High-stability sodium metal negative electrode based on gel electrolyte as well as preparation method and application of high-stability sodium metal negative electrode

Abstract

The invention discloses a high-stability sodium metal negative electrode based on gel electrolyte as well as a preparation method and application of the high-stability sodium metal negative electrode. The preparation method comprises the following steps: directly carbonizing lignin, preparing a small-particle-size hard carbon material through wet ball milling, coating a metal foil with the hard carbon material, dropwise adding a polytetrahydrofuran precursor solution for in-situ polymerization, and finally depositing sodium metal to obtain the high-stability sodium metal negative electrode based on the gel electrolyte. The method does not need to add chemical reagents, is simple to operate and has low requirements on equipment. The gel electrolyte is prepared by adopting an in-situ polymerization method, heating is not needed, the needed energy consumption is low, the preparation method is simple, and the potential of large-scale production is achieved. By preparing the gel electrolyte and improving the performance of the negative electrode substrate material, the nucleation and growth overpotential of sodium dendrites are effectively reduced, the growth of the sodium dendrites is doubly inhibited, and the stability of the sodium metal battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium metal battery technology, specifically relating to a highly stable sodium metal anode based on gel electrolyte, its preparation method, and its application. Background Technology

[0002] Sodium resources are evenly distributed in the Earth's crust, with an abundance higher than lithium, ensuring ample supply and low raw material costs. This makes sodium-ion batteries the most likely alternative to lithium-ion batteries. However, room-temperature sodium-ion batteries suffer from drawbacks such as unsatisfactory specific capacity, energy density, and rate capability. In contrast, sodium metal batteries, using metallic sodium as the negative electrode, possess superior theoretical specific capacity (1166 mA hg). -1 ) and low reduction potential (-2.71 V) vs. Compared with sodium-ion batteries, sodium metal batteries have advantages and broad prospects in energy storage systems.

[0003] However, sodium metal batteries are plagued by dendrite growth. Under the influence of the "sharp tip effect," sodium dendrites grow continuously and pierce the separator, eventually leading to a short circuit. Simultaneously, sodium dendrites easily break off to form "dead sodium," resulting in increased battery impedance and irreversible capacity, reducing the cycle stability of sodium metal batteries. The sodium affinity of the substrate is a crucial factor affecting the uniformity of sodium metal nucleation on its surface. Improving the sodium affinity of the substrate material helps reduce the sodium metal nucleation overpotential, i.e., helps lower the energy barrier for sodium nucleation, allowing for more uniform sodium deposition on the substrate surface. An article (ACS Nano 19 (2025) 23193-23208) reports that the electric field on the surface of copper current collectors is non-uniform and exhibits significant sodium repellency; therefore, sodium metal deposition on the surface of copper current collectors easily forms sodium dendrites. The article (Journal of the American Chemical Society 143 (2021) 3280-3) reports that biomass-based carbon materials, by reducing local current density and ensuring uniform sodium deposition in the electrode, result in sodium metal batteries assembled with these materials exhibiting a high CE (ceasefire) of over 190 days and 99.5%. Hard carbon is widely available, inexpensive, and structurally stable during battery charge and discharge. Its abundant porous structure provides numerous active sites for sodium ions, and its good sodium affinity typically results in low overpotentials in metal batteries. Therefore, coating the surface of a copper current collector with hard carbon can effectively suppress sodium dendrite formation. Simultaneously, particle size affects the ion diffusion rate; smaller particle sizes facilitate rapid sodium ion diffusion, eliminating concentration gradients, and increasing exposed active sites, promoting uniform sodium metal nucleation. Therefore, small and uniform hard carbon particles contribute to more uniform sodium metal deposition. Notably, designing the electrolyte to construct a stable and uniform interface is another important measure to achieve uniform sodium metal deposition and suppress dendrite growth.

