Process for the preparation of anhydrous iron-based prussian white compounds and use thereof

Abstract

This invention belongs to the technical field of sodium-ion battery cathode materials and discloses a method for preparing anhydrous iron-based Prussian white compounds, comprising the following steps: forming a suspension A with an iron-based Prussian white compound prepared by a traditional liquid-phase co-precipitation method and water; adding an aqueous solution B prepared with persulfate, surfactant, and sodium additive to suspension A to obtain suspension C; heating, stirring, and aging suspension C under the protection of an inert gas; removing the supernatant, centrifuging and washing the precipitate to obtain a white or light blue precipitate; and vacuum drying the precipitate to obtain the anhydrous iron-based Prussian white compound. This invention uses persulfate ions and surfactants to remove the water of crystallization from the iron-based Prussian white compound synthesized by liquid-phase co-precipitation under the strong oxidizing effect of persulfate, which can reduce the adverse effects of water of crystallization during battery charging and discharging on the stability of the organic electrolyte, and improve cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material technology, and relates to a method for preparing anhydrous iron-based Prussian white compound and its application. Background Technology

[0002] Currently, the application of lithium-ion batteries in electric vehicles, 3C products, and energy storage is growing rapidly. It is projected that global available lithium resources will not meet future demand, necessitating the search for alternative battery materials. Sodium and lithium belong to the same group of elements. Sodium's abundance in the Earth's crust is 2.83%, more than 1400 times that of lithium (20 ppm). Moreover, sodium resources are widely distributed globally. Therefore, sodium-ion battery cathode materials can replace lithium-ion battery cathode materials at a lower cost. Furthermore, sodium-ion batteries operate on similar principles to lithium-ion batteries, allowing the use of the same manufacturing equipment without the need for new process development. Therefore, sodium-ion batteries based on sodium-ion compounds as cathode materials have significant industrial application prospects, particularly in large-scale energy storage, low-speed electric vehicles, and two-wheeled electric vehicles.

[0003] Among existing sodium-ion battery cathode materials, Prussian blue compounds have attracted considerable attention due to their spacious sodium-ion diffusion channels and abundant sodium-storage active sites. Iron-based Prussian white compounds, in particular, possess an open framework structure that facilitates sodium-ion insertion / extraction and exhibit high theoretical specific capacity, suggesting their potential as cathode materials for sodium-ion batteries. However, due to their open crystal framework and co-precipitation synthesis in aqueous systems, iron-based Prussian white compounds often contain a certain amount of water of crystallization, which reduces their cycle stability as cathode materials in sodium-ion batteries. Therefore, removing the water of crystallization from iron-based Prussian white compounds synthesized via liquid-phase co-precipitation is crucial for promoting their application in sodium-ion batteries.

[0004] The invention patent with publication number CN 116409801 A discloses a method for preparing polypyrrole-coated Prussian blue cathode composite material. Prussian blue wet material is obtained by co-precipitation and coated in an alcohol-water solution without drying treatment. This method can reduce the activity of water and reduce the influence of water on Prussian blue, thereby improving the cycle stability of the cathode material.

[0005] The invention patent with publication number CN115321557A discloses a Prussian white composite material for sodium-ion batteries, which is synthesized by ball milling in an aqueous solution. During the ball milling process, the water of crystallization can be slowly released from the aqueous precursor through the thermal and mechanical energy provided by the ball milling. This small portion of released water of crystallization can dissolve the reactants and allow the reaction to proceed further. In addition, this portion of water of crystallization also makes the reaction more uniform, improves the crystallinity of Prussian white, and enhances the stability of Prussian white. By adding reinforcing modifiers and thiophene, its ball milling effect can be further improved, its defects can be further improved, and its conductivity and electrochemical performance can be enhanced. Summary of the Invention

[0006] This invention addresses the technical problem of reduced cycle stability of sodium-ion battery cathode materials due to the presence of water of crystallization in iron-based Prussian white compounds prepared by traditional liquid-phase coprecipitation methods. It provides a method for preparing anhydrous iron-based Prussian white compounds, which removes the water of crystallization under the strong oxidizing effect of persulfate. This reduces the adverse impact of water of crystallization during battery charging and discharging on the stability of the organic electrolyte, thereby improving the cycle stability and rate performance of sodium-ion batteries.

