Prussian blue sodium ion material as well as preparation method and application thereof

Abstract

The invention provides a Prussian blue sodium ion material and a preparation method and application thereof.According to the method, the reversible adsorption characteristic of an MOF material on alkaline earth metal ions or transition metal ions is utilized, and the alkaline earth metal ions or transition metal ions are adsorbed into the MOF material; and reacting the MOF material adsorbed with the alkaline earth metal ions or the transition metal ions with sodium ferrocyanide to generate the Prussian blue sodium ion material. In the process of generating the Prussian blue sodium ion material, the MOF material can slowly release metal ions adsorbed in the MOF material into a reaction system, so that the generation speed of the Prussian blue sodium ion material is slowed down, and the lattice defects and the vacancy content of the Prussian blue sodium ion material are further controlled. According to the method, a chelating agent does not need to be additionally added, lattice defects and vacancy content in the Prussian blue sodium ion material can be effectively controlled on the premise of not increasing the cost, and when the Prussian blue sodium ion material is applied to the sodium ion battery, the capacity and cycling stability of the sodium ion battery can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and in particular, to a Prussian blue sodium-ion material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing global demand for renewable and clean energy, battery technology, as the core link of energy storage and conversion, has received unprecedented attention. Lithium-ion batteries, with their advantages such as high energy density and long cycle life, have dominated in the fields of portable electronic devices, electric vehicles, and large-scale energy storage. However, the geographical distribution of lithium resources is extremely uneven, mainly concentrated in a few regions such as South America, China, and Australia, and the extraction cost is high, which leads to the uncertainty of the raw material cost of lithium-ion batteries and concerns about the stability of the supply chain. The shortage and uneven distribution of lithium resources not only limit the production capacity expansion of lithium-ion batteries but also affect their wide application globally, especially in countries or regions with scarce resources.

[0003] In view of the limitations of lithium-ion batteries, finding alternative energy storage systems has become a research hotspot. Sodium-ion batteries, as a potential low-cost and high-performance energy storage technology, have gradually come into view due to their abundant sodium resources and similar working mechanisms to lithium-ion batteries. Sodium is abundant in reserves and widely distributed on the earth, and the extraction and processing costs are relatively low, which gives sodium-ion batteries an obvious advantage in cost control. In addition, sodium-ion batteries show good potential in large-scale energy storage applications, especially in fixed energy storage systems, where the cost sensitivity is high and the performance requirements are relatively loose.

[0004] The performance of the positive electrode material of sodium-ion batteries directly affects the overall performance of the battery. Currently, the positive electrode materials of sodium-ion batteries are mainly divided into three categories: layered oxide materials, polyanion materials, and Prussian blue materials. Layered oxide materials such as NaMO 2 (M = Fe, Mn, Ni, etc.) have a relatively high energy density, but the synthesis conditions are harsh, and the structure is prone to collapse during the cycling process. Polyanion materials such as Na 3 V 2 (PO 4 ) 3It has good structural stability and safety, but its theoretical specific capacity is relatively low. Prussian blue materials have become the focus of researchers due to their high theoretical specific capacity (up to 170 mAh / g), simple synthesis method and environmental friendliness. However, this type of material is prone to introduce lattice defects, especially vacancy defects, during the preparation process. These defects will carry lattice water. These water molecules will promote the decomposition of the material during the cycle of sodium ion batteries, resulting in capacity attenuation and decreased cycle performance, which seriously restricts the commercialization process of Prussian blue materials.

[0005] In order to solve the defect problem of Prussian blue materials, existing technical solutions mostly use chelating agents to control the interaction between metal ions and Fe(CN) 6 4- of reaction rates to reduce the formation of defects in the lattice. Chelating agents slow down the crystallization rate of Prussian blue materials by forming stable complexes with metal ions, thereby reducing defects in the lattice structure. For example, in the Chinese patent document CN117902595 A, a method for preparing Prussian blue positive electrode materials by adding efficient chelating agents is disclosed. This method can effectively control the lattice defects inside the material, improve the specific capacity and cycle stability of the material. However, the use of chelating agents increases the material cost and may introduce new chemical impurities, affecting the purity of the material and the electrochemical performance of the battery. Therefore, exploring a new method that does not require the additional addition of chelating agents, is simple to operate and low-cost, to further reduce the lattice defects in Prussian blue materials is of great significance for promoting the commercial application of sodium ion battery technology.

[0006] Therefore, how to effectively control the lattice defects and vacancy content in Prussian blue materials without increasing additional costs, improve the cycle stability and capacity of the materials, and then improve the cycle stability of sodium ion batteries, is a challenge to be solved in the current research field. To this end, the present invention is proposed. Summary of the invention

[0007] The main purpose of the present invention is to provide a method for preparing a Prussian blue sodium ion material, aiming to effectively control the lattice defects and vacancy content in the Prussian blue sodium ion material without increasing additional costs, thereby improving the cycle stability and battery capacity of a sodium ion battery.

[0008] The present invention provides a preparation method of a Prussian blue sodium ion material. The preparation method includes the following steps: performing a first mixing on a MOF material and a soluble metal salt solution to obtain a mixed slurry; subjecting the mixed slurry to a first separation and a first washing to obtain a pre-treated MOF material; wherein the metal ions in the soluble metal salt solution are at least one of alkaline earth metal ions or transition metal ions; performing a second mixing on the pre-treated MOF material and a sodium ferrocyanide solution and reacting to obtain a reaction slurry; subjecting the reaction slurry to a second separation to obtain a solid material; and subjecting the solid material to a second washing, drying, and grinding to obtain the Prussian blue sodium ion material. This method achieves the purpose of effectively controlling the lattice defects and their vacancy content in the Prussian blue sodium ion material without additional cost. Using the prepared Prussian blue sodium ion material as the active material of the positive electrode plate in a sodium ion battery can effectively improve the capacity and cycle stability of the sodium ion battery.