[0004] In liquid electrolytes, the decomposition of numerous free solvent molecules easily forms a fragile and uneven solid electrolyte interphase (SEI) film. During battery charging and discharging, the rupture of this fragile SEI leads to uneven electric field distribution on the electrode surface, exacerbating the uneven deposition of sodium metal and becoming a significant cause of uncontrolled sodium dendrite growth on the sodium metal anode surface. Without SEI protection, sodium metal continuously undergoes side reactions with the electrolyte, consuming active sodium and shortening battery life. In sodium metal batteries, the high volatility and flammability of organic electrolytes increase the risk of explosion in failed batteries, and liquid electrolytes also pose a leakage risk, further aggravating safety hazards. In contrast, gel electrolytes, with their superior mechanical properties, can inhibit sodium dendrite growth to some extent, preventing short-circuit failure. The three-dimensional cross-linked network structure of gel electrolytes gives them the high ion mobility of liquid electrolytes and the safety of solid electrolytes, making them more advantageous in sodium metal batteries. However, the effective contact between the electrolyte and the electrode also affects battery performance.

[0005] Compared to non-in-situ polymerization, in-situ polymerization effectively solves the problem of contact between the electrolyte and the electrode. Because the electrolyte can fully wet and fill the electrode voids before polymerization, the in-situ polymerized gel electrolyte exhibits better contact with the electrode, effectively reducing interfacial impedance and improving battery cycle performance. In-situ polymerized gel electrolytes also address the issue of excessive electrolyte thickness, reducing ion transport distance.

[0006] Chinese patent application CN116435592A discloses a high-voltage ether-based gel electrolyte, its preparation method, and its application. This patent first adds a crosslinking agent monomer material to a liquid electrolyte containing lithium / sodium salts and additives, then adds AIBN to obtain a gel electrolyte precursor solution. The precursor solution is then added to a battery, allowed to stand for 1–20 h, and polymerized at 45–70 °C for 2–10 h. However, this process requires continuous heating, resulting in high energy consumption and complex procedures.

[0007] In summary, it is of great significance to develop a low-cost sodium metal anode that effectively suppresses sodium dendrite growth, thereby enabling sodium metal batteries to have lower nucleation overpotential and more stable cycle performance. Summary of the Invention

[0008] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a highly stable sodium metal anode based on a gel electrolyte.

[0009] This invention selects lignin as a precursor material and prepares hard carbon material through simple carbonization. The particle size of the hard carbon is then reduced by wet ball milling to obtain small-sized hard carbon. This small-sized hard carbon is then coated onto the surface of the current collector to enhance its sodium affinity. Simultaneously, a polytetrahydrofuran (PTF) electrolyte precursor is drop-added to the hard carbon surface and in-situ polymerized to prepare a sodium metal anode with a PTF gel electrolyte. The sodium metal anode is prepared using the gel electrolyte precursor, which is formed through in-situ polymerization. During this process, the initiator, acting as a Lewis acid, interacts with the lone pair electrons in the TTF monomer, causing the carbon-oxygen bonds of the monomer to break, resulting in ring-opening polymerization. Both the gel electrolyte and the small-sized hard carbon help suppress dendrite growth, achieving high stability of the sodium metal anode.

[0010] Another object of the present invention is to provide a highly stable sodium metal anode based on a gel electrolyte prepared by the above preparation method.

[0011] Another object of the present invention is to provide the application of the above-mentioned highly stable sodium metal anode based on gel electrolyte in sodium metal batteries.

[0012] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a highly stable sodium metal anode based on a gel electrolyte, comprising the following steps: (1) Mix the sodium salt, tetrahydrofuran and initiator evenly to obtain a gel electrolyte precursor solution; (2) The lignin was carbonized in an inert gas atmosphere and then wet-milled to obtain hard carbon material; (3) After mixing the hard carbon material, conductive material and binder from step (2), the mixture is coated onto a metal foil. After drying, the gel electrolyte precursor solution from step (1) is added dropwise, polymerized at room temperature, and finally deposited with metallic sodium to obtain a highly stable sodium metal anode based on gel electrolyte.

