Flexible composite sodium metal negative electrode and preparation method thereof, sodium ion battery and electric equipment

Abstract

The invention provides a flexible composite sodium metal negative electrode and a preparation method thereof, a sodium ion battery and electric equipment, and relates to the field of sodium ion batteries. The method comprises the following steps: carrying out acid leaching on a metal framework to obtain a treated framework; carrying out first mixing on the treated framework and first alkali liquor, and electrifying to obtain a framework coated with copper hydroxide; sequentially carrying out annealing treatment and heat treatment on the copper hydroxide coated framework under reducing gas to obtain a copper nanowire coated metal framework; carrying out second mixing and reaction on the copper nanowire coated metal framework, tartaric acid, bismuth nitrate and water, and then cleaning by adopting second alkali liquor and water to obtain a bismuth modified sodium-philic three-dimensional metal framework; and injecting the bismuth-modified sodium-philic three-dimensional metal skeleton into molten sodium metal or electrochemically depositing the sodium metal to obtain the flexible composite sodium metal negative electrode. The method has the advantages of being wide in raw material source, simple to operate, good in repeatability, low in cost, beneficial to large-scale production and the like, and has the possibility of practical application.

Description

Technical Field

[0001] This application relates to the field of sodium-ion batteries, and more particularly to a flexible composite sodium metal anode and its preparation method, sodium-ion batteries, and electrical devices. Background Technology

[0002] The rapid development of technology and the ever-increasing demand for consumer electronics, electric vehicles, and energy storage devices have driven the further development of rechargeable batteries. Lithium-ion batteries (LIBs), due to their ultra-high energy density and cycle life, have become the dominant force in the rechargeable battery field and are widely used in all aspects of life. However, the shortage of lithium resources has become a focus of social concern, urgently requiring a new type of rechargeable battery to address this issue. Sodium-based batteries, such as sodium-ion batteries (SIBs) and sodium metal batteries (SMBs), are considered the best alternative to LIBs, especially in low-temperature and energy storage applications. Sodium (Na) accounts for 2.74% of the Earth's crust, more than 400 times the content of lithium (Li). Furthermore, sodium metal, as the negative electrode, has an extremely high energy density of 1166 mAh / g and a very low electrochemical potential of -2.71 V (compared to a standard hydrogen electrode). When matched with a sodium-free positive electrode, it can form an SMB with ultra-high energy density.

[0003] However, in practical applications, sodium metal as a battery anode still faces many problems. For example, the growth of sodium dendrites caused by uneven deposition of sodium ions leads to repeated rupture and reformation of the solid electrolyte interphase (SEI) film on the anode surface, resulting in the loss of active sodium and continuous consumption of electrolyte. Furthermore, the unlimited growth of sodium dendrites can eventually puncture the separator, causing internal short circuits, explosions, and fires, leading to serious safety accidents. In addition, sodium dendrites can break and fragment during growth, causing sodium metal to detach from the substrate, forming "dead sodium," resulting in reduced active sodium and volume expansion. These numerous problems severely affect the cycle life and safety of batteries, hindering the practical application of SMBs (Supersonic Battery).

[0004] In existing technologies, most composite sodium metal anodes are synthesized using carbon materials as the framework. Compared to metal matrices, carbon matrices have several drawbacks: First, they have poor conductivity, affecting the battery's rate performance, and the uneven distribution of local current density can lead to sodium dendrite growth. Second, they have lower mechanical strength, making the battery prone to cracking during cycling and affecting cycle life. Third, carbon's sodium-repellent properties result in higher interfacial impedance and uneven sodium ion deposition. Fourth, they have insufficient adaptability to volume expansion; repeated insertion and extraction of sodium ions during cycling can cause the carbon framework to collapse, reducing battery life. Finally, these electrodes have poor flexibility, making them difficult to handle complex and variable operating environments, and their manufacturing process is complex and costly, thus presenting significant limitations.

[0005] Therefore, there is an urgent need to provide a method for preparing a flexible composite sodium metal anode to solve the above problems. Summary of the Invention

[0006] The purpose of this application is to provide a flexible composite sodium metal anode and its preparation method, sodium-ion battery and electrical device, to solve the problems of sodium dendrite growth, dead sodium generation and serious volume expansion caused by uneven deposition of sodium ions during cycling, thereby effectively improving the cycle performance and safety of SMB, and providing an effective modification strategy for the practical application of SMB.

