Positive electrode material and preparation method therefor, positive electrode sheet, and sodium-ion battery

Abstract

The present application relates to the technical field of sodium-ion batteries, and provides a positive electrode material and a preparation method therefor, a positive electrode sheet, and a sodium-ion battery, wherein the positive electrode material comprises a Prussian blue material having a molecular formula of NaxFeyFe(CN)zF6-z•nH2O•mHCl, wherein 1.90≤x≤2.20, 0.9≤y≤1.2, 4.20≤z≤5.50, 1.00≤n≤1.75, and 0.001≤m≤0.007. The present application is beneficial for improving the structural stability of the positive electrode material, and enabling the efficient diffusion channel of sodium ions to be optimized, thereby improving the sodium storage capacity and cycle stability. By means of the synergistic effect between the ions, the problem of a high crystal water content in the positive electrode material is solved, the structural stability and the stability of the electrochemical sodium storage performance of the positive electrode material are improved, the production cost is also reduced, and the application range of the sodium ion battery is expanded.

Description

Positive electrode materials and their preparation methods, positive electrode sheets and sodium-ion batteries Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a positive electrode material and its preparation method, a positive electrode sheet, and a sodium-ion battery. Background Technology

[0002] Prussian blue (PB) and its analogues (PBAs) are composed of a three-dimensional framework structure, providing wide channels for the insertion and extraction of sodium ions, making them a relatively ideal cathode material for sodium-ion batteries (SIB). However, the presence of a large number of water molecules and vacancies in PBA materials significantly reduces the number of sodium ion storage sites, and transition metal ions in the metal-organic framework are prone to precipitation during cycling, resulting in limited sodium storage capacity and poor cycle stability of PBA cathode materials. In recent years, various PBA modification techniques have been developed, significantly improving their electrochemical sodium storage performance.

[0003] Metal doping is a fundamental method for adjusting capacity, lifetime, rate performance, and production cost, and has been widely applied in the preparation of SIB materials. Metal ions are typically doped at the M-site or Na-site, with transition metal ions such as Ni... 2+ Co 2+ Cu 2+ Mn 2+ Sn 4+ Replace the metal at position M, K + Typically, doping occurs at the Na site. However, doping with metal cations does not reduce the water of crystallization content in PBAs, and expensive metal doping also increases the production cost of SIB products. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a positive electrode material and its preparation method, a positive electrode sheet and a sodium-ion battery, aiming to solve the technical problem that the Prussian blue sodium battery material has poor rate performance and cycle performance due to its high water content.

[0005] In a first aspect, embodiments of this application provide a positive electrode material, which includes Prussian blue material, the molecular formula of which is Na. x Fe y Fe(CN) z F 6-z ·nH2O·mHCl, where 1.90≤x≤2.20, 0.9≤y≤1.2, 4.20≤z≤5.50, 1.00≤n≤1.75, and 0.001≤m≤0.007.

[0006] In the technical solution of this application embodiment, by controlling the chemical composition of Prussian blue material, introducing fluorine to replace part of the cyanide ions to reduce the content of water of crystallization, and using HCl to occupy the vacancies of water of crystallization, the stability of the cathode material is effectively improved and the electrochemical performance of the cathode material is enhanced.

[0007] In some embodiments, the diffusion coefficient of sodium ions in the above-described Prussian blue material is 3.00 × 10⁻⁶. -13 cm 2 / s~1.00×10 -10 cm 2 / s.

[0008] In this embodiment, controlling the diffusion coefficient of sodium ions in the Prussian blue material within the above-mentioned range is beneficial to improving the transport speed of sodium ions, thereby enabling sodium ions to be inserted and extracted into the cathode material more quickly, which is beneficial to improving the electrochemical performance such as rate performance and cycle performance of sodium-ion batteries using cathode materials.

[0009] Secondly, embodiments of this application provide a method for preparing a positive electrode material, the method comprising: providing a base liquid, the base liquid comprising sodium ions, iron ions and hydrogen fluoride; mixing the base liquid, sodium ferrocyanide solution, ferrous salt solution and sodium salt solution, and aging the mixture to obtain an aged slurry; subjecting the aged slurry to a first solid-liquid separation process to obtain an intermediate product; subjecting the intermediate product to a slurry-forming process to obtain a reaction slurry; and subjecting the reaction slurry to a reaction process to obtain the positive electrode material.

[0010] In the technical solution of this application embodiment, under the high concentration of fluoride ions in the base liquid, fluoride ions with strong complexing ability form complexes with the added ferrous ions and replace part of the cyanide ions, thereby partially introducing fluoride ions into the Prussian blue material. The aging treatment is conducive to the full crystallization of the Prussian blue material, and the reaction treatment further reduces the crystal water inside the Prussian blue material, which is beneficial to improving the stability of the cathode material and improving the electrochemical performance of the cathode material in terms of cycle stability and rate performance.

[0011] In some embodiments, the step of obtaining the above-mentioned base liquid includes: mixing a first solution and a second solution to obtain a base liquid, wherein the first solution includes sodium fluoride and ferric fluoride, and the second solution includes hydrogen fluoride; the pH value of the base liquid is 2.5 to 3.5; the molar ratio of the solute in the sodium ferrocyanide solution, the solute in the ferrous salt solution, and the solute in the sodium salt solution is 1:(1.2 to 1.5):(2 to 3); wherein the concentration of the sodium ferrocyanide solution is 1 mol / L to 2 mol / L; and / or the concentration of the ferrous salt solution is 1.5 mol / L to 2.5 mol / L, and the ferrous salt solution is selected from any one or more of ferrous chloride solution, ferrous sulfate solution, and ferrous acetate solution; The ferrous salt solution may also include a reducing agent and a complexing agent; and / or, the reducing agent is sulfite and / or hydrazine hydrate; and / or, the concentration of the reducing agent in the ferrous salt solution is 0.1 mol / L to 0.5 mol / L; and / or, the complexing agent is ethylenediaminetetraacetic acid and / or citric acid; and / or, the concentration of the complexing agent in the ferrous salt solution is 0.01 mol / L to 0.2 mol / L; and / or, the concentration of the sodium salt solution is 3 mol / L to 5 mol / L, the mass percentage of sodium fluoride in the solute of the sodium salt solution is 10% to 20%, and the remaining sodium salt in the solute of the sodium salt solution is selected from any one or more of sodium chloride, sodium sulfate, sodium acetate, and sodium citrate.

[0012] In this embodiment, controlling the formation steps of the base solution and the composition, ratio, and concentration of each solution within the aforementioned range is beneficial for optimizing the synthesis conditions of the cathode material, thereby improving the overall performance of the cathode material. Simultaneously, controlling the pH value within the aforementioned range is beneficial for improving the effectiveness of fluoride ion doping. Furthermore, optimizing these parameters not only promotes uniform fluoride ion doping but also improves the structural integrity of the cathode material, thereby enhancing its overall performance.

[0013] In some embodiments, the aging treatment temperature is 70℃~90℃, the aging treatment time is 1h~2h; the molar ratio of sodium fluoride to iron fluoride in the first solution is 1:(0.1~0.2); and / or, the total concentration of fluoride ions in the first solution is 2mol / L~4mol / L; and / or, the concentration of the second solution is 5mol / L~8mol / L.

[0014] Controlling the temperature and time of aging treatment, and controlling the concentration of the above solution and the ratio of the amount of solute in the above solution within the corresponding ranges, is more conducive to improving the efficiency and effect of fluoride ion doping, thereby improving the structural stability of the cathode material and enhancing its electrochemical performance.

