Sodium-philic ultrathin aluminum current collector, preparation method thereof and application of sodium-philic ultrathin aluminum current collector in negative-electrode-free sodium ion battery

Abstract

The invention discloses a sodium-philic ultrathin aluminum current collector, a preparation method thereof and an application of the sodium-philic ultrathin aluminum current collector in a negative-electrode-free sodium ion battery. Belongs to the technical field of batteries. The ultrathin aluminum current collector prepared by the method adopts argon ion pre-etching, ion implantation and acid-free electrolyte electrochemical etching means, the method is efficient, environment-friendly and pollution-free, and the prepared nanopore structure can promote uniform deposition of sodium ions and close combination with the current collector, so that the performance of the ultrathin aluminum current collector is improved. The addition of the sodium-philic element not only can refine crystal grains and improve the mechanical strength of the ultrathin aluminum foil, but also can effectively reduce the sodium deposition nucleation barrier, inhibit the growth of sodium dendrites and prolong the cycle life of the sodium ion battery. The prepared sodium-philic ultrathin aluminum current collector is applied to a negative-electrode-free sodium-ion battery, the cost is saved, and the energy density of the sodium-ion battery can be improved through the light weight of the battery and the light volume of the battery.

Description

Technical Field

[0001] The present invention relates to a sodium-philic ultrathin aluminum current collector, a preparation method thereof, and application thereof in a negative-electrode-free sodium-ion battery, belonging to the field of battery technology, and particularly to the field of sodium-ion battery technology. Background Art

[0002] Sodium-ion batteries are expected to supplement and replace lithium-ion batteries in the future and become the preferred solution for electrochemical energy storage due to their abundant raw material resources, low cost, low temperature resistance, long life, and compatibility with lithium-ion battery manufacturing processes. However, the energy density of traditional sodium-ion batteries is about 105~150Wh•kg -1 , and the sodium-ion battery developed by CATL announced at the 2025 Shanghai Auto Show has an energy density of 175 Wh•kg -1 However, it is still far lower than the energy density of currently commercialized lithium iron phosphate and ternary lithium batteries. Therefore, improving energy density is the key to enhancing the competitive advantage of sodium-ion batteries. Currently, sodium ions mainly use hard carbon as the negative electrode, which has low capacity, many surface defects, and low initial charge and discharge efficiency, which limits the improvement of energy density. The negative electrode-free sodium-ion battery is a special battery design to improve energy density. Its core is not to use negative electrode active materials. During the first charge, the sodium ions in the electrolyte are in situ deposited on the negative electrode current collector to form a metallic sodium layer. The negative electrode current collector is usually made of aluminum foil. The thinning of aluminum foil can not only reduce the weight proportion of inactive materials, directly improve the energy density of the battery, but also reduce the cost of raw materials.

[0003] However, the binding energy between smooth Al foil and sodium metal is low, which will lead to uneven sodium metal deposition and easy formation of sodium dendrites. In addition, the negative electrode formed by sodium metal deposition will fall off due to volume expansion / contraction during the charge and discharge cycle, resulting in irreversible loss of battery capacity, poor cycle stability and safety issues, which limit the practical application of negative electrode-free sodium ion batteries. Patent CN202210391946.X - Negative electrode sheet, electrochemical device and electronic equipment of sodium ion battery, proposes to coat the surface of the negative electrode aluminum current collector with a carbon material coating. Although it can reduce the overpotential of metal deposition, improve the kinetics of sodium metal nucleation in sodium ion batteries, and inhibit the formation of sodium dendrites, this method greatly increases the overall weight and reduces the energy density of the battery. Therefore, the development of sodium-philic ultra-thin aluminum foil current collectors to reduce dendrites can greatly improve the cycle efficiency and energy density of sodium ion batteries and promote commercial applications. Summary of the Invention

[0004] To address the poor sodium affinity of commercial aluminum current collectors and the resulting poor anode stability, the present invention provides a method for preparing a sodium-affinity ultrathin aluminum current collector. By introducing sodium-affinity elements (Zn and Sn) into aluminum foil, the mechanical strength of the foil is enhanced while simultaneously forming sodium-affinity nucleation sites, inducing uniform sodium ion deposition during charging. A uniform nanopore structure is formed on the surface of the ultrathin aluminum foil using an environmentally friendly and efficient composite etching method. A specific electrochemical etching process and solution system are employed to ensure control of the Sn and Zn content on the aluminum current collector surface, increase the number of uniform sodium metal deposition sites, achieve highly reversible sodium deposition / stripping, and inhibit the growth of sodium dendrites. The sodium-affinity ultrathin aluminum foil current collector prepared using this invention can be applied to anode-free sodium-ion batteries, improving the long-term cycling stability and significantly increasing the energy density of these batteries.

