Based on ultra-small Na x Fe y M z (SO4)3: a lossless fast-charging cathode material, its preparation method, and its application.

Abstract

This invention belongs to the field of electrode materials, and specifically discloses a method based on ultra-small Na particles. x Fe y M z Lossless Fast-Charging Cathode Material of (SO4)3, its Preparation Method and Application. The molecular formula of this cathode material is Na. x Fe y M z (SO4)3, where 1.0≤x≤3.0, 0.5≤y≤2.0, 0.5≤z≤1.5, and M is a transition metal; and the particle size of the cathode material is between 10-80 nm. This invention synthesizes a Na with ultra-small particles using a low-temperature solvothermal, flash drying, and low-temperature calcination method. x Fe y M z (SO4)3 is a lossless fast-charging cathode material, which is used in sodium-ion batteries. Its ultra-small particle size helps to shorten the diffusion path of ions and electrons, enabling rapid transport of sodium ions. In addition, the partial substitution of transition metal ions further improves the reactivity of the material, thereby enhancing the rate performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of electrode materials, and particularly relates to a method based on ultra-small Na particles. x Fe y M z (SO4)3 non-destructive fast-charging cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their small size, light weight, and high energy density. However, the scarcity and uneven distribution of global lithium resources limit their large-scale development. Sodium-ion batteries share a similar structure and working mechanism with lithium-ion batteries, both based on a rocking chair electrochemical energy storage mechanism. Furthermore, sodium resources are abundant and inexpensive, thus fueling a surge in sodium-ion battery research and development. The cathode material is the most crucial component of the sodium-ion battery system, largely determining its performance, including cost, energy density, rate capability, and cycle life. An ideal battery cathode material should possess the following characteristics: First, it should provide active sodium ions. Second, it should have suitable variable valence elements to provide a relatively high redox potential, enabling higher battery operating voltage and energy density. Third, it should ideally be safe to store in air and non-toxic, reflecting the trend of green chemistry and the mainstream of future development. Stable storage also greatly benefits battery consistency. Developing low-cost, highly electrochemically reversible, and long-cycle-life sodium-ion cathode materials is currently a challenging, key, and hot research topic both domestically and internationally.

[0003] In recent years, reports on cathode materials for sodium-ion batteries have mainly focused on layered oxides, Prussian blue systems, and polyanionic systems. Layered oxides, such as Na... x VO2, Na x MnO2 and similar compounds, due to their layered frameworks connected only by weak ionic bonds, are prone to irreversible phase transitions during electrochemical processes, leading to insufficient cycling performance. Prussian blue systems, such as Na... 1.72 Materials like MnFe(CN)6 readily form [Fe(CN)6] vacancies in their structure, which are easily occupied by water of crystallization, leading to poor battery cycle performance and low coulombic efficiency. Sodium vanadium phosphate cathode materials in polyanionic systems face resource scarcity risks due to the scarcity of vanadium in the Earth's crust, and vanadium's environmental unfriendliness further increases the risks of its use. Therefore, there is an urgent need for a sodium-ion battery cathode material that is suitable for industrial production, environmentally friendly, low-cost, and possesses excellent electrochemical performance to meet the application requirements of sodium-ion batteries.

[0004] Sodium ferric sulfate requires sodium, iron, and sulfur, all elements abundant in the Earth's crust, thus possessing the inherent advantage of low raw material costs. Furthermore, because sulfate ions affect Fe...2+ / Fe 3+ Due to its strong inductive effect, sodium ferric sulfate exhibits a high operating voltage of up to 3.8V in iron-based polyanionic cathode materials, coupled with its suitable theoretical specific capacity of 120mAh g / g. -1 The theoretical energy density of this cathode material is as high as 456 Wh / kg, second only to lithium iron phosphate cathode. However, the sodium iron sulfate material synthesized by existing technology has a large particle size and low material utilization, resulting in poor rate performance, cycle stability, and low sodium storage capacity, which seriously affects its industrialization process.

[0005] To further advance the practical application of sodium ferric sulfate as a cathode material in sodium-ion batteries, modification of sodium ferric sulfate is crucial. In recent years, numerous studies have employed strategies such as ion doping and coating to modulate the electrochemical performance of sodium ferric sulfate materials. Cao et al. constructed graphene-coated sodium ferric sulfate within a three-dimensional graphene microsphere network using a spray-drying method. 2.4 Fe 1.8 (SO4)3 nanoparticles. The unique micro / nano structure and compositional advantages of the material enable the electrode to exhibit good rate performance and long cycle life. However, the entire preparation process is too time-consuming, lasting approximately 48 hours, and requires harsh conditions, including spray drying (J. Energy Chem., 2021, 54, 564). Chinese invention patent CN 106058251 A discloses a method for preparing a core-shell structured Na2Fe2(SO4)3@alumina composite material, which exhibits good physicochemical properties. However, the addition of alumina leads to a decrease in the material's energy density, resulting in a final electrode discharge specific capacity of 69 mAh g. -1 Approximately. Furthermore, existing methods for synthesizing sodium ferric sulfate materials require high temperatures, resulting in a low safety factor; and the resulting material particles are relatively large, leading to low material utilization and poor electrical performance, making it difficult to meet the needs of high-rate charge and discharge. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method based on ultra-small Na... x Fe y M z The non-destructive fast-charging cathode material of (SO4)3, its preparation method, and its application were synthesized by low-temperature solvothermal, flash drying, and low-temperature calcination method, resulting in a material with ultra-small Na particles. x Fe y M z(SO4)3 is a lossless fast-charging cathode material, which is used in sodium-ion batteries. Its ultra-small particle size helps to shorten the diffusion path of ions and electrons, enabling rapid transport of sodium ions. In addition, the partial substitution of transition metal ions further improves the reactivity of the material, thereby enhancing the rate performance of the material.

