Sodium vanadium phosphate and its preparation method and application

Abstract

The present invention discloses a sodium vanadium phosphate, a preparation method thereof and an application. The preparation method includes: adding an acid or a base to a vanadium-containing waste material or its dispersion liquid, dissolving, adjusting the pH value during dissolution, and then filtering to obtain a solution of the vanadium-containing waste material; adding a valence regulator to the solution of the vanadium-containing waste material to react until the vanadium ions react completely, so that all the vanadium ions in the obtained solution are in the +4 valence state; heating the solution until no obvious bubbles are precipitated; adding an alkali solution to the solution, stirring and reacting to obtain a precursor slurry; adding a phosphate to the precursor slurry to carry out an ion exchange reaction to obtain sodium vanadium phosphate. By the regulation of the valence regulator, the method of the present invention controls the uniformity of the vanadium valence states in different vanadium-containing waste materials, obtains a vanadium source solution with all vanadium in the +4 valence state, and then utilizes the ion exchange technology to realize the recycling of vanadium resources from vanadium-containing waste materials to nano-sodium vanadium phosphate. The prepared nano-sodium vanadium phosphate has good electrochemical properties.

Description

Technical Field

[0001] The present invention belongs to the field of electrode materials. Specifically, the present invention relates to sodium vanadium phosphate, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its unique ion channel structure, sodium vanadium phosphate has good sodium ion intercalation and deintercalation performance, showing a high sodium ion migration efficiency. It is a sodium ion superconducting material and can be used as the positive electrode material of a sodium ion secondary battery. However, the relatively high price of vanadium raw materials restricts to a certain extent the application and development of sodium vanadium phosphate-based positive electrode materials in real life.

[0003] In order to reduce the electrode cost of sodium vanadium phosphate-based materials, it is a practical method to reduce the usage of vanadium by introducing cheap transition metal elements to in-situ replace vanadium elements. For example, in the invention patent 202211113663.5, it is proposed to use cheap iron elements to partially replace expensive vanadium elements to prepare sodium iron vanadium phosphate, realizing cost reduction and efficiency increase of sodium vanadium phosphate-based materials. Selecting cheap vanadium sources, such as using vanadium-containing waste materials such as spent vanadium redox flow battery electrolytes to efficiently prepare sodium vanadium phosphate, is also an effective way. However, the research on preparing sodium vanadium phosphate from vanadium-containing waste materials is still in its infancy, and there are few relevant research reports. Summary of the Invention

[0004] The present invention is based on the inventor's discovery and recognition of the following facts and problems: At present, the relatively high price of vanadium raw materials restricts to a certain extent the application and development of sodium vanadium phosphate-based positive electrode materials in real life. The recycling and reuse of vanadium-containing waste materials are of great significance. The use of vanadium-containing waste materials can reduce the cost of vanadium sources on the one hand, and on the other hand, it can also realize the recycling and reuse of resources, reducing the full life cycle cost of vanadium-based electrode materials.

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an embodiment of the present invention provides a sodium vanadium phosphate, a preparation method thereof, and an application thereof. Through the regulation of a valence regulator, the valence of vanadium in different vanadium-containing waste materials is unified, and a vanadium source solution with all +4 valence is obtained. Then, using ion exchange technology, the vanadium resource recycling from vanadium-containing waste materials to nano sodium vanadium phosphate is realized, and the prepared nano sodium vanadium phosphate has good electrochemical performance.

[0006] A preparation method of sodium vanadium phosphate according to an embodiment of the present invention includes the following steps:

[0007] (1) Add acid or alkali to the vanadium-containing waste material or a dispersion of the vanadium-containing waste material, dissolve it, adjust the pH value while dissolving, and then filter to obtain a solution of the vanadium-containing waste material;

[0008] (2) Add a valence regulator to the solution of the vanadium-containing waste material and react to completely react the vanadium ions, so that all the vanadium ions in the obtained solution are in the +4 valence;

[0009] (3) Heat the solution obtained in the step (2) until no obvious bubbles are evolved;

[0010] (4) Add an alkali solution to the solution obtained in the step (3), stir and react to obtain a precursor slurry;

[0011] (5) Add phosphate to the precursor slurry and carry out an ion exchange reaction to obtain sodium vanadium phosphate.

[0012] The advantages and technical effects brought by the preparation method of sodium vanadium phosphate in the embodiment of the present invention: The preparation method of sodium vanadium phosphate includes steps such as dissolution of vanadium-containing waste material, vanadium valence regulation, alkaline vanadium precipitation, and ion exchange. Through the regulation of the valence regulator, the vanadium valence in different vanadium-containing waste materials is unified, and a vanadium source solution with all valence states of +4 is obtained. Then, by using ion exchange technology, the vanadium resource recycling from vanadium-containing waste materials to nano-sodium vanadium phosphate is realized. The prepared nano-sodium vanadium phosphate has good electrochemical properties and can be used as an electrode material for alkali metal secondary batteries.

