Preparation method and application of anion-doped sodium-ion battery negative electrode material

Abstract

This invention relates to a method for preparing anion-doped sodium-ion battery anode materials and their applications, belonging to the field of sodium-ion battery technology. This invention utilizes a reducing atmosphere sintering process to reduce anionic oxides to anions, which then act as dopants and crystallization inhibitors. This regulates nanoscale disorder within phosphate-based materials, optimizing the ion transport performance and surface activity of the phosphate-based sodium-ion battery anode material. The anion-doped sodium-ion battery anode of this invention exhibits a significantly reduced electrode voltage plateau to near disappearance within the 3–0.01 V voltage range, while possessing a discharge specific capacity of 220–240 mAh / g and a discharge specific energy of 260–315 mWh / g. It demonstrates excellent rate performance at low rates (0.2C, 223.33 mAh / g) and high rates (10C, 170.26 mAh / g); and exhibits stable performance after 2000 cycles at high rates (with 85% capacity retention at 20C).

Description

Technical Field

[0001] This invention relates to a method for preparing anion-doped sodium-ion battery anode material and its application, belonging to the field of sodium-ion battery technology. Background Technology

[0002] Sodium titanium phosphate is a phosphate-based crystalline electrode material, and crystalline electrode materials also face certain challenges. Especially under high current density operating conditions, significant volume expansion and contraction can lead to cycle stability issues. With repeated charge and discharge cycles, the insertion and extraction of sodium ions in the electrode material often damages the crystal structure, thereby causing a decline in the battery's electrochemical performance. Summary of the Invention

[0003] To address the issues of electrochemical performance degradation in sodium-ion batteries, this invention proposes a method for preparing and applying anion-doped sodium-ion battery anode materials. It employs a three-pronged design strategy of "disordering-conductivity-interface stabilization" to overcome the dependence of crystalline materials on long-range order, providing a high-power, long-life sodium-ion battery system. By sintering in a reducing atmosphere to reduce anionic oxides to anions, which then act as dopants and crystallization inhibitors, nanoscale disorder is regulated within the phosphate-based material, optimizing the ion transport performance and surface activity of the phosphate-based sodium-ion battery anode material.

[0004] A method for preparing anion-doped sodium-ion battery anode material, the specific steps of which are as follows: (1) Dissolve raw material A and ammonium dihydrogen phosphate in deionized water to obtain mixed solution B. Add sodium carbonate, mixed solution B and tetrabutyl titanate to ethylene glycol solution and mix to obtain mixed solution C. Adjust the pH of mixed solution C to 7.0~10.5 with ammonia water. Co-precipitate under stirring to obtain gel. The raw material A is thiourea, selenium dioxide or tellurium dioxide. (2) The gel was placed at a temperature of 100~160℃ for hydrothermal reaction for 18~30h, cooled to room temperature, and the solid and liquid were separated. The solid was washed with deionized water and anhydrous ethanol in sequence, dried, and ground to obtain anion-doped precursor powder. (3) Anion-doped precursor powder is calcined at 500~800℃ for 2~8h to obtain anion-doped sodium titanium phosphate powder. (4) The anion-doped sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain anion-doped sodium titanium phosphate dispersion. The carbon source is added to the anion-doped sodium titanium phosphate dispersion and stirred for 2-6 hours. The solvent is evaporated and then calcined at 600-900℃ for 2-6 hours to obtain anion-doped sodium titanium phosphate electrode material.

[0005] Preferably, in step (1), the molar ratio of raw material A to ammonium dihydrogen phosphate is 3~9:1; the molar ratio of sodium carbonate, ammonium dihydrogen phosphate, and tetrabutyl titanate is (0.505~2.25):(2.8~3.2):(1.5~2.6).

[0006] Preferably, in step (4), the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1~4, and the concentration of the anion-doped sodium titanium phosphate dispersion is 0.04~0.08 g / mL.

[0007] Preferably, the carbon source in step (4) is citric acid, carbon nanotubes, graphene, dopamine, or rhodamine.

[0008] Preferably, the mass ratio of the carbon source to the anion-doped sodium titanium phosphate powder is 0.04~0.15:1.

