A novel sodium-ion battery sodium ferrosilicate sulfate composite polyanion positive electrode material and a preparation method thereof

Abstract

The application relates to the technical field of sodium ion battery materials, and discloses a novel silicate sulfate sodium ion battery positive electrode material and a preparation method thereof. The application aims to provide the novel silicate sulfate sodium ion battery positive electrode material and the preparation method thereof, solves the preparation problem that high-temperature decomposition of a sulfate polyanion material cannot in-situ coat biocarbon, and verifies the electrochemical activity. The Na2FeSiO4SO4 / C-700 electrode material has a first discharge capacity of 57.79 mAh / g at 0.05 C, and has potential application value in sodium ion batteries.

Description

Technical Field

[0001] This invention relates to a novel sodium iron silicate-sulfate composite polyanionic cathode material for sodium-ion batteries and its preparation method, belonging to the field of sodium-ion battery technology. Background Technology

[0002] With the increasing global energy demand and the growing severity of environmental problems, the development of new and efficient energy storage systems has become particularly important. Lithium-ion batteries, as the most mainstream rechargeable battery technology, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density and long cycle life. However, the uneven geographical distribution of lithium resources and cost issues limit their feasibility for large-scale application. Therefore, the development of novel sodium-ion batteries as an alternative technology has attracted widespread attention. Sodium-ion batteries have a similar working principle to lithium-ion batteries, but sodium resources are more abundant and inexpensive, giving sodium-ion batteries a potential advantage in the field of large-scale energy storage.

[0003] In the research and development of sodium-ion batteries, polyanionic cathode materials have attracted much attention due to their unique structural advantages and excellent electrochemical performance. In particular, sulfate-based polyanionic materials, such as Alluaudite-type Na₂Fe₂(SO₄)₃ and Eldfellite-type NaFe(SO₄)₂, are considered highly promising cathode materials for sodium-ion batteries due to their high operating voltage, long cycle life, and low cost. However, these materials face some problems in practical applications. First, sulfate-based cathode materials are prone to sulfate decomposition at high temperatures, producing SO₂. x The gaseous nature of FeO6 limits the possibility of carbon coating modification through traditional high-temperature pyrolysis processes. Furthermore, the non-conductive SO4 groups connecting FeO6 particles hinder electron transport during charge and discharge, leading to insufficient capacity and rapid capacity decay at high rates. Additionally, solid-state ball milling and low-temperature sintering techniques struggle to achieve uniform mixing of Na, Fe, S, and O elements at the molecular level, hindering element concentration diffusion during low-temperature sintering and easily generating impurities such as Fe3O4 or Na6Fe(SO4)4, affecting the material's electrochemical performance. Finally, although ultrasonic dispersion followed by low-temperature sintering in an aqueous solution containing sodium sulfate and ferrous sulfate can yield composite cathode materials with improved electronic conductivity, conductive carbon materials are generally nanoscale hydrophobic and prone to agglomeration. Simple ultrasonic dispersion is insufficient to achieve complete and uniform dispersion in the aqueous solution, resulting in uneven conductivity distribution within the composite cathode material particles, impacting the battery's high-rate performance and cycle stability. Summary of the Invention

[0004] The purpose of this invention is to provide a novel sodium iron silicate-sulfate composite polyanionic cathode material for sodium-ion batteries and its preparation method. By introducing silicate components, a novel sodium iron silicate-sulfate composite polyanionic cathode material is designed to improve the structural stability and electrochemical performance of the material. This solves the problem that sulfate-based polyanionic materials cannot be thermally decomposed in situ to coat biomass conductive carbon, and further confirms its electrochemical activity and potential application value.

[0005] The objective of this invention can be achieved through the following technical solutions: A sodium-ion battery prepared from a novel sodium iron silicate composite polyanionic cathode material includes the following steps: (1) Sodium source, iron source, silicon source, sulfate, antioxidant and / or carbon source are added to deionized water and continuously stirred to disperse them evenly to obtain a yellow suspension. The suspension is then spray-dried to obtain composite precursor powder.