[0013] In the embodiment of the present invention, different from the oxidation or reduction methods used in the traditional vanadium valence regulation process, the valence regulator adopted in the present invention is an amphoteric substance. By using the oxidizing and reducing properties of the valence regulator, based on the strength trend of the oxidation-reduction ability of substances and combining with the principle of the Nernst equation, the electrode potential of the amphoteric substance of the valence regulator for oxidation-reduction is controlled to be between ψ(V 3+ ) and ψ(V 5+ ) to realize the unified adjustment of the valence states of various different mixed vanadium ions to +4 valence. The vanadium-containing waste material used can be a vanadium raw material containing vanadium ions in any valence state, especially suitable for vanadium raw materials with unknown vanadium ion valence compositions or vanadium raw materials that may contain various different valence states of vanadium ions. And before and after valence regulation, there is no need to pre-detect and quantitatively analyze the composition of each valence state of vanadium elements in the vanadium-containing waste material or solution and the content of each valence state respectively. By adjusting the pH, dissolving and filtering, and then adding an excessive valence regulator to react to completely react the vanadium ions, any valence state of vanadium ions in the solution can be uniformly adjusted to tetravalent to obtain a tetravalent vanadium solution, which greatly broadens the selection range of vanadium raw materials. At the same time, when treating a solution that may contain both low-valent vanadium and high-valent vanadium, there is no need to pre-detect and add an oxidant when oxidizing low-valent vanadium and a reductant when reducing high-valent vanadium according to the valence state and valence composition of vanadium ions in the detection result, avoiding the compound use of a single oxidant / reductant in the traditional method and simplifying the process flow.

[0014] In the embodiments of the present invention, by utilizing the self-decomposition property of redox amphoteric substances upon heating, the excessive valence regulators are removed, eliminating the influence of the valence regulators on the preparation process of sodium vanadium phosphate, meeting the requirements of the ion exchange method for vanadium source raw materials, and thus achieving the efficient preparation of sodium vanadium phosphate from vanadium-containing waste materials, realizing the recycling and reuse of vanadium resources.

[0015] In the embodiments of the present invention, by using the vanadium valence regulation strategy, the vanadium sources in different vanadium-containing waste materials are collected and the valence is adjusted and unified. Assisted by the ion exchange method, the cyclic and efficient recovery of different vanadium-containing waste materials and the efficient preparation of sodium vanadium phosphate-based electrode materials are realized. At the same time, by avoiding the combined use of traditional single oxidants / reductants, the cumbersome steps of removing residual oxidants / reductants are simplified, and the influence of residual oxidants / reductants on the preparation process of sodium vanadium phosphate is minimized. The method of the present invention has low cost, simple operation, high efficiency, and is easy to scale up industrially. The prepared sodium vanadium phosphate nanoparticles have good electrochemical properties, enabling the efficient and low-cost preparation of sodium vanadium phosphate materials, which is conducive to promoting the research and application of sodium vanadium phosphate-based materials in the field of electrochemical energy storage.

[0016] In some embodiments, in step (1), the vanadium-containing waste material includes at least one of spent vanadium redox flow battery electrolyte, spent sodium vanadium phosphate electrode material, and mixed vanadium oxides.

[0017] In some embodiments, in step (1), the valence of vanadium in the vanadium-containing waste material includes at least one of +2, +3, +4, and +5.

[0018] In some embodiments, in step (1), the pH value after dissolution is 0 - 3; the pH value is adjusted using an acid and / or a base.

[0019] In some embodiments, in step (1), the concentration of vanadium ions in the solution of the vanadium-containing waste material is 0.01 - 5.0 mol / L.

[0020] In some embodiments, in step (2), the valence regulator includes at least one of hydrogen peroxide, hydroxylamine compounds, nitrous acid, sodium nitrite, and iodine.

[0021] In some embodiments, under the pH condition of the solution of the vanadium-containing waste material obtained in step (1), the electrode potential of the valence regulator is between ψ(V 3+ ) and ψ(V 5+ ).

[0022] In some embodiments, the valence regulator exhibits oxidizing and / or reducing properties.

[0023] In some embodiments, the molar ratio of the valence state regulator to vanadium ions in the solution of vanadium-containing waste material is more than 1:1.

[0024] In some embodiments, in step (4), an alkali solution is added to the solution obtained in step (3) until the pH of the solution is 4-9;

[0025] and / or, the alkali solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water;

[0026] and / or, the concentration of the alkali solution is 0.01-5.0 mol / L.

[0027] In some embodiments, in step (5), the phosphate includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium polyphosphate;

[0028] and / or, in step (5), the phosphate and the composite anion mixture are added to the precursor slurry for an ion exchange reaction to obtain sodium vanadium phosphate; the composite anion mixture includes a mixture of sodium fluoride and sodium chloride; the molar ratio of the phosphate to the composite anion mixture is 1:0-1; the molar ratio of F- to Cl- in the composite anion mixture is 1:0-1;

[0029] and / or, the molar ratio of vanadium ions to phosphate in the solution of vanadium-containing waste material is 1:1-3;

[0030] and / or, the time of the ion exchange reaction is 3-24 h.

[0031] An embodiment of the present invention provides sodium vanadium phosphate prepared by the preparation method of the embodiment of the present invention. In the embodiment of the present invention, sodium vanadium phosphate has good electrochemical performance.