[0015] In some embodiments, the above intermediate product and acid solution are mixed and slurried to obtain a reaction slurry; during the slurrying process; and / or, the reaction temperature is 110°C to 130°C, and the reaction time is 30 min to 60 min; and / or, the stirring speed during the reaction process is 100 r / min to 300 r / min; and / or, the acid solution is a hydrochloric acid-ethanol solution, and the concentration of hydrogen ions in the acid solution is 0.5 mol / L to 1 mol / L; and / or, the mass ratio of solid to liquid in the reaction slurry is 1:(3 to 4).

[0016] Controlling the slurry treatment steps as described above is beneficial to improving the dispersion effect of the slurry. At the same time, controlling the reaction treatment conditions within the corresponding ranges mentioned above is beneficial to fully utilizing the ethanol-hydrogen chloride system at high temperatures to erode intermediate products and partially replace the azeotropic and water-of-crystallization, thereby further reducing the content of water-of-crystallization in the cathode material and improving the stability and electrochemical performance of the cathode material.

[0017] In some embodiments, the intermediate product is subjected to a second washing and a second drying sequentially before pulping, wherein the conductivity of the washing water after the second washing is ≤150μS / cm and the moisture content in the intermediate product is less than 0.2%.

[0018] By controlling the conditions of the second washing and the second drying, it is beneficial to reduce the moisture content of the reaction slurry obtained after the intermediate product is slurried, which is more conducive to further reducing the content of internal crystallization moisture of the cathode material through reaction treatment, thereby improving the stability and electrochemical performance of the cathode material.

[0019] In some embodiments, the product obtained from the reaction treatment is sequentially subjected to a second solid-liquid separation treatment, a first washing, a first drying, and pulverization to obtain a positive electrode material; and / or, the first washing is performed with alcohol until the pH value of the washing liquid after washing is 5.5 or higher; the first drying is performed under protective gas protection until the mass fraction of ethanol in the material is less than 0.1%, the temperature of the first drying is 110℃ to 150℃, and the oxygen content of the environment during the first drying is less than 1000ppm; the particle size of the positive electrode material obtained after pulverization is 1μm to 5μm.

[0020] Controlling the conditions for the first washing and first drying within the aforementioned range is beneficial for removing residual acid solution and impurities, thereby improving the purity of the cathode material. Simultaneously, controlling the oxygen content during the first drying process and conducting the first drying under a protective gas atmosphere helps reduce oxidation of the cathode material and moisture adsorption. Controlling the particle size of the pulverized cathode material within the aforementioned range is beneficial for improving particle size uniformity and compaction density. Through the synergistic effect of the above steps, the electrochemical performance of sodium-ion batteries using the cathode material is further enhanced.

[0021] Thirdly, embodiments of this application provide a positive electrode sheet, which includes the above-described positive electrode material or a positive electrode material prepared by the above-described method for preparing positive electrode material.

[0022] In this embodiment, thanks to the low water of crystallization content of the cathode material, and since the cathode sheet including the above-mentioned cathode material is prepared from the cathode material of this application, the electrochemical performance of the cathode sheet, such as cycle stability and rate performance, is superior.

[0023] Fourthly, embodiments of this application provide a sodium-ion battery, including a positive electrode sheet, which is the aforementioned positive electrode sheet.

[0024] In this embodiment, since the sodium-ion battery is prepared from the positive electrode sheet of this application, the sodium-ion battery not only has high cycle performance and rate performance, but also the low water content of the positive electrode material reduces the risk of hydrolysis of the electrolyte of the sodium-ion battery, thereby improving the stability and electrochemical performance of the sodium-ion battery.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0027] Figure 1 is a process flow diagram of the preparation process of the cathode material in Example 1 of this application;

[0028] Figure 2 shows the test results of the charge specific capacity and discharge specific capacity of the sodium-ion battery using the positive electrode material of Example 1 of this application. Detailed Implementation

[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0035] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0036] In the description of the embodiments of this application, unless otherwise specified, the solvents of "base liquid", "solution" and "slurry" are selected from at least one of deionized water, deionized water, distilled water, pure water and ultrapure water.

[0037] In the description of the embodiments of this application, "ppm" represents a concentration in parts per million by mass.

[0038] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0039] Firstly, this application provides a cathode material, which includes Prussian blue material with the molecular formula Na. x Fe y Fe(CN) z F 6-z ·nH2O·mHCl, where 1.90≤x≤2.20, 0.9≤y≤1.2, 4.20≤z≤5.50, 1.00≤n≤1.75, and 0.001≤m≤0.007.

[0040] Furthermore, 1.90≤x≤2.16, preferably 2.00≤x≤2.16, for example, the value of x can be 2.00, 2.08 or 2.16, etc., or other values ​​within the above range, which are not limited here;

[0041] Furthermore, 0.93 ≤ y ≤ 1.12, for example, the value of y can be 0.93, 0.97, 1.00, 1.02, 1.05 or 1.12, etc., or other values ​​within the above range, which are not limited here;

[0042] Furthermore, 4.21≤z≤5.50, preferably 4.21≤z≤5.38, for example, the value of z can be 4.21, 4.92, 4.96, 4.99, 5.00, 5.06, 5.08 or 5.38, etc., or other values ​​within the above range, which are not limited here;

[0043] Furthermore, 1.00≤n≤1.74, preferably 1.10≤n≤1.74, for example, the value of n can be 1.10, 1.12, 1.13, 1.19, 1.24, 1.38, 1.44, 1.48, 1.55, 1.58 or 1.74, etc., or other values ​​within the above range, which are not limited here;

[0044] Furthermore, when 0.001≤m≤0.007, the value of m can be 0.001, 0.002, 0.003, 0.004, or 0.007, or other values ​​within the above range, which are not limited here;

[0045] Furthermore, the preferred molecular formula of the Prussian blue material can be Na. 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 ·1.12H₂O·0.003HCl

[0046] Na 2.00 Fe 1.05 Fe(CN) 4.92 F 1.08 ·1.10H₂O·0.003HCl, Na 2.00 Fe 1.12 Fe(CN) 4.21 F 1.79 ·1.48H₂O·0.004HCl, Na 2.00 Fe 1.00 Fe(CN) 5.00 F 1.00 ·1.13H₂O·0.003HCl, Na 2.00 Fe 1.00 Fe(CN) 5.06 F 0.94 ·1.38H₂O·0.003HCl, Na 2.08 Fe 0.97 Fe(CN) 4.96 F 1.04 ·1.44H₂O·0.004HCl, Na 2.16 Fe 0.93 Fe(CN) 5.08 F 0.92 ·1.58H₂O·0.007HCl, Na 2.00 Fe 1.02 Fe(CN) 4.99 F 1.01 ·1.19H₂O·0.003HCl, Na 2.16 Fe 1.12 Fe(CN) 5.38 F 1.01 ·1.55H₂O·0.004HCl, Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 ·1.24H₂O·0.002HCl or Na 2.00 Fe 1.00 Fe(CN)4.99 F 1.01 ·1.74H2O·0.001HCl, or other molecular formulas that conform to the general molecular formula of the above Prussian blue materials, are not limited here.

[0047] In the technical solution of this application embodiment, by controlling the chemical composition of Prussian blue material, introducing fluorine to replace part of the cyanide ions to reduce the content of water of crystallization, and using HCl to occupy the vacancies of water of crystallization, the stability of the cathode material is effectively improved and the electrochemical performance of the cathode material is enhanced.

