Positive electrode material and preparation method thereof, positive electrode plate and sodium ion battery

Abstract

The invention provides a positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery, and belongs to the technical field of sodium ion batteries, the positive electrode material comprises a Prussian blue material, the molecular formula of the Prussian blue material is NaxFeyFe (CN) zF6-z.nH2O.mHCl, 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. According to the invention, the structural stability of the positive electrode material is improved, and meanwhile, an efficient diffusion channel of sodium ions is optimized, so that the sodium storage capacity and the cycling stability are improved. Through the synergistic effect of the ions, the problem that the content of crystal water in the positive electrode material is high is solved, the structural stability of the positive electrode material and the stability of electrochemical sodium storage performance are improved, meanwhile, the production cost is reduced, and the application range of the sodium ion battery is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery. Background Art

[0002] Prussian blue (PB) and its analogs (PBAs) are composed of a three-dimensional framework structure, which can provide a wide channel for the insertion and extraction of sodium ions. Prussian blue and its analogs are an ideal cathode material for sodium ion batteries (SIBs). However, there are a large number of water molecules and vacancies in PBAs, which greatly reduce the storage sites of sodium ions, and the transition metal ions in the metal organic framework are easily precipitated during the cycle, resulting in limited sodium storage capacity and poor cycle stability of PBAs cathode materials. In recent years, a variety of PBAs modification technologies have been studied, which have significantly improved their electrochemical sodium storage performance.

[0003] Among them, metal element doping is a basic method to adjust capacity, life, rate performance and production cost, and has been widely used in the preparation of SIB materials. Metal ions are usually doped at the M or Na position. Transition metal ions, such as Ni 2+ 、Co 2+ , Cu 2+ , Mn 2+ Sn 4+ etc. to partially replace the metal in the M position, K + Usually doped at the Na position. However, doping with metal cations cannot reduce the crystalline water content in PBAs, and expensive metal doping will also increase the production cost of SIB products. Summary of the invention

[0004] In view of the technical problems existing in the background technology, the present application provides a positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery, aiming to solve the technical problem that the Prussian blue sodium battery material has poor rate performance and cyclability due to the high content of crystalline water.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode material, the positive electrode material includes a Prussian blue material, the molecular formula of the Prussian blue material is Na x Fe y Fe(CN) z F 6-z ·nH 2 O·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.

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

[0007] In some embodiments, the diffusion coefficient of sodium ions in the Prussian blue material is 3.00×10 -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 range is beneficial to increasing the transmission speed of sodium ions, thereby allowing sodium ions to be embedded in and extracted from the positive electrode material more quickly, which is beneficial to improving the electrochemical properties of the sodium ion battery using the positive electrode material, such as the rate performance and cycle performance.

[0009] In the second aspect, an embodiment of the present application provides a method for preparing a positive electrode material, which comprises: 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 subjecting the mixture to aging treatment to obtain an aged slurry; subjecting the aged slurry to a first solid-liquid separation treatment to obtain an intermediate product; subjecting the intermediate product to a slurry treatment to obtain a reaction slurry; and subjecting the reaction slurry to a reaction treatment to obtain a positive electrode material.

[0010] In the technical solution of the embodiment of the present application, in the high concentration fluoride ion environment of the base liquid, the fluoride ions with strong complexing ability form a complex with the added ferrous ions and replace part of the cyanide, thereby partially introducing fluoride ions into the Prussian blue material. The aging treatment is beneficial to the full crystallization of the Prussian blue material, and the reaction treatment further reduces the crystallization water inside the Prussian blue material, which is beneficial to improve the stability of the positive electrode material and improve the electrochemical properties of the positive electrode material in terms of cycle stability and rate performance.

[0011] In some embodiments, the step of obtaining the above-mentioned base solution includes: mixing a first solution and a second solution to obtain a base solution, wherein the first solution includes sodium fluoride and ferric fluoride, and the second solution includes hydrogen fluoride; the pH value of the base solution is 2.5-3.5; the amount of solute of the sodium ferrocyanide solution, the solute of the ferrous salt solution and the solute of the sodium salt solution is 1:(1.2-1.5):(2-3); wherein the concentration of the sodium ferrocyanide solution is 1 mol / L-2 mol / L; and / or the concentration of the ferrous salt solution is 1.5 mol / L-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 also 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 proportion 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 above range is conducive to optimizing the synthesis conditions of the positive electrode material, thereby improving the overall performance of the positive electrode material; at the same time, controlling the pH value within the above range is conducive to improving the effectiveness of fluoride ion doping. In addition, by optimizing the above parameters, not only the uniform doping of fluoride ions is promoted, but also the structural integrity of the positive electrode material is improved, thereby improving the overall performance of the positive electrode material.

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

[0014] Controlling the temperature and time of the aging treatment, and controlling the concentration of the above-mentioned solution and the ratio of the amount of solute in the above-mentioned solution to be within the above-mentioned corresponding ranges, is more conducive to improving the efficiency and effect of fluorine ion doping, thereby helping to improve the structural stability of the positive electrode material and improve the electrochemical performance of the positive electrode material.

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

[0016] The steps of controlling the slurry treatment as described above are beneficial to improving the dispersion effect of the slurry; at the same time, controlling and reacting the treatment conditions within the above-mentioned corresponding range is beneficial to making full use of the ethanol-hydrogen chloride system at high temperature to erode the intermediate product and the azeotropic and replacement of part of the crystalline water, thereby further reducing the content of crystalline water in the positive electrode material and improving the stability and electrochemical performance of the positive electrode material.

[0017] In some embodiments, the intermediate product undergoes a second washing and a second drying in sequence before the slurry treatment, wherein the conductivity of the washing water after the second washing is ≤150 μS / 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 crystallized moisture inside the positive electrode material through reaction treatment, thereby improving the stability and electrochemical performance of the positive electrode 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, alcohol is used for the first washing until the pH value of the washing liquid after washing is 5.5 and above; 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°C to 150°C, and the ambient oxygen content 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 of the first washing and the first drying within the above range is conducive to removing residual acid solution and impurities and improving the purity of the positive electrode material. At the same time, controlling the ambient oxygen content during the first drying and performing the first drying under the protection of a protective gas is conducive to reducing the oxidation of the positive electrode material and the adsorption of moisture. Controlling the particle size of the positive electrode material after pulverization within the above range is conducive to improving the particle size uniformity and compaction density of the positive electrode material. The synergistic effect of the above steps is more conducive to improving the electrochemical performance of the sodium ion battery using the positive electrode material.

