Sodium-sulfur battery

Abstract

The invention belongs to the technical field of sodium-sulfur batteries, and provides a sodium-sulfur battery, an electrolyte of the sodium-sulfur battery comprises cyanogen-containing sodium salt and chlorine-containing Lewis acid, and a positive electrode is mainly composed of a positive electrode current collector and an elemental sulfur-containing conductive coating on the surface of the positive electrode current collector, or is directly composed of an elemental sulfur-containing material. The battery is based on a high-valence S / SCl4 positive electrode chemical reaction, the cyanamide anions in the electrolyte play an important role in unlocking the S / SCl4 positive electrode chemical reaction and improving the sodium deposition / stripping reversibility of the negative electrode, the limitation of the room-temperature sodium-sulfur battery on the discharge voltage, the energy density and the rate capability is overcome, and the battery has excellent electrochemical performance and practicability. According to the invention, a sodium-sulfur battery which is dominated by S0 / S2-positive electrode chemistry and excessive sodium metal negative electrode at present is remodeled, and a new way of a low-cost, sustainable and high-performance energy storage solution is opened up.

Description

Technical Field

[0001] This invention belongs to the field of sodium-sulfur battery technology, and relates to a sodium-sulfur battery based on a high-valence S / SCl4 cathode chemical reaction, specifically involving a 32-electron conversion reaction between S8 and SCl4. It can be applied to the field of energy storage. Background Technology

[0002] Compared to traditional lithium (Li) batteries, room-temperature sodium-sulfur (Na-S) batteries have high element abundance, lower material costs, and higher theoretical specific capacity, providing a promising solution for large-scale grid energy storage.

[0003] However, the practical application of conventional room-temperature sodium-sulfur batteries is severely limited by their low discharge voltage and the need for an excess of sodium metal anode.

[0004] For example, the discharge voltage of conventional room-temperature sodium-sulfur batteries is generally below 1.6 V, which is significantly lower than the voltage achievable by the cathodes of current lithium and sodium batteries. Furthermore, the anode uses a large amount of sodium metal, typically tens of times more than in conventional sodium batteries, which greatly reduces cost-effectiveness and safety, while also affecting the battery's actual energy density and power density. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a sodium-sulfur battery based on a high-valence S / SCl4 cathode chemical reaction. This battery utilizes the cyanamide anion in the electrolyte to play a crucial role in unlocking the S / SCl4 cathode chemistry and improving the reversibility of sodium deposition / stripping at the anode. This overcomes the limitations of room-temperature sodium-sulfur batteries in discharge voltage, energy density, and rate capability, exhibiting excellent electrochemical performance and practicality. The present invention reshapes the current technology based on S... 0 / S 2- Sodium-sulfur batteries, dominated by cathode chemistry and excess sodium metal anodes, open up new avenues for low-cost, sustainable, and high-performance energy storage solutions.

[0006] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0007] In one aspect, the present invention provides a sodium-sulfur battery, wherein the electrolyte comprises sodium cyanide salt and chloro Lewis acid, and the positive electrode is mainly composed of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface, or is directly composed of elemental sulfur material.

[0008] In this document, the sodium salt containing cyanide is a sodium salt having a cyanide ion (-C≡N); generally, the sodium salt containing cyanide is selected from commercially available or known compounds that can be synthesized based on existing technical literature, such as, but not limited to, sodium dicyandiamide and sodium cyanide; further based on experimental evidence, sodium dicyandiamide is the most preferred.

[0009] The chemical formula of sodium dicyandiamide (NaDCA) is C2N3Na, CAS: 1934-75-4;

[0010] The sodium cyanide has the chemical formula CNNa and CAS number 143-33-9.

[0011] In this document, the chlorinated Lewis acid refers to a Lewis acid containing chloride ions, which is a conventional electrolyte salt choice in the battery field. Those skilled in the art can select a suitable chlorinated Lewis acid based on the Lewis acids described in the prior art.

[0012] To better illustrate the present invention and provide a technical solution for reference, the chlorinated Lewis acid is selected from at least one of aluminum trichloride, gallium trichloride, ferric chloride, and zinc chloride.

[0013] In this document, the electrolytes include sodium cyanide salts and chloro Lewis acids. The electrolyte may consist of sodium cyanide salts and chloro Lewis acids, or it may consist of sodium cyanide salts, chloro Lewis acids, and other conventional electrolytes. However, it should be noted that sodium cyanide salts are the primary electrolyte component in this document.

[0014] In this article, the sodium-sulfur battery can be a liquid sodium-sulfur battery or a solid sodium-sulfur battery.

[0015] The liquid sodium-sulfur battery is a sodium-sulfur battery that uses a liquid electrolyte. The liquid electrolyte is mainly composed of sodium salt containing cyanide and Lewis acid containing chlorine dissolved in a solvent. The solvent can be a conventional electrolyte solvent, preferably a chlorine-based electrolyte solvent.

[0016] To better illustrate the present invention and provide a technical solution for reference, the solvent preferably includes either thionyl chloride (SOCl2) or sulfonyl chloride (SO2Cl2); more preferably, the solvent is thionyl chloride.

[0017] Preferably, the liquid electrolyte further includes other conventional electrolyte additives or those inherent in conventional commercial chlorine-based electrolyte compositions, especially functional additives, which can be selected and added according to the required functional needs by those skilled in the art. It should be emphasized that the liquid electrolyte in the present invention may or may not contain other conventional electrolyte additives.

[0018] It should be noted that the solubility of sodium cyanide salts (especially sodium dicyandiamide) in solvents usually varies with the molar concentration of chloro Lewis acids. Without the addition of chloro Lewis acids, sodium cyanide salts are difficult to dissolve in solvents under normal conditions. Therefore, chloro Lewis acids are necessary electrolytes.

[0019] Typically, the molar concentration of the chloro Lewis acid in the liquid electrolyte can be referenced to the conventional addition amount of Lewis acid in liquid batteries as described in the prior art, and the sodium cyanide salt is preferably 80 to 100% of the solubility saturation in the solvent.

[0020] To better illustrate the present invention and provide a preferred technical solution for reference, the molar concentration of the chloro Lewis acid in the solvent is 2-10 mol / L, and the sodium cyanide salt, based on its solubility saturation in the solvent, is preferably 80-100% of its solubility saturation. In some embodiments, when the chloro Lewis acid is aluminum trichloride and the sodium cyanide salt is sodium dicyanamide, the molar ratio of aluminum trichloride to sodium dicyanamide can be selected as 2:1.2, 4:2.3, 8:4.5, or 10:5.7, etc.

[0021] The solid-state sodium-sulfur battery is a sodium-sulfur battery that uses a solid electrolyte. The solid electrolyte is mainly composed of sodium salt containing cyanide and Lewis acid containing chloride as electrolytes dissolved in a solvent, and then combined with solid or colloidal small molecule polymer materials. The solid or colloidal small molecule polymer materials are selected in accordance with conventional solid-state batteries.

[0022] To better illustrate the present invention and provide a preferred technical solution for reference, the solid or colloidal small molecule polymer material is selected to include 3,3-bis(chloromethyl)oxetane. The ratio of the sodium cyanide salt, the chloro Lewis acid, the solvent, and the solid or colloidal small molecule polymer material can refer to that of conventional solid-state batteries. For example, after preparing the liquid electrolyte as described above, the solid or colloidal small molecule polymer material can be added to the liquid electrolyte and mixed evenly to obtain a solid electrolyte; the volume ratio of the liquid electrolyte to the solid or colloidal small molecule polymer material is (2~10):1.

[0023] In this document, the sodium-sulfur battery, based on the common knowledge of sodium metal batteries or sodium-ion batteries in the prior art, also includes a negative electrode and / or a negative electrode current collector, and the material selection, material ratio, and preparation process of the negative electrode and / or negative electrode current collector all follow the conventional sodium metal battery or sodium-ion battery process. Preferably, it refers to a sodium metal battery without a negative electrode that only uses a negative electrode current collector. Those skilled in the art can select a suitable process to prepare a sodium-sulfur battery based on the conventional preparation process of sodium metal batteries or sodium-ion batteries or the required battery type.

[0024] To better illustrate the present invention, and to provide an example of the sodium-sulfur battery provided by the present invention, specifically, the sodium-sulfur battery is mainly composed of a positive electrode, the above-mentioned liquid electrolyte or the above-mentioned solid electrolyte, and a negative electrode and / or a negative electrode current collector;

[0025] The positive electrode is a component commonly known in batteries. The positive electrode used in this invention can be a conventional sulfur-based battery positive electrode, or the positive electrode described in this invention: the positive electrode mainly consists of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface, or it can be directly composed of elemental sulfur-containing materials. Specifically, the positive electrode mainly consists of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface. The conductive coating containing elemental sulfur is formed by mixing and coating the surface of the positive electrode current collector with carbon-based materials for conductive coating, sulfur powder, and a binder as raw material components; or, the positive electrode is directly composed of elemental sulfur-containing materials, which is formed by mixing and curing carbon-based materials for conductive coating, sulfur powder, and a binder as raw material components to create the positive electrode.