[0013] Preferably, the concentration of the sodium salt in tetrahydrofuran in step (1) is 0.1 to 3 mol / L.

[0014] Preferably, the sodium salt in step (1) includes at least one of NaPF6, NaBF4, NaClO4, NaTFSI and NaFSI.

[0015] Preferably, the initiator in step (1) includes at least one of SnF2, BF3, PF5, Al(OfT)3 and Sn(OfT)2.

[0016] Preferably, the initiator in step (1) accounts for 0.5 to 10% of the mass of the sodium salt.

[0017] Preferably, the lignin in step (2) includes at least one of enzymatically hydrolyzed lignin, alkali lignin, lignin sulfonate, and solvent-based lignin.

[0018] Preferably, the inert gas in step (2) includes at least one of nitrogen, argon and helium.

[0019] Preferably, the flow rate of the inert gas in step (2) is 40–80 mL / min. -1 More preferably, 50 mL min -1 .

[0020] Preferably, the carbonization temperature in step (2) is 1100-1600 °C and the time is 2-8 h; more preferably, it is 1100-1300 °C and carbonization time is 2-6 h; most preferably, it is carbonization time is 1300 °C for 2 h.

[0021] Preferably, the heating rate of carbonization in step (2) is 2 to 10 °C / min, more preferably 5 °C / min.

[0022] Preferably, the wet ball milling in step (2) specifically involves mixing the carbonized product with a solvent at a mass ratio of 1:(30-50) and ball milling at 300-600 rpm for 0.2-24 h.

[0023] More preferably, the solvent includes at least one of water and acetone.

[0024] Preferably, the conductive material in step (3) includes at least one of conductive carbon black and acetylene black.

[0025] Preferably, the adhesive in step (3) comprises at least one of polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA).

[0026] Preferably, the mass ratio of the hard carbon material, conductive material and binder in step (3) is (7-8):(1-2):1.

[0027] Preferably, the ratio of the mass of the hard carbon material to the coating area of ​​the metal foil in step (3) is (1-1.5) mg : (1-1.2) cm. 2 .

[0028] Preferably, the metal foil in step (3) includes at least one of copper foil and aluminum foil.

[0029] Preferably, the drying temperature in step (3) is 60-80 °C and the drying time is 6-12 h.

[0030] Preferably, the ratio of the mass of the hard carbon material in step (3) to the volume of the gel electrolyte precursor solution is 1.3 mg: (190-210) μL.

[0031] Preferably, the room temperature polymerization time in step (3) is 1 hour to 7 days; the room temperature range is 15 to 40°C.

[0032] Preferably, the process of depositing sodium metal in step (3) is electrochemical deposition.

[0033] Preferably, the amount of sodium metal deposited in step (3) is 0.4–0.6 mAh cm⁻¹. -2 .

[0034] Secondly, the present invention provides a highly stable sodium metal anode based on a gel electrolyte obtained by the above preparation method.

[0035] Thirdly, the present invention provides the application of the above-mentioned highly stable sodium metal anode based on gel electrolyte in sodium metal batteries.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The gel electrolyte prepared by in-situ polymerization in this invention has a high electrochemical window, which enables the gel electrolyte to achieve high energy density, while improving the stability and safety of the battery. The preparation process of the gel electrolyte is simple and does not require additional heating technology, thus reducing costs.

[0037] (2) This invention uses lignin as a precursor for hard carbon and directly prepares hard carbon through carbonization. This method has a simple preparation process, does not require the introduction of any chemical additives, reduces production costs, simplifies the production process, and is conducive to large-scale production.

