High-entropy Prussian blue positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of novel energy storage battery materials, and particularly relates to a high-entropy Prussian blue positive electrode material as well as a preparation method and application thereof. The chemical formula of the positive electrode material is NaxM [Fe (CN) 6] y.mH2O (at) C, M comprises five different elements of Fe, Ni, Co, Mn, Zn, Ti, V or Cu, the molar ratio of the five different elements is 1: 1: 1: 1: 1-1: 3: 3: 3: 3, x is larger than 0 and smaller than or equal to 2, y is larger than 0 and smaller than or equal to 3, m is larger than 0 and smaller than or equal to 5, and the molar ratio of a carbon component to a high-entropy Prussian blue component is 1: 5-1: 10. Different physical and chemical properties of a plurality of metal elements are utilized, different transition metal elements are coordinated with cyano groups, respective advantages are exerted, the defects of a single metal element are overcome, a stable continuous transmission channel for sodium ions and electrons is constructed in a Prussian blue structure, and the performance of the Prussian blue is improved. Jahn-Teller distortion can be effectively inhibited through the synergistic effect of various metals, and the long cycle stability of the Prussian blue material is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy storage battery materials, and particularly relates to a high-entropy Prussian blue-based cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the implementation of the national goals of "carbon peak and carbon neutrality", the electric power energy of renewable energy sources such as solar energy and wind energy has developed rapidly, promoting remarkable progress in new energy technologies. Under this background, the demand for efficient energy storage technologies in fields such as mobile electronic devices, electric vehicles, and energy storage power stations is increasing day by day. Secondary batteries, due to their high energy conversion efficiency, convenient operation characteristics, and the advantage of being not restricted by geographical conditions, have become an important development direction for future energy storage. The goal of scientific researchers is to develop secondary battery technologies with high safety, low cost, rich resources, high energy density, and long service life. Currently, lithium-ion batteries have been widely used in fields such as electric vehicles and mobile electronic devices due to their relatively high specific energy and excellent cycle stability. However, lithium-ion batteries still face many challenges, including high costs, limitations in lithium resource reserves, uncertainties in future production processes, as well as performance degradation and safety issues in low-temperature environments. Therefore, developing a new battery technology to overcome the above limitations has become an urgent need in current research.

[0003] Prussian blue and its analogues are a class of typical coordination polymers. In its crystal structure, two iron atoms located at the vertex positions are respectively bonded to the carbon atom and nitrogen atom in the cyano group, and are diagonally distributed on each crystal plane. Initially, Prussian blue materials were mainly widely used as pigments in the industrial field. With the in-depth research, their electrochemical properties have gradually attracted attention, especially the application in the electrode materials of sodium-ion batteries has been widely explored. Experimental results show that such materials exhibit excellent electrochemical properties in sodium-ion batteries and show potential application prospects. However, Prussian blue materials still face significant challenges in the application of sodium-ion batteries: their crystal structure is prone to irreversible changes during the charge-discharge cycle, resulting in structure collapse and performance degradation, thus shortening the battery cycle life and making it difficult to meet the requirements of long-term stable operation. In addition, structural instability may also affect the rate performance and safety of the battery, limiting its large-scale application. Therefore, improving the structural stability and cycle performance of Prussian blue materials has become the focus of current research. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the unstable crystal structure of Prussian blue materials shortens the battery cycle life. To overcome the above-mentioned deficiencies and defects in the background art, a high-entropy Prussian blue-based cathode material, a preparation method thereof, and an application thereof are provided.

[0005] To solve the above technical problem, the technical solution proposed by the present invention is as follows: A high-entropy Prussian blue-based cathode material, the chemical formula of the cathode material is Na x M[Fe(CN)6] y ·mH2O@C, where M includes five different elements among Fe, Ni, Co, Mn, Zn, Ti, V or Cu, and the molar ratio between the five different elements is 1:1:1:1:1 to 1:3:3:3:3, 0 < x ≤ 2, 0 < y ≤ 3, 0 < m ≤ 5, and the molar ratio of the carbon component to the high-entropy Prussian blue-based component is 1:5 to 1:10. The present invention utilizes the different physical and chemical properties of multiple metal elements. Through the coordination of different transition metal elements with cyanide groups, their respective advantages are exerted to make up for the deficiencies of single metal elements, and a stable sodium ion and electron continuous transmission channel is constructed in the Prussian blue structure. The synergistic effect of multiple metals can effectively inhibit the Jahn-Teller distortion and significantly improve the long-cycle stability of the Prussian blue material.