[0009] An anion-doped sodium titanium phosphate-based electrode sheet is disclosed, wherein the active component is anion-doped sodium-ion battery anode material. Specifically, anion-doped sodium titanium phosphate electrode material powder, a conductive agent, a binder, and an organic solvent are mixed evenly to obtain an electrode slurry. The electrode slurry is uniformly coated on the surface of a cathode current collector and vacuum dried to obtain the anion-doped sodium titanium phosphate-based electrode sheet.

[0010] The amount of conductive agent added is 15-25% of the mass of the anion-doped sodium titanate electrode material powder, and the amount of binder added is 5-15% of the mass of the anion-doped sodium titanate electrode material powder.

[0011] The conductive agent is conductive graphite, conductive carbon black, acetylene black, Super P or carbon nanoparticles, the binder is polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE) or sodium alginate, the organic solvent is N-methylpyrrolidone (NMP), and the cathode current collector is copper foil, aluminum foil, microporous copper foil coated with carbon, or titanium foil.

[0012] The active layer thickness on the surface of the cathode current collector is 10~14μm.

[0013] A method for testing battery performance using anion-doped sodium titanium phosphate-based electrode sheets as sodium-ion electrodes: A sodium-ion half-cell is assembled with anion-doped sodium titanium phosphate-based electrode sheet as the anode, a metallic sodium sheet as the cathode and reference electrode, a glass fiber membrane as the separator, and an ether-based electrolyte. Charge-discharge performance tests are conducted at different rates. The ether-based electrolyte contains NaPF6 as the electrolyte and diethylene glycol dimethyl ether as the solvent. The concentration of NaPF6 is 0.5~1.5 mol / L.

[0014] The beneficial effects of this invention are: (1) The present invention reduces anionic oxides to anions by sintering in a reducing atmosphere, which serves as a dopant and crystallization inhibitor, thereby regulating nanoscale disorder in phosphate-based materials and optimizing the ion transport performance and surface activity of phosphate-based sodium-ion battery anode materials. (2) The method of preparing carbon source coated electrode negative electrode powder in segments according to the present invention makes the carbon source coating more uniform, breaks through the dependence of crystal materials on long-range order, and provides a high-power, long-life sodium-ion battery system. (3) The negative electrode of the anion-doped sodium-ion battery of the present invention has a significantly reduced electrode voltage plateau in the voltage range of 3~0.01V to almost disappear and has a discharge specific capacity of 220~240mAh / g and a discharge specific energy of 260~315mWh / g. It has good rate performance at low rate of 0.2C (223.33mAh / g) and high rate of 10C (170.26mAh / g). It has stable performance for 2000 long cycles at high rate (the specific capacity retention rate is still 85% at 20C rate). Attached Figure Description