[0026] Furthermore, the carbon-based material used for the conductive coating is selected from at least one of Ketjen black, graphite, conductive carbon black, carbon nanotubes, hard carbon, activated carbon, and metal-organic framework materials (such as UiO-66).

[0027] The binder is selected from any one of aqueous binders and non-aqueous binders; the aqueous binder is a conventional aqueous binder described in the prior art that is suitable for use in battery positive electrodes, and uses water as the main solvent during use, such as any one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), sodium alginate, polyacrylic acid, polyacrylates (such as LA133), natural polymers (such as chitosan, starch, etc.), and conductive polymers (such as PEDOT:PSS); the non-aqueous binder is a conventional non-aqueous binder described in the prior art that is suitable for use in battery positive electrodes, and uses conventional organic reagents (such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), tetrahydrofuran (THF), acetone, cyclohexanone, chloroform, dichloromethane, ethyl acetate) as the main solvent during use, such as any one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyurethane (PU), and epoxy resin;

[0028] The positive current collector can be selected from any one of the following: nickel foil, nickel foam, stainless steel foil, aluminum foil, carbon-coated aluminum foil, aluminum foam, titanium foil, carbon-based materials, and metal-organic polymer composites.

[0029] Typically, the mass percentage of elemental sulfur (sulfur powder) in the conductive coating and material containing elemental sulfur can be referenced to the cathode material ratio of conventional sulfur-based batteries. To better illustrate the invention and provide a preferred technical solution for reference, the mass percentage of elemental sulfur in the conductive coating and material containing elemental sulfur is 30-60 wt%. The remaining components, including the carbon-based material for the conductive coating and the binder, follow the specifications for cathode preparation in conventional sulfur-based batteries.

[0030] In one preferred embodiment, the elemental sulfur-containing conductive coating is formed by coating the surface of the positive electrode current collector with a mixture of carbon-based materials for conductive coating, sulfur powder, and a binder as raw material components; wherein, the raw material components further include a bismuth-coordinated covalent organic framework (Bi-COF) catalyst, which is disclosed in a prior paper (S. Zheng, Z. Ouyang, M. Liu, S. Bi, G. Liu, X. Li, Q. Xu, G. Zeng. Carbon Neutralization 3, 415–422 (2024).). Specifically, the preparation method of the bismuth-coordinated covalent organic framework catalyst mainly includes the following steps:

[0031] 25.0 mg of tetraaldehyde compound, 15.2 mg of triaminopyridine, 1 mL of o-dichlorobenzene and 0.1 mL of 6 M acetic acid aqueous solution were mixed evenly in a reaction vessel and then frozen at -196.15 °C. The mixture was then degassed under vacuum three times. The reaction vessel was then sealed and heated at 120 °C for 72 hours. The collected product was washed sequentially with tetrahydrofuran, N,N-dimethylacetamide and methanol, and then transferred to a Soxhlet extractor for overnight extraction. Finally, the product was vacuum dried for 6 hours to obtain COF.

[0032] Add 50 mg of COF to a 50 mg / 50 mL Bi(NO3)3 methanol solution and reflux with stirring for at least 12 h to ensure sufficient adsorption of Bi3. + The precipitate was washed three times with ethanol and then extracted with tetrahydrofuran by Soxhlet extraction for 24 hours to remove impurities, thus obtaining the bismuth coordination covalent organic framework catalyst.

[0033] The amount of the bismuth-coordinated covalent organic framework catalyst added is 5-20 wt% of the sulfur powder.

[0034] Similarly, in the positive electrode comprising carbon-based material for conductive coating, sulfur powder and binder as raw material components mixed, molded and cured, the raw material components also include bismuth-coordinated covalent organic framework catalyst.

[0035] The negative electrode and / or negative electrode current collector are components commonly known in batteries. In sodium-sulfur batteries without a negative electrode, only the negative electrode current collector is used. Both the negative electrode and / or the negative electrode current collector can be obtained commercially or prepared according to existing technical literature and conventional processes for sodium metal batteries or sodium-ion batteries. For example, the negative electrode can be made directly from elemental sodium metal, or it can be made directly from conventional carbon-containing materials or alloys. Another example is that the negative electrode is formed by loading sodium foil onto the surface of the negative electrode current collector.

[0036] Furthermore, the negative electrode current collector can be selected from any one of nickel foil, nickel foam, stainless steel foil, aluminum foil, carbon-coated aluminum foil, aluminum foam, titanium foil, carbon-based materials, and metal-organic polymer composites;

[0037] The process of loading the sodium foil onto the surface of the negative electrode current collector includes any one of direct rolling, electrochemical deposition, mechanical coating, and melt impregnation.

[0038] Based on common knowledge about batteries in the prior art, the sodium-sulfur battery may also include conventional negative electrode shell, gasket, spring sheet, separator for loading electrolyte, positive electrode shell and other conventional structures / components / parts. Those skilled in the art can select a suitable process to prepare the sodium-sulfur battery based on the conventional preparation process of sodium metal battery or sodium ion battery or the required battery type.

[0039] Furthermore, based on common knowledge in the prior art regarding sodium metal batteries or sodium-ion batteries, in the sodium-sulfur battery, in addition to the technical content already described above, the specifications and assembly ratios of the positive electrode, liquid electrolyte or solid electrolyte, negative electrode and / or negative electrode current collector all follow conventional sodium metal battery or sodium-ion battery processes. Those skilled in the art can select a suitable process based on the conventional preparation process of sodium metal batteries or sodium-ion batteries or the required battery model to prepare the sodium-sulfur battery product. Attached Figure Description

[0040] Figure 1This is a summary of the positive electrode chemistry results for verifying the reversible S / SCl4 conversion based on the battery provided in Example 1 of this invention. Figure a shows the SK edge XAS spectra of the S positive electrode in the negative electrode-free sodium-sulfur battery of Example 1 under charging (400 and 800 mAh / g) and fully discharged states. Figure b shows the in-situ Raman spectrum of the S positive electrode in the first cycle of the negative electrode-free sodium-sulfur battery using NaDCA electrolyte (Example 1). Figure c shows the initial constant current charging curves and corresponding Raman spectra of the S positive electrode in the negative electrode-free sodium-sulfur batteries using NaDCA electrolyte (Example 1) and NaCl electrolyte (Comparative Example 1). Figure d shows the S 2p XPS spectra of the S positive electrode of Example 1 after preparation, under charging (800 mAh / g) and fully discharged states; the charging capacity and current density are both 800 mAh / g (1.92 mAh / cm²). 2 ) and 500 mA / g (1.20 mA / cm 2 Figures e and f show the SCl3 from the positive electrode under different charge and discharge states of the battery in Example 1. + The extracted ion chromatogram and the corresponding mass spectrum obtained by GC-HRMS in positive ion mode; the retention time was 7.19 minutes, and the charging capacity and current density were both 800 mAh / g (0.83 mAh / cm³). 2 ) and 500 mA / g (0.52 mA / cm 2 Figure g shows the differential charge density distribution of S-adsorbed graphene cathodes in NaDCA electrolyte (Example 1) and NaCl electrolyte (Comparative Example 1) calculated using density functional theory (DFT); blue and yellow represent the charge dissipation and accumulation regions, respectively, and the isosurface value used in the differential charge density plot is 0.01 e / Å. 3 Figure h shows the Gibbs free energy changes of S oxidation in NaDCA electrolyte (Example 1) and NaCl electrolyte (Comparative Example 1) based on DFT calculations.

[0041] Figure 2 This is a summary graph of the deposition / stripping reversibility and kinetic results of Na metal in NaDCA electrolyte, based on the battery provided in Verification Example 1. Figure a shows the Na–Al battery (Verification Example 1) using NaDCA and NaCl electrolytes at 1 mA / cm². 2 and 1 mAh / cm 2 The cycling performance is shown in the figure; the inset illustrates the Na–Al battery. Figure b shows the galvanostatic charge-discharge curves of the Na–Al battery using NaDCA electrolyte and NaCl electrolyte; the current density and deposition capacity are 1 mA / cm². 2 and 1mAh / cm 2Figures c and d show the NaCN produced by deposited Na aluminum foil in NaDCA and NaCl electrolytes, obtained by TOF-SIMS. – Na3N – and NaCl – In-depth analysis of secondary ion fragments; visualization area is 70 × 70 μm. 2 The current density and charging capacity are 1 mA / cm². 2 and 1 mAh / cm 2 Figure e shows the depth profile of the N 1s, C 1s, and Cl 2p XPS spectra of Na deposited on aluminum foil using NaDCA electrolyte. Figure f shows in-situ optical images of Na deposition on aluminum foil in Na–Al cells using NaDCA and NaCl electrolytes; the current density and deposition capacity are 1 mA / cm². 2 and 1 mAh / cm 2 The scale bar is 500 µm. Figure g shows a Na–Al battery using NaDCA electrolyte at current densities from 10 mA / cm². 2 Increased to 60 mA / cm 2 The constant current charge-discharge curve under these conditions shows a deposition capacity of 1 mAh / cm³. 2 Figure h shows a Na–Al battery using NaDCA electrolyte at a current density of 2 mA / cm². 2 In this case, the surface capacity is from 5 mAh / cm² 2 Increased to 12 mAh / cm 2 The constant current charge-discharge curves are shown in Figure i. Figure i compares the maximum areal capacity and current density of the Na-Al battery provided in Verification Example 1 with those of previously reported excellent Na-Al batteries.