[0005] At the same time, the present invention provides a sodium-philic ultra-thin aluminum current collector.

[0006] At the same time, the present invention provides an application of a sodium-philic ultra-thin aluminum current collector in a negative electrode-free sodium ion battery.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: A sodium-philic ultra-thin aluminum current collector has the following composition: Fe: 0.3-0.45%; Si: 0.1-0.15%; Cu: 0.02-0.08%; Ti: 0.01-0.015%; Mn ≤ 0.02%; Mg ≤ 0.02%; Zn: 0.003-0.01%; Sn: 0.003-0.02%; the remainder is Al. The addition of the microalloying elements Zn and Sn refines the aluminum foil grains, preventing the formation of coarse, needle-like secondary phases and improving the mechanical strength of the ultra-thin aluminum foil. Furthermore, the strong affinity of Sn and Zn for sodium promotes uniform sodium ion deposition during charge and discharge.

[0008] A method for preparing a sodium-philic ultrathin aluminum current collector, the preparation process of which is as follows: Step 1: Clean the aluminum foil with alcohol and dry it; Step 2: First, ion etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of at least 2×10 -4 Pa, using bias power supply, argon etching to clean the surface, and argon gas was introduced to 4~6 Pa. Subsequently, a vacuum high-energy metal ion source was used to perform ion implantation with Sn and Zn as cathode targets, respectively, and the working vacuum was 1×10 -4 ~1×10 -5 Pa, and the temperature of the aluminum foil during the injection process is 25~150℃.

[0009] Step three: using the aluminum foil obtained in step two as the anode, the aluminum foil as the cathode, and the iron nitrate-based metal salt solution containing a complexing agent and a preservative as the electrolyte, applying electrochemical process parameters, and electrochemically etching the anode ultra-thin aluminum foil current collector.

[0010] Step 4: Clean and dry the treated aluminum foil with deionized water.

[0011] In step 2, the argon ion etching process is performed at a voltage of -150 to -200 V for 10 to 15 minutes. This process removes impurities from the aluminum foil surface through argon ion etching under high vacuum conditions and activates the surface to facilitate the introduction of Sn and Zn elements.

[0012] The purity of Sn and Zn targets in step 2 is greater than 99.9%.

[0013] In the ion implantation process of step 2, the Sn ion implantation voltage is 20~50 kV and the implantation dose is 1×10 15 ~1×10 17 ions / cm 2 The Zn ion implantation voltage is 40~60 kV and the implantation dose is 1×10 15 ~1×10 17 ions / cm 2 .

[0014] The concentration of the ferric nitrate solution in step three is 0.01 to 0.3 mol / L. Nitrate ions, driven by electricity, produce a highly efficient and gentle etching action, forming a uniform nanopore structure on the surface of the ultra-thin aluminum foil.

[0015] The complexing agent in step three is NaF-modified ammonium nitrate or NaF-modified sodium citrate, with a concentration of 0.01 to 0.1 mol / L. The preparation steps are: dissolve ammonium nitrate or sodium citrate and NaF in deionized water at a molar ratio of 1:1 to 1:2, adjust the pH to 4.5 to 7.5, stir at 50 to 80°C for at least 2 hours, and finally freeze-dry to obtain a modified powder. The complexing agent, modified with NaF, can form complexes with Al and Fe, reducing the electrode potential and promoting their dissolution. However, its complexing ability for Sn and Zn is limited. Furthermore, by complexing the metal ions in the solution, it prevents metal ion precipitation, ensures solution activity, and promotes uniform redox reactions on the aluminum foil surface.

[0016] The preservative in step three is SDS-modified thiourea or SDS-modified benzotriazole, with a concentration of 0.05-0.5%. The preparation steps are as follows: dissolve thiourea or benzotriazole and SDS in deionized water at a molar ratio of 1:1-1:2, and adjust the pH to 5-7; stir at 30-50°C for at least 2 hours, cool to room temperature, filter at room temperature, and vacuum dry to obtain a modified powder. After SDS modification, the preservative can inhibit perforation caused by localized over-etching of the aluminum foil, improve etching uniformity and selectivity, and ensure that the aluminum foil's mechanical strength is not compromised. Furthermore, the modified preservative preferentially adsorbs on the surfaces of Sn and Zn elements, forming a passivation film, thereby inhibiting their dissolution during electrochemical etching.

[0017] In step three, the etching voltage is 2.0-5.0 V, the etching time is 2-7 minutes, and the etching solution temperature is 40-60°C. By specifying the electrochemical etching voltage, time, and temperature, the micromorphology of the ultra-thin aluminum foil and the content of the sodium-philic elements Sn and Zn on the surface can be controlled, thereby inducing uniform deposition of sodium ions.