[0007] To achieve the above objectives, the first aspect of this application provides a method for preparing a flexible composite sodium metal anode, comprising: The copper-containing metal skeleton is acid-leached to obtain the treated skeleton. The treated skeleton and the first alkaline solution are mixed and subjected to an electric current treatment to obtain a skeleton coated with copper hydroxide. Under a reducing gas atmosphere, the copper hydroxide-coated framework is subjected to annealing and heat treatment in sequence to obtain a copper nanowire-coated metal framework. A second mixing and reaction was carried out on copper nanowire-coated metal framework, tartaric acid, bismuth nitrate and water, followed by washing with a second alkali solution and water to obtain a bismuth-modified sodium-loving three-dimensional metal framework. The bismuth-modified sodium-loving three-dimensional metal framework is injected into molten sodium metal or electrochemically deposited into sodium metal to obtain a flexible composite sodium metal anode.

[0008] Optionally, the copper-containing metal skeleton includes at least one of copper and / or copper-tin alloys and aluminum-based composite materials; And / or, the shape of the copper-containing metal skeleton includes at least one of metal foil, mesh, and porous foam; And / or, the porosity of the copper-containing metal skeleton is 85-95%, and the pore size is 100-300µm.

[0009] Optionally, the mass fraction of the acid in the acid leaching is 1-10%; And / or, the acid in the acid leaching includes at least one of acetic acid, oxalic acid, sulfuric acid, nitric acid, and hydrochloric acid; The acid leaching time is 30-120 minutes; The mass fraction of the first alkaline solution is 0.1-5 mol / L; And / or, the first alkaline solution comprises sodium hydroxide and / or potassium hydroxide; And / or, the second alkaline solution comprises a sodium carbonate solution.

[0010] Optionally, the current density of the energizing process is 0.01-1 A / cm². -2 ; And / or, the energizing process takes 1-200 minutes.

[0011] Optionally, the final temperature of the annealing treatment is 200-500℃, and the time is 30-120 min; And / or, the endpoint temperature of the heat treatment is 400-700℃, and the time is 120-240 min.

[0012] Optionally, the molar ratio of tartaric acid to bismuth nitrate is 0.1-1.5:60-130; And / or, the pH of the mixed solution obtained from the tartaric acid, the bismuth nitrate and the water is 2-7; And / or, the reaction time is 1-120 min.

[0013] The second aspect of this application provides a flexible composite sodium metal anode, which is prepared by the method described above.

[0014] A third aspect of this application provides a sodium-ion battery, including the aforementioned flexible composite sodium metal anode.

[0015] Optionally, the sodium-ion battery further includes a positive electrode, a separator, and an electrolyte; The positive electrode material in the positive electrode includes at least one of sodium vanadium phosphate, sodium copper iron manganate, Prussian white, sodium iron pyrophosphate, sodium iron sulfate, sodium nickel iron manganate, and sulfur. The diaphragm includes at least one of the following: glass fiber diaphragm, polyethylene diaphragm, polypropylene diaphragm, polyethylene-polypropylene diaphragm, aramid diaphragm, cellulose membrane, polyamide membrane, and spandex membrane; The electrolyte includes ester-based electrolytes and / or ether-based electrolytes.

[0016] A fourth aspect of this application provides an electrical device including the aforementioned sodium-ion battery.

[0017] Compared with the prior art, the beneficial effects of this application include: The method for preparing the flexible composite sodium metal anode provided in this application involves treating a copper-containing metal substrate with sodium affinity, followed by injection of molten sodium metal or electrochemical deposition of sodium metal. The composite anode synthesized using copper metal as a framework exhibits excellent flexibility, meeting diverse application scenarios and expanding its application range. Simultaneously, the copper-containing metal framework possesses good conductivity, effectively improving the battery's charge / discharge rate. Furthermore, the introduction of sodium-affinity bismuth particles into the copper-containing metal framework not only serves as nucleation sites, guiding sodium ion nucleation, but also reduces the overpotential for sodium ion nucleation, promoting uniform and rapid sodium ion deposition. Finally, the three-dimensional metal framework possesses a large specific surface area and excellent mechanical properties, reducing local current density, homogenizing the electric field and ion concentration field at the electrode surface, and suppressing the volume expansion problem caused by repeated sodium ion stripping / deposition. This method offers advantages such as wide availability of raw materials, simple operation, good repeatability, low cost, and suitability for large-scale production, making it highly promising for practical applications.

[0018] The flexible composite sodium metal anode provided in this application has good flexibility, high mechanical strength, and excellent stability.

