Negative electrode metal foil and preparation method therefor, and battery

Abstract

The present disclosure relates to a negative electrode metal foil and a preparation method therefor, and a battery. The preparation method for a negative electrode metal foil comprises the following steps: using a metal foil substrate as a working electrode, using graphite or a platinum sheet as a counter electrode, placing the metal foil substrate and the graphite or the platinum sheet in an electrolyte, and carrying out anodic oxidation at a constant voltage to obtain a composite metal foil having an oxide layer on the surface; and carrying out ultrasonic treatment on the composite metal foil, and removing the oxide layer to obtain a negative electrode metal foil, wherein the surface of at least one side of the negative electrode metal foil is provided with a plurality of recessed structures, and the plurality of recessed structures are distributed in an array. By means of the anodic oxidation and ultrasonic treatment, an array of nano recessed structures having an electric field uniformization function is prepared on the surface of the metal foil substrate, so that an electric field for lithium deposition is uniformized to improve the cycling stability of a negative electrode-free lithium-ion battery having a high energy density, thereby obtaining a negative electrode-free lithium-ion battery having both high specific energy and long circulation.

Description

Negative electrode metal foil, preparation method thereof, and battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 2023105752475 filed with the China Patent Office on May 19, 2023, entitled “Negative Electrode Metal Foil, Preparation Method and Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure relates to the technical field of batteries, and in particular to a negative electrode metal foil, a preparation method thereof, and a battery. Background Art

[0004] In recent years, with the rapid development of new energy vehicles, people have higher and higher requirements for their cruising range and battery life. The total cruising range of electric vehicles is directly related to the energy density and cycle stability of the power batteries they carry. Therefore, how to develop lithium-ion batteries with both high energy density and long cycle stability has been a research hotspot in recent years.

[0005] At present, the specific energy density of lithium-ion batteries can be improved mainly from two aspects: chemical and physical: (1) improving the energy density of positive and negative electrode materials at the chemical level: for example, the positive electrode material is developing towards high nickel content ternary positive electrode, and the negative electrode is developing towards silicon-based, lithium metal negative electrode that undergoes alloying reaction. However, high energy positive and negative electrode materials often mean higher gas production, worse cycle stability, and safety issues caused by dendrite growth; (2) at the physical level, the specific energy density can be improved mainly by simplifying the structural parts of the battery cell and reducing the weight of the battery cell, such as simplifying the cover, thinning the shell, and thinning the current collector. Among them, J. Neudecker et al. first proposed the concept of negative electrode-free battery, which uses negative electrode current collector copper foil instead of traditional graphite negative electrode material, thereby reducing battery mass and improving energy density.

[0006] Electrodeless lithium batteries replace traditional graphite anodes with metal foil. During charging, lithium ions escape from the positive electrode, pass through the separator, and deposit on the surface of the negative electrode metal foil to form metallic lithium. During discharge, these metallic lithium ions are reinserted into the positive electrode, forming lithium ions. Therefore, the properties of the negative electrode metal foil play a crucial role in determining the cycling stability of lithium-ion batteries. However, during the manufacturing process, the surface of the bare negative electrode metal foil often exhibits uneven cracks and defects, resulting in uneven lithium ion deposition and stripping, leading to dendrite growth, which can pierce the separator, causing short circuits and posing safety concerns.

[0007] Summary of the Invention

[0008] The present disclosure provides a method for preparing a negative electrode metal foil, comprising the following steps:

[0009] A metal foil substrate is used as a working electrode, and a graphite or platinum sheet is used as a counter electrode. The electrodes are placed in an electrolyte and anodic oxidation is performed at a constant voltage to obtain a composite metal foil having an oxide layer on the surface. The composite metal foil is ultrasonically treated to remove the oxide layer to obtain a negative electrode metal foil. At least one side of the surface of the negative electrode metal foil has multiple recessed structures, and the multiple recessed structures are distributed in an array.

[0010] In one embodiment, the metal foil substrate includes at least one of titanium foil, aluminum foil, copper foil, nickel foil and iron foil.

[0011] In one embodiment, the metal foil substrate is pre-treated by ultrasonic cleaning; the cleaning agents used in the ultrasonic cleaning include acetone and ethanol.

[0012] In one embodiment, the thickness of the metal foil substrate is 6 to 200 μm.