[0015] Figure 1 The XRD pattern of anion-doped sodium titanium phosphate powder in Example 1; Figure 2 Here is a SEM image of anion-doped sodium titanium phosphate powder from Example 1; Figure 3 The image shows the XRD patterns of anion-doped sodium titanium phosphate powder coated with carbon source at different temperatures in Example 1. Figure 4 Here is a SEM image of the anion-doped sodium titanium phosphate low-temperature (600℃) carbon source-coated powder from Example 1; Figure 5 Here is a SEM image of the anion-doped sodium titanium phosphate high-temperature (760°C) carbon source-coated powder from Example 1. Figure 6 This is a charge-discharge curve of the first two cycles of a CR2032 stainless steel button sodium-ion half-cell assembled with anion-doped sodium titanium phosphate electrode sheet and an uncoated sodium titanium phosphate electrode sheet, as shown in Example 1. Figure 7 This is a charge-discharge curve of a CR2032 stainless steel button sodium-ion half-cell assembled with uncoated carbon titanium phosphate sodium-based electrode sheets under different charge-discharge rates, as shown in Example 1. Figure 8 The charge-discharge curves of the CR2032 stainless steel button sodium-ion half-cell assembled with anion-doped sodium titanium phosphate-based electrode sheet in Example 1 are shown at different charge-discharge rates. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0017] Example 1: A method for preparing anion-doped sodium-ion battery anode material, the specific steps of which are as follows: (1) Raw material A (selenium dioxide) and ammonium dihydrogen phosphate are dissolved in deionized water to obtain mixed solution B. Sodium carbonate, mixed solution B and tetrabutyl titanate are added to ethylene glycol solution and mixed to obtain mixed solution C. The pH of mixed solution C is adjusted to 7.0 with ammonia water. Co-precipitation is carried out under stirring to obtain gel. The molar ratio of raw material A (selenium dioxide) to ammonium dihydrogen phosphate is 3:1. The molar ratio of sodium carbonate, ammonium dihydrogen phosphate and tetrabutyl titanate is 0.525:3:2. Sodium carbonate is slightly in excess to balance the loss of sodium ions in subsequent processes. (2) The gel was placed at 160℃ for hydrothermal reaction for 18h, cooled to room temperature, and the solid and liquid were separated. The solid was washed 4 times with deionized water and anhydrous ethanol respectively, dried at 60℃, and ground to obtain anion-doped precursor powder. (3) The anion-doped precursor powder was calcined at 620℃ for 3 hours to obtain anion-doped sodium titanium phosphate powder; the XRD pattern of the anion-doped sodium titanium phosphate powder in this embodiment is shown in the figure. Figure 1 ,from Figure 1 It can be seen that the structure of selenium-doped sodium titanium phosphate powder is mainly amorphous, exhibiting a broad peak in the range of 2θ = 18°-35°. This broad peak reflects the short-range atomic order of the selenium-doped sodium titanium phosphate powder material, but the long-range crystallinity is suppressed. However, at 2θ = 24.3°, corresponding to the (113) crystal plane, a low-intensity and identifiable diffraction peak was observed, indicating that local nanocrystalline domains are embedded in the amorphous matrix. The SEM image of the anion-doped sodium titanium phosphate powder in this embodiment is shown in [image missing]. Figure 2 ,from Figure 2 The SEM images reveal the temperature-dependent morphological evolution of the selenium-doped sodium titanium phosphate (NTP / Se) material under carbon coating treatment. For the uncoated NTP / Se, its microstructure consists of numerous fine nanoparticles aggregated into larger clusters, a characteristic consistent with the amorphous properties confirmed by X-ray diffraction (XRD) analysis. These amorphous nanoparticles may originate from the lattice distortion caused by selenium doping during argon-hydrogen reduction, leading to selenium substitution at oxygen sites and promoting the formation of PO3Se. 3- The formation of the structure generated significant local stress, which disrupted the long-range order of the NaTi2(PO4)3 framework and dynamically locked the structure in a metastable amorphous state. (4) Anion-doped sodium titanium phosphate powder was uniformly dispersed in a deionized water-ethanol mixed solution (the volume ratio of deionized water to ethanol was 1:1) to obtain an anion-doped sodium titanium phosphate dispersion with a concentration of 0.8 g / mL. A carbon source (dopamine hydrochloride) was added to the anion-doped sodium titanium phosphate dispersion and stirred for 2 h. The solvent was evaporated and then calcined at 600℃ and 760℃ for 2 h respectively to obtain anion-doped sodium titanium phosphate electrode material. The mass ratio of the carbon source to the anion-doped sodium titanium phosphate powder was 0.05:1. The XRD patterns of the anion-doped sodium titanate powder coated with carbon source at different temperatures in this embodiment are shown below. Figure 3 Phase characterization of Se-doped NTP materials and material samples obtained at different coating temperatures was performed under an argon-hydrogen reducing atmosphere. The X-ray diffraction (XRD) spectra of the synthesized selenium-doped sodium titanium phosphate powder showed that its structure was mainly amorphous, exhibiting a broad peak in the range of 2θ = 18°-35°. This broad peak reflects the short-range atomic order of the material, but the long-range crystallinity is suppressed. However, at 2θ = 24.3°, corresponding to the (113) crystal plane, a low-intensity and identifiable diffraction peak was observed, indicating that local nanocrystalline domains are embedded in the amorphous matrix. This partial crystallization phenomenon may originate from the kinetic confinement crystallization process under an argon-hydrogen reducing atmosphere. In this process, it is possible that the Se element introduced through the SeO2 precursor replaces the oxygen sites (PO4) in the phosphate framework. 3- →PO3Se 3- This leads to lattice distortion. Furthermore, a strongly reducing environment may promote the growth of Ti. 4+ To Ti 3+The reduction, which can be inferred from the slightly broadened diffraction peaks and reduced crystal size, further disrupts the periodic arrangement of the NaTi2(PO4)3 parent structure. The coexistence of amorphous and nanocrystalline phases can be attributed to the doping of the non-uniform crystalline phase Se element. The low-angle region retains a certain degree of residual crystallinity, while the high-angle region becomes amorphous due to severe lattice strain. By comparing and analyzing with the reference XRD pattern (PDF#00-033-1296), it was found that the position of the (113) peak is consistent with the parent structure, indicating that the substitution of Se element did not significantly change the primary lattice parameters, but rather disrupted the long-range periodic arrangement. If these structural features are mainly amorphous, the crystalline structure is expected to improve ionic conductivity and surface reactivity, thus benefiting electrochemical applications. During the carbon coating process, the XRD pattern of the powder material obtained by carbon-coated NTP / C anode material was obtained by sintering at 760℃ for 3h under an argon atmosphere. As shown in the figure, the material underwent secondary recrystallization, which is consistent with the conclusion on crystallization-coating in Chapter 3. The XRD pattern of the carbon-coated NTP / C anode material obtained by sintering at 600℃ for 3h under argon atmosphere shows that carbon source coating treatment at a temperature lower than the powder preparation temperature can