mm.

[0507] Example 22

[0508] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 6mm, wherein the width of the third sub-region 121a is 5mm and the width of the fourth sub-region 122a is 1mm.

[0509] Example 23

[0510] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 7mm, wherein the width of the third sub-region 121a is 6mm and the width of the fourth sub-region 122a is 1mm.

[0511] Example 24

[0512] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 8mm, wherein the width of the third sub-region 121a is 7mm and the width of the fourth sub-region 122a is 1mm.

[0513] Example 25

[0514] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 9mm, wherein the width of the third sub-region 121a is 8mm and the width of the fourth sub-region 122a is 1mm.

[0515] Example 26

[0516] The difference between this embodiment and embodiment 16 is that, in the process of preparing the negative electrode 100a, the width of the fourth region 120a is 10mm, wherein the width of the third sub-region 121a is 9mm and the width of the fourth sub-region 122a is 1mm.

[0517] Example 27

[0518] The difference between this embodiment and embodiment 26 is that, in the process of preparing the negative electrode 100a, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is 15wt%.

[0519] Example 28

[0520] The difference between this embodiment and embodiment 26 is that, in the process of preparing the negative electrode 100a, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is 25wt%.

[0521] Example 29

[0522] The difference between this embodiment and embodiment 26 is that, in the process of preparing the negative electrode 100a, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is 40wt%.

[0523] Example 30

[0524] The difference between this embodiment and embodiment 26 is that, in the process of preparing the negative electrode 100a, the ratio of the mass content of the conductive agent in the fourth region 120a to the mass content of the conductive agent in the third region 110a is 50wt%.

[0525] Comparative Example 5

[0526] This comparative example provides a negative electrode 100a and a battery, the preparation method of which is basically the same as that of Example 16. The difference is that in the preparation of the negative electrode 100a, the mass content of the conductive agent in the slurry on the negative electrode current collector 101 is the same. In other words, the slurry formed by mixing in the same proportion is coated on the third region 110a and the fourth region 120a.

[0527] Comparative Example 6

[0528] This comparative example provides a negative electrode 100a and a battery, the preparation method of which is basically the same as that of Example 16. The difference is that in the preparation of the negative electrode 100a, the mass content of the conductive agent in the fourth region 120a is 115wt% of the mass content of the conductive agent in the third region 110a.

[0529] Test case

[0530] The following tests were performed on the batteries of Examples 16-30 and Comparative Examples 5-6 above:

[0531] The charge / discharge cycles were set to 500, 1000, and 1500 cycles respectively. In each cycle, the battery was first charged to full capacity using a constant current and constant voltage method, and then discharged to a set cutoff voltage using a constant current method. The charging and discharging capacities for each cycle were recorded. After each cycle, the battery's capacity retention rate was calculated.

[0532] The testing methods for the 500-cycle, 1000-cycle, and 1500-cycle tests of lithium-ion batteries are the same. Specifically, the 500-cycle test at room temperature is described as an example. In a 25℃ environment, the lithium-ion battery is first discharged to 2.0V (2.5V for lithium iron phosphate and ternary materials) at 0.33C (i.e., the current value required to completely discharge the theoretical capacity within 3 hours), then left to stand for 5 minutes before starting the test. The test process is as follows: the lithium-ion battery is charged at a constant current of 1C to 3.8V (4.2V for lithium iron phosphate and ternary materials), then charged at a constant voltage of 3.8V until the current drops to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to 2.0V (2.5V for lithium iron phosphate and ternary materials). The discharge capacity at this point is taken as the discharge capacity of the first cycle. The lithium-ion battery is then subjected to 500 charge-discharge cycles using the above method. The same steps apply to cycles of 1000 and 1500.

[0533] The capacity retention rate of a lithium-ion battery after 500 cycles = (discharge capacity after 500 cycles / discharge capacity of the first cycle) × 100%.

[0534] Table 6

[0535] The following conclusions can be drawn from Table 6:

[0536] By setting the mass content of the conductive agent in the fourth region 120a to be lower than that in the third region 110a, the performance of the battery can be effectively improved.

[0537] Figure 11 shows a negative electrode sheet in the related art, where the area within the black box represents lithium plating. Figure 12 shows a negative electrode sheet 100a according to an embodiment of this disclosure. Combining Figures 11 and 12, it can be easily seen that no lithium plating is observed on the fourth region 120a of the negative electrode sheet 100a in this embodiment, and no obvious lithium plating is observed on the negative electrode sheet 100a. Therefore, the capacity retention rate of the battery after multiple charge-discharge cycles can be effectively improved.