[0013] In one embodiment, the electrolyte comprises ammonium fluoride, ethylene glycol and water; in the electrolyte, the mass fraction of ammonium fluoride is 0.05% to 0.8%, and the mass fraction of ethylene glycol is 0.5% to 5%.

[0014] In one embodiment, the constant voltage ranges from 30V to 120V.

[0015] In one embodiment, the power of the ultrasonic treatment is 500-5000 W, and the time of the ultrasonic treatment is 30-600 s.

[0016] In one embodiment, the shape of the recessed structure includes a bowl shape.

[0017] In one embodiment, the opening diameter of the recessed structure is 50-500 nm.

[0018] In one embodiment, the depth of the recessed structure is 25-250 nm.

[0019] In one embodiment, on a single side surface of the negative electrode metal foil, the total opening area of ​​the recessed structures accounts for 50% to 99.9% of the single side surface area of ​​the negative electrode metal foil.

[0020] The negative electrode metal foil is prepared by the method for preparing the negative electrode metal foil as described above.

[0021] A battery comprises at least one positive electrode sheet, at least one separator and at least one negative electrode metal foil, wherein the negative electrode metal foil is a negative electrode metal foil prepared by the method for preparing a negative electrode metal foil as described above or the negative electrode metal foil as described above; the positive electrode sheets and the negative electrode metal foil are alternately stacked, and the separator is arranged between adjacent positive electrode sheets and negative electrode metal foils; the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector.

[0022] In one embodiment, in the stacking direction of the positive electrode sheet, the separator and the negative electrode metal foil, the projection of the separator forms a first region, the projection of the positive electrode sheet forms a second region, and the projection of the negative electrode metal foil forms a third region. The third region is within the first region, and the second region is within the third region.

[0023] In one embodiment, the positive electrode material layer includes a positive electrode active material; the positive electrode active material includes at least one of lithium ferrous phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, a ternary material and a cobalt-free positive electrode material.

[0024] In one embodiment, the diaphragm includes at least one of a PP film, a PE film, and a composite diaphragm; the composite diaphragm includes a PP base film and / or a PE base film, and the surface of the base film contains ceramics and PVDF.

[0025] In one embodiment, the thickness of the separator is 3 to 50 μm.

[0026] In one embodiment, the thickness of the positive electrode current collector is 5 to 50 μm.

[0027] In one embodiment, the thickness of the positive material layer is 5 to 500 μm.

[0028] In one embodiment, the positive electrode sheet, separator and negative electrode metal foil are all rectangular; the length of the separator is 2 to 10 mm greater than the length of the negative electrode metal foil, and the width of the separator is 2 to 10 mm greater than the width of the negative electrode metal foil; the length of the negative electrode metal foil is 2 to 10 mm greater than the length of the positive electrode sheet, and the width of the negative electrode metal foil is 2 to 10 mm greater than the width of the positive electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only represent the embodiments of the present disclosure by way of example, and the dimensional ratios in the drawings do not directly correspond to the actual ratios of the embodiments. At the same time, the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope.

[0030] FIG1 is a schematic diagram of the preparation of the negative electrode metal foil disclosed in the present invention;

[0031] FIG2 is a scanning electron microscope image of the surface of the negative electrode metal foil with a concave structure according to Example 1 of the present disclosure;

[0032] FIG3 is an electric field simulation diagram of the negative electrode metal foil disclosed in the present invention;

[0033] FIG4 is a schematic diagram of the deposition of lithium ions on the surface of the negative electrode metal foil according to the present disclosure;

[0034] FIG5 is a schematic structural diagram of a single-layer lithium-ion battery disclosed herein;

[0035] FIG6 is a schematic structural diagram of a multi-layer lithium-ion battery disclosed in the present invention.

[0036] Reference numerals: 1-negative electrode metal foil, 101-recessed structure, 2-separator, 3-positive electrode current collector, 4-positive electrode material layer. DETAILED DESCRIPTION

[0037] The advantages of the embodiments in the application content will be explained in the embodiment section of the specification below, and some of them are obvious from the specification, or can be obtained through some embodiments of the embodiments of the present disclosure.

[0038] The technical solution of the present disclosure will be further described below with reference to the accompanying drawings and through some implementation methods.

[0039] In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the embodiments described herein are only used to explain the present disclosure and are not intended to limit the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present disclosure, several improvements and modifications can be made, and these improvements and modifications are also considered to be within the scope of protection of the embodiments of the present disclosure.

