A prussian blue-based sodium ion battery cathode material aftertreated by an organic solvent, and a preparation method and application thereof

Abstract

The application discloses a kind of organic solvent post-treatment's prussian blue sodium-ion battery positive electrode material and its preparation method and application;Belong to sodium-ion battery manufacturing technical field.Washed with water after prussian blue material is soaked in organic solvent for several times, centrifugal and vacuum drying obtain the positive electrode material.The raw material used in the positive electrode material is simple, low in cost, environmentally friendly;Simple, feasible operation, and organic solvent recovery process is mature;Can be enlarged for industrial production;The material prepared has excellent cycle performance and high rate performance.

Description

Technical Field

[0001] This invention belongs to the field of Prussian blue sodium-ion battery material preparation technology, and more specifically, relates to an organic solvent post-treatment Prussian blue sodium-ion battery cathode material, its preparation method and application. Background Technology

[0002] Currently, lithium-ion batteries (LIBs) are widely used in portable devices and electric vehicles due to their superior volumetric and gravimetric energy density and long cycle life. However, the expensive and scarce lithium resources limit the further expansion of LIBs in large-scale stationary energy storage. While sodium-ion batteries (SIBs) share a common operating principle with LIBs, they lag behind in energy density and reaction kinetics. However, due to their advantages such as fast charging performance, excellent high and low temperature performance, good safety performance, and good device compatibility, SIBs are considered an effective alternative for their chosen applications.

[0003] The main challenges to the commercialization of SiBs (Synthetic Induction Bodies) are the low energy density and limited cycle life of electrode materials. The cathode, as a crucial component of the battery, is particularly important, as it significantly determines the battery's energy density and cycle life. PBAs (Polydioxanone Basis) possess advantages such as open 3D diffusion channels and easily controllable crystal structures. Furthermore, compared to other cathodes, PBAs do not require high-temperature calcination during synthesis, effectively reducing manufacturing costs and thus showing broad prospects for energy storage applications.

[0004] However, despite the many advantages of Prussian blue (PBAs), their often low cycle stability and rate performance in electrochemical tests limit their practical application in sodium-ion batteries. Vacancies and coordinated water in the crystal structure occupy some of the [Fe(CN)6] holes, reducing the material's specific capacity. Furthermore, sodium ion migration can cause structural distortion or collapse, leading to low specific capacity and rate performance. As cathode materials for sodium-ion batteries, PBAs themselves have low electronic conductivity, resulting in poor rate performance and cycle stability. Moreover, practical applications require higher energy densities, which need to be improved.

[0005] Therefore, developing PBAs with good crystal structures is crucial, and the development of high-performance, high-energy-density, and high-quality Prussian blue is urgently needed. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, one of the objectives of this invention is to provide a boundary-rich Prussian blue-like material (Na) for cathode materials. x M[Fe(CN)6] yThe Prussian blue sodium-ion battery cathode material (nH₂O) has a well-structured crystal lattice, a large specific surface area, high rate performance, and excellent cycle stability under high current. It possesses the following chemical formula: Na x M[Fe(CN)6] y ·nH2O; wherein M includes at least one of Fe, Mn, and Co, 0 <x≤2,0<y<1,n=1-7。

[0007] The second objective of this invention is to provide a method for preparing Prussian blue-based sodium-ion battery cathode materials by post-treatment with organic solvents. This method is simple to prepare, uses low-cost raw materials, and can be scaled up for production.

[0008] A method for preparing a Prussian blue-based sodium-ion battery cathode material after organic solvent post-treatment, wherein the Prussian blue-based material is soaked in an organic solvent.

[0009] The preparation method described above produces a Prussian blue sodium-ion battery cathode material with the following chemical formula: Na x M[Fe(CN)6] y ·nH2O; wherein M includes at least one of Fe, Mn, and Co, 0 <x≤2,0<y<1,n=1-7。

[0010] The organic solvent in the preparation method includes at least one of acetone, anhydrous ethanol, isopropanol, n-butanol, and acetic acid.

[0011] The preparation method described above involves soaking for no more than 96 hours, preferably 24 to 72 hours, and more preferably 48 hours.

[0012] The preparation method specifically includes the following steps:

[0013] Step 1: Weigh out the sodium salt of the complexing agent and the ferrocyanide according to the proportion, and dissolve them in deionized water to obtain solution A. Stir thoroughly under an inert atmosphere; the stirring time ranges from 0.5h to 4h, preferably 3h.

[0014] Step 2: Weigh out the sodium salt of the complexing agent and the soluble transition metal salt according to the proportion, and dissolve them in deionized water to obtain solution B. Stir thoroughly under an inert atmosphere; the stirring time ranges from 0.5h to 4h, preferably 3h.