[0007] To address the aforementioned technical problems, a first aspect of the present invention provides a cathode material, wherein the cathode material has the molecular formula Na. x Fe y M z (SO4)3, wherein 1.0≤x≤3.0, 0.5≤y≤2.0, 0.5≤z≤1.5, and M is a transition metal; the particle size of the cathode material is between 10-80 nm.

[0008] Specifically, the cathode material of this invention has a particle size in the nanometer range. The nanostructured electrode material possesses a shorter ion diffusion path and a larger specific surface area, which facilitates the rapid transport of sodium ions and provides abundant active energy storage sites, thereby improving the material's specific capacity. Simultaneously, the nanostructure of the cathode material helps mitigate the volume expansion caused by sodium ion insertion and extraction, thus improving cycle performance. Furthermore, this invention utilizes transition metal ions to partially replace iron ions to further enhance the material's reactivity, thereby improving its rate performance.

[0009] Preferably, the transition metal is selected from at least one of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ag, Pt, Au, and Hg.

[0010] More preferably, x = 2.0, y = 1, z = 1; and the transition metal is at least one of Mn and Ni.

[0011] A second aspect of the present invention provides a method for preparing a cathode material, used to prepare the cathode material described in the first aspect, comprising the following steps:

[0012] (1) Disperse sodium source, iron source, transition metal source and sulfur source in solvent to obtain suspension;

[0013] (2) The suspension is heated to carry out a solvothermal reaction; after cooling, the products of the solvothermal reaction are sequentially separated, washed, and flash-dried to obtain a product based on Na. x Fe y M z (SO4)3 powder particles;

[0014] (3) The powder particles are calcined under an inert gas atmosphere to obtain the positive electrode material.

[0015] Specifically, this invention synthesizes a Na+ with ultra-small particles using a low-temperature solvothermal, flash drying, and low-temperature calcination method. x Fe y M z A non-destructive, fast-charging positive electrode material of (SO4)3. Compared to the harsh conditions of high preparation temperature and long preparation time in existing technologies, the preparation method of this invention is simple and easy to implement, with low energy consumption, material costs, and equipment requirements, making it more suitable for large-scale industrial production. Specifically, low-temperature solvothermal processes allow for more uniform mixing of the precursor in the solvent, ensuring the uniformity of the synthesized product; the addition of a transition metal source further enhances the reactivity of the product; flash drying facilitates rapid and batch reduction of the water of crystallization content in the product and promotes the large-scale nucleation of solid matter, inhibiting crystal growth and thus forming ultra-small particle precursors; calcination in an inert gas atmosphere promotes the reaction of the precursor to generate the product and improves the product's cycle performance.

[0016] Preferably, the sodium source is selected from at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium chloride, sodium phosphate, sodium nitrate, sodium phosphite, sodium formate, sodium propionate, sodium acrylate, sodium benzoate, sodium hypochlorite, sodium chlorate, sodium thiosulfate, sodium persulfate, sodium silicate, sodium bromate, sodium bromide, sodium iodide, sodium fluoride, sodium bisulfite, sodium nitrite, sodium oxalate, sodium persulfate, sodium hydroxide, sodium pyrosulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium metabisulfite, sodium pyrophosphate, sodium hydrogen phthalate, sodium bioxalate, sodium sulfite, sodium sorbate, trisodium phosphate, sodium gluconate, sodium oleate, and hydrates of the above substances.

[0017] More preferably, the sodium source is at least one of sodium sulfate, sodium bisulfate, and sodium bicarbonate.

[0018] Preferably, the iron source is selected from at least one of ferrous sulfate, ferrous oxide, ferric chloride, ferric nitrate, ferric acetate, ferrous bromide, ferrous nitrate, ferrous phosphate, ferrous iodide, ferrous acetate, ferrous metasilicate, ferrous metatitanate, disodium triferric sulfate, ammonium ferrous sulfate, ferrous carbonate, ferrous chloride, ferrous sulfate, ferrous hydroxide, ferric oxide, ferric dioxide, ferric chloride, ferric hydroxide, and hydrates of the above substances.

[0019] More preferably, the iron source is ferrous sulfate.

[0020] Preferably, the transition metal source is selected from at least one of the soluble salts of scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, silver, platinum, gold, mercury, and hydrates of the above substances.

[0021] More preferably, the transition metal source is at least one of manganese sulfate and nickel sulfate.

[0022] Preferably, the sulfur source is selected from at least one of ferric sulfate, ferrous sulfate, sodium bisulfate, potassium sulfate, ferrous dithionite, ferrous thiosulfate, ferrous dithionite, triferric tetrasulfide, sodium sulfate, sodium sulfite, sodium dithionite, sodium thiosulfate, sodium dithionite, sulfurous acid, sulfuric acid, ammonium persulfate, potassium persulfate, sodium persulfate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and hydrates of the above substances.

[0023] More preferably, the sulfur source is ferrous sulfate and / or sodium bisulfate.

[0024] Preferably, the molar ratio of the sodium source, iron source, transition metal source and sulfur source is (1-3):(0.5-2):(0.5-1.5):3.

[0025] More preferably, the molar ratio of the sodium source, iron source, transition metal source and sulfur source is 2:1:1:3.

[0026] Preferably, the solvent is selected from at least one of water, methanol, ethanol, acetone, ethylene glycol, and pyridine.

[0027] More preferably, the solvent is water.

[0028] Preferably, in step (2), the temperature of the solvothermal reaction is 40-220°C; more preferably, the temperature of the solvothermal reaction is 40-220°C.