[0048] Specifically, fluoride ions, with their high electronegativity and small ionic radius, can effectively replace some cyanide ions, forming a stable complex structure. This not only increases the conductivity of the cathode material but also reduces the water of crystallization content, minimizing structural damage caused by water molecules during cycling due to insertion / extraction, thus improving the structural stability of the cathode material. Simultaneously, the doping of fluoride ions optimizes the sodium ion insertion / extraction channels in the cathode material, thereby increasing the sodium ion insertion / extraction rate and enhancing the electrochemical performance of the cathode material in terms of rate capability and cycle performance. The HCl in Prussian blue materials occupies the vacancies in the water of crystallization, reducing the water of crystallization content while preventing structural damage caused by water of crystallization extraction, effectively improving the stability of the cathode material.

[0049] In some embodiments of this application, the diffusion coefficient of sodium ions in the Prussian blue material is 3.00 × 10⁻⁶. -13 cm 2 / s~1.00×10 -10 cm 2 / s.

[0050] The diffusion coefficient of sodium ions in Prussian blue materials is 1.00 × 10⁻⁶. -13 cm 2 / s~1.00×10 -10 cm 2 / s, preferably 3.74×10 -13 cm 2 / s~8.97×10 -11 cm 2 / s, for example, could be 8.97×10 -11 cm 2 / s, 5.67×10 -11 cm 2 / s, 4.89×10 -13 cm 2 / s, 7.69×10 -11 cm 2 / s, 7.57×10 -13 cm 2 / s, 1.32×10 -11 cm 2 / s, 8.65×10 -13 cm 2 / s, 8.12×10 -11 cm 2 / s, 3.74×10 -13 cm 2 / s, 4.72×10 -11 cm 2 / s or 9.23×10 -13 cm 2 / s, etc., can also be other values ​​within the above range, and are not limited here.

[0051] Controlling the diffusion coefficient of sodium ions in Prussian blue materials within the above-mentioned range is beneficial to improving the transport speed of sodium ions, thereby enabling sodium ions to be inserted and extracted into the cathode material more quickly. This is beneficial to improving the electrochemical performance of sodium-ion batteries using cathode materials, such as rate performance and cycle performance.

[0052] In some embodiments, the loose packing density of the positive electrode material is 0.58 g / mL to 0.78 g / mL. For example, the loose packing density can be 0.58 g / mL, 0.60 g / mL, 0.61 g / mL, 0.63 g / mL, 0.64 g / mL, 0.66 g / mL, 0.69 g / mL, or 0.78 g / mL, or other values ​​within the above range, which are not limited here.

[0053] In some embodiments, the tap density of the positive electrode material is 1.15 g / mL to 1.39 g / mL. For example, the tap density can be 1.15 g / mL, 1.16 g / mL, 1.18 g / mL, 1.20 g / mL, 1.21 g / mL, 1.23 g / mL, 1.29 g / mL, 1.31 g / mL, or 1.39 g / mL, or other values ​​within the above range, which are not limited here.

[0054] In some embodiments, the compaction density of the cathode material is 1.78 g / mL to 2.09 g / mL. For example, the compaction density can be 1.78 g / mL, 1.87 g / mL, 1.91 g / mL, 1.93 g / mL, 1.94 g / mL, 1.97 g / mL, 1.98 g / mL, 2.04 g / mL, or 2.09 g / mL, or other values ​​within the above range, which are not limited here.

[0055] Controlling the loose packing density, tapped density, and compacted density of the cathode material within the corresponding ranges mentioned above is beneficial for obtaining cathode materials with improved energy density, thereby improving the electrochemical performance of the cathode material, such as its charge specific capacity and discharge specific capacity.

[0056] In some embodiments, the D10 particle size of the cathode material is 0.3 μm to 0.8 μm. For example, the D10 particle size can be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, or other values ​​within the above range, which are not limited here.

[0057] In some embodiments, the D50 particle size of the cathode material is 2.3 μm to 3.1 μm. For example, the D50 particle size can be 2.3 μm, 2.4 μm, 2.5 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3.1 μm, or other values ​​within the above range, which are not limited here.

[0058] In some embodiments, the D10 and D50 particle sizes of the cathode material are obtained by laser particle size analyzer. The D10 particle size represents the particle size corresponding to a cumulative volume distribution percentage of 10% for the cathode material, and the D50 particle size represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the cathode material.

[0059] Controlling the D10 and D50 particle sizes of the cathode material to be within the corresponding ranges mentioned above is beneficial for obtaining cathode materials with concentrated particle size distribution, thereby improving the consistency of the cathode material during the charge-discharge process and enhancing the electrochemical performance of the cathode material.

[0060] In some embodiments, the iron leaching amount of the positive electrode material is 6.4 ppm to 59.2 ppm. For example, the iron leaching amount can be 6.4 ppm, 6.7 ppm, 10.3 ppm, 11.2 ppm, 11.3 ppm, 12.1 ppm, 12.5 ppm, 13.8 ppm, 15.3 ppm, or 59.2 ppm, or other values ​​within the above range, which are not limited here.

[0061] In some embodiments, the magnetic material content of the positive electrode material is 0.11ppm to 0.14ppm. For example, the magnetic material content can be 0.11ppm, 0.12ppm, or 0.14ppm, or other values ​​within the above range, which are not limited here.

[0062] In some embodiments, the free water content of the cathode material is 103ppm to 399ppm. For example, the free water content can be 103ppm, 109ppm, 137ppm, 168ppm, 178ppm, 189ppm, 198ppm, 212ppm, 256ppm or 399ppm, or other values ​​within the above range, which are not limited here.

[0063] Controlling the iron leaching amount, magnetic material mass, and free water content of the cathode material within the corresponding ranges mentioned above is beneficial to improving the product quality of the cathode material and enhancing its performance in sodium-ion batteries.

[0064] Secondly, this application provides a method for preparing a cathode material, the method comprising: providing a base liquid comprising sodium ions, iron ions and hydrogen fluoride; mixing the base liquid, sodium ferrocyanide solution, ferrous salt solution and sodium salt solution, and aging the mixture to obtain an aged slurry; subjecting the aged slurry to a first solid-liquid separation process to obtain an intermediate product; subjecting the intermediate product to a slurry-forming process to obtain a reaction slurry; and subjecting the reaction slurry to a reaction process to obtain the cathode material.

[0065] In the technical solution of this application embodiment, under the high concentration of fluoride ions in the base liquid, fluoride ions with strong complexing ability form complexes with the added ferrous ions and replace part of the cyanide ions, thereby partially introducing fluoride ions into the Prussian blue material. The aging treatment is conducive to the full crystallization of the Prussian blue material, and the reaction treatment further reduces the crystal water inside the Prussian blue material, which is beneficial to improving the stability of the cathode material and improving the electrochemical performance of the cathode material in terms of cycle stability and rate performance.

[0066] In some embodiments of this application, the step of obtaining the base liquid includes: mixing a first solution and a second solution to obtain the base liquid, wherein the first solution includes sodium fluoride and iron fluoride, and the second solution includes hydrogen fluoride.

[0067] The addition of ferric fluoride provides both fluoride ions and ferric fluoride complex ions, laying the foundation for subsequent fluorine substitution.

[0068] In some embodiments, the pH of the substrate solution is 2.5 to 3.5.

[0069] Too low a pH value is detrimental to the stability of the material structure, while too high a pH value is detrimental to the insertion of fluoride ions. Controlling the pH value within the above range is beneficial to improving the effectiveness of fluoride ion doping.

