A Prussian white positive electrode active material and its preparation method and application

Abstract

The present invention relates to the field of sodium ion battery positive electrode materials, and in particular to a Prussian white positive electrode active material and its preparation method and application. The chemical formula of the Prussian white positive electrode active material is Na x M[T(CN)6] y zH2O, where M is at least one of Mn, Fe, Ni, and Cu, T is one of Mn and Fe, and 1.9 < x ≤ 3, 0 < y ≤ 1, and 0 < z < 1. The Prussian white positive electrode active material of the present invention has a low water content and a high sodium content, significantly improving the rate capability of sodium-ion batteries while ensuring high capacity and excellent cycle performance. The preparation method of the Prussian white positive electrode active material of the present invention is a room-temperature reaction, which is simple to prepare, has a short reaction time, is easily mass-produced, and has promising application prospects. This invention provides a new approach to improving the performance of Prussian white positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion battery positive electrode materials, and in particular to a Prussian white positive electrode active material and a preparation method and application thereof. Background Art

[0002] Since Sony Corporation of Japan commercialized lithium-ion batteries, they have experienced rapid development, particularly in their large-scale use in electric vehicles. However, with the rapid depletion of lithium resources, supply has outstripped demand, leading to a sharp increase in lithium prices. In contrast, sodium, an element with abundant reserves and widespread availability, is significantly cheaper than lithium. Consequently, sodium-ion batteries have gained widespread attention in recent years, offering promising applications in low-speed vehicles and energy storage.

[0003] Among the numerous sodium-ion battery cathode materials currently available, Prussian white (Prussian blue) boasts a rigid lattice framework and large ion channels, facilitating the insertion and extraction of sodium ions. Its high theoretical specific capacity of 170 mAh / g makes it one of the most promising sodium-ion cathode materials. Improving the electrochemical performance of Prussian white (Prussian blue) has become a hot topic. Patent 201810236557 proposes a carbon-coated iron-based Prussian blue (PBAs) synthesized via a liquid-phase reaction using uniformly carbon-coated nanometals or metal oxides as precursors. However, due to the dissolution / precipitation process involved in the precursor reaction, uniform carbon coating cannot be guaranteed on the Prussian blue surface. This coating modification method is complex in preparation and offers limited improvement in the electrochemical performance of the Prussian white cathode material.

[0004] Typical synthesis methods for Prussian White materials include co-precipitation and hydrothermal methods. Both methods are typically performed in aqueous solution. However, due to the rapid reaction rates of these methods, the growth of Prussian White crystals is often accompanied by a large number of lattice defects and crystalline water. These lattice defects and crystalline water are detrimental to their stability in high-temperature environments. Simultaneously, a large amount of crystalline water reduces the sodium ion content in the material. Prussian White materials synthesized by the hydrothermal and precipitation methods have a high crystalline water content and a low sodium ion content, which not only significantly impacts the battery's cycle performance but also reduces the energy density of the entire battery. While vacuum baking can be used to remove the crystalline water, this requires a high level of equipment capability, increases time costs, and does not address the low sodium ion content.

[0005] Therefore, how to develop Prussian white positive electrode materials with low crystalline water and high sodium content and excellent electrochemical properties is an urgent problem that needs to be solved. Summary of the Invention

[0006] The present invention provides a Prussian white positive electrode active material, its preparation method, and its application, addressing the poor electrochemical performance of existing Prussian white positive electrode materials due to high crystalline water content and low sodium content. The present invention utilizes a low-sodium-content Prussian blue compound in a secondary reaction with an aryl sodium solution to obtain a sodium-rich or over-sodium-rich Prussian white with low water content.