[0538] Example 31

[0539] This embodiment provides a negative electrode 100b and a battery, the preparation method of which is as follows:

[0540] 1. Preparation of negative electrode 100b

[0541] The negative electrode active material, conductive agent, and binder are mixed and a solvent is added to form a homogeneous slurry. Specifically, in the slurry of region 5 110b, the negative electrode active material (graphite), conductive agent (carbon black), water-soluble thickener (polyhydroxymethyl cellulose (CMC), and water-soluble binder (styrene-butadiene rubber (SBR)) are mixed in a mass ratio of 95:1:1:3. The solvents are water and NMP.

[0542] The sixth region 120b is located at both sides of the length direction Y and the width direction X of the fifth region 110b. Since the mass content of the binder in the sixth region 120b of this embodiment is higher than that in the fifth region 110b, two different mass contents of binder are used in the early electrode material slurry preparation process to prepare two different slurries.

[0543] The two mixed electrode material slurries are coated onto the negative electrode current collector 101 (copper foil). A slurry with a higher binder content is coated onto the sixth region 120b. Specifically, the mass ratio of the binder content in the sixth region 120b to that in the fifth region 110b is 110wt%, meaning that the slurry in the sixth region 120b contains graphite (negative electrode active material), carbon black (conductive agent), polyhydroxymethyl cellulose (CMC) (water-soluble thickener), and styrene-butadiene rubber (SBR) (water-soluble binder) in a mass ratio of 95:1:1:3.3. The width of the sixth region 120b is 1mm, with the fifth sub-region 121a having a width of 0mm and the sixth sub-region 122b having a width of 1mm. Then, the electrode material is uniformly adhered to the negative electrode current collector 101 using methods such as scraping, rolling, or spraying.

[0544] The electrode material after coating is dried.

[0545] The dried electrode material is pressed into shape to form the negative electrode 100b.

[0546] 2. Preparation of the positive electrode sheet

[0547] The positive electrode active material, conductive material, binder, etc., are mixed, and a solvent is added to obtain a mixed slurry. Specifically, the positive electrode active material (lithium iron phosphate), the conductive agent (carbon nanotubes), and the binder (PVDF) are mixed in a mass ratio of 91:6:3. The solvent is NMP.

[0548] The electrode material slurry is coated onto the positive current collector (e.g., aluminum foil).

[0549] The electrode material after coating is dried.

[0550] The dried electrode material is pressed into shape to form a positive electrode sheet.

[0551] 3. Preparation of lithium-ion batteries

[0552] The prepared positive electrode, separator, and negative electrode 10 are stacked in sequence, with the separator positioned between the positive and negative electrode 100a to act as a separator. The separator is mainly a polyolefin separator, primarily composed of polyethylene (PE) and polypropylene (PP) membranes, as well as a separator derived from polyethylene (PE) and polypropylene (PP) membranes with a ceramic layer added to the surface of the polyolefin separator.

[0553] After the positive electrode, separator, and negative electrode 100a undergo a winding or stacking process, they are placed in an outer packaging foil (aluminum-plastic film). After drying, an electrolyte is injected into them, ultimately forming a lithium-ion battery. The electrolyte is a mixed solution of lithium electrolyte salt and carbonate organic solvent. The lithium electrolyte salt is lithium hexafluorophosphate (LPF6), and the solvent is a mixed solvent of chain and cyclic carbonates. The chain carbonates are at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or other chain organic esters containing unsaturated bonds. Propylene carbonate (PC), vinylene carbonate (VC), and other cyclic carbonates can be at least one of ethylene carbonate (EC) or unsaturated cyclic organic esters.

[0554] Example 32

[0555] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 1mm, wherein the width of the fifth sub-region 121b is 1mm and the width of the sixth sub-region 122b is 0mm.

[0556] Example 33

[0557] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 2mm, wherein the width of the fifth sub-region 121b is 1mm and the width of the sixth sub-region 122b is 1mm.

[0558] Example 34

[0559] The difference between this embodiment and embodiment 33 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 3mm, wherein the width of the fifth sub-region 121b is 2mm and the width of the sixth sub-region 122b is 1mm.