effectively avoid crystallization and achieve the purpose of carbon source coating at the same time. SEM images of anion-doped sodium titanium phosphate low-temperature (600℃) carbon source-coated powder are shown below. Figure 4 SEM images of anion-doped sodium titanium phosphate high-temperature (760℃) carbon source-coated powder are shown below. Figure 5 ,from Figure 4-5 It can be seen that when carbon coating is applied at 600℃, the size of the nanoparticles is moderately increased while maintaining their amorphous properties, which is verified by the amorphous peaks in the XRD spectrum. The improved particle dispersion may be due to the carbon layer acting as a physical barrier, effectively mitigating the van der Waals forces between particles. In contrast, the sample treated at 760℃ shows distinct NTP / C crystalline particles with clear cross-sections, highly similar to the crystalline NTP / C material described in Chapter 3. This significant transformation indicates that the high-temperature carbon coating partially eliminates the lattice strain caused by selenium doping by providing a reducing atmosphere; enhancing the Ti... 4 + / Ti 3+ The migration ability of ions, thereby overcoming the kinetic barriers to crystallization and promoting atomic rearrangement, contributes to crystal growth. Notably, the persistent presence of amorphous nanoparticles at 600℃ indicates that selenium doping exhibits a good effect in suppressing crystallization below the critical temperature. It is speculated that the mismatch between the Se-O bond strength and the PO bond strength leads to bond length disorder, thereby increasing the activation energy required for nucleation and thus stabilizing the amorphous layer. An anion-doped sodium titanium phosphate-based electrode sheet, wherein the active component is anion-doped sodium-ion battery negative electrode material; specifically, anion-doped sodium titanium phosphate electrode material powder coated with a carbon source at 600°C (compared to the anion-doped sodium titanium phosphate powder in step (3)), a conductive agent (Super P), a binder (polyvinylidene fluoride PVDF), and an organic solvent (N methyl 2 Pyrrolidone (NMP) is mixed evenly to obtain an electrode slurry. The electrode slurry is uniformly coated on the surface of the cathode current collector (copper foil), and vacuum dried to obtain anion-doped sodium titanium phosphate-based electrode sheet (or uncoated sodium titanium phosphate-based electrode sheet). The amount of conductive agent (Super P) added is 20% of the mass of the anion-doped sodium titanium phosphate electrode material powder (or the anion-doped sodium titanium phosphate powder in step (3)). The amount of binder (NMP) is 20% of the mass of the anion-doped sodium titanium phosphate electrode material powder (or the anion-doped sodium titanium phosphate powder in step (3)). methyl 2 The amount of pyrrolidone (NMP) added is 10% of the mass of the anion-doped sodium titanium phosphate electrode material powder (step (3) anion-doped sodium titanium phosphate powder); the active layer thickness on the cathode current collector surface is 14 μm; A method for testing battery performance using anion-doped sodium titanium phosphate-based electrode sheets (or uncoated sodium titanium phosphate-based electrode sheets) as sodium-ion electrodes: Anion-doped sodium titanium phosphate-based electrode sheets were used as the anode, a metallic sodium sheet as the cathode and reference electrode, and a glass fiber membrane as the separator. The cells were assembled with an ether-based electrolyte in a glove box filled with argon gas and containing less than 1 ppm of moisture to form a CR2032 stainless steel coin-type sodium-ion half-cell. After standing for 8 hours, the electrochemical charge-discharge performance of the sodium titanium phosphate-based electrode sheets was tested (see...). Figure 6 The electrolyte in the ether-based electrolyte is NaPF6, the solvent is diethylene glycol dimethyl ether, and the concentration of NaPF6 is 1 mol / L. In the performance tests at different rates from 0.2C to 20C, the charge-discharge performance curves show that the charge-discharge plateaus of the battery samples assembled with NTP / Se carbon-free coating (uncoated sodium titanium phosphate electrode sheet) and NTP / Se 600℃ carbon-coated coating (anion-doped sodium titanium phosphate electrode sheet in this embodiment) have disappeared, and the charge-discharge curves are sloping. The NTP / Se carbon-free coating (uncoated sodium titanium phosphate electrode sheet) exhibits reversible electrochemical performance. The electrode with original crystalline NTP coated C (anion-doped sodium titanium phosphate electrode sheet in this embodiment) exhibits a voltage plateau of two-phase transition (2.1 V charging / 1.9 V discharging), corresponding to the Na+ phase transition brought about by the remotely ordered framework-controlled two-phase phase transition. +Intercalation / extraction; both the uncoated NTP / Se electrode (uncoated sodium titanate phosphate electrode sheet) and the 600°C carbon-coated NTP / Se electrode (anion-doped sodium titanate phosphate electrode sheet in this embodiment) showed no characteristic slope linearity, indicating a single-phase solid solution reaction mechanism. CR2032 stainless steel coin cell sodium-ion half-cells assembled with uncoated carbon-based titanium phosphate electrode sheets were tested for charge-discharge performance at different rates (see [link to test results]). Figure 7 The reversible specific capacities of the uncoated sodium titanium phosphate-based electrode at rates of 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, and 20 C were 223.44 mAh g, respectively. -1 203.37mAh g -1 185.55mAh g -1 167.04mAh g -1 132.86mAh g -1 89.40mAh g -1 and 56.93mAh g -1 Furthermore, after 20C charge-discharge cycles, the sample's charge-discharge specific capacity remained at 187.81 mAh g after recovering to a 0.2C rate. -1 The reversible specific capacity and anion doping allow it to surpass the limitations of traditional crystalline polyanionic materials. Se doping at oxygen sites disrupts the long-range order of NTP materials, and the modification suppresses the phase transition, as shown by the sloping charge-discharge curve, resulting in anisotropy with reduced activation energy. + diffusion channels; In this embodiment, the CR2032 stainless steel coin cell sodium-ion half-cell assembled with anion-doped sodium titanium phosphate-based electrode sheets was subjected to charge-discharge performance tests at different rates (see...). Figure 8 The reversible specific capacities of the anion-doped sodium titanium phosphate-based electrode at rates of 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, and 20 C were 337.69 mAh g, respectively. -1 288.98mAh g -1 259.79mAh g -1 236.75mAh g -1 212.02mAh g -1 187.24mAh g -1 and 170.26mAhg -1 Furthermore, after 20 C charge-discharge cycles, the sample's charge-discharge specific capacity remained at 223.33 mAh g after recovering to a 0.2 C rate. -1The reversible specific capacity; carbon-coated NTP / Se-C (anion-doped sodium titanium phosphate-based electrode) exhibits good specific capacity at different rates and improves sodium storage performance, demonstrating the synergistic interaction between Se-induced amorphization and transport enhancement by the carbon layer; Se doping creates a permeable Na+ structure through the P-Se-O / Ti-O-Se structure. + The diffusion channels are reflected in the near-linear retention of specific capacity; at the same time, the carbon layer confines the amorphous NTP / Se nanoparticles and passivates the selenium-doped surface, inhibiting the growth of unwanted SEI and the dissolution and extraction of Se.

