Manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material and preparation method and application thereof

Abstract

The invention relates to a manganese-iron bimetal synergistic modified nickel-based Prussian blue positive electrode material and a preparation method and application thereof, and belongs to the technical field of sodium ion battery positive electrode materials. According to the preparation method of the ferromanganese bimetal synergistic modified nickel-based Prussian blue positive electrode material, NiMnHCF is synthesized through a coprecipitation method, and a FeHCF shell layer is constructed on the surface of the NiMnHCF through an epitaxial growth technology to prepare the NiMnHCF-coated FeHCF-X material. The prepared NiMnHCl-coated FeHCl-X sample keeps a cubic system structure, lattice parameters are changed through doping of manganese and epitaxial growth of FeHCF, and meanwhile the conductivity and electrochemical performance of the material are remarkably improved. An electrochemical test shows that the high specific capacity and the excellent rate capability of the NiMnHCl-coated FeHCl-X series of samples are remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion battery positive electrode materials, and in particular to a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material, and a preparation method and application thereof. Background Art

[0002] With the transformation of the global energy structure and the continuous advancement of new energy technologies, the demand for efficient and sustainable batteries is growing for electric vehicles and large-scale energy storage systems. Lithium-ion batteries are widely used in these fields due to their high energy density and mature technology, but the uneven distribution of lithium resources and price fluctuations limit their long-term sustainable development. Sodium-ion batteries, as an emerging secondary battery technology, are considered an ideal alternative to lithium-ion batteries due to their abundant sodium resources, low cost, and environmental friendliness.

[0003] Nickel-based Prussian blue, an inorganic compound with a 3D open framework structure, has shown great potential as a positive electrode sample for sodium-ion batteries due to its environmental friendliness, simple preparation method and good thermal stability. However, the open framework structure of nickel-based Prussian blue is prone to lattice volume changes during charge and discharge, leading to structural collapse, which in turn affects the cycle life of the battery. At the same time, the presence of Fe(CN)6 vacancies not only reduces the redox active centers and the sodium content in the lattice, resulting in a decrease in the actual sodium storage capacity, but also increases the water content in the lattice. These inherent lattice defects will lead to its insufficient rate performance and cycle performance in practical applications.

[0004] The existing Chinese patent publication number CN118405706A discloses a nickel-based Prussian blue material and its preparation method. The nickel-based Prussian blue nanoparticles are prepared by hydrothermal reaction of water-soluble nickel salt and water-soluble ferrocyanide in the presence of polyvinyl pyrrolidone. However, the initial discharge capacity of the material is only 25.08 mAh·g -1 The nickel-based Prussian blue material prepared according to this invention cannot effectively solve the lattice defect problem and still has the disadvantage of low rate performance. Summary of the Invention

[0005] In view of this, the present application provides a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material and its preparation method and application, which realizes precise control of the sample morphology and structure through doping and epitaxy, and optimizes the traditional co-precipitation synthesis method. This method not only improves the structural stability and rate performance of the sample, but also extends the service life of the electrode, and can effectively overcome the defects of the above-mentioned existing technology.

[0006] The first aspect of the present application provides a method for preparing a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material, comprising the following steps:

[0007] (1) Add ethylenediaminetetraacetic acid, sodium hydroxide, nickel sulfate hexahydrate, and manganese acetate tetrahydrate into deionized water and stir to prepare solution A; dissolve sodium hexacyanoferrate in deionized water and stir to prepare solution B; dissolve polyvinylpyrrolidone and sodium chloride in deionized water and stir to prepare solution C;

[0008] (2) adding the solution A and the solution B dropwise to the solution C simultaneously, stirring to obtain a mixed solution; heating the mixed solution, and then allowing it to stand at room temperature to obtain a precipitate; centrifuging, washing, and drying the precipitate to obtain a NiHCF sample;

[0009] (3) The NiHCF sample is mixed with potassium ferrocyanide, added to deionized water, and ultrasonically treated and then nitric acid is added to prepare a suspension; the suspension is heated and continuously stirred, and then nitric acid is added to the suspension, and heating and stirring are continued to obtain a precipitate; the precipitate is washed and dried to obtain a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material NiMnHCF@FeHCF-X, wherein X is 1, 2 or 3, respectively representing different amounts of manganese acetate tetrahydrate added.

[0010] This application proposes a novel synthesis strategy for a manganese-iron bimetallic modified nickel-based Prussian blue cathode material: The precursor is first doped with manganese, and then potassium ferrocyanide is used as an iron source. Its slow self-decomposition in a nitric acid medium slows down the nucleation process, enabling the precise epitaxial growth of a NiMnHCF@FeHCF-X core-shell structure. Furthermore, the addition of manganese early in the synthesis of NiHCF facilitates its uniform distribution.

