Three-dimensional structure modified current collector, preparation method thereof and application thereof in gel-state negative electrode-free sodium battery

Abstract

The application belongs to the field of battery materials, and discloses a three-dimensional structure modified current collector, a preparation method thereof and application of the three-dimensional structure modified current collector in a gel-state sodium battery without a negative electrode, solves the problems of unstable coulomb efficiency, poor battery cycle life, excessive growth of sodium dendrites and sodium source loss caused by solid-state electrolyte interface reconstruction of a traditional current collector in a gel-state sodium metal battery without a negative electrode. The three-dimensional structure modified current collector is obtained through a silver-ammonia replacement reaction on a copper foil with three-dimensional Cu nanowires. The current collector improves the affinity of the original copper foil to metal sodium, and the three-dimensional structure of the current collector can effectively alleviate the volume change in the cycle process of the sodium metal battery without a negative electrode, effectively reduce the nucleation overpotential of sodium ions on the current collector and significantly improve the battery life. When the current collector is applied to the gel-state sodium metal battery without a negative electrode, the battery can achieve high average coulomb efficiency and excellent cycle life under different current densities and surface capacities.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a method for preparing a current collector with a three-dimensional structure modification. Background Technology

[0002] With the rapid development of renewable energy storage technologies and the rapid growth in demand for electric vehicles, the need for high-performance, low-cost, and highly safe energy storage batteries is becoming increasingly urgent. While lithium-ion batteries dominate the market, their scarcity, uneven distribution, and continuously rising costs necessitate the development of novel electrochemical energy storage systems. Sodium-ion batteries, due to abundant sodium resources (approximately 2.3% of the Earth's crust), low cost, and an electrochemical mechanism similar to lithium, are considered a highly promising alternative. However, traditional sodium-ion batteries still face numerous challenges:

[0003] (1) Bottleneck of negative electrode: The specific capacity of commonly used negative electrode materials such as hard carbon is limited (usually <300 mAh g). -1 This limits the theoretical battery energy density (typically between 120-160 Wh / kg). -1 (This is the minimum standard for lithium-ion batteries).

[0004] (2) Electrolyte safety hazards: Liquid organic electrolytes are prone to leakage and flammability, and pose a risk of thermal runaway;

[0005] (3) Poor interface stability: Sodium dendrites gradually grow during battery use and can easily penetrate the separator, causing a short circuit.

[0006] To overcome these limitations, anode-free sodium batteries (AFSIBs) have emerged. By eliminating the use of anode materials and instead employing ultra-thin copper current collectors matched with the cathode, anode-free sodium batteries are expected to achieve power outputs exceeding 300 Wh / kg. -1 High energy density. However, traditional copper and aluminum current collectors have low affinity for sodium metal, leading to low reversibility of metal deposition / stripping reactions and the formation of unstable solid electrolyte interphase (SEI), which is the root cause of the short lifespan of negative electrode-free sodium batteries. In particular, the combination of liquid electrolyte and separator has no significant inhibitory effect on problems such as dead sodium and sodium dendrites caused by irreversible metal deposition / stripping reactions on the current collector side, which greatly affects the safety of negative electrode-free sodium batteries.

[0007] In recent years, the design of electrodeless batteries has mainly focused on the control of current collector structure; however, the most crucial aspect of battery safety has often been overlooked. To improve the safety of electrodeless batteries, solid-state electrolytes (thermal stability temperature > 200℃) are considered a powerful driver of safety improvement. However, the low ion transport rate (<10⁻⁶) at room temperature... -4 S cm -1The poor electrode / electrolyte contact and other defects cause its performance to be significantly lower than that of batteries using conventional liquid electrolytes under the same conditions. Gel electrolytes combine the safety of solid electrolytes with the high ionic conductivity (>10) of liquid electrolytes. -3 S cm -1 Sodium gel-based batteries, which can immobilize liquid components through polymer networks while providing flexible interfacial contacts, are considered an ideal solution to the aforementioned problems. Research on anode-free sodium gel batteries is still in its early stages, with significant technological gaps remaining in areas such as long-term cycling interfacial stability, uniform sodium deposition / stripping behavior at high current densities, and large-scale manufacturing processes.

[0008] While the existing technology CN109108276A discloses a nanowire electrode material, its preparation method, and its application, it suffers from several problems. Firstly, the method of obtaining copper-based nanowires with various coating materials through physical deposition followed by reduction inherently reduces the three-dimensional porosity between nanowires, lowering the specific surface area and affecting local current density and sodium deposition efficiency. This, in turn, leads to metal dendrite growth and a decrease in battery cycle life. Secondly, the physical deposition methods employed, such as magnetron sputtering and evaporation, which deposit the coating layer from top to bottom on the substrate, easily create dead zones at the roots of the nanowires, resulting in incomplete or excessive coating coverage. Furthermore, the final high-temperature reduction method can easily damage the three-dimensional structure of the nanowires, reducing their stress performance and failing to effectively buffer volume expansion during battery cycle charging and discharging, thus leading to poor electrode structure stability and shortened cycle life.

[0009] Therefore, developing a novel anode-free current collector that can maintain the integrity of the three-dimensional porous copper-silver framework, has high sodium affinity, and can form a stable interpenetrating network with the gel electrolyte, and its preparation method, is of great significance for promoting the practical application of high-safety, high-energy-density sodium batteries. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes a three-dimensional structure-modified current collector, its preparation method, and its application in a gel-state negative electrode-free sodium battery.