[0018] Example 2: A method for preparing anion-doped sodium-ion battery anode material, the specific steps of which are as follows: (1) Dissolve raw material A (thiourea) and ammonium dihydrogen phosphate in deionized water to obtain mixed solution B. Add sodium carbonate, mixed solution B and tetrabutyl titanate to ethylene glycol solution and mix to obtain mixed solution C. Adjust the pH of mixed solution C to 9.0 with ammonia water and co-precipitate to obtain gel under stirring conditions. The molar ratio of raw material A (thiourea) to ammonium dihydrogen phosphate is 6:1; the molar ratio of sodium carbonate, ammonium dihydrogen phosphate and tetrabutyl titanate is 1.0:3.0:2.0; sodium carbonate is slightly in excess to balance the loss of sodium ions in subsequent processes. (2) The gel was placed at 140℃ for hydrothermal reaction for 24h, cooled to room temperature, and the solid and liquid were separated. The solid was washed 4 times with deionized water and anhydrous ethanol respectively, dried at 70℃, and ground to obtain anion-doped precursor powder. (3) Anion-doped precursor powder was calcined at 760℃ for 5h to obtain anion-doped sodium titanium phosphate powder. (4) Anion-doped sodium titanium phosphate powder was uniformly dispersed in a deionized water-ethanol mixed solution (the volume ratio of deionized water to ethanol was 1:2) to obtain anion-doped sodium titanium phosphate dispersion with a concentration of 0.6 g / mL. The carbon source (citric acid) was stirred in the anion-doped sodium titanium phosphate dispersion for 4 h, the solvent was evaporated, and then calcined at 760 °C for 4 h to obtain anion-doped sodium titanium phosphate electrode material; the mass ratio of the carbon source to the anion-doped sodium titanium phosphate powder was 0.1:1. An anion-doped sodium titanium phosphate-based electrode sheet, wherein the active component is anion-doped sodium-ion battery negative electrode material; specifically, anion-doped sodium titanium phosphate electrode material powder (compared to the anion-doped sodium titanium phosphate powder in step (3)), conductive agent (conductive carbon black), binder (sodium carboxymethyl cellulose CMC), and organic solvent (N methyl 2 Pyrrolidone (NMP) is mixed evenly to obtain an electrode slurry. The electrode slurry is uniformly coated on the surface of the cathode current collector (copper foil). Vacuum drying yields anion-doped sodium titanate phosphate-based electrode sheet (or uncoated sodium titanate phosphate-based electrode sheet). The amount of conductive agent (conductive carbon black) added is 20% of the mass of the anion-doped sodium titanate phosphate electrode material powder (or the anion-doped sodium titanate phosphate powder in step (3)). The amount of binder (sodium carboxymethyl cellulose CMC) added is 10% of the mass of the anion-doped sodium titanate phosphate electrode material powder (the anion-doped sodium titanate phosphate powder in step (3)). The active layer thickness on the cathode current collector surface is 14 μm. A method for testing battery performance using anion-doped sodium titanium phosphate-based electrode sheets as sodium-ion electrodes: A CR2032 stainless steel coin cell sodium-ion half-cell is assembled with an ether-based electrolyte in a glove box filled with argon gas and containing less than 1 ppm of moisture. After standing for 8 hours, the electrochemical charge-discharge performance of the sodium titanium phosphate-based electrode sheet is tested. The electrolyte in the ether-based electrolyte is NaPF6, the solvent is diethylene glycol dimethyl ether, and the concentration of NaPF6 is 1 mol / L. In this embodiment, a CR2032 stainless steel coin cell sodium-ion half-cell assembled with anion-doped sodium titanium phosphate-based electrode was tested for charge-discharge performance at different rates. The reversible specific capacity of the anion-doped sodium titanium phosphate-based electrode at rates of 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, and 20 C was 320.54 mAh g⁻¹. -1 280.52mAh g -1 250.61mAh g -1 230.21mAh g -1 210.56mAh g -1 176.32mAh g -1 and 162.33mAh g -1 Furthermore, after 20 C charge-discharge cycles, the sample's charge-discharge specific capacity remained at 210.26 mAh g after recovering to a 0.2 C rate. -1 The reversible specific capacity; carbon-coated NTP / SC (anion-doped sodium titanium phosphate-based electrode) exhibits good specific capacity at different rates and improves sodium storage performance, demonstrating the synergistic interaction between S-induced amorphization and transport enhancement by the carbon layer; S doping creates a permeable Na through the PSO / Ti-OS structure. +The diffusion channels are reflected in the near-linear retention of specific capacity; at the same time, the carbon layer confines the amorphous NTP / S nanoparticles and passivates the sulfur-doped surface, inhibiting the growth of unwanted SEI and the dissolution and extraction of S.