[0070] In some embodiments, the pH value of the above-mentioned base solution can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.1, 3.2, 3.3, 3.4 or 3.5, or other values ​​within the above range, which are not limited here.

[0071] In some embodiments, the molar ratio of the solute in the sodium ferrocyanide solution, the solute in the ferrous salt solution, and the solute in the sodium salt solution is 1:(1.2-1.5):(2-3).

[0072] Controlling the above molar ratios helps to more precisely control the chemical composition of the final cathode material, making its molecular formula closer to Na. xFe y Fe(CN) z F 6-z The optimal ratio of ·nH₂O·mHCl is crucial. This ratio helps optimize the structural stability and ion diffusion channels of the cathode material, thereby improving its capacity and cycle stability.

[0073] In some embodiments, the molar ratio of the solute in the sodium ferrocyanide solution, the solute in the ferrous salt solution, and the solute in the sodium salt solution can be 1:1.2:2, 1:1.3:2, 1:1.4:2, 1:1.5:2, 1:1.2:2.5, 1:1.3:2.5, 1:1.4:2.5, 1:1.5:2.5, 1:1.2:3, 1:1.3:3, 1:1.4:3, or 1:1.5:3, or other values ​​within the above range, which are not limited here.

[0074] In some embodiments, the concentration of the sodium ferrocyanide solution is 1 mol / L to 2 mol / L.

[0075] In some embodiments, the concentration of the ferrous salt solution is 1.5 mol / L to 2.5 mol / L; the ferrous salt solution is selected from any one or more of ferrous chloride solution, ferrous sulfate solution, and ferrous acetate solution. In some embodiments, the concentration of the sodium ferrocyanide solution can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, or 2.5 mol / L, or other values ​​within the above range, which are not limited here.

[0076] Based on considerations of reaction kinetics and chemical equilibrium, the concentrations of the sodium ferrocyanide solution and the ferrous salt solution are controlled within the aforementioned corresponding ranges to ensure efficient reaction while reducing the risk of side reactions or material structure damage due to excessive reactants. The preferred types of ferrous salts are widely available and moderately priced, contributing to improved economic efficiency of the entire production process. Furthermore, their good solubility in solution facilitates control and operation, contributing to process stability and cost control.

[0077] In some embodiments, the ferrous salt solution also includes a reducing agent and a complexing agent.

[0078] Fe 2+It is crucial to the formation of the framework of Prussian blue-like materials. Maintaining its reduced state is essential for the formation of the correct crystal structure. The presence of a reducing agent helps ensure that ferrous ions remain in the divalent state during synthesis, preventing them from being oxidized to ferric ions (Fe3+). 3+ Complexing agents help form stable complexes with ferrous ions, reducing the risk of premature precipitation or oxidation of ferrous ions in solution, thereby improving the uniform dispersion and stable existence of ferrous ions during the reaction process, which is beneficial for the formation of a uniform crystal structure.

[0079] In some embodiments, the reducing agent is sulfite and / or hydrazine hydrate.

[0080] Sulfites and / or hydrazine hydrate, as reducing agents, help to promote the synthesis reaction, especially the steps involving the reaction of sodium ferrocyanide solution with the base liquid.

[0081] In some embodiments, the concentration of the reducing agent in the ferrous salt solution is 0.1 mol / L to 0.5 mol / L.

[0082] Excessively high concentrations of reducing agent may produce unnecessary side reactions and consume too many resources, while excessively low concentrations may not effectively promote the reduction reaction, affecting the quality of the materials and the progress of the reaction. Controlling the concentration of the reducing agent within the above range helps to balance the efficiency of the reducing agent and the cost of use in the reaction.

[0083] In some embodiments, the concentration of the reducing agent in the ferrous salt solution can be 0.1 mol / L, 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, 0.30 mol / L, 0.35 mol / L, 0.40 mol / L, 0.45 mol / L, or 0.50 mol / L, or other values ​​within the above range, which are not limited here.

[0084] In some embodiments, the complexing agent is ethylenediaminetetraacetic acid (EDTA) and / or citric acid.

[0085] The above-mentioned complexing agents help to form more stable complexes with ferrous ions, which is conducive to the formation of a uniform crystal structure and thus improves the structural stability of the cathode material.

[0086] In some embodiments, the concentration of the complexing agent in the ferrous salt solution is 0.01 mol / L to 0.2 mol / L.

[0087] Controlling the concentration of the complexing agent within the above range helps to improve the effectiveness of the complexation reaction and the controllability of the material structure.

[0088] In some embodiments, the concentration of the complexing agent in the ferrous salt solution can be 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, or 0.2 mol / L, or other values ​​within the above range, which are not limited here.

[0089] In some embodiments, the concentration of the sodium salt solution is 3 mol / L to 5 mol / L, the mass percentage of sodium fluoride in the solute of the sodium salt solution is 10% to 20%, and the remaining sodium salt in the solute of the sodium salt solution is selected from any one or more of sodium chloride, sodium sulfate, sodium acetate, and sodium citrate. In some embodiments, the concentration of the sodium salt solution can be 3 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.7 mol / L, 3.8 mol / L, 3.9 mol / L, 4.0 mol / L, 4.1 mol / L, 4.2 mol / L, 4.3 mol / L, 4.4 mol / L, 4.5 mol / L, 4.6 mol / L, 4.7 mol / L, 4.8 mol / L, 4.9 mol / L, or 5 mol / L, or other values ​​within the above range, which are not limited here.

[0090] By controlling the concentration of the sodium salt solution, the mass ratio of sodium fluoride, and selecting different sodium salts, it is possible to optimize the synthesis conditions of the cathode material, promote the efficient progress of the reaction, regulate the microstructure of the cathode material, improve the electrochemical performance of the cathode material, and simultaneously balance cost and performance.

[0091] In summary, controlling the formation steps of the base solution and the composition, ratio, and concentration of each solution within the above-mentioned range is beneficial to optimizing the synthesis conditions of the cathode material, thereby improving the overall performance of the cathode material. At the same time, optimizing the above parameters not only promotes the uniform doping of fluoride ions but also improves the internal structural integrity of the cathode material, thereby improving the overall performance of the cathode material.

[0092] In some embodiments, the step of mixing the base solution, sodium ferrocyanide solution, ferrous salt solution, and sodium salt solution includes:

[0093] Maintain the temperatures of the sodium ferrocyanide solution, ferrous salt solution, and sodium salt solution, respectively.

[0094] Sodium ferrocyanide solution, ferrous salt solution, and sodium salt solution are added to the base solution during the first mixing time.

[0095] In some embodiments, the temperature of the sodium ferrocyanide solution, the ferrous salt solution, and the sodium salt solution is maintained at 70°C to 90°C.

[0096] In some embodiments, the temperature of the base liquid is maintained at 70°C to 90°C before adding the sodium ferrocyanide solution, ferrous salt solution and sodium salt solution to the base liquid.

[0097] In some embodiments, the temperature of the sodium ferrocyanide solution, ferrous salt solution, sodium salt solution and / or substrate is maintained at the same temperature as the aging treatment.

[0098] In some embodiments, the sodium ferrocyanide solution, the ferrous salt solution, and the sodium salt solution are added to the base solution respectively during the first mixing time; or, the sodium ferrocyanide solution, the ferrous salt solution, and the sodium salt solution are mixed and then added to the base solution during the first mixing time.