[0006] (2) After sintering the composite precursor in a tube furnace with an inert atmosphere and cooling it to room temperature, the sodium iron silicate composite cathode material can be obtained.

[0007] (3) Weigh the positive electrode material, conductive carbon black, and binder in a mass ratio of 70:20:10 and dry grind them in an agate mortar for 20-30 min. Add the solvent NMP and wet grind for 30 min to obtain a black slurry with good fluidity. Coat the black slurry evenly on aluminum foil and dry it in a vacuum oven at 100 ℃ for 8 h. Then cut it into circular positive electrode sheets using a cutting machine. Assemble sodium-ion batteries in a glove box filled with Ar (water and oxygen content are both below 0.1 ppm).

[0008] Furthermore, in step (1), the sodium source is sodium sulfate, the iron source is ferrous oxalate or ferrous sulfate, and the silicon source is silicon dioxide.

[0009] Furthermore, in step (1), the molar ratio of sodium sulfate to silicon dioxide is 1~2:1, the molar ratio of ferrous sulfate to silicon dioxide is 0~2:1, the molar ratio of ferrous oxalate to silicon dioxide is 1~2:1, and the chemical formula of the obtained positive electrode material is Na2Fe2(SiO4). x (SO4) y (0.05≤x≤1, 1≤y≤2).

[0010] Furthermore, in step (1), the antioxidant can be citric acid or ascorbic acid, and the molar ratio of citric acid to ferrous heptahydrate is 1:10.

[0011] Furthermore, in step (1), the carbon source accounts for 0-5% of the mass of sodium iron silicate sulfate, and the carbon source can be glucose, sucrose or maltose.

[0012] Furthermore, in step (1), the spray drying temperature is 150~200 ℃.

[0013] Furthermore, in step (1), the inert atmosphere is Ar or N2.

[0014] Furthermore, in step (2), the calcination temperature is 350~700 ℃ and the calcination time is 8~12 h. Beneficial effects

[0015] This invention discloses a novel sulfate silicate Na2Fe2(SiO4). x (SO4) y This (0.05≤x≤1, 1≤y≤2) sodium-ion battery cathode material utilizes a simple spray drying and sintering process. By innovatively introducing silicate ions, a novel sodium iron silicate-sulfate composite polyanionic cathode material was designed, significantly improving the material's thermodynamic stability and effectively preventing sulfate decomposition during high-temperature synthesis. Furthermore, it allows for in-situ coating with low-cost biochar at high temperatures, reducing production costs and enhancing electronic conductivity. The initial discharge specific capacity of Na2Fe2SiO4SO4 / C-700 at 0.05 C is 57.79 mAh / g. This invention not only solves the stability problem of traditional sulfate materials at high temperatures but also provides a new solution for improving the performance and reducing the cost of sodium-ion batteries. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0017] Figure 1 This is a SEM image of the Na2Fe2SiO4SO4 / C-700 material in Example 1.

[0018] Figure 2 This is the XRD pattern of the Na2Fe2SiO4SO4 / C-700 material in Example 1.

[0019] Figure 3 It is the Na2Fe2(SiO4) prepared in Example 11. 0.5 SEM image of (SO4)2 / C-700 material.

[0020] Figure 4 It is the Na2Fe2(SiO4) prepared in Example 11. 0.5XRD pattern of (SO4)2 / C-700 material.

[0021] Figure 5 The first constant current charge-discharge performance at 0.05 C of the Na2Fe2SiO4SO4 / C-700 cathode material in Example 1 is shown.

[0022] Figure 6 This is a rate performance test of the Na2Fe2SiO4SO4 / C-700 cathode material in Example 1. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0024] Preparation of Na2FeSiO4SO4 / C-700 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. The sodium sulfate, ferrous oxalate, and silica mixed suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 700 °C for 10 h and then cooled to room temperature to obtain the Na2FeSiO4SO4 / C-700 composite cathode material.