[0011] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0012] A method for preparing a three-dimensional structure-modified current collector, comprising the following steps:

[0013] (1) Dissolve ammonium persulfate in water, add sodium hydroxide to prepare a mixed solution, and soak the pretreated copper foil to obtain a copper foil with three-dimensional Cu(OH)2 nanowires grown on it.

[0014] (2) In the electrolyte, a platinum sheet electrode is used as the anode and a copper foil with three-dimensional Cu(OH)2 nanowires is used as the cathode. Through electrochemical reduction, a copper foil with three-dimensional Cu nanowires is obtained.

[0015] (3) The copper foil with three-dimensional Cu nanowires grown in step (2) is immersed in silver ammonia solution. After immersion, the surface of the copper foil is cleaned with deionized water and 75% alcohol in sequence, and dried overnight at 60-80℃ to obtain a current collector with three-dimensional structure modification, named Cu-Ag-NWs.

[0016] In step (1) above, the pretreated copper foil refers to the copper foil that has been wiped with 75% alcohol to remove oil stains from its surface, and treated with an acidic solution (such as HCl, H2SO4, CH3COOH solution) with a concentration of not less than 1 M for more than 60 seconds (to remove oxidized impurities on the surface of the copper foil); in the mixed solution, the concentration of ammonium persulfate is 0.1-0.2 M, and the concentration of sodium hydroxide is 2-3 M; the soaking time is 180-360 seconds.

[0017] In step (2) above, the solute in the electrolyte is at least one of sodium sulfate, potassium nitrate, potassium sulfate, ammonium sulfate, and sodium chloride, and the concentration of the electrolyte is 0.4-2 M; the current density for electrochemical reduction is 8-10 mA cm⁻¹. -2 The time is 20-35 minutes.

[0018] In step (3) above, the silver ammonia solution is prepared by adding 1-3 M ammonia water to 0.1-0.5 M silver nitrate aqueous solution until the solution changes from turbid to clear, thus obtaining the silver ammonia solution; the immersion time in the silver ammonia solution is not less than 210 s.

[0019] A three-dimensional modified current collector was prepared using the above-described method. The three-dimensional modification layer consists of copper-silver nanowires with a diameter of 70.0-300.0 nm, stacked to form a modification layer with a thickness of approximately 5.2-8.7 μm.

[0020] The above-mentioned three-dimensional structure-modified current collector is used in gel-state sodium-ion batteries without negative electrodes.

[0021] A gel-state sodium-ion battery without a negative electrode includes a positive electrode, a gel electrolyte, a separator, and a current collector modified with the above-mentioned three-dimensional structure.

[0022] The raw materials for the above-mentioned gel electrolyte include monomers, crosslinking agents, initiators, and liquid electrolytes; wherein the monomer is trifluoroethyl methacrylate, the crosslinking agent is N,N-methylenebisacrylamide, and the initiator is at least one of azobisisobutyronitrile, azobisisovalerate, and azobisisobutyramidine hydrochloride.

[0023] Furthermore, the liquid electrolyte comprises a sodium salt and an organic solvent, the concentration of the liquid electrolyte is 1 M, and each g of liquid electrolyte contains 0.02-0.03 g of monomer, 0.02-0.03 g of crosslinking agent, and 0.0005-0.001 g of initiator. The sodium salt is at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide; the organic solvent is at least one of diethylene glycol monomethyl ether (DGM), 1,3-cyclopentanediol, ethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

[0024] The aforementioned positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is at least one of sodium vanadium phosphate (NVP), sodium iron phosphate pyrophosphate, sodium iron phosphate pyrophosphate, and sodium iron manganese phosphate pyrophosphate. The conductive agent is any one or more of graphene, carbon nanotubes, acetylene black, Ketjen black, and Super P Li; the separator is any one of polyethylene, polypropylene microporous membrane, glass fiber membrane, and polyacrylonitrile membrane.

[0025] Specifically, the preparation method of the above-mentioned gel-state sodium-ion battery without a negative electrode is as follows:

[0026] (a) A slurry was prepared by dissolving the positive electrode active material, binder, and conductive agent in N-methylpyrrolidone solvent at a mass ratio of 8:1:1 and stirring until homogeneous. The slurry was then coated onto a current collector and vacuum-dried overnight at 120°C. A 12 mm perforated electrode sheet was then punched to serve as the positive electrode sheet, with a positive electrode sheet loading of 8-10 mg cm⁻¹. -2 ;

[0027] (b) The three-dimensional modified current collector prepared according to the present invention is punched into an electrode (16 mm in diameter). The electrode and the positive electrode are separated by a diaphragm. A gel electrolyte precursor (such as sodium hexafluorophosphate (NaPF6) as the sodium salt, diethylene glycol dimethyl ether (DGM) as the organic solvent, and trifluoroethyl methacrylate and N,N-methylenebisacrylamide as the polymer backbone) is added dropwise. A stainless steel shell is used as the outer casing to assemble a CR2025 button battery.

[0028] (c) Let the assembled battery stand for more than two hours to ensure that the battery is fully wetted, and then put it in a 70°C oven for thermal polymerization for 1 hour to ensure that the gel electrolyte precursor is polymerized into a gel electrolyte.