[0032] An embodiment of the present invention provides an application of sodium vanadium phosphate prepared by the preparation method of the embodiment of the present invention or sodium vanadium phosphate of the embodiment of the present invention in an alkali metal secondary battery. In the embodiment of the present invention, sodium vanadium phosphate has good electrochemical performance and can be used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium, which is beneficial to promoting the research and popularization and application of sodium vanadium phosphate-based materials in the field of electrochemical energy storage. Description of the Drawings

[0033] Figure 1 is a process schematic diagram for preparing sodium vanadium phosphate from vanadium-containing waste material.

[0034] Figure 2 is the ultraviolet absorption curve of the spent vanadium battery electrolyte used in Example 1.

[0035] Figure 3It is the ultraviolet absorption curve of the solution after being regulated by the valence regulator described in the method of Example 1.

[0036] Figure 4 It is the ultraviolet absorption curve of the solution after being regulated by the valence regulator described in the method of Example 2.

[0037] Figure 5 It is the XRD curve of sodium vanadium phosphate prepared by the method of Example 3.

[0038] Figure 6 It is the ultraviolet absorption curve of the solution after being regulated by the valence regulator described in the method of Comparative Example 1. Detailed implementation manners

[0039] The embodiments of the present invention will be described in detail below. The examples are shown in the accompanying drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0040] As Figure 1 shown, a preparation method of sodium vanadium phosphate according to an embodiment of the present invention includes the following steps:

[0041] (1) Add acid or alkali to the vanadium-containing waste material or the dispersion of the vanadium-containing waste material, dissolve it, adjust the pH value while dissolving, and then filter to obtain a solution of the vanadium-containing waste material;

[0042] (2) Add a valence regulator to the solution of the vanadium-containing waste material for reaction to completely react the vanadium ions, so that all the vanadium ions in the obtained solution are in the +4 valence state;

[0043] (3) Heat the solution obtained in step (2) until no obvious bubbles are evolved;

[0044] (4) Add an alkali solution to the solution obtained in step (3), stir and react to obtain a precursor slurry;

[0045] (5) Add phosphate to the precursor slurry to carry out an ion exchange reaction to obtain sodium vanadium phosphate.

[0046] The preparation method of sodium vanadium phosphate according to the embodiment of the present invention includes steps such as dissolution of vanadium-containing waste materials, regulation of vanadium valence, precipitation of vanadium with alkali, and ion exchange. Through the regulation of the valence regulator, the uniformity of the vanadium valence in different vanadium-containing waste materials is controlled to obtain a vanadium source solution with all vanadium in the +4 valence state. Then, by using ion exchange technology, the recycling of vanadium resources from vanadium-containing waste materials to nano-sodium vanadium phosphate is realized. The prepared nano-sodium vanadium phosphate has good electrochemical properties and can be used as an electrode material for alkali metal secondary batteries.

[0047] In the embodiments of the present invention, different from the oxidation or reduction methods used in the traditional vanadium valence regulation process, the valence regulator used in the present invention is an amphoteric substance. By utilizing the oxidizing and reducing properties of the valence regulator and based on the strength trend of the oxidation-reduction ability of substances, combined with the principle of the Nernst equation, the electrode potential of the amphoteric substance for valence regulation is controlled to be between ψ(V 3+ ) and ψ(V 5+ ), so as to uniformly adjust various different mixed vanadium ion valences to +4 valence. The used vanadium-containing waste materials can be vanadium raw materials containing vanadium ions in any valence state, and are particularly suitable for vanadium raw materials with unknown vanadium ion valence compositions or vanadium raw materials that may contain various different valence vanadium ions. Moreover, before and after valence regulation, it is not necessary to pre-detect and quantitatively analyze the composition of each valence state of vanadium elements and the content of each valence state in the vanadium-containing waste materials or solutions. By adjusting the pH, dissolving and filtering, and then adding an excessive amount of valence regulator to react until the vanadium ions react completely, any valence vanadium ions in the solution can be uniformly adjusted to tetravalent, obtaining a tetravalent vanadium solution, which greatly broadens the selection range of vanadium raw materials. At the same time, when treating a solution that may contain both low-valence vanadium and high-valence vanadium, it is not necessary to pre-detect and add an oxidizing agent when oxidizing low-valence vanadium and a reducing agent when reducing high-valence vanadium according to the valence state and valence composition of vanadium ions in the detection results, avoiding the combined use of a single oxidizing agent / reducing agent in the traditional method and simplifying the process flow.

[0048] In the embodiments of the present invention, by utilizing the self-decomposition property of the oxidation-reduction amphoteric substance upon heating, the excessive valence regulator is removed, eliminating the influence of the valence regulator on the preparation process of sodium vanadium phosphate, meeting the requirements of the ion exchange method for vanadium source raw materials, and thus realizing the efficient preparation of sodium vanadium phosphate nanomaterials from vanadium-containing waste materials and achieving the recycling and reuse of vanadium resources.