[0040] The present disclosure relates to a method for preparing a negative electrode metal foil, comprising the following steps:

[0041] A metal foil substrate is used as a working electrode, and a graphite or platinum sheet is used as a counter electrode. The electrodes are placed in an electrolyte and anodic oxidation is performed at a constant voltage to obtain a composite metal foil having an oxide layer on the surface. The composite metal foil is ultrasonically treated to remove the oxide layer to obtain a negative electrode metal foil. At least one side of the surface of the negative electrode metal foil has multiple recessed structures, and the multiple recessed structures are distributed in an array.

[0042] The present invention discloses a nano-recessed structure array with a uniform electric field function prepared on a metal foil substrate through the above method, thereby uniformizing the electric field of lithium deposition, thereby improving the cycle stability of the negative electrode-free lithium ion battery that already has a high energy density, and developing a negative electrode-free lithium ion battery with both high specific energy and long cycle life.

[0043] In one embodiment, the metal foil includes at least one of titanium foil, aluminum foil, copper foil, nickel foil and iron foil.

[0044] In one embodiment, the metal foil substrate is pre-treated with ultrasonic cleaning, wherein the cleaning agents used in the ultrasonic cleaning process include acetone and ethanol. In one embodiment, the metal foil substrate is cleaned 2 to 4 times with acetone and ethanol respectively to remove impurities on the surface of the metal foil substrate.

[0045] In one embodiment, the thickness of the metal foil substrate is 6 to 200 μm, for example, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, etc.

[0046] In one embodiment, the electrolyte includes ammonium fluoride, ethylene glycol and water; in the electrolyte, the mass fraction of ammonium fluoride is 0.05% to 0.8%, for example, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.8%, etc., and the mass fraction of ethylene glycol is 0.5% to 5%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.

[0047] In one embodiment, the constant voltage ranges from 30 to 120 V, such as 30 V, 50 V, 60 V, 70 V, 90 V, 100 V, 120 V, etc.

[0048] In one embodiment, the present disclosure can adjust the bowl-shaped diameter and depth of the recessed structure by adjusting the concentration of the electrolyte and the magnitude of the constant voltage.

[0049] In one embodiment, the power of the ultrasonic treatment is 500-5000 W, for example, 500 W, 1000 W, 1500 W, 2000 W, 2500 W, 3000 W, 4000 W, 5000 W, etc. The time of the ultrasonic treatment is 30-600 s, for example, 30 s, 50 s, 60 s, 100 s, 200 s, 300 s, 500 s, 600 s, etc. The ultrasonic treatment used in the present disclosure can effectively remove the oxide layer and form a bowl-shaped concave structure.

[0050] In one embodiment, the recessed structure comprises a bowl shape.

[0051] In one embodiment, the opening diameter of the recessed structure is 50-500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 350 nm, 400 nm, 500 nm, etc.

[0052] In one embodiment, the depth of the recessed structure is 25 to 250 nm, for example, 25 nm, 30 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, etc.;

[0053] In one embodiment, on a single side surface of the negative electrode metal foil, the total opening area of ​​the recessed structure accounts for 50% to 99.9% of the single side surface area of ​​the negative electrode metal foil, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0054] The present disclosure also relates to a negative electrode metal foil prepared by the above method for preparing the negative electrode metal foil.

[0055] According to another aspect of the present disclosure, the present disclosure also relates to a battery, comprising at least one positive electrode sheet, at least one separator and at least one negative electrode metal foil, wherein the negative electrode metal foil is a negative electrode metal foil prepared by a preparation method of a negative electrode metal foil or a negative electrode metal foil; the positive electrode sheets and the negative electrode metal foil are alternately stacked, and a separator is arranged between adjacent positive electrode sheets and negative electrode metal foils; the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of at least one side of the positive electrode current collector.

[0056] The battery disclosed herein contains the above-mentioned negative electrode metal foil, and each nano-recessed structure is equivalent to a lithium ion rivet, inducing uniform nucleation of lithium ions, thereby inducing uniform growth of subsequent lithium ions and improving the cycle stability of the lithium-ion battery; compared with the metal negative electrode without nano-recessed structure, the negative electrode metal foil disclosed herein has more reserved space for storing lithium metal, thereby reducing the overall weight of the battery and improving the energy density of the battery.

[0057] In one embodiment, the battery of the present disclosure includes an alkali metal ion battery such as a lithium ion battery, a sodium ion battery, a potassium ion battery, a zinc ion battery, a magnesium ion battery, a calcium ion battery, or a liquid metal battery.