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

[0008] In a first aspect, the present invention provides a method for preparing anhydrous iron-based Prussian white compounds, comprising the following steps:

[0009] a. A suspension A is formed by mixing iron-based Prussian white compounds prepared by the traditional liquid-phase co-precipitation method with water;

[0010] b. Add the aqueous solution B prepared with persulfate, surfactant and sodium additive to suspension A to obtain suspension C;

[0011] c. Under the protection of an inert gas, suspension C is stirred at 20–90 °C for 0.5–24 h, and then aged for 0.5–24 h.

[0012] d. After aging, remove the supernatant, centrifuge and wash the precipitate to obtain a white or light blue precipitate;

[0013] e. The precipitate is dried under vacuum at 80–210 °C for 6–48 h to obtain anhydrous iron-based Prussian white compounds.

[0014] In one technical solution, the mass ratio of persulfate, surfactant, sodium additive and iron-based Prussian white compound in step b is 0.5-6:0-0.5:1-3:1.

[0015] In one technical solution, the persulfate in step b is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, or potassium peroxymonosulfate.

[0016] In one technical solution, the sodium additive in step b is one or more of sodium chloride, sodium sulfate, sodium carbonate, sodium acetate, trisodium citrate, sodium ascorbate, or sodium nitrate.

[0017] In one technical solution, the surfactant in step b is a quaternary ammonium salt surfactant or a polymeric surfactant.

[0018] In one technical solution, the quaternary ammonium salt surfactant is selected from one of hexadecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, and octadecyldimethylhydroxyethylammonium nitrate.

[0019] In one technical solution, the polymeric surfactant is selected from one of polyethyleneimine, polyvinylpyrrolidone, polymaleimide, quaternized polyacrylamide, polyvinylpyridine salt, and polydimethylamine epichlorohydrin.

[0020] In one technical solution, the general structural formula of the anhydrous iron-based Prussian white compound in step e is: Na x M (1-m) Fe m [N(CN)4]6, where x is 0.01 to 2.0, m is 0 to 1, and M and N are any one of Fe, Mn, Ni, Cu, Zn, Co, and Cs.

[0021] Secondly, the present invention provides the application of the anhydrous iron-based Prussian white compound prepared by the above preparation method in the cathode material of sodium-ion batteries.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) In this invention, by using persulfate ions and surfactants, the iron-based Prussian white compounds synthesized by liquid-phase coprecipitation are dehydrated under the strong oxidizing effect of persulfate, and the crystal phase is transformed from monoclinic to rhombohedral. At the same time, materials with poor crystallinity are eliminated, and the overall crystallinity of the material is improved. In addition, sodium additives are added during the oxidation process to provide a Na-rich environment and avoid changes in the material structure.

[0024] (2) The anhydrous iron-based Prussian white compound after oxidation treatment can be used as the positive electrode material of sodium-ion battery. It can reduce the adverse effects of water crystallization during battery charging and discharging on the stability of organic electrolyte, improve the cycle stability and rate performance of sodium-ion battery, and improve the charging and discharging performance in a wider temperature range. Attached Figure Description

[0025] Figure 1 The images show the XRD patterns of materials S0 and S1 obtained in Example 1.

[0026] Figure 2 The image shows an SEM image of material S1 obtained in Example 1.

[0027] Figure 3 The graph shows the cycling performance of the half-cell assembled from material S1 obtained in Example 1 at 20 C.

[0028] Figure 4 The charge / discharge rate performance of the half-cell assembled from material S2 obtained in Example 2 is shown in the graph (1 C, 2 C, 5 C, 10 C, 20 C, 50 C, 20 C, 10 C, 5 C, 2 C, 1 C).

[0029] Figure 5 The graph shows the cycling performance of the half-cell assembled from material S3 obtained in Example 3 at 50 C.

[0030] Figure 6 The graph shows the cycling performance of a half-cell assembled from material S1 obtained in Example 1 and materials L1 and L2 obtained in Comparative Examples 1 and 2 at 20 C.

[0031] Figure 7 The graph shows the cycling performance of a half-cell assembled from material S1 obtained in Example 1 and material L3 obtained in Comparative Example 3 at 20 C.

[0032] Figure 8 The graph shows the cycling performance of a half-cell assembled from material S1 obtained in Example 1 and material L4 obtained in Comparative Example 4 at 20 C.