[0029] The beneficial effects of this invention are:

[0030] (1) This invention uses a three-step method (alkali immersion oxidation, electrochemical reduction, and chemical displacement) to grow and construct metal nanowires with a diameter of approximately 70.0-300.0 nm on the surface of copper foil, which are then stacked into a three-dimensional porous structure modification layer with a thickness of approximately 5.2-8.7 μm. First, the presence of sodium-loving element metallic silver in this structure significantly optimizes the deposition effect of metallic sodium, exhibiting a more stable coulombic efficiency during the constant current charge-discharge process of the half-cell with sodium current collector. Moreover, this three-dimensional structure buffers the stress changes of the negative electrode-free battery during cycling, significantly reducing the capacity decay caused by SEI breakage and reconstruction due to stress changes compared to traditional two-dimensional copper foil. In addition, the Cu-Ag interface structure formed by the displacement reaction avoids the problem of incomplete or excessive deposition of the coating layer due to uneven sputtering, which is beneficial to the uniform deposition of metallic sodium.

[0031] (2) When the current collector prepared in this application is applied to a gel-state sodium battery without a negative electrode, the SEI formed after cycling is thinner and more uniform than that formed by conventional bare copper foil, and has more inorganic components and stronger mechanical properties.

[0032] (3) This invention uses a gel electrolyte instead of a liquid electrolyte. This design confines the electrolyte, greatly reducing the safety hazards caused by short circuits in negative electrode-free batteries. At the same time, the gel electrolyte, which has a certain mechanical modulus, can also effectively block the growth of sodium dendrites caused by uneven deposition. Furthermore, the Ag element on the Cu-Ag-NWs on the current collector and the N,N-methylenebisacrylamide in the gel electrolyte generate Ag-N coordination, which strengthens the contact between the electrolyte and the current collector. This is beneficial for ions to gain electrons uniformly on the current collector and be reduced to nuclei, thereby leading to the uniform deposition and stripping of sodium metal on the current collector.

[0033] (4) The present invention applies the design of a negative electrode-free battery to a gel battery, which improves the energy density (322.72 Wh / kg) and safety of the battery. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 Optical comparison images of the current collector modified with the three-dimensional modification layer prepared in Example 1 of the present invention and the unmodified copper foil in Comparative Example 1. The left image shows the current collector modified with the three-dimensional modification layer; the right image shows the bare copper foil current collector.

[0036] Figure 2 The X-ray diffraction (XRD) patterns are of the current collector modified with the three-dimensional modification layer prepared in Example 1 of the present invention and the bare copper foil of Comparative Example 1.

[0037] Figure 3 The image shows a transmission electron microscope (TEM) image of the current collector modified with the three-dimensional modification layer prepared in Example 1 of this invention.

[0038] Figure 4 The planar and cross-sectional morphology of the current collector modified by the three-dimensional modification layer prepared in Example 1 of the present invention is shown by scanning electron microscopy (SEM).

[0039] Figure 5 This is an EDS image of a single Cu-Ag-NWs nanowire prepared in Example 1 of the present invention.

[0040] Figure 6 This is the preparation process of the gel electrolyte used in this invention.

[0041] Figure 7 Optical photographs of sodium deposition and stripping on unmodified copper foil and Cu-Ag-NWs; wherein, (a) is an optical photograph of sodium deposition on unmodified copper foil (Comparative Example 1); (b) is an optical photograph of sodium stripping on unmodified copper foil (Comparative Example 1); (c) is an optical photograph of sodium deposition on Cu-Ag-NWs (Example 1); and (d) is an optical photograph of sodium stripping on Cu-Ag-NWs (Example 1).

[0042] Figure 8 The electrochemical performance of Cu-Ag-NWs||Na and Cu||Na half-cells assembled with current collectors prepared in Example 1 and Comparative Example 1 of this invention is shown; wherein, (a) is the electrochemical performance at 1.0 mA cm⁻¹ -2 1.0 mAh cm -2 (a) shows the long cycle and first cycle curves; (b) shows the charge and discharge curves when cycling to 150 cycles.

[0043] Figure 9 A comparison of the performance of the Cu-Ag-NWs current collector prepared in this invention in gel electrolytes and conventional liquid electrolytes.

[0044] Figure 10 The cycling stability of the gel-state electrodeless battery assembled with the current collector prepared in Example 1 of the present invention under different current densities is shown.

[0045] Figure 11The electrochemical performance of Cu-Ag-NWs||Na and Cu-NWs||Na half-cells assembled with current collectors prepared in Example 1 and Comparative Example 2 of this invention is shown; wherein, (a) is the electrochemical performance of the above half-cells at 1.0 mA cm⁻¹. -2 1.0 mAh cm -2 (a) is a long-cycle comparison; (b) is the charge-discharge curve of the half-cell Cu-Ag-NWs||Na assembled in Example 1 at different cycles; (c) is the charge-discharge curve of the half-cell Cu-NWs||Na assembled in Comparative Example 2 at different cycles.