[0018] The surface grain size and morphology of the aluminum foil (i.e., the ultra-thin aluminum foil current collector for the anode) were observed before and after treatment. The distribution of Sn and Zn elements was investigated using EDS. The strength of the treated aluminum foil was tested according to GB / T 2884. The sodium-ion battery preparation process is as follows: First, the positive electrode sheet was prepared: sodium vanadium phosphate (NVP) positive electrode active material, conductive carbon black, and PVDF binder were mixed in a mass ratio of 8:1:1 in NMP as the solvent to form a mixed slurry. After magnetic stirring for 6 hours, the slurry was evenly coated onto 9μm-thick, untreated aluminum foil (both the positive and negative electrodes were aluminum foils; the positive electrode was the original 9μm thick aluminum foil; the negative electrode was the aluminum foil treated according to the present invention). The positive electrode sheet was then vacuum-dried at 120°C for 12 hours and cut into pieces. 2032-type button cells were assembled in a glove box using 1.0M NaClO₄ (EC:PC = 1:1 vol%) as the electrolyte, the ultra-thin aluminum foil treated in this example as the negative electrode, and glass fiber as the separator. The test voltage range is 2.0~3.4V, the test temperature is 25℃, and the charge and discharge cycle test is carried out at a rate of 0.1C for 200 cycles. In addition, the battery is tested at 1 mA / cm 2 Constant current charge-discharge cycle tests were carried out at a current density of 100 nm to characterize the inhibition of dendrite growth.

[0019] The sodium-philic ultra-thin aluminum current collector prepared by the preparation method of the present invention preferably has a Zn content of 0.58-1.27% and a Sn content of 0.09-1.68% on the surface of the sodium-philic ultra-thin aluminum current collector; further preferably, the Zn content of 0.58-1.27% and the Sn content of 0.63-1.68% on the surface of the sodium-philic ultra-thin aluminum current collector; the tensile strength of the ultra-thin aluminum foil after treatment is 193-234 MPa; further preferably, the tensile strength of the ultra-thin aluminum foil after treatment is 223-234 MPa. MPa; the first discharge capacity of the ultra-thin aluminum foil at 0.1C after treatment is 94.5~115.3mAh / g, and is further preferably 108.7~115.3mAh / g; the first coulombic efficiency of the ultra-thin aluminum foil at 0.1C after treatment is 80.1~98.3%, and is further preferably 92.9~98.3%; the capacity retention rate of the ultra-thin aluminum foil after treatment after 0.1C cycle 200 cycles is 74.8~92.1%, and is further preferably 85.4~92.1%.

[0020] Application of the sodium-philic ultra-thin aluminum current collector of the present invention in a negative electrode-free sodium ion battery.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. Adding Sn and Zn microalloying elements to the aluminum current collector can effectively refine the internal grains of the aluminum foil, reduce the aggregation of large-sized impurities, and improve the mechanical strength of the ultra-thin aluminum foil.

[0022] 2. Through vacuum argon ion pre-etching, impurities on the aluminum foil surface are removed, the surface activity is improved, which is conducive to the introduction of Sn and Zn ions into the aluminum foil surface. After the injection of Sn and Zn ions, the potential difference with the matrix Al element can be utilized to promote the preferential dissolution of Al element in the electrochemical reaction, while the sodium-philic elements Sn and Zn are retained.

[0023] 3. By regulating a mild, efficient, and environmentally friendly electrochemical etching process and electrolyte system, a uniform nanopore structure is produced on the surface of the ultra-thin aluminum foil. The modified chelating agent and modified preservative synergistically regulate the dissolution of Al, while inhibiting the dissolution of Sn and Zn, ensuring the surface Sn and Zn content. Sn and Zn, as sodium-philic elements, can effectively reduce the sodium deposition nucleation barrier, promote the rapid and uniform deposition of sodium ions, inhibit the growth of sodium dendrites, and improve the charge and discharge efficiency of sodium-ion batteries.

[0024] 4. The uniform nanopore structure has a uniform sodium storage space and a relatively rough surface, which increases the deposition sites of sodium in the nanopores and promotes the uniform and tight bonding of the deposited sodium layer and the current collector; and the nanopore structure can absorb the volume expansion space of sodium particles during the charge and discharge process, reduce sodium shedding, and improve the cycle life of sodium-ion batteries.

[0025] 5. The uniform surface nanostructure is conducive to achieving highly reversible sodium deposition and stripping during the charge and discharge process, eliminating the growth of sodium dendrites, and improving the long-term cycle stability of negative electrode-free sodium batteries; the nanostructure forms a conductive network, promotes uniform sodium deposition, inhibits the growth of sodium dendrites, and improves the cycle life of sodium batteries.