[0099] In some embodiments, the first mixing time is 30 min to 60 min, for example, it can be 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0100] In some embodiments, the base solution, sodium ferrocyanide solution, ferrous salt solution, and sodium salt solution are mixed under stirring. The stirring speed can be from 100 r / min to 300 r / min.

[0101] In some embodiments of this application, the aging temperature is 70°C to 90°C, and the aging time is 1h to 2h; the molar ratio of sodium fluoride to iron fluoride in the first solution is 1:(0.1 to 0.2).

[0102] Aging within the above temperature and time range helps reduce the risk of excessively large agglomerations or excessively small particles, thereby promoting the formation of a uniform and ordered crystal structure, improving the conductivity and ion diffusion efficiency of the cathode material, and thus enhancing the battery's sodium storage capacity and cycle stability. In some embodiments of this application, the aging temperature can be 70℃, 72℃, 74℃, 75℃, 76℃, 78℃, 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, or 90℃, or other values ​​within the above range, without limitation; the aging time can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, or 1.8h. The time can be 1.9h or 2h, or other values ​​within the above range, and is not limited here; the molar ratio of sodium fluoride to iron fluoride in the first solution can be 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19 or 1:0.2, or other values ​​within the above range, and is not limited here.

[0103] In some embodiments, the total concentration of fluoride ions in the first solution is 2 mol / L to 4 mol / L.

[0104] By controlling the molar ratio of sodium fluoride to iron fluoride in the first solution within the above range, it is beneficial to achieve uniform doping of fluoride ions in the cathode material. In some embodiments, the total concentration of fluoride ions in the first solution can be 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.7 mol / L, 3.8 mol / L, 3.9 mol / L, or 4 mol / L, or other values ​​within the above range, which are not limited here.

[0105] In some embodiments, the concentration of the second solution is 5 mol / L to 8 mol / L.

[0106] Controlling the concentration of the second solution within the above range helps to suppress side reactions, improve the purity and performance of the cathode material, and also benefits the structural stability of the cathode material. In some embodiments, the concentration of the second solution can be 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.5 mol / L, 5.7 mol / L, 5.8 mol / L, 6.0 mol / L, 6.2 mol / L, 6.4 mol / L, 6.5 mol / L, 6.7 mol / L, 6.8 mol / L, 7.0 mol / L, 7.2 mol / L, 7.4 mol / L, 7.5 mol / L, 7.7 mol / L, 7.8 mol / L, or 8 mol / L, or other values ​​within the above range, which are not limited here.

[0107] Controlling the temperature and time of aging treatment, and controlling the concentration of the above solution and the ratio of the amount of solute in the above solution within the corresponding ranges, is more conducive to improving the efficiency and effect of fluoride ion doping, thereby improving the structural stability of the cathode material and enhancing its electrochemical performance.

[0108] In some embodiments, the first solid-liquid separation process can be carried out by means of atmospheric pressure filtration, pressure filtration, vacuum filtration, centrifugal separation, etc.

[0109] In some embodiments of this application, the above-mentioned intermediate product and acid solution are mixed and slurried to obtain a reaction slurry.

[0110] The above steps help reduce water of crystallization, optimize sodium ion diffusion pathways, improve material purity, enhance the dispersibility of intermediate products, and control microstructure, thereby improving the performance of cathode materials such as high sodium storage capacity, good cycle stability, and rate performance.

[0111] In some embodiments, the reaction temperature is 110°C to 130°C, and the reaction time is 30 min to 60 min.

[0112] Controlling the reaction temperature and time within the above range helps the water of crystallization to escape fully in the form of water vapor, while maintaining the integrity and stability of the cathode material structure. In some embodiments, the reaction temperature can be 110°C, 112°C, 115°C, 117°C, 120°C, 122°C, 125°C, 128°C, or 130°C, or other values ​​within the above range, which are not limited here; the reaction time can be 30 min, 32 min, 35 min, 38 min, 40 min, 42 min, 45 min, 48 min, 50 min, 52 min, 55 min, or 60 min, or other values ​​within the above range, which are not limited here.

[0113] In some embodiments, the stirring speed of the reaction process is 100 r / min to 300 r / min.

[0114] Controlling the stirring speed helps promote uniform mixing of reactants, improve reaction efficiency, control the particle size of the cathode material, and reduce the formation of by-products, thereby contributing to the synthesis of high-performance cathode materials. In some embodiments, the stirring speed of the reaction process can be 100 r / min, 120 r / min, 150 r / min, 200 r / min, 250 r / min, or 300 r / min, or other values ​​within the above range, which are not limited here.

[0115] In some embodiments, the acid solution is a hydrochloric acid-ethanol solution, and the concentration of hydrogen ions in the acid solution is 0.5 mol / L to 1 mol / L.

[0116] This invention utilizes an ethanol-hydrogen chloride system at high temperatures to achieve the erosion of the cathode material and the azeotropic substitution of some of the water of crystallization. Specifically, the reaction treatment of the reaction slurry in this application utilizes the ethanol-hydrogen chloride system at high temperatures to erode the intermediate product and partially substitute the water of crystallization. At high temperatures, some of the water of crystallization and hydrogen chloride form an azeotrope, thereby being released from the intermediate product. The resulting vacancy is occupied by hydrogen chloride, which reduces the water of crystallization content of the Prussian blue material and effectively reduces the structural collapse of the Prussian blue material caused by water removal.

[0117] Furthermore, hydrogen ions can accelerate the formation of vacancies in the cathode material, which are subsequently occupied by chloride ions. Controlling the hydrogen ion concentration within the above range helps to optimize the diffusion channels of sodium ions while removing water of crystallization, thereby increasing the diffusion coefficient of sodium ions. This facilitates the formation of the complex structure unique to Prussian blue materials and improves the rate performance and cycle stability of the cathode material. In addition, the presence of ethanol can act as a dispersant, helping to reduce excessive aggregation of cathode material particles. In some embodiments, the concentration of hydrogen ions in the acid solution can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, or 1 mol / L, or other values ​​within the above range, which are not limited here.

[0118] In some embodiments, the mass ratio of solid to liquid in the reaction slurry is 1:(3-4), that is, the solid-liquid ratio in the reaction slurry is 1:(3-4).

[0119] Controlling the above mass ratio is not only beneficial for removing water of crystallization from intermediate products, but also for reducing agglomeration, and for improving the electrochemical performance, production efficiency, and reducing costs of cathode materials. In some embodiments, the mass ratio of solid to liquid in the reaction slurry can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, or 1:4, or other values ​​within the above range, which are not limited here.

[0120] In summary, controlling the slurry processing within the aforementioned range is beneficial to improving the dispersion effect of the slurry. At the same time, controlling the reaction processing conditions within the aforementioned range is beneficial to fully utilizing the ethanol-hydrogen chloride system at high temperatures to erode intermediate products and partially replace the azeotropic reaction of water of crystallization, thereby further reducing the content of water of crystallization in the cathode material and improving the stability and electrochemical performance of the cathode material.

[0121] In some embodiments, the intermediate product is subjected to a second washing and a second drying process in sequence before pulping.

[0122] In some embodiments, the washing solution for the second wash can be at least one of deionized water, deionized water, distilled water, pure water, and ultrapure water. The conductivity of the washing water after the second wash is less than or equal to 150 μS / cm, that is, the conductivity of the washing solution after the second wash is less than or equal to 150 μS / cm.

[0123] In some embodiments, after the second drying is completed, the moisture content of the intermediate product is less than 0.2%.

[0124] In some embodiments, the second drying may be performed using vacuum drying.