[0021] In a third aspect, an embodiment of the present application provides a positive electrode plate, which includes the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned method for preparing the positive electrode material.

[0022] In this embodiment, thanks to the lower crystalline water content of the positive electrode material, since the positive electrode plate including the above-mentioned positive electrode material is prepared from the positive electrode material of the present application, the electrochemical properties such as cycle stability and rate performance of the positive electrode plate are better.

[0023] In a fourth aspect, an embodiment of the present application provides a sodium ion battery, comprising a positive electrode plate, which is the positive electrode plate described above.

[0024] In this embodiment, since the above-mentioned sodium ion battery is prepared by the positive electrode sheet of the present application, the sodium ion battery not only has high cycle performance and rate performance, but also the lower crystalline 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 the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 This is a process flow chart for preparing the positive electrode material in Example 1 of the present application;

[0028] Figure 2 This is a graph showing the test results of the charge specific capacity and discharge specific capacity of a sodium ion battery using the positive electrode material of Example 1 of the present application. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0031] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0034] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0035] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise specified, the solvent of the "base liquid", "solution" or "slurry" is selected from at least one of deionized water, secondary water, distilled water, pure water and ultrapure water.

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

[0038] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0039] In a first aspect, the present application provides a positive electrode material, which includes a Prussian blue material, the molecular formula of which is Na x Fe y Fe(CN) z F 6-z ·nH 2 O·mHCl, wherein 1.90≤x≤2.20, 0.9≤y≤1.2, 4.20≤z≤5.50, 1.00≤n≤1.75, 0.001≤m≤0.007.

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

[0041] Further, 0.93≤y≤1.12, for example, the value of y may 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 herein;

[0042] Further, 4.21≤z≤5.50, preferably 4.21≤z≤5.38, for example, the value of z may 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] Further, 1.00≤n≤1.74, preferably 1.10≤n≤1.74, for example, the value of n may 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] Further, when 0.001≤m≤0.007, the value of m may be 0.001, 0.002, 0.003, 0.004 or 0.007, or other values ​​within the above range, which are not limited herein;

[0045] Further, the molecular formula of the preferred Prussian blue material can be Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 1.12H 2 O·0.003HCl、Na 2.00 Fe 1.05 Fe(CN) 4.92 F 1.08 1.10H 2 O·0.003HCl、Na 2.00 Fe 1.12 Fe(CN) 4.21 F 1.79 1.48H 2 O·0.004HCl、Na 2.00 Fe 1.00 Fe(CN) 5.00 F 1.00 1.13H 2 O·0.003HCl、Na 2.00 Fe 1.00 Fe(CN) 5.06 F 0.94 1.38H 2 O·0.003HCl、Na 2.08 Fe 0.97 Fe(CN) 4.96 F 1.04 1.44H 2 O·0.004HCl、Na 2.16 Fe 0.93 Fe(CN) 5.08 F 0.92 1.58H 2 O·0.007HCl、Na 2.00 Fe 1.02 Fe(CN) 4.99 F 1.01 1.19H 2 O·0.003HCl、Na 2.16 Fe 1.12 Fe(CN) 5.38 F 1.01 1.55H 2 O·0.004HCl、Na 2.00 Fe 1.00 Fe(CN)4.99 F 1.01 1.24H 2 O·0.002HCl or Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 1.74H 2 O·0.001HCl, etc., or other molecular formulas that conform to the molecular formula of the above-mentioned Prussian blue material, are not limited here.

[0046] In the technical solution of the embodiment of the present application, by controlling the chemical composition of the Prussian blue material, introducing fluorine element to replace part of the cyanide ions to reduce the content of crystallization water and using HCl to occupy the crystallization water vacancies, the stability of the positive electrode material is effectively improved and the electrochemical performance of the positive electrode material is improved.

[0047] Specifically, fluoride ions have high electronegativity and small ionic radius, and can effectively replace part of cyanide ions to form a stable complex structure, which not only increases the conductivity of the positive electrode material, but also reduces the content of crystal water, and reduces the damage to the structure of the positive electrode material caused by the deintercalation of water molecules during the cycle, thereby improving the structural stability of the positive electrode material; at the same time, due to the doping of fluoride ions, the deintercalation channel of sodium ions in the positive electrode material is optimized, thereby increasing the deintercalation speed of sodium ions and improving the electrochemical performance of the positive electrode material in terms of rate performance and cycle performance. HCl in the Prussian blue material occupies the vacancy of crystal water, while reducing the content of crystal water, avoiding the structural damage of the positive electrode material caused by the deintercalation of crystal water, and effectively improving the stability of the positive electrode material.

[0048] In some embodiments of the present application, the diffusion coefficient of sodium ions in the above Prussian blue material is 3.00×10 - 13 cm 2 / s~1.00×10 -10 cm 2 / s.

[0049] The diffusion coefficient of sodium ions in Prussian blue is 1.00×10 -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, it can 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., and may also be other values ​​within the above range, which are not limited here.

[0050] Controlling the diffusion coefficient of sodium ions in the Prussian blue material within the above range is beneficial to increasing the transmission speed of sodium ions, so that sodium ions can be embedded in and extracted from the positive electrode material more quickly, which is beneficial to improving the electrochemical properties of sodium ion batteries using the positive electrode material, such as rate performance and cycle performance.

[0051] In some embodiments, the bulk density of the positive electrode material is 0.58 g / mL to 0.78 g / mL. For example, the bulk 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, etc., or other values ​​within the above range, which are not limited here.

[0052] 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, etc., or other values ​​within the above range, which are not limited here.

[0053] In some embodiments, the compaction density of the positive electrode 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, etc., or other values ​​within the above range, which are not limited here.

[0054] Controlling the loose density, tap density and compacted density of the positive electrode material within the above-mentioned corresponding ranges is conducive to obtaining a positive electrode material with improved energy density, thereby improving the electrochemical properties of the positive electrode material, such as the charge specific capacity and discharge specific capacity.

