A sodium-ion battery with positive / negative coupling pre-sodiation and a construction method thereof

Abstract

The application discloses a kind of positive / negative coupling pre-sodium sodium-ion battery and its construction method, it is related to electrochemistry technical field.The specific is: after using sodium thiophene to pre-sodium hard carbon material and handle, it is placed in NaPF6 / G2 solution and is soaked, and pre-sodium hard carbon negative electrode is obtained;Pre-sodium sodium vanadium phosphate positive electrode is obtained by using lithium square acid to pre-sodium positive active material and handle;Then based on pre-sodium hard carbon negative electrode, pre-sodium sodium vanadium phosphate positive electrode, NaPF6 / G2 solution is used as electrolyte and constructs sodium-ion battery.The application is coupled by pre-sodium hard carbon negative electrode and pre-sodium sodium vanadium phosphate positive electrode, and the active sodium ion loss in the process of SEI generation is supplemented on the negative side, the active sodium ion consumption in the process of SEI continuous generation and breakage in the process of electrochemistry is supplemented on the positive side, which improves the first coulomb efficiency of sodium-ion battery, and improves long-term cycle stability.The construction method of the application is simple in operation, short in technological process and high in safety.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a sodium-ion battery with positive / negative electrode coupling and pre-sodiumation, and a method for constructing the same. Background Technology

[0002] Lithium-ion batteries are widely used in 3C electronics and smart cars due to their high energy density and long cycle life. However, with the continued growth in demand for large-scale energy storage, the limited reserves and uneven distribution of lithium resources restrict the further development of lithium-ion batteries. Against this backdrop, sodium-ion batteries have attracted widespread attention as an emerging electrochemical energy storage technology. Compared with lithium, sodium has advantages such as abundant resources, low cost, and wide distribution. Furthermore, sodium's electrode potential is approximately -2.71 V (vs. RHE), only about 0.33 V higher than lithium, demonstrating good electrochemical feasibility. Therefore, sodium-ion batteries show significant application potential in the field of large-scale energy storage.

[0003] Electrochemical energy storage technology relies on battery performance, which in turn depends on the optimization of electrode materials and electrolytes. Although numerous high-performance positive and negative electrode materials and electrolytes for sodium-ion batteries have been developed, sodium loss during the initial charge and subsequent cycles reduces battery life and energy density. In particular, during the initial charge and discharge process, the SEI film formed on the surface of the negative electrode material irreversibly consumes a large amount of sodium ions from the positive electrode, leading to a decrease in the battery's initial coulombic efficiency and reversible capacity. This severely restricts the commercial application of sodium-ion batteries.

[0004] Currently, methods such as material modification and electrolyte composition adjustment are commonly used to improve the initial coulombic efficiency of batteries. However, these methods have limited effectiveness and are accompanied by problems such as complex processes and increased costs, making them unsuitable for large-scale commercial applications. In contrast, pre-sodiuming technology, by supplementing the sodium source to offset sodium loss caused by the SEI film, is compatible with various positive and negative electrode materials and has promising prospects for industrialization. CN119650698A discloses a sodium-ion battery positive electrode, which is prepared by mixing a lithium-containing compound (LiC4O4), a positive electrode active material (sodium vanadium phosphate), a binder, and a conductive agent. CN119419269A discloses a method of pre-sodiuming a hard carbon negative electrode by immersing it in a polycyclic aromatic hydrocarbon (PAHs-Na-ether) pre-sodiuming agent, followed by leaching and rinsing with ethylene glycol dimethyl ether. The polycyclic aromatic hydrocarbon (PAH) pre-sodiuming agent is prepared from polycyclic aromatic hydrocarbons (PAHs) (naphthonitrile, naphthylacetonitrile, methylbiphenyl, methylphenanthrene, and dimethylbiphenyl), an ether solvent, and metallic sodium. CN120809754A discloses a method for pre-sodiumizing anode materials (hard carbon) using organic sodium sulfonates (sodium methanesulfonate, sodium benzenesulfonate, sodium naphthalenesulfonate). This demonstrates that existing technologies generally employ strategies of pre-sodiumizing either the cathode material or the anode material separately. While these methods can improve the initial coulombic efficiency to some extent, their long-term cycle stability is not ideal.