[0006] Preferably, the cathode material includes a carbon substrate with a network structure and high-entropy Prussian blue-based cubes. The high-entropy Prussian blue-based cubes are three-dimensional framework skeletons in a cubic shape formed by transition metal elements bridged by cyanide groups, and the high-entropy Prussian blue-based cubes are embedded in the carbon substrate with a network structure. The cubic crystal structure of the high-entropy Prussian blue-based cubes in this application is clear and the surface is smooth. The transition metal elements form a stable three-dimensional framework skeleton through cyanide (-C≡N-) bridging, and the structure can be maintained stable during charge and discharge. The carbon material has a network structure, and the high-entropy Prussian blue is embedded in it, jointly constituting an efficient conductive network to promote the transmission of sodium ions and electrons.

[0007] Under the same technical concept, this application also provides a preparation method of a high-entropy Prussian blue-based cathode material, including the following steps: (1) Fully disperse and dissolve a carbon source and a sodium supplement agent in deionized water to obtain solution C; (2) Dissolve sodium ferrocyanide in deionized water to obtain solution A; (3) Dissolve at least five different transition metal salt solutions, a chelating agent and a polyvinylpyrrolidone dispersant in deionized water to obtain solution B; (4) Under an inert gas atmosphere, simultaneously drop solution A and solution B into solution C for coprecipitation reaction; (5) Continue heating and stirring to obtain a suspension, age, wash and separate the suspension to obtain a precipitate, and dry the precipitate to obtain the high-entropy Prussian blue-based cathode material.

[0008] Preferably, the carbon source in step (1) includes at least one of carbon nanotubes, Ketjen black, acetylene black, conductive carbon black, or carbon nanofibers. The concentration of the carbon source in solution C is 0.5 - 1 g / L. The sufficient dissolution and dispersion specifically mean: heating and stirring in a water bath at 30 - 60 °C for 20 - 60 min, and then ultrasonically dispersing in an ultrasonic oscillator for 10 - 30 min. The dissolution of carbon elements is relatively difficult, and they are dispersed and dissolved separately to ensure the dispersion degree of solution C. The addition of the carbon source stabilizes the material structure and enhances the electrical conductivity of the material.

[0009] Preferably, the sodium supplementing agent in step (1) includes at least one of sodium sulfate, sodium nitrate, sodium chloride, or sodium acetate. The mass ratio of the carbon source to the sodium supplementing agent is 1:30 - 50.

[0010] Preferably, the concentration of sodium ferrocyanide in solution A in step (2) is 0.05 - 0.2 mol / L.

[0011] Preferably, the chelating agent in step (3) includes at least one of disodium ethylenediaminetetraacetate, sodium citrate, sodium tripolyphosphate, or sodium hexametaphosphate. The concentration of the chelating agent in solution B is 0.1 - 0.5 mol / L.

[0012] Preferably, the transition metal salt solution in step (3) includes five or more of FeCl2, Fe(NO3)2, FeSO4, Fe3(PO4)2, NiCl2, Ni(NO3)2, NiSO4, Ni3(PO4)2, Co(NO3)2, CoSO4, Co3(PO4)2, MnCl2, Mn(NO3)2, MnSO4, Mn3(PO4)2, ZnCl2, Zn(NO3)2, ZnSO4, Zn3(PO4)2, TiCl4, Ti(SO4)2, Ti(NO3)4, VCl3, NH4VO3, CuCl2, Cu(NO3)2, CuSO4, or Cu3(PO4)2. The total concentration of the transition metal salts in solution B is 0.01 - 0.2 mol / L. Mn is the main active center, which improves the capacity of the material. Co can increase the voltage of the material. Ni greatly enhances the stability of the framework structure and inhibits the occurrence of phase transformation. Cu improves the electrical conductivity of the material.

