Preparation method of transition metal ion doped and regulated Prussian blue sodium battery positive electrode material

Abstract

The invention relates to a preparation method of a transition metal ion doped and regulated Prussian blue sodium-ion battery positive electrode material, and belongs to the technical field of sodium-ion battery positive electrode materials. The preparation method comprises the following steps: completely dissolving sodium ferrocyanide, a complexing agent and sodium salt in deionized water to obtain a solution A; completely dissolving ferric salt, transition metal salt, a complexing agent and sodium salt in deionized water to obtain a solution B; dropwise adding the solution B into the solution A, carrying out coprecipitation reaction at the temperature of 20-60 DEG C under a stirring condition, standing and aging at room temperature for 12-48 hours, carrying out solid-liquid separation, washing a solid with deionized water and absolute ethyl alcohol in sequence, and drying to obtain a precursor; and carrying out heat treatment on the precursor in a protective atmosphere to obtain the transition metal ion doped and regulated Prussian blue sodium battery positive electrode material. According to the method, toxic gas is not generated, the synthesis temperature is low, the sodium content of Prussian blue is increased, the structural stability is enhanced, and the lattice water content is inhibited.

Description

Technical Field

[0001] This invention relates to a method for preparing Prussian blue sodium battery cathode material by transition metal ion doping, belonging to the technical field of sodium-ion battery cathode materials. Background Technology

[0002] The development of cathode materials is a key factor in sodium-ion battery research, as they largely determine the overall energy density and cycle life of the battery. Iron-based Prussian blue analogues (Fe-PBA, chemical formula Na2Fe[Fe(CN)6]) have attracted considerable attention due to their open framework structure and high theoretical capacity (~170 mAh / g). However, their practical application has long been limited by the following inherent drawbacks: (1) Lattice defects lead to deterioration of sodium ion transport kinetics: In Fe-PBA materials prepared by the traditional co-precipitation method, the Fe(CN)6 vacancy defect rate is as high as 15%-20%, which seriously hinders the diffusion channels of sodium ions. Moreover, during the charging and discharging process, defect sites will cause local stress concentration, which accelerates the pulverization of materials.

[0003] (2) Residual water of crystallization causes structural collapse: Fe-PBA crystals are prone to encapsulating large amounts of water of crystallization. These water molecules cause harm in the following two ways: Electrochemical side reactions: Under high voltage (>3.5V vs Na) + / Na) decomposes into OH- - It reacts with the electrolyte to form an inert interface layer (such as Na2CO3), which leads to increased interfacial impedance and deterioration of mechanical stability: the dehydration-rehydration process causes lattice volume fluctuations.

[0004] (3) Irreversible phase transition during cycling: Fe-PBA undergoes a transformation from cubic phase (Na2FeFe(CN)6) to sodium-depleted phase (NaFeFe(CN)6) during sodium ion insertion / extraction. Due to insufficient Fe-N bond strength (bond energy approximately 250 kJ / mol), this phase transition is accompanied by lattice distortion.

[0005] Although researchers have attempted to improve the performance of Fe-PBA through transition metal doping (such as Mn and Co) or surface coating, a key bottleneck remains: poor dopant element matching, particularly with Mn. 2+ (Ionic radius 0.83 Å) and Fe 2+ The radius difference of (0.78Å) is >6%; the introduction of lattice stress leads to insufficient process controllability of crack generation, and conventional co-precipitation methods are difficult to precisely control the nucleation rate; the material has a wide particle size distribution and the dehydration process is crude. Although direct high-temperature calcination (>300℃) can remove crystal water, it leads to the decomposition of CN skeleton and a decrease in specific surface area. Summary of the Invention

[0006] To address the aforementioned technical problems of Prussian blue sodium cathode materials, this invention provides a method for preparing Prussian blue sodium cathode materials by transition metal ion doping. This method reduces lattice defects through metal doping with matching ion radii, precisely controls the crystal nucleation rate by complexing agent-assisted co-precipitation to improve morphological uniformity, and selectively removes adsorbed water and lattice water through gradient heat treatment to enhance the cycle stability of the cubic phase structure.