[0046] Figure 12 The comparison of SEI formed on the two current collectors after cycling is shown for Cu-Ag-NWs||Na and Cu||Na gel half-cells assembled with the two current collectors prepared in Example 1 and Comparative Example 1, respectively. The comparison includes: (a, b) SEI thickness; (c, d) SEI elemental composition; (e, f) SEI Young's modulus; and (g, h) Na... + Activation energy for passing through SEI and desolvation.

[0047] Figure 13 The cycling performance of Cu-Ag-NWs-Na||Cu-Ag-NWs-Na and Cu-Na||Cu-Na symmetric cells assembled with current collectors prepared in Example 1 and Comparative Example 1 of this invention is evaluated.

[0048] Figure 14 The electrochemical performance of the full cells assembled with current collectors prepared in Example 1 and Comparative Example 1 of this invention is shown below; (a) shows the long-term cycling performance of Cu-Ag-NWs||NVP and Cu||NVP at 0.5 C rate when N / P=0.5; (b) shows the long-term cycling performance of Cu-Ag-NWs||NVP at 0.5 C rate when N / P=1.5 and N / P=2.5 and Cu||NVP at N / P=3; (c) shows the charge-discharge curves of Cu-Ag-NWs||NVP at different cycle numbers when N / P=0.5; and (d) shows the charge-discharge curves of Cu||NVP at different cycle numbers when N / P=0.5. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1

[0051] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0052] (1) Prepare a 1 M HCl solution;

[0053] (2) Cut the copper foil into 4×4 cm squares;

[0054] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0055] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 270 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0056] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0057] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0058] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0059] Example 2

[0060] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0061] (1) Prepare a 1 M HCl solution;

[0062] (2) Cut the copper foil into 4×4 cm squares;

[0063] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0064] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 180 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0065] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0066] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0067] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0068] Example 3

[0069] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0070] (1) Prepare a 1 M HCl solution;

[0071] (2) Cut the copper foil into 4×4 cm squares;

[0072] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0073] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 210 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0074] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0075] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0076] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0077] Example 4

[0078] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0079] (1) Prepare a 1 M HCl solution;

[0080] (2) Cut the copper foil into 4×4 cm squares;

[0081] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0082] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution. Soak the copper foil treated above for 240 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0083] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0084] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0085] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0086] Example 5

[0087] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0088] (1) Prepare a 1 M HCl solution;

[0089] (2) Cut the copper foil into 4×4 cm squares;

[0090] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0091] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 300 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0092] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0093] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0094] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0095] Example 6

[0096] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0097] (1) Prepare a 1 M HCl solution;

[0098] (2) Cut the copper foil into 4×4 cm squares;

[0099] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0100] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 330 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0101] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0102] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0103] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0104] Example 7

[0105] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0106] (1) Prepare a 1 M HCl solution;

[0107] (2) Cut the copper foil into 4×4 cm squares;

[0108] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0109] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 360 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0110] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0111] (6) Add 1 M NH3•H2O dropwise to 0.1 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0112] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0113] Example 8

[0114] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0115] (1) Prepare a 1 M HCl solution;

[0116] (2) Cut the copper foil into 4×4 cm squares;

[0117] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0118] (4) Dissolve 1.37 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 4.8 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 270 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0119] (5) Use 250 mL of deionized water to dissolve 71 g of sodium sulfate solution as the electrolyte for electrochemical reduction. The anode is a platinum sheet electrode and the cathode is the Cu foil treated in step (4). The current is set to 290 mA and the time is 30 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0120] (6) Add 2 M NH3•H2O dropwise to 0.5 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0121] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0122] Example 9

[0123] The preparation method of the three-dimensional structure-modified current collector in this embodiment includes the following steps:

[0124] (1) Prepare a 1 M HCl solution;

[0125] (2) Cut the copper foil into 4×4 cm squares;

[0126] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0127] (4) Dissolve 2.74 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 7.2 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 270 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0128] (5) Use 250 mL of deionized water to dissolve 43.6 g of potassium sulfate solution as the electrolyte for electrochemical reduction. The anode is a platinum sheet electrode and the cathode is the Cu foil treated in step (4). The current is set to 320 mA and the time is 20 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0129] (6) Add 3 M NH3•H2O dropwise to 0.4 M silver nitrate solution until the solution changes from turbid to clear, i.e., silver ammonia solution. Immerse the copper foil treated in step (5) in silver ammonia solution for 210 s. After immersion, clean the surface of the copper foil with deionized water and 75% alcohol in turn.

[0130] (7) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modification.

[0131] Comparative Example 1

[0132] In this comparative example, the copper foil current collector is not modified with any layer and is used as the working electrode.

[0133] Comparative Example 2

[0134] The preparation method of the Cu-NWs current collector in this comparative example differs from that in Example 1 in that it does not involve step (6). The specific preparation process is as follows:

[0135] (1) Prepare a 1 M HCl solution;

[0136] (2) Cut the copper foil into 4×4 cm squares;

[0137] (3) Soak the copper foil in the above HCl solution for 1 min to remove the oxide layer on the surface of the copper foil to facilitate subsequent preparation;

[0138] (4) Dissolve 1.78 g of ammonium persulfate in 60 mL of deionized water. After dissolving, add 6.0 g of sodium hydroxide to prepare a mixed solution and soak the above-treated copper foil for 270 s to grow Cu(OH)2 nanowires. After soaking, wash the surface of the copper foil with deionized water to remove residual ammonium persulfate and sodium hydroxide.