[0007] The preparation method of the present invention can not only remove the crystal water in the Prussian white positive electrode active material, but also increase the sodium ion content. The preparation method is simple and easy to implement, easy to mass produce, and the comprehensive performance of the battery can also be greatly improved.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] In the first aspect, the present invention provides a Prussian white positive electrode active material, wherein the chemical formula of the Prussian white positive electrode active material is Na x M[T(CN)6] y ·zH2O, wherein M is at least one of Mn, Fe, Ni, and Cu, T is one of Mn and Fe, 1.9<x≤3 (for example, x is 2.0, 2.2, 2.4, 2.6, or 2.8), 0<y≤1 (for example, y is 0.2, 0.4, 0.6, or 0.8), and 0<z<1 (for example, z is 0.2, 0.4, 0.6, or 0.8).

[0010] In the above-mentioned Prussian white positive electrode active material, as a preferred embodiment, the Prussian white positive electrode active material has a cubic secondary grain morphology, the secondary grains are formed by stacking primary grains, the primary grains are cubic morphology, and the particle size of the secondary grains is 1μm to 20μm (for example, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm).

[0011] The cubic shape mentioned in the present invention includes a cubic shape or a quasi-cube shape.

[0012] In a second aspect, the present invention provides a method for preparing the above-mentioned Prussian white positive electrode active material, which comprises: adding a Prussian blue compound to an aryl sodium solution for reaction, and after the reaction is completed, separating the precipitate in the reaction system, and the obtained precipitate is the Prussian white positive electrode active material.

[0013] In the above preparation method, as a preferred embodiment, the chemical formula of the Prussian blue compound is: Na a M[T(CN)6] bcH2O, wherein M is at least one of Mn, Fe, Ni, and Cu, T is one of Mn and Fe, 0≤a≤1.9 (for example, a is 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, or 1.8), 0.8≤b≤1 (for example, b is 0.85, 0.9, or 0.95), and 0.8≤c (for example, c is 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, or 3.0).

[0014] The present invention reacts a Prussian blue compound with a low sodium content with an aryl sodium solution to reduce the water content while enriching the sodium, thereby obtaining a Prussian white positive electrode active material in a sodium-rich state or an over-sodium-rich state with a low water content.

[0015] In the above preparation method, as a preferred embodiment, the preparation method of the Prussian blue compound comprises the following steps in sequence:

[0016] S1, dissolving sodium ferrocyanide or sodium cyanide and an inorganic sodium salt in water to obtain a first solution; dissolving a transition metal salt in water to obtain a second solution;

[0017] S2. Mixing the first solution and the second solution, and then stirring to react. After the reaction is completed, separating the precipitate in the reaction system, and the obtained precipitate is a Prussian blue compound.

[0018] In a preferred embodiment of the present invention, a Prussian blue compound is first prepared via an aqueous coprecipitation method. This compound is then reacted with a sodium aryl solution to successfully produce a Prussian white cathode active material with low water content and high sodium content. The Prussian white cathode active material prepared by this method can significantly improve the rate capability of sodium-ion batteries while maintaining high capacity and excellent cycle performance. This method, which operates at room temperature, offers simple preparation, short reaction times, and amenability to mass production, promising promising applications. This invention provides a new approach for improving the performance of Prussian white cathode active materials.

[0019] In the above preparation method, as a preferred embodiment, in step S1, the inorganic sodium salt includes one or more of NaCl, NaNO3, and Na2SO4.

[0020] In the above preparation method, as a preferred embodiment, in step S1, the transition metal salt includes one or more of Fe(NO3)3, Fe2(SO4)3, FeCl3, Fe(CH3COO)3, Ni(NO3)2, NiSO4, NiCl2, Ni(CH3COO)2, Mn(NO3)2, MnSO4, Mn(CH3COO)2, MnCl2, CuSO4, CuCl2, and Cu(NO3)2.

[0021] In the above preparation method, as a preferred embodiment, in step S1, the molar ratio of sodium ferrocyanide or sodium cyanide to the inorganic sodium salt is 1:(90-100) (for example, 1:91, 1:92, 1:93, 1:94, 1:95, 1:96, 1:97, 1:98, 1:99); preferably, the total solute concentration of the first solution is 24-26 mol / L (for example, 24.5 mol / L, 25 mol / L, 25.5 mol / L).