[0007] A method for preparing Prussian blue sodium cathode material with transition metal ion doping, the specific steps of which are as follows: (1) Under a protective atmosphere, sodium ferrocyanide, complexing agent, and sodium salt are completely dissolved in deionized water to obtain solution A; (2) Under a protective atmosphere, iron salt, transition metal salt, complexing agent and sodium salt are completely dissolved in deionized water to obtain solution B; (3) Under a protective atmosphere, solution B is added dropwise to solution A, and a co-precipitation reaction is carried out at a temperature of 20~60℃ with stirring. The mixture is then aged at room temperature for 12~48h, and the solid and liquid are separated. The solid is washed with deionized water and anhydrous ethanol in sequence, and then dried under vacuum to obtain the precursor. (4) The precursor is heat-treated under a protective atmosphere to obtain a Prussian blue sodium cathode material with transition metal ion doping control.

[0008] Preferably, in step (1), the molar ratio of the complexing agent added to sodium ferrocyanide is 1~1.7:1, the molar ratio of sodium salt to sodium ferrocyanide is 0.8~17:1, and the concentration of sodium ferrocyanide in solution A is 0.05~0.1mol / L.

[0009] Preferably, the complexing agent in steps (1) and (2) is sodium citrate, disodium ethylenediaminetetraacetate, sodium pyrophosphate, or sodium acetate, and the sodium salt is sodium nitrate, sodium chloride, or sodium sulfate.

[0010] Preferably, the iron salt in step (2) is one or more of ferric chloride, ferric sulfate, ferric nitrate, and ferric acetate, and the transition metal salt is one or more of Ni, Cu, Co, and Zn.

[0011] More preferably, the transition metal salt is one or more of chloride, sulfate, nitrate, and acetate.

[0012] Preferably, the molar ratio of the transition metal salt in step (2) to the sodium ferrocyanide in step (1) is 1.5~4.0:10.

[0013] Preferably, the molar ratio of iron salt to sodium ferrocyanide in step (2) is 0.6~0.8:1, the molar ratio of the amount of complexing agent added to iron salt is 20~50:15, and the molar ratio of sodium salt to iron salt is 1.5~3:1.

[0014] Preferably, the concentration of iron salt in solution B in step (2) is 0.035~1.7 mol / L.

[0015] Preferably, in step (3), the dropping rate of solution B is 25~38 ml / h; the vacuum drying temperature is 60~85℃, and the time is 12~18h.

[0016] Preferably, the protective atmosphere in step (4) is nitrogen or an inert gas, the heat treatment temperature is 135~180℃, and the time is 15~20h.

[0017] The beneficial effects of this invention are: (1) The present invention uses a complexing agent-assisted coprecipitation method to improve structural stability and cycle performance by precisely controlling the molar ratio of iron salt and copper salt; (2) This invention uses three strategies in synergy: transition metal ion doping, complexing agents (reduction / complexation), and sodium salts (ionic strength / co-ionizing agents) to achieve multi-dimensional and precise control of Prussian blue analogue (PBAs) synthesis. The complexing agent slows down the reaction kinetics through complexation, reducing lattice vacancies from the source; the sodium salt utilizes high Na+... + The concentration is stable and the open framework inhibits defect generation; the doped ions directly occupy the vacancy sites, and the three form a defect eradication closed loop of "reaction inhibition-environmental stabilization-physical filling", resulting in a near-ideal stoichiometry and ultra-low water content structure. (3) The synergistic effect of this invention endows PBAs with ultra-high specific capacity (retaining all active sites + doping with multi-electron reaction), excellent rate performance (unobstructed ion channels + pre-sodiumization optimized diffusion), and ultra-long cycle life (defect / water content approaching zero + lattice strengthening). At the same time, by flexibly customizing the voltage platform and functional characteristics through doping, it establishes itself as the "gold standard" for high-performance sodium battery cathodes. (4) Compared with single-element iron-based Prussian blue, the Prussian blue sodium electrode material of the present invention, which is controlled by transition metal ion doping, reduces structural distortion and improves cycle stability; moreover, the preparation process is simple, the required equipment is not complicated, and the raw material cost is low, which makes the material have great potential for industrial production; the present invention combines laboratory-level defect control strategy (transition metal doping / complexing agent / sodium salt synergy) with industrial-friendly process, which solves the biggest bottleneck in the industrialization of Prussian blue material (short lifespan caused by structural defects). Attached Figure Description