[0026] 6. The present invention directly uses an ultra-thin aluminum current collector as the negative electrode sheet, eliminating the negative electrode material in traditional batteries, saving costs, and greatly improving the energy density of sodium-ion batteries by reducing the weight and volume of the battery, thereby expanding the scope of application.

[0027] The present invention belongs to the technical field of batteries, and particularly relates to a sodium-philic ultra-thin aluminum current collector, a preparation method thereof, and application thereof in a negative electrode-free sodium ion battery. The composition thereof, in terms of mass percentage, is as follows: Fe: 0.3-0.45%; Si: 0.1-0.15%; Cu: 0.02-0.08%; Ti: 0.01-0.015%; Mn≤0.02%; Mg≤0.02%; Zn: 0.003-0.01%; Sn: 0.003-0.02%; and the remainder is Al. The ultra-thin aluminum foil electrochemical etching method is as follows: first, the aluminum foil (ultra-thin aluminum foil is 9 μm) is cleaned and dried; the aluminum foil surface is pre-etched with argon gas, and then Sn and Zn ions are implanted into the aluminum foil surface; finally, the aluminum foil is electrochemically etched using an iron nitrate-based metal salt solution containing a complexing agent and a preservative as an electrolyte, wherein the concentration of the iron nitrate solution is 0.01-0.3 mol / L, the complexing agent is sodium fluoride (NaF)-modified ammonium nitrate or sodium fluoride (NaF)-modified sodium citrate, and the concentration is 0.01-0.1 mol / L, and the preservative is sodium dodecyl sulfonate (SDS)-modified thiourea or sodium dodecyl sulfonate (SDS)-modified benzotriazole, and the concentration is 0.05-0.5 wt%. The ultra-thin aluminum current collector prepared by the present invention adopts argon ion pre-etching, ion implantation and acid-free electrolyte electrochemical etching means. The method is efficient, environmentally friendly and pollution-free. The prepared nanoporous structure can promote the uniform deposition of sodium ions and close bonding with the current collector. The addition of sodium-philic elements can not only refine the grains and improve the mechanical strength of the ultra-thin aluminum foil, but also effectively reduce the sodium deposition nucleation barrier, inhibit the growth of sodium dendrites, and improve the cycle life of the sodium ion battery. The sodium-philic ultra-thin aluminum current collector prepared by the present invention is applied to negative-electrode-free sodium ion batteries, saving costs and helping to improve the energy density of sodium ion batteries by reducing the weight and volume of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the tissue diagram of the ultra-thin aluminum foil in Example 2; Figure 2 This is the surface morphology of the ultra-thin aluminum foil prepared in Example 2; Figure 3The distribution of Zn and Sn elements on the surface of the ultra-thin aluminum foil prepared in Example 2; Figure 4 The sodium battery assembled with the aluminum foil prepared in Example 2 was tested at 1 mA·cm -2 Time-overpotential curve under current density; Figure 5 This is the surface morphology of the ultra-thin aluminum foil prepared in Example 2 after the cyclic stability test; Figure 6 This is the surface morphology of the ultra-thin aluminum foil prepared in Comparative Example 2; Figure 7 This is the distribution of Zn and Sn elements on the surface of the ultra-thin aluminum foil prepared in Comparative Example 2; Figure 8 The sodium battery assembled with the aluminum foil prepared in Comparative Example 2 was -2 Time-overpotential curves at current density. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Example 1

[0030] The sodium-philic ultra-thin aluminum current collector described in this embodiment has the following specific components: Fe: 0.4%; Si: 0.15%; Cu: 0.08%; Ti: 0.012%; Mn: 0.02%; Mg: 0.02%; Zn: 0.005%; Sn: 0.003%; and the remainder is Al.

[0031] A method for preparing a sodium-philic ultra-thin aluminum current collector, wherein the etching process is as follows: 1. Use alcohol to clean the aluminum foil and dry it; 2. First, ion etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of 2×10 -4 Pa, using bias power supply, argon etching to clean the surface, purging argon to 4 Pa, etching voltage to -150 V, time 10min. Then, using vacuum high energy metal ion source, ion implantation was performed with Sn and Zn as cathode targets (>99.9%), respectively, and the working vacuum was 1×10 -4 Pa, the Sn ion implantation voltage was 30 kV, and the implantation dose was 1×10 15 ions / cm 2 Subsequently, Zn ion implantation was performed at a voltage of 40 kV and an implantation dose of 1×10 15 ions / cm 2 The temperature of the aluminum foil during the injection process was 25°C.