[0055] In some embodiments, the D10 particle size of the positive electrode material is 0.3 μm to 0.8 μm. For example, the D10 particle size may be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, etc. It may also be other values ​​within the above range, which is not limited here.

[0056] In some embodiments, the D50 particle size of the positive electrode material is 2.3 μm to 3.1 μm. For example, the D50 particle size may be 2.3 μm, 2.4 μm, 2.5 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3.1 μm, etc. It may also be other values ​​within the above range, which is not limited here.

[0057] In some embodiments, the D10 particle size and D50 particle size of the positive electrode material are obtained by testing with a laser particle size analyzer. The D10 particle size indicates the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 10%, and the D50 particle size indicates the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%.

[0058] Controlling the D10 particle size and D50 particle size of the positive electrode material within the above corresponding ranges is conducive to obtaining a positive electrode material with a concentrated particle size distribution, thereby improving the consistency of the positive electrode material during the charge-discharge process and improving the electrochemical performance of the positive electrode material.

[0059] In some embodiments, the iron dissolution amount of the positive electrode material is 6.4ppm to 59.2ppm. For example, the iron dissolution amount can be 6.4ppm, 6.7ppm, 10.3ppm, 11.2ppm, 11.3ppm, 12.1ppm, 12.5ppm, 13.8ppm, 15.3ppm or 59.2ppm, etc., or other values ​​within the above range, which are not limited here.

[0060] In some embodiments, the amount of magnetic substance in the positive electrode material is 0.11ppm to 0.14ppm. For example, the magnetic substance can be 0.11ppm, 0.12ppm or 0.14ppm, etc., or other values ​​within the above range, which are not limited here.

[0061] In some embodiments, the free moisture content of the positive electrode material is 103ppm to 399ppm. For example, the free moisture content may be 103ppm, 109ppm, 137ppm, 168ppm, 178ppm, 189ppm, 198ppm, 212ppm, 256ppm or 399ppm, etc. It may also be other values ​​within the above range, which is not limited here.

[0062] Controlling the iron dissolution amount, magnetic material mass and free water content of the positive electrode material within the above corresponding ranges is beneficial to improving the product quality of the positive electrode material and improving the effect of the positive electrode material when used in sodium ion batteries.

[0063] In the second aspect, the present application provides a method for preparing a positive electrode material, which comprises: 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 subjecting the mixture to aging treatment to obtain an aged slurry; subjecting the aged slurry to a first solid-liquid separation treatment to obtain an intermediate product; subjecting the intermediate product to slurry treatment to obtain a reaction slurry; and subjecting the reaction slurry to a reaction treatment to obtain a positive electrode material.

[0064] In the technical solution of the embodiment of the present application, in the high concentration fluoride ion environment of the base liquid, the fluoride ions with strong complexing ability form a complex with the added ferrous ions and replace part of the cyanide, thereby partially introducing fluoride ions into the Prussian blue material. The aging treatment is beneficial to the full crystallization of the Prussian blue material, and the reaction treatment further reduces the crystallization water inside the Prussian blue material, which is beneficial to improve the stability of the positive electrode material and improve the electrochemical properties of the positive electrode material in terms of cycle stability and rate performance.

[0065] In some embodiments of the present application, the step of obtaining the above-mentioned base solution includes: mixing a first solution and a second solution to obtain a base solution, the first solution includes sodium fluoride and ferric fluoride, and the second solution includes hydrogen fluoride.

[0066] Among them, the addition of ferric fluoride provides fluoride ions and ferrofluoride complex ions at the same time, providing a basis for the subsequent fluorine substitution.

[0067] In some embodiments, the pH value of the base solution is 2.5-3.5.

[0068] Too low a pH value is not conducive to the stability of the material structure, while too high a pH value is not conducive to the embedding of fluoride ions. Controlling the pH value within the above range is beneficial to improving the effectiveness of fluoride ion doping.

[0069] In some embodiments, the pH value of the above 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, etc., or other values ​​within the above range, which are not limited here.

[0070] In some embodiments, the molar ratio of the solute of the sodium ferrocyanide solution, the solute of the ferrous salt solution, and the solute of the sodium salt solution is 1:(1.2-1.5):(2-3).

[0071] The control of the above molar ratio helps to more accurately control the chemical composition of the final cathode material, making its molecular formula closer to Na x Fe y Fe(CN) z F 6-z ·nH 2 The optimal ratio of O·mHCl. Such a ratio helps to optimize the structural stability and ion diffusion channels of the positive electrode material, thereby improving the capacity and cycle stability of the positive electrode material.

[0072] In some embodiments, the molar ratio of the solute of the sodium ferrocyanide solution, the solute of the ferrous salt solution and the solute of 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, etc., and can also be other values ​​within the above range, which is not limited here.

[0073] In some embodiments, the concentration of the sodium ferrocyanide solution is 1 mol / L to 2 mol / L.

[0074] 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, etc., or other values ​​within the above range, which are not limited here.

[0075] Based on the consideration of reaction kinetics and chemical equilibrium, the concentration of sodium ferrocyanide solution and the concentration of ferrous salt solution are controlled within the above corresponding ranges, so as to facilitate the efficient reaction and reduce the risk of side reactions or material structure damage caused by excessive reactants. The preferred ferrous salts of the above types have a wide range of sources and are moderately priced, which helps to improve the economy of the entire production process. At the same time, their solubility in the solution is also good, which is easy to control and operate, and is conducive to the stability and cost control of the production process.

[0076] In some embodiments, the ferrous salt solution further includes a reducing agent and a complexing agent.

[0077] Fe 2+ It is the key to the framework of Prussian blue materials. Maintaining its reduced state is essential for forming the correct crystal structure. The presence of a reducing agent is beneficial to ensure that the ferrous ions remain in a divalent state during the synthesis process and avoid oxidation to trivalent ferrous ions (Fe 3+ The complexing agent helps to form a stable complex with the ferrous ions, reducing the risk of premature precipitation or oxidation of the ferrous ions in the solution, thereby improving the uniform dispersion and stable existence of the ferrous ions during the reaction, and is conducive to the formation of a uniform crystal structure.

[0078] In some embodiments, the reducing agent is sulfite and / or hydrazine hydrate.

[0079] Sulfite and / or hydrazine hydrate as reducing agents are helpful in promoting the synthesis reaction, especially the step involving the reaction of the sodium ferrocyanide solution with the base solution.

