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

Abstract

Provided are a Prussian blue positive electrode material and a preparation method therefor, a positive electrode sheet and a sodium-ion battery. The Prussian blue positive electrode material comprises a Prussian blue compound, the general chemical formula of the Prussian blue compound being NaxFe[Fe(CN)6]y•nH2O. The Prussian blue positive electrode material is simple in terms of a synthesis method and low in terms of raw material cost, and is beneficial for improving the performance such as the specific capacity, coulombic efficiency, rate capability and long cycle stability of a sodium-ion battery when being applied to the sodium-ion battery.

Description

A Prussian blue positive electrode material and preparation method thereof, positive electrode sheet, and sodium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China National Intellectual Property Administration on June 27, 2023, with application number 202310772356.6 and application name “A Prussian blue positive electrode material, its preparation method and application”, all contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention belongs to the technical field of batteries and electrochemical energy storage, and in particular relates to a Prussian blue positive electrode material and a preparation method thereof, a positive electrode sheet, and a sodium ion battery. Background Art

[0004] Energy storage has become a key issue in modern society for utilizing renewable energy and promoting smart grids. Room-temperature sodium-ion batteries (SIBs), operating under similar chemical conditions to lithium-ion batteries (LIBs), have become promising candidates for energy storage systems (ESSs) due to the worldwide abundance and low cost of sodium. Rechargeable sodium-ion batteries (SIBs) are emerging as promising candidates for large-scale energy storage system applications due to their abundant resources and manageable costs. Prussian blue (PB) and its analogs (PBAs) have been considered as potential cathodes and have attracted increasing attention due to their inherent rigid open frameworks and large interstitial sodium storage sites, high theoretical capacity, and non-toxic properties. In addition, the convenient synthesis process and low cost of PBAs are also very attractive for potential large-scale applications. However, PBAs have poor rate capability and cycling stability due to their low electronic conductivity and defects in the PBA framework.

[0005] In a typical PB framework, the iron center is low-spin (Fe LS (C)) or high spin (Fe HS (N)) structures exist, depending on whether the iron atom is on the carbon or nitrogen side of the cyanide ligand. LS (C) and Fe HS (N) participates in the redox reaction of sodium storage at different potentials and theoretically provides the same number of coulombs because the number of two Fe sites is equal in a perfect PB framework. However, existing literature shows that the Fe HS (N) redox reaction compared to Fe LS (C) The capacity contribution of the redox reaction couple is much lower. In addition, this under-activated low-spin Fe LS(C) Redox couple, which is electrochemically active at higher potentials, will inevitably drag down the average potential platform of the PBA-based cathode. It has been reported that Fe LS (C) redox couple, although the cycling stability is optimized, the capacity is sacrificed. Therefore, in order to realize the full potential of PBA-based cathode materials, it is urgent to solve this problem, and unsatisfactory rate capability is another obstacle to the commercialization of PBA materials.

[0006] Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a Prussian blue positive electrode material and its preparation method and application, aiming to solve the problem of poor capacity caused by optimizing cycle stability when the existing Prussian blue material is used in sodium ion batteries. The positive electrode material provided by the present invention has higher rate performance and better cycle stability.

[0008] In view of this, the purpose of the present invention is to provide a Prussian blue positive electrode material and its preparation method and application, aiming to solve the problem that the existing Prussian blue material causes poor capacity in order to optimize the cycle stability. The positive electrode material provided by the present invention has higher rate performance and better cycle stability.

[0009] In a first aspect, the present invention provides a Prussian blue positive electrode material having the general chemical formula:

[0010] Na x Fe[Fe(CN)]6·nH2O Formula I,

[0011] In formula I, x is 0.01 to 3,

[0012] n is 0.01 to 3.

[0013] In an embodiment of the present invention, x can be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5. When x is less than 1.5, the cycle stability of the obtained Prussian blue positive electrode material will be better, the Na ion content is relatively low and it belongs to a sodium-poor state, the reaction rate is faster, and the lattice defects and water content will be less, thereby having better performance; n can be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5; x and n are both molar ratios.

[0014] The Prussian blue positive electrode material provided by the present invention has a block structure.

[0015] In an embodiment of the present invention, the nanocube size of the Prussian blue positive electrode material is 500-2000 nm.