[0032] Third, using ultrathin aluminum foil as the anode and aluminum foil as the cathode, and a ferric nitrate-based metal salt solution containing a chelating agent and a preservative as the electrolyte, electrochemical process parameters were applied to electrochemically etch the ultrathin aluminum foil current collector. The ferric nitrate solution had a concentration of 0.1 mol / L; the chelating agent was sodium fluoride-modified sodium citrate at a concentration of 0.05 mol / L. The preparation steps were as follows: sodium citrate and sodium fluoride were dissolved in deionized water at a molar ratio of 1:1, and the pH was adjusted to 4.5. The mixture was stirred at 50°C for 2 hours, and finally freeze-dried to obtain a modified powder. The preservative was SDS-modified benzotriazole at a concentration of 0.25%. The preparation steps were as follows: benzotriazole and SDS were dissolved in deionized water at a molar ratio of 1:1, and the pH was adjusted to 5. The mixture was stirred at 30°C for 2 hours, cooled to room temperature, filtered at room temperature, and vacuum-dried to obtain a modified powder. The etching voltage was 2.5 V, the etching time was 5 minutes, and the etching solution temperature was 50°C.

[0033] 4. Wash and dry the treated aluminum foil with deionized water.

[0034] The Sn and Zn element content and distribution were measured using an energy dispersive spectrometer. After treatment, the surface Zn and Sn element mass percentages were 0.58% and 0.63%, respectively. The strength of the treated aluminum foil was tested according to GB / T 2884, and the tensile strength of the aluminum foil prepared in this example was 223 MPa. Sodium battery charge and discharge tests were conducted using a blue electric tester with a test voltage range of 2.0–3.4 V, a test temperature of 25°C, and 200 cycles of charge and discharge at a rate of 0.1C. Coulombic efficiency was calculated as (discharge capacity / charge capacity) × 100%, and capacity retention was calculated as (current capacity / initial capacity) × 100%. The prepared sodium-ion battery had an initial discharge capacity of 108.7 mAh / g and an initial coulombic efficiency of 92.9% at a rate of 0.1C. However, after 200 charge and discharge cycles, its capacity retention dropped to 85.4%.

[0035] The application of the sodium-philic ultra-thin aluminum current collector of this embodiment in a negative electrode-free sodium ion battery. Example 2

[0036] The sodium-philic ultra-thin aluminum current collector described in this embodiment has the following specific components: Fe: 0.35%; Si: 0.1%; Cu: 0.02%; Ti: 0.011%; Mn: 0.01%; Mg: 0.01%; Zn: 0.005%; Sn: 0.01%; and the remainder is Al.

[0037] A method for preparing a sodium-philic ultra-thin aluminum current collector, wherein the etching process is as follows: 1. Use alcohol to clean the aluminum foil and dry it; 2. First, ion etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of 2×10 -4 Pa, using bias power supply, argon etching to clean the surface, purging argon to 5Pa, etching voltage of -180 V, time of 15min. Then, using vacuum high energy metal ion source, ion implantation was performed with Sn and Zn as cathode targets (>99.9%), respectively, and the working vacuum was 1×10 -5 Pa, the Sn ion implantation voltage was 40 kV, and the implantation dose was 1×10 17 ions / cm 2 Subsequently, Zn ion implantation was performed at a voltage of 60 kV and an implantation dose of 1×10 16 ions / cm 2 The temperature of the aluminum foil during the injection process was 80°C.

[0038] Third, using ultrathin aluminum foil as the anode and aluminum foil as the cathode, and a ferric nitrate-based metal salt solution containing a chelating agent and preservative as the electrolyte, electrochemical process parameters were applied to electrochemically etch the ultrathin aluminum foil current collector. The ferric nitrate solution had a concentration of 0.1 mol / L. The chelating agent was sodium citrate modified with NaF at a concentration of 0.08 mol / L. The preparation steps were as follows: sodium citrate and NaF were dissolved in deionized water at a molar ratio of 1:2, and the pH was adjusted to 7.5. The mixture was stirred at 80°C for 2 hours, and finally freeze-dried to obtain a modified powder. The preservative was thiourea modified with SDS at a concentration of 0.2%. The preparation steps were as follows: thiourea and SDS were dissolved in deionized water at a molar ratio of 1:2, and the pH was adjusted to 7.0. The mixture was stirred at 50°C for 2 hours, cooled to room temperature, filtered at room temperature, and vacuum-dried to obtain a modified powder. The etching voltage was 2.8 V, the etching time was 2 minutes, and the etching solution temperature was 55°C.

[0039] 4. Wash and dry the treated aluminum foil with deionized water.