[0015] Step 3: Under an inert atmosphere, add solution B obtained in step 2 dropwise to solution A obtained in step 1 and stir to mix and age.

[0016] Step 4: Pour off the supernatant from the mixed solution obtained in Step 3, pour the bottom suspension into a centrifuge tube, add deionized water, and perform solid-liquid separation. High-speed centrifugation is preferred for solid-liquid separation, and the operation should be repeated at least three times. Then add organic solvent to the centrifuge tube and soak for a certain period of time before solid-liquid separation and drying. Preferably, place it in a vacuum oven at 120°C for drying to obtain Prussian blue materials.

[0017] The complexing agent sodium salt includes at least one of sodium citrate, sodium pyrophosphate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium tartrate, trisodium aminotriacetate, sodium gluconate, and sodium hexametaphosphate; preferably sodium citrate.

[0018] The ferrocyanide includes at least one of sodium ferrocyanide, sodium ferrocyanide decahydrate, and ferric ferrocyanide; sodium ferrocyanide is preferred.

[0019] The soluble transition metal salts include: Fe 2+ Mn 2+ Co 2+ It contains at least one of the following: phosphate, nitrate, sulfate, and oxalate.

[0020] The addition ratio of ferrocyanide to sodium complexing agent in step 1 is a molar ratio of 1:7.9 to 8.1, preferably 1:8; the amount of deionized water added meets the standard of ferrocyanide to deionized water ratio of 3.9 to 4.1 mmol:100 mL, preferably 4 mol:100 mL;

[0021] The addition ratio of the soluble transition metal salt to the complexing agent sodium salt in step 2 is a molar ratio of 1:4.9 to 5.1, preferably 1:5; the amount of deionized water added meets the standard of a soluble transition metal salt to deionized water ratio of 5.9 to 6.1 mmol:100 mL, preferably 6 mol:100 mL.

[0022] In step 3, the dropping rate is less than 50 mL / h, preferably 28 mL / h. The mixing speed of solution A and solution B is 600-800 r / min, and the mixing time is 4-6 h. The aging time is 2-48 h, preferably 2 h.

[0023] Step 4, solid-liquid separation, is performed by centrifugation. The centrifugation speed is 6000-10000 r / min, preferably 8000 r / min; the centrifugation time is 3-10 min, preferably 3 min.

[0024] After soaking in the organic solvent in step 4, dry in a vacuum oven for 12–48 hours, preferably 24 hours.

[0025] The inert atmosphere mentioned in steps 1, 2, and 3 is argon or nitrogen.

[0026] The third objective of this invention is to provide the application of the Prussian blue-based sodium-ion battery cathode material post-treated with the aforementioned organic solvent in the preparation of sodium-ion batteries.

[0027] The Prussian blue Na of the present invention x M[Fe(CN)6] y • nH2O was used as the positive electrode material for sodium-ion batteries. Existing methods were used to assemble the batteries, and electrochemical performance was tested. Active material, Ketjen black (conductive agent), and polyvinylidene fluoride (binder) were weighed at a mass ratio of 7:2:1 and thoroughly ground in an agate mortar. The mixture was transferred to a weighing bottle, and N-methylpyrrolidone (NMP) was added. The mixture was stirred for 12 hours to form a uniform slurry, which was then coated onto an aluminum foil current collector as the test electrode. A coin cell was assembled using metallic sodium as the counter electrode. The electrolyte used was 1.0 M NaClO4 in PC with 5% FEC. Electrochemical performance was tested at 1C = 170 mA g. -1 .

[0028] This invention obtains a Prussian blue suspension through co-precipitation. After simple washing and centrifugation, the suspension is immersed in solvents such as acetone to form a boundary-rich Prussian blue material with a good crystal structure and a large specific surface area. Furthermore, a good CEI film is formed during subsequent electrochemical cycling, resulting in low impedance. Specifically, the iron-based Prussian blue material exhibits high impedance at 1 A g / L. -1 It retains 81.7% capacity after 1000 cycles at high current density, and at 4A g -1 It still has 104.4 mAh g at a current density. -1 It exhibits high discharge specific capacity and energy density. This material is expected to become a strong competitor to sodium-ion cathode materials and is also likely to be mass-produced and industrialized.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The boundary-rich Prussian blue-like material prepared by this invention has a good crystal lattice structure and uniform particle distribution.

[0031] 2. The material of the present invention forms a stable CEI film during electrochemical cycling, which inhibits structural damage and dissolution of transition metal elements, and exhibits lower impedance performance.

[0032] 3. The material of the present invention only undergoes a simple soaking process, which greatly improves the electrochemical performance of the material.

[0033] 4. The sodium-ion battery prepared from the material of the present invention can be cycled more than 1,000 times and still has excellent cycle stability with a capacity retention rate of 81.7% and high rate performance.