[0005] Therefore, there is an urgent need to develop a method for constructing sodium-ion batteries with positive / negative electrode coupling and pre-sodiumation to improve the initial coulombic efficiency and long-term cycle stability of the battery. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a sodium-ion battery with pre-sodium-coated positive / negative electrodes and its construction method. Specifically, the method involves: pre-sodium-coating a hard carbon material with sodium thiophene, followed by immersion in a NaPF6 / G2 solution to obtain a pre-sodium-coated hard carbon negative electrode; pre-sodium-coated a positive electrode material with lithium squaric acid to obtain a pre-sodium-coated sodium vanadium phosphate positive electrode; and then constructing a sodium-ion battery based on the pre-sodium-coated hard carbon negative electrode, the pre-sodium-coated sodium vanadium phosphate positive electrode, and the NaPF6 / G2 solution as the electrolyte. This invention, by coupling the pre-sodium-coated hard carbon negative electrode and the pre-sodium-coated sodium vanadium phosphate positive electrode, compensates for the loss of active sodium ions during SEI formation on the negative electrode side and for the consumption of active sodium ions during the continuous formation and breakdown of SEI on the positive electrode side. This improves both the initial coulombic efficiency and long-term cycle stability of the sodium-ion battery. Specifically, the sodium-ion battery constructed using the method of this invention exhibits an initial coulombic efficiency of 97.2%-100.5% and a capacity retention of 98.2%-99.5% after 200 cycles.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a method for constructing a sodium-ion battery with positive / negative electrode coupling and pre-sodiumation, comprising the following steps:

[0009] (1) Under an inert atmosphere, the hard carbon material is immersed in a sodium thiophene / diethylene glycol dimethyl ether solution for the first time, then washed and immersed in a sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (NaPF6 / G2 solution) for the second time, then dried to obtain a pre-sodium hard carbon anode.

[0010] (2) After mixing sodium vanadium phosphate, conductive agent and binder, add to solvent for homogenization to obtain slurry; add lithium squaric acid to slurry, mix well and coat onto substrate, dry to obtain pre-sodium vanadium phosphate positive electrode;

[0011] (3) Construct a sodium-ion battery using a pre-sodium hard carbon anode, a pre-sodium vanadium phosphate cathode, and an electrolyte.

[0012] Preferably, in step (1), the inert atmosphere is an argon atmosphere.

[0013] Preferably, in step (1), the hard carbon material is prepared by the following method:

[0014] Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of (6-10):1:1 to obtain a mixture; the mixture is added to water for homogenization to obtain a homogenate; the homogenate is coated onto aluminum foil and dried at 50-70℃ for 8-12 hours to obtain hard carbon material.

[0015] Furthermore, the mixture and water have a material-to-liquid ratio of 1g:(3-5)mL, and the coating amount of the homogenate on the aluminum foil is 1.0-2.0g / cm². 2 .

[0016] Preferably, in step (1), the concentration of the sodium thiophene / ethylene glycol dimethyl ether solution is 0.4-0.6M, and the concentration of the sodium hexafluorophosphate / diethylene glycol dimethyl ether solution is 0.8-1.2M.

[0017] Preferably, in step (1), the first soaking time is 1-10 min and the second soaking time is 1-5 min.

[0018] Preferably, in step (1), the washing operation is as follows: the hard carbon material after the first soaking is washed with ethylene glycol dimethyl ether.

[0019] Preferably, in step (2), the conductive agent is one or more of Super P, KB, CNTs, and conductive graphite, the binder is one or more of polyvinylidene fluoride, PTFE, sodium carboxymethyl cellulose, or sodium alginate, and the solvent is N-methylpyrrolidone.

[0020] Preferably, in step (2), the ratio of sodium vanadium phosphate, conductive agent, binder and solvent is (0.6-1.0) g: (0.05-0.15) g: (0.05-0.15) g: 2 mL.

[0021] Preferably, in step (2), the amount of lithium squaric acid added is 0.5%-10% of the mass of sodium vanadium phosphate.

[0022] Preferably, in step (2), the substrate is aluminum foil, and the coating amount is 2.0-3.0 g / cm³. 2 .

[0023] Preferably, in step (2), the drying temperature is 70-90℃ and the drying time is 8-12h.