[0022] In the above preparation method, as a preferred embodiment, in step S1, the concentration of the second solution is 0.125 to 0.25 mol / L (e.g., 0.15 mol / L, 0.175 mol / L, 0.2 mol / L, 0.225 mol / L).

[0023] In the above preparation method, as a preferred embodiment, in step S2, the first solution and the second solution are mixed by adding the first solution dropwise into the second solution, or adding the second solution dropwise into the first solution; preferably, the dropping speed is 0.5 mL / min to 1000 mL / min (for example, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, 700 mL / min, 800 mL / min, 900 mL / min).

[0024] In the above preparation method, as a preferred embodiment, in step S2, when the first solution and the second solution are mixed, the molar ratio of sodium ferrocyanide or sodium cyanide to the transition metal salt is (1-2):1 (for example, 1.2:1, 1.4:1, 1.6:1, 1.8:1,).

[0025] In the above preparation method, as a preferred embodiment, in step S2, the stirring reaction time is 1 to 24 hours (for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours).

[0026] In the above preparation method, as a preferred embodiment, the solvent of the sodium aryl solution is one or more of dimethyl sulfoxide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and diethyl ether.

[0027] In the above preparation method, as a preferred embodiment, the solute of the aryl sodium solution is one or more of sodium pyrene, sodium biphenyl, sodium naphthalene, and sodium anthracene.

[0028] In the above preparation method, as a preferred embodiment, the concentration of the sodium aryl solution is 0.005-0.5 mol / L (e.g., 0.01 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L); preferably, 0.45-0.5 mol / L (e.g., 0.46 mol / L, 0.47 mol / L, 0.48 mol / L, 0.49 mol / L).

[0029] In the above preparation method, as a preferred embodiment, the molar ratio of the Prussian blue compound to the sodium element in the aryl sodium solution is 1:(0.01~50) (for example, 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:5, 1:10, 1:20, 1:30, 1:40, 1:45); preferably 1:(1~5) (for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:4).

[0030] In the above preparation method, as a preferred embodiment, the reaction time of the Prussian blue compound and the sodium aryl solution is 1 min to 30 min (for example, 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min).

[0031] In the above preparation method, as a preferred embodiment, the reaction of the Prussian blue compound and the aryl sodium solution is carried out under an inert atmosphere.

[0032] In a third aspect, the present invention provides the above-mentioned positive electrode material, which includes the Prussian white positive electrode active material of the above-mentioned first aspect or the Prussian white positive electrode active material prepared by the preparation method of the above-mentioned second aspect.

[0033] In a fourth aspect, the present invention provides a sodium ion battery comprising the positive electrode material described in the third aspect, the battery further comprising a battery housing and a positive electrode, a separator, and a negative electrode located within the battery housing, the positive electrode comprising a positive electrode current collector and the positive electrode material described in the third aspect located on the positive electrode current collector. Compared with the prior art, the present invention has the following advantages:

[0034] The present invention produces a Prussian white cathode active material by reacting a Prussian blue compound with a sodium aryl solution. This material has a low content of water of crystallization and a high content of sodium ions. The sodium ion battery assembled with this cathode active material exhibits exceptional rate performance, high capacity, and excellent cycle stability. The preparation method provided by the present invention is simple, facilitates industrial production, and has promising commercial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a comparison chart of the test results of the batteries prepared in Example 1 and Comparative Example 1 according to Test 1 in Example 1.

[0036] Figure 2 This is a comparison chart of the test results of the batteries prepared in Example 1 and Comparative Example 1, performed according to Test 2 in Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0038] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0039] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0040] In the present invention, unless otherwise specified and / or explained, all numerical values involving the amounts of components are "parts by weight". The process parameters in the following examples that are not specified in specific conditions are generally based on conventional conditions.