[0016] In a second aspect, the present invention provides a method for preparing a Prussian blue positive electrode material, comprising:

[0017] Solution A and solution B are mixed to obtain a solid precipitate;

[0018] Washing and drying the solid precipitate to obtain a Prussian blue positive electrode material;

[0019] The solution A comprises: a carbonaceous material, sodium ferrocyanide and a first solvent;

[0020] The solution B comprises: iron salt, sodium citrate and a second solvent.

[0021] In an embodiment of the present invention, the carbonaceous material may be selected from conductive carbon black, activated carbon, etc. For example, Ketjen black may be used.

[0022] In an embodiment of the present invention, the first solvent may include: water and solvent A; water may be selected from deionized water; solvent A may be selected from one or more of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol, such as ethylene glycol; the volume ratio of water to solvent A may be selected from 1:(0.01-100), such as 1:(0.05-90), 1:(0.1-80), 1:(0.5-70), 1:(1-60), 1:(5-50), 1:(10-40), and 1:(20-30). In an embodiment of the present invention, the preparation method of the first solvent may include: uniformly mixing water and solvent A; the mixing is performed under stirring, and the stirring time may be selected from 1 to 100 minutes, such as 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, and 90 minutes.

[0023] In an embodiment of the present invention, the concentration of sodium ferrocyanide in solution A can be selected from 0.1 to 100 g / L, such as 0.5 g / L, 1 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, and 90 g / L.

[0024] In an embodiment of the present invention, the method for preparing solution A may include:

[0025] The carbonaceous material is dispersed in a first solvent to obtain a dispersion liquid, and sodium ferrocyanide is dissolved in the dispersion liquid to obtain a solution A.

[0026] In an embodiment of the present invention, the dispersion may be performed by ultrasonic stirring.

[0027] In an embodiment of the present invention, the iron salt may be selected from divalent iron salts, such as one or more of FeSO4·7H2O, Fe(NO3)2, and FeCl2·4H2O.

[0028] In an embodiment of the present invention, sodium citrate can be selected from one or more of anhydrous sodium citrate, dihydrate sodium citrate, and pentahydrate sodium citrate.

[0029] In an embodiment of the present invention, the second solvent may include: water and solvent B; water may be selected from deionized water; solvent B may be selected from one or more of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol, such as ethylene glycol; the volume ratio of water to solvent B may be selected from 1:(0.01-100), such as 1:(0.05-90), 1:(0.1-80), 1:(0.5-70), 1:(1-60), 1:(5-50), 1:(10-40), and 1:(20-30). In an embodiment of the present invention, the preparation method of the second solvent may include: uniformly mixing water and solvent B; the mixing is carried out under stirring, and the stirring time may be selected from 1 to 100 minutes, such as 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, and 90 minutes.

[0030] In an embodiment of the present invention, the preparation method of solution B may include:

[0031] The iron salt and sodium citrate are dissolved in the second solvent to obtain solution B.

[0032] In the embodiment of the present invention, a uniform solution B can be obtained by stirring and dissolving.

[0033] In an embodiment of the present invention, the molar ratio of the carbonaceous material and sodium ferrocyanide can be selected from 1:(1-100), such as 1:(5-90), 1:(10-80), 1:(20-70), 1:(30-60), 1:(40-50); the molar ratio of sodium ferrocyanide and iron salt can be selected from 1:(1-3), such as 1:2; the molar ratio of iron salt and sodium citrate can be selected from 1:(1-100), such as 1:(5-90), 1:(10-80), 1:(20-70), 1:(30-60), 1:(40-50); the volume ratio of solution A and solution B can be selected from 1:(0.1-10), such as 1:(0.5-9), 1:(1-8), 1:(2-7), 1:(3-6), 1:(4-5).

[0034] In the embodiment of the present invention, solvent A and solvent B are both solvents that are poorly soluble in sodium ferrocyanide, and their function is to adjust the solubility to control the reaction rate and thus control the defect generation during the crystal growth process.

[0035] In an embodiment of the present invention, mixing can be performed by dropping solution A into solution B, or by dropping solution B into solution A; the dropping speed can be selected from 0.1 to 100 mL / min, such as 0.5 mL / min, 1 mL / min, 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, and 90 mL / min.

[0036] In the embodiment of the present invention, the function of mixing solution A and solution B is to adjust the dissolution rate and control the reaction speed.