[0019] Example 3: A method for preparing anion-doped sodium-ion battery anode material, the specific steps of which are as follows: (1) Raw material A (tellurium dioxide) and ammonium dihydrogen phosphate are dissolved in deionized water to obtain mixed solution B. Sodium carbonate, mixed solution B and tetrabutyl titanate are added to ethylene glycol solution and mixed to obtain mixed solution C. The pH of mixed solution C is adjusted to 10.0 with ammonia water. Co-precipitation is carried out under stirring to obtain gel. The molar ratio of raw material A (tellurium dioxide) to ammonium dihydrogen phosphate is 9:1. The molar ratio of sodium carbonate, ammonium dihydrogen phosphate and tetrabutyl titanate is 2.25:3.2:2.6. Sodium carbonate is slightly in excess to balance the loss of sodium ions in subsequent processes. (2) The gel was placed at 100℃ for hydrothermal reaction for 30h, cooled to room temperature, and the solid and liquid were separated. The solid was washed 4 times with deionized water and anhydrous ethanol respectively, dried at 65℃, and ground to obtain anion-doped precursor powder. (3) Anion-doped precursor powder was calcined at 500℃ for 8 hours to obtain anion-doped sodium titanium phosphate powder. (4) Anion-doped sodium titanium phosphate powder was uniformly dispersed in a deionized water-ethanol mixed solution (the volume ratio of deionized water to ethanol was 1:4) to obtain an anion-doped sodium titanium phosphate dispersion with a concentration of 0.4 g / mL. A carbon source (rhodamine) was added to the anion-doped sodium titanium phosphate dispersion and stirred for 6 h. The solvent was evaporated and then calcined at 900 °C for 2 h to obtain anion-doped sodium titanium phosphate electrode material. The mass ratio of the carbon source to the anion-doped sodium titanium phosphate powder was 0.15:1. An anion-doped sodium titanium phosphate-based electrode sheet, wherein the active component is anion-doped sodium-ion battery negative electrode material; specifically, anion-doped sodium titanium phosphate electrode material powder (compared to the anion-doped sodium titanium phosphate powder in step (3)), conductive agent (conductive graphite), binder (polytetrafluoroethylene PTFE), and organic solvent (N methyl 2 Pyrrolidone (NMP) is mixed evenly to obtain an electrode slurry. The electrode slurry is uniformly coated on the surface of the cathode current collector (copper foil). Vacuum drying yields anion-doped sodium titanate phosphate-based electrode sheet (or uncoated sodium titanate phosphate-based electrode sheet). The amount of conductive agent (conductive graphite) added is 20% of the mass of the anion-doped sodium titanate phosphate electrode material powder (or the anion-doped sodium titanate phosphate powder in step (3)). The amount of binder (polytetrafluoroethylene PTFE) added is 10% of the mass of the anion-doped sodium titanate phosphate electrode material powder (the anion-doped sodium titanate phosphate powder in step (3)). The active layer thickness on the cathode current collector surface is 14 μm. A method for testing battery performance using anion-doped sodium titanium phosphate-based electrode sheets as sodium-ion electrodes: A CR2032 stainless steel coin cell sodium-ion half-cell is assembled with an ether-based electrolyte in a glove box filled with argon gas and containing less than 1 ppm of moisture. After standing for 8 hours, the electrochemical charge-discharge performance of the sodium titanium phosphate-based electrode sheet is tested. The electrolyte in the ether-based electrolyte is NaPF6, the solvent is diethylene glycol dimethyl ether, and the concentration of NaPF6 is 1 mol / L. In this embodiment, a CR2032 stainless steel coin cell sodium-ion half-cell assembled with anion-doped sodium titanium phosphate-based electrode was tested for charge-discharge performance at different rates. The reversible specific capacity of the anion-doped sodium titanium phosphate-based electrode at rates of 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, and 20 C was 330.66 mAh g⁻¹. -1 286.57mAh g -1 257.45mAh g -1 237.89mAh g -1 220.47mAh g -1 185.58mAh g -1 and 173.69mAh g -1 Furthermore, after 20 C charge-discharge cycles, the sample's charge-discharge specific capacity remained at 221.31 mAh g after recovering to a 0.2 C rate. -1 The reversible specific capacity; carbon-coated NTP / Te-C (anion-doped sodium titanium phosphate-based electrode) exhibits good specific capacity at different rates and improves sodium storage performance, demonstrating the synergistic interaction between Te-induced amorphization and transport enhancement by the carbon layer; Te doping creates a permeable Na+ structure through the P-Te-O / Ti-O-Te structure. +The diffusion channels are reflected in the near-linear retention of specific capacity; at the same time, the carbon layer confines the amorphous NTP / Te nanoparticles and passivates the tellurium-doped surface, inhibiting the growth of unwanted SEI and the dissolution and extraction of Te.