[0024] Preferably, in step (3), the electrolyte is a sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (NaPF6 / G2 solution) with a concentration of 0.8-1.2M.

[0025] In a second aspect, the present invention provides a sodium-ion battery prepared by the above-described construction method.

[0026] The beneficial effects of this invention are:

[0027] In this invention, a pre-sodium-treated hard carbon material is subjected to sodium thiophene pretreatment, followed by immersion in a NaPF6 / G2 solution to obtain a pre-sodium-treated hard carbon anode. A pre-sodium-treated positive electrode active material is subjected to lithium squaric acid pretreatment to obtain a pre-sodium-treated sodium vanadium phosphate positive electrode. Then, a sodium-ion battery is constructed based on the pre-sodium-treated hard carbon anode, the pre-sodium-treated sodium vanadium phosphate positive electrode, and the NaPF6 / G2 solution as the electrolyte. This invention improves both the initial coulombic efficiency and long-term cycle stability of the sodium-ion battery by simultaneously pre-sodium-treated both the positive and negative electrodes. Specifically, the sodium-ion battery constructed using this method exhibits an initial coulombic efficiency of 97.2%-100.5% and a capacity retention of 98.2%-99.5% after 200 cycles.

[0028] Furthermore, this invention enables the pre-sodiuming of the positive and negative electrodes and the construction of sodium-ion batteries at room temperature. It is simple to operate, has a short process flow, and is highly safe, which is of great significance for the development of high-performance sodium-ion batteries suitable for large-scale energy storage. Attached Figure Description

[0029] Figure 1 Example 1: First-cycle charge-discharge curves of hard carbon material and pre-sodium hard carbon anode;

[0030] Figure 2 Example 1: Charge-discharge curve of lithium squaric acid electrode during the first cycle;

[0031] Figure 3Example 1: First-cycle charge-discharge curves of sodium vanadium phosphate cathode and pre-sodium vanadium phosphate cathode. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] In existing technologies, a common strategy is to pre-sodium-modify either the positive electrode material or the negative electrode material separately. However, when only sacrificial sodium-adding additives (LiC4O4) are used for pre-sodium-modification of the positive electrode material, two problems arise. First, the sodium-adding additive has poor conductivity and does not participate in subsequent electrochemical reactions. Excessive use of this additive can lead to a decrease in the electrode's rate performance, necessitating strict limitations on its dosage and thus restricting the maximum lithium replenishment it can provide. Second, the positive electrode sodium-adding additive cannot effectively replenish the irreversible active sites on the negative electrode side. Furthermore, the active ion supply from the positive electrode sodium-adding additive is typically concentrated in the first few cycles. As cycling progresses into the later stages, the active ion consumption caused by the continuous formation and breakdown of SEI / CEI continues, but the active ions provided by the sodium-adding additive are exhausted. Conversely, simple negative electrode pre-sodium-modification only considers the formation of the SEI on the hard carbon negative electrode, neglecting the formation of the CEI on the positive electrode side and the active ion loss caused by the repeated formation of SEI and CEI during subsequent cycles. Therefore, although pre-sodium treatment of the positive electrode material alone or pre-sodium treatment of the negative electrode material alone can improve the initial coulombic efficiency to a certain extent, the long-term cycle stability is not ideal.

[0034] Based on this, the present invention provides a sodium-ion battery with positive / negative electrode coupling and pre-sodiumation, which is composed of a pre-sodiumation hard carbon negative electrode, a pre-sodiumation sodium vanadium phosphate positive electrode and a NaPF6 / G2 solution (electrolyte). The preparation process of the pre-sodium-modified hard carbon anode is as follows: First, the hard carbon material is immersed in a sodium thiophene / ethylene glycol dimethyl ether solution. Sodium thiophene, acting as a highly efficient electron and sodium ion donor, undergoes a chemical pre-sodiumization reaction with the hard carbon. During the reaction, sodium ions are adsorbed at the defect sites of the hard carbon. The sodium thiophene / ethylene glycol dimethyl ether solution contains a large number of negative electrons, which are transferred through the hard carbon network. The sodium ions adsorbed at the defect sites gain some electrons and are reduced to form near-metallic sodium. After removing the pre-sodium-modified hard carbon material, it is immersed in a sodium hexafluorophosphate / ethylene glycol dimethyl ether solution, allowing the near-metallic sodium in the pre-sodium-modified hard carbon to react with the sodium hexafluorophosphate / ethylene glycol dimethyl ether solution. An SEI layer is generated in situ before cycling, effectively reducing the loss of active sodium ions due to SEI formation during subsequent electrochemical cycles. The pre-sodium-modified sodium vanadium phosphate cathode is prepared by mixing lithium squaric acid as a sodium supplement agent with sodium vanadium phosphate.