[0038] (3) The hard carbon after ball milling in this invention exhibits a significant change in particle size and a concentrated distribution. This structural change significantly reduces the deposition overpotential and nucleation overpotential of sodium metal, enabling the negative electrode of the battery to effectively suppress the growth of sodium dendrites, thereby improving the battery stability. Attached Figure Description

[0039] Figure 1 A schematic diagram of a sodium metal anode structure consisting of a gel electrolyte and a hard carbon material-coated substrate.

[0040] Figure 2 The overpotential diagrams are for Comparative Example 1 and Comparative Example 2.

[0041] Figure 3 Comparative Examples 1 and 2 were compared at 1 mA cm⁻¹ -2 Coulomb efficiency at current density.

[0042] Figure 4 For Comparative Examples 1, 2 and 4, 1 mA cm⁻¹ was deposited. -2SEM image of sodium metal cross section.

[0043] Figure 5 SEM images of Comparative Example 3 and Example 4.

[0044] Figure 6 Comparative Examples 2, 4, and 4 were tested at 0.5 mA cm⁻¹ -2 Overpotential diagram under current density.

[0045] Figure 7 Comparative Examples 2, 4, and 4 were measured at 1 mA cm⁻¹ -2 Coulomb efficiency at current density. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0047] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0048] Example 1 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min.

[0049] (2) The 0.5 g hard carbon material from step (1) was wet-milled for 5 h with 20 g of ultrapure water in the solution and a rotation speed of 300 rpm to obtain small-particle-size hard carbon material, which was named HC-5.

[0050] (3) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0051] (4) Add SnF2, which accounts for 0.5% of the mass of NaPF6, to the electrolyte obtained in step (3) and stir evenly to obtain a gel electrolyte precursor solution.

[0052] (5) The HC-5 obtained in step (2) was placed in an 80 ℃ drying oven and dried for 4 h. Hard carbon material: conductive carbon black: polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 8:1:1, ground evenly, coated onto copper foil, and dried in an 80 ℃ vacuum drying oven for 12 h. It was then cut into circles with a diameter of 12 mm and a carbon material loading of 1.3 mg. 200 μL of the gel electrolyte precursor solution from step (4) was dropped onto the mixture of hard carbon material, conductive carbon black and polyvinylidene fluoride. The mixture was allowed to stand at room temperature for 7 days to polymerize and obtain the electrode sheet.

[0053] (6) Using electrochemical deposition, with a sodium sheet as the counter electrode, the electrode sheet from step (5) was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ pressure was applied to the electrode sheet obtained in step (5). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0054] (7) At 1mA cm -2 1mAh cm -2 The stability of the negative electrode's coulombic efficiency was tested under the following conditions: 0.5 mAcm. -2 Sodium affinity test was performed on the negative electrode at current density.

[0055] Example 2 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min.

[0056] (2) The 0.5 g hard carbon material from step (1) was wet-milled for 10 h with 20 g of ultrapure water in the solution and a rotation speed of 300 rpm to obtain small-particle-size hard carbon material, which was named HC-10.

[0057] (3) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0058] (4) Add SnF2, which accounts for 0.5% of the mass of NaPF6, to the electrolyte obtained in step (3) and stir evenly to obtain a gel electrolyte precursor solution.

[0059] (5) The HC-10 obtained in step (2) was placed in an 80 ℃ drying oven and dried for 4 h. Hard carbon material: conductive carbon black: polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 8:1:1, ground evenly, coated onto copper foil, and dried in an 80 ℃ vacuum drying oven for 12 h. The mixture was then cut into circles with a diameter of 12 mm and a carbon material loading of 1.3 mg. 200 μL of the gel electrolyte precursor solution from step (4) was dropped onto the mixture of hard carbon material, conductive carbon black and polyvinylidene fluoride. The mixture was allowed to stand at room temperature for 7 days to polymerize and obtain the electrode sheet.