[0013] Preferably, the nitrogen protection in step (4) specifically means: dispersing nitrogen in the reaction solution to create a nitrogen atmosphere. When dispersing, the stirring speed is controlled at 300 - 600 rpm, the reaction temperature is 20 - 50 °C, the dropping speeds of solution A and solution B are controlled at 15 - 20 ml / h, and the dropping speed ratio of solution A to solution B is controlled at 1:1 - 1:1.5.

[0014] Preferably, the temperature for continued heating in step (5) is 20-50°C, the stirring time is 1-5h, the aging is allowed to stand at room temperature away from light, the aging time is 10-30h, and the drying process adopts a gradient heating method, in a vacuum environment, first pre-drying at 80°C for 2h, then heating to 100°C for drying for 10h, and finally vacuum drying at 120°C for 10h.

[0015] Under the same technical concept, the present application also provides an application of a high-entropy Prussian blue-based positive electrode material, wherein the above-mentioned high-entropy Prussian blue-based positive electrode material is used as a positive electrode plate of a sodium ion battery, and the positive electrode plate includes a current collector, a binder and the high-entropy Prussian blue-based positive electrode material.

[0016] Preferably, the method for preparing the positive electrode sheet comprises: mixing a high entropy Prussian blue positive electrode material with a binder, coating the mixture on a current collector, drying the mixture, and slicing the mixture to obtain a positive electrode sheet.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention relates to a high-entropy Prussian blue sodium cathode material, which builds a stable three-dimensional framework structure through the synergistic effect of multiple metal elements, and the introduction of polyvinyl pyrrolidone and composite carbon improves the conductive properties of the material; (2) The present invention relates to a method for preparing a high-entropy Prussian blue-type sodium positive electrode material. The method adopts multi-component doping of multiple transition metal elements, stabilizes the crystal structure of the material by virtue of the characteristics of each element, and composites carbon materials to successfully prepare a stable high-entropy Prussian blue-type positive electrode material for sodium ion batteries. According to tests, the long-cycle stability of the material of the present invention is significantly improved compared with the traditional iron-based Prussian blue material. The excellent performance makes the material of the present invention have great development potential in application scenarios with strict requirements on battery stability and cycle life, greatly expanding the application scope of sodium ion batteries and providing a new technical solution for the development of this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is the SEM image of HE-PBA@C prepared in Example 1.

[0020] Figure 2 This is the XRD curve of HE-PBA@C prepared in Example 1.

[0021] Figure 3Charge-discharge curves of PW prepared in Comparative Example 1 at a current density of 100 mA g−1 during long-term cycling tests, including the 1st, 150th, and 300th cycles.

[0022] Figure 4 Charge-discharge curves of HE-PBA prepared in Comparative Example 2 at a current density of 100 mA g−1 during long-term cycling tests, including the 1st, 150th, and 300th cycles.

[0023] Figure 5 Charge-discharge curves of HE-PBA@C prepared in Example 1 at a current density of 100 mA g−1 during long-term cycling tests, including the 1st, 150th, and 300th cycles.

[0024] Figure 6 Long-term cycling test curves of PW prepared in Comparative Example 1 at a current density of 100 mA g−1.

[0025] Figure 7 Long-term cycling test curves of HE-PBA prepared in Comparative Example 2 at a current density of 100 mA g−1.

[0026] Figure 8 Long-term cycling test curves of HE-PBA@C prepared in Example 1 at a current density of 100 mA g−1.

[0027] Figure 9 Long-term cycling test curves of HE-PBA@C prepared in Example 1 at a high current density of 5000 mA g−1 for 6000 cycles. Detailed implementation manners

[0028] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in combination with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0029] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0030] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0031] Example 1 This example provides a high-entropy Prussian blue-based sodium battery cathode material. The cathode material has a cubic morphology and the chemical formula is Na 1.41 Mn 0.32 Fe0.11 Co 0.28 Ni 0.32 Cu 0.32 [Fe(CN)6] 2.89 ·2.89H2O@KB (where KB represents Ketjenblack), and the molar ratio of Ketjenblack to the high-entropy Prussian blue-like component is 1:6 to 1:8.