[0019] The sodium-ion battery and electrical device provided in this application have significantly improved electrochemical performance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0021] Figure 1 Comparison chart of cycle performance tests of half-cells provided in Example 1 and Comparative Example 1; Figure 2 Comparison chart of cycle performance tests for symmetrical batteries provided in Example 1 and Comparative Example 1; Figure 3 Comparison chart of cycle performance tests of full cells provided in Example 1 and Comparative Example 1. Detailed Implementation

[0022] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a method for preparing a flexible composite sodium metal anode, comprising: The copper-containing metal skeleton is acid-leached to obtain the treated skeleton. It should be noted that acid leaching can remove oxides from the surface of the metal framework, preparing it for the subsequent synthesis of metal nanowires on the substrate surface. The treated skeleton and the first alkaline solution are mixed and subjected to an electric current treatment to obtain a skeleton coated with copper hydroxide. This can be understood as the copper hydroxide-coated framework referring to the growth of copper hydroxide (Cu(OH)2) nanowires on a metal framework; Under a reducing gas atmosphere, the copper hydroxide-coated framework is subjected to annealing and heat treatment in sequence to obtain a copper nanowire-coated metal framework. It should be noted that annealing transforms Cu(OH)2 nanowires into CuO nanowires, while heat treatment transforms CuO nanowires into Cu nanowires. A second mixing and reaction was carried out on copper nanowire-coated metal framework, tartaric acid, bismuth nitrate and water, followed by washing with a second alkali solution and water to obtain a bismuth-modified sodium-loving three-dimensional metal framework. The bismuth-modified sodium-loving three-dimensional metal framework is injected into molten sodium metal or electrochemically deposited into sodium metal to obtain a flexible composite sodium metal anode.

[0023] In some embodiments, the copper-containing metal framework comprises copper and / or a copper-tin alloy; And / or, the shape of the copper-containing metal skeleton includes at least one of metal foil, mesh, and porous foam; Preferably, the shape of the copper-containing metal skeleton includes a mesh; In some embodiments, copper foam has good physical properties and stable chemical properties, and will not form an alloy with sodium during cycling, thus preventing volume expansion; however, if zinc metal is used as the base, repeated oxidation and dealloying will cause severe volume expansion, leading to electrode shattering. And / or, the porosity of the copper-containing metal skeleton is 85-95%, and the pore size is 100-300µm.

[0024] Optionally, the porosity of the copper-containing metal skeleton can be any value between 85%, 90%, 95% or 85-95%, and the pore size can be any value between 100µm, 150µm, 200µm, 250µm, 300µm or 100-300µm.

[0025] It is worth noting that higher porosity provides more ion transport channels, which is beneficial for rapid ion transport and improves the rate performance of the battery; when the pore size is 100-300µm, there is enough space to control the growth amount and length of metal nanowires.

[0026] In some embodiments, the mass fraction of the acid in the acid leaching is 1-10%; Optionally, the mass fraction of acid in the pickling process can be 1%, 5%, 10%, or any value between 1% and 10%. And / or, the acid in the acid leaching includes at least one of acetic acid, oxalic acid, sulfuric acid, nitric acid, and hydrochloric acid; The acid leaching time is 30-120 minutes; Optionally, the pickling time can be any value between 30 min, 60 min, 90 min, 120 min, or 30-120 min; The mass fraction of the first alkaline solution is 0.1-5 mol / L; Optionally, the mass fraction of the first alkali solution can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or any value between 0.1 and 5 mol / L; And / or, the first alkaline solution comprises sodium hydroxide and / or potassium hydroxide; And / or, the second alkaline solution comprises a sodium carbonate solution.

[0027] In some embodiments, the current density of the energizing process is 0.01-1 A / cm². -2 ; Optionally, the current density for energizing the process can be 0.01 A / cm². -2 0.05 A / cm -2 0.1 A / cm -2 0.5A / cm -2 1 A / cm -2 Or 0.01-1 A / cm -2 Any value between; And / or, the energizing process takes 1-200 minutes.

[0028] Optionally, the power-on processing time can be any value between 1 min, 10 min, 50 min, 100 min, 150 min, 200 min, or 1-200 min.

[0029] In some embodiments, the endpoint temperature of the annealing treatment is 200-500°C, and the time is 30-120 min; Optionally, the endpoint temperature of the annealing treatment can be any value between 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃ or 200-500℃, and the time can be any value between 30min, 60min, 90min, 120min or 30-120min. And / or, the endpoint temperature of the heat treatment is 400-700℃, and the time is 120-240 min.