[0049] In the embodiments of the present invention, by using the vanadium valence regulation strategy, the vanadium sources in different vanadium-containing waste materials are collected and the valence is adjusted and unified. Assisted by the ion exchange method, the cyclic and efficient recovery of different vanadium-containing waste materials and the efficient preparation of sodium vanadium phosphate-based electrode materials are realized. At the same time, by avoiding the combined use of traditional single oxidizing agents / reducing agents, the cumbersome steps of removing residual oxidizing / reducing agents are simplified, and the influence of residual oxidizing / reducing agents on the preparation process of sodium vanadium phosphate is minimized to the greatest extent. The method of the present invention has low cost, simple operation, high efficiency, and is easy to scale up industrially. The prepared sodium vanadium phosphate nanomaterials have good electrochemical properties, enabling the efficient and low-cost preparation of sodium vanadium phosphate materials, which is conducive to promoting the research and popularization and application of sodium vanadium phosphate-based materials in the field of electrochemical energy storage.

[0050] In some embodiments, in the step (1), the acid includes HCl; the base includes sodium hydroxide.

[0051] In some embodiments, in the step (1), the vanadium-containing waste material includes at least one of spent vanadium redox flow battery electrolyte, spent sodium vanadium phosphate electrode material, and mixed vanadium oxides. In the embodiments of the present invention, the vanadium-containing waste material used can be a vanadium raw material containing vanadium ions in any valence state.

[0052] In some embodiments, in the step (1), the valence states of vanadium in the vanadium-containing waste material include at least one of +2, +3, +4, and +5. In the embodiments of the present invention, the vanadium-containing waste material used can be a vanadium raw material containing vanadium ions in any valence state, and is particularly suitable for vanadium raw materials with unknown valence state compositions of vanadium ions or vanadium raw materials that may contain multiple different valence states of vanadium ions.

[0053] In some embodiments, in the step (1), the pH value after dissolution is 0 to 3. Specifically, for example, 0, 0.5, 1, 1.5, 2, 2.5, 3; the pH value is adjusted using an acid and / or a base. In the embodiments of the present invention, the pH value after dissolution is preferably selected. The influence of pH on the electrode potential is similar to that of concentration, and the relationship is proportional to RTlg[V][H + , where [V] and [H + are the concentrations of vanadium ions and H + respectively.

[0054] In some embodiments, in the step (1), the concentration of vanadium ions in the solution of the vanadium-containing waste material is 0.01 to 5.0 mol / L. Specifically, for example, 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 3 mol / L, 5.0 mol / L. In the embodiments of the present invention, the concentration of the solution of the vanadium-containing waste material can be measured by ICP without prior detection of the valence state and valence state composition of vanadium ions. By preferably selecting the concentration of vanadium ions in the solution, it is beneficial to reasonably control and optimize the formation of sodium vanadium phosphate. When the concentration of vanadium ions is too high, the vanadium precipitation process is too fast, and the local alkalinity is too strong, affecting the yield; when the concentration of vanadium ions is too low, the output is too small and the yield is too low.

[0055] In some embodiments, in the step (1), the dissolution is performed by ultrasonic dissolution.

[0056] In some embodiments, in the step (2), the valence state regulator includes at least one of hydrogen peroxide, hydroxylamine compounds, nitrous acid, sodium nitrite, and iodine. In the embodiments of the present invention, the type of valence state regulator is preferably selected. The valence state regulator is an amphoteric substance. By using the oxidizing and reducing properties of the valence state regulator, based on the strength trend of the redox ability of substances and in combination with the Nernst equation principle, the electrode potential of the amphoteric valence state regulator for redox is controlled to be between ψ(V 3+ ) and ψ(V 5+ ) to achieve unified adjustment of various different mixed vanadium ion valence states to +4.

[0057] In some embodiments, in step (2), the reaction is carried out at room temperature.

[0058] In some embodiments, in step (2), the reaction time is 0.5 - 1 h.

[0059] In some embodiments, under the pH condition of the solution of vanadium-containing waste material obtained in step (1), the electrode potential of the valence regulator is between ψ(V 3+ ) and ψ(V 5+ ), optionally, the electrode potential of the valence regulator is equal to ψ(V 4 + ). In the embodiments of the present invention, by optimizing the electrode potential of the valence regulator, it is beneficial to accurately control the vanadium valence in the system to be uniformly +4 valence.

[0060] In some embodiments, the valence regulator exhibits oxidizing and / or reducing properties.

[0061] In some embodiments, the molar ratio of the valence regulator to vanadium ions in the solution of vanadium-containing waste material is more than 1:1. Specifically, for example, 1:1, 2:1, 3:1, 4:1. In the embodiments of the present invention, by optimizing the dosage of the valence regulator to ensure that the valence regulator is in excess, the vanadium ions can react completely. Without prior knowledge of the valence and valence composition of vanadium ions, any valence of vanadium ions in the solution can be uniformly adjusted to tetravalent to obtain a tetravalent vanadium solution.