[0035] In this invention, on the negative electrode side, the hard carbon material is first pre-sodiumized using sodium thiophene, followed by non-electrochemical in-situ film formation. This process enables the pre-formation of an SEI on the negative electrode before battery cycling. During subsequent battery cycling, no Na is consumed. + To form SEI, Na + Sodium ions are largely retained for reversible insertion / extraction reactions, fundamentally reducing irreversible capacity loss during the first charge / discharge cycle, thereby improving the battery's initial coulombic efficiency. On the positive electrode side, Li₂ produced by the decomposition of lithium squaric acid... + It can replenish the active sodium ions consumed by the CEI generated on the positive electrode side. At the same time, as the cycling process proceeds, SEI and CEI are continuously generated and broken down, requiring more active sodium ions to replenish the consumption. At this time, the active lithium ions introduced on the positive electrode side can replace sodium ions to participate in the SEI generation process, which is more conducive to improving cycle stability.

[0036] Therefore, this invention improves both the initial coulombic efficiency and long-term cycle stability of sodium-ion batteries by coupling a pre-sodium hard carbon anode and a pre-sodium vanadium phosphate cathode, supplementing the loss of active sodium ions during the SEI generation process on the anode side and the consumption of active sodium ions during the continuous generation and breakdown of SEI on the cathode side.

[0037] Furthermore, in existing technologies, PAHs-Na-ethers and organic sulfonates are used for pre-sodiumization of hard carbon materials. However, organic sulfonates require high-voltage decomposition, resulting in additional gas generation. PAHs-Na-ethers, prepared from naphthonitrile, naphthiacetonitrile, methylbiphenyl, methylphenanthrene, or dimethylbiphenyl, have excessively low reduction voltages (typically around 0.2 V), leading to uncontrollable and uneven pre-sodiumization. In contrast, this invention uses sodium thiophene for pre-sodiumization of hard carbon materials. The reduction potential of sodium thiophene is approximately 0.5-0.6 V, while the sodiumization potential of hard carbon is around 0.8 V. These closer reduction potentials indicate a more similar reduction process. Therefore, compared to other types of reducing agents, the pre-sodiumization process using sodium thiophene is milder, more uniform, and more controllable.

[0038] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels. The concentration of the sodium thiophene / ethylene glycol dimethyl ether solution refers to the concentration of sodium thiophene in the sodium thiophene / ethylene glycol dimethyl ether solution.

[0040] In this invention, the structural formula of sodium thiophene is as follows: Its CAS number is 83682-19-3.

[0041] Example 1:

[0042] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 8:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:4mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 1.5g / cm³. 2 The coating amount is applied to aluminum foil and dried at 60°C for 10 hours to obtain hard carbon material;

[0043] Under an inert atmosphere, the hard carbon material was immersed in a 0.5 M sodium thiophene / ethylene glycol dimethyl ether solution for 5 min, then rinsed with ethylene glycol dimethyl ether, and then immersed in a 1 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 5 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0044] (2) After mixing sodium vanadium phosphate, KB and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF and N-methylpyrrolidone is 8g:1g:1g:20mL. Then, lithium squaric acid is added to the slurry at 5% of the mass of sodium vanadium phosphate and mixed well. The mixture is then homogenized at 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain pre-sodium vanadium phosphate cathode.

[0045] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte), and glass fiber (separator).