[0060] (6) Using electrochemical deposition, with a sodium sheet as the counter electrode, the electrode sheet from step (5) was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ pressure was applied to the electrode sheet obtained in step (5). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0061] (7) At 1mA cm -2 1mAh cm -2 The stability of the negative electrode's coulombic efficiency was tested under the following conditions: 0.5 mAcm. -2 Sodium affinity test was performed on the negative electrode at current density.

[0062] Example 3 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min.

[0063] (2) The 0.5 g hard carbon material from step (1) was wet-milled for 15 h with 20 g of ultrapure water in the solution and a rotation speed of 300 rpm to obtain small-particle-size hard carbon material, which was named HC-15.

[0064] (3) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0065] (4) Add SnF2, which accounts for 0.5% of the mass of NaPF6, to the electrolyte obtained in step (3) and stir evenly to obtain a gel electrolyte precursor solution.

[0066] (5) The HC-15 obtained in step (2) was placed in an 80 ℃ drying oven and dried for 4 h. Hard carbon material: conductive carbon black: polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 8:1:1, ground evenly, coated onto copper foil, and dried in an 80 ℃ vacuum drying oven for 12 h. The mixture was then cut into circles with a diameter of 12 mm and a carbon material loading of 1.3 mg. 200 μL of the gel electrolyte precursor solution from step (4) was dropped onto the mixture of hard carbon material, conductive carbon black and polyvinylidene fluoride. The mixture was allowed to stand at room temperature for 7 days to polymerize and obtain the electrode sheet.

[0067] (6) Using electrochemical deposition, with a sodium sheet as the counter electrode, the electrode sheet from step (5) was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ pressure was applied to the electrode sheet obtained in step (5). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0068] (7) At 1mA cm -2 1mAh cm -2 The stability of the negative electrode's coulombic efficiency was tested under the following conditions: 0.5 mAcm. -2 Sodium affinity test was performed on the negative electrode at current density.

[0069] Example 4 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min.

[0070] (2) The 0.5 g hard carbon material from step (1) was wet-milled for 20 h with 20 g of ultrapure water in the solution and a speed of 300 rpm to obtain small-particle-size hard carbon material, which was named HC-20.

[0071] (3) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0072] (4) Add SnF2, which accounts for 0.5% of the mass of NaPF6, to the electrolyte obtained in step (3) and stir evenly to obtain a gel electrolyte precursor solution.

[0073] (5) The HC-20 obtained in step (2) was placed in an 80 ℃ drying oven and dried for 4 h. The hard carbon material, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1, ground evenly and coated onto copper foil. The mixture was then placed in an 80 ℃ vacuum drying oven and dried for 12 h. The mixture was cut into a circle with a diameter of 12 mm and a carbon material loading of 1.3 mg. 200 μL of the gel electrolyte precursor solution from step (4) was dropped onto the mixture of hard carbon material, conductive carbon black and polyvinylidene fluoride. The mixture was allowed to stand at room temperature for 7 days to polymerize and obtain the electrode sheet.

[0074] (6) Using electrochemical deposition, with a sodium sheet as the counter electrode, the electrode sheet from step (5) was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ pressure was applied to the electrode sheet obtained in step (5). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0075] (7) At 1mA cm -2 1mAh cm -2 The stability of the coulombic efficiency of the negative electrode was tested at 0.5 mAcm. -2 Sodium affinity test was performed on the negative electrode at current density.

[0076] Comparative Example 1 (1) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0077] (2) 200 μL of the electrolyte obtained in step (1) was added dropwise onto a circular copper foil with a diameter of 12 mm to obtain an electrode sheet. Using electrochemical deposition with a sodium sheet as the counter electrode, the electrode sheet was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ current was applied to the electrode sheet. -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode; (3) At 1 mA cm -2 1 mAh cm -2 The stability of the coulombic efficiency of the negative electrode was tested at 0.5 mA cm⁻¹. -2 Sodium affinity test was performed on the negative electrode at current density.