[0042] Figure 3 This is a summary graph of the electrochemical performance of the battery provided in Example 1 of this invention. Figure a shows the linear sweep voltage characteristics of the Na–Ni battery (Verification Example 2) using NaDCA and NaCl electrolytes at a scan rate of 1.0 mV / s; nickel foil is used as the working electrode, and sodium metal foil serves as both the reference and counter electrode. Figure b shows the constant current charge-discharge curves of a negative electrode-free sodium-sulfur battery in AlCl3 / SOCl2 electrolyte incorporating 4.5 M NaDCA (Example 1) or NaCl (Comparative Example 1); the sulfur loading is 1.04 mg / cm³. 2 The charging capacity and current density shown in this figure are 800 mAh / g (0.83 mAh / cm³). 2 ) and 500 mA / g (0.52 mA / cm 2Figure c shows the constant current charge-discharge curves of the battery provided in Example 1, comparing the presence and absence of sulfur (S) at the positive electrode. Figure d shows the constant current charge-discharge curves of the battery of Example 1 using NaDCA electrolyte, with charging capacity starting from 800 mAh / g (0.83 mAh / cm³). 2 Gradually increase to 1,500 mAh / g (1.56 mAh / cm³). 2 Figure e shows a comparison of the rate performance of the electrodeless sodium-sulfur batteries provided in Example 1 and Comparative Example 1 using NaDCA and NaCl electrolytes. Figure f shows a comparison of the cycle performance of the electrodeless sodium-sulfur batteries in Example 1 and Comparative Example 1 using NaDCA and NaCl electrolytes; the batteries initially cycled at 1000 mA / g (1.04 mA / cm). 2 ) and 200 mAh / g (0.21 mAh / cm 2 Ten charge-discharge cycles were performed at a discharge cutoff voltage of 2.0 V for activation. Figure g shows the charging capacity of 200 mAh / g (0.21 mAh / cm³) at different temperatures (from 80 °C to -40 °C). 2 Example 1: Discharge capacity of a sodium-sulfur battery without a negative electrode; current density at 80 °C, 50 °C, 25 °C, and 0 °C is 500 mA / g (0.52 mA / cm²). 2 The concentrations were 250 mA / g (0.26 mA / cm) at -20 °C and -40 °C, respectively. 2 ) and 125 mA / g (0.13 mA / cm 2 Figure 1 shows typical constant current discharge curves at 80 °C, 0 °C, and -40 °C. Figure 2 shows a comparison of the constant current charge-discharge curves of the electrodeless sodium-sulfur batteries using S and Bi-COF / S cathodes in Examples 1 and 3 at a current density of 500 mA / g.

[0043] Figure 4 This is a summary of the electrochemical performance of the anode-free sodium-sulfur battery based on the Bi-COF / S cathode provided in Examples 3 and 4 of this invention. Figures a and b show the structural model of Bi-COF and the Pawley-refined XRD pattern of the catalyst powder, respectively. Figure c shows the electrolyte / sulfur ratio (E / S = 5.0 μL / mg) in Example 4. sulfur Under the following conditions, the representative galvanostatic charge-discharge curves of a cathode-based sodium-sulfur battery without an anode are obtained; the sulfur areal density of this cathode is 2.4 mg / cm³. 2 The charging capacity and current density are 800 mAh / g (1.92 mAh / cm³). 2 ) and 2 A / g (4.80 mA / cm 2Based on the total mass including electrolyte, positive and negative electrode active and inactive materials, the battery's electrode-level energy density and power density reach 226 Wh / kg and 694 W / kg, respectively.

[0044] Figure 5 This is a summary diagram demonstrating the practicality of the sodium-sulfur battery of the present invention. Figure a shows a comparison of the flammability tests of the organic electrolyte and the NaDCA electrolyte in Comparative Example 2; the scale bar is 3 cm. Figure b shows the 108 mAh negative electrode-free sodium-sulfur soft-pack battery provided in Example 4 at 1200 mA / g (2.40 mA / cm²). 2 The figures show a comparison of cycle performance under different current densities; the inset shows photos of the high-voltage, electrodeless sodium-sulfur pouch battery before and after cutting, with the scale bar at 5 cm. Figure c shows the temperature and voltage changes of the electrodeless sodium-sulfur pouch battery provided in Example 4 and the electrodeless sodium-sulfur pouch battery provided in Comparative Example 3 during the puncture test; the inset shows the temperature distribution at the puncture site (marked by a white circle), with the scale bar at 3 cm. Figures d and e show photographs and constant current charge-discharge curves of the 1.06 Ah electrodeless sodium-sulfur battery provided in Example 5; the charging capacity is 1.12 Ah, and the current density is 0.5 A / g (1.20 mA / cm²). 2 Figure f is a schematic diagram illustrating sulfur resource development, negative electrode-free sodium-sulfur battery production, and renewable energy storage applications based on the battery of Example 5. Figure g shows the battery of Example 5 and a state-of-the-art rechargeable battery (HC, NVP, PBA, and NFM are hard carbon, Na3V2(PO4)3, Na2MnFe(CN)6, and NaNi, respectively). 1 / 3 Fe 1 / 3 Mn 1 / 3 Comparison of unit prices (O2). Figure h shows the constant current charge-discharge curves of the fibrous, electrodeless sodium-sulfur battery of Example 6 at a current density of 500 mA / g. The inset shows a schematic diagram of the structure of the fibrous, electrodeless sodium-sulfur battery. Figure i is a photograph of the fibrous, electrodeless sodium-sulfur battery of Example 6 and an energy storage textile woven from polyester fibers. The scale bar is 2 cm.

[0045] Figure 6 This is a constant current charge-discharge curve of a sodium-sulfur button cell using a hard carbon negative electrode in Example 7 of the present invention. The charging capacity is 200 mAh / g, and the current density is 0.5 A / g.

[0046] Figure 7 This is a constant current charge-discharge curve of a sodium-sulfur button cell using a silicon-carbon anode in Example 8 of the present invention. The charging capacity is 200 mAh / g, and the current density is 0.5 A / g.

[0047] Figure 8This is a constant current charge-discharge curve of the negative electrode-free sodium-sulfur button gel solid-state battery provided in Example 9 of the present invention. The charging capacity is 800 mAh / g, and the current density is 0.5 A / g.

[0048] Figure 9 The figures show the constant current charge-discharge curves of the batteries provided in Examples 1, 10-13 of this invention under different electrolyte molar concentrations. The charging capacity is 800 mAh / g, and the current density is 0.5 A / g. Detailed Implementation

[0049] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0050] In one aspect, the present invention provides a sodium-sulfur battery, wherein the electrolyte comprises sodium cyanide salt and chloro Lewis acid, and the positive electrode is mainly composed of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface, or is directly composed of elemental sulfur material.

[0051] In this document, the sodium salt containing cyanide is a sodium salt having a cyanide ion (-C≡N); generally, the sodium salt containing cyanide is selected from commercially available or known compounds that can be synthesized based on existing technical literature, in one embodiment, for example including but not limited to sodium dicyandiamide and sodium cyanide; further based on experimental evidence, sodium dicyandiamide is the most preferred.

[0052] The chemical formula of sodium dicyandiamide (NaDCA) is C2N3Na, CAS: 1934-75-4;

[0053] The sodium cyanide has the chemical formula CNNa and CAS number 143-33-9.

[0054] In this document, the chlorinated Lewis acid refers to a Lewis acid containing chloride ions, which is a conventional electrolyte salt choice in the battery field. Those skilled in the art can select a suitable chlorinated Lewis acid based on the Lewis acids described in the prior art.

[0055] To better illustrate the present invention and to provide an embodiment for reference, the chlorinated Lewis acid is selected from at least one of aluminum trichloride, gallium trichloride, ferric chloride, and zinc chloride.

[0056] In this document, the electrolyte comprises a sodium cyanide salt and a chloro Lewis acid. The electrolyte may be composed of a sodium cyanide salt and a chloro Lewis acid. In one embodiment, the electrolyte may also be composed of a sodium cyanide salt, a chloro Lewis acid, and other conventional electrolytes. However, it should be noted that the sodium cyanide salt is the primary electrolyte component in this document.

[0057] In this article, the sodium-sulfur battery can be a liquid sodium-sulfur battery or a solid sodium-sulfur battery.