[0009] Further, the MOF material is at least one of MIL series MOF materials, FeCo-MOF series MOF materials, UiO series MOF materials, or ZIF series MOF materials; preferably, the MIL series MOF materials are at least one of MIL-100 type, MIL-101 type, MIL-53 type, or MIL-53(Al) type; preferably, the FeCo-MOF series MOF materials are at least one of FeCo-MOF-74 type or FeCo-MOF-235 type; preferably, the UiO series MOF materials are at least one of UiO-66 type, UiO-67 type, or UiO-68 type; preferably, the ZIF series MOF materials are at least one of ZIF-8 type, ZIF-90 type, or ZIF-67 type. The above types of MOF materials can better play the role of slowly releasing alkaline earth metal ions or transition metal ions.

[0010] Further, the concentration of metal ions in the soluble metal salt solution is 0.1 - 1 mol / L; preferably, the concentration of metal ions in the soluble metal salt solution is 0.1 - 0.3 mol / L; preferably, the soluble metal salt is at least one of sulfates or their hydrates, nitrates or their hydrates, acetates or their hydrates, or chlorides or their hydrates of alkaline earth metals or transition metals. Controlling the concentration of metal ions in the soluble metal salt solution within the above range is beneficial for the MOF material to stably and continuously adsorb metal ions, and can further control the adsorption amount of the MOF material for alkaline earth metal ions or transition metal ions.

[0011] Further, the transition metal ion is Fe 2+ 、Ni 2+ 、Mn 2+ 、Cu 2+ 、Co 2+ 、Zr2+ 、 Zn 2+ 、 Cr 2+ 、 Ti 2+ or Ru 2+ ; Preferably, the alkaline earth metal ion is Ca 2+ or Mg 2+ at least one of them. Using the above types of transition metal ions and alkaline earth metal ions to prepare the Prussian blue sodium ion material, the electrochemical performance of the Prussian blue sodium ion material is better.

[0012] Further, the first mixing includes: mixing the MOF material and the soluble metal salt solution evenly and then performing a standing operation; preferably, the standing time is 30 - 120 min; preferably, the weight ratio of the MOF material to the soluble metal salt solution is (0.05 - 10):100; preferably, the first washing process is carried out using the first washing solvent, and the first washing solvent is a saturated aqueous solution of soluble sodium salt; more preferably, the first washing solvent is a saturated aqueous solution of at least one of sodium sulfate or its hydrate, sodium chloride or its hydrate, sodium nitrate or its hydrate, sodium acetate or its hydrate; preferably, the first separation method is centrifugation or suction filtration; more preferably, the first separation method is suction filtration. Controlling the weight ratio of the MOF material to the soluble metal salt solution within the above range is beneficial to further improving the comprehensive performance of the prepared Prussian blue sodium ion material.

[0013] Further, the concentration of the sodium ferrocyanide solution is 0.1 - 1 mol / L; preferably, the concentration of the sodium ferrocyanide solution is 0.1 - 0.5 mol / L. Controlling the concentration of the sodium ferrocyanide solution within the above range can further control the formation rate of the Prussian blue sodium ion material within a lower range, which is beneficial to further improving the electrochemical performance of the Prussian blue sodium ion material.

[0014] Further, the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.05 - 10):60; preferably, the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.5 - 5):60. By controlling the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution within the above range, the formation rate of the Prussian blue sodium ion material can be in a better range, which is beneficial to better controlling the lattice defects and their vacancy content of the Prussian blue sodium ion material within a lower range, thereby further improving the electrochemical performance of the Prussian blue sodium ion material.

[0015] Further, the second mixing includes: first mixing the MOF pretreatment material with a sodium ferrocyanide solution and stirring for reaction, and then standing and aging the obtained reaction solution to obtain a reaction slurry; preferably, the stirring reaction time is 1 to 3 h; preferably, the standing and aging time is 12 to 24 h; preferably, the drying temperature is 120 to 170 °C and the drying time is 12 to 24 h; preferably, the second separation method is centrifugation. Controlling the stirring reaction time and the standing and aging time within the above ranges can make the reaction for generating the Prussian blue sodium ion material proceed more fully.

[0016] According to another aspect of the present invention, there is also provided a Prussian blue sodium ion material, which is prepared by the above preparation method, and the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y < 1, M is an alkaline earth metal or a transition metal, and □ is a Fe(CN) 6 4- vacancy; preferably, the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y ≤ 0.2, M is an alkaline earth metal or a transition metal, and □ is a Fe(CN) 6 4- vacancy; more preferably, the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y ≤ 0.1, M is an alkaline earth metal or a transition metal, and □ is a Fe(CN) 6 4- vacancy; preferably, the particle size of the Prussian blue sodium ion material is 50 nm ≤ D50 ≤ 5 μm. Using the preparation method provided by the present invention to prepare the Prussian blue sodium ion material can control the lattice defects and the vacancy content in the Prussian blue sodium ion material within a better range.

[0017] According to the third aspect of the present invention, there is also provided a sodium ion battery, which includes a positive electrode plate, and the active material in the positive electrode plate includes the above Prussian blue sodium ion material. Using the Prussian blue sodium ion material prepared by the preparation method provided by the present invention as the active material in the positive electrode plate for a sodium ion battery can effectively control the problems of capacity attenuation and decline in cycle performance of the sodium ion battery.

[0018] ​​​The present invention provides a Prussian blue sodium ion material, a preparation method thereof and an application. The preparation method utilizes the reversible adsorption characteristics of MOF materials for metal ions. First, alkaline earth metal ions or transition metal ions are adsorbed into the MOF material, and then the MOF material adsorbed with alkaline earth metal ions or transition metal ions is used to react with a sodium ferrocyanide solution to generate a Prussian blue sodium ion material. During the process of generating the Prussian blue sodium ion material, the MOF material can slowly release the alkaline earth metal ions or transition metal ions adsorbed therein into the reaction system, thereby slowing down the generation rate of the Prussian blue sodium ion material and achieving effective control over the lattice defects and vacancy content in the Prussian blue sodium ion material. Using the preparation method of the Prussian blue sodium ion material provided by the present invention, no additional chelating agent needs to be added, and the purpose of effectively controlling the lattice defects and vacancy content in the Prussian blue sodium ion material is achieved without additional cost. Using the prepared Prussian blue sodium ion material as the active material of the positive electrode plate in a sodium ion battery can effectively improve the cycle stability and battery capacity of the sodium ion battery. In addition, the MOF material used in this preparation method can be recycled, which can further reduce the preparation cost of the Prussian blue sodium ion material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0020] Figure 1 The SEM diagram of the Prussian blue sodium ion material prepared in Example 1 of the present invention is shown;