[0011] Preferably, the specific process of step (2) is:

[0012] A peristaltic pump was used at a rate of 1 mL min -1 The solution A and the solution B were simultaneously added dropwise to the solution C at a rate of , and reacted for 4 hours under stirring to obtain a mixed solution; the mixed solution was heated at 60° C. for 3 hours, and then allowed to stand at room temperature for 24 hours to obtain a precipitate; the precipitate was subjected to high-speed centrifugation, washed three times, and then dried for 12 hours to obtain a NiHCF sample.

[0013] Preferably, the specific process of step (3) is:

[0014] (31) The NiHCF sample was mixed with potassium ferrocyanide, added to deionized water, and ultrasonicated at a frequency of 40 kHz for 20 minutes, followed by addition of 1 mol·L -1 Nitric acid, to prepare the suspension;

[0015] (32) The suspension was heated to 60 °C and stirred for 1 hour, and then 1 mol·L -1 nitric acid, and stirred at 60 ° C for 5 hours to obtain a precipitate; the precipitate was washed three times and then dried for 12 hours to obtain a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material NiMnHCF@FeHCF-X.

[0016] Preferably, in step (31), the usage ratio of the NiHCF sample, potassium ferrocyanide, deionized water and nitric acid is 1 g:1.48 g:200 mL:10 mL.

[0017] Preferably, in step (32), the ratio of the suspension to nitric acid is 200 mL:10 mL.

[0018] Preferably, in step (1), the amount of EDTA, sodium hydroxide, nickel sulfate hexahydrate, manganese acetate tetrahydrate and deionized water is 1.46 g: 0.50 g: 1.31 g: (0.12-0.61) g: 50 mL; or

[0019] The amount of sodium hexacyanoferrate and deionized water is 1.52g:50mL; or

[0020] The amount of polyvinyl pyrrolidone, sodium chloride and deionized water is 1g:10g:50mL.

[0021] Specifically, the amount of manganese acetate tetrahydrate added is selected from any one of 0.12 g, 0.21 g, and 0.61 g.

[0022] Preferably, in step (1), the stirring time is 30 minutes.

[0023] The second aspect of the present application also provides a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material, and the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material prepared by the above method, the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material is a composite positive electrode material NiMnHCF@FeHCF-X based on NiHCF internally doped with manganese metal and externally epitaxially grown FeHCF, which has a cubic core-shell structure with NiMnHCF as the core and FeHCF formed by epitaxial growth as the shell, wherein X is 1, 2 or 3, respectively representing different amounts of manganese acetate tetrahydrate added.

[0024] The third aspect of the present application further provides a positive electrode sheet, comprising the above-mentioned manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material.

[0025] The fourth aspect of the present application further provides a sodium ion battery comprising the above-mentioned positive electrode sheet.

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] 1. The NiMnHCF@FeHCF-X sample prepared by the method of this application significantly improved the electrochemical performance of nickel-based Prussian blue, especially in terms of rate performance and cycle life.

[0028] 2. MnHCF has the advantage of high specific capacity. Mn doping can increase the discharge specific capacity of NiHCF materials. Nitric acid corrodes NiHCF and dissolves Ni, thereby generating Ni vacancies. These vacancies provide locations for Fe embedding, thereby promoting heteroepitaxial growth between FeHCF, thereby realizing the synthesis of NiMnHCF@FeHCF-X (X=1,2,3) series composite materials. The low-strain FeHCF shell structure grown by epitaxial growth can alleviate the volume changes of the material structure caused by the embedding and extraction of sodium ions with larger radii during the charge and discharge process, reduce the stress of the electrode, and extend the life of the electrode. The design of manganese doping and core-shell structure combines the high specific capacity of the core with the good conductivity of the shell, providing excellent charge transfer and ion diffusion channels.