[0125] In some embodiments, the temperature of the second drying process may be lower than the temperature of the reaction process.

[0126] In some embodiments of this application, the product obtained from the reaction treatment is subjected to a second solid-liquid separation treatment, a first washing, a first drying, and pulverization in sequence to obtain a positive electrode material.

[0127] In some embodiments, the pulverized cathode material is sequentially sieved, iron removed, and packaged to obtain the final cathode material.

[0128] Screening, iron removal, and packaging processes help improve the quality of cathode materials in terms of particle size, purity, and storage conditions, thereby enhancing the overall performance of cathode materials in sodium-ion batteries, including improving cycle stability, rate performance, energy density, and extending battery life.

[0129] In some embodiments, the second solid-liquid separation process can be carried out by means of atmospheric pressure filtration, pressure filtration, vacuum filtration, centrifugal separation, etc.

[0130] In some embodiments, the first washing is performed with alcohol until the pH value of the washing solution after washing is 5.5 or higher; the first drying is performed under the protection of a protective gas until the mass fraction of ethanol in the material is less than 0.1%, the temperature of the first drying is 110°C to 150°C, and the oxygen content of the environment during the first drying is less than 1000 ppm; the particle size of the positive electrode material obtained after pulverization is 1 μm to 5 μm.

[0131] Alcohol washing effectively removes residual impurities, improves the purity of the cathode material, reduces the risks posed by impurities in sodium-ion batteries, and enhances the stability and lifespan of sodium-ion batteries. Washing to a pH of 5.5 or higher helps ensure that the cathode material can be used in a neutral or near-neutral environment, which is beneficial for improving the battery's cycle performance and stability.

[0132] Conducting the first drying under a protective gas atmosphere effectively reduces the risk of oxidation of the cathode material due to contact with oxygen in the air, minimizes byproducts, and maintains the electrochemical activity of the cathode material. Controlling the first drying temperature to 110℃–150℃ helps to rapidly evaporate ethanol and control its mass fraction to less than 0.1%, while minimizing the content of water of crystallization in the cathode material, improving its structural stability, and reducing the negative impact of moisture precipitation during battery cycling on the performance of sodium-ion batteries. Controlling the oxygen content in the environment during the first drying process to less than 1000 ppm helps to provide a near-oxygen-free environment, further reducing the possibility of oxidation. In some embodiments, the temperature of the first drying can be 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, or 150°C, or other values ​​within the above range, which are not limited here; the particle size of the positive electrode material obtained after pulverization can be 1μm, 1.5μm, 2μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, or 5μm, or other values ​​within the above range, which are not limited here.

[0133] Controlling the particle size of the pulverized cathode material within the aforementioned range is beneficial for improving the particle size uniformity and compaction density of the cathode material. Through the synergistic effect of the above steps, the electrochemical performance of sodium-ion batteries is further enhanced.

[0134] Furthermore, in some embodiments, the protective gas for the first drying is nitrogen, the first drying is carried out in an oven, and the ambient oxygen content during the first drying refers to the oxygen content in the oven.

[0135] In a third aspect, this application provides a positive electrode sheet, which includes the above-described positive electrode material or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0136] In this embodiment, thanks to the low water of crystallization content of the cathode material, and since the cathode sheet including the above-mentioned cathode material is prepared from the cathode material of this application, the electrochemical performance of the cathode sheet, such as cycle stability and rate performance, is superior.

[0137] Fourthly, this application provides a sodium-ion battery, including a positive electrode, which is the aforementioned positive electrode.

[0138] In this embodiment, since the sodium-ion battery is prepared from the positive electrode sheet of this application, the sodium-ion battery not only has high cycle performance and rate performance, but also the low water content of the positive electrode material reduces the risk of hydrolysis of the electrolyte of the sodium-ion battery, thereby improving the stability and electrochemical performance of the sodium-ion battery.

[0139] Fifthly, this application provides an electrical device including a sodium-ion battery, which is the sodium-ion battery described above. In this embodiment, the electrical device includes the aforementioned sodium-ion battery, thus exhibiting good stability and electrochemical performance.

[0140] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0141] I. Preparation Method

[0142] Example 1

[0143] Referring to the process flow diagram of the positive electrode material shown in Figure 1, sodium fluoride and iron fluoride are mixed to prepare a first solution, with a molar ratio of sodium fluoride to iron fluoride of 1:0.15 and a fluoride ion concentration of 3.45 mol / L in the first solution. The first solution is then mixed with a second solution, which is a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution is adjusted to 3.1 to prepare a base solution.

[0144] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0145] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 ·1.12H2O·0.003HCl.

[0146] The obtained cathode material test data are as follows:

[0147] Table 1

[0148] Example 2

[0149] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0150] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0151] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.05 Fe(CN) 4.92 F 1.08 ·1.10H2O·0.003HCl.

[0152] The obtained cathode material test data are as follows:

[0153] Table 2

[0154] Example 3

[0155] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.3. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0156] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent, with a concentration of 0.08 mol / L in the ferrous salt solution. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0157] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.12 Fe(CN) 4.21 F 1.79 ·1.48H2O·0.004HCl.

[0158] The obtained cathode material test data are as follows:

[0159] Table 3

[0160] Example 4

[0161] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2 and a fluoride ion concentration of 2 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0162] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0163] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00Fe 1.00 Fe(CN) 5.00 F 1.00 ·1.13H2O·0.003HCl.

[0164] The obtained cathode material test data are as follows:

[0165] Table 4

[0166] Example 5

[0167] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 1.5 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0168] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent, with a concentration of 0.08 mol / L in the ferrous salt solution. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0169] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.00 Fe(CN) 5.06 F 0.94 ·1.38H2O·0.003HCl.

[0170] The obtained cathode material test data are as follows:

[0171] Table 5

[0172] Example 6

[0173] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 2.5 to prepare a base solution.

[0174] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0175] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.08 Fe 0.97 Fe(CN) 4.96 F 1.04 ·1.44H2O·0.004HCl.

[0176] The obtained cathode material test data are as follows:

[0177] Table 6

[0178] Example 7

[0179] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 2.0 to prepare a base solution.

[0180] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0181] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.16 Fe 0.93 Fe(CN) 5.08 F 0.92 ·1.58H2O·0.007HCl.

[0182] The obtained cathode material test data are as follows:

[0183] Table 7

[0184] Example 8

[0185] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0186] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 2 mol / L for sodium ferrocyanide, 2.5 mol / L for ferrous salt, and 3 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.5 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.2 mol / L in the ferrous salt solution. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0187] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.02 Fe(CN) 4.99 F 1.01 ·1.19H2O·0.003HCl.

[0188] The obtained cathode material test data are as follows:

[0189] Table 8

[0190] Example 9

[0191] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0192] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1:1.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0193] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second wash). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.8 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.16 Fe 1.12 Fe(CN) 5.38 F 1.01 ·1.55H2O·0.004HCl.

[0194] The obtained cathode material test data are as follows:

[0195] Table 9

[0196] Example 10

[0197] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0198] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0199] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second washing). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.5 mol / L hydrochloric acid-ethanol solution was added to slurry the mixture, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2 The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na.2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 ·1.24H2O·0.002HCl.

[0200] The obtained cathode material test data are as follows:

[0201] Table 10

[0202] Example 11

[0203] Sodium fluoride and ferric fluoride were mixed to prepare a first solution, with a molar ratio of sodium fluoride to ferric fluoride of 1:0.2. The fluoride ion concentration in the first solution was 3.45 mol / L. The first solution was then mixed with a second solution, which was a 6.5 mol / L hydrogen fluoride solution. The pH of the mixed solution was adjusted to 3.1 to prepare a base solution.