[0032] The preparation method of the high-entropy Prussian blue-like sodium-ion battery cathode material is as follows: (1) Heat 6 g of NaCl and 160 mg of acetylene black in a water bath at 30 - 60 °C with stirring for 20 - 60 min, then ultrasonically disperse in an ultrasonic oscillator for 10 - 30 min, and fully dissolve and disperse in 200 ml of deionized water to prepare solution C; (2) Dissolve 7 mmol of Na4Fe(CN)6 in 100 mL of deionized water to prepare solution A; (3) Respectively take 1 mmol of MnSO4, FeSO4, CoSO4, NiSO4, CuSO4 and 5 mmol of sodium citrate and dissolve them in 100 mL of deionized water to prepare solution B; (4) Under the conditions of heating and stirring, disperse nitrogen into the reaction solution through an f-tube to create a nitrogen atmosphere, and simultaneously drip solution A and solution B into solution C through a peristaltic pump for coprecipitation reaction, controlling the dropping rate of solution A to be 0.8 mL / min -1 and the dropping rate of solution B to be 1 mL / min -1 ; (5) After the dropping is completed, continue to stir for 2 h at the original temperature and rotation speed, then stand and age in the dark at room temperature for 24 h, centrifuge and wash to collect the aged precipitate, pre-dry in a vacuum oven at 80 °C for 2 h, then raise the temperature to 100 °C and dry for 10 h, and finally dry at 120 °C for 10 h to obtain the high-entropy Prussian blue-like sodium-ion battery cathode material, denoted as HE-PBA@C.

[0033] The application of the high-entropy Prussian blue-like sodium-ion battery cathode material is as follows: Mix HE-PBA@C, conductive agent and binder in a mass ratio of 8:1:1, add N-methylpyrrolidone solvent, place it in a 5 mL glass container, and continuously stir at a speed of 1500 rpm for 12 h. Uniformly coat the obtained slurry on the surface of aluminum foil, blow-dry in a blast oven at 60 °C for 3 h to dry the solvent, and then vacuum-dry at 100 °C and 120 °C for 10 h respectively. Cut the dried electrode sheet into circular electrode sheets with a diameter of 15 mm.

[0034] Using the above-mentioned electrode as the positive electrode, metallic sodium as the negative electrode, a mixed solution of 1M NaClO4 in diethyl carbonate (DEC) and ethylene carbonate (EC) (volume ratio 1:1) as the electrolyte base solution, and adding 5wt% fluoroethylene carbonate (FEC) as the electrolyte additive. A glass fiber separator is used, and a button cell is assembled in a CR2032 type battery case.

[0035] The assembled battery is subjected to an electrochemical performance test, and the test voltage range is 2 - 4V.

[0036] Figure 1 It is the SEM image of HE-PBA@C. It can be seen the successful combination of the high-entropy Prussian blue-like material and the carbon material, as well as the nanoscale cubic crystal structure of the material. Figure 2 It is the XRD test pattern of HE-PBA@C. Figure 5 It is the charge-discharge curves of HE-PBA@C at a current density of 100 mA g −1 at the 1st, 150th, and 300th cycles during the long-cycle test. Figure 8 It is the long-cycle test curve of HE-PBA@C at a current density of 100mA g −1 The discharge specific capacities at the 1st, 150th, and 300th cycles are 94.4mAh / g, 91.4mAh / g, and 90.1mAh / g respectively. The capacity retention rates at the 150th and 300th cycles are 96.8% and 95.4% respectively. The cycling stability performance of HE-PBA@C is excellent. By compounding with conductive carbon materials, the cycling stability performance of the material is further improved. Figure 9 It is the performance curve of the long-cycle test of HE-PBA@C material at a high rate of 50C. The discharge specific capacities at the 1st and 6000th cycles are 70.5 mAh / g and 57 mAh / g respectively, and the capacity retention rate is 80.85%, further indicating the excellent long-cycle stability performance of HE-PBA@C material.