[0029] 3. The present application discloses a composite cathode material based on nickel-based Prussian blue (NiHCF) doped with manganese metal internally and epitaxially grown iron-based Prussian blue (FeHCF) externally, and its preparation method. NiMnHCF is synthesized by co-precipitation, and a FeHCF shell is constructed on its surface using epitaxial growth technology to prepare NiMnHCF@FeHCF-X material. The prepared NiMnHCF@FeHCF-X sample maintains a cubic crystal structure. The doping of manganese and the epitaxial growth of FeHCF change the lattice parameters, while significantly improving the conductivity and electrochemical properties of the material. Electrochemical tests show that the NiMnHCF@FeHCF-X series samples show significant improvements in high specific capacity and excellent rate performance, especially the NiMnHCF@FeHCF-3 sample at 100mA·g -1 The specific capacity at the current density is 93.3 mAh g -1 After 200 cycles, the capacity retention rate reached 62.9%. The synthesis method of the present application is simple, controllable, low-cost, suitable for large-scale preparation, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following briefly introduces the drawings required for use in the description of the present application or the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 X-ray diffraction (XRD) patterns of the materials prepared in Comparative Example 1 and Examples 1 to 3;

[0032] Figure 2 This is a scanning electron microscope (SEM) image of the material prepared in Comparative Example 1;

[0033] Figure 3 This is the SEM image of the material prepared in Example 1;

[0034] Figure 4 This is the SEM image of the material prepared in Example 2;

[0035] Figure 5 This is the SEM image of the material prepared in Example 3;

[0036] Figure 6 The materials prepared in Comparative Example 1 and Examples 1 to 3 were tested at 100 mA·g -1 Cycling performance diagram of 200 cycles at the current density;

[0037] Figure 7 This is an operational flow chart for the preparation of materials in Example 1. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0039] Unless otherwise specified, the experimental methods used in the examples of this application are all conventional methods.

[0040] In the following examples, unless otherwise specified, all raw materials can be purchased commercially or prepared by conventional methods.

[0041] Example 1

[0042] The preparation method of the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material of this embodiment includes the following steps:

[0043] (1) 1.46 g of ethylenediaminetetraacetic acid, 0.50 g of sodium hydroxide, 0.12 g of manganese acetate tetrahydrate, and 1.31 g of nickel sulfate hexahydrate were added to 50 mL of deionized water and stirred for 30 minutes to prepare solution A;

[0044] (2) Dissolve 1.52 g of sodium hexacyanoferrate in 50 mL of deionized water and stir for 30 minutes to prepare solution B;

[0045] (3) Dissolve 1 g of polyvinyl pyrrolidone and 10 g of sodium chloride in 50 mL of deionized water and stir for 30 minutes to prepare solution C;

[0046] (4) Use a peristaltic pump at 1 mL min -1 Solution A and solution B were added dropwise to solution C at a rate of , and reacted for 4 hours under stirring;

[0047] (5) The resulting mixed solution was heated at 60°C for 3 hours and then allowed to stand at room temperature for 24 hours;

[0048] (6) The precipitate was separated by high-speed centrifugation, washed twice with deionized water and once with 75% ethanol, and then vacuum-dried for 12 h to obtain a NiHCF sample.

[0049] (7) 1 g of NiHCF sample was mixed with 1.48 g of potassium ferrocyanide, added to 200 mL of deionized water, and ultrasonicated at a frequency of 40 kHz for 20 minutes before adding 10 mL of 1 mol·L -1 Nitric acid, to prepare the suspension;

[0050] (8) Heat the suspension to 60°C and continue stirring for 1 hour;

[0051] (9) Add 10mL 1mol·L -1 Nitric acid was added to 200 mL of the suspension and stirred at 60 °C for 5 h;

[0052] (10) The obtained precipitate was washed twice with deionized water and once with 75% alcohol, and then vacuum dried for 12 h to obtain the NiMnHCF@FeHCF-1 sample.

[0053] Example 2

[0054] The manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material and its preparation method provided in this embodiment can refer to Example 1, except that the amount of manganese acetate tetrahydrate added is changed to 0.21 g, and the other conditions are the same to obtain the NiMnHCF@FeHCF-2 sample.

[0055] Example 3

[0056] The manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material and its preparation method provided in this embodiment can refer to Example 1, except that the addition amount of manganese acetate tetrahydrate is changed to 0.61 g, and the other conditions are the same to obtain the NiMnHCF@FeHCF-3 sample.

[0057] Comparative Example 1

[0058] The preparation method of the nickel-based Prussian blue positive electrode material of this comparative example comprises the following steps:

[0059] (1) 1.46 g of ethylenediaminetetraacetic acid, 0.50 g of sodium hydroxide, and 1.31 g of nickel sulfate hexahydrate were added to 50 mL of deionized water and stirred for 30 minutes to prepare solution A;

[0060] (2) Dissolve 1.52 g of sodium hexacyanoferrate in 50 mL of deionized water and stir for 30 minutes to prepare solution B;

[0061] (3) Dissolve 1 g of polyvinyl pyrrolidone and 10 g of sodium chloride in 50 mL of deionized water and stir for 30 minutes to prepare solution C;

[0062] (4) Use a peristaltic pump at 1 mL min -1 Solution A and solution B were added dropwise to solution C at a rate of , and reacted for 4 hours under stirring;

[0063] (5) The resulting mixed solution was heated at 60°C for 3 hours and then allowed to stand at room temperature for 24 hours;

[0064] (6) The precipitate was separated by high-speed centrifugation, washed twice with deionized water and once with 75% ethanol, and then vacuum-dried for 12 h to obtain a comparative example NiHCF sample.