[0021] Figure 2 The partial enlarged view of the SEM diagram of the Prussian blue sodium ion material prepared in Example 1 of the present invention is shown;

[0022] Figure 3 The SEM diagram of the Prussian blue sodium ion material prepared in Comparative Example 1 of the present invention is shown;

[0023] Figure 4 The first-cycle charge and discharge curve of the sodium ion battery using the Prussian blue sodium ion material prepared in Example 1 as the active material of the positive electrode plate at a charge and discharge rate of 0.1C is shown;

[0024] Figure 5 The first-cycle charge and discharge curve of the sodium ion battery using the Prussian blue sodium ion material prepared in Comparative Example 1 as the active material of the positive electrode plate at a charge and discharge rate of 0.1C is shown;

[0025] Figure 6The charge-discharge specific capacity curves of sodium-ion batteries with Prussian blue sodium-ion materials prepared in Example 1 and Comparative Example 1 as the active material of the positive electrode sheet are respectively shown under 200 cycles at 1C. Detailed implementation manners

[0026] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0027] As described in the background art section, Prussian blue sodium-ion materials have advantages such as high theoretical specific capacity (up to more than 170 mAh / g), simple synthesis method, and environmental friendliness. However, Prussian blue sodium-ion materials are prone to introducing lattice defects during the preparation process. The vacancy defects therein will carry lattice water, and these water molecules will promote the decomposition of the material during the cycling process of sodium-ion batteries, resulting in capacity attenuation and serious decline in cycling performance, restricting the commercialization process of Prussian blue sodium-ion materials. In the prior art, the method of using chelating agents to control the reaction rate of metal ions with Fe(CN) 6 4- to reduce the defects in the lattice will increase the preparation cost of Prussian blue sodium-ion materials and may introduce new chemical impurities, affecting the purity of the material and the electrochemical performance of the battery. Therefore, how to effectively control the lattice defects and their vacancy content in Prussian blue sodium-ion materials without increasing additional costs is an urgent problem to be solved at present.

[0028] To solve the above problems, the present invention provides a preparation method of Prussian blue sodium-ion materials. The preparation method includes the following steps: performing a first mixing on a MOF material and a soluble metal salt solution to obtain a mixed slurry; subjecting the mixed slurry to a first separation and a first washing to obtain a MOF pretreated material; wherein the metal ions in the soluble metal salt solution are at least one of alkaline earth metal ions or transition metal ions; performing a second mixing on the MOF pretreated material and a sodium ferrocyanide solution and reacting to obtain a reaction slurry; subjecting the reaction slurry to a second separation to obtain a solid material; and drying and grinding the solid material to obtain Prussian blue sodium-ion materials.

[0029] Specifically, in the preparation method of the above-mentioned Prussian blue sodium ion material, first, the MOF material is mixed with an alkaline earth metal soluble metal salt solution or a transition metal soluble metal salt solution, so that the alkaline earth metal ions or transition metal ions in the soluble salt solution are fully adsorbed into the MOF material to obtain a mixed slurry; then, the MOF material in the mixed slurry that has fully adsorbed the alkaline earth metal ions or transition metal ions is separated from the soluble salt solution, and the soluble salt solution attached to the surface of the MOF material is washed away to obtain a pre-treated MOF material. Then, the sodium ferrocyanide solution is mixed with the pre-treated MOF material to fully react, and a Prussian blue sodium ion material can be generated. During this reaction process, affected by the slow-release characteristics of the MOF material for alkaline earth metal ions or transition metal ions, the pre-treated MOF material can slowly release alkaline earth metal ions or transition metal ions into the reaction system, and the slowly released alkaline earth metal ions or transition metal ions can further slowly react with the sodium ferrocyanide solution to generate a Prussian blue sodium ion material. Finally, the solid material of the Prussian blue sodium ion material obtained after separation is dried and ground to obtain the Prussian blue sodium ion material.

[0030] In the preparation method of the Prussian blue sodium ion material provided by the present invention, by utilizing the reversible adsorption characteristics of the MOF material for alkaline earth metal ions or transition metal ions, first, the alkaline earth metal ions or transition metal ions are adsorbed into the MOF material, and then the MOF material adsorbed with the alkaline earth metal ions or transition metal ions is used to react with the sodium ferrocyanide solution to generate a Prussian blue sodium ion material. During the process of generating the Prussian blue sodium ion material, the MOF material can slowly release the alkaline earth metal ions or transition metal ions adsorbed therein into the reaction system, slowing down the generation rate of the Prussian blue sodium ion material, thereby effectively controlling the lattice defects and the content of their vacancies in the material. Using the preparation method of the Prussian blue sodium ion material provided by the present invention, without the need to additionally add a chelating agent, the purpose of effectively controlling the lattice defects and the content of their vacancies in the Prussian blue sodium ion material is achieved without additional cost. Using the prepared Prussian blue sodium ion material as the active material of the positive electrode plate in a sodium ion battery can effectively improve the capacity and cycle stability of the sodium ion battery. The MOF material used in the preparation method provided by the present invention can also be reused, further reducing the preparation cost of the Prussian blue sodium ion material. In addition, this preparation method also has the advantage of simple preparation process, and the above advantages are especially important for large-scale production.

[0031] In a preferred embodiment, the MOF material includes, but is not limited to, at least one of MIL series MOF materials, FeCo-MOF series MOF materials, UiO series MOF materials, or ZIF series MOF materials; all MOF materials capable of adsorbing and slowly releasing alkaline earth metal ions and transition metal ions are acceptable. By way of example but not limitation, the MIL series MOF materials are at least one of MIL-100 type, MIL-101 type, MIL-53 type, or MIL-53(Al) type; the FeCo-MOF series MOF materials are at least one of FeCo-MOF-74 type or FeCo-MOF-235 type; the UiO series MOF materials are at least one of UiO-66 type, UiO-67 type, or UiO-68 type; the ZIF series MOF materials are at least one of ZIF-8 type, ZIF-90 type, or ZIF-67 type. It is not difficult for those skilled in the art to understand that in the actual process of preparing Prussian blue sodium ion materials, MOF materials with appropriate slow-release rates can be selected according to experimental requirements to achieve the preparation of Prussian blue sodium ion materials with corresponding characteristics. The above types of MOF materials can all play a good role in slowly releasing alkaline earth metal ions or transition metal ions.