[0062] In some embodiments, in step (4), an alkali solution is added to the solution obtained in step (3) until the pH of the solution is 4 - 9. Specifically, for example, 4, 5, 6, 7, 8, 9;

[0063] and / or, the alkali solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water;

[0064] and / or, the concentration of the alkali solution is 0.01 - 5.0 mol / L. Specifically, for example, 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 3 mol / L, 5.0 mol / L.

[0065] In some embodiments, in step (5), the phosphate includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium polyphosphate.

[0066] In some embodiments, in the step (5), phosphate and a composite anion mixture are added to the precursor slurry for an ion exchange reaction to obtain sodium vanadium phosphate; the composite anion mixture includes a mixture of sodium fluoride and sodium chloride; preferably, the molar ratio of the phosphate to the composite anion mixture is 1:0 to 1, specifically, for example, 1:0, 1:0.5, 1:1; the molar ratio of F- to Cl- in the composite anion mixture is 1:0 to 1, specifically, for example, 1:0, 1:0.5, 1:1. In the embodiments of the present invention, by utilizing the regulation effect of the composite anion on the electronic structure of sodium vanadium phosphate, a multi-anion system of F- and Cl- is introduced, improving the electron / ion conductivity of sodium vanadium phosphate, such that the prepared nano sodium vanadium phosphate exhibits excellent electrochemical performance.

[0067] In some embodiments, the molar ratio of vanadium ions to phosphate in the solution of the vanadium-containing waste is 1:1 to 3, specifically, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3;

[0068] and / or, the time of the ion exchange reaction is 3 to 24 h, specifically, for example, 3 h, 4 h, 6 h, 8 h, 10 h, 15 h, 20 h, 24 h.

[0069] In the embodiments of the present invention, by optimizing the ratio of vanadium ions to phosphate, it is beneficial to promote the ion exchange reaction and improve the economy. If the dosage of phosphate is too high, the phosphate content in the waste liquid after the reaction is too high, causing large pollution and being difficult to treat; if the dosage of phosphate is too low, the ion exchange reaction is insufficient and the reaction is incomplete.

[0070] The embodiments of the present invention provide a sodium vanadium phosphate prepared by the preparation method of the embodiments of the present invention. In the embodiments of the present invention, the sodium vanadium phosphate has good electrochemical performance.

[0071] In some embodiments, the molecular formula of the sodium vanadium phosphate is Na 2 VOPO 4 F 0.5 Cl 0.5 。

[0072] The embodiments of the present invention provide an application of the sodium vanadium phosphate prepared by the preparation method of the embodiments of the present invention or the sodium vanadium phosphate of the embodiments of the present invention in an alkali metal secondary battery. In the embodiments of the present invention, the sodium vanadium phosphate has good electrochemical performance and can be used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium, which is beneficial to promoting the research and popularization application of sodium vanadium phosphate-based materials in the field of electrochemical energy storage.

[0073] In some embodiments, the alkali metal secondary battery includes one of lithium, sodium, and potassium alkali metal secondary batteries.

[0074] The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0075] Example 1

[0076] A method for preparing sodium vanadium phosphate includes the following steps:

[0077] 1) Take 50 mL of the spent vanadium redox flow battery electrolyte, add sodium hydroxide, dissolve it by ultrasonic, and at the same time adjust the pH = 1, filter to obtain a solution containing vanadium waste material, and the concentration of vanadium ions in the solution containing vanadium waste material is 1.6 mol / L;

[0078] 2) Take hydrogen peroxide (30% wt H 2 O 2 ) as a valence regulator, and drop it into the solution containing vanadium waste material. The molar ratio of H 2 O 2 to vanadium ions in the solution containing vanadium waste material is 1:1, and react to make the vanadium ions react completely, so that all the vanadium ions in the obtained solution are +4 valence;

[0079] 3) Heat the solution adjusted in step 2) until no obvious bubbles are evolved;

[0080] 4) Weigh 2.4 g of sodium hydroxide, dissolve it in 50 mL of deionized water, and prepare an alkali solution. Drop the alkali solution into the solution obtained in step (3) at a certain dropping rate, and continuously stir until the solution pH = 7 to obtain a precursor slurry;

[0081] 5) Weigh 10.0 g of sodium phosphate, dissolve it in 50 ml of the precursor slurry obtained in step 4). The molar ratio of vanadium ions to phosphate in the solution containing vanadium waste material is 1:1.2. Continuously stir at room temperature for 24 h, filter and dry to obtain the sodium vanadium phosphate product.

[0082] Figure 2 is the ultraviolet absorption curve of the spent vanadium battery electrolyte used in Example 1. As Figure 2 can be seen, the curve shows ultraviolet characteristic absorption peaks corresponding to +3-valent vanadium and +4-valent vanadium at 400 and 780 nm respectively, indicating that the spent vanadium battery electrolyte used contains +3-valent and +4-valent vanadium ions, and the average valence state is +3.8.