[0037] In an embodiment of the present invention, mixing can be a reaction; the mixing temperature can be selected from 5 to 100°C, such as 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C; the mixing can be carried out under stirring conditions, and the stirring speed can be selected from 100 to 1500rpm, such as 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, 1100rpm, 1200rpm, 1300rpm, and 1400rpm; the mixing time can be selected from 12 to 72h, such as 24h, 36h, 48h, and 60h.

[0038] In an embodiment of the present invention, the washing reagent can be selected from water or ethanol, water can be selected from deionized water; ethanol can be selected from anhydrous ethanol; water and ethanol can be used for alternating washing, the number of water washings can be twice, and the number of ethanol washings can be once.

[0039] In an embodiment of the present invention, the drying temperature may be selected from 60 to 120° C., such as 70° C., 80° C., 90° C., 100° C., and 110° C.; and the drying time may be greater than 2 hours.

[0040] In an embodiment of the present invention, a method for preparing a Prussian blue positive electrode material may include:

[0041] Deionized water and ethylene glycol are stirred and mixed uniformly in a volume ratio of 1: (0.01-50) for 10-60 minutes, and then Ketjen black is added to the mixture and ultrasonically stirred until it is uniformly dispersed; then, the raw material sodium ferrocyanide (Na4Fe(CN)6·10H2O) is added to the dispersion and stirred for 30 minutes to obtain a 5-50 g / L sodium ferrocyanide dispersion; and in addition, according to the ratio of the amount of ferrous salt and sodium citrate of 1: (0.01-100) and the ratio of the amount of sodium ferrocyanide to the metal salt (total) of 1: (1-2), the ferrous salt and sodium citrate are weighed and added to a certain volume of the deionized water and ethylene glycol mixed solution, ensuring that the volume ratio of the sodium ferrocyanide dispersion to the mixed metal salt solution is 1: (0.1-10), and stirring to fully dissolve to obtain a transparent mixed metal salt solution;

[0042] The mixed solution obtained above is slowly added dropwise to another mixed solution through a constant pressure funnel or a peristaltic pump at a dropping rate of 1 to 100 mL / min. At the same time, the reaction is carried out at a reaction temperature of 5 to 100° C. and a stirring rate of 100 to 1500 rpm for 12 to 72 hours, followed by filtration or centrifugation to obtain a blue Prussian blue precipitate;

[0043] The Prussian blue precipitate obtained above is washed clean with a detergent, and then placed in a vacuum oven at 60-120° C. for drying for more than 2 hours to obtain the Prussian blue positive electrode material for sodium ion batteries of the present invention.

[0044] In an embodiment of the present invention, the divalent iron salt is selected from one or more of FeSO4·7H2O, Fe(NO3)2 or FeCl2·4H2O, the sodium citrate is selected from one or more of anhydrous sodium citrate, sodium citrate dihydrate and sodium citrate pentahydrate; and the detergent is selected from deionized water or anhydrous ethanol.

[0045] The present invention also provides a Prussian blue positive electrode material, wherein the Prussian blue positive electrode material comprises a Prussian blue compound, and the chemical formula of the Prussian blue compound is:

[0046] Na x Fe[Fe(CN)6] y nH2O Formula I,

[0047] In formula I, x is 0.01 to 3, 0 <y<1,

[0048] n is 0.01 to 3.5.

[0049] The Prussian blue positive electrode material provided by the present invention, when applied to sodium ion batteries, is beneficial to improving the performance of sodium ion batteries in terms of specific capacity, coulombic efficiency, rate performance and long-cycle stability.

[0050] The present invention also provides a method for preparing a Prussian blue positive electrode material, comprising:

[0051] mixing the first dispersion and the second dispersion to obtain a solid precipitate;

[0052] The solid precipitate is washed and dried to obtain a Prussian blue positive electrode material.

[0053] Wherein, the first dispersion liquid comprises: a ferrocyanide source, a first sodium source and a first dispersant;

[0054] The second dispersion liquid includes: a divalent iron source, a complexing agent and a second dispersant.

[0055] The present invention provides a method for preparing a Prussian blue positive electrode material. The method comprises mixing a ferrocyanide source, a first sodium source, and a divalent iron source to coprecipitate and generate a Prussian blue compound, thereby obtaining the Prussian blue positive electrode material. The addition of a complexing agent forms a strong complexation with ferrous ions provided by the divalent iron source, which is beneficial for controlling the generation rate of the Prussian blue compound, reducing defects in the Prussian blue compound, increasing the yield of the Prussian blue compound, improving the performance of the Prussian blue positive electrode material, and facilitating improving the cycle stability, specific capacity, coulombic efficiency, rate performance, and other properties of a sodium ion battery using the prepared Prussian blue positive electrode material.