[0139] (5) Use 250 mL of deionized water to dissolve 14.2 g of sodium sulfate solution as the electrolyte for electrochemical reduction. Use a platinum sheet electrode as the anode and the Cu foil after step (4) as the cathode. Set the current to 256 mA and the time to 35 min to ensure that Cu(OH)2 is completely reduced to Cu nanowires.

[0140] (6) The modified copper foil was placed in a vacuum oven at 80°C and dried overnight to obtain a current collector with a three-dimensional structure modified, which was named Cu-NWs.

[0141] Implementation Results Example

[0142] The method of the present invention utilizes the electrochemical reduction of copper foil after oxidation to grow a layer of metallic copper nanowires on ordinary copper foil. Subsequently, metallic silver is grown on the copper nanowires through a displacement reaction of copper nanowires and silver ammonia solution. Finally, a copper current collector is obtained as a three-dimensional porous structure modified layer formed by stacking copper and silver nanowires on a copper foil substrate. Figure 1 Optical comparison photographs of a conventional copper foil current collector (right image) and a current collector modified with the three-dimensional modification layer prepared according to this invention (left image). Furthermore, the conventional copper foil current collector and the three-dimensional current collector were subjected to X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests, such as... Figure 2 and Figure 4 As shown, the current collector modified with the three-dimensional modification layer has an additional silver (111) crystal facet compared to the bare copper foil current collector, confirming the presence of silver. Furthermore, the sodium affinity of this silver facet has been demonstrated using DFT calculations. SEM results show that the surface of the three-dimensional modification layer is filled with nanowires with a diameter of approximately 117.65 nm, and these nanowires stack to form a three-dimensional porous modification layer with a thickness of approximately 7.51 μm.

[0143] Figure 3 The image shown is a transmission electron microscope (TEM) image of the current collector modified by the three-dimensional modification layer prepared in Example 1 of the present invention. It can be seen that the nanowire modification layer is composed of an inner layer of metallic copper and an outer layer of metallic silver, with the inner and outer layers corresponding to the two dominant crystal planes Cu (200) and Ag (111), respectively.

[0144] Figure 5 EDS testing confirmed the uniform distribution of Cu and Ag elements on the current collector. Combining these two tests, the introduction of silver significantly enhanced the conductivity of the current collector, while silver's affinity for sodium induced uniform sodium deposition. Furthermore, the three-dimensional structure of the current collector effectively promoted the penetration of the gel electrolyte, mitigating the volume expansion during the metal deposition stripping process in the electrodeless battery. This design resulted in a stable SEI on the current collector surface after the first cycle, optimizing the coulombic efficiency of the gel-state electrodeless battery and achieving stable cycling.

[0145] The current collectors prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention were applied to gel-state negative electrode-free batteries. The specific battery preparation process and results are as follows:

[0146] 1. Half-cell

[0147] Using the current collectors prepared in Example 1, Comparative Example 1, and Comparative Example 2 as working electrodes and sodium metal as the counter electrode, coin cells (half-cells) were assembled. The coulombic efficiency and cycle stability of these half-cells were then tested. The specific assembly and performance testing procedures of the half-cells are as follows:

[0148] (1) The three-dimensional current collectors prepared in Example 1, Comparative Example 1 and Comparative Example 2 were dried in vacuum at 80°C and then cut to obtain working electrode sheets with a diameter of 16 mm.

[0149] (2) 0.05 g of trifluoroethyl methacrylate, 0.05 g of N,N-methylenebisacrylamide, 0.0014 g of AIBN and 2 g of 1 M sodium salt-organic solvent (sodium salt is sodium hexafluorophosphate and organic solvent is diethylene glycol dimethyl ether) were added to prepare a gel electrolyte precursor.

[0150] (3) A sodium metal sheet (12 mm in diameter) is used as the counter electrode, polypropylene (PP) is used as the separator, and a gel electrolyte precursor is used as the electrolyte for battery assembly. A stainless steel shell is used as the outer shell, and the battery is assembled into a CR2025 button cell.

[0151] (4) The assembled battery was left to stand for two hours to allow the gel electrolyte precursor to fully wet the sodium metal on both electrodes and the current collector modified by the three-dimensional modification layer. Then, it was placed in an oven for thermal polymerization at 70°C for 1 hour to obtain a gel-state negative electrode-free half-cell. The gel electrolyte preparation process in the battery is as follows: Figure 6 As shown.

[0152] The above-described assembled gel-state half-cells (Cu||Na and Cu-Ag-NWs||Na) were used at 1.0 mA cm⁻¹. -2 A quantitative amount of metallic sodium was deposited after discharging at a current density for 1 hour. The battery was then disassembled, and optical photographs of the sodium deposition morphology were taken. Optical photographs of sodium deposition and stripping on two different current collectors are shown below. Figure 7 As shown. Figure 7 Image a and image 7b are optical photographs showing the deposition and stripping of sodium metal on a Cu current collector. It can be seen that the morphology of sodium deposition on the Cu current collector is not uniform, and after stripping, many dead sodium particles remain on the current collector, causing capacity loss and safety hazards in the battery. Compared to Cu current collectors, Figure 7Images c and 7d show optical photographs of sodium deposition and stripping on Cu-Ag-NWs. The sodium deposition on this current collector is highly uniform and dense, with virtually no visible dead sodium residue in the stripped state. The inherent three-dimensional structure of Cu-Ag-NWs and the presence of sodium-loving elements enable uniform and dense sodium deposition, significantly reducing the formation of dead sodium. It is precisely this perfect sodium deposition and stripping effect of the Cu-Ag-NWs current collector that achieves high charge-discharge efficiency and cycle life without a negative electrode, making it a promising current collector for gel-state negative electrode-free batteries.