[0033] Figure 9 The graph shows the cycling performance of a full cell prepared from material S4 obtained in Example 4 at 2 C at room temperature and low temperature. Detailed Implementation

[0034] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0035] Example 1

[0036] (1) Synthesis of manganese-doped iron-based Prussian white compound by liquid-phase coprecipitation: 1.35 g of ferrous sulfate (FeSO4·7H2O) and 0.023 g of manganese sulfate (MnSO4) mixed aqueous solution and 2.4 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) aqueous solution were injected into 2 g of sodium chloride (NaCl) solution by peristaltic pump. The mixture was stirred and aged under nitrogen protection, and the solid and liquid were separated. The mixture was thoroughly washed by centrifugation with deionized water and anhydrous ethanol to remove reaction residues, yielding manganese-doped iron-based Prussian white compound with the molecular formula Na4Fe(CN)6·10H2O. 1.72 Mn 0.03 Fe 0.97 [Fe(CN)6]·1.92H2O, labeled as S0.

[0037] (2) Disperse 0.6 g of the iron-based Prussian white compound prepared in step 1) in 50 ml of deionized water to form suspension A;

[0038] (3) Dissolve 2.4 g ammonium persulfate ((NH4)2S2O8), 0.2 g polyvinylpyrrolidone, and 1.2 g sodium chloride (NaCl) in 50 ml of deionized water to form aqueous solution B, and add it to suspension A to obtain suspension C;

[0039] (4) The suspension C was heated to 60 °C and stirred at 300 rpm for 12 h under the condition of N2 blowing, and then aged for 12 h; then it was washed by centrifugation with deionized water and anhydrous ethanol more than 3 times to obtain a white or light blue precipitate.

[0040] (5) The precipitate was dried in a vacuum oven at 140 °C for 24 h to obtain anhydrous manganese-doped iron-based Prussian white compound with the molecular formula Na. 1.72 Mn 0.03 Fe 0.97 [Fe(CN)6], labeled as S1.

[0041] The XRD patterns of the manganese-doped iron-based Prussian white compound synthesized by liquid-phase coprecipitation and the anhydrous manganese-doped iron-based Prussian white compound after post-treatment are shown in the figure. Figure 1 As shown. From Figure 1 It can be seen that the double diffraction peaks at 24.5° of the manganese-doped iron-based Prussian white compound after persulfate treatment become single peaks, indicating that the sulfidation treatment transforms the iron-based Prussian white compound into a monoclinic phase structure containing water of crystallization (space group ). P twenty one / n ) transforms into a dehydrated rhombohedral structure (space group is R -3), the rhombohedral structure has greater symmetry, which is conducive to the insertion and extraction of sodium ions.

[0042] Figure 2SEM image of anhydrous manganese-doped iron-based Prussian white compound. From Figure 2 It can be clearly seen that the surface of the anhydrous manganese-doped iron-based Prussian white compound treated with sulfate has pores of different sizes. This is because the poorly crystallized material is oxidized during the peroxidation process, leaving pores, which makes the overall material more crystallized.

[0043] Example 2

[0044] (1) Synthesis of cesium-doped iron-based Prussian white compound by liquid-phase coprecipitation: A mixed aqueous solution of 1.35 g ferrous sulfate (FeSO4·7H2O) and 0.054 g cesium sulfate (Cs2SO4) and an aqueous solution of 2.4 g sodium ferrocyanide (Na4Fe(CN)6·10H2O) were injected into a 2 g sodium chloride (NaCl) solution using a peristaltic pump. The mixture was stirred and aged under nitrogen protection, and the solid and liquid were separated. The mixture was thoroughly washed with deionized water and anhydrous ethanol by centrifugation to remove reaction residues. After vacuum drying at 140 °C for 24 h, the cesium-doped iron-based Prussian white compound with the molecular formula Na4Fe(CN)6·10H2O was obtained. 1.75 Cs 0.03 Fe 0.97 [Fe(CN)6]·3.1 H2O.

[0045] (2) Disperse 0.6 g of the nickel-doped iron-based Prussian white compound prepared in step 1) in 50 ml of deionized water to form suspension A;

[0046] (3) Dissolve 2.4 g ammonium persulfate ((NH4)2S2O8), 0.2 g polyvinylpyrrolidone, and 1.2 g sodium chloride (NaCl) in 50 ml of deionized water to form aqueous solution B, and add it to suspension A to obtain suspension C;

[0047] (4) The suspension C was heated to 60 °C and stirred at 300 rpm for 5 h under the condition of N2 blowing, and then aged for 5 h; then it was washed by centrifugation with deionized water and anhydrous ethanol more than 3 times to obtain a white or light blue precipitate.

[0048] (5) The precipitate was dried in a vacuum oven at 140 °C for 24 h to obtain anhydrous cesium-doped iron-based Prussian white compound with the molecular formula Na. 1.75 Cs 0.03 Fe 0.97 [Fe(CN)6], labeled S2.