[0025] The Na2FeSiO4SO4 / C-700 positive electrode material prepared in Example 1 of this invention was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C ~ 0.5 C (1 C = 135 mA / g).

[0026] Figure 1 The image shows a SEM image of the Na2FeSiO4SO4 / C-700 material prepared in Example 1. The composite material has an irregular blocky morphology.

[0027] Figure 2 The XRD pattern of the Na2FeSiO4SO4 / C-700 material prepared in Example 1 shows that the material has good crystallinity.

[0028] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 1 at 0.05 C is 57.79 mAh / g. Example 2

[0029] Preparation of Na2FeSiO4SO4 / C-600 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. The sodium sulfate, ferrous oxalate, and silica mixed suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 600 °C for 10 h and then cooled to room temperature to obtain the Na2FeSiO4SO4 / C-600 composite cathode material.

[0030] The Na2FeSiO4SO4 / C-600 positive electrode material prepared in Example 2 of this invention was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0031] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 2 at 0.05 C is 46.05 mAh / g. Example 3

[0032] Preparation of Na2FeSiO4SO4 / C-500 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. The sodium sulfate, ferrous oxalate, and silica mixed suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 500 °C for 10 h and then cooled to room temperature to obtain the Na2FeSiO4SO4 / C-500 composite cathode material.

[0033] The Na2FeSiO4SO4 / C-500 positive electrode material prepared in Example 3 of this invention was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0034] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 3 at 0.05 C is 36.62 mAh / g. Example 4

[0035] Preparation of Na2FeSiO4SO4-700 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 700 °C for 10 h and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-700 composite cathode material.

[0036] The Na2FeSiO4SO4-700 positive electrode material prepared in Example 4 of this invention was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0037] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 4 at 0.05 C is 45.44 mAh / g. Example 5

[0038] Preparation of Na2FeSiO4SO4-600 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 600 °C for 10 h and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-600 composite cathode material.

[0039] The Na2FeSiO4SO4-600 positive electrode material prepared in Example 5 of this invention was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 (1 C = 135 mA / g).

[0040] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 5 at 0.05 C is 33.70 mAh / g. Example 6

[0041] Preparation of Na2FeSiO4SO4-550 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 550 °C for 10 h, and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-550 composite cathode material.

[0042] The Na2FeSiO4SO4-550 positive electrode material prepared in Example 6 of this invention was mixed with a conductive agent and a binder in a ratio of 40:40:20 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0043] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 6 at 0.05 C is 25.62 mAh / g. Example 7

[0044] Preparation of Na2FeSiO4SO4-500 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 500 °C for 10 h and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-500 composite cathode material.

[0045] The Na2FeSiO4SO4-500 positive electrode material prepared in Example 7 of this invention was mixed with a conductive agent and a binder in a ratio of 40:40:20 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0046] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 7 at 0.05 C is 80.06 mAh / g. Example 8

[0047] Preparation of Na2FeSiO4SO4-450 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 450 °C for 10 h and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-450 composite cathode material.

[0048] The Na2FeSiO4SO4-450 positive electrode material prepared in Example 8 of this invention was mixed with a conductive agent and a binder in a ratio of 40:40:20 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0049] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 8 at 0.05 C is 97.12 mAh / g. Example 9

[0050] Preparation of Na2FeSiO4SO4-400 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 400 °C for 10 h, and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-400 composite cathode material.

[0051] The Na2FeSiO4SO4-400 positive electrode material prepared in Example 9 of this invention was mixed with a conductive agent and a binder in a ratio of 40:40:20 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0052] The electrochemical performance of the assembled batteries is shown in Table 1. As can be seen from the table, Example 9 had an initial discharge capacity of 157.73 mAh / g at 0.05 C. The fact that Example 9's discharge capacity at 0.05 C exceeded the theoretical specific capacity may be due to electrolyte decomposition. Example 10

[0053] Preparation of Na2FeSiO4SO4-350 material: Weigh sodium sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 1:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 350 °C for 10 h, and then cooled to room temperature to obtain the Na₂FeSiO₄SO₄-350 composite cathode material.