[0065] Test Case

[0066] The samples prepared in Comparative Example 1 and Examples 1 to 3 were used as positive electrode materials to prepare positive electrode sheets. The positive electrode samples were pressed into 1×1 cm2 sheets with a ratio of 75:20:5 (positive electrode sample: conductive carbon: binder). 2 The negative electrode used a large area zinc sheet and the electrolyte was a 10M sodium nitrate solution. The constant current charge and discharge test was performed using a Xinwei battery test system at 100mA·g -1 Up to 50mA·g -1 The long-term cycle stability test was conducted at 100 mA g -1 The test results are shown in Table 1.

[0067] Table 1 Electrochemical properties of materials of Comparative Example 1 and Examples 1 to 3

[0068]

[0069] The electrochemical performance test results in Table 1 show that compared with the NiHCF sample, the synthesized NiMnHCF@FeHCF-X samples (X=1, 2, 3) exhibit higher specific capacity and better cycle stability. This performance improvement is attributed to the high electrochemical activity of manganese and iron, as well as the synergistic effect of the core-shell structure, which together improve the rate performance of the NiHCF sample. Specifically, the first cycle discharge specific capacities of NiMnHCF@FeHCF-X are 76.5, 85.7, and 93.3 mAh g, respectively. -1 The capacity retention rates after 200 cycles were 72.3, 64.5 and 62.9 mAh·g -1 .

[0070] As the amount of manganese acetate tetrahydrate added gradually increased, the first cycle discharge capacity of the sample increased significantly, but the capacity retention rate continued to decrease. This shows that although increasing the manganese content can increase the specific capacity, during the cycle, due to the increase in Mn 2 + / Mn 3+ The structural collapse caused by the Jahn-Teller effect and the side reactions triggered by the crystal water will accelerate the capacity decay. Therefore, optimizing the amount of manganese added is crucial for preparing ideal NiMnHCF@FeHCF samples with high specific capacity and excellent cycling stability.

[0071] This application successfully prepared a NiMnHCF@FeHCF-X material by optimizing the coprecipitation method. Experimental results show that the NiMnHCF@FeHCF-X sample exhibits significant improvements in specific capacity, rate capability, and cycle stability, especially at high current density. This material preparation method is simple, easy to operate, and low-cost, with good prospects for industrial application. It is expected to significantly improve the electrochemical performance of sodium-ion batteries and provide new ideas for future research on energy storage materials.

[0072] from Figure 1 It can be seen that the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode materials prepared in Examples 1-3 of the present application have a cubic crystal structure, and the lattice structure meets the following conditions:

[0073] (1) The X-ray diffraction pattern of the material has a characteristic diffraction peak of the (200) crystal plane at a diffraction angle in the range of 16.9°-17.5°; (2) The X-ray diffraction pattern of the material has a characteristic diffraction peak of the (220) crystal plane at a diffraction angle in the range of 24.1°-24.9°; (3) The X-ray diffraction pattern of the material has a characteristic diffraction peak of the (400) crystal plane at a diffraction angle in the range of 34.1°-35.5°.

[0074] like Figure 1 As shown, due to Mn 2+and Fe 2+ The ionic radius of ions is larger than that of Ni 2+ , after adding Mn 2+ and Fe 2+ After that, the lattice parameters of the sample changed significantly, resulting in the overall left shift of the diffraction peak in its X-ray diffraction pattern. This phenomenon can be attributed to the lattice expansion effect, that is, the larger Mn 2+ and Fe 2+ ions replace Ni 2+ After that, the distance between atoms in the crystal structure increases, which causes the change of diffraction angle. Figure 2-5 The SEM characterization results further confirmed this trend. 2+ and Fe 2+ The gradual introduction of manganese and iron resulted in a significant increase in the particle size of the sample. This suggests that ion doping not only affects the microscopic arrangement of the crystal structure but also has a significant impact on the macroscopic morphology of the particles. This change may be due to the fact that the introduction of manganese and iron promotes the kinetics of crystal growth, leading to the increase in particle size.