[0153] The sodium deposition stripping efficiency of the above-mentioned half-cells assembled with the two current collectors prepared in Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 8 As shown. At 1.0 mA cm -2 1.0 mAh cm -2 At a current density of [value missing], the Cu||Na half-cell exhibited an initial coulomb efficiency (ICE) of 88.71% and showed instability during charging. This indicates that sodium metal stripping occurred during the first cycle of Cu||Na. In contrast, the Cu-Ag-NWs||Na half-cell showed an ICE of 94.28%, higher than Cu||Na, and its curve was completely normal. This demonstrates that the original copper current collector caused more sodium source loss during the formation of the SEI and sodium metal stripping in the first cycle, which is detrimental to subsequent cycling in a cathode-less full cell. In subsequent cycles, the CE of Cu||Na fluctuated sharply. Figure 8 a). Cu-Ag-NWs exhibited excellent cycling stability, maintaining an CE of over 99% throughout 400 cycles, while the average coulomb efficiency (ACE) remained at 99.95%. This improved cycling stability coupled with higher CE provides direct electrochemical evidence that Cu-Ag-NWs can achieve less sodium loss. The half-cells assembled using the current collectors prepared in Example 1 and Comparative Example 1 of this invention achieved a CE of 1.0 mAcm⁻¹. -2 Comparing the charge-discharge curves at current density for 150 cycles, Cu-Ag-NWs (39 mV) can achieve a lower metal deposition stripping potential difference compared to copper foil (64 mV). Figure 8(b) This indicates that after 150 cycles, the Cu surface exhibits slower sodium deposition and stripping kinetics compared to Cu-Ag-NWs. Furthermore, due to its lower CE, Cu||Na cannot achieve complete sodium stripping after 150 cycles, resulting in capacity loss. This demonstrates that under the same testing conditions, Cu-Ag-NWs can exhibit easier sodium deposition and less sodium loss, which is crucial for the assembly of anode-free full cells.

[0154] Using Cu-Ag-NWs prepared in Example 1 as the current collector, a negative electrode-free half-cell was assembled using conventional DGM liquid electrolyte (LE, 1 M NaPF6-DGM). This was then compared with a gel-state negative electrode-free half-cell (GPE) assembled using the current collector prepared in Example 1 at 1.0 mA cm⁻¹. -2 1.0 mAh cm -2 The following long-loop test was performed, and the results are as follows: Figure 9 As shown, the half-cell assembled by LE was very stable in the early stages of cycling, but the CE began to fluctuate significantly around cycle 350, while the cell assembled by GPE remained stable throughout the 350-cycle period. Figure 9 a), which again demonstrates the superior performance of the three-dimensional current collector. Similarly, to demonstrate the reversibility of sodium deposition and stripping during battery cycling, charge-discharge curves were analyzed on four randomly selected weeks. Figure 9 (b and 9c) The charging curves of the half-cells assembled using LE were abnormal after 300 cycles, indicating that the metallic sodium in the LE system could not be properly stripped off in the later stages of cycling.

[0155] The cycling results of the gel-state electrodeless half-cell assembled with the current collector prepared in Example 1 at different current densities are as follows: Figure 10 As shown. It can be seen that at 0.3 mA cm -2 At a current density of [value missing], Cu-Ag-NWs||Na exhibits an ICE of 80.49% in the first week and maintains a very stable cycling state with a high ACE of 99.78% in the subsequent 900 charge-discharge cycles. Figure 10 a). At 1.0 mA cm -2 At current density, Cu-Ag-NWs||Na exhibits 94.28% ICE in the first week and a high ACE of 99.95% during charge-discharge cycles exceeding 400 cycles. Figure 10 b). At 1.5 mA cm -2 At current density, the ICE of Cu-Ag-NWs||Na is 94.92%, and it can be stably cycled for more than 400 cycles, with an ACE of 99.94%. Figure 10 c). At 2.0 mAcm -2At high current densities, the ICE of Cu-Ag-NWs||Na is 90.06%, and the ACE is 99.9%. Figure 10 d). Under the above current densities, the sodium deposition voltage of the battery did not change significantly, demonstrating the reversibility and durability of sodium deposition and stripping on Cu-Ag-NWs.