[0054] The Na2FeSiO4SO4-350 positive electrode material prepared in Example 10 of this invention was mixed with a conductive agent and a binder in a ratio of 40:40:20 to form a uniform slurry. Subsequently, the resulting black slurry was coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain a working electrode. Then, the obtained working electrode was cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance testing was performed under Neware system monitoring, with a test voltage range of 1.5~4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 135 mA / g).

[0055] The electrochemical performance of the assembled batteries is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 10 at 0.05 C was 273.29 mAh / g. The fact that the discharge capacity of Example 10 at 0.05 C exceeded the theoretical specific capacity may be due to electrolyte decomposition. Example 11

[0056] Preparation of Na2Fe2(SiO4) 0.5 (SO4)2 / C-700 material: Weigh out sodium sulfate, ferrous sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 2:2:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a pale yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 700 °C for 10 h and then cooled to room temperature to obtain Na₂Fe₂(SiO₄). 0.5 (SO4)2 / C-700 cathode material.

[0057] The Na2Fe2(SiO4) prepared in Example 11 of this invention 0.5(SO4)2 / C-700 positive electrode material was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 120 mA / g).

[0058] Figure 3 Preparation of Na2Fe2(SiO4) for Example 11 0.5 SEM image of (SO4)2 / C-700 material, which has a micron-scale bulk structure.

[0059] Figure 4 Preparation of Na2Fe2(SiO4) for Example 11 0.5 The XRD pattern of (SO4)2 / C-700 material shows that the material has good crystallinity.

[0060] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 11 at 0.05 C is 44.18 mAh / g. Example 12

[0061] Preparation of Na2Fe2(SiO4) 0.5 (SO4)2 / C-600 material: Weigh out sodium sulfate, ferrous sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 2:2:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a pale yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 600 °C for 10 h and then cooled to room temperature to obtain Na₂Fe₂(SiO₄). 0.5 (SO4)2 / C-600 cathode material.

[0062] The Na2Fe2(SiO4) prepared in Example 12 of this invention 0.5 (SO4)2 / C-600 positive electrode material was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 120 mA / g).

[0063] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 12 at 0.05 C is 32.44 mAh / g. Example 13

[0064] Preparation of Na2Fe2(SiO4) 0.5 (SO4)2 / C-500 material: Weigh out sodium sulfate, ferrous sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 2:2:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid and 5 wt% glucose were added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a pale yellow solid powder, which was then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 500 °C for 10 h and then cooled to room temperature to obtain Na₂Fe₂(SiO₄). 0.5 (SO4)2 / C-500 cathode material.

[0065] The Na2Fe2(SiO4) prepared in Example 13 of this invention 0.5(SO4)2 / C-500 positive electrode material was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.05 C (1 C = 120 mA / g).

[0066] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 13 at 0.05 C is 23.01 mAh / g. Example 14

[0067] Preparation of Na2Fe2(SiO4) 0.5 (SO4)2-700 Material: Weigh out sodium sulfate, ferrous sulfate, ferrous oxalate, and silicon dioxide according to a molar ratio of 2:2:2:1 and add them to deionized water. Stir continuously for 2-3 hours, while maintaining the ratio of citric acid to Fe. 2+ A suitable amount of citric acid was added at a molar ratio of 10:1, resulting in a yellow and uniformly dispersed mixed suspension of sodium sulfate, ferrous sulfate, ferrous oxalate, and silica. This suspension was dried in a spray dryer at 200 °C to obtain a pale yellow solid powder, which was then vacuum-dried in a vacuum oven at 100 °C for 10 h to obtain the precursor powder. The precursor powder was sintered in a tube furnace under an Ar atmosphere at 700 °C for 10 h and then cooled to room temperature to obtain Na₂Fe₂(SiO₄). 0.5 (SO4)2-700 cathode material.