[0078] Comparative Example 2 (1) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0079] (2) SnF2, which accounts for 0.5% of NaPF6 by mass, is added to the above electrolyte and stirred evenly to obtain a gel electrolyte precursor solution.

[0080] (3) 200 μL of the gel electrolyte precursor solution obtained in step (2) was added dropwise onto a circular copper foil with a diameter of 12 mm, and allowed to stand at room temperature for 7 days to polymerize, resulting in an electrode sheet. Electrochemical deposition was used, with a sodium sheet as the counter electrode, and the electrode sheet was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ electrode was then applied to the electrode sheet. -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode. (4) At 1 mA cm⁻¹ -2 1 mAh cm -2 The stability of the coulombic efficiency of the negative electrode was tested at 0.5 mA cm⁻¹. -2 Sodium affinity test was performed on the negative electrode at current density.

[0081] Comparative Example 3 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min to obtain hard carbon material, which was named HC.

[0082] (2) Add NaPF6 to tetrahydrofuran at a concentration of 1 mol / L and stir until no solid residue remains to obtain an electrolyte solution.

[0083] (3) Add SnF2, which accounts for 0.5% of the mass of NaPF6, to the electrolyte obtained in step (2) and stir evenly to obtain a gel electrolyte precursor solution.

[0084] (4) The HC obtained in step (1) was placed in an 80 ℃ drying oven and dried for 4 h. Hard carbon material: conductive carbon black: polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 8:1:1, ground evenly, coated onto copper foil, and dried in an 80 ℃ vacuum drying oven for 12 h. The mixture was then cut into circles with a diameter of 12 mm and a carbon material loading of 1.3 mg. 200 μL of the gel electrolyte precursor solution from step (3) was dropped onto the mixture of hard carbon material, conductive carbon black and polyvinylidene fluoride. The mixture was allowed to stand at room temperature for 7 days to polymerize and obtain the electrode sheet.

[0085] (5) Using electrochemical deposition, with a sodium sheet as the counter electrode, the battery was assembled in an argon-protected glove box. A 0.1 mA cm⁻¹ current was applied to the electrode sheet obtained in step (4). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0086] (6) At 1mA cm -2 1mAh cm -2 The stability of the coulombic efficiency of the negative electrode was tested at 0.5 mAcm. -2 The negative electrode was subjected to sodium affinity testing at the current density.

[0087] Comparative Example 4 (1) 1 g of alkali lignin was pyrolyzed and carbonized at 1300 °C for 2 h under a nitrogen atmosphere and a gas flow rate of 50 mL / min at a heating rate of 5 °C / min.

[0088] (2) The 0.5 g hard carbon material from step (1) was wet-milled for 20 h with 20 g of ultrapure water at a speed of 300 rpm to obtain small-particle-size hard carbon material, which was named HC-20.

[0089] (3) The HC-20 obtained in step (2) was placed in an 80 ℃ drying oven and dried for 4 h. Hard carbon material: conductive carbon black: polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 8:1:1, ground evenly, coated onto copper foil, and dried in an 80 ℃ vacuum drying oven for 12 h. The mixture was then cut into circles with a diameter of 12 mm and a carbon material loading of 1.3 mg to obtain electrode sheets.

[0090] (4) Using electrochemical deposition, with a sodium sheet as the counter electrode, the electrode sheet from step (3) was assembled into a battery in an argon-protected glove box. A 0.1 mA cm⁻¹ pressure was applied to the electrode sheet obtained in step (3). -2 Current-induced electrochemical deposition of 0.5 mAh cm⁻¹ -2 Sodium metal is used to obtain the negative electrode.

[0091] (5) At 1mA cm -2 1mAh cm -2 The stability of the negative electrode's coulombic efficiency was tested under the following conditions: 0.5 mAcm. -2 Sodium affinity test was performed on the negative electrode at current density.