[0058] The liquid sodium-sulfur battery is a sodium-sulfur battery that uses a liquid electrolyte. The liquid electrolyte is mainly composed of sodium salt containing cyanide and Lewis acid containing chlorine dissolved in a solvent. In one embodiment, the solvent can be a conventional electrolyte solvent, preferably a chlorine-based electrolyte solvent.

[0059] To better illustrate the present invention and to provide an embodiment for reference, the solvent preferably includes either thionyl chloride (SOCl2) or sulfonyl chloride (SO2Cl2); more preferably, the solvent is thionyl chloride.

[0060] Preferably, the liquid electrolyte further includes other conventional electrolyte additives or those inherent in conventional commercial chlorine-based electrolyte compositions, especially functional additives, which can be selected and added according to the required functional needs by those skilled in the art. It should be emphasized that the liquid electrolyte in the present invention may or may not contain other conventional electrolyte additives.

[0061] It should be noted that the solubility of sodium cyanide salts (especially sodium dicyandiamide) in solvents usually varies with the molar concentration of chloro Lewis acids. Without the addition of chloro Lewis acids, sodium cyanide salts are difficult to dissolve in solvents under normal conditions. Therefore, chloro Lewis acids are necessary electrolytes.

[0062] Typically, the molar concentration of the chloro Lewis acid in the liquid electrolyte can be referenced to the conventional addition amount of Lewis acid in liquid batteries as described in the prior art. In one embodiment, the sodium cyanide salt is preferably 80-100% of the solubility saturation in the solvent, for example, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any range or point value between them.

[0063] To better illustrate the present invention and provide a preferred embodiment for reference, the molar concentration of the chloro Lewis acid in the liquid electrolyte is 2~10 mol / L, for example 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L, 10 mol / L, or any range or point value between them; the sodium cyanide salt, based on its solubility saturation in the solvent, is preferably 80~100% of its solubility saturation. In some embodiments, when the chloro Lewis acid is aluminum trichloride and the cyanide sodium salt is sodium dicyandiamide, the molar ratio of aluminum trichloride to sodium dicyandiamide may include 2:1.2, 4:2.3, 8:4.5 or 10:5.7, etc.

[0064] The solid-state sodium-sulfur battery is a sodium-sulfur battery that uses a solid electrolyte. The solid electrolyte is mainly composed of sodium salt containing cyanide and Lewis acid containing chloride as electrolytes dissolved in a solvent, and then combined with solid or colloidal small molecule polymer materials. The solid or colloidal small molecule polymer materials are selected in accordance with conventional solid-state batteries.

[0065] To better illustrate the present invention and provide a preferred embodiment for reference, the solid or colloidal small molecule polymer material is selected to include 3,3-bis(chloromethyl)oxetane. The ratio of the sodium cyanide salt, the chloro Lewis acid, the solvent, and the solid or colloidal small molecule polymer material can be referenced to that of a conventional solid-state battery. In one embodiment, after preparing the liquid electrolyte as described above, the solid or colloidal small molecule polymer material is added to the liquid electrolyte and mixed evenly to obtain a solid electrolyte; the volume ratio of the liquid electrolyte to the solid or colloidal small molecule polymer material is (2~10):1, for example 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any range or value between them.

[0066] In this document, the sodium-sulfur battery, based on the common knowledge of sodium metal batteries or sodium-ion batteries in the prior art, also includes a negative electrode and / or a negative electrode current collector, and the material selection, material ratio, and preparation process of the negative electrode and / or negative electrode current collector all follow the conventional sodium metal battery or sodium-ion battery process. Preferably, it refers to a sodium metal battery without a negative electrode that only uses a negative electrode current collector. Those skilled in the art can select a suitable process to prepare a sodium-sulfur battery based on the conventional preparation process of sodium metal batteries or sodium-ion batteries or the required battery type.

[0067] To better illustrate the present invention, and to provide an example of the sodium-sulfur battery provided by the present invention, specifically, the sodium-sulfur battery is mainly composed of a positive electrode, the above-mentioned liquid electrolyte or the above-mentioned solid electrolyte, and a negative electrode and / or a negative electrode current collector;

[0068] The positive electrode is a component commonly known in batteries. The positive electrode used in this invention can be a conventional sulfur-based battery positive electrode, or the positive electrode described in this invention: the positive electrode mainly consists of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface, or it can be directly composed of elemental sulfur-containing materials. Specifically, the positive electrode mainly consists of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface. The conductive coating containing elemental sulfur is formed by mixing and coating the surface of the positive electrode current collector with carbon-based materials for conductive coating, sulfur powder, and a binder as raw material components; or, the positive electrode is directly composed of elemental sulfur-containing materials, which is formed by mixing and curing carbon-based materials for conductive coating, sulfur powder, and a binder as raw material components to create the positive electrode.

[0069] Furthermore, in one embodiment, the carbon-based material used for the conductive coating is selected from at least one of Ketjen black, graphite, conductive carbon black, carbon nanotubes, hard carbon, activated carbon, and metal-organic framework materials (such as UiO-66).

[0070] In one embodiment, the binder is selected from any one of aqueous binders and non-aqueous binders; the aqueous binder is a conventional aqueous binder described in the prior art that is suitable for use in battery positive electrodes, and uses water as the main solvent during use, such as any one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), sodium alginate, polyacrylic acid, polyacrylates (such as LA133), natural polymers (such as chitosan, starch, etc.), and conductive polymers (such as PEDOT:PSS); the non-aqueous binder is a conventional non-aqueous binder described in the prior art that is suitable for use in battery positive electrodes, and uses conventional organic reagents (such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), tetrahydrofuran (THF), acetone, cyclohexanone, chloroform, dichloromethane, ethyl acetate) as the main solvent during use, such as any one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyurethane (PU), and epoxy resin;

[0071] In one embodiment, the positive current collector is selected from any one of nickel foil, nickel foam, stainless steel foil, aluminum foil, carbon-coated aluminum foil, aluminum foam, titanium foil, carbon-based materials, and metal-organic polymer composites;

[0072] Typically, the mass percentage of elemental sulfur (sulfur powder) in the conductive coating and material containing elemental sulfur can be referenced to the cathode material ratio of conventional sulfur-based batteries. To better illustrate the invention and provide a preferred embodiment for reference, the mass percentage of elemental sulfur in the conductive coating and material containing elemental sulfur is 30-60 wt%, for example, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, or any range or point value between them. The proportions of the remaining materials, including the carbon-based materials for the conductive coating and the binder, all follow the conventional records for the preparation of the positive electrode in sulfur-based batteries.

[0073] In one preferred embodiment, the elemental sulfur-containing conductive coating is formed by coating the surface of the positive electrode current collector with a mixture of carbon-based material for conductive coating, sulfur powder, and binder as raw material components; wherein, the raw material components further include a bismuth coordination covalent organic framework (Bi-COF) catalyst, which is disclosed in a prior paper (S. Zheng, Z. Ouyang, M. Liu, S. Bi, G. Liu, X. Li, Q. Xu, G. Zeng. Carbon Neutralization 3, 415–422 (2024).). Specifically, the preparation method of the bismuth coordination covalent organic framework catalyst mainly includes the following steps:

[0074] 25.0 mg of tetraaldehyde compound, 15.2 mg of triaminopyridine, 1 mL of o-dichlorobenzene and 0.1 mL of 6 M acetic acid aqueous solution were mixed evenly in a reaction vessel and then frozen at -196.15 °C. The mixture was then degassed under vacuum three times. The reaction vessel was then sealed and heated at 120 °C for 72 hours. The collected product was washed sequentially with tetrahydrofuran, N,N-dimethylacetamide and methanol, and then transferred to a Soxhlet extractor for overnight extraction. Finally, the product was vacuum dried for 6 hours to obtain COF.

[0075] Add 50 mg of COF to a 50 mg / 50 mL Bi(NO3)3 methanol solution and reflux with stirring for at least 12 h to ensure sufficient adsorption of Bi3. + The precipitate was washed three times with ethanol and then extracted with tetrahydrofuran by Soxhlet extraction for 24 hours to remove impurities, thus obtaining the bismuth coordination covalent organic framework catalyst.

[0076] The amount of the bismuth-coordinated covalent organic framework catalyst added is 5-20 wt% of the sulfur powder.

[0077] Similarly, in one embodiment, the raw material components, including carbon-based materials for conductive coating, sulfur powder and binder, are mixed, molded and cured to form a positive electrode. The raw material components also include a bismuth-coordinated covalent organic framework catalyst.

[0078] The negative electrode and / or negative electrode current collector are components commonly known in batteries. In sodium-sulfur batteries without a negative electrode, only the negative electrode current collector is used. Both the negative electrode and / or the negative electrode current collector can be obtained commercially or prepared according to existing technical literature and conventional processes for sodium metal batteries or sodium-ion batteries. For example, the negative electrode can be made directly from elemental sodium metal, or it can be made directly from conventional carbon-containing materials or alloys. Another example is that the negative electrode is formed by loading sodium foil onto the surface of the negative electrode current collector.