[0018] Figure 1 Here is a SEM image of FeCu-PBA1, the Prussian blue sodium electrode material from Example 1. Figure 2 The XPS full spectrum of FeCu-PBA1, the Prussian blue sodium electrode material in Example 1; Figure 3 Capacity retention diagrams for the Prussian blue sodium cathode materials in comparative examples and Examples 1-3; Figure 4 This is a SEM image of the Prussian blue sodium electrode material FeCu-PBA1 after 200 cycles in Example 1. Figure 5 Here is the charge-discharge curve of FeCu-PBA1, the Prussian blue sodium electrode material in Example 1; Figure 6 This is a capacity retention diagram of the Prussian blue sodium electrode material in Example 4; Figure 7 This is a capacity retention diagram of the Prussian blue sodium electrode material in Example 5; Figure 8 This is a capacity retention diagram of the Prussian blue sodium electrode material in Example 6. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0020] Example 1: A method for preparing a Prussian blue sodium cathode material by transition metal ion doping, the specific steps of which are as follows: (1) Under a nitrogen atmosphere, sodium ferrocyanide Na4Fe(CN)6·10H2O, a complexing agent (sodium citrate), and sodium salt (Na2SO4) were completely dissolved in deionized water to obtain solution A; the molar ratio of the complexing agent (sodium citrate) to sodium ferrocyanide was 1.7:1, and the molar ratio of sodium salt (Na2SO4) to sodium ferrocyanide was 1.4:1; the concentration of sodium ferrocyanide in solution A was 0.066 mol / L; (2) Under a nitrogen atmosphere, iron salt (FeSO4·7H2O), transition metal salt (CuSO4·5H2O), complexing agent (sodium citrate), and sodium salt (Na2SO4) are completely dissolved in deionized water to obtain solution B; the molar ratio of the transition metal salt (CuSO4·5H2O) to sodium ferrocyanide in step (1) is 2:10, the molar ratio of iron salt (FeSO4·7H2O) to sodium ferrocyanide in step (1) is 8:10, the molar ratio of the amount of complexing agent (sodium citrate) added to iron salt (FeSO4·7H2O) is 1.5:1, the molar ratio of sodium salt (Na2SO4) to iron salt (FeSO4·7H2O) is 1.2:1, and the concentration of iron salt (FeSO4·7H2O) in solution B is 0.08 mol / L; (3) Solution B was added dropwise to solution A at a rate of 30 mL / h. The co-precipitation reaction was carried out for 8 h under nitrogen atmosphere, temperature of 25 °C and stirring. The mixture was then aged at room temperature for 24 h. The solid and liquid were separated. The solid was washed three times each with deionized water and anhydrous ethanol and then dried under vacuum at 80 °C for 12 h to obtain the precursor. (4) The precursor was heat-treated at a protective atmosphere (argon atmosphere) and a temperature of 180°C for 18 hours to obtain a transition metal ion doped Prussian blue sodium cathode material, denoted as FeCu-PBA1. The SEM image of the Prussian blue sodium cathode material FeCu-PBA1 in this embodiment is shown below. Figure 1 ,from Figure 1 It can be seen that the Prussian blue cathode material maintains a cubic outline, with uniform particle size and a particle size of 1~2 μm; The XPS full spectrum of the Prussian blue sodium cathode material FeCu-PBA1 in this embodiment is shown below. Figure 2 ,from Figure 2 As can be seen, the XPS full spectrum of the Prussian blue sodium electrode material FeCu-PBA1 in this embodiment is shown in the figure below. Figure 2 X-ray photoelectron spectroscopy (XPS) was used to probe the elemental composition and oxidation state during the synthesis process. The scanning spectrum of FeCu-PBA1 confirmed the presence of Na1s, Cu2p, Fe2p, O1s, N1s and C1s core energy level signals, verifying successful Cu incorporation and oxygen from the water of crystallization.