[0056] The present invention also provides a positive electrode plate, which includes the Prussian blue positive electrode material as described above; or, the positive electrode plate includes the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above.

[0057] The positive electrode plate provided in an embodiment of the present invention includes the Prussian blue positive electrode material as described above or the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above, so when applied to a sodium ion battery, it is beneficial to improve the performance of the sodium ion battery in terms of specific capacity, coulombic efficiency, rate performance and long-cycle stability.

[0058] The present invention provides a sodium ion battery, comprising: the Prussian blue positive electrode material described in the above technical solution; or the Prussian blue positive electrode material prepared by the method described in the above technical solution; or the positive electrode plate described in the above technical solution.

[0059] In an embodiment of the present invention, a sodium ion battery includes: a positive electrode, a negative electrode, a separator and an electrolyte.

[0060] In an embodiment of the present invention, a method for preparing a positive electrode may include:

[0061] mixing a positive electrode material, a binder, a conductive agent and a solvent to obtain a slurry;

[0062] The slurry was coated on an aluminum foil and then dried to obtain a positive electrode.

[0063] In an embodiment of the present invention, the positive electrode material is the Prussian blue positive electrode material described in the above technical solution; the binder can be selected from polyvinylidene fluoride (PVDF); the conductive agent can be selected from Super P; the mass ratio of the positive electrode material, the binder and the conductive agent can be selected from (6-8): (1-3): (0.5-1.5), or can be selected from (6.5-7.5): (1.5-2.5): (0.8-1.2), or can be selected from 7:2:1; the solvent is selected from dimethylpyrrolidone.

[0064] In an embodiment of the present invention, the negative electrode can be selected from metallic sodium; the separator can be selected from a glass fiber membrane; and the electrolyte can be selected from 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroacetate) (EC:PC:FEC=0.45:0.45:0.05, vol).

[0065] In an embodiment of the present invention, the positive electrode, the negative electrode, the separator and the electrolyte can be assembled into a CR2032 button cell in a glove box.

[0066] The present invention provides a high-capacity and high-rate Prussian blue positive electrode material for sodium ion batteries. The chemical composition of the positive electrode material is Na x Fe[Fe(CN)]6·nH2O has a stable, highly dispersed hierarchical structure (Scanning electron microscopy reveals that the Prussian blue material is not a regular cube, but rather a cube-like morphology formed by stacked layers), ensuring high rate performance and good cycling stability. The method for preparing Prussian blue cathode material for sodium-ion batteries provided by this invention features low raw material costs, a simple preparation process, easy control, and low energy consumption, making it suitable for industrialization.

[0067] The present invention provides a pure phase Prussian blue positive electrode material for sodium ion batteries. The positive electrode material in the present invention is an Fe-based Prussian blue material with a general chemical formula of Na xFe[Fe(CN)]6·nH2O; the present invention utilizes the characteristics of sodium ferrocyanide being poorly soluble in the organic solvent used but easily soluble in water, resulting in different solubility of sodium ferrocyanide in mixed solvents of organic solution and water in different volume ratios, so that the reaction system presents a solid-liquid two-phase state, thereby forming a new synthesis mechanism of Prussian blue; the presence of the organic solvent in the reaction system slows down the reaction rate between the various ions to a certain extent; the excess sodium citrate can not only form a strong complexation with the ferrous ions, but also effectively increase the content of sodium ions in the solution, which greatly slows down the generation rate of the precipitate and effectively increases the content of sodium ions in the elemental composition of the precipitate; based on the above characteristics, the reaction mechanism of the present invention can effectively control the generation rate of Prussian blue and effectively increase the yield, so the Prussian blue prepared by the method provided by the present invention has fewer defects and higher yield.