[0079] Furthermore, in one embodiment, the negative electrode current collector is selected from any one of nickel foil, nickel foam, stainless steel foil, aluminum foil, carbon-coated aluminum foil, aluminum foam, titanium foil, carbon-based materials, and metal-organic polymer composites;

[0080] In one embodiment, the process of loading the sodium foil onto the surface of the negative electrode current collector includes any one of direct rolling, electrochemical deposition, mechanical coating, and melt impregnation.

[0081] Based on common knowledge about batteries in the prior art, in one embodiment, the sodium-sulfur battery may also include a conventional negative electrode shell, gasket, spring, separator for loading electrolyte, positive electrode shell, and other conventional structures / components / parts. Those skilled in the art can select a suitable process to prepare the sodium-sulfur battery based on the conventional preparation process of sodium metal batteries or sodium ion batteries or the required battery type.

[0082] Furthermore, based on common knowledge in the prior art regarding sodium metal batteries or sodium-ion batteries, in the sodium-sulfur battery, in addition to the technical content already described above, the specifications and assembly ratios of the positive electrode, liquid electrolyte or solid electrolyte, negative electrode and / or negative electrode current collector all follow conventional sodium metal battery or sodium-ion battery processes. Those skilled in the art can select a suitable process based on the conventional preparation process of sodium metal batteries or sodium-ion batteries or the required battery model to prepare the sodium-sulfur battery product.

[0083] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0084] Example

[0085] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0086] Example 1

[0087] In this embodiment, a sodium-sulfur button cell without a negative electrode is assembled as a test sample.

[0088] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0089] S-type cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with approximately 5 min intervals between each addition to ensure sufficient ethanol evaporation. This process was repeated until the target sulfur loading was achieved. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed. The sulfur loading of the button cell was 1.0–1.2 mg / cm³. 2 .

[0090] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The negative electrode-less sodium-sulfur button battery (type 2032) was assembled using the above-mentioned liquid electrolyte, S positive electrode and aluminum foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The diameter of the S positive electrode and the aluminum foil were both 14 mm, and the liquid electrolyte was 120 μL.

[0091] Verification Example 1

[0092] This verification example assembles a Na-Al half-cell as a test sample.

[0093] A liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm. 1.067 g (8 mmol) of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 0.401 g (4.5 mmol) of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved. The resulting liquid electrolyte was denoted as NaDCA electrolyte.

[0094] Weigh 1.067 g (8 mmol) AlCl3 and add it to 1 mL SOCl2. Stir for 2 hours until completely dissolved. Then add 0.263 g (4.5 mmol) sodium chloride (NaCl) and stir for another 2 hours until completely dissolved to prepare a liquid electrolyte, which is denoted as NaCl electrolyte.

[0095] The battery was assembled in an argon-filled glove box (water and oxygen content less than 1 ppm). The Na-Al half-cell (type 2032) was assembled using the above-mentioned NaDCA or NaCl electrolyte, sodium sheet and aluminum foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The sodium sheet was 0.42 mm thick, and both the sodium sheet and the aluminum foil were 14 mm in diameter. The electrolyte was 120 μL.

[0096] Verification Example 2

[0097] This verification example assembles a Na-Ni half-cell battery as a test sample.

[0098] A liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm. 1.067 g (8 mmol) of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 0.401 g (4.5 mmol) of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved. The resulting liquid electrolyte was denoted as NaDCA electrolyte.

[0099] Weigh 1.067 g (8 mmol) AlCl3 and add it to 1 mL SOCl2. Stir for 2 hours until completely dissolved. Then add 0.263 g (4.5 mmol) sodium chloride (NaCl) and stir for another 2 hours until completely dissolved to prepare a liquid electrolyte, which is denoted as NaCl electrolyte.

[0100] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The sodium-aluminum half-cell (type 2032) was assembled using the above-mentioned NaDCA or NaCl electrolyte, sodium sheet and nickel foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The sodium sheet was 0.42 mm thick, and both the sodium sheet and the nickel foil were 14 mm in diameter. The electrolyte was 120 μL.

[0101] Example 2

[0102] In this embodiment, a sodium-sulfur button cell without a negative electrode is assembled as a test sample.

[0103] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0104] S-type positive electrode: Ketjen black, sulfur powder, and PTFE powder were ball-milled in a mass ratio of 47.5:47.5:5, ground in a mortar for 5 min to form agglomerates, and then pressed into a self-standing electrode using a roller press (MSK-2150, MTI). The sulfur loading of the button cell was 3.80~5.60 mg / cm³. 2 .

[0105] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The negative electrode-less sodium-sulfur button battery (type 2032) was assembled using the above-mentioned liquid electrolyte, S positive electrode and aluminum foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The diameter of the S positive electrode and the aluminum foil were both 14 mm, and the liquid electrolyte was 120 μL.

[0106] Example 3

[0107] In this embodiment, a sodium-sulfur button cell without a negative electrode is assembled as a test sample.

[0108] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0109] Bi-COF / S cathode: 42 wt% sulfur powder, 8 wt% bismuth-coordinated covalent organic framework catalyst, 42 wt% Ketjen black, and 8 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with approximately 5 min intervals between each addition to ensure sufficient ethanol evaporation. This process was repeated until the target loading was achieved. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed. The sulfur loading of the button cell was 1.20–2.40 mg / cm³. 2 .

[0110] Bismuth-coordinated covalent organic framework (Bi-COF) catalyst: 25.0 mg of a tetraaldehyde compound, 15.2 mg of triaminopyridine, 1 mL of o-dichlorobenzene, and 0.1 mL of 6 M acetic acid aqueous solution were mixed thoroughly in a reaction vessel and then frozen at -196.15 °C. The mixture was then subjected to three freeze-thaw cycles under vacuum to remove gas. The reaction vessel was sealed and heated at 120 °C for 72 hours. The collected product was washed sequentially with tetrahydrofuran, N,N-dimethylacetamide, and methanol, and then transferred to a Soxhlet extractor for overnight extraction. Finally, the product was vacuum dried for 6 hours to obtain COF. 50 mg of COF was added to a 50 mg / 50 mL Bi(NO3)3 methanol solution, and the mixture was refluxed and stirred for at least 12 hours to ensure sufficient adsorption of Bi3. + The precipitate was washed three times with ethanol and then extracted with tetrahydrofuran by Soxhlet extraction for 24 hours to remove impurities, thus obtaining the bismuth coordination covalent organic framework catalyst.

[0111] Battery assembly was carried out in an argon-filled glove box (water and oxygen content below 1 ppm). The negative electrode-less sodium-sulfur button battery (type 2032) was assembled using the above-mentioned liquid electrolyte, Bi-COF / S positive electrode, aluminum foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The diameter of the Bi-COF / S positive electrode and the aluminum foil were both 14 mm, and the liquid electrolyte was 120 μL.

[0112] Example 4

[0113] In this embodiment, a sodium-sulfur pouch cell without a negative electrode is assembled as a test sample.

[0114] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0115] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0116] Bi-COF / S cathode: 42 wt% sulfur powder, 8 wt% bismuth-coordinated covalent organic framework catalyst, 42 wt% Ketjen black, and 8 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0117] Battery assembly was carried out in an argon-filled glove box (with water and oxygen content below 1 ppm).

[0118] 108 mAh pouch battery: 5 aluminum foils (53 × 73 mm) 2 ) and 4 S positive electrodes (50 × 70 mm) 2 ) Using a glass fiber diaphragm (GF / A, 55 × 75 mm) 2 The electrodes are separated by a 260 μm thick layer, ultrasonically welded and led out through a Ni label (15 mm wide), injected with 12 mL of NaDCA electrolyte (20.64 g), and packaged in an aluminum-plastic bag (DM-L086N).

[0119] 273 mAh pouch cell (lean electrolyte): 5 Bi-COF / S positive electrodes (50 × 70 mm) 2 2.4 mg / cm 2 Layered with 6 aluminum foil sheets, glass fiber diaphragm (GF, 100 μm thick, 55 × 75 mm) 2 Separate the two portions and inject 2.1 mL of NaDCA electrolyte (3.61 g), with a sulfur electrolyte ratio (E / S) of 5.0 μL / mg.

[0120] Example 5

[0121] In this embodiment, a 1.06 Ah negative electrode-free sodium-sulfur battery was assembled as a test sample.

[0122] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0123] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0124] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). Seven S-type positive electrodes (10 × 11 cm) were used. 2 ) and 8 pieces of aluminum foil (11 × 11.5 cm) 2 ), glass fiber diaphragm (GF / A, 12 × 12 cm) 2 ), 36 mL of NaDCA electrolyte (61.92 g) was injected, and the mixture was sealed using a glass mold. Both the electrode and the current collector were led out using Ni tags (1 cm wide).