[0068] The Na2Fe2(SiO4) prepared in Example 14 of this invention 0.5(SO4)2-700 positive electrode material was mixed with a conductive agent and a binder in a ratio of 70:20:10 to form a uniform slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular positive electrode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheets were used as the negative electrode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.05 C–0.5 C (1 C = 120 mA / g).

[0069] The electrochemical performance of the assembled battery is shown in Table 1. As can be seen from the table, the initial discharge capacity of Example 14 at 0.05 C is 21.03 mAh / g. Comparative Example 1

[0070] Preparation of Na 2+2x Fe 2-x (SO4)3 Material: Na₂SO₄ and FeSO₄·7H₂O in a molar ratio of 1:1 were dissolved in 25 ml of deionized water, and the solution was stirred continuously until dissolved. During this process, appropriate amounts of ascorbic acid and glucose were added, and the solution was stirred thoroughly for 10 min to obtain a clear solution. The mixed solution was added dropwise to 100 ml of ethanol solution to obtain a grayish-green precipitate. The precipitate was washed with alcohol, filtered, and dried at 60 °C for 12 h to obtain a precursor powder. The precursor powder was calcined at 350 °C under an Ar atmosphere for 2 h to obtain the product Na. 2+2x Fe 2-x (SO4)3.

[0071] Na prepared according to Comparative Example 1 of the present invention 2+2x Fe 2-x (SO4)3 cathode material was mixed with conductive agent and binder in a ratio of 70:20:10 to form a homogeneous slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular cathode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheet was used as the anode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.1 C (1 C = 100 mA / g).

[0072] The electrochemical performance of the battery assembled in Comparative Example 1 is 22.5 mAh / g at a discharge capacity of 0.1 C. Comparative Example 2

[0073] Preparation of Na 2+2x Fe 2-x (SO4)3 Material: Na₂SO₄ and FeSO₄·7H₂O in a molar ratio of 1:2 were dissolved in 25 ml of deionized water and stirred continuously until dissolved. During this process, appropriate amounts of ascorbic acid and glucose were added, and the mixture was stirred thoroughly for 10 min to obtain a clear solution. The mixed solution was added dropwise to 100 ml of ethanol solution to obtain a grayish-green precipitate. The precipitate was washed with alcohol, filtered, and dried at 60 °C for 12 h to obtain a precursor powder. The precursor powder was calcined at 350 °C under an Ar atmosphere for 2 h to obtain the product Na. 2+2x Fe 2-x (SO4)3.

[0074] Na prepared according to Comparative Example 2 of the present invention 2+2x Fe 2-x (SO4)3 cathode material was mixed with conductive agent and binder in a ratio of 70:20:10 to form a homogeneous slurry. The resulting black slurry was then coated onto aluminum foil using a scraper and dried in a vacuum oven at 100 °C for 10 h to obtain the working electrode. The working electrode was then cut into circular cathode sheets with a diameter of 1.1 cm using a cutting machine. Sodium sheet was used as the anode material, 1 M NaClO4EC:PC = 1:1 and 5 vol% FEC were used as the electrolyte, and glass fiber was used as the separator to prepare a button cell. Electrochemical performance tests were performed under Neware system monitoring, with a test voltage range of 1.5–4.5 V, a test temperature of 30 °C, and a current density of 0.1 C (1 C = 100 mA / g).

[0075] The electrochemical performance of the battery assembled in Comparative Example 2 is 21.0 mAh / g at a discharge capacity of 0.1 C.

[0076] Table 1 shows the electrochemical performance test results of the half-cell in the examples. It can be seen that carbon coating improves the first-cycle discharge capacity of the material, further demonstrating that the introduction of silicate ions can improve the thermodynamic stability of sulfate, enabling in-situ coating of bio-carbon at high temperatures. Carbon coating increases the Na... + The increased ion transport rate resulted in a higher discharge specific capacity. Overall, the performance of Na₂FeSiO₄SO₄ material is superior to that of Na₂Fe₂(SiO₄). 0.5 (SO4)2 is more stable, possibly due to its superior crystal structure and Na.+ Diffusion channel.