[0068] The reaction mechanism of the Prussian blue cathode material for sodium ion batteries of the present invention includes: first, a small amount of solid phase sodium ferrocyanide is partially dissolved in an organic solvent to produce Na + and [Fe(CN)6] 4- ions, then Na + and [Fe(CN)6] 4- With water-soluble Fe 2+ A coprecipitation reaction occurs in the liquid phase; the new synthesis mechanism of Prussian blue in the two-phase synthesis preparation process helps to reduce the reaction rate and control the crystal growth process. When forming Prussian blue crystals, they tend to grow on the surface of the formed precipitate. Therefore, the prepared Prussian blue is a stable and highly dispersed hierarchical micro-nano structure self-assembled by micron cubes, with characteristics such as appropriate grain size, large specific surface area and high sodium ion migration rate, ensuring that high rate performance and good cycle stability can be obtained. Specific examples show that the battery obtained by the present invention has a 200-cycle specific capacity of >100 mA g -1 , after 800 cycles, the specific capacity is >84mA g -1 . The Prussian blue positive electrode material for sodium ion batteries in the present invention greatly improves the disadvantage of poor conductivity of single Prussian blue positive electrode material due to the addition of a certain amount of Ketjen black. In addition, Ketjen black, as a common conductive carbon black, is relatively easy to obtain and the cost is controllable. The raw materials used in the method provided by the present invention are cheap and easy to obtain, the synthesis process is safe, controllable and low in energy consumption, and the waste liquid generated in the reaction system is relatively easy to recycle, so it has large-scale production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] (a) in FIG1 is an X-ray diffraction pattern of the positive electrode material prepared in Example 1;

[0070] (b) in FIG1 is a scanning electron microscope image of the positive electrode material prepared in Example 1;

[0071] Figure 2 (a) is an X-ray diffraction pattern of the positive electrode material prepared in Example 2;

[0072] Figure 2 (b) is a scanning electron microscope image of the positive electrode material prepared in Example 2;

[0073] Figure 3 (a) is an X-ray diffraction pattern of the positive electrode material prepared in Example 3;

[0074] Figure 3 (b) is a scanning electron microscope image of the positive electrode material prepared in Example 3;

[0075] Figure 4 (a) is an X-ray diffraction pattern of the positive electrode material prepared in Comparative Example 1;

[0076] Figure 4 (b) is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1;

[0077] Figure 5 (a) is an X-ray diffraction pattern of the positive electrode material prepared in Comparative Example 2;

[0078] Figure 5 (b) is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 2;

[0079] FIG6 is a graph showing the charge and discharge performance of the positive electrode material prepared in Example 1;

[0080] Figure 7 (a) is a charge and discharge performance diagram of the positive electrode material prepared in Example 2;

[0081] Figure 7 (b) is a rate performance diagram of the positive electrode material prepared in Example 2;

[0082] Figure 7 (c) is a cycle performance diagram of the positive electrode material prepared in Example 2;

[0083] FIG8 is a graph showing the charge and discharge performance of the positive electrode material prepared in Example 3;

[0084] FIG9 is a charge and discharge performance diagram of the positive electrode material prepared in Comparative Example 1;

[0085] FIG10 is a graph showing the charge and discharge performance of the positive electrode material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0086] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0087] An embodiment of the present invention provides a Prussian blue positive electrode material, wherein the Prussian blue positive electrode material includes a Prussian blue compound, and the chemical formula of the Prussian blue compound is:

[0088] Na x Fe[Fe(CN)6] y ·nH2O, Formula I

[0089] In Formula I, x is from 0.01 to 3, 0 < y < 1,

[0090] n is from 0.01 to 3.5.

[0091] When the Prussian blue positive electrode material provided by the present invention is applied to a sodium ion battery, it is beneficial to improve the performance of the sodium ion battery in terms of specific capacity, Coulomb efficiency, rate performance, long cycle stability, etc.

[0092] In some embodiments, x can be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, or any value between 0.01 and 3. Preferably, x < 1.5. A lower Na ion content belongs to a sodium-deficient state, and the reaction rate is faster, which is beneficial to reducing the lattice defects and water content of the Prussian blue compound, thus having better performance and being beneficial to improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery to which the Prussian blue positive electrode material is applied. More preferably, x < 1, further controlling the Prussian blue compound to be in a sodium-deficient state, further accelerating the reaction rate and reducing the lattice defects and water content of the Prussian blue compound, which is beneficial to further improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery to which the Prussian blue positive electrode material is applied. At the same time, x > 0.5, controlling the sodium ion content of the Prussian blue compound to be in a more appropriate range, which is more beneficial to improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery to which the Prussian blue positive electrode material is applied.

[0093] In some embodiments, n can be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.1, 3.2, or any value between 0.01 and 3.5, so as to control the water content of the Prussian blue compound, obtain better performance, and be beneficial to improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery to which the Prussian blue positive electrode material is applied.