[0041] Example 1

[0042] S1. Under a protective atmosphere, 0.25 mol of sodium ferrocyanide and 25 mol of sodium chloride were dissolved in 1 L of deionized water and stirred thoroughly to obtain a first solution;

[0043] Dissolve 0.125 mol MnCl2 in 1 L of deionized water and stir thoroughly to obtain a second solution;

[0044] S2, the second solution prepared in step S1 was added dropwise to the first solution prepared in step S1 at a rate of 10 mL / min, and the reaction was stirred for 6 h. After the reaction was completed, the precipitate was separated from the reaction system and washed and dried to obtain Na 1.8 Mn[Fe(CN)6] 0.97 2.33H2O;

[0045] S3. Then, under protective atmosphere, Na 1.8 Mn[Fe(CN)6] 0.97 ·2.33H2O and 0.5mol / L sodium naphthalene (C 10 H8Na) solution was mixed and reacted for 10 min, wherein Na 1.8 Mn[Fe(CN)6] 0.97 The molar ratio of 2.33H2O to sodium in sodium naphthalene is 1:1.1. After the reaction, the sodium-rich and low-water content Prussian white positive electrode active material Na is obtained by filtration, washing, and drying. 2.06 Mn[Fe(CN)6] 0.97 0.12H2O.

[0046] Preparation of test battery: The sodium-rich low-water content Prussian white positive electrode active material Na 2.06 Mn[Fe(CN)6] 0.97 0.12H2O was mixed with carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8:1:1 to form the electrode. A sodium metal sheet was used as the negative electrode, a Whatman GF / D membrane was used as the separator, and 1 mol / L NaPF6 (solvent and volume ratio of EC:DEC:FEC = 49:49:2) was used as the electrolyte. The battery (theoretical capacity 170 mAh / g) was assembled in a glove box filled with high-purity argon with oxygen and water pressures below 1 ppm. Charge and discharge tests were then conducted on a battery testing system.

[0047] Test 1: The battery prepared in this embodiment was subjected to charge and discharge cycles with a voltage range of 2-4V and a current density of 1C = 170mA / g. The first 1-5 weeks were charged and discharged at a constant current of 0.1C, the 6-10 weeks were charged and discharged at a constant current of 0.2C, the 11-15 weeks were charged and discharged at a constant current of 0.5C, the 16-20 weeks were charged and discharged at a constant current of 1C, the 21-25 weeks were charged and discharged at a constant current of 2C, and the 26-30 weeks were charged and discharged at a constant current of 0.1C. The test results are as follows: Figure 1 As shown (the vertical axis is the charge capacity per cycle).

[0048] Test 2: The battery prepared in this embodiment was charged and discharged at a constant current of 0.1C for 3 cycles, and then charged and discharged at a constant current of 1C (170mA / g) for the 4th to 200th cycles (voltage range of 2-4V). The test results are as follows: Figure 2 As shown (the vertical axis is the charge capacity per cycle).

[0049] Figure 1 The average charge specific capacity at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 0.1C were 155.5 mAh / g (average charge specific capacity of weeks 1-5), 149.4 mAh / g (average charge specific capacity of weeks 6-10), 140.8 mAh / g (average charge specific capacity of weeks 11-15), 135.4 mAh / g (average charge specific capacity of weeks 16-20), 130.1 mAh / g (average charge specific capacity of weeks 21-25), and 152.5 mAh / g (average charge specific capacity of weeks 26-30).

[0050] Figure 2 In this example, Na 2.06 Mn[Fe(CN)6] 0.97 A battery prepared using 0.12H2O as the active material had a first-cycle specific capacity of 154.8 mAh / g at 0.1C. After cycling the battery at 1C for 4-200 cycles, the capacity retention rate (200th-cycle discharge capacity / 4th-cycle discharge capacity × 100%) was 88.4%, demonstrating high specific capacity and excellent cycling performance.