[0046] Example 2:

[0047] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 8:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:4mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 1.5g / cm³. 2 The coating amount is applied to aluminum foil and dried at 60°C for 10 hours to obtain hard carbon material;

[0048] Under an inert atmosphere, the hard carbon material was immersed in a 0.5 M sodium thiophene / ethylene glycol dimethyl ether solution for 5 min, then rinsed with ethylene glycol dimethyl ether, and then immersed in a 1 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 5 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0049] (2) After mixing sodium vanadium phosphate, KB and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF and N-methylpyrrolidone is 8g:1g:1g:20mL. Lithium squaric acid is added to the slurry at 10% of the mass of sodium vanadium phosphate and mixed well. Then, at 2.5g / cm³, the mixture is homogenized. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain pre-sodium vanadium phosphate cathode.

[0050] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte), and glass fiber (separator).

[0051] Example 3:

[0052] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 8:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:4mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 1.5g / cm³. 2 The coating amount is applied to aluminum foil and dried at 60°C for 10 hours to obtain hard carbon material;

[0053] Under an inert atmosphere, the hard carbon material was immersed in a 0.5 M sodium thiophene / ethylene glycol dimethyl ether solution for 10 min, then rinsed with ethylene glycol dimethyl ether, and then immersed in a 1 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 5 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0054] (2) After mixing sodium vanadium phosphate, KB and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF and N-methylpyrrolidone is 8g:1g:1g:20mL. Then, lithium squaric acid is added to the slurry at 5% of the mass of sodium vanadium phosphate and mixed evenly at 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain pre-sodium vanadium phosphate cathode.

[0055] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte), and glass fiber (separator).

[0056] Example 4:

[0057] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 8:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:4mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 1.5g / cm³. 2 The coating amount is applied to aluminum foil and dried at 60°C for 10 hours to obtain hard carbon material;

[0058] Under an inert atmosphere, the hard carbon material was immersed in a 0.5 M sodium thiophene / ethylene glycol dimethyl ether solution for 10 min, then rinsed with ethylene glycol dimethyl ether, and then immersed in a 1 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 5 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0059] (2) After mixing sodium vanadium phosphate, KB and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF and N-methylpyrrolidone is 8g:1g:1g:20mL. Then, lithium squaric acid is added to the slurry at 10% of the mass of sodium vanadium phosphate and mixed evenly at 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain pre-sodium vanadium phosphate cathode.

[0060] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte), and glass fiber (separator).

[0061] Example 5:

[0062] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 6:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:3mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 1.0g / cm³. 2 The coating amount is applied to aluminum foil and dried at 50°C for 8 hours to obtain hard carbon material;

[0063] Under an inert atmosphere, the hard carbon material was immersed in a 0.4 M sodium thiophene / ethylene glycol dimethyl ether solution for 1 min, rinsed with ethylene glycol dimethyl ether, and then immersed in a 0.8 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 1 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0064] (2) After mixing sodium vanadium phosphate, KB, and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF, and N-methylpyrrolidone is 6g:0.5g:0.5g:20mL. Then, lithium squaric acid is added to the slurry at 0.5% of the mass of sodium vanadium phosphate and mixed thoroughly. The mixture is then homogenized at 2.0g / cm³. 2 The coating amount was applied to aluminum foil and dried at 70°C for 8 hours to obtain pre-sodium vanadium phosphate cathode.

[0065] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 0.8M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0066] Example 6:

[0067] (1) Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of 10:1:1 to obtain a mixture; the mixture and water are mixed in a material-to-liquid ratio of 1g:5mL to obtain a homogenate; the homogenate is prepared at a mass ratio of 2.0g / cm³. 2 The coating amount was applied to aluminum foil and dried at 70°C for 12 hours to obtain hard carbon material.

[0068] Under an inert atmosphere, the hard carbon material was immersed in a 0.6 M sodium thiophene / ethylene glycol dimethyl ether solution for 10 min, then rinsed with ethylene glycol dimethyl ether, and then immersed in a 1.2 M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for 3 min. After drying, a pre-sodium-modified hard carbon anode was obtained.

[0069] (2) After mixing sodium vanadium phosphate, KB, and PVDF, add them to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF, and N-methylpyrrolidone is 10g:1.5g:1.5g:20mL. Then, lithium squaric acid is added to the slurry at 5% of the mass of sodium vanadium phosphate and mixed thoroughly. The mixture is then homogenized at 3.0g / cm³. 2 The coating amount was applied to aluminum foil and dried at 90°C for 12 hours to obtain pre-sodium vanadium phosphate cathode.