[0058] In one embodiment, the battery of the present disclosure is assembled in a manner including lamination and winding, etc. The battery shape includes soft pack, square shell and cylinder, etc.

[0059] In one embodiment, the positive electrode sheet, separator and negative electrode metal foil in the battery are each one, as shown in Figure 5, which includes a negative electrode metal foil, a separator, a positive electrode material layer and a positive electrode current collector in sequence, and the side of the negative electrode metal foil with the concave structure is connected to the separator.

[0060] In one embodiment, the number of the positive electrode sheet, the separator and the negative electrode metal foil in the battery is multiple, as shown in FIG6 . In this case, positive electrode material layers are provided on both sides of the positive electrode sheet.

[0061] In one embodiment, in the stacking direction of the positive electrode sheet, separator, and negative electrode metal foil, the projection of the separator forms a first region, the projection of the positive electrode sheet forms a second region, and the projection of the negative electrode metal foil forms a third region. The third region is within the first region, and the second region is within the third region. That is, the area of ​​the separator is larger than the area of ​​the negative electrode metal foil, and the area of ​​the negative electrode metal foil is larger than the area of ​​the positive electrode sheet. In one embodiment, the center points of any positive electrode sheet, separator, and negative electrode metal foil lie on the same straight line.

[0062] In one embodiment, the positive electrode material layer includes a positive electrode active material; the positive electrode active material includes at least one of lithium ferrous phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, a ternary material, and a cobalt-free positive electrode material. In one embodiment, the thickness of the positive electrode material layer is 5 to 500 μm, for example, 5 μm, 10 μm, 20 μm, 25 μm, 30 μm, 50 μm, 70 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 450 μm, or 500 μm.

[0063] In one embodiment, the positive electrode current collector comprises aluminum foil and has a thickness of 5 to 50 μm, such as 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc.

[0064] In one embodiment, the separator comprises at least one of a PP film, a PE film, and a composite separator; the composite separator comprises a PP base film and / or a PE base film, the surface of the base film containing ceramic and polyvinylidene fluoride (PVDF). In one embodiment, the separator has a thickness of 3 to 50 μm (e.g., 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc.).

[0065] In one embodiment, the positive electrode sheet, separator, and negative electrode metal foil are all rectangular; the length of the separator is 2 to 10 mm greater than the length of the negative electrode metal foil (e.g., 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, etc.); the width of the separator is 2 to 10 mm greater than the width of the negative electrode metal foil (e.g., 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, etc.); the length of the negative electrode metal foil is 2 to 10 mm greater than the length of the positive electrode sheet (e.g., 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, etc.); and the width of the negative electrode metal foil is 2 to 10 mm greater than the width of the positive electrode sheet (e.g., 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, etc.). The above-mentioned structure of the present disclosure is more conducive to ensuring that the battery has excellent electrochemical performance.

[0066] In one embodiment, the battery further includes an electrolyte; the electrolyte is an organic solvent electrolyte containing a lithium salt and an additive, the lithium salt is one or more of LiPF6, LiTFSI and LiFSI, the organic solvent is one or more of EC, EMC, DMC, DEC, DOL, FEC and DME, and the additive is one or more of LiNO3, KNO3 and KPF6.

[0067] In one embodiment, the battery further comprises a positive tab and a negative tab.

[0068] The following are typical but non-limiting embodiments of the present disclosure:

[0069] Example 1

[0070] A method for preparing a negative electrode metal foil 1 comprises the following steps:

[0071] (a) The metal foil substrate is subjected to ultrasonic cleaning treatment in advance; the ultrasonic cleaning treatment uses detergents including acetone and ethanol, and is performed three times respectively;

[0072] (b) The washed metal foil substrate is used as a working electrode and graphite is used as a counter electrode in an electrolyte solution, and anodized at a constant voltage to obtain a composite metal foil having an oxide layer on the surface; the composite metal foil is ultrasonically treated to remove the oxide layer to obtain a negative electrode metal foil 1; the surface of the negative electrode metal foil 1 has a plurality of bowl-shaped recessed structures 101, and the plurality of recessed structures 101 are distributed in an array;

[0073] The metal foil substrate is titanium foil;

[0074] The electrolyte comprises ammonium fluoride, ethylene glycol and water; in the electrolyte, the mass fraction of ammonium fluoride is 0.4%, and the mass fraction of ethylene glycol is 2.5%;

[0075] The constant voltage is 75V;

[0076] The power of ultrasonic treatment was 3000 W, and the time of ultrasonic treatment was 300 s;

[0077] The opening diameter of the recessed structure 101 is 250 nm;

[0078] The depth of the recessed structure 101 is 125 nm;

[0079] On a single side surface of the negative electrode metal foil 1 , the total opening area of ​​the recessed structures 101 accounts for 80% of the single side surface area of ​​the negative electrode metal foil 1 .