[0125] Example 6

[0126] In this embodiment, a fibrous, electrodeless sodium-sulfur battery was assembled as a test sample.

[0127] Positive electrode: Sulfur-loaded multi-walled carbon nanotube fibers (approximately 20 μm in diameter) were used as the positive electrode. Sulfur powder and multi-walled carbon nanotube (MWCNT) fibers were sealed in a container at a mass ratio of 2:1 and heated at 155 °C for 12 hours to prepare sulfur-loaded multi-walled carbon nanotube fibers, denoted as S / MWCNT fibers, with a sulfur loading of 0.53 mg / cm.

[0128] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0129] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). Celgard 2340 separators were wrapped around aluminum wire (0.2 mm in diameter) using a twisting machine, then S / MWCNT fibers were wound around them, and after assembly, they were inserted into PTFE tubes (2.6 mm outer diameter, 2 mm inner diameter). NaDCA electrolyte (85 μL / cm, 146.2 mg / cm) was injected, and both ends were sealed with silicone (Kafuter, K-704).

[0130] Example 7

[0131] In this embodiment, a sodium-sulfur button cell was assembled as a test sample.

[0132] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0133] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0134] Hard carbon anode: Hard carbon, Ketjen black, and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 8:1:1, using N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a homogeneous slurry. The slurry was coated onto the surface of aluminum foil (10 μm thick) using a doctor blade, and then dried in a vacuum oven at 100 °C for 12 hours. The resulting electrode was stamped into a disc shape (14 mm in diameter) and pressed under 10 MPa pressure to increase the electrode density. The active material loading was 2.0–3.0 mg / cm³. 2 .

[0135] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The sodium-sulfur button cell (type 2032) was assembled using the above-mentioned liquid electrolyte, S positive electrode and hard carbon negative electrode, and glass fiber separator (GF / D, 675 μm thick, Whatman). The liquid electrolyte was 120 μL.

[0136] Example 8

[0137] In this embodiment, a sodium-sulfur button cell was assembled as a test sample.

[0138] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.401 g (4.5 mmol) sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaDCA electrolyte.

[0139] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0140] Silicon-carbon anode: Commercial silicon-carbon anode material, Ketjen black, and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 8:1:1, using N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a homogeneous slurry. The slurry was coated onto the surface of aluminum foil (10 μm thick) using a doctor blade, and then dried in a vacuum oven at 100 °C for 12 hours. The resulting electrode was stamped into a disc shape (14 mm in diameter) and pressed under 10 MPa pressure to increase the electrode density. The active material loading was 2.0–3.0 mg / cm³. 2 .

[0141] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The sodium-sulfur button cell (type 2032) was assembled using the above-mentioned liquid electrolyte, S positive electrode and silicon-carbon negative electrode, and glass fiber separator (GF / D, 675 μm thick, Whatman). The liquid electrolyte was 120 μL.

[0142] Example 9

[0143] In this embodiment, a sodium-sulfur button gel solid-state battery without a negative electrode was assembled as a test sample.

[0144] Gel-solid electrolyte: A liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm. 1.067 g (8 mmol) of AlCl3 was weighed and added to 1 mL of SOCl2, stirred for 2 hours until completely dissolved. Then, 0.401 g (4.5 mmol) of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved, yielding a liquid electrolyte, denoted as NaDCA electrolyte. The NaDCA electrolyte and 3,3-bis(chloromethyl)oxetane (BCMO) were mixed thoroughly at a volume ratio of 5:1 to prepare the gel-solid electrolyte.

[0145] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0146] Battery assembly was carried out in an argon-filled glove box (water and oxygen content below 1 ppm). The negative electrode-free sodium-sulfur button gel solid-state battery (type 2032) was assembled using the above-mentioned gel solid electrolyte, S positive electrode and aluminum foil, and glass fiber separator (GF / D, 675 μm thick, Whatman). The diameter of the S positive electrode and aluminum foil is 14 mm, and the liquid electrolyte is 120 μL.

[0147] Examples 10-13

[0148] Examples 10-13 are test samples assembled with a negative electrode-free sodium-sulfur button cell according to the implementation scheme of Example 1. The molar concentration of the electrolyte used in Examples 10-13 is different from that in Example 1, but the rest is the same as in Example 1.

[0149] In Example 10, 2 mmol of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 1.2 mmol of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved to prepare a liquid electrolyte.

[0150] In Example 11, 4 mmol of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 2.3 mmol of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved to prepare a liquid electrolyte.

[0151] In Example 12, 6 mmol of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 3.4 mmol of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved to prepare a liquid electrolyte.

[0152] In Example 13, 10 mmol of AlCl3 was weighed and added to 1 mL of SOCl2 and stirred for 2 hours until completely dissolved. Then, 5.6 mmol of sodium dicyandiamide (NaDCA) was added and stirred for another 2 hours until completely dissolved to prepare a liquid electrolyte.

[0153] Comparative Example 1

[0154] This comparative example uses sodium-sulfur button batteries without negative electrodes assembled by replacing sodium dicyandiamide with NaCl as the test sample.

[0155] Liquid electrolyte: The liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1.067 g (8 mmol) AlCl3 was weighed and added to 1 mL SOCl2 and stirred for 2 hours until completely dissolved, then 0.263 g (4.5 mmol) NaCl was added and stirred for another 2 hours until completely dissolved, thus preparing the liquid electrolyte, which was denoted as NaCl electrolyte.

[0156] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0157] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The negative electrode-less sodium-sulfur button battery (type 2032) was assembled using the above-mentioned liquid electrolyte, S positive electrode and aluminum foil, and glass fiber separator (GF / D, 675 μm, Whatman). The diameter of the S positive electrode and aluminum foil is 14 mm, and the liquid electrolyte is 120 μL.

[0158] Comparative Example 2

[0159] This comparative example uses a sodium-sulfur button cell without a negative electrode, assembled with a conventional organic electrolyte, as the test sample.

[0160] Organic electrolyte: Liquid electrolyte was prepared in an argon-protected glove box with water and oxygen content below 1 ppm; 1 M NaClO4 was dissolved in a binary solvent of ethylene carbonate / propylene carbonate (EC / PC, volume ratio 1:1), and 5 wt% fluoroethylene carbonate (FEC) was added.

[0161] S-Cathode: 45 wt% sulfur powder, 45 wt% Ketjen black, and 10 wt% PTFE (60 wt% aqueous dispersion) were mixed in ethanol at a mass ratio of ethanol to solids of 20:1. After uniform dispersion, the resulting sulfur-containing slurry was slowly added dropwise (80 μL at a time) onto nickel foam suspended on a hot plate at 100 °C, with each drop added approximately 5 min apart to ensure sufficient ethanol evaporation. This process was repeated until the target loading was reached. Finally, the mixture was vacuum dried overnight at 70 °C, flattened using a roller press, and weighed.

[0162] Battery assembly was carried out in an argon-filled glove box (water and oxygen content less than 1 ppm). The negative electrode-less sodium-sulfur button cell (type 2032) was assembled using the above-mentioned organic electrolyte, S positive electrode and aluminum foil, and glass fiber separator (GF / D, 675 μm, Whatman). The diameter of the S positive electrode and the aluminum foil were both 14 mm, and the organic electrolyte was 120 μL.

[0163] Comparative Example 3

[0164] This comparative example uses a sodium-sulfur pouch cell without a negative electrode, assembled with a conventional organic electrolyte, as the test sample.

[0165] The organic electrolyte was the same as in Comparative Example 2, and the rest was the same as in Example 4. A 108 mAh soft-pack battery was assembled.

[0166] Electrochemical testing

[0167] All tests were conducted in a 25 °C constant temperature chamber (Neware MHW-200). Battery performance was characterized using a Neware CT–4008 system. Cycling tests: 10 pre-charge-discharge cycles were performed to activate the battery, with capacity limits (e.g., 200, 400, 800 mAh / g) and a discharge cutoff voltage of 2.0 V, followed by long-cycle testing. Electrochemical impedance spectroscopy (EIS) was performed using a CHI660E workstation at a frequency of 0.01–106 Hz and an amplitude of 5 mV. Linear sweep voltammetry was performed at a scan rate of 1.0 mV / s, with nickel foil as the working electrode and Na metal as the counter and reference electrodes, and 120 μL of NaDCA electrolyte (0.21 g) injected. High and low temperature performance were tested in a blower (Shanghai Yiheng DHG–9030) and a cryogenic freezer (Haier BC / BD–307HEM), respectively. Cyclic voltammetry was performed at a rate of 0.05 mV / s, with S or NaCl as the working electrode and aluminum foil as the counter and reference electrodes. A forward scan corresponded to the deposition of Na on the aluminum foil. Each cell used 120 μL of NaDCA electrolyte (0.21 g) or NaCl electrolyte (0.20 g). EIS of the Na–Na symmetric cell was used to determine Na. + Transition number (t_Na) + (Frequency 0.01~106 Hz, amplitude 5 mV, time-amplitude test with bias voltage of 10 mV).