[0032] In a preferred embodiment, the concentration of metal ions in the soluble metal salt solution is 0.1 - 1 mol / L, specifically for example 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any concentration between any two of the above values. The concentration of metal ions in the soluble metal salt solution will affect the adsorption of the MOF material. Controlling the concentration of metal ions in the soluble metal salt solution within the above range is beneficial for the MOF material to stably and continuously adsorb metal ions, and can further control the adsorption amount of the MOF material for alkaline earth metal ions or transition metal ions within a better range. Preferably, the concentration of metal ions in the soluble metal salt solution is 0.1 - 0.3 mol / L, specifically for example 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.22 mol / L, 0.25 mol / L, 0.28 mol / L, 0.3 mol / L, or any concentration between any two of the above values. Controlling the concentration of metal ions in the soluble metal salt solution within the above preferred range has better effects. Preferably, the soluble metal salt is at least one of sulfates or their hydrates, nitrates or their hydrates, acetates or their hydrates, chlorides or their hydrates of alkaline earth metals or transition metals. The present invention does not make specific limitations on the types of soluble metal salts, and the above types of soluble salts are all acceptable.

[0033] In a preferred embodiment, the transition metal ion is Fe 2+ , Ni 2+ , Mn 2+ , Cu 2+ , Co 2+ , Zr 2+ , Zn 2+ , Cr 2+ , Ti 2+ or Ru 2+ or at least one of the above. Preferably, the alkaline earth metal ion is Ca 2+ or Mg 2+ or at least one of the above. Using the above types of transition metal ions or alkaline earth metal ions to prepare Prussian blue sodium ion materials, the obtained Prussian blue sodium ion materials have better electrochemical performance. More preferably, the transition metal ion is Fe 2+ or Mn 2+ . Using Fe 2+ or Mn 2+ to prepare Prussian blue sodium ion materials, the obtained Prussian blue sodium ion materials have better comprehensive performance.

[0034] In a preferred embodiment, the first mixing includes: after uniformly mixing the MOF material and the soluble metal salt solution, a standing operation is performed; preferably, the standing time is 30 to 120 minutes; preferably, the weight ratio of the MOF material to the soluble metal salt solution is (0.05 to 10):100, specifically, for example, 0.05:100, 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, or any ratio between any two of the above ratios. The first mixing process is to enable the alkaline earth metal ions or transition metal ions in the soluble salt solution to be fully adsorbed into the MOF material. Therefore, after uniformly mixing the MOF material and the soluble metal salt solution and then standing it, the alkaline earth metal ions or transition metal ions in the soluble salt solution can be more fully adsorbed into the MOF material. Controlling the weight ratio of the MOF material to the soluble metal salt solution within the above range can further control the adsorption amount of the MOF material for alkaline earth metal ions or transition metal ions within a better range, which is beneficial to further improving the comprehensive performance of the prepared Prussian blue sodium ion material. Preferably, the first washing process is carried out using a first washing solvent, and the first washing solvent is a saturated aqueous solution of a soluble sodium salt; more preferably, the first washing solvent is a saturated aqueous solution of at least one of sodium sulfate or its hydrate, sodium chloride or its hydrate, sodium nitrate or its hydrate, and sodium acetate or its hydrate. Washing the MOF material adsorbed with alkaline earth metal ions or transition metal ions with a saturated aqueous solution of a soluble sodium salt can wash away the residual soluble salt solution on the surface of the MOF material while further avoiding the desorption of alkaline earth metal ions or transition metal ions in the MOF material. Preferably, the first separation method is centrifugation or suction filtration; more preferably, the first separation method is suction filtration. Preferably, the second washing includes: the solid substance obtained after separating the reaction slurry is first washed 2 to 5 times with deionized water and then washed 1 to 3 times with absolute ethanol.

[0035] In a preferred embodiment, the concentration of the sodium ferrocyanide solution is 0.1 to 1 mol / L, specifically, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any concentration between any two of the above values. In the process of reacting the sodium ferrocyanide solution with the MOF pretreatment material to form the sodium prussian blue ion material, by controlling the concentration of the sodium ferrocyanide solution within the above range, the rate of release of alkaline earth metal ions or transition metal ions from the MOF pretreatment material in the reaction system can be controlled within a lower range, and further the formation rate of the sodium prussian blue ion material can be controlled within a lower range, which is beneficial to making the performance of the sodium prussian blue ion material better. Preferably, the concentration of the sodium ferrocyanide solution is 0.1 to 0.5 mol / L, specifically, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, or any concentration between any two of the above values. By controlling the concentration of the sodium ferrocyanide solution within the above preferred range, the above effects are better, and the performance of the prepared sodium prussian blue ion material is better. More preferably, the concentration of the sodium ferrocyanide solution is 0.1 to 0.3 mol / L, and controlling the concentration of the sodium ferrocyanide solution within the above range has better effects.

[0036] In a preferred embodiment, the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.05 to 10):60; by controlling the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution within the above range, the rate of release of alkaline earth metal ions or transition metal ions from the MOF pretreatment material in the reaction system can be made within a lower range, and further the formation rate of the sodium prussian blue ion material can be controlled within a lower range, thereby being beneficial to further improving the performance of the sodium prussian blue ion material. Preferably, the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.5 to 5):60. By setting the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution within the above preferred range, the performance of the prepared sodium prussian blue ion material is better.