[0021] Comparative Example 1: The difference between the comparative example and Example 1 is that the molar amount of transition metal salt (CuSO4·5H2O) in step (2) is completely replaced with iron salt (FeSO4·7H2O) to prepare Prussian blue sodium electrode material, denoted as FeCu-PBA0.

[0022] Example 2: The difference between this example and Example 1 is that the molar ratio of transition metal salt (CuSO4·5H2O) to sodium ferrocyanide in step (1) is 3:10, and the molar ratio of iron salt (FeSO4·7H2O) to sodium ferrocyanide in step (1) is 7:10; Prussian blue sodium electrode material was prepared and denoted as FeCu-PBA2.

[0023] Example 3: The difference between this example and Example 1 is that the molar ratio of transition metal salt (CuSO4·5H2O) to sodium ferrocyanide in step (1) is 4:10, and the molar ratio of iron salt (FeSO4·7H2O) to sodium ferrocyanide in step (1) is 6:10; Prussian blue sodium cathode material was prepared, denoted as FeCu-PBA3; Battery Assembly: Using Prussian blue sodium cathode materials from Comparative Example 1 and Examples 1-3 as active materials, the active materials, SuperP carbon black (conductive additive), and polyvinylidene fluoride (PVDF) binder were mixed uniformly to obtain a mixture. The mass ratio of active materials, SuperP carbon black (conductive additive), and PVDF in the mixture was 7:2:1. N-methyl-2-pyrrolidone (NMP) solvent was gradually added and stirred to obtain a uniformly dispersed cathode slurry. The cathode slurry was uniformly coated onto a clean aluminum foil current collector, and the N-methyl-2-pyrrolidone solvent was removed by vacuum drying to obtain an electrode film. The electrode film was subjected to cold pressing to improve the adhesion between particles, and then stamped into a disc electrode. The average mass loading of the active material (Prussian blue sodium cathode material) on the disc electrode was 1.2~1.5 mg / cm³. 2 The disk electrode was quickly transferred to an argon-filled glove box (H2O / O2<0.1ppm), and a CR2032 button cell was assembled using sodium metal as the counter electrode and glass fiber as the positive electrode. The constant current charge and discharge test voltage window of the CR2032 button cell was 2-4.2V. The capacity retention graphs of the Prussian blue sodium cathode materials in Comparative Examples and Examples 1-3 at a current density of 0.5C are shown below. Figure 3 The initial specific discharge capacity of the undoped comparative sample was 132.63 mAh g. −1 However, after 200 cycles, only 38% of the capacity was retained, mainly due to structural degradation caused by lattice water and Fe. 2+ Dissolve; Cu 2+ The doped electrodes of Examples 1-3 exhibited significantly enhanced stability, attributed to reduced lattice water content and enhanced framework structure; specifically, the Cu-doped Prussian blue sodium cathode material with a molar amount of 20% in Example 1 achieved an initial capacity of 151.81 mAh g⁻¹. −1 The initial capacities of the Cu-doped Prussian blue sodium cathode materials in Example 2 (30% molar content) and Example 3 (40% molar content) were relatively low (148.61 mAh g⁻¹, respectively). −1 and 120.39mAhg −1 This may be due to an excess of non-reactive Cu. 2+ Occupying redox-active Fe sites, hindering Na + Intercalation / delamination kinetics, SEM image of Prussian blue sodium cathode material after 200 cycles in Example 1 is shown below. Figure 4 ,from Figure 4 As can be seen from the data, the Prussian blue sodium electrode material exhibits good particle morphology and minimal surface erosion after cycling, demonstrating excellent structural integrity and resistance to cyclic degradation. Example 1: The charge-discharge curves of the Prussian blue sodium electrode material FeCu-PBA1 are shown in the figure. Figure 5 ,from Figure 5 It can be seen that FeCu-PBA1 has two distinct redox peaks in the 2.461-3.254 V range, which are attributed to the redox process of high-spin Fe (FeHS) coordinated with the nitrogen atom in the cyanide group; the voltage range above 3.5 V corresponds to the low-spin Fe (FeLS) Fe bonded to the carbon atom within the cyanide framework. 3+ / Fe 2+ Redox transition.