[0029] Preferably, in step (2), the solvothermal reaction time is 4-12 hours; more preferably, the solvothermal reaction time is 4-8 hours.

[0030] Preferably, in step (2), the moisture content of the flash-dried imported material is 5-40 wt%; more preferably, the moisture content of the flash-dried imported material is 5-15 wt%.

[0031] Preferably, in step (2), the size of the flash drying chamber is 0.5-10m. 3 More preferably, the size of the flash drying chamber is 1-3m². 3 .

[0032] Preferably, in step (2), the flash drying temperature is 120-350℃; more preferably, the flash drying temperature is 120-200℃.

[0033] Preferably, in step (2), the flash drying time is 0.2-6 hours; more preferably, the flash drying time is 0.2-1 hours.

[0034] Preferably, in step (2), the gas flow rate for flash drying is 1-30 m / s; more preferably, the gas flow rate for flash drying is 1-10 m / s.

[0035] Preferably, in step (3), the calcination temperature is 200-400℃; more preferably, the calcination temperature is 250-350℃.

[0036] Preferably, in step (3), the heating rate of the calcination treatment is 0.5-10℃ / min; more preferably, the heating rate of the calcination treatment is 1-4℃ / min.

[0037] Preferably, in step (3), the calcination treatment time is 2-48 hours; more preferably, the calcination treatment time is 4-12 hours.

[0038] Preferably, in step (3), the inert gas is at least one of nitrogen, argon, or a mixture of argon and hydrogen.

[0039] A third aspect of the present invention provides a positive electrode sheet for a sodium-ion battery, comprising a current collector and a positive electrode material layer coated on the surface of the current collector; the positive electrode material layer contains a positive electrode active material, wherein the positive electrode active material is the positive electrode material described in the first aspect.

[0040] Preferably, the positive electrode material layer also contains a conductive agent and a binder.

[0041] This invention does not have special requirements for conductive agents and binders. Commonly used conductive agents (such as conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fiber, graphene, reduced graphene oxide, etc.) and binders (such as polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, SBR rubber, polyolefins, etc.) for sodium-ion battery positive electrode sheets can be used.

[0042] A fourth aspect of the present invention provides a sodium-ion battery, comprising the sodium-ion battery positive electrode sheet described in the third aspect.

[0043] The fifth aspect of the present invention provides for the application of the sodium-ion battery described in the fourth aspect.

[0044] Preferably, the applications include mobile electronic communication devices, electric vehicles, electric bicycles, energy storage batteries, power batteries, or energy storage power stations.

[0045] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0046] (1) The positive electrode material of the present invention is sodium ferric sulfate (Na) partially substituted with a transition metal. x Fe y Mz (SO4)3, this material features nanoscale ultra-small particle size, significantly shortening the diffusion distance of ions / electrons and electrolytes, lowering the sodium ion diffusion barrier, and facilitating rapid sodium ion diffusion, thus enabling fast charging and discharging of the electrode material. Furthermore, the small grain size and ample intergranular porosity help alleviate the deformation stress caused by sodium ion insertion / extraction, improving cycle stability and enabling lossless charging and discharging. Simultaneously, the material has a large specific surface area, providing abundant active energy storage sites and promoting the material's specific capacity. In addition, the partial substitution of transition metal ions further enhances the material's reactivity, thereby improving its rate performance.

[0047] (2) The sodium-ion battery cathode material of the present invention is prepared by low-temperature solvothermal, flash drying and low-temperature calcination. The process is simple and easy to operate, with low energy consumption, material cost and equipment requirements, and is suitable for large-scale industrial production. Attached Figure Description

[0048] Figure 1 FESEM image of the cathode material prepared in Example 1;

[0049] Figure 2 FESEM image of the cathode material prepared in Comparative Example 1;

[0050] Figure 3 This is a comparison chart of the cycle performance of the cathode materials prepared in Example 1 and Comparative Examples 1-2;

[0051] Figure 4 The graph shows a comparison of the rate performance of the cathode materials prepared in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0052] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0053] Example 1

[0054] A cathode material with the chemical formula Na₂FeMn(SO₄)₃. The preparation method of this cathode material includes the following steps:

[0055] (1) Weigh out 0.05 mol sodium bicarbonate, 0.1 mol ferrous sulfate, 0.1 mol manganese sulfate and 0.1 mol sodium sulfate respectively and disperse them in 50 ml of water. Stir magnetically until completely dissolved to obtain a suspension.

[0056] (2) The suspension obtained in step (1) was placed in a hydrothermal reactor with an inner liner volume of 80 mL and subjected to a solvothermal reaction at 100 °C for 4 h. After naturally cooling to room temperature, the product of the solvothermal reaction was centrifuged and then washed with ethanol and deionized water to obtain a primary product with a water content of about 20%. The primary product was then placed in a drying chamber with a volume of 1 mL. 3 In a dryer, flash drying was carried out at 200℃ and a gas flow rate of 2m / s for 0.5h to obtain powder particles based on Na2FeMn(SO4)3.

[0057] (3) The powder particles obtained in step (2) are calcined at 350°C for 8 hours under an argon atmosphere, wherein the heating rate is 1°C / min, to obtain the Na2FeMn(SO4)3 cathode material of this embodiment.

[0058] Figure 1 The image shown is a field emission scanning electron microscope (FESEM) image of the cathode material prepared in Example 1. Figure 1 It can be seen that the prepared cathode material has a relatively uniform size and a particle size of about 10-80 nm.

[0059] Example 2

[0060] A cathode material with the chemical formula: Na3Fe 0.5 Mn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol ferric sulfate and 0.1 mol sodium sulfate used in step (1) are replaced with 0.05 mol ferric sulfate and 0.15 mol sodium sulfate, while the rest are the same as in Example 1.