[0080] In some embodiments, the concentration of the reducing agent in the ferrous salt solution is 0.1 mol / L to 0.5 mol / L.

[0081] Too high a concentration of reducing agent may produce unnecessary side reactions and consume too many resources, while too low a concentration may not effectively promote the reduction reaction, affecting the quality of the material and the progress of the reaction. Controlling the concentration of the reducing agent within the above range helps to balance the efficiency and cost of the reducing agent in the reaction.

[0082] 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, etc., or other values ​​within the above range, which are not limited here.

[0083] In some embodiments, the complexing agent is ethylenediaminetetraacetic acid (EDTA) and / or citric acid.

[0084] The above types of complexing agents help to form a more stable complex with the ferrous ions, thereby facilitating the formation of a uniform crystal structure, thereby improving the structural stability of the positive electrode material.

[0085] In some embodiments, the concentration of the complexing agent in the ferrous salt solution is 0.01 mol / L to 0.2 mol / L.

[0086] Controlling the concentration of the complexing agent within the above range is more helpful to improve the effectiveness of the complexing reaction and the controllability of the material structure.

[0087] In some embodiments, the concentration of the complexing agent in the ferrous salt solution can be 0.01mol / L, 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, 0.06mol / L, 0.07mol / L, 0.08mol / L, 0.09mol / L, 0.1mol / L, 0.11mol / L, 0.12mol / L, 0.13mol / L, 0.14mol / L, 0.15mol / L, 0.16mol / L, 0.17mol / L, 0.18mol / L, 0.19mol / L or 0.2mol / L, etc., or it can be other values ​​within the above range, which is not limited here.

[0088] In some embodiments, the concentration of the sodium salt solution is 3mol / L to 5mol / L, the mass proportion 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 3mol / L, 3.1mol / L, 3.2mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L, 3.6mol / L, 3.7mol / L, 3.8mol / L, 3.9mol / L, 4.0mol / L, 4.1mol / L, 4.2mol / L, 4.3mol / L, 4.4mol / L, 4.5mol / L, 4.6mol / L, 4.7mol / L, 4.8mol / L, 4.9mol / L or 5mol / L, etc., and can also be other values ​​within the above range, which are not limited here.

[0089] By controlling the concentration of the sodium salt solution, the mass proportion of sodium fluoride and selecting different sodium salts, it is helpful to optimize the synthesis conditions of the positive electrode material, promote the efficient reaction, regulate the microstructure of the positive electrode material, improve the electrochemical properties of the positive electrode material, and balance cost and performance at the same time.

[0090] In summary, controlling the formation steps of the base solution and the composition, ratio and concentration of each solution within the above range is beneficial to optimizing the synthesis conditions of the positive electrode material, thereby improving the overall performance of the positive electrode material; at the same time, by optimizing the above parameters, not only the uniform doping of fluoride ions is promoted, but also the structural integrity inside the positive electrode material is improved, thereby improving the overall performance of the positive electrode material.

[0091] In some embodiments, the step of mixing the base solution, the sodium ferrocyanide solution, the ferrous salt solution and the sodium salt solution comprises:

[0092] maintaining the temperatures of the sodium ferrocyanide solution, the ferrous salt solution and the sodium salt solution respectively;

[0093] The sodium ferrocyanide solution, the ferrous salt solution and the sodium salt solution are added to the base solution within the first mixing time.

[0094] 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.

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

[0096] In some embodiments, the temperature of the sodium ferrocyanide solution, the ferrous salt solution, the sodium salt solution and / or the base solution is maintained at the same temperature as the aging treatment.

[0097] In some embodiments, the sodium ferrocyanide solution, the ferrous salt solution and the sodium salt solution are added to the base solution separately 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.

[0098] In some embodiments, the first mixing time is 30 min to 60 min, for example, 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0099] In some embodiments, the base solution, sodium ferrocyanide solution, ferrous salt solution and sodium salt solution are stirred at a stirring speed of 100 r / min to 300 r / min.

[0100] In some embodiments of the present application, the temperature of the aging treatment is 70° C. to 90° C., and the time of the aging treatment is 1 h to 2 h; the molar ratio of sodium fluoride to ferric fluoride in the first solution is 1:(0.1 to 0.2).

[0101] Aging treatment within the above temperature range and time range helps to reduce the risk of producing excessively large agglomerates or excessively small particles, which is conducive to forming a uniform and ordered crystal structure, improving the conductivity and ion diffusion efficiency of the positive electrode material, and thus improving the sodium storage capacity and cycle stability of the battery. In some embodiments of the present application, the temperature of the above aging treatment can be 70°C, 72°C, 74°C, 75°C, 76°C, 78°C, 80°C, 82°C, 84°C, 85°C, 86°C, 88°C or 90°C, etc., or other values ​​within the above range, which are not limited here; the aging treatment time can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h , 1.9h or 2h, etc., or other values ​​within the above range, which are not limited here; the molar ratio of sodium fluoride to ferric 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, etc., or other values ​​within the above range, which are not limited here.

[0102] In some embodiments, the total concentration of fluoride ions in the first solution is 2 mol / L to 4 mol / L.

[0103] By controlling the amount of sodium fluoride in the first solution to the amount of ferric fluoride in the above range, it is beneficial to uniformly dope fluoride ions in the positive electrode material. In some embodiments, the total concentration of fluoride ions in the first solution can be 2mol / L, 2.1mol / L, 2.2mol / L, 2.3mol / L, 2.4mol / L, 2.5mol / L, 2.6mol / L, 2.7mol / L, 2.8mol / L, 2.9mol / L, 3.0mol / L, 3.1mol / L, 3.2mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L, 3.6mol / L, 3.7mol / L, 3.8mol / L, 3.9mol / L or 4mol / L, etc., or other values ​​within the above range, which are not limited here.

[0104] In some embodiments, the concentration of the second solution is 5 mol / L to 8 mol / L.