[0024] Example 4: A method for preparing a Prussian blue sodium cathode material by transition metal ion doping, the specific steps of which are as follows: (1) Under a nitrogen atmosphere, sodium ferrocyanide Na4Fe(CN)6·10H2O, a complexing agent (sodium pyrophosphate), and sodium salt (NaCl) are completely dissolved in deionized water to obtain solution A; the molar ratio of the complexing agent (sodium pyrophosphate) to sodium ferrocyanide is 1.1:1, and the molar ratio of sodium salt (NaCl) to sodium ferrocyanide is 17:1; the concentration of sodium ferrocyanide in solution A is 0.1 mol / L; (2) Under a nitrogen atmosphere, iron salt (FeCl2·4H2O), transition metal salt (NiSO4·6H2O), complexing agent (sodium pyrophosphate), and sodium salt (NaCl) are completely dissolved in deionized water to obtain solution B; the molar ratio of the transition metal salt (NiSO4·6H2O) to sodium ferrocyanide in step (1) is 2:10, the molar ratio of iron salt (FeCl2·4H2O) to sodium ferrocyanide in step (1) is 8:10, the molar ratio of the amount of complexing agent (sodium pyrophosphate) added to iron salt (FeCl2·4H2O) is 11:8, the molar ratio of sodium salt (NaCl) to iron salt (FeCl2·4H2O) is 17:8, and the concentration of iron salt (FeCl2·4H2O) in solution B is 0.08 mol / L; (3) Solution B was added dropwise to solution A at a rate of 25 mL / h. The co-precipitation reaction was carried out under nitrogen atmosphere, temperature of 30℃ and stirring for 6 h. The mixture was then aged at room temperature for 10 h. The solid and liquid were separated. The solid was washed three times each with deionized water and anhydrous ethanol and then vacuum dried at 60℃ for 18 h to obtain the precursor. (4) The precursor was heat-treated at a protective atmosphere (argon atmosphere) and a temperature of 150°C for 20 hours to obtain a transition metal ion doped Prussian blue sodium cathode material, denoted as Fe-PBA4. In this embodiment, the Prussian blue sodium electrode material Fe-PBA4 was assembled into a CR2032 button cell according to the scheme in Example 3; the constant current charge and discharge test voltage window of the CR2032 button cell was 2-4.2V. The capacity retention diagram of the Prussian blue sodium cathode material in this embodiment is shown below. Figure 6 ,from Figure 6 It can be seen that at a current density of 0.5C, the initial discharge capacity of the Fe-PBA4 sample is 140mAhg-1. After 200 cycles, the specific capacity of the battery in Example 4 has decreased, but it still maintains a certain level, with a capacity retention rate of 67.8%.