[0083] Figure 3 is the ultraviolet absorption curve of the solution after being regulated by the valence regulator hydrogen peroxide in step 3) in Example 1. As Figure 3It can be seen that the curve only has an ultraviolet characteristic absorption peak (780 nm) corresponding to vanadium in the +4 valence state, indicating that after being regulated by the valence state regulator, all the vanadium in the +3 valence state in the spent vanadium battery electrolyte has been converted into the +4 valence state, making all vanadium ions in the solution in the +4 valence state, and there is no need to pre-detect the valence state and valence composition of vanadium ions in the spent electrolyte of the vanadium battery. In Example 1, by controlling the pH, hydrogen ion and vanadium concentration, and temperature of the solution of the vanadium-containing waste material at room temperature, the electrode potential of the valence state regulator is between ψ(V 3+ ) and ψ(V 5+ ), which can spontaneously oxidize low-valent vanadium, realize the adjustment and unification of vanadium valence states, and then prepare sodium vanadium phosphate.

[0084] Example 2

[0085] A method for preparing sodium vanadium phosphate, comprising the following steps:

[0086] 1) Weigh 5 g of the spent sodium vanadium phosphate electrode slurry and disperse it in 50 mL of deionized water to obtain a dispersion of vanadium-containing waste material. Add HCl and dissolve it by ultrasonic treatment. At the same time, adjust the pH = 0, filter to obtain a solution of vanadium-containing waste material, and the concentration of vanadium ions in the solution of vanadium-containing waste material is 0.5 mol / L;

[0087] 2) Take 10 ml of hydroxylamine solution as the valence state regulator and drop it into the solution of vanadium-containing waste material. The molar ratio of hydroxylamine to vanadium ions in the solution of vanadium-containing waste material is 3:1, and react until the vanadium ions react completely, so that all vanadium ions in the obtained solution are in the +4 valence state;

[0088] 3) Heat the solution adjusted in step 2) until no obvious bubbles are evolved;

[0089] 4) Weigh 2.4 g of sodium hydroxide, dissolve it in 50 mL of deionized water, and prepare an alkali solution. Drop the alkali solution into the solution obtained in step (3) at a certain dropping rate, and continuously stir until the solution pH = 7 to obtain a precursor slurry;

[0090] 5) Weigh 10.0 g of sodium phosphate and dissolve it in 50 ml of the precursor slurry obtained in step 4). The molar ratio of vanadium ions to phosphate in the solution of vanadium-containing waste material is 1:1. Stir continuously at room temperature for 24 h, filter and dry to obtain the sodium vanadium phosphate product.

[0091] As determined by the ultraviolet absorption curve, the vanadium in the used spent sodium vanadium phosphate is in the +3 valence state.

[0092] Figure 4 It is the ultraviolet absorption curve of the solution after being regulated by the valence state regulator hydroxylamine in step 3) described in Example 2. From Figure 4It can be seen that the curve has only characteristic absorption peaks corresponding to vanadium ions with a +4 valence state, indicating that after being adjusted by the valence state regulator, all vanadium ions have been converted to the +4 valence state, making all vanadium ions in the solution be in the +4 valence state, and there is no need to pre-detect the valence state and valence state composition of vanadium ions in the failed electrolyte of the vanadium battery.

[0093] Example 3

[0094] A preparation method of sodium vanadium phosphate includes the following steps:

[0095] 1) Take 50 mL of the spent electrolyte containing pentavalent vanadium, add sodium hydroxide, dissolve it by ultrasonic treatment and filter, and at the same time adjust the pH to 0.5 to obtain a solution containing vanadium waste materials, and the concentration of vanadium ions in the solution containing vanadium waste materials is 1 mol / L;

[0096] 2) Take 10 ml of 1 mol / L NaNO 2 solution as the valence state regulator and drop it into the solution containing vanadium waste materials. The molar ratio of NaNO 2 to vanadium ions in the solution containing vanadium waste materials is 1:1, and react to make the vanadium ions react completely, so that all vanadium ions in the obtained solution are in the +4 valence state;

[0097] 3) Heat the solution adjusted in step 2) until no obvious bubbles are evolved;

[0098] 4) Weigh 2.8 g of sodium hydroxide, dissolve it in 50 mL of deionized water, and prepare an alkali solution. Drop the alkali solution into the solution obtained in step (3) at a certain dropping rate, and continuously stir until the solution pH = 7 to obtain a precursor slurry;

[0099] 5) Weigh 10.6 g of disodium hydrogen phosphate and dissolve it in 50 ml of the precursor slurry obtained in step 4). The molar ratio of vanadium ions to phosphate in the solution containing vanadium waste materials is 1:1.8. Continuously stir at room temperature for 12 h, filter and dry to obtain the sodium vanadium phosphate product.

[0100] As determined by the ultraviolet absorption curve and potentiometric titration, the vanadium in the spent electrolyte containing pentavalent vanadium is in the +3, +4, and +5 valence states. The initial electrolyte contains +3 and +4 valence vanadium, and the ratio is 1:1. After a long time, +5 valence vanadium will accumulate. Although the standard electrode potential of +5 valence vanadium is higher than that of +3 valence vanadium, due to the low concentration of +5 valence vanadium, the actual electrode potential of +5 valence vanadium is lower than the actual electrode potential of +3 valence vanadium. Therefore, +3, +4, and +5 valence coexist in the spent electrolyte containing pentavalent vanadium.