[0560] Example 35

[0561] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 4mm, wherein the width of the fifth sub-region 121b is 3mm and the width of the sixth sub-region 122b is 1mm.

[0562] Example 36

[0563] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 5mm, wherein the width of the fifth sub-region 121b is 4mm and the width of the sixth sub-region 122b is 1mm.

[0564] Example 37

[0565] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 6mm, wherein the width of the fifth sub-region 121b is 5mm and the width of the sixth sub-region 122b is 1mm.

[0566] Example 38

[0567] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 7mm, wherein the width of the fifth sub-region 121b is 6mm and the width of the sixth sub-region 122b is 1mm.

[0568] Example 39

[0569] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 8mm, wherein the width of the fifth sub-region 121b is 7mm and the width of the sixth sub-region 122b is 1mm.

[0570] Example 40

[0571] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 9mm, wherein the width of the fifth sub-region 121b is 8mm and the width of the sixth sub-region 122b is 1mm.

[0572] Example 41

[0573] The difference between this embodiment and embodiment 31 is that, in the process of preparing the negative electrode 100b, the width of the sixth region 120b is 10mm, wherein the width of the fifth sub-region 121b is 9mm and the width of the sixth sub-region 122b is 1mm.

[0574] Example 42

[0575] The difference between this embodiment and embodiment 41 is that, in the process of preparing the negative electrode 100b, the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b is 105wt%.

[0576] Example 43

[0577] The difference between this embodiment and embodiment 41 is that, in the process of preparing the negative electrode 100b, the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b is 115wt%.

[0578] Example 44

[0579] The difference between this embodiment and embodiment 41 is that, in the process of preparing the negative electrode 100b, the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b is 120wt%.

[0580] Example 45

[0581] The difference between this embodiment and embodiment 41 is that, in the process of preparing the negative electrode 100b, the ratio of the mass content of the binder in the sixth region 120b to the mass content of the binder in the fifth region 110b is 130wt%.

[0582] Comparative Example 7

[0583] This comparative example provides a negative electrode 100b and a battery, the preparation method of which is basically the same as that of Example 31. The difference is that in the preparation of the negative electrode 100b, the mass content of the binder in the slurry on the negative electrode current collector 101 is the same. In other words, the slurry formed by mixing in the same proportion is coated on the fifth region 110b and the sixth region 120b.

[0584] Comparative Example 8

[0585] This comparative example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of Example 31. The difference is that in the preparation of the negative electrode sheet 100b, the mass content of the binder in the sixth region 120b is 85 wt% of the mass content of the binder in the fifth region 110b.

[0586] Test case

[0587] The following tests were performed on the batteries of Examples 31-45 and Comparative Examples 7-8 above:

[0588] The charge / discharge cycles were set to 500, 1000, and 1500 cycles respectively. In each cycle, the battery was first charged to full capacity using a constant current and constant voltage method, and then discharged to a set cutoff voltage using a constant current method. The charging and discharging capacities for each cycle were recorded. After each cycle, the battery's capacity retention rate was calculated.

[0589] The testing methods for the 500-cycle, 1000-cycle, and 1500-cycle tests of lithium-ion batteries are the same. Specifically, the 500-cycle test at room temperature is described as an example. In a 25℃ environment, the lithium-ion battery is first discharged to 2.0V (2.5V for lithium iron phosphate and ternary materials) at 0.33C (i.e., the current value required to completely discharge the theoretical capacity within 3 hours), then left to stand for 5 minutes before starting the test. The test process is as follows: the lithium-ion battery is charged at a constant current of 1C to 3.8V (4.2V for lithium iron phosphate and ternary materials), then charged at a constant voltage of 3.8V until the current drops to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to 2.0V (2.5V for lithium iron phosphate and ternary materials). The discharge capacity at this point is taken as the discharge capacity of the first cycle. The lithium-ion battery is then subjected to 500 charge-discharge cycles using the above method. The same steps apply to cycles of 1000 and 1500.

[0590] The capacity retention rate of a lithium-ion battery after 500 cycles = (discharge capacity after 500 cycles / discharge capacity of the first cycle) × 100%.

[0591] Table 7

[0592] The following conclusions can be drawn from Table 7:

[0593] By setting the mass content of the binder in the sixth region 120b to be higher than that in the fifth region 110b, the performance of the battery can be effectively improved.