[0037] Comparative Example 1 This example provides a Prussian blue-based sodium battery positive electrode material. The positive electrode material has a cubic morphology and the chemical formula is Na2MnFe(CN)6.

[0038] The preparation method of the Prussian blue-based sodium battery positive electrode material is as follows: (1) Dissolve 14 g of NaCl fully and disperse it in 200 ml of deionized water to prepare solution C; (2) Take 3 mmol of Na4Fe(CN)6 and dissolve it in 50 mL of deionized water to prepare solution A; (3) Take 6 mmol of MnCl2 and 6 mmol of sodium citrate, dissolve them in 50 mL, and add 1.2 g of polyvinylpyrrolidone dispersant to prepare solution B; (4) Under the conditions of heating and stirring, disperse nitrogen into the reaction solution through tube f to create a nitrogen atmosphere. Drop solution A and solution B into solution C simultaneously through a peristaltic pump for coprecipitation reaction. Control the dropping rate of solution A to be 0.8 mL / min -1 , and the dropping rate of solution B to be 1 mL / min -1 ; (5) After the dropping is completed, continue to stir for 2 h while maintaining the original temperature and rotation speed, then let it stand and age in the dark at room temperature for 24 h. Centrifuge and wash to collect the aged precipitate, pre-dry it in a vacuum oven at 80 °C for 2 h, then raise the temperature to 100 °C and dry for 10 h, and finally dry at 120 °C for 10 h to obtain the high-entropy Prussian blue-based sodium ion cathode material, denoted as PW.

[0039] The application of the high-entropy Prussian blue-based sodium ion cathode material is as follows: Mix PW, conductive agent, and binder in a mass ratio of 8:1:1, add N-methylpyrrolidone solvent, place it in a 5 mL glass container, and continuously stir at a speed of 1500 rpm for 12 h. Coat the obtained slurry evenly on the surface of the aluminum foil, dry it in a blast oven at 60 °C for 3 h to dry the solvent, and then vacuum dry it at 100 °C and 120 °C for 10 h respectively. Cut the dried electrode sheet into circular electrode sheets with a diameter of 15 mm.

[0040] Use the above electrode sheet as the positive electrode, use metallic sodium as the negative electrode, and use a mixed solution of 1 M NaClO4 in diethyl carbonate (DEC) and ethylene carbonate (EC) (volume ratio 1:1) as the electrolyte base solution, and add 5 wt% fluoroethylene carbonate (FEC) as the electrolyte additive. Use a glass fiber separator and assemble a button cell in a CR2032 type battery case.

[0041] Conduct electrochemical performance tests on the assembled battery, and the test voltage range is 2~4V.

[0042] Figure 3 is the charge-discharge curves of PW at the 1st, 150th, and 300th cycles in the long-term cycling test at a current density of 100 mA / g −1 ; Figure 6 is the charge-discharge curves of PW at the 1st, 150th, and 300th cycles in the long-term cycling test at a current density of 100 mA / g −1Long cycle test curve at a certain current density. The discharge specific capacities of the 1st, 150th, and 300th cycles are 100.2 mAh / g, 35.9 mAh / g, and 25.8 mAh / g respectively. The capacity retention rates of the 150th and 300th cycles are 35.8% and 25.7% respectively. Therefore, it can be seen that the cycling stability of the PW material is very poor, which is mainly due to the structural defects of the material caused by the Jahn-Teller distortion of the Mn element.

[0043] Comparative Example 2 This comparative example provides a Prussian blue-based sodium-ion battery cathode material. The cathode material has a cubic morphology and the chemical formula is Na 1.41 Mn 0.32 Fe 0.11 Co 0.28 Ni 0.32 Cu 0.32 [Fe(CN)6] 2.89 ·H2O[dc1].