[0075] like Figure 7 As shown in the figure, in this application, we use K4Fe(CN)6·3H2O as the Fe source, take advantage of its slow self-decomposition characteristics under nitric acid conditions, and introduce Mn with high electrochemical performance to optimize the co-precipitation synthesis method. At the same time, nitric acid will corrode NiHCF and dissolve Ni, thereby generating Ni vacancies. These vacancies provide locations for the embedding of Fe, thereby promoting the growth of the FeHCF shell structure. Figure 6 As shown in Table 1, the introduction of two highly active metals, Fe and Mn, successfully improved the discharge capacity of the material, reaching 93.3 mAh g -1 Moreover, the FeHCF shell structure can alleviate the structural collapse disadvantage caused by the Jahn-Teller effect of Mn, thereby improving the capacity retention rate to 62.9%.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material, characterized in that: The following steps are involved: (1) Add ethylenediaminetetraacetic acid, sodium hydroxide, nickel sulfate hexahydrate, and manganese acetate tetrahydrate into deionized water and stir to prepare solution A; dissolve sodium hexacyanoferrate in deionized water and stir to prepare solution B; dissolve polyvinylpyrrolidone and sodium chloride in deionized water and stir to prepare solution C; (2) adding the solution A and the solution B dropwise to the solution C simultaneously, stirring to obtain a mixed solution; heating the mixed solution, and then allowing it to stand at room temperature to obtain a precipitate; centrifuging, washing, and drying the precipitate to obtain a NiHCF sample; (3) The NiHCF sample is mixed with potassium ferrocyanide, added to deionized water, and ultrasonically treated and then nitric acid is added to prepare a suspension; the suspension is heated and continuously stirred, and then nitric acid is added to the suspension, and heating and stirring are continued to obtain a precipitate; the precipitate is washed and dried to obtain a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material NiMnHCF@FeHCF-X, wherein X is 1, 2 or 3, respectively representing different amounts of manganese acetate tetrahydrate added.

2. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 1, characterized in that: The specific process of step (2) is as follows: A peristaltic pump was used at a rate of 1 mL min -1 The solution A and the solution B were simultaneously added dropwise to the solution C at a rate of , and reacted for 4 hours under stirring to obtain a mixed solution; the mixed solution was heated at 60° C. for 3 hours, and then allowed to stand at room temperature for 24 hours to obtain a precipitate; the precipitate was subjected to high-speed centrifugation, washed three times, and then dried for 12 hours to obtain a NiHCF sample.

3. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 1, characterized in that: The specific process of step (3) is as follows: (31) The NiHCF sample was mixed with potassium ferrocyanide, added to deionized water, and ultrasonicated at a frequency of 40 kHz for 20 minutes, followed by addition of 1 mol·L -1 Nitric acid, to prepare the suspension; (32) The suspension was heated to 60 °C and stirred for 1 hour, and then 1 mol·L -1 nitric acid, and stirred at 60 ° C for 5 hours to obtain a precipitate; the precipitate was washed three times and then dried for 12 hours to obtain a manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material NiMnHCF@FeHCF-X.

4. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 3, characterized in that: In step (31), the usage ratio of the NiHCF sample, potassium ferrocyanide, deionized water and nitric acid is 1 g:1.48 g:200 mL:10 mL.

5. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 3, characterized in that: In step (32), the ratio of the suspension to nitric acid is 200 mL:10 mL.

6. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 1, characterized in that: In step (1), the amount of EDTA, sodium hydroxide, nickel sulfate hexahydrate, manganese acetate tetrahydrate and deionized water is 1.46 g: 0.50 g: 1.31 g: (0.12-0.61) g: 50 mL; or The amount of sodium hexacyanoferrate and deionized water is 1.52g:50mL; or The amount of polyvinyl pyrrolidone, sodium chloride and deionized water is 1g:10g:50mL.

7. The method for preparing the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material according to claim 1, characterized in that: In step (1), the stirring time is 30 minutes.

8. A manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material, characterized in that: The manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material prepared by the method according to any one of claims 1 to 7, wherein the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material is a composite positive electrode material NiMnHCF@FeHCF-X based on NiHCF internally doped with manganese metal and externally epitaxially grown FeHCF, which has a cubic core-shell structure with NiMnHCF as the core and FeHCF formed by epitaxial growth as the shell, wherein X is 1, 2 or 3, respectively representing different amounts of manganese acetate tetrahydrate added.

9. A positive electrode sheet, characterized in that: It includes the manganese-iron bimetallic synergistically modified nickel-based Prussian blue positive electrode material as described in claim 8.

10. A sodium ion battery, characterized in that: Including the positive electrode sheet according to claim 9.

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