[0094] In some embodiments, 0 < y < 1, and y can be selected from 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5, 0.6, 0.65, 0.7, 0.8, 0.85, 0.9, 0.93, 0.95, 0.97, 0.99, or any value greater than 0 and less than 1.

[0095] In some embodiments, y can be expressed as y = 1 - δ, where δ represents the content of vacancies of ferrocyanide ions. Here, 0 < δ < 1, and δ can be selected from 0.01, 0.02, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0096] Preferably, 0.8 < y < 1, that is, 0 < δ < 0.2, so as to control the lattice defects of the Prussian blue compound to be in a less state, improve the performance of the Prussian blue compound, and thus be beneficial to improving the cycle stability, specific capacity, Coulomb efficiency, rate performance and other properties of the sodium-ion battery using the Prussian blue cathode material.

[0097] In some embodiments, when y is expressed as y = 1 - δ, the general chemical formula of the Prussian blue compound can also be expressed as:

[0098] Na x Fe[Fe(CN)6] 1-δ □ δ ·nH2O Formula II,

[0099] Where, □ represents the vacancy of ferrocyanide ions. The value ranges of x, n, and δ are as described above.

[0100] In some embodiments, at least part of the crystals of the Prussian blue compound are in a cube-like shape, that is, when observing the crystals of the Prussian blue compound through a scanning electron microscope, the crystals of the Prussian blue compound exhibit an obvious cubic structure. The difference is that the edges of the crystals of the Prussian blue compound intersect in an arc shape.

[0101] In some embodiments, at least part of the crystals of the Prussian blue compound are in a sphere-like shape. Different from the cube-like crystals of the Prussian blue compound, when observing the crystals of the Prussian blue compound in a sphere-like shape through a scanning electron microscope, the edges of the crystals of the Prussian blue compound are in an arc shape.

[0102] In some embodiments, the size of the crystals of the Prussian blue compound is greater than or equal to 0.1 μm and less than or equal to 2.5 μm. For example, the size of the crystals of the Prussian blue compound can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.3 μm, or any other size value between 0.1 μm and 2.5 μm.

[0103] In some embodiments, the chemical formula of the Prussian blue compound is selected from Na0.647 Fe[Fe(CN)6] 0.93 2.6H2O and Na 0.517 Fe[Fe(CN)6] 0.85 ·3.15H2O, thereby obtaining a Prussian blue compound with better performance, which is beneficial to improving the cycle stability, specific capacity, coulombic efficiency, rate performance and other properties of the sodium ion battery using the Prussian blue positive electrode material.

[0104] In some embodiments, the Prussian blue positive electrode material further includes a carbonaceous material, the carbonaceous material being at least partially attached to the surface of the Prussian blue compound crystals. The addition of the carbonaceous material helps suppress the generation of defects during the production of the Prussian blue compound and improves the conductivity of the Prussian blue positive electrode material, thereby improving the cycle stability, specific capacity, coulombic efficiency, rate performance, and other properties of sodium-ion batteries using the Prussian blue positive electrode material.

[0105] In some embodiments, the carbonaceous material is selected from a conductive carbon black material, such as Ketjen Black. Conductive carbon black is a common conductive carbon black material that helps suppress defects during the production of the Prussian blue compound while improving the conductivity of the Prussian blue cathode material and reducing costs.

[0106] The present invention also provides a method for preparing a Prussian blue positive electrode material, comprising:

[0107] S100, mixing the first dispersion and the second dispersion to obtain a solid precipitate;

[0108] S200, washing and drying the solid precipitate to obtain a Prussian blue positive electrode material.

[0109] Wherein, the first dispersion liquid comprises: a ferrocyanide source, a first sodium source and a first dispersant;

[0110] The second dispersion liquid includes: a divalent iron source, a complexing agent and a second dispersant.

[0111] The present invention provides a method for preparing a Prussian blue positive electrode material. The method comprises mixing a ferrocyanide source, a first sodium source, and a divalent iron source to coprecipitate and generate a Prussian blue compound, thereby obtaining the Prussian blue positive electrode material. The addition of a complexing agent forms a strong complexation with ferrous ions provided by the divalent iron source, which is beneficial for controlling the generation rate of the Prussian blue compound, reducing defects in the Prussian blue compound, increasing the yield of the Prussian blue compound, improving the performance of the Prussian blue positive electrode material, and facilitating improving the cycle stability, specific capacity, coulombic efficiency, rate performance, and other properties of a sodium ion battery using the prepared Prussian blue positive electrode material.