[0037] In a preferred embodiment, the second mixing includes: first mixing the MOF pretreatment material with a sodium ferrocyanide solution and stirring for reaction, and then allowing the obtained reaction solution to stand for aging to obtain a reaction slurry; preferably, the stirring reaction time is 1 to 3 h; preferably, the standing aging time is 12 to 24 h. The second mixing process is to enable the MOF material adsorbed with alkaline earth metal ions or transition metal ions to fully react with the sodium ferrocyanide solution to generate a sodium prussian blue material. Controlling the stirring reaction time and the standing aging time within the above ranges can make the reaction for generating the sodium prussian blue material more complete, and at the same time can also make the particle size range of the prepared sodium prussian blue material better. Further, controlling the reaction time of the MOF pretreatment material and the sodium ferrocyanide solution within the above range can also avoid problems such as the increase in the particle size of the sodium prussian blue material caused by too long reaction time, and the volume expansion and cracks caused by the sodium prussian blue material when applied to sodium ion batteries. More preferably, the standing aging time is 12 to 18 h. Controlling the standing aging time within the above preferred range will have better above effects. Preferably, the drying temperature is 120 to 170 °C, and the drying time is 12 to 24 h; preferably, the second separation method is centrifugation. Preferably, during the second separation by centrifugation, the preferred centrifugation rate is 5000 to 7500 rpm, and the centrifugation time is 5 to 10 min.

[0038] According to another aspect of the present invention, a sodium prussian blue material is also provided. The sodium prussian blue material is prepared by the above preparation method, and the molecular formula of the sodium prussian blue material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y < 1, M is an alkaline earth metal or a transition metal, and □ is Fe(CN) 6 4- vacancy. Using the preparation method of the present invention to prepare the sodium prussian blue material can control the lattice defects in the sodium prussian blue material and control the vacancy content of the sodium prussian blue material. Preferably, the molecular formula of the sodium prussian blue material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y ≤ 0.2, M is an alkaline earth metal or a transition metal, and □ is Fe(CN) 6 4- ​​Vacancy; controlling the vacancy content in the Prussian blue sodium ion material within the above preferred range, the Prussian blue sodium ion material can exhibit advantages such as high capacity, long cycle life, and wide temperature adaptability when applied to sodium ion batteries. More preferably, the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN) 6 1-y ·□ y , where 0 ≤ x ≤ 2, 0 ≤ y ≤ 0.1, M is an alkaline earth metal or a transition metal, and □ is Fe(CN) 6 4- vacancy. Controlling the vacancy content in the Prussian blue sodium ion material within the above more preferred range, the capacity, cycle life, and wide temperature adaptability of the Prussian blue sodium ion material are better when applied to sodium ion batteries. Preferably, the particle size of the Prussian blue sodium ion material is 50 nm ≤ D50 ≤ 5 μm. Controlling the particle size of the Prussian blue sodium ion material within the above range is beneficial to further improving the comprehensive performance of the Prussian blue sodium ion material. Preferably, the particle size of the Prussian blue sodium ion material is 50 nm ≤ D50 ≤ 3 μm; controlling the particle size of the Prussian blue sodium ion material within the above preferred range has a better use effect.

[0039] It should be particularly noted here that due to the particularity of the material field and the limitations of existing testing and characterization methods, it is impossible to comprehensively characterize the materials obtained by the above preparation method. However, it has been experimentally confirmed that the Prussian blue sodium ion material has the beneficial effect of being able to control its lattice defects and vacancies within a lower range, indicating the improvement of the preparation method of the present invention for the material itself.

[0040] According to the third aspect of the present invention, a sodium ion battery is also provided. The sodium ion battery includes a positive electrode plate, and the active material in the positive electrode plate includes the above Prussian blue sodium ion material. Using the Prussian blue sodium ion material prepared by the preparation method of the present invention as the active material in the positive electrode plate for a sodium ion battery can effectively control the problems of capacity attenuation and decline in cycle performance of the sodium ion battery.

[0041] The following further describes the present application in detail with specific examples, and these examples should not be construed as limiting the scope claimed by the present application.

[0042] It should be further noted here that for the Prussian blue sodium ion materials prepared in the examples and comparative examples, the present application measured the metal ion content therein by inductively coupled plasma emission spectroscopy (ICAP-6300 Radial type plasma emission spectrometer), measured the content of non-metallic elements such as C and N therein by an elemental analyzer (Vario-EL Cube type elemental analyzer), and finally obtained the molecular formula of the prepared Prussian blue sodium ion material by combining the above analysis results and the molar ratio and charge conservation between elements.​

[0043] Example 1

[0044] Put 0.05 g of MIL-100 type MOF material into 100 g of ferrous sulfate solution with a concentration of 0.1 mol / L. After stirring for 5 min to make it evenly mixed, let it stand for 30 min to obtain a mixed slurry. The mixed slurry is filtered by suction, washed with saturated sodium sulfate solution, and air-dried to obtain a MOF pretreated material.

[0045] Put the MOF pretreated material into a sodium ferrocyanide solution with a concentration of 0.174 mol / L. The weight ratio of the MOF pretreated material to the sodium ferrocyanide solution is 0.05:60. After mixing, stir and react for 1 h, then let the obtained suspension stand and age for 12 h to obtain a mixed slurry. Centrifuge the mixed slurry to separate the solid and liquid. The obtained solid material is washed 3 times with deionized water and 1 time with absolute ethanol, then dried at 120 °C for 12 h, and then ground to obtain a Prussian blue sodium ion material with a particle size of D50 = 2 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.47 Fe[Fe(CN) 6 0.94 ·□ 0.06 .

[0046] Test the prepared Prussian blue sodium ion material by SEM, and the results are as Figure 1 and Figure 2 shown. It can be seen from Figure 1 that the Prussian blue sodium ion material prepared by the method for preparing Prussian blue sodium ion material provided by the present invention is in the shape of a cube, evenly dispersed, and no agglomeration phenomenon occurs; Figure 2 is Figure 1 a partial enlarged view of. It can be seen from the partial enlarged view in Figure 2 that the morphology of the Prussian blue sodium ion material prepared in this example is regular and there are no obvious lattice defects.

[0047] Use the above-prepared Prussian blue sodium ion material as the active material in the positive electrode sheet for a sodium ion battery.

[0048] Example 2

[0049] Put 0.05 g of UiO-66 type MOF material into 100 g of ferrous sulfate solution with a concentration of 0.1 mol / L. After stirring for 5 min to make it evenly mixed, let it stand for 30 min to obtain a mixed slurry. The mixed slurry is filtered by suction, washed with saturated sodium sulfate solution, and air-dried to obtain a MOF pretreated material.