[0049] Example 3

[0050] (1) Synthesis of nickel-doped iron-based Prussian white compound by liquid-phase coprecipitation: 1.35 g of ferrous sulfate (FeSO4·7H2O) and 0.023 g of nickel sulfate (NiSO4) mixed aqueous solution and 2.4 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) aqueous solution were injected into 2 g of sodium chloride (NaCl) solution by peristaltic pump. The mixture was stirred and aged under nitrogen protection, and the solid and liquid were separated. The mixture was thoroughly washed with deionized water and anhydrous alcohol by centrifugation to remove reaction residues. After vacuum drying at 140 °C for 24 h, nickel-doped iron-based Prussian white compound with the molecular formula Na4Fe(CN)6·10H2O was obtained. 1.66 Ni 0.03 Fe 0.97 [Fe(CN)6]·2.6 H2O.

[0051] (2) Disperse 0.6 g of the nickel-doped iron-based Prussian white compound prepared in step 1) in 50 ml of deionized water to form suspension A;

[0052] (3) Dissolve 2.4 g (NH4)2S2O8, 0.2 g polyvinylpyrrolidone and 1.2 g NaCl in 50 ml of deionized water to form aqueous solution B, and add it to suspension A to obtain suspension C;

[0053] (4) The suspension C was heated to 60 °C and stirred at 300 rpm for 5 h under the condition of N2 blowing, and then aged for 5 h; then it was washed by centrifugation with deionized water and anhydrous ethanol more than 3 times to obtain a white or light blue precipitate.

[0054] (5) The precipitate was dried in a vacuum oven at 140 °C for 24 h to obtain anhydrous nickel-doped iron-based Prussian white compound with the molecular formula Na. 1.66 Ni 0.03 Fe 0.97 [Fe(CN)6], labeled S3.

[0055] Example 4

[0056] (1) Synthesis of manganese-doped iron-based Prussian white compound by liquid-phase coprecipitation: 1.35 g of ferrous sulfate (FeSO4·7H2O) and 0.023 g of manganese sulfate (MnSO4) mixed aqueous solution and 2.4 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) aqueous solution were injected into 2 g of sodium chloride (NaCl) solution by peristaltic pump. The mixture was stirred and aged under nitrogen protection, and the solid and liquid were separated. The mixture was thoroughly washed with deionized water and anhydrous alcohol by centrifugation to remove reaction residues. After vacuum drying at 140 °C for 24 h, manganese-doped iron-based Prussian white compound with the molecular formula Na4Fe(CN)6·10H2O was obtained. 1.76 Mn 0.03 Fe 0.97[Fe(CN)6]·1.62H2O.

[0057] (2) Disperse 0.6 g of the nickel-doped iron-based Prussian white compound prepared in step 1) in 50 ml of deionized water to form suspension A;

[0058] (3) Dissolve 2.4 g sodium persulfate (Na2S2O8), 0.2 g polyvinylpyrrolidone and 1.2 g sodium chloride (NaCl) in 50 ml of deionized water to form aqueous solution B, and add it to suspension A to obtain suspension C;

[0059] (4) The suspension C was heated to 60 °C and stirred at 300 rpm for 5 h under the condition of N2 blowing, and then aged for 5 h; then it was washed by centrifugation with deionized water and anhydrous ethanol more than 3 times to obtain a white or light blue precipitate.

[0060] (5) The precipitate was dried in a vacuum oven at 140 °C for 24 h to obtain anhydrous manganese-doped iron-based Prussian white compound with the molecular formula Na. 1.76 Mn 0.03 Fe 0.97 [Fe(CN)6], labeled S4.

[0061] Comparative Example 1

[0062] This comparative example is basically the same as Example 1, except that: in step 3), the aqueous solution B does not contain polyvinylpyrrolidone, and the synthetic material is labeled as L1.

[0063] Comparative Example 2

[0064] This comparative example is basically the same as Example 1, except that: sodium chloride (NaCl) is not added to the aqueous solution B in step 3), and the synthetic material is labeled as L2.

[0065] Comparative Example 3

[0066] This comparative example is basically the same as Example 1, except that: in step 3), the persulfate in aqueous solution B is replaced with ammonium fluoride (NH4F), and the synthetic material is labeled as L3.

[0067] Comparative Example 4

[0068] This comparative example is basically the same as Example 1, except that the amount of ammonium persulfate ((NH4)2S2O8) in aqueous solution B in step 3) is adjusted to 0.2 g, and the synthetic material is labeled as L4.