[0112] In some embodiments, the Prussian blue positive electrode material prepared by the method for preparing the Prussian blue positive electrode material is as described above.

[0113] In some embodiments, step S100 includes:

[0114] S110, a ferrocyanide source and a first sodium source are dispersed in the first dispersant to obtain a first dispersion.

[0115] S120, a divalent iron source, and a complexing agent are dispersed in the second dispersant to obtain a second dispersion.

[0116] S130, mixing the first dispersion and the second dispersion to obtain a solid precipitate.

[0117] In some embodiments, the order of steps S110 and S120 is not critical. Step S110 may be performed before step S120, or step S120 may be performed before step S110, or step S110 and step S120 may be performed simultaneously.

[0118] In some embodiments, the ferrocyanide source and the first sodium source can be dispersed in the first dispersant by stirring. The stirring time can be controlled to be 5 minutes to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any time value between 5 minutes and 30 minutes.

[0119] In some embodiments, the ferrocyanide source and the first sodium source are derived from sodium ferrocyanide, that is, sodium ferrocyanide provides both ferrocyanide ions and sodium ions.

[0120] In some embodiments, sodium ferrocyanide can be Na4Fe(CN)6·10H2O.

[0121] In some embodiments, the concentration of sodium ferrocyanide in the first dispersant can be 5 g / L to 50 g / L, for example, 8 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, or any concentration value between 5 g / L and 50 g / L.

[0122] In some embodiments, the first dispersant comprises deionized water and a first solvent, wherein the ferrocyanide source is poorly soluble in the first solvent. When the ferrocyanide source is sodium ferrocyanide, the first solvent is selected from a solvent that is poorly soluble in sodium ferrocyanide. By using a solvent that is poorly soluble in the ferrocyanide source, the solubility of the ferrocyanide source in the mixed solvent varies, resulting in a solid-liquid two-phase reaction system. Furthermore, using an organic solvent as the first solvent slows the reaction rate, facilitating control of the rate of formation of the Prussian blue compound, reducing defects in the generated Prussian blue compound, and increasing the yield of the Prussian blue compound.

[0123] In some embodiments, the first solvent is selected from one or more of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

[0124] In some embodiments, the volume ratio of deionized water to the first solvent in the first dispersant is selected from 1:(0.01-100), for example, the volume ratio of deionized water to the first solvent in the first dispersant can be 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:1, 1:5, 1:10, 1:20, 1:50, 1:80, 1:90, or any ratio between 1:0.01 and 1:100.

[0125] In some embodiments, the deionized water in the first dispersant and the first solvent can be uniformly mixed by stirring to obtain the first dispersant. The stirring time after the deionized water in the first dispersant and the first solvent are mixed can be controlled to be 1 minute to 100 minutes, for example, 2 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, or any time value between 1 minute and 100 minutes.

[0126] In some embodiments, the first dispersion further includes a carbonaceous material. The carbonaceous material is selected from a conductive carbon black material, for example, Ketjen black. Conductive carbon black is a common conductive carbonaceous material that helps suppress defects during the production of the Prussian blue compound while improving the conductivity of the Prussian blue positive electrode material and reducing costs. When the first dispersion further includes a carbonaceous material, step S110 includes:

[0127] S111, dispersing the carbonaceous material in the first dispersant;

[0128] S112, the ferrocyanide source and the first sodium source are dispersed in the first dispersant.

[0129] In some embodiments, when the first dispersion liquid includes the carbonaceous material, the first solvent is preferably ethylene glycol, which is conducive to uniform dispersion of the carbonaceous material in the first dispersant.

[0130] In some embodiments, when the first dispersion includes the carbonaceous material, the concentration of the carbonaceous material is 0.1 g / L to 10 g / L, for example, 0.2 g / L, 0.5 g / L, 1 g / L, 2 g / L, 5 g / L, 6 g / L, 8 g / L, 9 g / L, or any concentration value between 0.1 g / L and 10 g / L.

[0131] In some embodiments, the carbonaceous material can be uniformly dispersed in the first dispersant by ultrasonic dispersion. The ultrasonic dispersion time can be 5 minutes to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any time value between 5 minutes and 30 minutes.