[0105] Controlling the concentration of the second solution within the above range helps to inhibit side reactions, improve the purity and performance of the positive electrode material, and is beneficial to the structural stability of the positive electrode material. In some embodiments, the concentration of the second solution can be 5mol / L, 5.2mol / L, 5.4mol / L, 5.5mol / L, 5.7mol / L, 5.8mol / L, 6.0mol / L, 6.2mol / L, 6.4mol / L, 6.5mol / L, 6.7mol / L, 6.8mol / L, 7.0mol / L, 7.2mol / L, 7.4mol / L, 7.5mol / L, 7.7mol / L, 7.8mol / L or 8mol / L, etc., or other values ​​within the above range, which are not limited here.

[0106] Controlling the temperature and time of the aging treatment, and controlling the concentration of the above-mentioned solution and the ratio of the amount of solute in the above-mentioned solution to be within the above-mentioned corresponding ranges, is more conducive to improving the efficiency and effect of fluorine ion doping, thereby helping to improve the structural stability of the positive electrode material and improve the electrochemical performance of the positive electrode material.

[0107] In some embodiments, the first solid-liquid separation treatment can be performed by atmospheric pressure filtration, pressure filtration, suction filtration, centrifugal separation, etc.

[0108] In some embodiments of the present application, the intermediate product and the acid solution are mixed and slurried to obtain a reaction slurry.

[0109] The above steps help to reduce crystal water, optimize the sodium ion diffusion path, improve the purity of the material, improve the dispersibility of the intermediate product and control the microstructure, which improves the performance of the positive electrode material such as high sodium storage capacity, good cycle stability and rate performance.

[0110] In some embodiments, the reaction treatment temperature is 110° C. to 130° C., and the reaction treatment time is 30 min to 60 min.

[0111] Controlling the temperature and time of the reaction treatment within the above range helps the crystallization water to fully escape in the form of water vapor while maintaining the integrity and stability of the positive electrode material structure. In some embodiments, the temperature of the reaction treatment can be 110°C, 112°C, 115°C, 117°C, 120°C, 122°C, 125°C, 128°C or 130°C, etc., or other values ​​within the above range, which are not limited here; the time of the reaction treatment can be 30min, 32min, 35min, 38min, 40min, 42min, 45min, 48min, 50min, 52min, 55min or 60min, etc., or other values ​​within the above range, which are not limited here.

[0112] In some embodiments, the stirring speed of the reaction process is 100 r / min to 300 r / min.

[0113] Controlling the above stirring speed helps to promote uniform mixing of reactants, improve reaction efficiency, control the particle size of positive electrode materials, reduce the generation of by-products, and thus help to synthesize positive electrode materials with excellent performance. In some embodiments, the stirring speed of the reaction treatment can be 100r / min, 120r / min, 150r / min, 200r / min, 250r / min or 300r / min, etc., or other values ​​within the above range, which are not limited here.

[0114] 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.

[0115] The present invention utilizes an ethanol-hydrogen chloride system at high temperature to achieve erosion of the positive electrode material and azeotropic and replacement of part of the crystal water. Specifically, the reaction treatment of the reaction slurry in the present application utilizes the ethanol-hydrogen chloride system at high temperature to erode the intermediate product and azeotropic and replace part of the crystal water. At high temperature, part of the crystal water and hydrogen chloride form an azeotropic reaction, thereby escaping from the intermediate product, and the resulting vacant position is occupied by hydrogen chloride, which effectively reduces the collapse of the structure of the Prussian blue material caused by the escaping of water while reducing the crystal water content of the Prussian blue material.

[0116] Further, hydrogen ions can accelerate the formation of vacancies in the positive electrode material, which are then occupied by chloride ions. Controlling the hydrogen ion concentration within the above range helps to optimize the diffusion channel of sodium ions while removing crystal water, improve the diffusion coefficient of sodium ions, and help to form a complex structure unique to Prussian blue materials, and improve the rate performance and cycle stability of positive electrode materials. In addition, the presence of ethanol can be used as a dispersant to help reduce excessive aggregation of positive electrode material particles. In some embodiments, the concentration of hydrogen ions in the acid solution can be 0.5mol / L, 0.55mol / L, 0.6mol / L, 0.65mol / L, 0.7mol / L, 0.75mol / L, 0.8mol / L, 0.85mol / L, 0.9mol / L, 0.95mol / L or 1mol / L, etc., or other values ​​within the above range, which are not limited here.

[0117] 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).

[0118] Controlling the above mass ratio is not only beneficial to the removal of crystal water in the intermediate product, but also to reducing agglomeration, and is beneficial to improving the electrochemical performance, production efficiency and cost reduction of the positive electrode material. 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, etc., or other values ​​within the above range, which are not limited here.

[0119] In summary, by controlling the slurry treatment within the above-mentioned corresponding range, it is beneficial to improve the dispersion effect of the slurry; at the same time, controlling the reaction treatment conditions within the above-mentioned corresponding range is beneficial to fully utilize the ethanol-hydrogen chloride system at high temperature to erode the intermediate products and the azeotropic and replacement of part of the crystalline water, thereby further reducing the content of crystalline water in the positive electrode material and improving the stability and electrochemical performance of the positive electrode material.

[0120] In some embodiments, the intermediate product is subjected to a second washing and a second drying in sequence before being slurried.

[0121] In some embodiments, the washing liquid of the second washing can be at least one of deionized water, secondary water, distilled water, pure water, and ultrapure water. The conductivity of the washing water after the second washing is completed is less than or equal to 150 μS / cm, that is, the conductivity of the washing liquid after the second washing is completed is less than or equal to 150 μS / cm.

[0122] In some embodiments, after the second drying is completed, the moisture content of the intermediate product is less than 0.2%.

[0123] In some embodiments, the second drying may be performed by vacuum drying.

[0124] In some embodiments, the second drying temperature may be lower than the reaction treatment temperature.

[0125] In some embodiments of the present application, the product obtained by 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.

[0126] In some embodiments, the crushed positive electrode material is screened, iron removed and packaged in sequence to obtain the final positive electrode material.

[0127] Screening, iron removal and packaging processes can help improve the quality of positive electrode materials in terms of particle size, purity and preservation state, thereby improving the comprehensive performance of positive electrode materials in sodium-ion batteries, including improving cycle stability, rate performance, energy density and extending battery life.

[0128] In some embodiments, the second solid-liquid separation treatment can be performed by atmospheric pressure filtration, pressure filtration, suction filtration, centrifugal separation, etc.