[0051] Example 2

[0052] S1. Under a protective atmosphere, 0.25 mol of sodium cyanide and 25 mol of sodium chloride were dissolved in 1 L of deionized water and stirred thoroughly to obtain a first solution;

[0053] Dissolve 0.25 mol MnCl2 in 1 L of deionized water and stir thoroughly to obtain a second solution;

[0054] S2, the second solution prepared in step S1 was added dropwise to the first solution prepared in step S1 at a rate of 5 mL / min, and the reaction was stirred for 10 h. After the reaction was completed, the precipitate was separated from the reaction system and washed and dried to obtain Na 1.96 Mn[Mn(CN)6] 0.98 2.48H2O;

[0055] S3. Then, under protective atmosphere, Na 1.96 Mn[Mn(CN)6]0.98 ·2.48H2O was mixed with 0.5mol / L sodium biphenyl solution and reacted for 0.5h, where Na 1.96 Mn[Mn(CN)6] 0.98 The molar ratio of 2.48H2O to sodium naphthalene is 1:1.2. After the reaction, the sodium-rich and low-water content Prussian white positive electrode active material Na is obtained by filtration, washing, and drying. 2.87 Mn[Mn(CN)6] 0.98 0.18H2O.

[0056] Preparation of test battery: The sodium-rich low-water content Prussian white positive electrode active material Na 2.87 Mn[Mn(CN)6] 0.98 0.18H2O was mixed with carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8:1:1 to form the electrode. A sodium metal sheet was used as the negative electrode, a Whatman GF / D membrane was used as the separator, and 1 mol / L NaPF6 (solvent and volume ratio of EC:DEC:FEC = 49:49:2) was used as the electrolyte. The battery (theoretical capacity 250 mAh / g) was assembled in a glove box filled with high-purity argon with oxygen and water pressures below 1 ppm. Charge and discharge tests were then conducted on a battery testing system.

[0057] Test 1: The battery prepared in this embodiment was subjected to charge and discharge cycles, 0.1C constant current charge and discharge cycles for 3 cycles, and then 1C constant current charge and discharge cycles for the 4th to 200th cycles, with a current density of 1C = 200mA / g and a voltage range of 1.4-4V.

[0058] Test results: The first-week charging capacity at 0.1C is 213.2 mAh / g, and the cycle performance is improved to a certain extent. After 100 cycles at 1C, the capacity retention rate (discharge capacity at the 100th week / discharge capacity at the 4th week×100%) is 78%.

[0059] Example 3

[0060] S1. Under a protective atmosphere, 0.25 mol of sodium ferrocyanide and 25 mol of sodium chloride were dissolved in 1 L of deionized water and stirred thoroughly to obtain a first solution;

[0061] Dissolve 0.125 mol FeCl3 in 1 L of deionized water and stir thoroughly to obtain a second solution;

[0062] S2, the second solution prepared in step S1 was added dropwise to the first solution prepared in step S1 at a rate of 20 mL / min, and the mixture was stirred for 10 h. After the reaction was completed, the precipitate was separated from the reaction system and washed and dried to obtain Na 0.82 Fe[Fe(CN)6] 0.87 1.89H2O;

[0063] S3. Then, under protective atmosphere, Na 0.82 Fe[Fe(CN)6] 0.87 1.89H2O was mixed with 0.5mol / L sodium biphenyl solution and reacted for 0.5h, where Na 0.82 Fe[Fe(CN)6] 0.87 The molar ratio of 1.89H2O to sodium naphthalene is 1:1.3. After the reaction, the sodium-rich and low-water content Prussian white positive electrode active material Na is obtained by filtration, washing, and drying. 1.93 Fe[Fe(CN)6] 0.87 0.14H2O.