[0030] Optionally, the final temperature of the heat treatment can be any value between 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, or 400-700℃, and the time can be any value between 120min, 150min, 180min, 210min, 240min, or 120-240min.

[0031] In some embodiments, the molar ratio of tartaric acid to bismuth nitrate is 0.1-1.5:60-130; Optionally, the molar ratio of tartaric acid to bismuth nitrate can be any value between 0.1:60, 0.5:100, 1:100, 1.5:130, or 0.1-1.5:60-130; And / or, the pH of the mixed solution obtained from the tartaric acid, the bismuth nitrate and the water is 2-7; Optionally, the pH of the mixed solution obtained from tartaric acid, bismuth nitrate and water can be 2, 3, 4, 5, 6, 7 or any value between 2 and 7; And / or, the reaction time is 1-120 min.

[0032] Optionally, the reaction time can be any value between 1 min, 10 min, 50 min, 100 min, 120 min, or 1-120 min.

[0033] The second aspect of this application provides a flexible composite sodium metal anode, which is prepared by the method described above.

[0034] The flexible composite sodium metal anode includes a metal framework and copper nanowires disposed on the surface of the metal framework.

[0035] A third aspect of this application provides a sodium-ion battery, including the aforementioned flexible composite sodium metal anode.

[0036] In some embodiments, the sodium-ion battery further includes a positive electrode, a separator, and an electrolyte; The positive electrode material in the positive electrode includes at least one of sodium vanadium phosphate, sodium copper iron manganate, Prussian white, sodium iron pyrophosphate, sodium iron sulfate, sodium nickel iron manganate, and sulfur. The diaphragm includes at least one of the following: glass fiber diaphragm, polyethylene diaphragm, polypropylene diaphragm, polyethylene-polypropylene diaphragm, aramid diaphragm, cellulose membrane, polyamide membrane, and spandex membrane; The electrolyte includes ester-based electrolytes and / or ether-based electrolytes.

[0037] A fourth aspect of this application provides an electrical device including the aforementioned sodium-ion battery.

[0038] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0039] Example 1 This embodiment provides a flexible composite sodium metal anode and its preparation method. The specific preparation steps are as follows: S1: Cut a 5×5 cm piece of copper foam (CF, porosity 90%, pore size 200µm), immerse it in 10% dilute hydrochloric acid for 60 min, rinse the metal skeleton after immersion with deionized water and anhydrous ethanol, and dry it in a drying oven at 70℃ for later use. S2: Place the CF sample cleaned in step S1 into a 1 mol / L NaOH solution and purge it with 10 mA / cm² water. -2 The current was applied for 30 min, and Cu(OH)2 nanowires were grown on copper foam by anodic oxidation. After being removed, they were rinsed with deionized water and anhydrous ethanol and dried in a drying oven at 70℃ for later use. S3: The CF obtained in S2 was annealed at 300℃ to transform Cu(OH)2 nanowires into CuO nanowires. Then, at 500℃ and under a hydrogen / argon (H2 / Ar) mixed gas, it was reduced for 180 min to obtain copper foam (Cu-nw / CF) with grown copper nanowires. S4: The metal framework obtained in step S3 is immersed in a mixed solution of tartaric acid and bismuth nitrate (the molar ratio of tartaric acid and bismuth nitrate is 1:100, and the pH value is 3) for 60 min. After being taken out, it is immediately immersed in 0.1 M sodium carbonate solution and rinsed with deionized water, and then dried with N2 to obtain a bismuth-modified sodium-loving three-dimensional metal framework (Bi-Cu-nw / CF). S5: Cut the obtained Bi-Cu-nw / CF into circular pieces with a diameter of 12mm, and contact them with sodium metal in a high-temperature molten state in a glove box. After complete wetting, a flexible composite sodium metal anode (Bi-Cu-nw / CF@Na) is obtained.

[0040] In this embodiment, the above-mentioned flexible composite sodium metal anode (Bi-Cu-nw / CF) and Na sheet are used to form a half cell (Bi-Cu-nw / CF@Na). The half cell (Bi-Cu-nw / CF@Na) is used as an electrode to assemble a symmetrical cell (Bi-Cu-nw / CF@Na||Bi-Cu-nw / CF@Na). The half cell (Bi-Cu-nw / CF@Na) and NVP positive electrode are used to assemble a full cell (Bi-Cu-nw / CF@Na||NVP).

[0041] The battery uses a glass fiber separator and a commercially available ester electrolyte.