[0050] ​The MOF pretreatment material is placed in a sodium ferrocyanide solution with a concentration of 0.174 mol / L, and the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is 0.05:60. After mixing, it is stirred and reacted for 1 h, and then the obtained suspension is allowed to stand and age for 12 h to obtain a mixed slurry. The mixed slurry is separated into solid and liquid by centrifugation. The obtained solid material is washed 3 times with deionized water and 1 time with absolute ethanol, dried at 120 °C for 12 h, and then ground to obtain a Prussian blue sodium ion material with a particle size of D50 = 2 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.54 Fe[Fe(CN) 6 0.93 ·□ 0.07 。

[0051] The Prussian blue sodium ion material prepared above is used as the active material in the positive electrode sheet for a sodium ion battery.

[0052] Example 3

[0053] 0.05 g of MIL-100 type MOF material is placed in 100 g of a ferrous sulfate solution with a concentration of 1 mol / L. After stirring for 5 min to mix evenly, it is allowed to stand for 30 min to obtain a mixed slurry. The mixed slurry is filtered by suction, washed with a saturated sodium sulfate solution, and air-dried to obtain the MOF pretreatment material.

[0054] The MOF pretreatment material is placed in a sodium ferrocyanide solution with a concentration of 1 mol / L, and the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is 0.05:60. After mixing, it is stirred and reacted for 3 h, and then the obtained suspension is allowed to stand and age for 12 h to obtain a mixed slurry. The mixed slurry is separated into solid and liquid by centrifugation. The obtained solid material is washed 3 times with deionized water and 1 time with absolute ethanol, dried at 170 °C for 12 h, and then ground to obtain a Prussian blue sodium ion material with a particle size of D50 = 3 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.71 Fe[Fe(CN) 6 0.81 ·□ 0.19 。

[0055] The Prussian blue sodium ion material prepared above is used as the active material in the positive electrode sheet for a sodium ion battery.

[0056] Example 4

[0057] 10 g of MIL-100 type MOF material is placed in 100 g of a ferrous sulfate solution with a concentration of 1 mol / L. After stirring for 5 min to mix evenly, it is allowed to stand for 120 min to obtain a mixed slurry. The mixed slurry is centrifuged, washed with a saturated sodium sulfate solution, and air-dried to obtain the MOF pretreatment material.​​

[0058] Place the MOF pretreated material in a sodium ferrocyanide solution with a concentration of 0.7 mol / L. The weight ratio of the MOF pretreated material to the sodium ferrocyanide solution is 10:60. After mixing, stir the mixture for 1 h, then let the obtained suspension stand and age for 24 h to obtain a mixed slurry. Separate the solid and liquid of the mixed slurry by centrifugation. Wash the obtained solid material 3 times with deionized water and 1 time with absolute ethanol, then dry it at 120 °C for 24 h, and then grind it to obtain a Prussian blue sodium ion material with a particle size of D50 = 3 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.66 Fe[Fe(CN) 6 0.83 ·□ 0.17 。

[0059] Use the Prussian blue sodium ion material prepared above as the active material in the positive electrode plate for a sodium ion battery.

[0060] Example 5

[0061] Place 1 g of MIL-100 type MOF material in 100 g of a ferrous sulfate solution with a concentration of 0.3 mol / L. Stir for 5 min to mix evenly, then let it stand for 30 min to obtain a mixed slurry. Filter the mixed slurry by suction, wash it with saturated sodium sulfate solution, and air-dry it to obtain the MOF pretreated material.

[0062] Place the MOF pretreated material in a sodium ferrocyanide solution with a concentration of 0.1 mol / L. The weight ratio of the MOF pretreated material to the sodium ferrocyanide solution is 0.5:60. After mixing, stir the mixture for 1 h, then let the obtained suspension stand and age for 12 h to obtain a mixed slurry. Separate the solid and liquid of the mixed slurry by centrifugation. Wash the obtained solid material 3 times with deionized water and 1 time with absolute ethanol, then dry it at 120 °C for 12 h, and then grind it to obtain a Prussian blue sodium ion material with a particle size of D50 = 2 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.48 Fe[Fe(CN) 6 0.87 ·□ 0.13 。

[0063] Use the Prussian blue sodium ion material prepared above as the active material in the positive electrode plate for a sodium ion battery.

[0064] Example 6

[0065] ​​Put 1 g of MIL-100 type MOF material into 100 g of ferrous sulfate solution with a concentration of 0.3 mol / L, stir for 5 min to make it evenly mixed, and then let it stand for 30 min to obtain a mixed slurry. Filter the mixed slurry by suction, wash it with saturated sodium sulfate solution, and air-dry it to obtain the MOF pretreated material.

[0066] Put the MOF pretreated material into a sodium ferrocyanide solution with a concentration of 0.5 mol / L. The weight ratio of the MOF pretreated material to the sodium ferrocyanide solution is 5:60. After mixing, stir and react for 1 h, and then let the obtained suspension stand and age for 12 h to obtain a mixed slurry. Centrifuge the mixed slurry to separate the solid and liquid. Wash the obtained solid material 3 times with deionized water and 1 time with absolute ethanol, dry it at 120 °C for 12 h, and then grind it to obtain a Prussian blue sodium ion material with a particle size of D50 = 2.5 μm. The molecular formula of the Prussian blue sodium ion material is: Na 1.54 Fe[Fe(CN) 6 0.85 ·□ 0.15 。

[0067] Use the Prussian blue sodium ion material prepared above as the active material in the positive electrode plate for sodium ion batteries.

[0068] Example 7

[0069] The difference between Example 7 and Example 1 is that the MOF material used is FeCo-MOF-74 type.

[0070] The molecular formula of the prepared Prussian blue sodium ion material is: Na 1.51 Fe[Fe(CN) 6 0.91 ·□ 0.09 , and the particle size is D50 = 2 μm.

[0071] Example 8

[0072] The difference between Example 8 and Example 1 is that the MOF material used is ZIF-8 type of the ZIF series.

[0073] The molecular formula of the prepared Prussian blue sodium ion material is: Na 1.53 Fe[Fe(CN) 6 0.89 ·□ 0.11 , and the particle size is D50 = 2 μm.

[0074] Example 9

[0075] The difference between Example 9 and Example 1 is that the metal ion adsorbed in the MOF pretreated material is Mn 2+ 。 ​​​

[0076] The molecular formula of the prepared Prussian blue sodium ion material is: Na 1.63 Mn[Fe(CN) 6 0.93 ·□ 0.07 , and the particle size is D50 = 2 μm.