[0069] Example 5

[0070] The S0-S3 and L1-L4 samples obtained from Examples 1-3 and Comparative Examples 1-4 were mixed with Ketjen Black and polyvinylidene fluoride at a mass ratio of 7:2:1, respectively, and diluted with N-methylpyrrolidone. The mixture was stirred to form a slurry, which was then coated onto clean aluminum foil. After vacuum drying, stamping, and pressing, a 12 mm diameter positive electrode material was formed. Using metallic sodium as the negative electrode, a Whatman GF / D glass fiber filter membrane as the separator, and a 4.5:4.5:1 electrolyte of ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) containing 1 mol / L NaClO4, three 2032 button-type half-cells were assembled in an inert gas glove box and left to stand overnight. Constant current charge-discharge tests were performed using a Newway battery tester, with the voltage range between 2.0 and 4.2 V. The results are as follows: Figures 3-8 As shown.

[0071] from Figure 3 It can be seen that the half-cell assembled using material S1 obtained in Example 1 has a first discharge specific capacity of 142.24 mA·h·g at a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 104.37 mA·h·g. -1 That is, the capacity retention rate is 74.38%, while the half-cell assembled from the material S0 before oxidation and dehydration treatment has a capacity retention rate of only 55.33% after 2000 cycles. The cycle retention rate of the half-cell after dehydration treatment is increased by 19.05%.

[0072] from Figure 4 It can be seen that ( Figure 4 The images from left to right show the charge / discharge rate performance at 1 C, 2 C, 5 C, 10 C, 20 C, 50 C, 20 C, 10 C, 5 C, 2 C, and 1 C, respectively. The half-cells assembled using material S2 obtained in Example 2 generally have a 20 C discharge specific capacity of 127 mA·h·g. -1 The specific capacity of 50 C discharge is generally 112 mA·h·g -1 The above demonstrates that the battery has excellent high-current charge and discharge performance; the coulombic efficiency is close to 100%, which also proves that the material has less degradation during charge and discharge and a longer cycle life.

[0073] from Figure 5 It can be seen that the half-cell assembled using material S3 obtained in Example 3 has a discharge specific capacity of 98.93 mA·h·g under a relatively high current intensity of 50 C in the first cycle. -1 After 6000 cycles, the discharge specific capacity is 73.67 mA·h·g. -1The capacity retention rate was 74.46%, and the coulombic efficiency remained almost 100%, indicating that the half-cell assembled using S3 material has ultra-high current cycling stability.

[0074] from Figure 6 It can be seen that the half-cell assembled using material S1 obtained in Example 1 has a first-cycle discharge specific capacity of 142.24 mA·h·g at room temperature under a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 104.37 mA·h·g. -1 The capacity retention rate was 74.38%; while the half-cell assembled using material L1 obtained in Comparative Example 1 had a first-cycle discharge specific capacity of 126.96 mA·h·g at room temperature under a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 95.22 mA·h·g. -1 The capacity retention rate was 75%, but capacity instability occurred during charge and discharge. Therefore, surfactants facilitate contact between the material and persulfate, and are more conducive to material dehydration. Furthermore, the half-cell assembled using material L2 from Comparative Example 2 exhibited a first-cycle specific capacity of 106.44 mA·h·g at room temperature under a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 93.69 mA·h·g. -1 The capacity retention rate was 88.02%. Clearly, the material treated with NaCl had a higher capacity than the material treated without it, indicating that the addition of sodium supplementation provided a Na-rich environment, preventing changes in sodium ions within the material that would lead to a decrease in capacity.

[0075] from Figure 7 It can be seen that the half-cell assembled using material L3 obtained in Comparative Example 3 has a first-cycle discharge specific capacity of 69.04 mA·h·g at room temperature under a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 68.57 mA·h·g. -1 That is, the capacity retention rate is 99.32%. Compared with the discharge data of the half-cell assembled from material S1 obtained in Example 1, it is obvious that the capacity is very low after changing the oxidant. This is probably because the other oxidants cause greater damage to the material structure during the dehydration process, resulting in a decrease in the sodium storage performance of the material, and thus the capacity.

[0076] from Figure 8 It can be seen that the half-cell assembled using material L4 obtained in Comparative Example 4 has a first-cycle discharge specific capacity of 109.77 mA·h·g at room temperature under a current intensity of 20 C. -1 After 2000 cycles, its discharge specific capacity is 96.17 mA·h·g. -1That is, the capacity retention rate is 87.61%. Compared with the discharge data of the half-cell assembled from material S1 obtained in Example 1, it is obvious that the reduction in the amount of oxidant will result in insufficient oxidation of the material and the presence of structurally defective materials, and the sodium storage performance of the material will not reach the optimal level.