[0594] Figure 16 shows a negative electrode sheet in the related art, where the area within the black box represents lithium plating. Figure 17 shows a negative electrode sheet 100b according to an embodiment of this disclosure. Combining Figures 16 and 17, it can be easily seen that no lithium plating is observed on the sixth region 120b of the negative electrode sheet 100b in this embodiment, and no obvious lithium plating is observed on the negative electrode sheet 100a. Therefore, the capacity retention rate of the battery after multiple charge-discharge cycles can be effectively improved.

[0595] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A copper foil, wherein, Based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil, the proportion of the (220) crystal plane texture coefficient is 75% to 98%.

2. The copper foil according to claim 1, wherein, Based on the sum of the (111) crystal plane texture coefficient, (200) crystal plane texture coefficient, (220) crystal plane texture coefficient and (311) crystal plane texture coefficient of the copper foil, the proportion of the (220) crystal plane texture coefficient is 80% to 90%.

3. The copper foil according to claim 1 or 2, wherein, The ratio of the texture coefficient of the (220) crystal plane to the texture coefficient of the (200) crystal plane is 6.1 to 17.

5.

4. The copper foil according to any one of claims 1 to 3, wherein, The ratio of the texture coefficient of the (220) crystal plane to the texture coefficient of the (200) crystal plane is 8.1 to 17.

5.

5. The copper foil according to any one of claims 1 to 4, wherein, The copper foil has a tensile strength of 350 MPa to 600 MPa, and / or the copper foil has an elongation of 2% to 10%.

6. The copper foil according to any one of claims 1 to 5, wherein, The thickness of the copper foil is 4μm to 15μm.

7. The copper foil according to any one of claims 1 to 6, wherein, The roughness of the copper foil satisfies: 0 < Ra ≤ 0.5 μm, and / or, 0 < Rz ≤ 4 μm.

8. A method for preparing copper foil, comprising: Provide copper ion-containing electrolytic solutions; The copper-containing electrolytic solution is mixed with an additive to obtain a mixture; the additive includes lithium salt and functional additive; the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, and the functional additive includes a grain refiner. The mixture is electrolyzed to obtain copper foil.

9. The method according to claim 8, wherein, Based on the mixture, the lithium salt content is 1 mg / L to 15 mg / L.

10. The method according to claim 8 or 9, wherein, Based on the mixture, the lithium salt content is 2 mg / L to 15 mg / L.

11. The method according to any one of claims 8 to 10, wherein, The grain refiner includes one or more of collagen, sodium 3-mercapto-1-propanesulfonate, and sodium dimethylformamide sulfonate; and / or, based on the mixture, the content of the grain refiner is 50 mg / L to 200 mg / L.

12. The method according to any one of claims 8 to 11, wherein, The functional additives also include one or more of the following: leveling agents, wetting agents, and brightening agents.

13. The method according to claim 12, wherein, The functional additive satisfies at least one of the following (a) to (c): (a) The leveling agent includes one or more of hydroxyethyl cellulose, tetrahydrothiazolyl thiophene, and gelatin; (b) The wetting agent includes one or more of polyethylene glycol, hydroxymethyl cellulose, and polypropylene glycol; (c) The brightener includes one or more of sodium dithiopropane sulfonate, sodium thiopropane sulfonate, and thiourea.

14. The method according to any one of claims 8 to 13, wherein, Based on the mixture, the content of the additive is less than or equal to 350 mg / L.

15. A negative electrode sheet comprising a negative electrode current collector, wherein the negative electrode current collector comprises the copper foil according to any one of claims 1 to 7, or comprises the copper foil prepared by the method according to any one of claims 8 to 14.

16. A battery comprising the negative electrode as described in claim 15.

17. The battery according to claim 16, wherein, The negative electrode current collector has a negative electrode film layer on at least one side, and the negative electrode film layer includes a negative electrode active material; the negative electrode active material includes one or more of natural graphite, artificial graphite, and silicon-based materials, or the negative electrode active material includes metallic lithium.

18. The battery according to claim 16 or 17, further comprising an electrolyte comprising an electrolyte salt comprising lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

19. The battery according to claim 18, wherein, Based on the electrolyte, the concentration of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide is 0.02 mol / L to 1 mol / L.

20. An electrical device comprising the battery as described in any one of claims 16 to 19.

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