[0042] Example 2 The difference from Example 1 is that in step S2, the current density is 0.02 A / cm. -2 .

[0043] Example 3 The difference from Example 1 is that in step S2, the current density is 0.03 A / cm. -2 .

[0044] Example 4 The difference from Example 1 is that in step S2, the mass fraction of the NaOH solution is 2 mol / L.

[0045] Example 5 The difference from Example 1 is that in step S2, the mass fraction of the NaOH solution is 2 mol / L, and the current density is 0.02 A / cm². -2 .

[0046] Example 6 The difference from Example 1 is that in step S2, the current is introduced for 15 minutes.

[0047] Example 7 The difference from Example 1 is that in step S2, the current is introduced for 45 minutes.

[0048] Example 8 The difference from Example 1 is that in step S4, the molar ratio of tartaric acid to bismuth nitrate is 1.5:100, and the pH value is 2.5.

[0049] Comparative Example 1 The difference from Example 1 is as follows: In this comparative example, copper foil without sodium affinity treatment (i.e., the treatment in steps S1-S4 of Example 1) was used as an electrode and assembled with a pure sodium sheet with a diameter of 15.4 mm to form a half cell; a pure sodium sheet with a diameter of 15.4 mm was used as an electrode to form a symmetrical cell; and a pure sodium sheet with a diameter of 15.4 mm was used as a negative electrode and assembled with an NVP positive electrode to form a full cell.

[0050] The half-cell (Bi-Cu-nw / CF@Na) provided in Example 1 and the half-cell (Bare Cu) provided in Comparative Example 1, at a current density of 1 mA / cm², 2 The deposition capacity is 1 mAh / cm³. 2 Under certain conditions, it can stably cycle for 500 times, and the test results are as follows. Figure 1 As shown, the half-cell (Bi-Cu-nw / CF@Na) exhibits excellent structural stability and reversibility.

[0051] The symmetrical cell (Bi-Cu-nw / CF@Na||Bi-Cu-nw / CF@Na) provided in Example 1 and the symmetrical cell provided in Comparative Example 1, at a current density of 1 mA / cm², 2 The deposition capacity is 1 mAh / cm³. 2 Tests were conducted under the specified conditions, and the test results are as follows: Figure 2 As shown, the symmetric cell (Bi-Cu-nw / CF@Na||Bi-Cu-nw / CF@Na) provided in Example 1 can cycle stably for 800 h, and its cycle life and polarization voltage are better than those of pure sodium.

[0052] The full cell (Bi-Cu-nw / CF@Na||NVP) provided in Example 1 and the full cell provided in Comparative Example 1 can stably cycle for 800 cycles at a current density of 1C. The test results are as follows. Figure 3 As shown, the full cell (Bi-Cu-nw / CF@Na||NVP) provided in Example 1 still has a capacity retention rate of 94%, which is much higher than the 44% capacity retention rate of the pure sodium sheet electrode after 300 cycles. This indicates that the flexible composite sodium metal anode provided in Example 1 can induce uniform deposition of sodium ions and effectively suppress the growth of sodium dendrites, exhibiting excellent electrochemical stability.

[0053] The above tests show that the flexible composite sodium metal anode provided in Example 1 can induce uniform deposition of sodium ions, effectively suppress the growth of sodium dendrites, and exhibit excellent electrochemical stability.

[0054] Comparative Example 2 The difference from Example 1 is that the acid leaching treatment in step S1 is not performed. Instead, the 5×5 cm copper foam is placed directly in a 1 mol / L NaOH solution and then the subsequent operations are performed.

[0055] Comparative Example 3 The difference from Example 1 is that step S2 is omitted, and the CF cleaned in step S1 is directly annealed and heat-treated.

[0056] Comparative Example 4 The difference from Example 1 is that the annealing process in step S3 is not performed.

[0057] Comparative Example 5 The difference from Example 1 is that the bismuth modification in step S4 is not performed; that is, the metal framework obtained in step S3 is subjected to step S5.

[0058] Comparative Example 6 The difference from Example 1 is that tartaric acid is not added in step S4.

[0059] Comparative Example 7 The difference from Example 1 is that in step S2, the current density is 5000 uA / cm. -2 .

[0060] Comparative Example 8 The difference from Example 1 is that in step S2, the current density is 1.2 A / cm². -2 .

[0061] In this application, the flexible composite sodium metal anodes provided in Examples 2-8 and Comparative Examples 2-8 were used to prepare half-cells according to the method in Example 1, and their electrochemical performance was tested. The specific data are shown in Table 1.