[0070] (3) In an argon-protected glove box, a sodium-ion battery is assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1.2M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0071] Comparative Example 1:

[0072] The difference between this comparative example and Example 1 is that a sodium vanadium phosphate cathode and hard carbon materials are used to construct a sodium-ion battery. The specific steps are as follows:

[0073] (1) Sodium vanadium phosphate, KB, and PVDF are mixed and then added to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF, and N-methylpyrrolidone is 8g:1g:1g:20mL. The slurry is prepared at a concentration of 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain sodium vanadium phosphate cathode.

[0074] (2) Hard carbon material was prepared according to the method of Example 1 and used as the negative electrode. In an argon-protected glove box, a sodium-ion battery was assembled using hard carbon material (negative electrode), sodium vanadium phosphate positive electrode, 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0075] Comparative Example 2:

[0076] The difference between this comparative example and Example 1 is that a sodium-vanadium phosphate positive electrode and a pre-sodium-treated hard carbon negative electrode are used to construct a sodium-ion battery. The specific steps are as follows:

[0077] (1) Sodium vanadium phosphate, KB, and PVDF are mixed and then added to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF, and N-methylpyrrolidone is 8g:1g:1g:20mL. The slurry is prepared at a concentration of 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain sodium vanadium phosphate cathode.

[0078] (2) A pre-sodium hard carbon anode was prepared according to the method of Example 1. In an argon-protected glove box, a sodium-ion battery was assembled using the pre-sodium hard carbon anode, sodium vanadium phosphate cathode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0079] Comparative Example 3:

[0080] The difference between this comparative example and Example 1 is that a sodium-ion battery is constructed using hard carbon material and a pre-sodium-vanadium phosphate cathode. The specific steps are as follows:

[0081] Hard carbon material and pre-sodium vanadium phosphate positive electrode were prepared according to the method of Example 1; a sodium-ion battery was assembled in an argon-protected glove box using hard carbon material (negative electrode), sodium vanadium phosphate positive electrode, 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0082] Comparative Example 4:

[0083] The difference between this comparative example and Example 1 is that the pre-sodium-modified hard carbon anode was not impregnated in a sodium hexafluorophosphate / diethylene glycol dimethyl ether solution during preparation. The specific steps are as follows:

[0084] (1) Hard carbon material was prepared according to the method of Example 1. Under an inert atmosphere, the hard carbon material was immersed in a 0.5M sodium thiophene / ethylene glycol dimethyl ether solution for 5 minutes. After being taken out, it was rinsed with ethylene glycol dimethyl ether and dried to obtain a pre-sodium hard carbon anode.

[0085] (2) A pre-sodium vanadium phosphate positive electrode was prepared according to the method of Example 1. In an argon-protected glove box, a sodium-ion battery was assembled using a pre-sodium hard carbon negative electrode, a pre-sodium vanadium phosphate positive electrode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0086] Comparative Example 5:

[0087] The difference between this comparative example and Example 3 is that a sodium vanadium phosphate positive electrode and a pre-sodium-treated hard carbon negative electrode are used to construct a sodium-ion battery. The specific steps are as follows:

[0088] (1) Sodium vanadium phosphate, KB, and PVDF are mixed and then added to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of sodium vanadium phosphate, KB, PVDF, and N-methylpyrrolidone is 8g:1g:1g:20mL. The slurry is prepared at a concentration of 2.5g / cm³. 2 The coating amount was applied to aluminum foil and dried at 80°C for 10 hours to obtain sodium vanadium phosphate cathode.

[0089] (2) A pre-sodium hard carbon anode was prepared according to the method of Example 3. In an argon-protected glove box, a sodium-ion battery was assembled using the pre-sodium hard carbon anode, sodium vanadium phosphate cathode, a 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0090] Comparative Example 6:

[0091] The difference between this comparative example and Example 2 is that a sodium-ion battery is constructed using hard carbon material and a pre-sodium-vanadium phosphate cathode. The specific steps are as follows:

[0092] Hard carbon material and pre-sodium vanadium phosphate positive electrode were prepared according to the method of Example 2; a sodium-ion battery was assembled in an argon-protected glove box using hard carbon material (negative electrode), sodium vanadium phosphate positive electrode, 1M sodium hexafluorophosphate / diethylene glycol dimethyl ether solution (electrolyte) and glass fiber (separator).