[0168] Energy density and power density are calculated based on the total mass (including active / inactive materials and electrolyte).

[0169] Viscosities were measured using a TA DHR-20 rheometer. At 25 °C, the viscosities of the three electrolytes (SOCl2 electrolyte with 8 M AlCl3 added, NaCl electrolyte, and NaDCA electrolyte) were 0.41, 8.48, and 12.89 mPa•s, respectively. At 300 s... -1 Rheological curves were recorded under shear rate and isothermal conditions of 25 ± 0.1 ℃. The ionic conductivity of the electrolyte was measured using a Mettler Toledo FE38 conductivity meter, and was 4.44, 8.28, and 6.33 mS / cm at 25 ℃. The conductivity meter was calibrated using KCl standard solution (1413 μS / cm). Before each test, 10 mL of electrolyte was placed in a sealed glass bottle and equilibrated for 20 minutes in a water bath at 25 ± 0.5 ℃.

[0170] The S8 molecule can be reduced to S... 2- Or it may be oxidized to a higher valence state, such as S. 4+ High-priced S 0 / S 4+The redox chemical reaction provides a significantly high discharge voltage of approximately 3.6 V. However, this reaction remains unrealizable in room-temperature sodium-sulfur batteries due to the large oxidation energy barrier and mismatched anionic ligands. Here, we unlock the potential of high-valent S... 0 / S 4+ The redox chemistry was used to achieve a high-voltage, electrodeless sodium-sulfur battery. For example, the battery sample shown in Example 1 consisted of an S8 positive electrode, aluminum (Al) foil as the negative electrode current collector, a glass fiber separator, and a non-flammable chloroaluminate electrolyte. Specifically, 8 M AlCl3 in SOCl2, 4.5 M NaCl + 8 M AlCl3 in SOCl2 (referred to as NaCl electrolyte), and 4.5 M NaDCA + 8 M AlCl3 in SOCl2 (referred to as NaDCA electrolyte) were mainly studied. The positive electrode reaction involved a 32-electron conversion reaction between S8 and SCl4 (…). This corresponds to a theoretical specific capacity of 3350 mAh / g. sulfur and 403mAh / g (SCl4+4Na) In comparison, the theoretical capacity of the conventional sodium-sulfur battery provided in Comparative Example 2 is 1675 mAh / g. sulfur and 690 mAh / g Na2S .

[0171] Reversible S 0 / S 4+ The conversion was verified by sulfur K-edge X-ray absorption spectroscopy (XAS). Figure 1 a) and the redox reaction of chlorine-based species was ruled out by K-edge XAS spectroscopy of chlorine. We further performed in-situ Raman spectroscopy to detect charge-discharge products at the positive electrode. At a charge of 800 mAh / g (based on the S8 mass), SCl4 was observed at 288.0 cm⁻¹. -1 The characteristic peaks appear and intensify at these points, while S8 shows peaks at 153.4 and 219.6 cm⁻¹. -1 The peak value at that location decreased ( Figure 1 b). An opposite trend was observed during discharge, indicating that reversible transformation between S8 and SCl4 occurs during charging and discharging. Figure 1 b).

[0172] DCA – The amide nitrogen in the anion plays an important role in forming intermolecular coordination with S, promoting nucleophilic Cl-. - Ligand binding generates SCl4. By replacing NaDCA with NaCl of the same concentration to obtain NaCl electrolyte, the resulting battery exhibits a significantly higher charging plateau at approximately 4.4 V, and the Raman spectrum of the S cathode shows almost no change at the characteristic peaks of S and SCl4. Figure 1c). Conversely, using NaDCA electrolyte to charge the S cathode (800 mAh / g) resulted in a reading at 288.0 cm⁻¹. -1 A significant SCl4 peak was observed. Figure 1 c), which reveals DCA – Anions unlock S 0 / S 4+ The key role in the transformation. X-ray photoelectron spectroscopy (XPS) also supports the redox reaction between S and SCl4 during charging and discharging. Figure 1 d). Strong SCl3 was detected at the positive electrode during the 10th and 100th charging cycles using gas chromatography and high-resolution mass spectrometry (GC-HRMS) in positive ion mode. + Signal( Figure 1 (e, f) confirmed that SCl4 is a charging product. In the 10th and 100th discharge states, SCl3... + The signal almost disappeared, revealing the reversible formation and consumption of SCl4 at the positive electrode during the cycling process.

[0173] DCA - Anions can mediate and enhance electron transfer between sulfur (S) and carbon, which is reflected in differential charge density calculations. Figure 1 g). In addition, DCA - Anions form stable DCA - …SCl x The intermediate significantly reduced the Gibbs free energy change of sulfur oxidation from 11.12 eV to 9.17 eV, as calculated by density functional theory (DFT). Figure 1 h) was verified by the [DCA…SCl3] detected on the positive electrode during the 100th charge. + This has been confirmed. The Gibbs free energy change calculated from the S8 to SCl4 path indicates that the oxidation reaction from SCl2 to SCl4 is a potential rate-determining step, consistent with results calculated from a single sulfur atom, providing preliminary support for the validity of the effective 32-electron mechanism model. Based on external Raman spectroscopy and X-ray absorption spectroscopy (XAS)... Figure 1 a) We confirmed the formation of the SCl2 and S2Cl2 intermediates. Furthermore, according to... Figure 1 Based on density functional theory calculations of h and other experimental evidence, it is reasonable to infer that sodium salts containing cyanide, other than sodium dicyandiamide, also have similar electrochemical properties. Therefore, based on experimental evidence, sodium dicyandiamide is the optimal choice.

[0174] We evaluated the reversibility of Na deposition / stripping using NaDCA electrolyte, and the results showed that at 1 mA / cm², the reversibility was achieved. 2 and 1mAh / cm 2Below, the battery provided in Example 1 demonstrates an average coulombic efficiency (CE) of approximately 96% over 160 cycles. Figure 2 a). In contrast, the battery provided in Comparative Example 1, using NaCl electrolyte, exhibited lower reversibility, with an CE of only 20-50%, and significantly higher overvoltage ( Figure 2 a, b). Time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling revealed that the SEI layer formed in the NaCl electrolyte contained a large amount of NaCl (a, b). Figure 2 c), indicating insufficient passivation of the deposited sodium, leading to poor electrochemical reversibility. Conversely, our NaDCA electrolyte formed a nitrogen-rich SEI layer containing sodium cyanide (NaCN) and sodium nitride (Na3N), with a low NaCl content ( Figure 2 d) This can suppress the unfavorable reaction between deposited sodium and the electrolyte, and due to the high Na content of Na3N and NaCN... + Conductivity and promote Na + Transport at the sodium metal / electrolyte interface. XPS confirmed the coexistence of these major SEI components, as well as several minor components derived from the decomposition of NaDCA ( Figure 2 e). This ensured uniform sodium deposition on the aluminum foil, which was verified by scanning electron microscopy (SEM) and dark-field microscopy. We also confirmed the uniform sodium deposition on the aluminum foil using NaDCA electrolyte using in-situ optical microscopy. Figure 2 f), while the use of NaCl electrolyte resulted in significant dendritic sodium deposition on the aluminum foil, indicating DCA - The important role of anions in achieving uniform sodium deposition.

[0175] The verification example 1 cell using NaDCA electrolyte exhibited an excellent critical current density, reaching 50 mA / cm². 2 The maximum area specific capacity is 12 mAh / cm². 2 ( Figure 2 g, h), far exceeding the most advanced sodium metal batteries currently available ( Figure 2 i). We observed that after the negative electrode at the 10th, 50th, and 100th charging, the Na in the electrolyte... + The anode spontaneously compensates. This behavior was confirmed by in-situ XRD and TOF-SIMS. This prevents NaCl accumulation and builds a nitrogen-rich SEI layer on the outer surface of the sodium deposition. Figure 2 d), which helps to form a more compact passivation layer and improves ionic conductivity and electrochemical stability.

[0176] According to the linear scan voltammetry ( Figure 3a) Our NaDCA electrolyte has an electrochemically stable voltage of 4.25 V, enabling the negative electrode-free sodium-sulfur coin cell provided in Example 1 to have a discharge voltage of 3.6 V and a reversible specific capacity of 744 mAh / g, which is significantly better than the 230 mAh / g obtained using a NaCl electrolyte with a lower electrochemically stable voltage (Comparative Example 1). Figure 3 b). Notably, when there is no sulfur loading on the positive electrode, the coulombic efficiency is only about 18%, and the charging plateau is significantly increased to 4.21 V ( Figure 3 c). We observed a significant correlation between the mass change of sulfur and the specific charge capacity, which is consistent with the relationship between S... 0 / S 4+ The calculated specific capacity of 3350 mAh / g from the redox reaction is consistent with the theoretical value. As the charge specific capacity increases from 800 to 1500 mAh / g, a higher charging plateau of 4.21 V is observed, indicating that electrolyte oxidation, as a side reaction, leads to a significant decrease in CE, from approximately 95% to approximately 55%.