[0062] Table 1 Electrochemical performance

[0063] analyze: The above tests show that in Examples 2 and 3, the reaction is too fast at higher current densities, consuming OH-. - Excessive ions cause concentration polarization; in Example 6, the growth time was too short, resulting in insufficient three-dimensional height and limited surface area. In Example 7, the overgrown structure is prone to instability during constant cycling.

[0064] In Comparative Examples 1-6, omitting S1 makes it difficult to remove surface impurities, affecting subsequent processing. Omitting S3 results in non-CuO nanowires as the final product, which deviates from the expected goal. Omitting S4 leads to poorer subsequent sodium-affinity treatment, making it impossible to guide Na deposition. Omitting S2 slightly increases the specific surface area but lacks a three-dimensional porous structure. Even with subsequent bismuth modification, the sodium-affinity guiding effect will be greatly reduced due to the lack of three-dimensional support.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0066] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a flexible composite sodium metal anode, characterized in that, include: The copper-containing metal skeleton is acid-leached to obtain the treated skeleton. The treated skeleton and the first alkaline solution are mixed and subjected to an electric current treatment to obtain a skeleton coated with copper hydroxide. Under a reducing gas atmosphere, the copper hydroxide-coated framework is subjected to annealing and heat treatment in sequence to obtain a copper nanowire-coated metal framework. A second mixing and reaction was carried out on copper nanowire-coated metal framework, tartaric acid, bismuth nitrate and water, followed by washing with a second alkali solution and water to obtain a bismuth-modified sodium-loving three-dimensional metal framework. The bismuth-modified sodium-loving three-dimensional metal framework is injected into molten sodium metal or electrochemically deposited into sodium metal to obtain a flexible composite sodium metal anode.

2. The method for preparing the flexible composite sodium metal anode according to claim 1, characterized in that, The copper-containing metal framework includes copper and / or copper-tin alloys; And / or, the shape of the copper-containing metal skeleton includes at least one of metal foil, mesh, and porous foam; And / or, the porosity of the copper-containing metal skeleton is 85-95%, and the pore size is 100-300µm.

3. The method for preparing the flexible composite sodium metal anode according to claim 1, characterized in that, The mass fraction of acid in the acid leaching is 1-10%; And / or, the acid in the acid leaching includes at least one of acetic acid, oxalic acid, sulfuric acid, nitric acid, and hydrochloric acid; The acid leaching time is 30-120 minutes; The mass fraction of the first alkaline solution is 0.1-5 mol / L; And / or, the first alkaline solution comprises sodium hydroxide and / or potassium hydroxide; And / or, the second alkaline solution comprises a sodium carbonate solution.

4. The method for preparing the flexible composite sodium metal anode according to claim 1, characterized in that, The current density for the energizing process is 0.01-1 A / cm². -2 ; And / or, the energizing process takes 1-200 minutes.

5. The method for preparing the flexible composite sodium metal anode according to claim 1, characterized in that, The final temperature of the annealing treatment is 200-500℃, and the time is 30-120 min; And / or, the endpoint temperature of the heat treatment is 400-700℃, and the time is 120-240 min.

6. The method for preparing the flexible composite sodium metal anode according to claim 1, characterized in that, The molar ratio of tartaric acid to bismuth nitrate is 0.1-1.5:60-130; And / or, the pH of the mixed solution obtained by the tartaric acid, the bismuth nitrate and the water is 2-7; And / or, the reaction time is 1-120 min.

7. A flexible composite sodium metal anode, characterized in that, It is prepared by the method for preparing flexible composite sodium metal anode according to any one of claims 1-6.

8. A sodium-ion battery, characterized in that, Including the flexible composite sodium metal anode as described in claim 7.

9. The sodium-ion battery according to claim 8, characterized in that, The sodium-ion battery also includes a positive electrode, a separator, and an electrolyte; The positive electrode material in the positive electrode includes at least one of sodium vanadium phosphate, sodium copper iron manganate, Prussian white, sodium iron pyrophosphate, sodium iron sulfate, sodium nickel iron manganate, and sulfur. The diaphragm includes at least one of the following: glass fiber diaphragm, polyethylene diaphragm, polypropylene diaphragm, polyethylene-polypropylene diaphragm, aramid diaphragm, cellulose membrane, polyamide membrane, and spandex membrane; The electrolyte includes ester-based electrolytes and / or ether-based electrolytes.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

Images