[0092] Figure 1 This is a schematic diagram of the sodium metal anode structure of the present invention, consisting of a gel electrolyte and a hard carbon material coated substrate. Hard carbon is coated onto copper or aluminum foil, a gel electrolyte precursor solution is added dropwise, and then 0.5 mAh / cm³ is electrochemically deposited. -2 Sodium metal was used as the negative electrode in sodium metal batteries. The gel electrolyte was prepared by in-situ polymerization, where the initiator, acting as a Lewis acid, interacted with the lone pair electrons in the polymer monomers, causing the carbon-oxygen bonds in the polymer monomers to break, thus initiating ring-opening polymerization. Then, at 0.5 mA cm⁻¹... -2 The sodium affinity of the sodium metal anode was tested at a current density of 1 mA cm⁻¹. -2 1 mAh cm -2 Stability tests of coulomb efficiency were conducted under the given conditions.

[0093] Figure 2 The diagrams show the overpotentials of Comparative Example 1 and Comparative Example 2. Figure 2 As shown, the sodium metal anode with added gel electrolyte precursor solution exhibits excellent interfacial ion transport kinetics, with nucleation and growth overpotentials of 32.2 mV and 27.1 mV, respectively, both of which are smaller than those of the sodium metal anode with added electrolyte.

[0094] Figure 3 Comparative Example 1 and Comparative Example 2 were shown at 1 mA cm⁻¹ -2 Coulombic efficiency at current density. As shown in the figure, the sodium metal anode with the added gel electrolyte precursor solution exhibits superior cycle life, maintaining a stable coulombic efficiency even after approximately 60 cycles. This is attributed to the mechanical properties of the gel electrolyte effectively suppressing dendrite formation and preventing short circuits. Simultaneously, the initiator facilitates the formation of a faster-migrating SEI layer on the anode, further inhibiting sodium dendrite growth.

[0095] Figure 4 For Comparative Examples 1, 2 and 4, 1 mA cm⁻¹ was deposited. -2SEM images of the sodium metal deposition cross-section. Observing the sodium deposition phenomenon through SEM images, under the same sodium metal deposition amount, the sodium metal deposition in Comparative Example 1 is loose and prone to dendrite formation. This is because the ion migration in the electrolyte is slower, resulting in a coarser SEI structure, making sodium dendrite formation easier. The sodium deposition in Comparative Example 2 shows less volume expansion and a more compact structure. In contrast, the sodium metal anode coated with small-particle-size hard carbon exhibits the smallest volume expansion.

[0096] Figure 5 The images show SEM images of Comparative Example 3 and Example 4. The SEM images show that Example 4, after ball milling, has a smaller particle size.

[0097] Figure 6 Comparative Examples 2, 4, and 4 were tested at 0.5 mA cm⁻¹ -2 Overpotential diagram at current density. Reducing particle size facilitates ion diffusion, and small-particle-size, uniform hard carbon promotes uniform sodium metal deposition. Initiator-induced SEI can lower the nucleation and growth overpotential of sodium metal. Copper foil has a relatively rough surface and exhibits significant sodium-repellent properties; therefore, this invention prepares a sodium-loving material to further reduce the growth and nucleation overpotential of sodium metal, inhibiting the formation of sodium dendrites. Figure 6 As shown, at a current of 0.5 mA cm -2 Compared with Comparative Examples 2 and 4, Example 4 has a lower nucleation overpotential for growth, which is due to the combined effect of the gel electrolyte and the small-sized hard carbon.

[0098] Figure 7 Comparative Examples 2, 4, and 4 were measured at 1 mA cm⁻¹ -2 Coulombic efficiency at current density. The cycle life of Example 4 is longer than that of the comparative example, indicating that the reduced hard carbon particle size facilitates sodium ion diffusion and inhibits sodium dendrite formation. Simultaneously, the mechanical properties of the gel electrolyte effectively prevent battery failure.

[0099] Table 1 shows the hard carbon materials prepared in the above embodiments in terms of d 002 d 100 and L a / L c Comparisons in various aspects, such as...