[0061] Example 3

[0062] A cathode material with the chemical formula: NaFeMn 1.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol manganese sulfate and 0.1 mol sodium sulfate used in step (1) are replaced with 0.15 mol manganese sulfate and 0.05 mol sodium sulfate, while the rest are the same as in Example 1.

[0063] Example 4

[0064] A positive electrode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.05 mol sodium bicarbonate used in step (1) is replaced with 0.05 mol sodium acetate, while the rest is the same as in Example 1.

[0065] Example 5

[0066] A positive electrode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol ferrous sulfate used in step (1) is replaced with 0.05 mol ferric sulfate, and the amounts of sodium bicarbonate and sodium sulfate are changed to 0.15 mol and 0.05 mol, respectively. All other aspects are the same as in Example 1.

[0067] Example 6

[0068] A positive electrode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol ferrous sulfate and 0.1 mol manganese sulfate used in step (1) are replaced with 0.15 mol ferrous sulfate and 0.05 mol manganese sulfate, respectively. All other steps are the same as in Example 1.

[0069] Example 7

[0070] A positive electrode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.05 mol sodium bicarbonate and 0.1 mol sodium sulfate used in step (1) are replaced with 0.25 mol sodium bicarbonate and 0.1 mol ammonium sulfate, while the rest are the same as in Example 1.

[0071] Example 8

[0072] A cathode material with the chemical formula: Na3FeMn 0.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol manganese sulfate and 0.1 mol sodium sulfate used in step (1) are replaced with 0.05 mol manganese sulfate and 0.15 mol sodium sulfate, while the rest are the same as in Example 1.

[0073] Example 9

[0074] A cathode material with the chemical formula: Na₂Fe 1.5 Mn 0.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol ferrous sulfate and 0.1 mol manganese sulfate used in step (1) are replaced with 0.15 mol ferrous sulfate and 0.05 mol manganese sulfate, while the rest are the same as in Example 1.

[0075] Example 10

[0076] A cathode material with the chemical formula: Na₂Fe 0.5 Mn 1.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol ferrous sulfate and 0.1 mol manganese sulfate used in step (1) are replaced with 0.05 mol ferrous sulfate and 0.15 mol manganese sulfate, while the rest are the same as in Example 1.

[0077] Example 11

[0078] A cathode material with the chemical formula Na2FeNi(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol nickel sulfate, while the rest is the same as in Example 1.

[0079] Example 12

[0080] A cathode material with the chemical formula Na2FeNi(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol nickel fluoride, while the rest is the same as in Example 1.

[0081] Example 13

[0082] A cathode material with the chemical formula Na2FeNi(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol nickel nitrate, while the rest is the same as in Example 1.

[0083] Example 14

[0084] A positive electrode material with the chemical formula Na2FeCo(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol cobalt sulfate, while the rest are the same as in Example 1.

[0085] Example 15

[0086] A positive electrode material with the chemical formula Na2FeCo(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol cobalt fluoride, while the rest are the same as in Example 1.

[0087] Example 16

[0088] A positive electrode material with the chemical formula Na2FeCo(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol cobalt nitrate, while the rest are the same as in Example 1.

[0089] Example 17

[0090] A positive electrode material with the chemical formula Na2FeZn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced by 0.1 mol zinc sulfate, while the rest are the same as in Example 1.

[0091] Example 18

[0092] A positive electrode material with the chemical formula Na2FeZn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced with 0.1 mol zinc fluoride, while the rest are the same as in Example 1.

[0093] Example 19

[0094] A positive electrode material with the chemical formula Na2FeZn(SO4)3. The preparation method of this positive electrode material differs from that of Example 1 in that the 0.1 mol manganese sulfate used in step (1) is replaced by 0.1 mol zinc nitrate, while the rest are the same as in Example 1.

[0095] Example 20

[0096] A cathode material with the chemical formula: Na₂Fe 1.5 Mn 0.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the molar ratio of sodium source: iron source: transition metal source: sulfur source in step (1) is 2.5:1.5:0.5:3, and the specific raw materials are 0.05 mol sodium bicarbonate, 0.15 mol ferrous sulfate, 0.05 mol manganese sulfate and 0.1 mol sodium sulfate, and the rest are the same as in Example 1.

[0097] Example 21

[0098] A cathode material with the chemical formula: Na₂Fe 0.5 Mn 1.5 (SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the molar ratio of sodium source: iron source: transition metal source: sulfur source in step (1) is 2.5:0.5:1.5:3, and the specific raw materials are 0.05 mol sodium bicarbonate, 0.05 mol ferrous sulfate, 0.15 mol manganese sulfate and 0.1 mol sodium sulfate, and the rest are the same as in Example 1.

[0099] Example 22

[0100] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvent used in step (2) is ethanol, while the rest is the same as in Example 1.

[0101] Example 23

[0102] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal temperature used in step (2) is 40°C, while the rest is the same as in Example 1.

[0103] Example 24

[0104] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal temperature used in step (2) is 80°C, while the rest is the same as in Example 1.

[0105] Example 25

[0106] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal temperature used in step (2) is 160°C, while the rest is the same as in Example 1.

[0107] Example 26

[0108] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal temperature used in step (2) is 220°C, while the rest is the same as in Example 1.

[0109] Example 27

[0110] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal reaction time used in step (2) is 2 hours, while the rest is the same as in Example 1.

[0111] Example 28

[0112] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal reaction time used in step (2) is 6 hours, while the rest is the same as in Example 1.

[0113] Example 29

[0114] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal reaction time used in step (2) is 8 hours, while the rest is the same as in Example 1.