[0101] Figure 5 The XRD curve of the sodium vanadium phosphate prepared by the method of Example 3; from Figure 5It can be seen that the obtained XRD curve has a high intensity and no impurity peaks appear, indicating that the prepared sodium vanadium phosphate sample has good purity and crystallinity.

[0102] Example 4

[0103] A preparation method of sodium vanadium phosphate, comprising the following steps:

[0104] 1) Take 50 mL of the spent pentavalent vanadium electrolyte, add sodium hydroxide, dissolve it by ultrasonic treatment, and at the same time adjust the pH = 0.5, filter to obtain a solution containing vanadium waste material, and the concentration of vanadium ions in the solution containing vanadium waste material is 1 mol / L;

[0105] 2) Take 10 ml of 1 mol / L NaNO 2 solution as a valence regulator, and drop it into the solution containing vanadium waste material. The molar ratio of NaNO 2 to vanadium ions in the solution containing vanadium waste material is 1:1, and react to completely react the vanadium ions, so that all vanadium ions in the obtained solution are +4 valence;

[0106] 3) Heat the solution adjusted in step 2) until no obvious bubbles are evolved;

[0107] 4) Weigh 2.8 g of sodium hydroxide, dissolve it in 50 mL of deionized water, and prepare an alkali solution. Drop the alkali solution into the solution obtained in step (3) at a certain dropping rate, and continuously stir until the solution pH = 7 to obtain a precursor slurry;

[0108] 5) Weigh 10.6 g of disodium hydrogen phosphate, 2.3 g of sodium chloride and 1.7 g of sodium fluoride, dissolve them in 50 ml of the precursor slurry obtained in step 4). The molar ratio of vanadium ions to phosphate in the solution containing vanadium waste material is 1:1.8, the molar ratio of phosphate to composite anions is 1:1, and the molar ratio of fluoride ions to chloride ions is 1:1. Stir continuously at room temperature for 12 h, filter and dry to obtain the sodium vanadium phosphate product.

[0109] It can be obtained by EDS test that the element ratio of the prepared sodium vanadium phosphate is Na:V:P:O:F:Cl = 4:2:2:10:1:1, and the corresponding molecular formula of sodium vanadium phosphate is Na 2 VOPO 4 F 0.5 Cl 0.5 .

[0110] Comparative Example 1

[0111] It includes the following steps:

[0112] 1) Weigh 5 g of the spent sodium vanadium phosphate electrode slurry and disperse it in 50 mL of deionized water to obtain a dispersion of vanadium-containing waste material. Add HCl to dissolve it, sonicate for dissolution, and adjust the pH to 8 with NaOH. Then filter to obtain a solution of vanadium-containing waste material, where the concentration of vanadium ions in the solution of vanadium-containing waste material is 0.5 mol / L;

[0113] 2) Weigh 10 ml of hydroxylamine solution as a valence state regulator and add it dropwise to the solution of vanadium-containing waste material, and use ultraviolet spectroscopy to analyze the valence state of vanadium ions in the solution.

[0114] Through the determination of the ultraviolet absorption curve, the vanadium in the spent sodium vanadium phosphate used is in the +3 valence state.

[0115] Figure 6 The ultraviolet absorption curve of the solution after being regulated by hydroxylamine, the valence state regulator described in the method of Comparative Example 1: Under the condition of pH 8, hydroxylamine can only exhibit reducibility and cannot exhibit oxidizing property. From Figure 6 It can be seen that the characteristic absorption peak of +4 valence vanadium does not appear in the curve, indicating that the single oxidation / reduction property of hydroxylamine cannot achieve the purpose of a valence state regulator. The electrode potential of the valence state regulator plays a decisive role in the regulation of the valence state of vanadium ions, and various factors affecting the strength of the electrode potential need to be comprehensively considered.

[0116] Comparative Example 2

[0117] A preparation method of sodium vanadium phosphate includes the following steps:

[0118] 1) Weigh 1.6 g of VOSO 4 After dissolving it in 50 mL of deionized water, prepare a vanadium-containing solution;

[0119] 2) Weigh 2.8 g of sodium hydroxide, dissolve it in 50 mL of deionized water, and prepare an alkali solution. Add the alkali solution dropwise to the vanadium-containing solution and continuously stir until the solution pH = 7 to obtain a precursor slurry;

[0120] 3) Weigh 10.6 g of disodium hydrogen phosphate, dissolve it in 50 mL of deionized water, and prepare a phosphate solution. Disperse the slurry obtained in step 2) in the phosphate solution, continuously stir at room temperature for 12 h, filter and dry to obtain nano sodium vanadium phosphate.

[0121] Table 1

[0122] Current density Example 3 Example 4 Comparative Example 2 1 mA / g 106 mAh / g 112 mAh / g 105 mAh / g

[0123] Table 1 shows the specific capacities of sodium vanadium phosphate prepared by the methods of Example 3, Example 4 and Comparative Example 2. As can be seen from Table 1, under the charge-discharge current density condition of 1 mA / g, the specific capacities of the nano-sodium vanadium phosphate prepared by the methods of Example 3 and Example 4 are 106 mAh / g and 112 mAh / g respectively, which are better than the specific capacity of the sodium vanadium phosphate material prepared by Comparative Example 2 (105 mAh / g), indicating that the method of the present invention can achieve efficient preparation and recycling from vanadium-containing waste to sodium vanadium phosphate.