[0040] The surface structure of the ultra-thin aluminum foil obtained in this embodiment is as follows Figure 1 As shown in the figure, it can be seen that by adding Zn and Sn microalloying elements, there are no coarse needle-shaped impurities inside the aluminum foil, and the grains are relatively fine. Figure 2 As shown in Figure 2, a uniform nanopore structure appears on the surface of the ultra-thin aluminum foil, and Figure 3It shows that after treatment, Zn and Sn elements are evenly and densely distributed on the surface of the aluminum foil, with their mass percentages reaching 1.27% and 1.68% respectively. The tensile strength of the aluminum foil is as high as 234MPa, which is improved compared with the mechanical strength of the ultra-thin aluminum foil prepared in Example 1. The battery test results show that at a charge and discharge rate of 0.1C, its discharge capacity is 115.3mAh / g, the first coulombic efficiency is as high as 98.3%, and after 200 cycles, its capacity retention rate is still as high as 92.1%, showing good cycle stability. Figure 4 The cycling stability test shows that the sodium ion battery prepared with the ultra-thin aluminum foil prepared in this embodiment can be cycled relatively stably for 300 h, achieving highly reversible sodium ion deposition / stripping during the charge and discharge process. Figure 5 This is the surface morphology of the aluminum foil after the cycle stability test, which shows that the aluminum foil treated in this embodiment significantly inhibits the growth of surface dendrites.

[0041] The application of the sodium-philic ultra-thin aluminum current collector of this embodiment in a negative electrode-free sodium ion battery. Example 3

[0042] The sodium-philic ultra-thin aluminum current collector described in this embodiment has the following specific composition: Fe: 0.45%; Si: 0.15%; Cu: 0.08%; Ti: 0.015%; Mn: 0.002%; Mg: 0.01%; Zn: 0.01%; Sn: 0.02%; and the rest is Al.

[0043] A method for preparing a sodium-philic ultra-thin aluminum current collector, wherein the etching process is as follows: 1. Use alcohol to clean the aluminum foil and dry it; 2. First, ion etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of 2×10 -4 Pa, using bias power supply, argon etching to clean the surface, purging argon to 6 Pa, etching voltage to -200 V, time for 10 min. Then, using vacuum high energy metal ion source, ion implantation was performed with Sn and Zn as cathode targets (>99.9%), respectively, and the working vacuum was 5×10 -5 Pa, the Sn ion implantation voltage was 50 kV, and the implantation dose was 5×10 16 ions / cm 2 Subsequently, Zn ion implantation was performed at a voltage of 60 kV and an implantation dose of 5×10 16 ions / cm 2 The temperature of the aluminum foil during the injection process was 100°C.

[0044] Third, using ultrathin aluminum foil as the anode and aluminum foil as the cathode, and a ferric nitrate-based metal salt solution containing a chelating agent and a preservative as the electrolyte, electrochemical process parameters were applied to electrochemically etch the ultrathin aluminum foil current collector. The ferric nitrate solution had a concentration of 0.3 mol / L. The chelating agent was sodium fluoride-modified ammonium nitrate at a concentration of 0.1 mol / L. The preparation steps were as follows: ammonium nitrate and sodium fluoride were dissolved in deionized water at a molar ratio of 1:1.5, and the pH was adjusted to 6. The mixture was stirred at 55°C for 3 hours, and finally freeze-dried to obtain a modified powder. The preservative was sodium fluoride-modified benzotriazole at a concentration of 0.5%. The preparation steps were as follows: benzotriazole and sodium fluoride were dissolved in deionized water at a molar ratio of 1:2, and the pH was adjusted to 6.5. The mixture was stirred at 45°C for 3 hours, cooled to room temperature, filtered at room temperature, and vacuum-dried to obtain a modified powder. The etching voltage was 5.0 V, the etching time was 6 minutes, and the etching solution temperature was 40°C.

[0045] 4. Wash and dry the treated aluminum foil with deionized water.

[0046] The aluminum foil prepared in this example had a tensile strength of 219 MPa. After treatment, the surface Zn and Sn elemental mass percentages were 0.62% and 0.73%, respectively. The prepared sodium-ion battery exhibited an initial discharge capacity of 103.8 mAh / g and an initial coulombic efficiency of 88.0% at a 0.1C rate. However, after 200 charge-discharge cycles, its capacity retention dropped to 80.5%.

[0047] The application of the sodium-philic ultra-thin aluminum current collector of this embodiment in a negative electrode-free sodium ion battery. Example 4

[0048] The sodium-philic ultra-thin aluminum current collector described in this embodiment has the following specific composition: Fe: 0.3%; Si: 0.12%; Cu: 0.06%; Ti: 0.01%; Mn: 0.01%; Mg: 0.005%; Zn: 0.003%; Sn: 0.01%; and the remainder is Al.

[0049] A method for preparing a sodium-philic ultra-thin aluminum current collector, wherein the etching process is as follows: 1. Use alcohol to clean the aluminum foil and dry it; 2. First, ion etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of 2×10 -5 Pa, using bias power supply, argon etching to clean the surface, purging argon to 5 Pa, etching voltage of -190 V, time of 12 min. Then, using vacuum high energy metal ion source, ion implantation was performed with Sn and Zn as cathode targets (>99.9%), respectively, and the working vacuum was 1×10 -5 Pa, the Sn ion implantation voltage was 20 kV, and the implantation dose was 1×1015 ions / cm 2 Subsequently, Zn ion implantation was performed at a voltage of 40 kV and an implantation dose of 1×10 17 ions / cm 2 The temperature of the aluminum foil during the injection process was 150°C.