[0115] Example 30

[0116] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the solvothermal reaction time used in step (2) is 12 h, while the rest is the same as in Example 1.

[0117] Example 31

[0118] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the water content of the imported material in step (2) is 10%, while the rest is the same as in Example 1.

[0119] Example 32

[0120] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the water content of the imported material in step (2) is 30%, while the rest is the same as in Example 1.

[0121] Example 33

[0122] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that in Example 1 in that the volume of the drying chamber in step (2) is 0.5 m³. 3 Everything else is the same as in Example 1.

[0123] Example 34

[0124] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that in Example 1 in that the drying chamber volume in step (2) is 2m³. 3 Everything else is the same as in Example 1.

[0125] Example 35

[0126] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the drying chamber temperature in step (2) is 120°C, while the rest is the same as in Example 1.

[0127] Example 36

[0128] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the drying chamber temperature in step (2) is 150°C, while the rest is the same as in Example 1.

[0129] Example 37

[0130] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the drying chamber temperature in step (2) is 250°C, while the rest is the same as in Example 1.

[0131] Example 38

[0132] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the drying time in step (2) is 0.2 h, while the rest is the same as in Example 1.

[0133] Example 39

[0134] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the drying time in step (2) is 1 hour, while the rest is the same as in Example 1.

[0135] Example 40

[0136] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the gas flow rate in the drying chamber in step (2) is 1 m / s, while the rest is the same as in Example 1.

[0137] Example 41

[0138] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the gas flow rate in the drying chamber in step (2) is 5 m / s, while the rest is the same as in Example 1.

[0139] Example 42

[0140] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination temperature in step (3) is 200℃, while the rest is the same as in Example 1.

[0141] Example 43

[0142] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination temperature in step (3) is 300℃, while the rest is the same as in Example 1.

[0143] Example 44

[0144] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination temperature in step (3) is 400℃, while the rest is the same as in Example 1.

[0145] Example 45

[0146] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the heating rate of the calcination treatment in step (3) is 0.5℃ / min, while the rest is the same as that of Example 1.

[0147] Example 46

[0148] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the heating rate of the calcination treatment in step (3) is 2℃ / min, while the rest is the same as in Example 1.

[0149] Example 47

[0150] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the heating rate of the calcination treatment in step (3) is 4℃ / min, while the rest is the same as in Example 1.

[0151] Example 48

[0152] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination time in step (3) is 2 hours, while the rest is the same as in Example 1.

[0153] Example 49

[0154] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination time in step (3) is 24 hours, while the rest is the same as in Example 1.

[0155] Example 50

[0156] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the calcination time in step (3) is 48 hours, while the rest is the same as in Example 1.

[0157] Example 51

[0158] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the gas atmosphere for calcination in step (3) is nitrogen, while the rest is the same as in Example 1.

[0159] Example 52

[0160] A cathode material with the chemical formula Na2FeMn(SO4)3. The preparation method of this cathode material differs from that of Example 1 in that the gas atmosphere for calcination in step (3) is a mixture of argon and hydrogen (volume ratio of 9.5:0.5), while the rest is the same as in Example 1.

[0161] Example 53

[0162] A sodium-ion battery, wherein the positive electrode active material is Na2FeMn(SO4)3 prepared in Example 1. The preparation method of this sodium-ion battery includes the following steps:

[0163] (1) Preparation of battery positive electrode: Na2FeMn(SO4)3 powder, carbon black and polyvinylidene fluoride are added to an appropriate amount of N-methylpyrrolidone in a mass ratio of 8:1:1 and ground thoroughly to obtain a uniform slurry; then the slurry is uniformly coated on the surface of aluminum foil and vacuum dried; then the dried electrode sheet is cut into round pieces with a diameter of 10mm, compacted and used as the positive electrode sheet of the battery for later use;

[0164] (2) Preparation of battery negative electrode: Press metallic sodium into thin sheets and cut them into round sheets with a diameter of 12 mm for use as battery negative electrode sheets;

[0165] (3) Battery assembly: Glass fiber film is used as separator, and 1M sodium hexafluorophosphate is dissolved in propylene carbonate and fluoroethylene carbonate (volume ratio 95:5) solvent as electrolyte. In a glove box protected by inert gas, the positive electrode sheet, separator and negative electrode sheet of the battery prepared in step (1) are stacked tightly in sequence. Electrolyte is added dropwise to completely wet the separator. Then the stacked part is sealed into the button cell to complete the battery assembly.

[0166] Examples 54-104

[0167] The sodium-ion batteries in Examples 54-104 use positive electrode materials corresponding to those prepared in Examples 2-52, and the preparation methods for each sodium-ion battery are the same as those in Example 53.

[0168] Comparative Example 1

[0169] A sodium-ion battery is prepared in a manner different from that in Example 53, the cathode material is changed to Na2FeMn(SO4)3 cathode material particles prepared by ball milling. All other aspects are the same as in Example 53. Specifically, 0.05 mol sodium bicarbonate, 0.1 mol ferrous sulfate, 0.1 mol manganese sulfate, and 0.1 mol sodium sulfate are dried and directly mixed, then ball-milled in a ball mill jar for 12 hours to ensure thorough and uniform mixing. The milled material is then transferred to a magnetic boat, placed in a tube furnace, and calcined at 350°C under an argon atmosphere for 8 hours at a heating rate of 1°C / min. After calcination, the material is ground to obtain Na2FeMn(SO4)3 cathode material particles.

[0170] Figure 2 The image shown is a FESEM image of the cathode material prepared by ball milling in Comparative Example 1. Figure 2 It can be seen that the particle size of Na2FeMn(SO4)3 cathode material prepared by ball milling is in the range of 1-5μm, which is relatively large and prone to agglomeration, forming bulk material.