[0204] Sodium ferrocyanide, ferrous salt, and sodium salt were prepared into solutions with concentrations of 1.5 mol / L for sodium ferrocyanide, 2 mol / L for ferrous salt, and 4 mol / L for sodium salt. The temperature of all solutions was maintained at 80°C. The ferrous salt was ferrous chloride. Sodium sulfite was added to the ferrous salt solution at a concentration of 0.3 mol / L. Ethylenediaminetetraacetic acid (EDTA) was used as the complexing agent at a concentration of 0.08 mol / L. The sodium salt solution contained 15% sodium fluoride by mass, with the remainder being sodium chloride. The molar ratio of the solutes in the sodium ferrocyanide, ferrous chloride, and sodium salt solutions was 1:1.35:2.5. Under stirring, all three solutions were added to the bottom liquid over 45 minutes. The reaction was continued at 80°C for 1.5 hours to obtain a reaction slurry.

[0205] The reaction slurry was filtered and washed with pure water until the conductivity of the washing solution was ≤150 μS / cm (second washing). The resulting washing material was vacuum dried (second drying) until the moisture content was less than 0.2%, yielding an intermediate product. The intermediate product was transferred to a sealed reactor, and a 0.3 mol / L hydrochloric acid-ethanol solution was added to slurry it, obtaining a reaction slurry with a solid-liquid ratio of 1:3.5. The sealed reactor was then heated to 120℃ and the pressure was 3.3 kg / cm². 2The reaction slurry was reacted under these conditions for 45 minutes with a stirring speed of 180 r / min. After cooling, it was filtered and washed using alcohol as the washing solution. Washing was stopped when the pH of the washing solution reached 5.5 or higher. The washed material was then subjected to a first drying process using a nitrogen gas stream at a temperature of 130℃. During the first drying, the oxygen content in the oven was maintained below 1000 ppm. Drying was stopped when the alcohol content in the material was below 0.1 wt%. The material was then pulverized until the particle size was 2.7 μm, at which point pulverization was stopped, yielding the positive electrode material with the specific chemical formula Na. 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 ·1.74H2O·0.001HCl.

[0206] The obtained cathode material test data are as follows:

[0207] Table 11

[0208] Comparative Example 1

[0209] The difference from Example 1 is that sodium fluoride and ferric fluoride were replaced with equal amounts of sodium chloride and ferric chloride, respectively, resulting in a comparative cathode material with the specific chemical formula Na. 2.00 Fe 1.00 Fe(CN) 5.75 F 0.25 ·1.65H2O·0.002HCl.

[0210] The test data of the Prussian blue sodium battery material obtained are as follows:

[0211] Table 12

[0212] Comparative Example 2

[0213] The difference from Example 1 is that hydrogen fluoride is not added, resulting in a comparative cathode material with the specific chemical formula Na. 2.00 Fe 1.00 Fe(CN) 5.55 F 0.45 ·1.45H2O·0.001HCl.

[0214] The test data of the Prussian blue sodium battery material obtained are as follows:

[0215] Table 13

[0216] Comparative Example 3

[0217] Preparation of Prussian blue-type cathode material: carbon-manganese nickel ferrocyanide:

[0218] (1) Weigh 0.04 mol of sodium ferrocyanide and 20 mg of activated Vulcan carbon and dissolve them in 100 mL of deionized water to prepare solution A, wherein the concentration of sodium ferrocyanide is 0.4 mol / L and the concentration of Vulcan carbon is 0.2 g / L;

[0219] (2) Weigh 0.032 mol manganese sulfate and 0.128 mol sodium citrate, dissolve them in 80 mL of deionized water to prepare solution B, wherein the concentration of manganese sulfate is 0.4 mol / L and the molar ratio of manganese sulfate to sodium citrate is 1:4;

[0220] (3) Weigh 0.008 mol of nickel sulfate and 0.032 mol of sodium citrate, dissolve them in 20 mL of deionized water, and prepare solution C. The concentration of nickel sulfate is 0.4 mol / L, the molar ratio of nickel sulfate to sodium citrate is 1:4, and the volume ratio of solution A and solution B to solution C is 1:0.8:0.2.

[0221] (4) Place solution A on a magnetic stirrer and stir. Heat to 60°C. Use a peristaltic pump to add solution B dropwise to solution A which is being stirred at high speed. A white precipitate is formed during the dropwise addition. The dropwise addition rate is 0.25 mL / min. The precursor solution is obtained.

[0222] (5) Continue stirring the precursor solution A for 2 hours, and use a peristaltic pump to add solution C dropwise to the high-speed stirred precursor solution A at a rate of 0.25 mL / min.

[0223] (6) Continue stirring the mixed solution for 0.5 hours and then let it stand for 6 hours;

[0224] (7) After standing, the mixed solution was centrifuged to obtain a light green precipitate. The light green precipitate was washed, centrifuged, and then dried in a vacuum at 120°C for 24 hours to obtain Prussian blue cathode material.

[0225] II. Testing Methods

[0226] Property testing of cathode materials

[0227] The free water content was tested using the Karl Fischer coulometric method;

[0228] The water of crystallization was tested using the high-temperature weight loss method.

[0229] The D10 / D50 / D90 particle sizes were measured using a laser particle size analyzer based on laser diffraction.

[0230] The BET specific surface area was tested using a BET analyzer and the nitrogen adsorption method.

[0231] Impurity elements were tested using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0232] The magnetic material was collected using a magnet, then dissolved in aqua regia, and obtained using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0233] Iron leaching amount: Add 1g of the test sample to 100mL of 0.1mol / L hydrogen fluoride-ethanol solution, stir and dissolve at 45℃ for 30min, then filter, and measure the iron content in the filtrate, which is the iron leaching amount.

[0234] Loose packing density was tested using the funnel method, in accordance with GB / T 31057.1-2014.

[0235] The tapped density was tested using a tapped density meter, with 5000 vibrations.

[0236] The compaction density was tested using a compaction density meter with a test pressure of 3T and a compaction time of 30s.

[0237] Chloride ions were tested using a chloride ion selective electrode.

[0238] The sodium ion diffusion coefficient was determined by electrochemical impedance spectroscopy (EIS).

[0239] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0240] The materials obtained above are assembled into a button cell. The assembly process is as follows:

[0241] The positive electrode material obtained in the examples or comparative examples was mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, as a binder) in a mass ratio of 85:10:5, and the mass was weighed to an accuracy of 0.001g to obtain a positive electrode active mixture. Using carbon-coated aluminum foil as the current collector, the positive electrode active mixture was mixed with N-methylpyrrolidone and stirred to form a slurry. The slurry was uniformly coated onto the carbon-coated aluminum foil, dried in an oven at 100°C, and cut into positive electrode sheets with a diameter of 15mm and a thickness of 0.10mm. The positive electrode sheets were weighed to an accuracy of 0.0001g.

[0242] Battery assembly

[0243] In an inert gas glove box with water and oxygen contents ≤0.0005%, a coin cell was assembled using a sodium metal sheet as the negative electrode, a polypropylene microporous membrane as the separator, and an electrolyte consisting of 1 mol / L sodium hexafluorophosphate and a mixed carbonate-based organic solvent [ethylene carbonate (EC) / diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) (the volume ratio of EC, DEC, and FEC is 1:1:0.05)]. After sealing, the coin cell was tested using a sodium-ion battery electrochemical performance tester.