[0034] 5. The raw materials of this invention are simple, the preparation method is simple, and the solvents such as acetone can be recycled and reused, making it easy to carry out large-scale industrial production. Attached Figure Description

[0035] Figure 1 X-ray diffraction patterns of Prussian blue cathode materials prepared in Example 1 and Comparative Example 1;

[0036] Figure 2 This is a scanning electron microscope image of the Prussian blue cathode material prepared in Example 1;

[0037] Figure 3 Examples 1, 4, 5, 6, and Comparative Example 1 were tested at 1000 mAg. -1 Comparison of long-cycle electrochemical performance under discharge at current density;

[0038] Figure 4 The Prussian blue-based cathode materials prepared in Examples 1, 7, and 8 were subjected to a 1000 mAg test. -1 Comparison of long-cycle electrochemical performance under discharge at current density;

[0039] Figure 5 The Prussian blue cathode materials prepared in Examples 1, 2, and 3 were tested at 10, 20, 50, 100, 200, 500, 1000, 2000, 3000, and 4000 mAg. -1 Comparison of discharge rate performance at different current densities;

[0040] Figure 6 Example 1 and Comparative Example 1 were compared at 10, 20, 50, 100, 200, 500, 1000, 2000, 3000, and 4000 mAg. -1 Comparison of discharge rate performance at different current densities;

[0041] Figure 7 This is a comparison graph of the CV curves of Example 1 and Comparative Example 1;

[0042] Figure 8 This is a comparison graph of the impedance curves of Example 1 and Comparative Example 1. Detailed Implementation

[0043] The present invention will be further illustrated by the following examples, but not by limiting the invention. Any simple modifications, equivalent changes, and alterations made to the following examples based on the technical essence of the present invention shall still fall within the scope of the present invention.

[0044] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0045] Example 1

[0046] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was discarded. The suspension was poured into centrifuge tubes, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetone was then added to the centrifuge tubes for soaking for 48 hours, followed by another solid-liquid separation. The suspension was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material.

[0047] In the preparation of coin cells, 140 mg of active material, 40 mg of Ketjen black, and 20 mg of polyvinylidene fluoride were weighed at a mass ratio of 7:2:1 and thoroughly ground in an agate mortar. A few drops of N-methylpyrrolidone (NMP) were added, and the mixture was stirred until homogeneous before coating. After drying in a vacuum drying oven at 80°C for 6 hours, the electrode sheets were punched into electrode plates with a diameter of approximately 12 mm, each containing approximately 1.5 mg of active material. Using metallic sodium as the negative electrode material, a 1M sodium perchlorate electrolyte containing 5% fluoroethylene carbonate and propylene carbonate was prepared. Coin cells (CR2016) were assembled in an inert gas glove box (UNILAB MBRAUN, Germany), with a high-purity argon gas operating system. Activation was performed at a constant temperature of 25°C for at least 8 hours, and the electrochemical data were tested using a Newway battery charge-discharge instrument. A constant current charge-discharge mode was used, with a voltage range of 2–4 V.

[0048] Example 2

[0049] Compared with Example 1, the difference is that the soaking time has been shortened, as detailed below:

[0050] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was then discarded. The suspension was poured into a centrifuge tube, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetone was added to the centrifuge tube, and solid-liquid separation was performed immediately again. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0051] Example 3

[0052] Compared with Example 1, the difference is that the soaking time is extended, as follows:

[0053] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was then discarded. The suspension was poured into centrifuge tubes, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetone was then added to the centrifuge tubes for soaking for 96 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0054] Example 4

[0055] Compared to Example 1, the difference lies in replacing the soaking reagent acetone with isopropanol, as detailed below:

[0056] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was poured off, and the bottom liquid was transferred to a centrifuge tube. Deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Isopropanol was then added to the centrifuge tube for soaking for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0057] Example 5

[0058] Compared to Example 1, the difference lies in replacing the soaking reagent acetone with anhydrous ethanol, as detailed below:

[0059] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was poured off, and the bottom liquid was transferred to a centrifuge tube. Deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Anhydrous ethanol was then added to the centrifuge tube for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0060] Example 6

[0061] Compared to Example 1, the difference is that the soaking reagent acetone is replaced with acetic acid, as detailed below:

[0062] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was then discarded. The suspension was poured into centrifuge tubes, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetic acid was then added to the centrifuge tubes for soaking for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0063] Example 7

[0064] Compared to Example 1, the difference is that ferrous sulfate heptahydrate is replaced with manganese sulfate monohydrate, as detailed below:

[0065] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 4.06g of manganese sulfate monohydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a suspension of Prussian blue analogue. The supernatant was then discarded. The bottom solution was poured into a centrifuge tube, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetone was then added to the centrifuge tube for soaking for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the Prussian blue analogue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0066] Example 8