[0171] Comparative Example 2

[0172] A sodium-ion battery is prepared in a manner different from that of Example 53, except that the cathode material is changed to Na2Fe2(SO4)3. The preparation method of the Na2Fe2(SO4)3 cathode material differs from that of Example 1 in that 0.2 mol of ferrous sulfate is used, and no manganese sulfate is added. All other aspects are the same as in Example 1.

[0173] Comparative Example 3

[0174] A sodium-ion battery is prepared in a manner different from that of Example 53, except that the cathode material is changed to Na2Fe2(SO4)3. The preparation method of the Na2Fe2(SO4)3 cathode material differs from that of Example 1 in that 0.2 mol of ferrous sulfate is used, and manganese sulfate and sodium bicarbonate are not added. The drying process uses solvent evaporation, and the mixed solution is dried at 130°C under continuous magnetic stirring. All other aspects are the same as in Example 1.

[0175] Comparative Example 4

[0176] A sodium-ion battery is disclosed, the preparation method of which differs from that of Example 53 in that the positive electrode material is changed to Na2FeMn(SO4)3, while the rest is the same as in Example 53. The preparation method of the Na2FeMn(SO4)3 positive electrode material differs from that of Example 1 in that sodium bicarbonate is not added, and the drying process uses solvent evaporation, with the mixed solution dried at 130°C under continuous magnetic stirring. The rest is the same as in Example 1.

[0177] Comparative Example 5

[0178] A sodium-ion battery is disclosed, the preparation method of which differs from that of Example 53 in that the positive electrode material is changed to Na2FeNi(SO4)3, while the rest is the same as in Example 53. The preparation method of the Na2FeNi(SO4)3 positive electrode material differs from that of Example 1 in that the nickel sulfate content is 0.1 mol, and manganese sulfate and sodium bicarbonate are not added. The drying process uses solvent evaporation, and the mixed solution is dried at 130°C under continuous magnetic stirring. All other aspects are the same as in Example 1.

[0179] Performance testing

[0180] The sodium-ion batteries prepared in Examples 53-104 and Comparative Examples 1-5 were subjected to performance tests. Constant current charge-discharge tests were conducted using a BTSDA testing system from Shenzhen Xinwei Electronics Co., Ltd., in a constant temperature and humidity chamber (25℃, 35%), with a test voltage range of 2-4.5V. The batteries were cycled 500 times at current densities of 1C and 10C (1C = 120mAh / g), and the test results are shown in Table 1.

[0181] Table 1: Comparison of electrochemical performance tests of Examples 53-104 and Comparative Examples 1-5

[0182]

[0183]

[0184]

[0185] As shown in Table 1, the sodium-ion batteries assembled from the cathode materials prepared in Examples 1-52 of this invention (Examples 53-104) have superior discharge specific capacity and rate performance compared to Comparative Examples 1-5.

[0186] Among them, Examples 2-10 used different sodium sources, iron sources, sulfur sources, and Na, Fe, S molar ratios to obtain Na. x Fe y Mn z(SO4)3 cathode material; Examples 54-62 are sodium-ion batteries assembled using the cathodes obtained in Examples 2-10. It was found that ultra-small Na particles obtained from reactions with different sodium, iron, and sulfur sources... x Fe y Mn z The (SO4)3 cathode material has little impact on the electrochemical performance of the battery because different types of sodium, iron, and sulfur sources only provide sodium, iron, and sulfate ions; the other ions do not participate in the reaction. However, the Na:Fe:S molar ratio has a certain influence on the product. When the proportion of sodium source is too high or too low, the conversion rate and purity of the product decrease, leading to a decline in the battery's cycle performance.

[0187] Examples 11-19 show Na₂Fe obtained by reacting with different transition metal sources. y M z (SO4)3 cathode material, Examples 63-71 are sodium-ion batteries assembled using the cathode materials obtained in Examples 11-19, and it was found that ultra-small Na2Fe particles were obtained by reacting different types of transition metals. y M z The (SO4)3 cathode material has a certain impact on the electrochemical performance of the battery. The capacity performance of products formed by Fe and Ni as transition metal ions is better than that of Co and Zn ions. This may be because the reactivity of different ions and the different chemical and coordination environments generated in the products lead to different electrochemical performances. Different salt solutions of the same type of transition metal ions have little effect on the electrochemical performance of the products because the salt solution only provides the transition metal ions required for the reaction, and other ions do not participate in the reaction.

[0188] Examples 20-21 show the Na₂Fe obtained by reacting different molar ratios of sodium, iron, transition metal, and sulfur sources. y Mn z (SO4)3 cathode material; Examples 72-73 are sodium-ion batteries assembled using the cathode material obtained in Examples 20-21. It was found that ultra-small Na2Fe particles were obtained by reacting with different ratios of sodium source, iron source, transition metal source, and sulfur source. y Mn z (SO4)3 cathode material has a certain impact on the electrochemical performance of the battery. When the proportion of transition metal ions is too high or too low, the cycle performance of the battery decreases. This is because an excessively high or low proportion of transition metal ions will affect the active energy storage sites of the product.

[0189] Example 22 describes Na2FeMn(SO4)3 cathode materials obtained by reacting with different solvents. Example 74 describes a sodium-ion battery assembled using the cathode material obtained in Example 13. It was found that the ultra-small Na2FeMn(SO4)3 cathode materials obtained by reacting with different solvents have a certain impact on the electrochemical performance of the battery. Using ethanol as a solvent resulted in a sharp decrease in the electrochemical performance of the product. This is because the reactants have very low solubility in ethanol, leading to low product purity and conversion rate, which affects product performance.