[0177] It is worth noting that our negative electrode-free sodium-sulfur battery exhibits excellent rate capability. For example, the battery provided in Example 1 has a maximum current density of 16 A / g and a discharge specific capacity of 715 mAh / g, while the battery in Comparative Example 1 using NaCl electrolyte has only 2 A / g and 102 mAh / g at the same charge specific capacity of 800 mAh / g. Figure 3 e). The maximum energy density and power density reached 1198 Wh / kg and 23773 W / kg, respectively, both calculated based on the total electrode mass. Furthermore, the battery provided in Example 1 exhibited an excellent cycle life of 1400 cycles at a charge specific capacity of 200 mAh / g, while the battery in Comparative Example 1 using NaCl electrolyte rapidly degraded within 20 cycles. Figure 3 f). This can be attributed to the stable SEI layer formed in the NaDCA electrolyte ( Figure 2 (d, f), and the high consistency of charge transfer resistance was verified through 1400 cycles. At a higher specific capacity of 800 mAh / g, the Example 1 battery maintained more than 200 cycles, which is better than 2 cycles of the anode-free Na-Na2S battery (Geng, M. et al. A stable anode-free Na–S full cell at room temperature. Energy Storage Mater. 52, 230–237 (2022).). Figure 3 f illustration).

[0178] Our anode-free sodium-sulfur battery can operate over an ultra-wide temperature range of -40 to 80 °C. Figure 3 g). Meanwhile, a good storage life of 400 days and a capacity retention rate of 96.1%–96.6% demonstrate its potential in practical applications. It is worth noting that through reasonable optimization of S... 0 / S 4+ Redox chemistry and electrochemical performance can still be further improved. In Example 3, after adding 8 wt% Bi-COF, the discharge specific capacity reached 1206 mAh / g based on the total mass of sulfur and Bi-COF. Figure 3 This allows for a maximum energy density of 2021 Wh / kg calculated from the total electrode mass, including both positive and negative electrodes. Figure 4 As shown, under lean electrolyte conditions, the electrolyte / sulfur (E / S) ratio is 5.0 μL / mg. sulfur The Bi-COF / S cathode achieved an electrode-level specific capacity of 63 mAh / g, an energy density of 226 Wh / kg, and a power density of 694 W / kg, all calculated based on the total mass of the electrode and electrolyte. We developed a solvent-free method (Example 2) to facilitate the scalable fabrication of large-area S cathodes and confirmed good uniformity and electrochemical performance. The sulfur areal density of this cathode is 2.4 mg / cm³. 2 The charging capacity and current density are 800 mAh / g (1.92 mAh / cm³). 2 ) and 2 A / g (4.80 mA / cm 2 Based on the total mass including electrolyte, positive and negative electrode active and inactive materials, the battery's electrode-level energy density and power density reach 226 Wh / kg and 694 W / kg, respectively.

[0179] Compared to the flammable organic electrolyte used in conventional sodium-sulfur batteries provided in Comparative Example 2, our NaDCA electrolyte is inherently non-flammable, ensuring better battery safety. Figure 5 a). We manufactured a 108 mAh pouch cell that underwent 100 cycles of stable performance ( Figure 5 b). We verified the stability and safety of fully charged pouch cells in cut and puncture tests. Figure 5 (b, c) Hydrogen chloride (HCl) was detected as the primary chlorine-containing gaseous hydrolysis product, rather than chlorine gas, consistent with previous reports in chloroaluminate electrolytes. This reaction was accompanied by rapid solidification of the electrolyte, with aluminum hydroxide (Al(OH)3) identified as the primary solid hydrolysis product. These factors collectively contributed to short-term battery operation without short circuits or thermal runaway. The air stability observed here is short-term and does not indicate inherent safety under long-term or large-scale exposure. The challenges of AlCl3 / SOCl2-based electrolytes in terms of corrosivity and handling difficulty require further investigation for practical applications.

[0180] To further verify scalability, we fabricated an ampere-hour-level, electrodeless sodium-sulfur battery. Figure 5 d). The battery provides a reversible specific capacity of 1.06 Ah over 30 cycles ( Figure 5 e), demonstrating its potential in grid energy storage ( Figure 5 f). The projected battery cost of $5.03 per kilowatt-hour makes the anode-free sodium-sulfur battery highly cost-effective and promising for practical energy storage applications. Figure 5 g). We also extend this battery concept to fiber batteries ( Figure 5 h), making it a promising candidate for wearable applications ( Figure 5 i).

[0181] Figures 6-9 The feasibility of sodium-sulfur batteries was demonstrated by constructing full cells with different negative electrodes and under different electrolyte molar concentrations.

[0182] In summary, we report a sodium-sulfur battery based on a high-cost S / SCl4 cathode chemistry, overcoming the limitations of room-temperature sodium-sulfur batteries in terms of discharge voltage, energy density, and rate capability. Mechanistic studies reveal that the cyanamide anion in the optimized chloroaluminate electrolyte plays a crucial role in unlocking the S / SCl4 cathode chemistry and improving the reversibility of sodium deposition / stripping at the anode. This combination enables a high-voltage, anode-free sodium-sulfur battery with excellent electrochemical performance and practicality. These batteries are scalable to the ampere-hour level, with an expected cost of $5.03 per kilowatt-hour (one to two orders of magnitude lower than current sodium batteries), and can also be extended to fiber batteries for wearable applications. This battery system holds promise for reshaping the current S / SCl4-based sodium-sulfur batteries. 0 / S 2- Alkali metal-sulfur batteries, dominated by positive electrode reaction and excess alkali metal negative electrode, open up new avenues for low-cost, sustainable, and high-performance energy storage solutions.

[0183] 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.

[0184] Figure 2 The references cited in Ref. 18-22 listed in i are as follows:

[0185] 18.Hu, L. et al. Restructuring electrolyte solvation by a versatilediluent toward beyond 99.9% Coulombic efficiency of sodium plating / strippingat ultralow temperatures. Adv. Mater. 36, 2312161 (2024).

[0186] 19.Liu, P. et al. Inorganic–organic hybrid multifunctional solidelectrolyte interphase layers for dendrite-free sodium metal anodes. Angew.Chem. Int. Ed. 62, e202312413 (2023).

[0187] 20.He, J. et al. Tuning the solvation structure with salts for stablesodium-metal batteries. Nat. Energy 9, 446–456 (2024).

[0188] 21.Sun, B. et al. Dendrite-free sodium-metal anodes for high-energysodium-metal batteries. Adv. Mater. 30, 1801334 (2018).

[0189] 22.Zhuang, R. et al. Fluorinated porous frameworks enable robustanode-less sodium metal batteries. Sci. Adv. 9, eadh8060 (2023).

Claims

1. A sodium-sulfur battery, characterized in that: The electrolyte includes sodium salts containing cyanide and Lewis acids containing chlorine. The positive electrode is mainly composed of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface, or it is directly composed of materials containing elemental sulfur.

2. The sodium-sulfur battery according to claim 1, characterized in that: The sodium cyanide salt includes at least one of sodium dicyandiamide and sodium cyanide.

3. The sodium-sulfur battery according to claim 1, characterized in that: The chlorinated Lewis acid includes at least one of aluminum trichloride, gallium trichloride, ferric chloride, and zinc chloride.

4. The sodium-sulfur battery according to claim 1, characterized in that: The molar concentration of the chloro Lewis acid in the solvent is 2~10 mol / L, and the sodium cyanide salt is 80~100% of the saturation in the solvent.

5. The sodium-sulfur battery according to claim 1, characterized in that: The sodium-sulfur battery is either a liquid sodium-sulfur battery or a solid sodium-sulfur battery.

6. The sodium-sulfur battery according to claim 1, characterized in that: The positive electrode is mainly composed of a positive electrode current collector and a conductive coating containing elemental sulfur on its surface. The conductive coating containing elemental sulfur is formed by mixing and coating the surface of the positive electrode current collector with carbon-based materials for conductive coating, sulfur powder and binder as raw material components; or, the positive electrode is mainly composed of materials containing elemental sulfur directly, which is formed by mixing and curing carbon-based materials for conductive coating, sulfur powder and binder as raw material components as raw material components.

7. The sodium-sulfur battery according to claim 6, characterized in that: The raw material components also include bismuth-coordinated covalent organic framework catalysts.

8. The sodium-sulfur battery according to claim 1, characterized in that: The sodium-sulfur battery also includes a negative electrode and / or a negative electrode current collector.

9. The sodium-sulfur battery according to claim 8, characterized in that: The negative electrode is made of elemental sodium, or a conventional carbon-containing negative electrode or an alloy negative electrode; or, the negative electrode is formed by loading sodium foil onto the surface of the negative electrode current collector.

10. The sodium-sulfur battery as described in claim 1 is applied to the field of energy storage.

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