[0093] Experimental Example 1:

[0094] This test was conducted at room temperature using the Land CT2001A battery testing system.

[0095] 1. Constant current charge-discharge tests were performed on the hard carbon material, pre-sodium hard carbon anode, pre-sodium sodium vanadium phosphate cathode (sodium vanadium phosphate + 5% lithium squartz oxide) prepared in Example 1, and the sodium vanadium phosphate cathode and lithium squartz oxide electrode prepared in Comparative Example 1.

[0096] The preparation method of the lithium squaric acid electrode is as follows: lithium squaric acid, KB, and PVDF are mixed and then added to N-methylpyrrolidone for homogenization to obtain a slurry. The material-to-liquid ratio of lithium squaric acid, KB, PVDF, and N-methylpyrrolidone is 8g:1g:1g:20mL. Then, at 2.0g / cm³... 2 The coating amount is applied to aluminum foil and dried at 80°C for 10 hours to obtain lithium succinate electrode.

[0097] During the testing process, the voltage range of the negative electrode was 0.01 V-1.5 V, and the voltage test range of the positive electrode was 1.8 V-4.15 V, with a current density of 50 mA g for both. -1 The result is as follows Figures 1-3 As shown.

[0098] like Figure 1 As shown, after pre-sodiumization, the open-circuit voltage of the hard carbon anode half-cell decreased from 1.27 V to 0.72 V, indicating successful pre-sodiumization. Furthermore, the initial charge / discharge capacity of the hard carbon anode was 263 / 342.2 mAh / g, while that of the pre-sodiumized hard carbon anode was 281.6 / 283.8 mAh / g. The initial coulombic efficiency increased from 76.86% for the initial hard carbon anode to 99.22% for the pre-sodiumized hard carbon anode, fully demonstrating that sodium thiophene effectively pre-sodiumized the hard carbon anode. Figure 2 As shown, within the voltage range of 1.8 V–4.15 V, the sodium replenishment capacity of lithium squarate is 256.8 mAh / g. (As...) Figure 3 As shown, the initial charge and discharge capacities of the initial sodium vanadium phosphate were 102.5 mAh / g and 99.4 mAh / g, respectively, while the initial charge and discharge capacities of the pre-sodiumized sodium vanadium phosphate cathode were 125.9 mAh / g and 101.1 mAh / g, respectively. The initial coulombic efficiency increased from 103.1% to 148.2%, which fully demonstrates that lithium squartz oxide effectively pre-sodiumized the sodium vanadium phosphate cathode.

[0099] 2. The initial coulombic efficiency and cycle life of the sodium-ion batteries of Examples 1-4 and Comparative Examples 1-5 were tested. During the testing, the voltage test range was 2 V-4.15 V, and the current density was 50 mA g. -1 The results are shown in Table 1.

[0100] Table 1. Initial coulombic efficiency and cycle life data of coin cell full cells

[0101]

[0102] As shown in Table 1, neither the positive nor negative electrode underwent pre-sodium treatment (Comparative Example 1), resulting in an initial coulombic efficiency of only 75.2% and a capacity retention of only 60.5% after 200 cycles. This is because the negative electrode consumes a large amount of active sodium ions during SEI formation, and the lack of pre-sodium treatment on the positive electrode leads to insufficient replenishment of active lithium / sodium ions during cycling, further causing SEI and CEI breakdown and accelerating the loss of active sodium ions. Consequently, both coulombic efficiency and cycle stability are significantly reduced.

[0103] Comparative Example 2 and Comparative Example 3, which only pre-sodium-treated the negative electrode, showed initial coulombic efficiencies of only 95.3% and 93.2%, respectively, and 200-cycle capacity retention rates of 92.5% and 94.4%, respectively. However, the present invention, which pre-sodium-treated both the positive and negative electrodes simultaneously (Example 1), achieved an initial coulombic efficiency of 97.2% and a 200-cycle capacity retention rate of 98.2%. Therefore, simultaneous pre-sodium-treated positive and negative electrodes not only improves initial coulombic efficiency but also enhances cycle stability.