[0050] Third, using ultrathin aluminum foil as the anode and aluminum foil as the cathode, and a ferric nitrate-based metal salt solution containing a chelating agent and preservative as the electrolyte, electrochemical process parameters were applied to electrochemically etch the ultrathin aluminum foil current collector. The ferric nitrate solution had a concentration of 0.01 mol / L. The chelating agent was sodium citrate modified with NaF at a concentration of 0.01 mol / L. The preparation steps were as follows: sodium citrate and NaF were dissolved in deionized water at a molar ratio of 1:1.2, and the pH was adjusted to 5.5; the mixture was stirred at 75°C for 2 hours, and finally freeze-dried to obtain a modified powder. The preservative was thiourea modified with SDS at a concentration of 0.05%. The preparation steps were as follows: thiourea and SDS were dissolved in deionized water at a molar ratio of 1:1.8, and the pH was adjusted to 5; the mixture was stirred at 35°C for 2 hours, cooled to room temperature, filtered at room temperature, and vacuum-dried to obtain a modified powder. The etching voltage was 2.0 V, the etching time was 7 min, and the etching solution temperature was 60 °C.

[0051] 4. Wash and dry the treated aluminum foil with deionized water.

[0052] The aluminum foil prepared in this example had a tensile strength of 193 MPa. After treatment, the surface Zn and Sn elemental contents were 1.0% and 0.09% by mass, respectively. The prepared sodium-ion battery exhibited an initial discharge capacity of 94.5 mAh / g and an initial coulombic efficiency of 80.1% at a 0.1C rate. However, after 200 charge-discharge cycles, the capacity retention dropped to 74.8%.

[0053] The application of the sodium-philic ultra-thin aluminum current collector of this embodiment in a negative electrode-free sodium ion battery.

[0054] Comparative Example 1

[0055] The only difference between this comparative example and Example 1 is that the formula is different. This comparative example does not contain Sn. Specifically, the sodium-philic ultra-thin aluminum current collector described in this comparative example has the following components: Fe: 0.45%; Si: 0.12%; Cu: 0.03%; Ti: 0.015%; Mn: 0.02%; Mg: 0.02%; Zn: 0.02%, and the rest is Al.

[0056] Also, during ion implantation, only Zn ions are implanted.

[0057] Comparative Example 2

[0058] The sodium-philic ultra-thin aluminum current collector described in this comparative example has the following specific components: Fe: 0.35%; Si: 0.15%; Cu: 0.02%; Ti: 0.011%; Mn: 0.02%; Mg: 0.02%; Zn: 0.01%; Sn: 0.02%; and the rest is Al.

[0059] The etching process is as follows: 1. Use alcohol to clean the aluminum foil and dry it; Second, a cleaned ultra-thin aluminum foil was used as the anode and the cathode. A ferric nitrate-based metal salt solution containing a chelating agent and a preservative was used as the electrolyte. Electrochemical process parameters were applied to electrochemically etch the ultra-thin aluminum foil current collector. The ferric nitrate solution had a concentration of 0.1 mol / L. The chelating agent was NaF-modified ammonium nitrate at a concentration of 0.08 mol / L. The preparation steps were as follows: ammonium nitrate and NaF were dissolved in deionized water at a molar ratio of 1:1.6, and the pH was adjusted to 5. The mixture was stirred at 60°C for 2 hours, and finally freeze-dried to obtain a modified powder. The preservative was SDS-modified thiourea at a concentration of 0.2%. The preparation steps were as follows: thiourea and SDS were dissolved in deionized water at a molar ratio of 1:1.2, and the pH was adjusted to 7. The mixture was stirred at 30°C for 2 hours, cooled to room temperature, filtered at room temperature, and vacuum-dried to obtain a modified powder. The etching voltage was 2.8 V, the etching time was 3 minutes, and the etching solution temperature was 55°C.

[0060] 3. Wash and dry the treated aluminum foil with deionized water.