[0244] Battery testing

[0245] The fabricated button cells were subjected to charge-discharge cycles at 25°C using a sodium-ion battery electrochemical performance tester. The charge-discharge tests are as follows:

[0246] a) 0.2C rate charging, with a charging voltage limit of 4.2V;

[0247] b) Discharge at a 0.2C rate current, with a discharge termination voltage of 2.0V.

[0248] The button cells were placed in a constant temperature chamber (25±0.2℃) for cycle performance testing. After 1000 cycles at 1C, the capacity retention was 89.9% (for conventional Prussian blue sodium battery materials, the capacity retention after 1000 cycles is generally below 85%). The test results are as follows:

[0249] Table 14

[0250] As can be seen from the data in Table 14, the cathode materials in this application embodiment all have a capacity retention rate of over 86% after 1000 cycles at 1C, and a first charge specific capacity of over 150mAh / g at 0.2C; the first discharge specific capacity of over 144mAh / g at 0.2C. This indicates that the overall electrical performance of the cathode materials in this application embodiment is significantly better than that of the Prussian blue sodium battery materials in Comparative Examples 1 to 3.

[0251] Furthermore, Figure 2 shows the test results of the charge specific capacity and discharge specific capacity of the sodium-ion battery with the cathode material of Example 1. As can be seen from Figure 2, the cathode material of Example 1 has excellent charge and discharge performance.

[0252] Comparative Example 1 shows that the chemical formula of the cathode material is Na. 2.00 Fe 1.00 Fe(CN) 5.75 F 0.25 The chemical formula of the comparative cathode material in Comparative Example 2 is Na, which is 1.65H₂O·0.002HCl. 2.00 Fe1.00 Fe(CN) 5.55 F 0.45 The formula ·1.45H₂O·0.001HCl indicates that the content of cyanide ions and fluoride ions in the Prussian blue material of this application is Na x Fe y Fe(CN) z F 6-z The content of fluoride ions in the cathode materials of Comparative Examples 1 and 2 is lower than that in the Prussian blue material obtained in the embodiments of this application, which results in the electrochemical performance of the sodium-ion batteries corresponding to the cathode materials of Comparative Examples 1 and 2 being worse than that of the sodium-ion batteries corresponding to the cathode materials obtained in the embodiments of this application.

[0253] Table 14 shows the electrochemical performance results of coin cells with the cathode materials provided in the examples and the electrochemical performance results of coin cells with the cathode materials provided in Comparative Examples 1 to 3. This demonstrates that by controlling the chemical composition of the Prussian blue material, introducing fluorine to replace part of the cyanide ions to reduce the water of crystallization content, and utilizing HCl to occupy the vacancies in the water of crystallization, this application effectively improves the stability of the cathode material and enhances its electrochemical performance.

[0254] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes Prussian blue, and the molecular formula of Prussian blue is Na. x Fe y Fe(CN) z F 6-z ·nH2O·mHCl, where 1.90≤x≤2.20, 0.9≤y≤1.2, 4.20≤z≤5.50, 1.00≤n≤1.75, and 0.001≤m≤0.

007.

2. The cathode material according to claim 1, characterized in that, The diffusion coefficient of sodium ions in the Prussian blue material is 3.00 × 10⁻⁶. -13 cm 2 / s~1.00×10 -10 cm 2 / s.

3. A method for preparing a positive electrode material, characterized in that, The method for preparing the cathode material includes: A base liquid is provided, the base liquid comprising sodium ions, iron ions, and hydrogen fluoride; The base liquid, sodium ferrocyanide solution, ferrous salt solution and sodium salt solution are mixed and then aged to obtain aged slurry; The aged slurry undergoes a first solid-liquid separation process to obtain an intermediate product; The intermediate product is subjected to pulping treatment to obtain a reaction slurry; The reaction slurry is processed to obtain the positive electrode material.

4. The method for preparing the cathode material according to claim 3, characterized in that, The steps for obtaining the base liquid include: mixing a first solution and a second solution to obtain the base liquid, wherein the first solution includes sodium fluoride and iron fluoride, and the second solution includes hydrogen fluoride; The pH value of the substrate solution is 2.5–3.5; The molar ratio of the solute in the sodium ferrocyanide solution, the solute in the ferrous salt solution, and the solute in the sodium salt solution is 1:(1.2-1.5):(2-3). The concentration of the sodium ferrocyanide solution is 1 mol / L to 2 mol / L. And / or, the concentration of the ferrous salt solution is 1.5 mol / L to 2.5 mol / L, and the ferrous salt solution is selected from any one or more of ferrous chloride solution, ferrous sulfate solution, and ferrous acetate solution; And / or, the ferrous salt solution further includes a reducing agent and a complexing agent; And / or, the reducing agent is sulfite and / or hydrazine hydrate; And / or, the concentration of the reducing agent in the ferrous salt solution is 0.1 mol / L to 0.5 mol / L; And / or, the complexing agent is ethylenediaminetetraacetic acid and / or citric acid; And / or, the concentration of the complexing agent in the ferrous salt solution is 0.01 mol / L to 0.2 mol / L; And / or, the concentration of the sodium salt solution is 3 mol / L to 5 mol / L, the mass percentage of sodium fluoride in the solute of the sodium salt solution is 10% to 20%, and the remaining sodium salt in the solute of the sodium salt solution is selected from any one or more of sodium chloride, sodium sulfate, sodium acetate and sodium citrate.

5. The method for preparing the cathode material according to claim 3 or 4, characterized in that, The aging process is carried out at a temperature of 70℃ to 90℃ for 1 hour to 2 hours. The molar ratio of sodium fluoride to ferric fluoride in the first solution is 1:(0.1-0.2); And / or, the total concentration of fluoride ions in the first solution is 2 mol / L to 4 mol / L; And / or, the concentration of the second solution is 5 mol / L to 8 mol / L.

6. The method for preparing the cathode material according to claim 3, characterized in that, The intermediate product and acid solution are mixed and slurried to obtain a reaction slurry; And / or, the reaction treatment temperature is 110℃~130℃, and the reaction treatment time is 30min~60min; And / or, the acid solution is a hydrochloric acid-ethanol solution, and the concentration of hydrogen ions in the acid solution is 0.5 mol / L to 1 mol / L; And / or, the mass ratio of solids to liquids in the reaction slurry is 1:(3-4).

7. The method for preparing the cathode material according to claim 3, characterized in that, The intermediate product is subjected to a second washing and a second drying process before the pulping treatment. The conductivity of the washing water after the second washing is ≤150μS / cm, and the moisture content of the intermediate product is less than 0.2%.

8. The method for preparing the cathode material according to claim 3, characterized in that, The product obtained from the reaction treatment is subjected to a second solid-liquid separation treatment, a first washing, a first drying, and pulverization in sequence to obtain the positive electrode material; And / or, the first washing is performed with alcohol until the pH of the washing solution after washing is 5.5 or higher; The first drying is carried out under the protection of a protective gas until the mass fraction of ethanol in the material is less than 0.1%, the temperature of the first drying is 110℃~150℃, and the oxygen content of the environment during the first drying is less than 1000ppm. The particle size of the positive electrode material obtained after pulverization is 1μm to 5μm.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 2 or the positive electrode material prepared by the method for preparing the positive electrode material according to any one of claims 3 to 8.

10. A sodium-ion battery, comprising a positive electrode, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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