[0080] A scanning electron microscope image of the surface of the negative electrode metal foil 1 with the recessed structure 101 of this embodiment is shown in FIG2 .

[0081] Example 2

[0082] A method for preparing a negative electrode metal foil 1 comprises the following steps:

[0083] (a) The metal foil substrate is subjected to ultrasonic cleaning treatment in advance; the ultrasonic cleaning treatment uses detergents including acetone and ethanol, and is performed three times respectively;

[0084] (b) The washed metal foil substrate is used as a working electrode and graphite is used as a counter electrode in an electrolyte solution and anodized at a constant pressure to obtain a composite metal foil having an oxide layer on the surface; the composite metal foil is ultrasonically treated to remove the oxide layer to obtain a negative electrode metal foil 1; the surface of the negative electrode metal foil 1 has a plurality of bowl-shaped recessed structures 101, and the plurality of recessed structures 101 are distributed in an array;

[0085] The metal foil substrate is titanium foil;

[0086] The electrolyte comprises ammonium fluoride, ethylene glycol and water; in the electrolyte, the mass fraction of ammonium fluoride is 0.05%, and the mass fraction of ethylene glycol is 0.5%;

[0087] The constant pressure is 30V;

[0088] The power of ultrasonic treatment was 500 W, and the ultrasonic treatment time was 30 s;

[0089] The opening diameter of the recessed structure 101 is 50 nm;

[0090] The depth of the recessed structure 101 is 50 nm;

[0091] On a single side surface of the negative electrode metal foil 1 , the total opening area of ​​the recessed structures 101 accounts for 50% of the single side surface area of ​​the negative electrode metal foil 1 .

[0092] Example 3

[0093] A method for preparing a negative electrode metal foil 1 comprises the following steps:

[0094] (a) The metal foil substrate is subjected to ultrasonic cleaning treatment in advance; the ultrasonic cleaning treatment uses detergents including acetone and ethanol, and is performed three times respectively;

[0095] (b) The washed metal foil substrate is used as a working electrode and graphite is used as a counter electrode in an electrolyte solution and anodized at a constant pressure to obtain a composite metal foil having an oxide layer on the surface; the composite metal foil is ultrasonically treated to remove the oxide layer to obtain a negative electrode metal foil 1; the surface of the negative electrode metal foil 1 has a plurality of bowl-shaped recessed structures 101, and the plurality of recessed structures 101 are distributed in an array;

[0096] The metal foil substrate is titanium foil;

[0097] The electrolyte comprises ammonium fluoride, ethylene glycol and water; in the electrolyte, the mass fraction of ammonium fluoride is 0.8%, and the mass fraction of ethylene glycol is 5%;

[0098] The constant pressure is 120V;

[0099] The power of ultrasonic treatment was 5000 W, and the ultrasonic treatment time was 600 s;

[0100] The opening diameter of the recessed structure 101 is 500 nm;

[0101] The depth of the recessed structure 101 is 250 nm;

[0102] On one side of the negative electrode metal foil 1 , the total opening area of ​​the recessed structures 101 accounts for 99% of the surface area of ​​the negative electrode metal foil 1 .

[0103] Example 4

[0104] A 3Ah lithium-ion battery comprising a positive electrode sheet, a separator 2, the negative electrode metal foil 1 of Example 1, and an electrolyte; the positive electrode sheets and the negative electrode metal foil 1 are alternately stacked, and the separator 2 is provided between adjacent positive electrode sheets and negative electrode metal foils 1; the positive electrode sheet comprises a positive electrode current collector 3 and a positive electrode material layer 4 provided on the surface of the positive electrode collector;

[0105] In the stacking direction of the positive electrode sheet, the diaphragm 2 and the negative electrode metal foil 1, the projection of the diaphragm 2 forms a first area, the projection of the positive electrode sheet forms a second area, and the projection of the negative electrode metal foil 1 forms a third area. The third area is located in the center of the first area, and the second area is located in the center of the third area. The positive electrode sheet, the diaphragm 2 and the negative electrode metal foil 1 are all rectangular. The length of the diaphragm 2 is 6 mm larger than the length of the negative electrode metal foil 1, and the width of the diaphragm 2 is 6 mm larger than the width of the negative electrode metal foil 1. The length of the negative electrode metal foil 1 is 6 mm larger than the length of the positive electrode sheet, and the width of the negative electrode metal foil 1 is 6 mm larger than the width of the positive electrode sheet.