[0020] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing anion-doped sodium-ion battery anode material, characterized in that, The specific steps are as follows: (1) Dissolve raw material A and ammonium dihydrogen phosphate in deionized water to obtain mixed solution B. Add sodium carbonate, mixed solution B and tetrabutyl titanate to ethylene glycol solution and mix to obtain mixed solution C. Adjust the pH of mixed solution C to 7.0~10.5 with ammonia water. Co-precipitate under stirring to obtain gel. The raw material A is thiourea, selenium dioxide or tellurium dioxide. (2) The gel was placed at a temperature of 100~160℃ for hydrothermal reaction for 18~30h, cooled to room temperature, and the solid and liquid were separated. The solid was washed with deionized water and anhydrous ethanol in sequence, dried, and ground to obtain anion-doped precursor powder. (3) Anion-doped precursor powder is calcined at 500~800℃ for 2~8h to obtain anion-doped sodium titanium phosphate powder. (4) The anion-doped sodium titanium phosphate powder is uniformly dispersed in a deionized water-ethanol mixed solution to obtain anion-doped sodium titanium phosphate dispersion. The carbon source is added to the anion-doped sodium titanium phosphate dispersion and stirred for 2-6 hours. The solvent is evaporated and then calcined at 600-900℃ for 2-6 hours to obtain anion-doped sodium titanium phosphate electrode material.