[0077] Example 6

[0078] Material S4 obtained in Example 4 was mixed with Ketjen black and polyvinylidene fluoride in a mass ratio of 7:2:1, diluted with N-methylpyrrolidone, and stirred to form a slurry. This slurry was then coated onto clean aluminum foil and vacuum dried, stamped, and pressed to form a positive electrode sheet with a diameter of 12 mm. A slurry of hard carbon, Ketjen black, and polyvinylidene fluoride in a mass ratio of 8:1:1 was prepared and coated onto copper foil. This slurry was then dried, stamped, and pressed to form the negative electrode sheet for the battery. Using a Whatman GF / D glass fiber membrane as the separator, and a 4.5:4.5:1 mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) containing 1 mol / L NaClO4 as the electrolyte, 2032 button-type full cells were assembled in an inert gas glove box and left to stand overnight. Constant current charge-discharge tests were then performed using a Newway battery tester at room temperature and -20 °C, with voltage ranges from 1.5 V to 3.8 V. The results are as follows: Figure 9 As shown.

[0079] from Figure 9 It can be seen that the full cell assembled using material S4 obtained in Example 4 has a specific capacity of 110.04 mA·h·g at room temperature during the first charge cycle at a current intensity of 2 C. -1 The specific capacity during the first charge cycle at -20℃ is 104 mA·h·g. -1 At -20 °C, the specific capacity of the full cell retained 94.5% compared to that at room temperature. After 800 cycles, the discharge specific capacity of the S4 full cell at room temperature was 71.47 mA·h·g. -1 The full-cell capacity retention rate after 800 cycles at room temperature is 64.9%; the discharge specific capacity at -20 °C after 800 cycles is 89.98 mA·h·g. -1 With a retention rate of 86.5%, it is clear that the full cell with S4 as the positive electrode can be used at room temperature and low temperature of -20 ℃, and even performs better at low temperature.

[0080] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for preparing anhydrous iron-based Prussian white compounds, characterized in that, Includes the following steps: a. A suspension A is formed by mixing iron-based Prussian white compounds prepared by the traditional liquid-phase co-precipitation method with water; b. Add an aqueous solution B prepared with persulfate, surfactant and sodium additive to suspension A to obtain suspension C; wherein the persulfate is one or more of ammonium persulfate, sodium persulfate, potassium persulfate or potassium peroxymonosulfate; c. Under the protection of an inert gas, suspension C is stirred at 20–90 °C for 0.5–24 h, and then aged for 0.5–24 h. d. After aging, remove the supernatant, centrifuge and wash the precipitate to obtain a white or light blue precipitate; e. The precipitate is dried under vacuum at 80–210 °C for 6–14 h to obtain anhydrous iron-based Prussian white compounds. The general structural formula of the anhydrous iron-based Prussian white compounds is: Na x M (1-m) Fe m [N(CN)4]6, where x is 0.01 to 2.0, m is 0 to 1, and M and N are any one of Fe, Mn, Ni, Cu, Zn, Co, and Cs.

2. The preparation method according to claim 1, characterized in that, In step b, the mass ratio of persulfate, surfactant, sodium additive, and iron-based Prussian white compound is 0.5–6:0–0.5:1–3:

1.

3. The preparation method according to claim 1, characterized in that, In step b, the sodium additive is one or more of sodium chloride, sodium sulfate, sodium carbonate, sodium acetate, trisodium citrate, sodium ascorbate, or sodium nitrate.

4. The preparation method according to claim 1, characterized in that, The surfactant in step b is a quaternary ammonium salt surfactant or a polymeric surfactant.

5. The preparation method according to claim 4, characterized in that, The quaternary ammonium salt surfactant is selected from one of hexadecyltrimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride, and octadecyl dimethyl hydroxyethyl ammonium nitrate.

6. The preparation method according to claim 4, characterized in that, The polymeric surfactant is selected from one of polyethyleneimine, polyvinylpyrrolidone, polymaleimide, quaternized polyacrylamide, polyvinylpyridine salt, and polydimethylamine epichlorohydrin.

7. The application of the anhydrous iron-based Prussian white compound prepared by the preparation method according to any one of claims 1 to 6 in the cathode material of sodium-ion batteries.

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