[0156] The electrochemical performance results of the above-mentioned half-cells assembled with the two current collectors prepared in Example 1 and Comparative Example 2 are as follows: Figure 11 As shown. By Figure 11 As can be seen, Cu-NWs exhibit 87.72% ICE and 99.1% ACE, while Cu-Ag-NWs exhibit 94.28% ICE and 99.9% ACE. During the first 80 cycles, the three-dimensional structure of the nanowires in both types of nanowires plays a crucial role, demonstrating relatively stable coulombic efficiencies. However, after 80 cycles, the insufficient sodium affinity of Cu-NWs leads to a continuous increase in dendrites and dead sodium, causing strong fluctuations in coulombic efficiency. To further verify the reversibility of sodium stripping through current collector deposition, the curves for cycles 1, 100, 200, 300, and 400 during the long cycling process were analyzed. Figure 11 In Cu-Ag-NWs half-cells (b and 11c), the presence of metallic silver reduces dendrite formation, resulting in slightly lower efficiency in the first cycle due to the formation of the SEI consuming sodium source; subsequent cycles exhibit good reversibility. However, in Cu-NWs half-cells, the curves for these weeks, except for the first week, show severe fluctuations during charging, indicating that metallic sodium inside the cell has punctured the separator, forming a soft short circuit, which is detrimental to long-term stable cycling.

[0157] The gel-state half-cells assembled with the two current collectors prepared in Example 1 and Comparative Example 1 were sampled after one electrochemical cycle, and their SEI thickness and composition were characterized by TEM. The results are as follows: Figure 12 As shown in Figure 12a, the surface of the Cu||Na half-cell after cycling is covered by a relatively thick (approximately 62 nm) and loosely uniform SEI layer. In contrast, the SEI on the surface of the Cu-Ag-NWs||Na half-cell after one cycle has a very clear boundary, and its thickness is significantly reduced to approximately 7.89 nm. Figure 12 b). The thinner SEI formed shortens the transport path for sodium ions during battery cycling, thus promoting sodium ion transport at the SEI.

[0158] To further investigate the composition of the SEI generated by the two current collectors after circulation, samples were collected at 1.0 mA cm⁻¹. -2 1.0 mAhcm -2Etching was performed on the current collectors after the first cycle at a certain current density for 60 s, and the presence of elements such as F and O in the inner SEI of the two current collectors after cycling was detected by X-ray photoelectron spectroscopy (XPS). The 1-s spectrum showed that in the inner SEI after etching, Cu mainly consisted of organic components of CO (RCH2ONa, etc.), while Cu-Ag-NWs mainly consisted of inorganic components of Na-O (Na2O). Figure 12 c). The F 1s energy spectrum also showed a high intensity of the Na-F peak in the experimental sample, which corresponds to the NaF generated by salt decomposition (c). Figure 12 d). XPS analysis of the Cu-Ag-NWs surface demonstrated a higher intensity of inorganic product (Na2O, NaF) signals in the inner layer compared to the unmodified copper foil, indicating that its SEI is composed of organic matter in the surface layer and inorganic matter in the inner layer. This endows the SEI with higher mechanical strength. Figure 12 e and 12f) can effectively prevent the continuous decomposition of the electrolyte and inhibit the growth of sodium dendrites.

[0159] In a cycled battery, the impedance can generally be fitted as two circular arcs. The first arc represents the ease with which sodium ions cross the SEI, while the second arc represents the ease with which sodium ions desolvate. To calculate the ease with which sodium ions cross these two processes, R was obtained at different temperatures by fitting the above temperature-varying impedance. SEI and R ct The value of . According to the Arrhenius formula (Formula 1), by applying lnR -1 Plotting and fitting the 1000 / T values ​​yielded the activation energies for sodium ions to cross the SEI and desolvation after half-cell cycling for both current collectors. Figure 12 (g and 12h). The activation energy for sodium ions to cross the SEI in Cu-Ag-NWs||Na is 5.57 kJ mol. -1 The activation energy for sodium ions in Cu||Na to cross the SEI is 7.23 kJ / mol. -1 This indicates that the SEI formed on the Cu-Ag-NWs current collector has a faster ion transport capability and exhibits rapid interfacial kinetics. Before the electrons on the negative electrode side are reduced, solvated sodium ions need to remove the solvent from their solvation shell to achieve deposition and realize a high-quality SEI. The desolvation energy of sodium ions in Cu-Ag-NWs||Na is 21.64 kJ mol. -1 The desolvation energy of sodium ions in Cu||Na is 26.25 kJ / mol. -1 Whether it's the ion crossing the SEI or the desolvation behavior, the Cu current collector exhibits a higher energy barrier. This indicates that sodium ions in the Cu||Na battery face greater resistance, resulting in poor kinetic performance.

[0160]

[0161] 2. Symmetrical battery

[0162] Using Cu-Ag-NWs and Cu as current collectors, a 12 mm sodium sheet was placed on its surface, and a symmetric cell was assembled using a gel electrolyte (as above) as the electrolyte, and the cell was tested at 1.0 mA cm⁻¹. −2 1.0 mAh cm −2 Long-cycle testing of symmetrical cells was conducted at a current density, and the results are as follows: Figure 13 As shown in the figure, the Cu-Na||Cu-Na symmetric cell exhibits a short circuit after 30 h of cycling, with a voltage drop to 0 V, while the Cu-Ag-NWs-Na||Cu-Ag-NWs-Na symmetric cell can cycle stably for over 2500 h with a polarization voltage of less than 10 mV. The time-voltage curves for 1000–1010 h and 2000–2010 h are shown in inset. The results of the symmetric cells further demonstrate the affinity of the current collector prepared in this invention for metallic sodium, enabling it to withstand prolonged sodium deposition and stripping.