[0044] The preparation method of the Prussian blue-based sodium-ion battery cathode material is as follows: (1) Dissolve 6 g of NaCl thoroughly in 200 ml of deionized water to prepare solution C; (2) Dissolve 7 mmol of Na4Fe(CN)6 in 100 mL of deionized water to prepare solution A; (3) Take 1 mmol of MnSO4, FeSO4, CoSO4, NiSO4, and CuSO4 each and 5 mmol of sodium citrate and dissolve them in 100 mL of deionized water, and add 1 g of polyvinylpyrrolidone dispersant to prepare solution B; (4) Under the conditions of heating and stirring, disperse nitrogen into the reaction solution through an f-tube to create a nitrogen atmosphere, and simultaneously drip solution A and solution B into solution C through a peristaltic pump for coprecipitation reaction. Control the dropping rate of solution A to be 0.8 mL / min -1 , and the dropping rate of solution B to be 1 mL / min -1 ; (5) After the dropping is completed, continue to stir for 2 h at the original temperature and rotation speed, then let it stand and age for 24 h in the dark at room temperature. Centrifuge and wash to collect the aged precipitate, pre-dry it in a vacuum oven at 80 °C for 2 hours, then raise the temperature to 100 °C and dry for 10 hours, and finally dry at 120 °C for 10 hours to obtain a high-entropy Prussian blue-based sodium-ion cathode material, denoted as HE-PBA.

[0045] The application of the Prussian blue-based sodium-ion battery cathode material is as follows: Mix HE-PBA, conductive agent, and binder in a mass ratio of 8:1:1, add N-methylpyrrolidone solvent, place it in a 5 mL glass container, and continuously stir at a speed of 1500 rpm for 12 hours. Uniformly coat the obtained slurry on the surface of the aluminum foil, and dry it in a blast dryer at 60 °C for 3 hours to dry the solvent, and then vacuum dry it at 100 °C and 120 °C for 10 hours respectively. Punch the dried electrode sheet into circular electrode sheets with a diameter of 15 mm.

[0046] Use the above electrode sheet as the positive electrode, use metallic sodium as the negative electrode, and use a mixed solution of diethyl carbonate (DEC) and ethylene carbonate (EC) with 1 M NaClO4 (volume ratio 1:1) as the electrolyte base solution, and add 5 wt% fluoroethylene carbonate (FEC) as the electrolyte additive. Use a glass fiber separator and assemble a button cell in a CR2032 type battery case.

[0047] Conduct electrochemical performance tests on the assembled battery, and the test voltage range is 2~4V.

[0048] Figure 4 It is the charge-discharge curves of the 1st, 150th, and 300th cycles in the long cycle test of HE-PBA at a current density of 100 mA g −1 The charge-discharge curves of the 1st, 150th, and 300th cycles in the long cycle test of HE-PBA at a current density of 100 mA g Figure 8 It is the long cycle test curve of HE-PBA at a current density of 100 mA g −1 The discharge specific capacities of the 1st, 150th, and 300th cycles are 75.1 mAh / g, 68.6 mAh / g, and 66.5 mAh / g respectively, and the capacity retention rates of the 150th and 300th cycles are 91.3% and 88.5% respectively. Therefore, it can be seen that the HE-PBA material has excellent cycle stability. By introducing different metal elements, the Jahn-Teller distortion of Mn is effectively weakened. Compared with the PW material, the cycle stability of the material is improved, but its conductivity needs to be improved, and the stability of the overall material structure needs to be optimized.

Claims

1. A high entropy Prussian blue cathode material, characterized in that: The positive electrode material chemical formula is Na x M[Fe(CN)6] y mH2O@C, wherein M comprises five different elements of Fe, Ni, Co, Mn, Zn, Ti, V or Cu, and the molar ratio of the five different elements is 1:1:1:1:1:1~1:3:3:3:3, 0<x≤2, 0<y≤3, 0<m≤5, and the molar ratio of the carbon component to the high-entropy Prussian blue-like component is 1:5~1:

10.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material includes a carbon substrate with a network structure and high entropy Prussian blue-like cubes. The high entropy Prussian blue-like cubes are transition metal elements that are connected by cyanide to form a cubic three-dimensional framework skeleton. The high entropy Prussian blue-like cubes are embedded in the carbon substrate with a network structure.