[0129] In some embodiments, alcohol is used for the first washing until the pH value of the washing liquid after washing is 5.5 or above; the first drying is carried out under the protection of 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 ambient oxygen content during the first drying is less than 1000ppm; the particle size of the positive electrode material obtained after crushing is 1μm to 5μm.

[0130] Alcohol washing is beneficial to effectively remove residual impurities, improve the purity of positive electrode materials, reduce the risks caused by impurities in sodium ion batteries, and improve the stability and life of sodium ion batteries. Washing to a pH value of 5.5 or above helps ensure that the positive electrode material can be used in a neutral or near-neutral environment, which is beneficial to improving the cycle performance and stability of the battery.

[0131] Carrying out the first drying under the protection of protective gas is conducive to effectively reducing the risk of oxidation reaction of the positive electrode material due to contact with oxygen in the air, reducing by-products, and maintaining the electrochemical activity of the positive electrode material. By controlling the temperature of the first drying to 110°C to 150°C, it is helpful to quickly evaporate ethanol and control the mass fraction of ethanol to less than 0.1%, and to reduce the content of crystal water in the positive electrode material as much as possible, improve the structural stability of the positive electrode material, and reduce the negative impact of the precipitation of water on the performance of the sodium ion battery during the battery cycle. Controlling the ambient oxygen content during the first drying to less than 1000ppm helps to provide a nearly oxygen-free environment for the first drying, further reducing the possibility of oxidation. In some embodiments, the temperature of the first drying may be 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, etc., or other values ​​within the above range, which are not limited here; the particle size of the positive electrode material obtained after crushing may be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm or 5 μm, etc., or other values ​​within the above range, which are not limited here.

[0132] Controlling the particle size of the positive electrode material after pulverization within the above range is conducive to improving the particle size uniformity and compaction density of the positive electrode material. The synergistic effect of the above steps is more conducive to improving the electrochemical performance of the sodium ion battery.

[0133] In addition, in some embodiments, the protective gas for the first drying is nitrogen, the first drying is performed in an oven, and the ambient oxygen content during the first drying refers to the oxygen content in the oven.

[0134] In a third aspect, the present application provides a positive electrode plate, which includes the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned method for preparing the positive electrode material.

[0135] In this embodiment, thanks to the lower crystalline water content of the positive electrode material, since the positive electrode plate including the above-mentioned positive electrode material is prepared from the positive electrode material of the present application, the electrochemical properties such as cycle stability and rate performance of the positive electrode plate are better.

[0136] In a fourth aspect, the present application provides a sodium ion battery, comprising a positive electrode plate, which is the positive electrode plate mentioned above.

[0137] In this embodiment, since the above-mentioned sodium ion battery is prepared by the positive electrode sheet of the present application, the sodium ion battery not only has high cycle performance and rate performance, but also the lower crystalline 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.

[0138] In a fifth aspect, the present 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 sodium ion battery described above, and thus has good stability and electrochemical performance.

[0139] The electric device provided in the embodiment of the present application may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0140] 1. Preparation method

[0141] Example 1

[0142] Reference Figure 1 The process flow chart for preparing the positive electrode material shown in the figure is as follows: sodium fluoride and ferric fluoride are mixed to form a first solution, the molar ratio of sodium fluoride to ferric fluoride is 1:0.15, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, the second solution is a hydrogen fluoride solution with a concentration of 6.5 mol / L, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0143] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0144] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 1.12H 2 O·0.003HCl.

[0145] The obtained positive electrode material test data are as follows:

[0146] Table 1

[0147]

[0148] Example 2

[0149] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0150] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0151] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.05 Fe(CN) 4.92 F 1.08 1.10H 2 O·0.003HCl.

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

[0153] Table 2

[0154]

[0155] Example 3

[0156] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.3, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0157] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0158] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.12 Fe(CN)4.21 F 1.79 1.48H 2 O·0.004HCl.

[0159] The obtained positive electrode material test data are as follows:

[0160] Table 3

[0161]

[0162]

[0163] Example 4

[0164] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 2 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0165] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0166] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm2, and the reaction slurry is reacted under this condition for 45m in, stirring speed is 180r / min, then cooling and filtering and washing, washing with alcohol as washing liquid, washing to the pH value of the washing liquid is 5.5 and above after stopping washing, the washed material is first dried with nitrogen gas flow, the first drying temperature is 130°C, the oxygen content in the oven is maintained below 1000ppm during the first drying, drying until the alcohol content in the material is less than 0.1wt% after stopping, then crushing to the particle size of the material is 2.7μm, then stop crushing, and obtain the positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 5.00 F 1.00 1.13H 2 O·0.003HCl.

[0167] The obtained positive electrode material test data are as follows:

[0168] Table 4

[0169]

[0170]

[0171] Example 5

[0172] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 1.5 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0173] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0174] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 5.06 F 0.94 1.38H 2 O·0.003HCl.

[0175] The obtained positive electrode material test data are as follows:

[0176] Table 5

[0177]

[0178]

[0179] Example 6

[0180] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 2.5 to prepare a base solution;

[0181] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0182] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.08 Fe 0.97 Fe(CN) 4.96 F 1.04 1.44H 2 O·0.004HCl.

[0183] The obtained positive electrode material test data are as follows:

[0184] Table 6

[0185]

[0186] Example 7

[0187] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 2.0 to prepare a base solution;

[0188] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0189] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.16 Fe 0.93Fe(CN) 5.08 F 0.92 1.58H 2 O·0.007HCl.

[0190] The obtained positive electrode material test data are as follows:

[0191] Table 7

[0192]

[0193] Example 8

[0194] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0195] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 2 mol / L, the concentration of ferrous salt solution is 2.5 mol / L, and the concentration of sodium salt solution is 3 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.5 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.2 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0196] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.02 Fe(CN) 4.99 F 1.01 1.19H 2 O·0.003HCl.

[0197] The obtained positive electrode material test data are as follows:

[0198] Table 8

[0199]

[0200] Example 9

[0201] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0202] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1:1.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0203] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.8mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.16 Fe 1.12 Fe(CN) 5.38 F 1.01 1.55H 2 O·0.004HCl.

[0204] The obtained positive electrode material test data are as follows:

[0205] Table 9

[0206]

[0207] Example 10

[0208] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0209] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0210] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.5mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 1.24H 2 O·0.002HCl.