[0061] like Figure 6 As shown in the figure, the surface morphology of the aluminum foil prepared in this comparative example does not form a uniform nanopore structure. The tensile strength of the aluminum foil prepared in this comparative example is 205 MPa. In addition, since the aluminum foil in this comparative example has not been treated with argon pre-etching and ion implantation, the surface active sites are uneven. After the subsequent electrochemical etching treatment, the Zn and Sn contents are low and uneven, as shown in the figure. Figure 7 As shown in the figure, the Zn and Sn element contents are 0.55% and 0.51% respectively. The prepared sodium ion battery has an initial discharge capacity of 84.9 mAh / g at a 0.1C rate and an initial coulombic efficiency of 72.6%. However, after 200 charge and discharge cycles, its capacity retention rate drops to 62.3%. Figure 8 The cycle stability test shows that the voltage of the sodium ion battery prepared with the ultra-thin aluminum foil prepared in this embodiment fluctuates violently during the entire cycle, and obvious voltage polarization occurs around 190h, indicating that the growth of sodium dendrites causes the battery to fail.

[0062] Comparative Example 3

[0063] The only difference between this comparative example and Example 1 is that sodium citrate is used as the complexing agent with a concentration of 0.05 mol / L; and benzotriazole is used as the preservative with a concentration of 0.25%.

[0064] Table 1 shows the performance results of the ultra-thin aluminum foils prepared in Examples 1 to 4 and Comparative Examples 1 to 3 when applied to sodium ion batteries.

[0065] Table 1

[0066] It should be understood that in order to streamline the present disclosure and aid understanding of one or more of the various inventive aspects, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the previously disclosed embodiments. Accordingly, the claims that follow the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the invention.

[0067] Although the present invention has been described with respect to a limited number of embodiments, it will be apparent to those skilled in the art, having benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Consequently, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative rather than restrictive of the scope of the invention, which is defined by the appended claims.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a sodium-philic ultrathin aluminum current collector, characterized in that: The following steps are involved: Step 1: Clean the aluminum foil and dry it; Step 2: Ion-etch the aluminum foil: Place the aluminum foil in a vacuum chamber with a vacuum degree of at least 2×10 -4 Pa, using bias power supply, argon etching to clean the surface, and argon gas was introduced to 4~6 Pa; then a vacuum high-energy metal ion source was used to perform ion implantation with Sn and Zn as cathode targets, respectively, and the working vacuum was 1×10 -4 ~1×10 -5 Pa, the aluminum foil temperature during the injection process is 25~150℃; Step 3: Using the aluminum foil obtained in step 2 as the anode, the aluminum foil as the cathode, and an iron nitrate-based metal salt solution containing a complexing agent and a preservative as the electrolyte, applying electrochemical process parameters, and electrochemically etching the anode ultra-thin aluminum foil current collector; The concentration of ferric nitrate solution is 0.01~0.3 mol / L; The complexing agent is NaF-modified ammonium nitrate or NaF-modified sodium citrate, with a concentration of 0.01~0.1mol / L; The preservative is SDS-modified thiourea or SDS-modified benzotriazole, with a concentration of 0.05-0.5%; The electrochemical process parameters are as follows: etching voltage 2.0–5.0 V, etching time 2–7 min, and etching solution temperature 40–60 °C; Step 4: Clean and dry the treated aluminum foil with deionized water.

2. The preparation method according to claim 1, characterized in that The first step is to use alcohol for cleaning.

3. The preparation method according to claim 1, characterized in that In the argon etching cleaning process of step 2, the voltage is -150~-200 V and the time is 10~15 minutes.

4. The preparation method according to claim 1, characterized in that The purity of Sn and Zn targets in step 2 is greater than 99.9%.

5. The preparation method according to claim 1, characterized in that In the ion implantation process of step 2, the Sn ion implantation voltage is 20~50 kV and the implantation dose is 1×10 15 ~1×10 17 ions / cm 2 The Zn ion implantation voltage is 40~60 kV and the implantation dose is 1×10 15 ~1×10 17 ions / cm 2 .

6. The preparation method according to claim 1, characterized in that The concentration of the ferric nitrate solution in step 3 is 0.01-0.3 mol / L.

7. The preparation method according to claim 1, characterized in that The preparation steps of NaF-modified ammonium nitrate or NaF-modified sodium citrate are as follows: dissolving ammonium nitrate or sodium citrate and NaF in deionized water at a molar ratio of 1:1 to 1:2, adjusting the pH to 4.5 to 7.5; stirring at 50 to 80° C. for at least 2 hours, and finally freeze-drying to obtain a modified powder.

8. The preparation method according to claim 1, characterized in that The preparation steps of SDS-modified thiourea or SDS-modified benzotriazole are as follows: dissolving thiourea or benzotriazole and SDS in deionized water at a molar ratio of 1:1 to 1:2, and adjusting the pH to 5 to 7; stirring at 30 to 50° C. for at least 2 hours, cooling to room temperature, filtering at room temperature, and vacuum drying to obtain a modified powder.

9. The sodium-philic ultra-thin aluminum current collector obtained by the preparation method according to any one of claims 1 to 7.

10. Use of the sodium-philic ultra-thin aluminum current collector according to claim 9 in a negative electrode-free sodium ion battery.

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