[0106] The positive electrode material layer 4 includes positive electrode active material NCM811, conductive carbon black (SP): carbon nanotubes (CNT): polyvinylidene fluoride (PVDF), and the mass ratio of NCM811, SP, CNT and PVDF is 96.5:0.5:1:2;

[0107] The positive electrode current collector 3 is aluminum foil;

[0108] The diaphragm 2 is a PP film;

[0109] The electrolyte is a carbonate-based electrolyte containing LiPF6.

[0110] Example 5

[0111] A lithium ion battery, except that the battery is 5Ah, other conditions are the same as those in Example 4.

[0112] Example 6

[0113] A lithium ion battery, except that the battery is 7Ah, other conditions are the same as those in Example 4.

[0114] Example 7

[0115] A lithium ion battery, except that the negative electrode metal foil 1 in Example 2 is used, other conditions are the same as those in Example 6.

[0116] Example 8

[0117] A lithium ion battery, except that the negative electrode metal foil 1 in Example 3 is used, other conditions are the same as those in Example 6.

[0118] Comparative Example 1

[0119] A lithium ion battery, wherein the negative electrode metal foil is a plain titanium foil without surface treatment, and other conditions are the same as those of Example 4.

[0120] Comparative Example 2

[0121] A lithium ion battery, wherein the negative electrode metal foil is a plain titanium foil without surface treatment, and other conditions are the same as those of Example 5.

[0122] Comparative Example 3

[0123] A lithium ion battery, wherein the negative electrode metal foil is a plain titanium foil without surface treatment, and other conditions are the same as those of Example 6.

[0124] Experimental example

[0125] 1. The present disclosure uses the concave size of the negative electrode metal foil of Example 1 as a parameter and uses Ansys software to perform electric field simulation. Since the nano bowl is centrally symmetrical, a two-dimensional finite element analysis is used to perform quantitative simulation on it to obtain the potential distribution diagram of the metal foil surface. As shown in Figure 3, the potential at the bottom of the concave structure is lower than the potential at the edge of its top opening, which is more conducive to the uniform deposition of lithium. Based on the fact that a lower potential has a stronger inductive force on the deposition of lithium ions, a schematic diagram of the deposition of lithium ions on the surface of the negative electrode metal foil with a concave structure is drawn. As shown in Figure 4, in the nano array, each nanostructure is equivalent to a lithium ion rivet, inducing the uniform nucleation of lithium ions, thereby inducing the uniform growth of subsequent lithium ions and improving the cycle stability of lithium-ion batteries.

[0126] 2. The batteries of Examples 4 to 8 and Comparative Examples 1 to 3 were subjected to performance tests. The capacity retention rate of each battery was observed after 500 cycles under the same cycle conditions. The results are shown in Table 1.

[0127] Table 1 Capacity retention test results

[0128] As shown in Table 1, the battery prepared using the negative electrode metal foil with the specific recessed structure array obtained by the specific method disclosed herein has a higher capacity retention rate. Comparative Examples 1 to 3, which used bare titanium foil without surface treatment as the negative electrode, all achieved lower capacity retention rates than the battery prepared using the specific negative electrode metal foil disclosed herein. Industrial Applicability

[0129] In summary, the present disclosure provides a negative electrode metal foil, a preparation method thereof, and a battery. By anodic oxidation and ultrasonic treatment, a nano-recessed structure array with a uniform electric field function is prepared on the surface of the metal foil substrate, thereby uniformizing the electric field of lithium deposition to improve the cycle stability of the negative electrode-free lithium ion battery, which already has a high energy density, and develop a negative electrode-free lithium ion battery with both high specific energy and long cycle. The negative electrode metal foil obtained by this method has a nano-recessed structure array with uniform size and regularity on its surface, forming a more uniform electric field, which is conducive to the uniform deposition and stripping of lithium ions. Each recessed structure is equivalent to a lithium ion rivet, inducing the uniform nucleation of lithium ions, thereby inducing the uniform growth of subsequent lithium ions, so as to improve the cycle stability of the lithium ion battery. The battery disclosed in the present disclosure uses the negative electrode metal foil as the negative electrode sheet. The metal negative electrode foil with the recessed structure has more reserved space for storing lithium metal, thereby reducing the overall weight of the battery, improving the overall specific energy density of the battery, and having a better capacity retention rate.