[0190] Examples 23-26 describe Na2FeMn(SO4)3 cathode materials obtained using different hydrothermal temperatures. Examples 75-78 describe sodium-ion batteries assembled using the cathode materials obtained in Examples 23-26. It was found that the ultra-small Na2FeMn(SO4)3 cathode materials obtained at different hydrothermal temperatures have a certain impact on the electrochemical performance of the batteries. When the hydrothermal temperature is too low (40-80℃) or too high (220℃), the cycle performance of the batteries decreases. When the hydrothermal temperature is between 100-160℃, the electrochemical performance of the products does not differ significantly. This is because the growth environment provided at a temperature between 100-160℃ already meets the growth requirements of the products. Excessively high or low hydrothermal temperatures can easily damage the crystal structure of the products.

[0191] Examples 27-30 show Na2FeMn(SO4)3 cathode materials obtained using different hydrothermal reaction times. Examples 79-82 show sodium-ion batteries assembled using the cathode materials obtained in Examples 27-30. It was found that the ultra-small Na2FeMn(SO4)3 cathode materials obtained by different hydrothermal reaction times have a certain impact on the electrochemical performance of the batteries. When the reaction time is too short (2 hours), the cycle performance of the batteries decreases. When the reaction time is between 6 and 12 hours, the difference in electrochemical performance is not significant. This is because insufficient reaction time results in incomplete reaction.

[0192] Examples 31-32 are Na2FeMn(SO4)3 cathode materials obtained by drying with different moisture contents of imported materials. Examples 83-84 are sodium-ion batteries assembled using the cathode materials obtained in Examples 31-32. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by drying with different moisture contents of imported materials have little effect on the electrochemical performance of the battery.

[0193] Examples 33-34 are Na2FeMn(SO4)3 cathode materials obtained by drying with different drying chamber volumes. Examples 85-86 are sodium-ion batteries assembled using the cathode materials obtained in Examples 33-34. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by drying with different drying chamber volumes have little effect on the electrochemical performance of the battery.

[0194] Examples 35-37 are Na2FeMn(SO4)3 cathode materials obtained by drying at different drying chamber temperatures. Examples 87-89 are sodium-ion batteries assembled using the cathode materials obtained in Examples 35-37. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by drying at different drying chamber temperatures have little effect on the electrochemical performance of the batteries.

[0195] Examples 38-39 are Na2FeMn(SO4)3 cathode materials obtained by drying at different times. Examples 90-91 are sodium-ion batteries assembled using the cathode materials obtained in Examples 38-39. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by drying at different times have little effect on the electrochemical performance of the battery.

[0196] Examples 40-41 are Na2FeMn(SO4)3 cathode materials obtained by drying with different gas flow rates in the drying chamber. Examples 92-93 are sodium-ion batteries assembled using the cathode materials obtained in Examples 40-41. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by drying with different gas flow rates have little effect on the electrochemical performance of the battery.

[0197] Examples 42-44 show Na2FeMn(SO4)3 cathode materials obtained by reacting at different calcination temperatures. Examples 94-96 show sodium-ion batteries assembled using the cathode materials obtained in Examples 42-44. It was found that the ultra-small Na2FeMn(SO4)3 cathode materials obtained by reacting at different calcination temperatures have a certain impact on the electrochemical performance of the batteries. Lower calcination temperatures result in a decrease in the electrochemical performance of the products. This is because lower annealing temperatures lead to lower crystallinity and less stable material structure.

[0198] Examples 45-47 are Na2FeMn(SO4)3 cathode materials obtained by reacting at different heating rates. Examples 97-99 are sodium-ion batteries assembled using the cathode materials obtained in Examples 45-47. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by reacting at different heating rates have little effect on the electrochemical performance of the batteries.

[0199] Examples 48-50 show Na2FeMn(SO4)3 cathode materials obtained by reacting with different calcination times. Examples 100-102 show sodium-ion batteries assembled using the cathode materials obtained in Examples 48-50. It was found that the ultra-small Na2FeMn(SO4)3 cathode materials obtained by reacting with different calcination times have a certain impact on the electrochemical performance of the batteries. Shorter calcination times result in a decrease in the electrochemical performance of the product. This is because shorter annealing times lead to lower crystallinity and less stable structure in the product.

[0200] Examples 51-52 are Na2FeMn(SO4)3 cathode materials obtained by reacting under different calcination gas atmospheres. Examples 103-104 are sodium-ion batteries assembled using the cathode materials obtained in Examples 51-52. It was found that the ultra-small particles of Na2FeMn(SO4)3 cathode materials obtained by reacting under different calcination gas atmospheres have little effect on the electrochemical performance of the batteries.

[0201] Comparative Example 1 is a Na2FeMn(SO4)3 positive electrode material for sodium-ion batteries prepared by ball milling and calcination. Figure 2 It can be seen that the particles are relatively large and prone to agglomeration, resulting in low material utilization and low discharge specific capacity. The capacity retention rate after 500 cycles is also low.

[0202] Comparative Example 2 is a Na2Fe2(SO4)3 cathode material without transition metal substitution. It can be seen that its first-cycle coulombic efficiency is low, and its capacity and cycle performance are poor. The reason may be that the loss of transition metal substitution reduces its reactivity.

[0203] Comparative Example 3 is a Na2Fe2(SO4)3 cathode material prepared by solvent evaporation. It can be seen that its capacity and cycle performance are poor. The reason may be that the grains agglomerate during the reaction process, forming secondary particles, and there is no transition metal to replace them, which leads to a decrease in the reactivity of the product.

[0204] Comparative Example 4 shows the Na2FeMn(SO4)3 cathode material prepared by solvent evaporation. It can be seen that its cycle performance is poor. The reason may be that the electrode material agglomerates during the reaction process, forming secondary particles.