[0104] As can be seen from Examples 1-4, increasing the sodium thiophene pretreatment time and appropriately increasing the amount of lithium squartz oxide added can improve the initial coulombic efficiency and cycle stability. In Example 4, due to the increased sodium thiophene pretreatment time and the addition of sufficient lithium squartz oxide, the lithium squartz oxide decomposes during charging, generating additional capacity contribution. The assembled battery achieved an initial coulombic efficiency of up to 100.5% and a 200-cycle retention rate of up to 99.5%.

[0105] As can be seen from Comparative Example 4, when preparing the pre-sodium hard carbon anode, only the sodium thiophene / ethylene glycol dimethyl ether solution was used to treat the hard carbon material, and the sodium hexafluorophosphate / diethylene glycol dimethyl ether solution was not used for treatment. Since SEI was not generated on the surface of the anode material, the initial coulombic efficiency of the sodium-ion battery was significantly lower than that of Example 1.

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for constructing a sodium-ion battery with positive / negative electrode coupling and pre-sodiumation, characterized in that, Includes the following steps: (1) Under an inert atmosphere, the hard carbon material is immersed in a sodium thiophene / diethylene glycol dimethyl ether solution for the first time, then washed and immersed in a sodium hexafluorophosphate / diethylene glycol dimethyl ether solution for the second time. After drying, a pre-sodium hard carbon anode is obtained. The inert atmosphere is argon; the concentration of sodium thiophene / ethylene glycol dimethyl ether solution is 0.4-0.6M; the concentration of sodium hexafluorophosphate / diethylene glycol dimethyl ether solution is 0.8-1.2M; the first immersion time is 1-10 min; the second immersion time is 1-5 min. (2) After mixing sodium vanadium phosphate, conductive agent and binder, add to solvent for homogenization to obtain slurry; add lithium squaric acid to slurry, mix well and coat onto substrate, dry to obtain pre-sodium vanadium phosphate positive electrode; (3) Construct a sodium-ion battery using a pre-sodium hard carbon anode, a pre-sodium vanadium phosphate cathode, and an electrolyte; The amount of lithium squaric acid added is 0.5%-10% of the mass of sodium vanadium phosphate.

2. The method for constructing a sodium-ion battery with positive / negative electrode coupling pre-sodiumization as described in claim 1, characterized in that, In step (1), the hard carbon material is prepared by the following method: Hard carbon, Super P, and CMC-Na are mixed in a mass ratio of (6-10):1:1 to obtain a mixture; the mixture is added to water for homogenization to obtain a homogenate; the homogenate is coated onto aluminum foil and dried at 50-70℃ for 8-12 hours to obtain hard carbon material. The mixture and water have a material-to-liquid ratio of 1g:(3-5)mL, and the coating amount of the homogenate on the aluminum foil is 1.0-2.0g / cm². 2 .

3. The method for constructing a sodium-ion battery with positive / negative electrode coupling pre-sodiumization as described in claim 1, characterized in that, In step (2), the conductive agent is one or more of Super P, KB, CNTs, and conductive graphite; the binder is one or more of polyvinylidene fluoride, PTFE, sodium carboxymethyl cellulose, or sodium alginate; and the solvent is N-methylpyrrolidone.

4. The method for constructing a sodium-ion battery with positive / negative electrode coupling pre-sodiumization as described in claim 1, characterized in that, In step (2), the ratio of sodium vanadium phosphate, conductive agent, binder and solvent is (0.6-1.0)g: (0.05-0.15)g: (0.05-0.15)g: 2mL.

5. The method for constructing a sodium-ion battery with positive / negative electrode coupling pre-sodiumization as described in claim 1, characterized in that, In step (2), the substrate is aluminum foil, and the coating amount is 2.0-3.0 g / cm³. 2 The drying temperature is 70-90℃ and the drying time is 8-12 hours.

6. The method for constructing a sodium-ion battery with positive / negative electrode coupling pre-sodiumization as described in claim 1, characterized in that, In step (3), the electrolyte is a sodium hexafluorophosphate / diethylene glycol dimethyl ether solution with a concentration of 0.8-1.2M.

7. A sodium-ion battery with positive / negative electrode coupling pre-sodiumization constructed by the construction method according to any one of claims 1-6.

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