Claims

1. A method for preparing a negative electrode metal foil, It is characterized in that The following steps are involved: The metal foil substrate is used as a working electrode, and the graphite or platinum sheet is used as a counter electrode, and is placed in an electrolyte, and anodized at a constant voltage to obtain a composite metal foil having an oxide layer on the surface; the composite metal foil is subjected to ultrasonic treatment to remove the oxide layer to obtain a negative electrode metal foil; At least one side surface of the negative electrode metal foil has a plurality of recessed structures, and the plurality of recessed structures are distributed in an array.

2. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The metal foil substrate includes at least one of titanium foil, aluminum foil, copper foil, nickel foil and iron foil.

3. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The metal foil substrate is preliminarily subjected to ultrasonic cleaning treatment; the cleaning agents used in the ultrasonic cleaning treatment include acetone and ethanol.

4. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The thickness of the metal foil substrate is 6-200 μm.

5. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The electrolyte comprises ammonium fluoride, ethylene glycol and water; In the electrolyte, the mass fraction of ammonium fluoride is 0.05% to 0.8%, and the mass fraction of ethylene glycol is 0.5% to 5%.

6. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The constant voltage ranges from 30V to 120V.

7. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that The power of the ultrasonic treatment is 500-5000W, and the time of the ultrasonic treatment is 30-600s.

8. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that Contains at least one of the following features (1) to (3): (1) The shape of the concave structure includes a bowl shape; (2) The opening diameter of the concave structure is 50 to 500 nm; (3) The depth of the recessed structure is 25 to 250 nm.

9. The method for preparing the negative electrode metal foil according to claim 1, It is characterized in that On a single side surface of the negative electrode metal foil, the total opening area of ​​the recessed structures accounts for 50% to 99.9% of the single side surface area of ​​the negative electrode metal foil. 10 . The negative electrode metal foil prepared by the method for preparing a negative electrode metal foil according to claim 1 .

11. A battery, It is characterized in that The invention comprises at least one positive electrode sheet, at least one separator and at least one negative electrode metal foil, wherein the negative electrode metal foil is a negative electrode metal foil prepared by the method for preparing a negative electrode metal foil according to any one of claims 1 to 9 or a negative electrode metal foil according to claim 10; the positive electrode sheets and the negative electrode metal foils are alternately stacked, and the separator is arranged between adjacent positive electrode sheets and negative electrode metal foils; The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one side surface of the positive electrode current collector.

12. The battery according to claim 11, It is characterized in that In the stacking direction of the positive electrode sheet, the separator and the negative electrode metal foil, the projection of the separator forms a first region, the projection of the positive electrode sheet forms a second region, and the projection of the negative electrode metal foil forms a third region. The third region is within the first region, and the second region is within the third region.

13. The battery according to claim 11, It is characterized in that The positive electrode material layer includes a positive electrode active material; the positive electrode active material includes at least one of lithium ferrous phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, a ternary material and a cobalt-free positive electrode material.

14. The battery according to claim 11, It is characterized in that The diaphragm includes at least one of a PP film, a PE film and a composite diaphragm; the composite diaphragm includes a PP base film and / or a PE base film, and the surface of the base film contains ceramics and PVDF.

15. The battery according to claim 11, It is characterized in that Contains at least one of the following features (1) to (3): (1) The thickness of the diaphragm is 3 to 50 μm; (2) The thickness of the positive electrode current collector is 5 to 50 μm; (3) The thickness of the positive material layer is 5 to 500 μm.

16. The battery according to claim 11, It is characterized in that The positive electrode sheet, separator and negative electrode metal foil are all rectangular; the length of the separator is 2 to 10 mm greater than the length of the negative electrode metal foil, and the width of the separator is 2 to 10 mm greater than the width of the negative electrode metal foil; the length of the negative electrode metal foil is 2 to 10 mm greater than the length of the positive electrode sheet, and the width of the negative electrode metal foil is 2 to 10 mm greater than the width of the positive electrode sheet.

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