[0077] Example 10

[0078] The difference between Example 10 and Example 1 is that the concentration of the ferrous sulfate solution is 1.2 mol / L, and the concentration of the sodium ferrocyanide solution is 1.1 mol / L. The molecular formula of the prepared Prussian blue sodium ion material is: Na 1.67 Fe[Fe(CN) 6 0.80 ·□ 0.20 , and the particle size is D50 = 4 μm.

[0079] Comparative Example 1

[0080] Take 2.780 g of ferrous sulfate heptahydrate, 2.581 g of sodium citrate, and 0.710 g of sodium sulfate and place them in a beaker. Add 100 mL of deionized water and stir to dissolve to obtain a clear solution A. Take another 4.841 g of sodium ferrocyanide decahydrate and place it in a beaker. Add 100 mL of deionized water and stir to obtain a clear solution B. Under a nitrogen atmosphere, add solution A dropwise into solution B with a peristaltic pump at a dropping rate of 0.5 mL / min, and keep stirring. After the reaction, continue to stir for 1 h and then stand for aging for 12 h. After centrifugally washing the blue precipitate, place the precipitate in a vacuum oven at 120 °C for 12 h, take it out, grind it, and sieve it to obtain the Prussian blue cathode material. The molecular formula of the Prussian blue sodium ion material is: Na 1.20 Fe[Fe(CN) 6 0.78 ·□ 0.22 , and the particle size is D50 = 5 μm.

[0081] The prepared Prussian blue sodium ion material was tested by SEM, and the results are as Figure 3 shown. It can be seen from Figure 3 that the Prussian blue sodium ion materials prepared by the above method are all cubic structures, but some of them show irregular cubic structures, indicating that there are many crystal defects in the prepared materials. In addition, there is an obvious agglomeration phenomenon in the structure, indicating the inhomogeneity of the structure of the prepared Prussian blue sodium ion material itself.

[0082] The Prussian blue sodium ion materials prepared in the above examples and comparative examples were used as the active materials in the positive electrode sheets of sodium ion batteries to prepare sodium ion batteries. The preparation method of the sodium ion batteries includes the following steps: ​​​

[0083] Take 0.14 g of Prussian blue sodium ion material, 0.04 g of Super P (conductive carbon black), and 0.02 g of PVDF (polyvinylidene fluoride), dissolve them in NMP (N-methylpyrrolidone) solvent and mix evenly. Coat it evenly on a 16-μm-thick aluminum foil with a thickness of 100 nm, and dry it in a blast dryer at 80 °C for 30 minutes. After vacuum drying at 120 °C for 12 hours, a positive electrode sheet for a sodium ion battery is obtained. The positive electrode sheet of the sodium ion battery is made into a circular positive electrode sheet with a diameter of 19 mm. Use a sodium metal sheet as the negative electrode of the battery. Mix PC (propylene carbonate): EMC (ethyl methyl carbonate): FEC (fluoroethylene carbonate): PST (allyl-1,3-sulfonic acid lactone): DTD (ethylene sulfate) according to a volume ratio of 40:58:2:1:1. Dissolve NaPF 6 in it to obtain a 0.6 mol / L NaPF 6 solution as the electrolyte. Assemble it into a button cell using a battery case in a glove box filled with argon, and a sodium ion battery can be obtained.

[0084] Perform relevant electrochemical performance tests on the sodium ion batteries prepared above. As shown in Table 1, the specific test methods are as follows:

[0085] 0.1C first-cycle charge-discharge performance test of sodium ion battery: Use a BlueTester, connect the positive and negative electrodes of the button cell, perform constant current charging at 2-4V / 0.1C, then perform constant voltage charging at 4V. After the current drops to 0.01C, perform constant current discharge at 2-4V / 0.1C; thus, the first-cycle discharge specific capacity at 0.1C is obtained;

[0086] 1C cycle 200-cycle charge-discharge performance test of sodium ion battery: Use a BlueTester, connect the positive and negative electrodes of the button cell. First, perform constant current charging at 2-4V / 0.1C, then perform constant voltage charging at 4V. After the current drops to 0.01C, perform constant current discharge at 2-4V / 0.1C. After 2 cycles of cyclic charge-discharge activation, use a 1C current for constant current charge-discharge and cycle 200 times; thus, the discharge specific capacity and capacity retention rate (%) after 1C cycle 200 times are obtained.

[0087] Table 1

[0088]

[0089]

[0090] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0091] Examples 1 to 10 are for preparing Prussian blue sodium ion materials by using the preparation method of Prussian blue sodium ion materials provided by the present invention. This preparation method can effectively control the vacancy content in the prepared Prussian blue sodium ion materials. In particular, by controlling the parameters in the preparation process within the preferred range, the vacancy content in the prepared Prussian blue sodium ion materials can be within a lower range. Further, the Prussian blue sodium ion materials prepared in Examples 1 to 10 are used as active materials in the positive electrode sheet for sodium ion batteries. As can be seen from the results in Table 1, the comprehensive performances such as the battery capacity and cycle stability of the corresponding sodium ion batteries are all within a good range, and the comprehensive performances such as the capacity and cycle stability of the sodium ion batteries corresponding to the examples with parameters in the preferred range during the preparation process are better. Thus, it can be seen that the Prussian blue sodium ion materials prepared by using the preparation method of Prussian blue sodium ion materials provided by the present invention can effectively improve the problems of capacity attenuation and cycle performance degradation of sodium ion batteries.

[0092] On the contrary, in Comparative Example 1, the Prussian blue sodium ion material was prepared by using a conventional preparation method. The prepared Prussian blue sodium ion material has a high vacancy content and obvious lattice defects. When it is used as the active material in the positive electrode sheet for sodium ion batteries, there is a large gap between the battery capacity and cycle stability of the corresponding sodium ion battery and those of the sodium ion battery corresponding to the example.