[0100] Table 1. Parameters of hard carbon materials prepared in the examples and comparative examples.

[0101] Table 2 compares the above-described embodiments and comparative examples in terms of nucleation overpotential, growth overpotential, and cycle life. The overpotential was tested under the condition of 0.5 mA cm⁻¹. -2 The test conditions for current density, cycle life, and CE are 1 mA cm⁻¹. -2Current density, 1 mAh cm -2 .

[0102] Table 2. Negative electrode performance of the examples and comparative examples

[0103] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly stable sodium metal anode based on a gel electrolyte, characterized in that, Includes the following steps: (1) Mix the sodium salt, tetrahydrofuran and initiator evenly to obtain a gel electrolyte precursor solution; (2) The lignin was carbonized in an inert gas atmosphere and then wet-milled to obtain hard carbon material; (3) After mixing the hard carbon material, conductive material and binder from step (2), the mixture is coated onto a metal foil. After drying, the gel electrolyte precursor solution from step (1) is added dropwise, polymerized at room temperature, and finally deposited with metallic sodium to obtain a highly stable sodium metal anode based on gel electrolyte.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the hard carbon material, conductive material, and binder in step (3) is (7-8):(1-2):1; And / or, the ratio of the mass of the hard carbon material to the coating area of ​​the metal foil in step (3) is (1-1.5) mg : (1-1.2) cm. 2 ; And / or, the mass ratio of the hard carbon material in step (3) to the volume of the gel electrolyte precursor solution is 1.3 mg: (190-210) μL; And / or, the amount of sodium metal deposited in step (3) is 0.4–0.6 mAh cm⁻¹. -2 .

3. The preparation method according to claim 1 or 2, characterized in that, The concentration of the sodium salt in tetrahydrofuran in step (1) is 0.1–3 mol / L; And / or, the sodium salt in step (1) includes at least one of NaPF6, NaBF4, NaClO4, NaTFSI and NaFSI.

4. The preparation method according to claim 1 or 2, characterized in that, The carbonization temperature in step (2) is 1100–1600 °C, and the time is 2–8 h; more preferably, it is 1100–1300 °C, and the carbonization time is 2–6 h. And / or, the heating rate of carbonization in step (2) is 2 to 10 °C / min; And / or, the lignin in step (2) includes at least one of enzymatically hydrolyzed lignin, alkali lignin, lignin sulfonate and solvent-based lignin; And / or, the inert gas in step (2) includes at least one of nitrogen, argon and helium; And / or, the flow rate of the inert gas in step (2) is 40–80 mL / min. -1 .

5. The preparation method according to claim 1 or 2, characterized in that, The wet ball milling in step (2) specifically involves mixing the carbonized product with a solvent at a mass ratio of 1:(30-50) and ball milling at 300-600 rpm for 0.2-24 h. The solvent includes at least one of water and acetone.

6. The preparation method according to claim 1 or 2, characterized in that, The time for room temperature polymerization in step (3) is 1 hour to 7 days; the room temperature range is 15 to 40°C. And / or, the process for depositing sodium metal in step (3) is electrochemical deposition.

7. The preparation method according to claim 1 or 2, characterized in that, The conductive material in step (3) includes at least one of conductive carbon black and acetylene black; And / or, the adhesive in step (3) includes at least one of polyvinylidene fluoride and polyacrylic acid; And / or, the metal foil in step (3) includes at least one of copper foil and aluminum foil.

8. The preparation method according to claim 1 or 2, characterized in that, The initiator in step (1) includes at least one of SnF2, BF3, PF5, Al(OfT)3 and Sn(OfT)2; And / or, the initiator in step (1) accounts for 0.5 to 10% of the sodium salt mass.

9. A highly stable sodium metal anode based on a gel electrolyte obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the highly stable sodium metal anode based on gel electrolyte as described in claim 9 in sodium metal batteries.

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