[0064] Preparation of test battery: The sodium-rich low-water content Prussian white positive electrode active material Na 1.93 Fe[Fe(CN)6] 0.87 0.14H2O was mixed with carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8:1:1 to form the electrode. A sodium metal sheet was used as the negative electrode, a Whatman GF / D membrane was used as the separator, and 1 mol / L NaPF6 (solvent and volume ratio of EC:DEC:FEC = 49:49:2) was used as the electrolyte. The battery (theoretical capacity 170 mAh / g) was assembled in a glove box filled with high-purity argon with oxygen and water pressures below 1 ppm. Charge and discharge tests were then conducted on a battery testing system.

[0065] Test 1: The battery prepared in this embodiment was charged and discharged at a constant current of 0.1C for 3 cycles, and then charged and discharged at a constant current of 1C for the 4th to 200th cycles, with a current density of 1C = 170mA / g and a voltage range of 2-4V.

[0066] Test results: The first-week charging capacity at 0.1C is 131.6 mAh / g, and the cycle performance is significantly improved. After 100 cycles at 1C, the capacity retention rate (discharge capacity at the 100th week / discharge capacity at the 4th week×100%) is 92%.

[0067] Comparative Example 1

[0068] This comparative example uses the Na 1.8 Mn[Fe(CN)6] 0.97 · 2.33H2O was used as the positive electrode active material, and a test cell was prepared according to the method in Example 1.

[0069] The battery prepared in this comparative example was tested according to the conditions of test 1 and test 2 in Example 1. The test results are shown in FIG. Figure 1 and Figure 2The battery prepared in this comparative example has a first-week charging capacity of 146.3 mAh / g at 0.1C. After 200 cycles at 1C, the capacity retention rate (200th-week discharge capacity / 4th-week discharge capacity × 100%) is only 70.3%.

[0070] Comparative Example 2

[0071] This comparative example uses the Na prepared in Example 2 1.96 Mn[Mn(CN)6] 0.98 · 2.48H2O was used as the positive electrode active material. A test cell was prepared according to the method in Example 2, and the test was performed according to the test conditions in Example 2.

[0072] Test results: The initial charging capacity of the battery prepared in this comparative example at 0.1C in the first week is only 143.2mAh / g. After 100 cycles at 1C, the capacity retention rate (discharge capacity at the 100th week / discharge capacity at the 4th week×100%) is only 70%.

[0073] Comparative Example 3

[0074] This comparative example uses the Na 0.82 Fe[Fe(CN)6] 0.87 1.89H2O was used as the positive electrode active material. A test cell was prepared according to the method in Example 3, and the test was performed according to the test conditions in Example 3.

[0075] Test results: The battery prepared in this comparative example has a first-week charging capacity of only 79.6 mAh / g at 0.1C. After 100 cycles at 1C, the capacity retention rate (discharge capacity at the 100th week / discharge capacity at the 4th week×100%) is only 76.5%.

[0076] Comparative Example 4

[0077] This comparative example is basically the same as Example 3, except that in step S3, Na 0.82 Fe[Fe(CN)6] 0.87 The molar ratio of 1.89H2O to sodium naphthalene was 1:60. After the reaction, the mixture was filtered, washed, and dried to obtain a Prussian white positive electrode active material. A test cell was prepared according to the method in Example 3, and the cell was tested according to the method in Example 3.

[0078] Test results: The first-cycle specific capacity at 0.1C was 53.2 mAh / g. The excessively high proportion of aryl sodium reagent used in this comparative example further reacted with the material, destroying the structure of the Prussian white cathode active material and resulting in an extremely low first-cycle capacity.

[0079] In summary, the present invention adopts low-sodium-content Prussian white or Prussian blue to react with the aryl sodium solution, which not only reduces the crystallization water content but also increases the sodium ion content, thereby significantly improving the electrochemical performance of the material. This method is simple and easy to implement, has high safety, and not only increases the capacity of the material but also improves the cycle performance of the material itself, and has broad research prospects and application value.