[0124] Compared with Example 3, in Example 4, by using the regulation effect of composite anions on the electronic structure of sodium vanadium phosphate, F - and Cl - are introduced into the multi-anion system, which improves the electron / ion conductivity of sodium vanadium phosphate, making the prepared nano-sodium vanadium phosphate exhibit more excellent electrochemical performance.

[0125] Comparative Example 3

[0126] The method is exactly the same as that of Example 3, except that in step (1), the pH value of the pentavalent vanadium spent electrolyte is not adjusted.

[0127] In Comparative Example 3, different valence vanadium ions can still be detected in the regulated solution in step 3), indicating that under this condition, the valence regulation of vanadium ions cannot be achieved.

[0128] Comparative Example 4

[0129] The method is exactly the same as that of Example 3, except that in step (1), the pH value is 8.

[0130] In Comparative Example 4, different valence vanadium ions can still be detected in the regulated solution in step 3), indicating that under the condition of pH value 8, the valence regulation of vanadium ions cannot be achieved.

[0131] Comparative Example 5

[0132] The method is exactly the same as that of Example 3, except that the reaction temperature of the solution system in step (2) is adjusted to 100 °C.

[0133] In Comparative Example 5, trivalent and tetravalent vanadium ions can still be detected. Pentavalent vanadium ions can be reduced, but trivalent vanadium ions cannot be oxidized, indicating that under this high temperature condition, the valence regulation of vanadium ions cannot be achieved. This is because under high temperature conditions, the reducibility of NaNO 2 is stronger, but the redox ability is weaker. In comparison, the normal temperature in Example 3 can make all vanadium ions in the solution be +4 valence, realizing the adjustment and unification of vanadium valence.

[0134] In the present invention, terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0135] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A preparation method of sodium vanadium phosphate, characterized in that, it comprises the following steps: (1) Adding acid or base to the vanadium-containing waste material or the dispersion of the vanadium-containing waste material, dissolving, adjusting the pH value while dissolving, and then filtering to obtain a solution of the vanadium-containing waste material; the pH value after dissolution is 0-3; (2) Adding a valence regulator to the solution of the vanadium-containing waste material for reaction to completely react the vanadium ions, so that all the vanadium ions in the obtained solution are +4 valence; the valence regulator includes at least one of hydrogen peroxide, hydroxylamine compounds, nitrous acid, sodium nitrite, and iodine; the reaction is carried out at room temperature; (3) Heating the solution obtained in step (2) until no obvious bubbles are evolved; (4) Adding an alkali solution to the solution obtained in step (3), stirring and reacting to obtain a precursor slurry; (5) Adding phosphate to the precursor slurry to carry out an ion exchange reaction to obtain sodium vanadium phosphate.

2. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (1), the vanadium-containing waste material includes at least one of spent vanadium redox flow battery electrolyte, spent sodium vanadium phosphate electrode material, and mixed vanadium oxides.

3. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (1), the valence of vanadium in the vanadium-containing waste material includes at least one of +2 valence, +3 valence, +4 valence, and +5 valence.

4. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (1), the pH value is adjusted by acid and / or base.

5. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (1), the concentration of vanadium ions in the solution of the vanadium-containing waste material is 0.01-5.0 mol / L.

6. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, In the step (2), under the pH condition of the solution of the vanadium-containing waste material obtained in the step (1), the electrode potential of the valence regulator is between ψV 3+ and ψV 5+ ; and / or, the valence regulator exhibits oxidizing and / or reducing properties; and / or, the molar ratio of the valence regulator to the vanadium ions in the solution of the vanadium-containing waste material is more than 1:

1.

7. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (4), adding the alkali solution to the solution obtained in step (3) until the pH of the solution is 4-9; and / or, the alkali solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water; and / or, the concentration of the alkali solution is 0.01-5.0 mol / L.

8. The preparation method of sodium vanadium phosphate according to claim 1, characterized in that, in the step (5), the phosphate includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium polyphosphate; And / or, in the step (5), adding a phosphate and a composite anion mixture into the precursor slurry to carry out an ion exchange reaction to obtain sodium vanadium phosphate; the composite anion mixture includes a mixture of sodium fluoride and sodium chloride; the molar ratio of the phosphate to the composite anion mixture is 1:0 to 1; F - and Cl - in the composite anion mixture have a molar ratio of 1:0 to 1; and / or, the molar ratio of vanadium ions to phosphate in the solution of the vanadium-containing waste material is 1:1-3; and / or, the time of the ion exchange reaction is 3-24 h.

9. A sodium vanadium phosphate, characterized in that, it is prepared by using the preparation method according to any one of claims 1-8.

10. Use of sodium vanadium phosphate prepared by the preparation method according to any one of claims 1-8 or sodium vanadium phosphate according to claim 9 in an alkali metal secondary battery.

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