[0211] The obtained positive electrode material test data are as follows:

[0212] Table 10

[0213]

[0214] Embodiment 11

[0215] Sodium fluoride and ferric fluoride are mixed to form a first solution, wherein the molar ratio of sodium fluoride to ferric fluoride is 1:0.2, and the fluoride ion concentration in the first solution is 3.45 mol / L; the first solution is mixed with a second solution, wherein the second solution is a 6.5 mol / L hydrogen fluoride solution, and the pH of the mixed solution is adjusted to 3.1 to prepare a base solution;

[0216] Sodium ferrocyanide, ferrous salt and sodium salt are respectively prepared into solutions, the concentration of sodium ferrocyanide solution is 1.5 mol / L, the concentration of ferrous salt solution is 2 mol / L, and the concentration of sodium salt solution is 4 mol / L. The temperature of sodium ferrocyanide solution, ferrous salt solution and sodium salt solution is maintained at 80°C. The ferrous salt is ferrous chloride. Sodium sulfite is added to the ferrous salt solution. The concentration of sodium sulfite in the ferrous salt solution is 0.3 mol / L. The complexing agent is ethylenediaminetetraacetic acid (EDTA). The concentration of EDTA in the ferrous salt solution is 0.08 mol / L. The mass proportion of sodium fluoride in the solute of the sodium salt solution is 15%, and the remaining sodium salt is sodium chloride. The molar ratio of the solute in the sodium ferrocyanide, ferrous chloride and sodium salt solution is 1:1.35:2.5. Under stirring, the three solutions are added to the bottom liquid together. The adding time is 45 min. The reaction and aging are continued at a temperature of 80°C for 1.5 h to obtain a reaction slurry.

[0217] The reaction slurry is filtered and washed with pure water until the conductivity of the washing liquid is ≤150μS / cm (second washing). The obtained washing material is vacuum dried (second drying) and the moisture content is less than 0.2% to obtain an intermediate product; the intermediate product is transferred to a sealed reactor, and a hydrochloric acid-ethanol solution with a hydrogen ion concentration of 0.3mol / L is added for slurry to obtain a reaction slurry, and the solid-liquid ratio of the reaction slurry is 1:3.5; the sealed reactor is then heated to a temperature of 120°C and a pressure of 3.3kg / cm 2 The reaction slurry was reacted under this condition for 45 minutes, with a stirring speed of 180r / min, and then filtered and washed after cooling. Alcohol was used as a washing liquid for washing. The washing was stopped after the pH value of the washing liquid reached 5.5 or above. The washed material was first dried with a nitrogen gas flow at a temperature of 130°C. During the first drying, the oxygen content in the oven was maintained below 1000ppm. The material was dried until the alcohol content was below 0.1wt% and then stopped. The material was then crushed to a particle size of 2.7μm, and then the crushing was stopped to obtain a positive electrode material, whose specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 4.99 F 1.01 1.74H 2 O·0.001HCl.

[0218] The obtained positive electrode material test data are as follows:

[0219] Table 11

[0220]

[0221] Comparative Example 1

[0222] The difference from Example 1 is that sodium fluoride and ferric fluoride are replaced by sodium chloride and ferric chloride in equal amounts, respectively, to finally obtain a comparative positive electrode material, the specific chemical formula of which is Na 2.00 Fe 1.00 Fe(CN) 5.75 F 0.25 1.65H 2 O.0.002HCl.

[0223] The obtained Prussian blue sodium battery material test data are as follows:

[0224] Table 12

[0225]

[0226] Comparative Example 2

[0227] The difference from Example 1 is that no hydrogen fluoride is added, and the final comparative positive electrode material is obtained, and its specific chemical formula is Na 2.00 Fe 1.00 Fe(CN) 5.55 F 0.45 1.45H 2 O·0.001HCl.

[0228] The obtained Prussian blue sodium battery material test data are as follows:

[0229] Table 13

[0230]

[0231] Comparative Example 3

[0232] Preparation of Prussian blue cathode material carbon-nickel manganese ferrocyanide:

[0233] (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;

[0234] (2) Weigh 0.032 mol of manganese sulfate and 0.128 mol of 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;

[0235] (3) Weigh 0.008 mol nickel sulfate and 0.032 mol sodium citrate, dissolve them in 20 mL deionized water to prepare solution C, wherein 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;

[0236] (4) Place solution A on a magnetic stirrer and stir, heat to 60°C, and use a peristaltic pump to dropwise add solution B into the high-speed stirred solution A. During the addition, a white precipitate is generated. The addition rate is 0.25 mL / min to obtain a precursor solution.

[0237] (5) Precursor solution A was stirred for 2 hours, and solution C was added dropwise into the high-speed stirred precursor solution A using a peristaltic pump at a dropping rate of 0.25 mL / min.

[0238] (6) The mixed solution was stirred for 0.5 h and then allowed to stand for 6 h;

[0239] (7) After standing, the mixed solution is centrifuged to obtain a light green precipitate. The light green precipitate is washed, centrifuged, and then dried at 120° C. in a vacuum oven for 24 h to obtain a Prussian blue cathode material.

[0240] 2. Test Method

[0241] Properties test of positive electrode materials

[0242] The free water content was tested by Karl Fischer coulometry;

[0243] Crystal water is tested by high temperature weight loss method;

[0244] The particle size of D10 / D50 / D90 is tested by laser particle size analyzer according to the laser diffraction method;

[0245] The BET specific surface area was tested using a BET tester and the nitrogen adsorption method;

[0246] Impurity elements were tested by inductively coupled plasma optical emission spectrometry (ICP-OES);

[0247] The magnetic material was collected by a magnet, dissolved in aqua regia, and tested by inductively coupled plasma optical emission spectroscopy.

[0248] Iron dissolution amount: Add 1g of the sample to be tested into 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 dissolution amount.

[0249] The bulk density refers to GB T 31057.1-2014 and is tested using the funnel method.

[0250] The tap density is tested using a tap density meter with 5000 vibrations.

[0251] The compaction density is tested by a compaction density meter with a test pressure of 3T and a pressing time of 30s.

[0252] Chloride ion was tested using a chloride ion selective electrode.

[0253] Testing method for sodium ion diffusion coefficient: obtained by electrochemical impedance spectroscopy (EIS) testing.