2. The method for preparing the anion-doped sodium-ion battery negative electrode material according to claim 1, characterized in that: Step (1) The molar ratio of raw material A to ammonium dihydrogen phosphate is 3~9:1; the molar ratio of sodium carbonate, ammonium dihydrogen phosphate and tetrabutyl titanate is (0.505~2.25):(2.8~3.2):(1.5~2.6).

3. The method for preparing the anion-doped sodium-ion battery negative electrode material according to claim 1, characterized in that: In step (4), the volume ratio of deionized water to ethanol in the deionized water-ethanol mixed solution is 1:1~4, and the concentration of the anion-doped sodium titanium phosphate dispersion is 0.04~0.08 g / mL.

4. The method for preparing the anion-doped sodium-ion battery negative electrode material according to claim 1, characterized in that: Step (4) The carbon source is citric acid, carbon nanotubes, graphene, dopamine or rhodamine.

5. The method for preparing the anion-doped sodium-ion battery negative electrode material according to claim 4, characterized in that: The mass ratio of carbon source to anion-doped sodium titanium phosphate powder is 0.04~0.15:

1.

6. An anion-doped sodium titanium phosphate-based electrode sheet, characterized in that: The active ingredient is the anion-doped sodium-ion battery anode material prepared by the preparation method described in any one of claims 1 to 5.

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