[0080] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a Prussian white positive electrode active material, characterized in that: The method comprises: adding a Prussian blue compound to an aryl sodium solution for reaction; after the reaction is completed, separating the precipitate in the reaction system; and obtaining the precipitate as the Prussian white positive electrode active material; and the preparation method of the Prussian blue compound comprises the following steps in sequence: S1, dissolving sodium ferrocyanide or sodium cyanide and an inorganic sodium salt in water to obtain a first solution; dissolving a transition metal salt in water to obtain a second solution; S2, mixing the first solution and the second solution, and then stirring to react. After the reaction is completed, separating the precipitate in the reaction system, and the obtained precipitate is a Prussian blue compound; The molar ratio of the Prussian blue compound to the sodium element in the aryl sodium solution is 1:(1-2); The chemical formula of the Prussian white positive electrode active material is Na x M[T(CN)6] y zH2O, wherein M is at least one of Mn, Fe, Ni, and Cu, T is one of Mn and Fe, 1.9<x≤3, 0<y≤1, and 0<z<1.

2. The preparation method according to claim 1, wherein The Prussian white positive electrode active material has a cubic secondary crystal grain morphology. The secondary crystal grains are formed by stacking primary crystal grains. The primary crystal grains have a cubic morphology. The particle size of the secondary crystal grains is 1 μm to 20 μm.

3. The preparation method according to claim 1, wherein In step S1, the inorganic sodium salt includes one or more of NaCl, NaNO3, and Na2SO4; And / or, in step S1, the transition metal salt includes one or more of Fe(NO3)3, Fe2(SO4)3, FeCl3, Fe(CH3COO)3, Ni(NO3)2, NiSO4, NiCl2, Ni(CH3COO)2, Mn(NO3)2, MnSO4, Mn(CH3COO)2, MnCl2, CuSO4, CuCl2, and Cu(NO3)2; and / or, in step S1, the molar ratio of sodium ferrocyanide or sodium cyanide to the inorganic sodium salt is 1:(90-100); and / or, in step S1, the total solute concentration of the first solution is 24 to 26 mol / L; and / or, in step S1, the concentration of the second solution is 0.125 to 0.25 mol / L; And / or, in step S2, the first solution and the second solution are mixed by dropwise adding the first solution into the second solution, or dropwise adding the second solution into the first solution, at a rate of 0.5 mL / min to 1000 mL / min; and / or, in step S2, when the first solution and the second solution are mixed, the molar ratio of sodium ferrocyanide or sodium cyanide to the transition metal salt is (1-2):1; And / or, in step S2, the stirring reaction time is 1 to 24 hours; and / or, the solvent of the sodium aryl solution is one or more of dimethyl sulfoxide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and diethyl ether; And / or, the solute of the aryl sodium solution is one or more of sodium pyrene, sodium biphenyl, sodium naphthalene, and sodium anthracene; and / or, the concentration of the sodium aryl solution is 0.005 to 0.5 mol / L; And / or, the reaction time of the Prussian blue compound and the sodium aryl solution is 1 min to 30 min; And / or, the reaction of the Prussian blue compound with the sodium aryl solution is carried out under an inert atmosphere.

4. The preparation method according to claim 3, wherein The concentration of the sodium aryl solution is 0.45-0.5 mol / L.

5. The preparation method according to claim 1, wherein The chemical formula of the Prussian blue compound is: Na a M[T(CN)6] b cH2O, wherein M is at least one of Mn, Fe, Ni, and Cu, T is one of Mn and Fe, 0≤a≤1.9, 0.8≤b≤1, and 0.8≤c.

6. A positive electrode material, comprising the Prussian white positive electrode active material prepared by the preparation method according to any one of claims 1 to 5.

7. A sodium ion battery, comprising a battery housing and a positive electrode, a separator, and a negative electrode located within the battery housing, wherein the positive electrode comprises a positive electrode current collector and the positive electrode material according to claim 6 located on the positive electrode current collector.

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