3. A method for preparing a high entropy Prussian blue cathode material, characterized in that: The following steps are involved: (1) Fully dispersing and dissolving the carbon source and the sodium supplement in deionized water to obtain solution C; (2) dissolving sodium ferrocyanide in deionized water to obtain solution A; (3) dissolving at least five different transition metal salt solutions, a chelating agent, and a polyvinyl pyrrolidone dispersant in deionized water to obtain a solution B; (4) Under an inert gas atmosphere, solution A and solution B are simultaneously dropped into solution C to perform a coprecipitation reaction; (5) Continue heating and stirring to obtain a suspension, age the suspension, wash, and separate to obtain a precipitate, and dry the precipitate to obtain a high-entropy Prussian blue-based positive electrode material.

4. The preparation method according to claim 3, characterized in that: The carbon source in step (1) includes at least one of carbon nanotubes, Ketjen black, acetylene black, conductive carbon black or nano-carbon fibers. The concentration of the carbon source in the solution C is 0.5-1 g / L. The sufficient dissolution and dispersion is specifically: heating and stirring in a water bath at 30-60° C. for 20-60 min, and then ultrasonically dispersing in an ultrasonic oscillator for 10-30 min.

5. The preparation method according to claim 3, characterized in that: The sodium supplement in step (1) includes at least one of sodium sulfate, sodium nitrate, sodium chloride or sodium acetate, and the mass ratio of the carbon source to the sodium supplement is 1:30-50.

6. The preparation method according to claim 3, characterized in that: The concentration of sodium ferrocyanide in solution A in step (2) is 0.05-0.2 mol / L.

7. The preparation method according to claim 3, characterized in that: The chelating agent in step (3) includes at least one of disodium ethylenediaminetetraacetic acid, sodium citrate, sodium tripolyphosphate or sodium hexametaphosphate, and the concentration of the chelating agent in the solution B is 0.1~0.5 mol / L; the transition metal salt solution includes FeCl2, Fe(NO3)2, FeSO4, Fe3(PO4)2, NiCl2, Ni(NO3)2, NiSO4, Ni3(PO4)2, Co (NO3)2, CoSO4, Co3(PO4)2, MnCl2, Mn (NO3)2, MnSO4, Mn3(PO4)2, ZnCl2, Zn(NO3)2, ZnSO4, Zn3(PO4)2, TiCl4, Ti(SO4)2, Ti(NO3)4, VCl3, NH4VO3, CuCl2, Cu Five or more of (NO3)2, CuSO4 or Cu3(PO4)2, the total concentration of the transition metal salts in solution B is 0.01~0.2 mol / L.

8. The preparation method according to claim 3, characterized in that: The nitrogen protection in step (4) is specifically as follows: nitrogen is dispersed in the reaction solution to create a nitrogen atmosphere, the stirring speed is controlled to be 300-600 rpm during dispersion, the reaction temperature is 20-50° C., the speed of dripping solution A and solution B is controlled to be 15-20 ml / h, and the dripping speed ratio of solution A to solution B is controlled to be 1:1-1:1.

5.

9. The preparation method according to claim 3, characterized in that: The temperature for continued heating in step (5) is 20-50°C, the stirring time is 1-5h, the aging is allowed to stand at room temperature away from light, the aging time is 10-30h, and the drying process adopts a gradient temperature rise method. In a vacuum environment, pre-drying is first performed at 30°C-80°C for 1h-10h, then the temperature is raised to 80°C-120°C for drying for 10h-20h, and finally vacuum drying is performed at 120°C-180°C for 10h-20h.

10. An application of a high entropy Prussian blue cathode material, characterized in that: The high entropy Prussian blue positive electrode material prepared as claimed in claims 1-2 or claims 3-9 is used as a positive electrode plate of a sodium ion battery, and the positive electrode plate includes a current collector, a binder and the high entropy Prussian blue positive electrode material.

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