[0093] To better compare the performances of the Prussian blue sodium ion materials prepared in the examples and comparative examples, the first-cycle charge-discharge curves of the sodium ion batteries corresponding to Example 1 and Comparative Example 1 were respectively plotted at a charge-discharge rate of 0.1C, and the results are respectively as Figure 4 and Figure 5 shown. By comparing the two, it can be known that the sodium ion battery corresponding to Example 1 has a higher battery capacity, while the battery capacity of the sodium ion battery corresponding to Comparative Example 1 is lower. Further, the charge-discharge specific capacity curves of the sodium ion batteries corresponding to Example 1 and Comparative Example 1 at 1C for 200 cycles were plotted, and the results are as Figure 6 shown. As can be seen from Figure 6 , after 200 cycles under the same conditions, the sodium ion battery corresponding to Example 1 has better cycle stability, and the capacity attenuation rate of the sodium ion battery corresponding to Comparative Example 1 is faster.

[0094] In summary, by using the preparation method of Prussian blue sodium ion materials provided by the present invention, without the need to additionally add a chelating agent, it is possible to effectively control the lattice defects and their vacancy content in the Prussian blue sodium ion materials without additional cost. Using the prepared Prussian blue sodium ion material as the active material of the positive electrode sheet in a sodium ion battery can effectively improve the cycle stability and battery capacity of the sodium ion battery.

[0095] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a Prussian blue sodium ion material, characterized in that: The preparation method comprises the following steps: The MOF material and the soluble metal salt solution are first mixed to obtain a mixed slurry; the mixed slurry is first separated and first washed to obtain a MOF pretreated material; wherein the metal ion in the soluble metal salt solution is at least one of an alkaline earth metal ion or a transition metal ion; The MOF pretreatment material is mixed with a sodium ferrocyanide solution for a second time and reacted to obtain a reaction slurry; the reaction slurry is separated for a second time to obtain a solid material; The solid material is subjected to a second washing, drying and grinding to obtain the Prussian blue sodium ion material.

2. The method for preparing the Prussian blue sodium ion material according to claim 1, characterized in that: The MOF material is at least one of a MIL series MOF material, a FeCo-MOF series MOF material, a UiO series MOF material or a ZIF series MOF material; Preferably, the MIL series MOF material is at least one of MIL-100, MIL-101, MIL-53 or MIL-53 (Al); Preferably, the FeCo-MOF series MOF material is at least one of FeCo-MOF-74 type or FeCo-MOF-235 type; Preferably, the UiO series MOF material is at least one of UiO-66, UiO-67 or UiO-68; Preferably, the ZIF series MOF material is at least one of ZIF-8, ZIF-90 or ZIF-67.

3. The method for preparing the Prussian blue sodium ion material according to claim 1, characterized in that: The concentration of the metal ions in the soluble metal salt solution is 0.1 to 1 mol / L; Preferably, the concentration of the metal ions in the soluble metal salt solution is 0.1 to 0.3 mol / L; Preferably, the soluble metal salt is selected from at least one of sulfates or hydrates thereof, nitrates or hydrates thereof, acetates or hydrates thereof, and chlorides or hydrates thereof of the alkaline earth metal or the transition metal.

4. The method for preparing the Prussian blue sodium ion material according to any one of claims 1 to 3, characterized in that: The transition metal ion is Fe 2+ 、Ni 2+ , Mn 2+ , Cu 2+ 、Co 2+ 、Zr 2+ 、Zn 2+ Cr 2+ 、Ti 2+ Or Ru 2+ At least one of; Preferably, the alkaline earth metal ion is Ca 2+ or Mg 2+ At least one of .

5. The method for preparing the Prussian blue sodium ion material according to any one of claims 1 to 3, characterized in that: The first mixing comprises: mixing the MOF material and the soluble metal salt solution uniformly, and then standing for a while; preferably, the standing time is 30 to 120 minutes; Preferably, the weight ratio of the MOF material to the soluble metal salt solution is (0.05-10):100; Preferably, the first washing process is carried out with a first washing solvent, and the first washing solvent is a saturated aqueous solution of a soluble sodium salt; more preferably, the first washing solvent is a saturated aqueous solution of at least one of sodium sulfate or its hydrate, sodium chloride or its hydrate, sodium nitrate or its hydrate, and sodium acetate or its hydrate; Preferably, the first separation method is centrifugation or filtration; more preferably, the first separation method is filtration.

6. The method for preparing the Prussian blue sodium ion material according to any one of claims 1 to 5, characterized in that: The concentration of the sodium ferrocyanide solution is 0.1-1 mol / L; Preferably, the concentration of the sodium ferrocyanide solution is 0.1-0.5 mol / L.

7. The method for preparing the Prussian blue sodium ion material according to any one of claims 1 to 5, characterized in that: The weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.05-10):60; Preferably, the weight ratio of the MOF pretreatment material to the sodium ferrocyanide solution is (0.5-5):

60.

8. The method for preparing the Prussian blue sodium ion material according to any one of claims 1 to 5, characterized in that: The second mixing comprises: firstly mixing the MOF pretreatment material with the sodium ferrocyanide solution to carry out stirring reaction, and then standing and aging the obtained reaction solution to obtain the reaction slurry; Preferably, the stirring reaction time is 1 to 3 hours; Preferably, the static aging time is 12 to 24 hours; Preferably, the drying temperature is 120-170°C, and the drying time is 12-24h; Preferably, the second separation method is centrifugation.

9. A Prussian blue sodium ion material, characterized in that: The Prussian blue sodium ion material is prepared by the preparation method according to any one of claims 1 to 8, and the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN)6] 1-y □ y , where 0≤x≤2, 0≤y<1, M is an alkaline earth metal or a transition metal, and □ is Fe(CN)6 4- vacant seat; Preferably, the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN)6] 1-y □ y , where 0≤x≤2, 0≤y≤0.2, M is an alkaline earth metal or a transition metal, and □ is Fe(CN)6 4- vacant seat; More preferably, the molecular formula of the Prussian blue sodium ion material is: Na x M[Fe(CN)6] 1-y □ y , where 0≤x≤2, 0≤y≤0.1, M is an alkaline earth metal or a transition metal, and □ is Fe(CN)6 4- vacant seat; Preferably, the particle size of the Prussian blue sodium ion material is 50nm≤D50≤5μm.

10. A sodium ion battery, comprising a positive electrode plate, characterized in that: The active material in the positive electrode plate includes the Prussian blue sodium ion material according to claim 9.

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