[0077] Table 1. Results of half-cell electrochemical performance tests

[0078] from Figure 5 It can be seen that the sodium-ion battery prepared in Example 1 has an initial discharge specific capacity of 57.79 mAh / g at a current density of 0.05 C, indicating that the Na2FeSiO4SO4 / C-700 composite cathode material can indeed achieve Na… + Reversible embedding.

[0079] from Figure 6 It can be seen that the sodium-ion battery prepared in Example 1 has a decent discharge specific capacity at current densities of 0.05 C, 0.1 C, and 0.2 C, but its discharge specific capacity is poor at higher current densities, such as 0.5 C, 1.0 C, and 2.0 C. The inherent low electronic conductivity of the polyanionic material limits the capacity utilization at high rates.

[0080] Combination Figure 5 and Figure 6 It can be inferred that Na2FeSiO4SO4 / C materials cannot fully realize their discharge specific capacity due to the inherent low electronic conductivity of polyanions, and require further hierarchical structures or nano-scale strategies to improve their energy storage performance.

[0081] The embodiments listed above are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that changes and improvements can be made to the invention without departing from the scope of the principles of the invention.

Claims

1. A method for preparing a sodium-ion battery composite polyanionic cathode material of iron iron silicate and sulfate, characterized in that, The sodium-ion battery iron silicate composite polyanionic cathode material is prepared using the following steps: (1) Sodium sulfate, iron source, silicon source, antioxidant and carbon source are added to deionized water and continuously stirred to disperse them evenly to obtain a yellow suspension. The suspension is then spray-dried to obtain a composite precursor powder. (2) After sintering the composite precursor in a tube furnace with an inert atmosphere and cooling it to room temperature, carbon-coated Na2Fe2(SiO4) can be obtained. x (SO4) y / C cathode material, 0.05≤x≤1, 1≤y≤2; the iron source is ferrous oxalate, the silicon source is silicon dioxide; the antioxidant is citric acid, the molar ratio of citric acid to ferrous oxalate is 1:10; the spray drying temperature is 150~200 ℃, and the carbon source is glucose, sucrose or maltose.

2. The method for preparing a sodium-ion battery composite polyanionic cathode material of sodium iron silicate sulfate according to claim 1, characterized in that, The molar ratio of sodium sulfate to silicon dioxide is 1~2:1, and the molar ratio of ferrous oxalate to silicon dioxide is 1~2:

1.

3. The method for preparing a sodium-ion battery composite polyanionic cathode material of sodium sulfate and iron silicate according to claim 1, characterized in that, The carbon source accounts for 0-5% of the mass of sodium iron silicate sulfate.

4. The method for preparing a sodium-ion battery composite polyanionic cathode material of sodium iron silicate sulfate according to claim 1, characterized in that, The inert atmosphere is Ar or N2.

5. The method for preparing a sodium-ion battery composite polyanionic cathode material of sodium iron silicate sulfate according to claim 1, characterized in that, The sintering temperature is 350~700 ℃, and the calcination time is 8~12 h.

6. A sodium-ion battery composite polyanionic cathode material made of sodium iron silicate sulfate, which is prepared according to any one of claims 1-5.

7. A method for preparing a sodium-ion battery, characterized in that, The sodium-ion battery is prepared using the sodium iron silicate composite polyanionic cathode material according to any one of claims 1-6, comprising the following steps: Weigh out the positive electrode material, conductive carbon black, and binder in a mass ratio of 70:20:10 and dry grind them in an agate mortar for 20-30 min. After adding NMP solvent, wet grind for 30 min to obtain a black slurry with good fluidity. Coat the black slurry evenly on aluminum foil and dry it in a vacuum oven at 100 ℃ for 8 h. Then cut it into circular positive electrode sheets using a cutting machine and assemble them in a glove box filled with Ar gas, where the water and oxygen contents are both less than 0.1 ppm.

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