[0025] Example 5: A method for preparing a Prussian blue sodium cathode material by transition metal ion doping, the specific steps of which are as follows: (1) Under a nitrogen atmosphere, sodium ferrocyanide Na4Fe(CN)6·10H2O, a complexing agent (disodium ethylenediaminetetraacetate), and sodium salt (NaNO3) were completely dissolved in deionized water to obtain solution A; the molar ratio of the complexing agent (disodium ethylenediaminetetraacetate) to sodium ferrocyanide was 1.3:1, and the molar ratio of sodium salt (NaNO3) to sodium ferrocyanide was 0.8:1; the concentration of sodium ferrocyanide in solution A was 0.05 mol / L; (2) Under a nitrogen atmosphere, iron salt (Fe(NO3)3·9H2O), transition metal salt (CoSO4·7H2O), complexing agent (disodium ethylenediaminetetraacetate), and sodium salt (NaNO3) are completely dissolved in deionized water to obtain solution B; the molar ratio of the transition metal salt (CoSO4·7H2O) to sodium ferrocyanide in step (1) is 1.5:10, the molar ratio of iron salt (Fe(NO3)3·9H2O) to sodium ferrocyanide in step (1) is 8.5:10, the molar ratio of the amount of complexing agent (disodium ethylenediaminetetraacetate) to iron salt (Fe(NO3)3·9H2O) is 5:15, the molar ratio of sodium salt (NaNO3) to iron salt (Fe(NO3)3·9H2O) is 2:1.5, and the concentration of iron salt (Fe(NO3)3·9H2O) in solution B is 1.7 mol / L; (3) Solution B was added dropwise to solution A at a rate of 35 mL / h. The co-precipitation reaction was carried out for 5 h under nitrogen atmosphere, temperature of 50 °C and stirring. The mixture was then aged at room temperature for 10 h. The solid and liquid were separated. The solid was washed three times each with deionized water and anhydrous ethanol. It was then vacuum dried at 65 °C for 12 h to obtain the precursor. (4) The precursor was heat-treated at a protective atmosphere (argon atmosphere) and a temperature of 135°C for 20 hours to obtain a transition metal ion doped Prussian blue sodium cathode material, denoted as Fe-PBA5. In this embodiment, the Prussian blue sodium electrode material Fe-PBA5 was assembled into a CR2032 button cell according to the scheme in Example 3; the constant current charge and discharge test voltage window of the CR2032 button cell was 2-4.2V. The capacity retention diagram of the Prussian blue sodium cathode material in this embodiment is shown below. Figure 7 ,like Figure 7 As shown, the initial discharge capacity of the sample in Example 5 was 122 mAh g⁻¹, and the capacity retention rate was 79.5% after 200 cycles at a current density of 0.5C. Compared with Example 4, the initial discharge capacity was lower, but the capacity retention rate was higher.

[0026] Example 6: A method for preparing a Prussian blue sodium cathode material by transition metal ion doping, the specific steps of which are as follows: (1) Under a nitrogen atmosphere, sodium ferrocyanide Na4Fe(CN)6·10H2O, a complexing agent (sodium citrate), and sodium salt (NaCl) are completely dissolved in deionized water to obtain solution A; the molar ratio of the complexing agent (sodium citrate) to sodium ferrocyanide is 1:1, and the molar ratio of sodium salt (NaCl) to sodium ferrocyanide is 4:1; the concentration of sodium ferrocyanide in solution A is 0.05 mol / L; (2) Under a nitrogen atmosphere, iron salt (Fe(CH3COO)3), transition metal salt (NiSO4·6H2O and FeSO4·7H2O), complexing agent (sodium citrate), and sodium salt (NaCl) are completely dissolved in deionized water to obtain solution B; the molar ratio of the transition metal salt (NiSO4·6H2O) to the transition metal salt (FeSO4·7H2O) is 1:1, and the total molar amount of the transition metal salt is the same as that in step (1) ferrocyanide The molar ratio of sodium ferrocyanide is 3:10, the molar ratio of iron salt (Fe(CH3COO)3) to sodium ferrocyanide in step (1) is 7:10, the molar ratio of the amount of complexing agent (sodium citrate) to iron salt (Fe(CH3COO)3) is 15:7, the molar ratio of sodium salt (NaCl) to iron salt (Fe(CH3COO)3) is 20:7, and the concentration of iron salt (Fe(CH3COO)3) in solution B is 0.035mol / L; (3) Solution B was added dropwise to solution A at a rate of 38 mL / h. The co-precipitation reaction was carried out under nitrogen atmosphere, temperature of 60℃ and stirring for 8 h. The mixture was then aged at room temperature for 18 h. The solid and liquid were separated. The solid was washed three times each with deionized water and anhydrous ethanol and then vacuum dried at 85℃ for 15 h to obtain the precursor. (4) The precursor was heat-treated at a protective atmosphere (argon atmosphere) and a temperature of 135°C for 15 hours to obtain a transition metal ion doped Prussian blue sodium cathode material, denoted as Fe-PBA6. In this embodiment, the Prussian blue sodium electrode material Fe-PBA6 was assembled into a CR2032 button cell according to the scheme in Example 3; the constant current charge and discharge test voltage window of the CR2032 button cell was 2-4.2V. The capacity retention diagram of the Prussian blue sodium cathode material in this embodiment is shown below. Figure 8 As shown in the figure, Example 6 has an initial discharge specific capacity of 90 mAh g⁻¹ at a current density of 0.5C, a maximum discharge specific capacity of 106 mAh g⁻¹, and a capacity retention rate of 90% after 200 cycles, which is the highest among all examples, but its initial specific capacity is the lowest.