[0067] Compared to Example 1, the difference is that ferrous sulfate heptahydrate is replaced with cobalt sulfate heptahydrate, as detailed below:

[0068] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.75g of cobalt sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a suspension of Prussian blue analogue. The supernatant was then discarded. The bottom solution was poured into a centrifuge tube, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Acetone was then added to the centrifuge tube for soaking for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the Prussian blue-like material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0069] Comparative Example 1

[0070] Compared to Example 1, the difference is that the soaking reagent acetone is replaced with water, as detailed below:

[0071] 30g of sodium citrate and 7.84g of sodium ferrocyanide decahydrate were weighed and dissolved in deionized water to obtain solution A, which was stirred thoroughly for 3 hours under a nitrogen atmosphere. 30g of sodium citrate and 6.68g of ferrous sulfate heptahydrate were weighed and dissolved in deionized water to obtain solution B, which was also stirred thoroughly for 3 hours under a nitrogen atmosphere. Under nitrogen protection, solution B was added dropwise to solution A and stirred at 800 rpm for 6 hours, followed by sedimentation for 2 hours to obtain a Prussian blue suspension. The supernatant was then discarded. The suspension was poured into centrifuge tubes, deionized water was added, and the mixture was centrifuged at high speed for solid-liquid separation. This process was repeated three times. Water was then added to the centrifuge tubes for soaking for 48 hours, followed by another solid-liquid separation. The mixture was then dried in a vacuum oven at 120°C for 24 hours to obtain the iron-based Prussian blue material. The preparation of the material coating and coin cell, as well as the electrochemical performance testing, were the same as in Example 1.

[0072] Table 1 shows the 10 mA g sodium-ion batteries assembled using the target materials prepared in Examples 1-8 and Comparative Example 1 as the positive electrode. -1 After 3 cycles of activation, at 1A g -1 Electrochemical performance at current density.

[0073] Table 1

[0074]

Claims

1. A Prussian blue-based sodium-ion battery cathode material post-treated with organic solvents, characterized in that, The Prussian blue sodium-ion battery cathode material has the following chemical formula: NaxM[Fe(CN)6]y·nH2O; wherein, M includes at least one of Fe, Mn, and Co, and O <x≤2,0<y<1,n=1-7; The method for preparing Prussian blue sodium-ion battery cathode material post-treated with organic solvent involves soaking Prussian blue material in organic solvent; specifically, the following steps are taken: Step 1: Weigh out sodium complexing agent and ferrocyanide according to the proportion, and dissolve them in deionized water to obtain solution A, and stir thoroughly under an inert atmosphere; Step 2: Weigh out sodium complexing agent and soluble transition metal salt according to the proportion, and dissolve them in deionized water to obtain solution B, and stir thoroughly under an inert atmosphere; Step 3: Under the protection of an inert atmosphere, add solution B obtained in step 2 dropwise to solution A obtained in step 1 and stir to mix, and then age; Step 4: Pour off the supernatant from the layered mixed solution obtained in step 3, pour the bottom suspension into a centrifuge tube, add deionized water, and perform solid-liquid separation; then add organic solvent to the centrifuge tube and soak for 24-72 hours, perform solid-liquid separation again, and then dry to obtain Prussian blue material; The organic solvents include at least one of acetone, anhydrous ethanol, isopropanol, n-butanol, and acetic acid. The soluble transition metal salts include: Fe 2+ Mn 2+ Co 2+ It contains at least one of the following: phosphate, nitrate, sulfate, and oxalate.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The complexing agent sodium salt includes at least one of sodium citrate, sodium pyrophosphate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium tartrate, trisodium aminotriacetate, sodium gluconate, and sodium hexametaphosphate; the ferrocyanide includes at least one of sodium ferrocyanide, sodium ferrocyanide decahydrate, and ferric ferrocyanide.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, In step 1, the addition ratio of ferrocyanide to sodium complexing agent is 1:7.9–8.1 (molar ratio); the amount of deionized water added meets the standard of ferrocyanide to deionized water ratio of 3.9–4.1 mmol:100 mL. In step 2, the addition ratio of soluble transition metal salt to sodium complexing agent is 1:4.9–5.1 (molar ratio); the amount of deionized water added meets the standard of soluble transition metal salt to deionized water ratio of 5.9–6.1 mmol:100 mL.

4. The sodium-ion battery cathode material according to claim 1, characterized in that, In step 3, the drop rate is less than 50 mL / h, the mixing speed of solution A and solution B is 600-800 r / min, the mixing time is 4-6 h, and the aging time is 2-48 h.

5. The application of the Prussian blue sodium-ion battery cathode material post-treated with organic solvent as described in any one of claims 1-4 in the preparation of sodium-ion batteries.

Images