[0254] III. Analysis of test results of various embodiments and comparative examples

[0255] Assemble the above-obtained materials into a button switch. The assembly process is as follows:

[0256] The positive electrode material obtained in the embodiment or comparative example was mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, as a binder) at a mass ratio of 85:10:5, and the mass was weighed accurately to 0.001g to obtain a positive electrode active mixture. A carbon-coated aluminum foil was used as a current collector, and the positive electrode active mixture was mixed with N-methylpyrrolidone and stirred to prepare a slurry. The slurry was evenly coated on 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, and the mass was accurate to 0.0001g.

[0257] Battery Assembly

[0258] In an inert gas glove box with water and oxygen contents ≤0.0005%, a metal sodium sheet was used as the negative electrode sheet, a polypropylene microporous film was used as the diaphragm, 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)], a positive electrode sheet, a negative electrode sheet, a diaphragm, and an electrolyte were assembled into a button cell, and after the button cell was sealed, it was tested using a sodium ion battery electrochemical performance tester.

[0259] Battery Testing

[0260] The button cell was charged and discharged on a sodium ion battery electrochemical performance tester at 25°C. The charge and discharge test was as follows:

[0261] a) 0.2C rate current charging, charging limit voltage 4.2V;

[0262] b) 0.2C discharge rate current, discharge termination voltage 2.0V.

[0263] The button cell was placed in an incubator (25 ± 0.2 °C) for cyclic performance testing. It was cycled 1000 times at 1C, and the capacity retention rate was 89.9% (for conventional sodium prussian blue battery materials, after 1000 cycles, the capacity retention rate was basically below 85%). The test results are as follows:

[0264] Table 14

[0265]

[0266]

[0267] It can be seen from the data in Table 14 that the capacity retention rate of the positive electrode material in the examples of this application was higher than 86% after 1000 cycles at 1C, and the initial charge specific capacity was above 150 mAh / g at 0.2C; the initial discharge specific capacity was above 144 mAh / g at 0.2C, indicating that the comprehensive electrical performance of the positive electrode material in the examples of this application was significantly better than that of the sodium prussian blue battery materials in Comparative Examples 1 to 3.

[0268] Furthermore, Figure 2 Figure showing the charge specific capacity and discharge specific capacity test results of the sodium ion battery with the positive electrode material of Example 1. It can be seen from Figure 2 that the positive electrode material of Example 1 has excellent charge and discharge performance.

[0269] The chemical formula of the comparative positive electrode material in Comparative Example 1 is Na 2.00 Fe 1.00 Fe(CN) 5.75 F 0.25 ·1.65H 2 O·0.002HCl, and the chemical formula of the comparative positive electrode material in Comparative Example 2 is Na 2.00 Fe 1.00 Fe(CN) 5.55 F 0.45 ·1.45H 2 O·0.001HCl. It can be known that the contents of their cyanide ions and fluoride ions are outside the range of 4.20 < z < 5.50 in the general chemical formula Na x Fe y Fe(CN) z F 6-z nH 2 O·mHCl of the prussian blue material in this application, and the content of fluoride ions in the positive electrode materials of Comparative Examples 1 and 2 is lower than that of the fluoride ions in the prussian blue material obtained in the examples of this application, resulting in the electrochemical performance of the sodium ion batteries corresponding to the positive electrode materials in Comparative Examples 1 and 2 being worse than that of the sodium ion batteries corresponding to the positive electrode materials obtained in the examples of this application.

[0270] The electrochemical performance results of the button cells with the positive electrode materials provided in the embodiment and the electrochemical performance results of the button cells with the positive electrode materials provided in Comparative Examples 1 to 3 in Table 14 indicate that the present application effectively improves the stability of the positive electrode material and the electrochemical performance of the positive electrode material by controlling the chemical composition of the Prussian blue material, introducing fluorine elements to replace part of the cyanide ions to reduce the content of crystallization water and using HCl to occupy the vacant crystallization water sites.

[0271] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

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

007.

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

3. A method for preparing a positive electrode material, characterized in that: The preparation method of the positive electrode material comprises: Providing a base liquid, wherein the base liquid includes sodium ions, iron ions and hydrogen fluoride; The base liquid, sodium ferrocyanide solution, ferrous salt solution and sodium salt solution are mixed and subjected to aging treatment to obtain an aged slurry; The aged slurry is subjected to a first solid-liquid separation process to obtain an intermediate product; The intermediate product is subjected to slurry treatment to obtain a reaction slurry; The reaction slurry is subjected to reaction treatment to obtain the positive electrode material.

4. The method for preparing the positive electrode material according to claim 3, characterized in that: The step of obtaining the base solution comprises: mixing a first solution and a second solution to obtain the base solution, wherein the first solution comprises sodium fluoride and ferric fluoride, and the second solution comprises hydrogen fluoride; The pH value of the base liquid is 2.5 to 3.5; The molar ratio of the solute of the sodium ferrocyanide solution, the solute of the ferrous salt solution and the solute of the sodium salt solution is 1:(1.2-1.5):(2-3); 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; And / or, the ferrous salt solution further comprises 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 proportion 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 positive electrode material according to claim 3 or 4, characterized in that: The aging treatment temperature is 70°C to 90°C, and the aging treatment time is 1h to 2h; 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 positive electrode material according to claim 3, characterized in that: mixing and slurrying the intermediate product and the acid solution to obtain a reaction slurry; And / or, the reaction treatment temperature is 110°C to 130°C, and the reaction treatment time is 30min to 60min; And / or, the acid solution is a hydrochloric acid-ethanol solution, and the concentration of hydrogen ions in the acid solution is 0.8 mol / L-1 mol / L; And / or, the mass ratio of solid to liquid in the reaction slurry is 1:(3-4).

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

8. The method for preparing the positive electrode material according to claim 3, characterized in that: The product obtained by the reaction treatment is sequentially subjected to a second solid-liquid separation treatment, a first washing, a first drying and a pulverization to obtain the positive electrode material; and / or, using alcohol to perform the first washing until the pH value of the washing liquid after washing is 5.5 or above; 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° 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 the pulverization is 1 μm to 5 μm.

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 a positive electrode material prepared by the method for preparing a positive electrode material according to any one of claims 3 to 8.

10. A sodium ion battery, comprising a positive electrode plate, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 9.

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