[0163] 3. Full battery

[0164] Using Cu from Comparative Example 1 and Cu-Ag-NWs prepared in Example 1 as current collectors on the negative electrode side, respectively, half-cells were assembled, activated for 2 weeks, and coated with metallic sodium of a specified N / P ratio as the negative electrode side. A 10 mg cm⁻¹ coating was then applied. -2 Using NVP with high surface loading as the positive electrode material, the aforementioned gel electrolyte as the electrolyte, and placing two layers of PP separators to block the contact between the positive and negative electrodes, a full cell is assembled.

[0165] The Cu-Ag-NWs||NVP full cell with an N / P ratio of 0.5 retains 81.9% capacity after 80 cycles, while the Cu||NVP cell with an N / P ratio of 0.5 experiences a short circuit immediately upon formal cycling at 0.5 C rate after 2 weeks of activation, with its capacity dropping to 0 mAh g. -1 Unable to maintain subsequent cycles ( Figure 14 a). This invention assembled various N / P full cells. At N / P ratios of 1.5 and 2.5, the experimental samples, after 110 cycles at 0.5 C rate, maintained 79.6% and 77.1% capacity retention, respectively. In contrast, the Cu||NVP battery, even with an N / P ratio as high as 3, experienced rapid capacity decay after 60 cycles, and by 100 cycles, the capacity was almost zero. This comparison demonstrates the optimizing effect of Cu-Ag-NWs in gel-state anode-free batteries. Figure 14b). To demonstrate the reversibility of full-cell cycling, charge-discharge curves for the experimental and control batteries with an N / P ratio of 0.5 were plotted and analyzed at cycles 1, 30, 60, and 80. Figure 14 c and Figure 14 d) It can be seen that the experimental sample can basically maintain the normal shape of the curve, but the capacity is reduced within a controllable range. This indicates that the full cell assembled by Cu-Ag-NWs current collector has higher cycle reversibility, while Cu||NVP has almost zero capacity in the 30th cycle and subsequent cycles. The cell is in a short circuit state and cannot cycle normally.

[0166] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional structure-modified current collector, characterized in that, The steps are as follows: (1) Dissolve ammonium persulfate in water, add sodium hydroxide to prepare a mixed solution, and soak the pretreated copper foil to obtain a copper foil with three-dimensional Cu(OH)2 nanowires grown on it. (2) In the electrolyte, a platinum sheet electrode is used as the anode and a copper foil with three-dimensional Cu(OH)2 nanowires is used as the cathode. Through electrochemical reduction, a copper foil with three-dimensional Cu nanowires is obtained. (3) The copper foil with three-dimensional Cu nanowires grown in step (2) is immersed in silver ammonia solution. After immersion, it is cleaned and dried.

2. The method for preparing a three-dimensional structure-modified current collector according to claim 1, characterized in that, The pretreated copper foil in step (1) refers to copper foil that has been treated with alcohol and acidic solution in sequence; in the mixed solution, the concentration of ammonium persulfate is 0.1-0.2 M and the concentration of sodium hydroxide is 2-3 M; the soaking time is 180-360 s.

3. The method for preparing a three-dimensional structure-modified current collector according to claim 2, characterized in that, In step (2), the solute in the electrolyte is at least one of sodium sulfate, potassium nitrate, potassium sulfate, ammonium sulfate, and sodium chloride, and the concentration of the electrolyte is 0.4-2 M; the current density for electrochemical reduction is 8-10 mA cm⁻¹. -2 The time is 20-35 minutes.

4. The method for preparing a three-dimensional structure-modified current collector according to claim 3, characterized in that, In step (3), the silver ammonia solution is prepared by adding 1-3 M ammonia water to 0.1-0.5 M silver nitrate aqueous solution until the solution changes from turbid to clear, thus obtaining the silver ammonia solution; the immersion time in the silver ammonia solution is not less than 210 s.

5. A three-dimensional modified current collector prepared by the preparation method according to any one of claims 1-4.

6. The application of the three-dimensional structure-modified current collector as described in claim 5 in a gel-state sodium battery without a negative electrode.

7. A gel-state sodium battery without a negative electrode, characterized in that, It includes a positive electrode, a gel electrolyte, a separator, and a current collector with a three-dimensional structure modified as described in claim 5.

8. The gel-state sodium-ion battery without a negative electrode according to claim 7, characterized in that, The raw materials of the gel electrolyte include monomers, crosslinking agents, initiators, and liquid electrolytes; wherein the monomer is trifluoroethyl methacrylate, the crosslinking agent is N,N-methylenebisacrylamide, the initiator is at least one of azobisisobutyronitrile, azobisisovalerate, and azobisisobutyramidine hydrochloride, and the liquid electrolyte includes sodium salts and organic solvents; the positive electrode includes a positive electrode active material.

9. The gel-state sodium-ion battery without a negative electrode according to claim 8, characterized in that, The concentration of the liquid electrolyte is 1 M, and each g of liquid electrolyte contains 0.02-0.03 g of monomer, 0.02-0.03 g of crosslinking agent and 0.0005-0.001 g of initiator; the positive electrode active material is at least one of sodium vanadium phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate and sodium iron manganese pyrophosphate.

10. The gel-state sodium-ion battery without a negative electrode according to claim 8, characterized in that, The sodium salt is at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide; the organic solvent is at least one of diethylene glycol dimethyl ether, 1,3-cyclopentanediol, ethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

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