[0205] Comparative Example 5 shows the Na2FeNi(SO4)3 cathode material prepared by solvent evaporation. It can be seen that its cycle performance is poor. The reason may be that the electrode material agglomerates during the reaction process, forming secondary particles.

[0206] Figure 3 This is a comparison chart of the cycle performance of sodium-based ferric sulfate cathode materials prepared by different methods in Example 1 and Comparative Examples 1-2. Figure 3It can be seen that the ultra-small particle Na2FeMn(SO4)3 lossless fast-charging cathode material prepared in Example 1 exhibits stable cycle performance and high capacity retention. In contrast, the sodium-based iron sulfate cathode materials prepared in Comparative Examples 1-2 show poor cycle performance and low capacity retention.

[0207] Figure 4 This is a comparison chart of the rate performance of the sodium-based ferric sulfate cathode materials prepared in Example 1 and Comparative Examples 1-2. Figure 4 It can be seen that the ultra-small particle Na2FeMn(SO4)3 lossless fast-charging cathode material prepared in Example 1 exhibits good cycle performance and high capacity retention under different current densities, demonstrating good rate performance. In contrast, the sodium-based iron sulfate cathode materials prepared in Comparative Examples 1-2 show poor rate performance and low capacity retention.

[0208] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for producing a positive electrode material, characterized by, Includes the following steps: (1) Disperse sodium source, iron source, transition metal source and sulfur source in solvent to obtain suspension; (2) heating the suspension, and performing a solvothermal reaction; after cooling, sequentially separating, washing, and flash drying the product of the solvothermal reaction to obtain powder particles based on Na x Fe y M z (SO4)3. (3) The powder particles are calcined under an inert gas atmosphere to obtain the positive electrode material; The molecular formula of the positive electrode material is Na x Fe y M z (SO4)3, wherein 1.0 ≤ x ≤ 3.0, 0.5 ≤ y ≤ 2.0, 0.5 ≤ z ≤ 1.5, and M is a transition metal; the particle size of the positive electrode material is between 10-80 nm measured by a field emission scanning electron microscope. The solvent is selected from at least one of water, methanol, acetone, and pyridine.

2. The method of claim 1, wherein the method further comprises a step of mixing the lithium transition metal oxide and the lithium source. The transition metal is selected from at least one of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ag, Pt, Au, and Hg.

3. The method for preparing the cathode material according to claim 1, characterized in that, The sodium source is selected from at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium chloride, sodium phosphate, sodium nitrate, sodium phosphite, sodium formate, sodium propionate, sodium acrylate, sodium benzoate, sodium hypochlorite, sodium chlorate, sodium thiosulfate, sodium persulfate, sodium silicate, sodium bromate, sodium bromide, sodium iodide, sodium fluoride, sodium bisulfite, sodium nitrite, sodium oxalate, sodium persulfate, sodium hydroxide, sodium pyrosulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium metabisulfite, sodium pyrophosphate, sodium hydrogen phthalate, sodium bioxalate, sodium sulfite, sodium sorbate, trisodium phosphate, sodium gluconate, sodium oleate, and hydrates of the above substances. And / or, the iron source is selected from at least one of ferrous sulfate, ferrous oxide, ferric chloride, ferric nitrate, ferric acetate, ferrous bromide, ferrous nitrate, ferrous phosphate, ferrous iodide, ferrous acetate, ferrous metasilicate, ferrous metatitanate, ferrous ammonium sulfate, ferrous carbonate, ferrous chloride, ferrous sulfate, ferrous hydroxide, ferric oxide, ferric hydroxide, and hydrates of the above substances; And / or, the transition metal source is selected from at least one of the soluble salts of scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, silver, platinum, gold, mercury, and hydrates of the above substances; And / or, the sulfur source is selected from at least one of ferric sulfate, ferrous sulfate, sodium bisulfate, potassium sulfate, ferrous dithionite, ferrous thiosulfate, ferrous dithionite, triferric tetrasulfide, sodium sulfate, sodium sulfite, sodium dithionite, sodium thiosulfate, sodium dithionite, sulfurous acid, sulfuric acid, ammonium persulfate, potassium persulfate, sodium persulfate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and hydrates of the above substances.

4. The method for preparing the cathode material according to claim 1 or 3, characterized in that, The molar ratio of the sodium source, iron source, transition metal source and sulfur source is (1-3):(0.5-2):(0.5-1.5):

3.

5. The method for preparing the cathode material according to claim 1, characterized in that, In step (2), the temperature of the solvothermal reaction is 40-220℃; and / or the time of the solvothermal reaction is 4-12h.

6. The method for preparing the cathode material according to claim 1, characterized in that, In step (2), the temperature of the flash drying is 120-350℃; and / or the time of the flash drying is 0.2-6h.

7. The method for preparing the cathode material according to claim 1, characterized in that, In step (3), the calcination temperature is 200-400℃; and / or the calcination time is 2-48h.

8. The method for preparing the cathode material according to claim 1, characterized in that, In step (3), the inert gas is at least one of nitrogen, argon, or a mixture of argon and hydrogen.

9. A positive electrode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A positive electrode sheet for a sodium-ion battery, characterized in that, It includes a current collector and a positive electrode material layer coated on the surface of the current collector; the positive electrode material layer contains a positive electrode active material, which is the positive electrode material according to claim 9.

11. A sodium-ion battery, characterized in that, Includes the sodium-ion battery positive electrode sheet as described in claim 10.

12. The application of the sodium-ion battery of claim 11 in mobile electronic communication devices, electric vehicles, electric bicycles, energy storage batteries, power batteries, or energy storage power stations.

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