[0027] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a Prussian blue sodium cathode material by transition metal ion doping, characterized in that, The specific steps are as follows: (1) Completely dissolve sodium ferrocyanide, complexing agent, and sodium salt in deionized water to obtain solution A; (2) Completely dissolve the iron salt, transition metal salt, complexing agent, and sodium salt in deionized water to obtain solution B; (3) Add solution B dropwise into solution A and coprecipitate under stirring at a temperature of 25~60℃. Let it stand at room temperature for 12~48h, then separate the solid and liquid. Wash the solid with deionized water and anhydrous ethanol in sequence, and then dry it under vacuum to obtain the precursor. (4) The precursor is heat-treated under a protective atmosphere to obtain a Prussian blue sodium cathode material with transition metal ion doping.

2. The preparation method of the transition metal ion doping controlled Prussian blue sodium cathode material according to claim 1, characterized in that: In step (1), the molar ratio of the complexing agent to sodium ferrocyanide is 1~1.7:1, and the molar ratio of sodium salt to sodium ferrocyanide is 0.8~17:1; the concentration of sodium ferrocyanide in solution A is 0.05~0.1mol / L.

3. The preparation method of the transition metal ion doping controlled Prussian blue sodium cathode material according to claim 1, characterized in that: In steps (1) and (2), the complexing agent is sodium citrate, disodium ethylenediaminetetraacetate, sodium pyrophosphate or sodium acetate, and the sodium salt is sodium nitrate, sodium chloride or sodium sulfate.

4. The preparation method of the transition metal ion doping controlled Prussian blue sodium cathode material according to claim 1, characterized in that: Step (2) The iron salt is one or more of ferric chloride, ferric sulfate, ferric nitrate, and ferric acetate, and the transition metal salt is one or more of Ni, Cu, Co, and Zn.

5. The method for preparing the Prussian blue sodium cathode material by transition metal ion doping according to claim 4, characterized in that: Transition metal salts are one or more of chlorides, sulfates, nitrates, and acetates.

6. The method for preparing the Prussian blue sodium cathode material by transition metal ion doping according to claim 1, characterized in that: The molar ratio of the transition metal salt in step (2) to sodium ferrocyanide in step (1) is 1.5~4.0:

10.

7. The method for preparing Prussian blue sodium cathode material by transition metal ion doping according to claim 1, characterized in that: The molar ratio of iron salt to sodium ferrocyanide in step (2) is 6~8:10, the molar ratio of the amount of complexing agent added to iron salt is 20~50:15, and the molar ratio of sodium salt to iron salt is 1.5~3:

1.

8. The method for preparing Prussian blue sodium cathode material by transition metal ion doping according to claim 1, characterized in that: In step (2), the concentration of iron salt in solution B is 0.035~1.7 mol / L.

9. The method for preparing the Prussian blue sodium cathode material by transition metal ion doping according to claim 1, characterized in that: In step (3), the dropping rate of solution B is 10~50 ml / h; the vacuum drying temperature is 60~85℃ and the time is 12~18h.

10. The method for preparing the Prussian blue sodium cathode material by transition metal ion doping according to claim 1, characterized in that: Step (4) The protective atmosphere is nitrogen or inert gas, and the heat treatment temperature is 135~180℃ for 15~20h.

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