[0132] In some embodiments, the ratio of the amount of the carbonaceous material to the amount of the ferrocyanide source is selected from 1:(0.01~100), for example, the ratio of the amount of the carbonaceous material to the amount of the ferrocyanide source can be 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.5, 1:0.8, 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:60, 1:80, or any ratio between 1:0.01 and 1:100.

[0133] In some embodiments, the ferrous iron source and the complexing agent can be dispersed in the second dispersant by stirring. The stirring time can be controlled to be 5 minutes to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any time value between 5 minutes and 30 minutes.

[0134] In some embodiments, the ferrous iron source comes from a ferrous iron salt, and the ferrous iron salt is selected from one or more of FeSO4·7H2O, Fe(NO3)2, and FeCl2·4H2O.

[0135] In some embodiments, the complexing agent is selected from one or more of anhydrous sodium citrate, sodium citrate dihydrate, sodium citrate pentahydrate, sodium oxalate, sodium tartrate, and sodium malate. The complexing agent forms a strong complex with the ferrous ions provided by the divalent iron source, and when the complexing agent is selected from the above-mentioned compounds, the complexing agent can also serve as a second sodium source, effectively increasing the sodium ion concentration in the solution after the first dispersion and the second dispersion are mixed, which is beneficial to controlling the generation rate of the Prussian blue compound, effectively increasing the sodium ion content in the Prussian blue compound, reducing the defects of the Prussian blue compound and increasing the yield of the Prussian blue compound, improving the performance of the Prussian blue positive electrode material, and being beneficial to improving the cycle stability, specific capacity, coulombic efficiency, rate performance and other properties of the sodium ion battery using the prepared Prussian blue positive electrode material.

[0136] In some embodiments, the ratio of the amount of the ferrous iron source to the amount of the chelating agent is selected from 1:(1 to 100). For example, the ratio of the amount of the ferrous iron source to the amount of the chelating agent can be 1:2, 1:4, 1:5, 1:10, 1:20, 1:50, 1:60, 1:80, 1:90, or any ratio between 1:1 and 1:100.

[0137] In some embodiments, the ratio of the amount of the ferrocyanide source to the amount of the ferrous iron source is selected from 1:(1 to 3). For example, the ratio of the amount of the ferrocyanide source to the amount of the ferrous iron source can be 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, or any ratio between 1:1 and 1:3.

[0138] In some embodiments, the second dispersant comprises deionized water and a second solvent, wherein the ferrocyanide source is poorly soluble in the second solvent. When the ferrocyanide source is sodium ferrocyanide, the second solvent is selected from a solvent that is poorly soluble in sodium ferrocyanide. By using a solvent that is poorly soluble in the ferrocyanide source, the solubility of the ferrocyanide source in the solvent after mixing the first and second dispersions differs, resulting in a solid-liquid two-phase reaction system. Furthermore, using an organic second solvent slows the reaction rate, which helps control the rate of Prussian blue compound formation, reduces defects in the generated Prussian blue compound, and increases the yield of the Prussian blue compound.

[0139] In some embodiments, the second solvent is selected from one or more of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

[0140] In some embodiments, the volume ratio of deionized water and the second solvent in the second dispersant is selected from 1:(0.01-100). For example, the volume ratio of deionized water and the second solvent in the second dispersant can be 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:1, 1:5, 1:10, 1:20, 1:50, 1:80, 1:90, or any ratio between 1:0.01 and 1:100.

[0141] In some embodiments, the first solvent and the second solvent are the same, which helps to reduce the types of solvents used in the preparation process and reduce process costs.

[0142] In some embodiments, step S130 includes:

[0143] S131, mixing the first dispersion and the second dispersion to obtain a mixture;

[0144] S132. After the mixture is stirred for a first time at a first reaction temperature, it is allowed to stand for a first standing time to obtain the solid precipitate.

[0145] In some embodiments, the first dispersion liquid and the second dispersion liquid can be mixed by dropping. For example, the first dispersion liquid can be mixed by adding the first dispersion liquid dropwise to the second dispersion liquid, or the second dispersion liquid can be mixed by adding the second dispersion liquid dropwise to the first dispersion liquid. Wherein, a constant pressure funnel or a peristaltic pump can be used for dropwise addition. The dropping speed can be 1mL / min to 100mL / min, for example, 2mL / min, 5mL / min, 10mL / min, 15mL / min, 20mL / min, 50mL / min, 60mL / min, 75mL / min, 80mL / min, 90mL / min, or any dropping speed value between 1mL / min and 100mL / min.

[0146] In some embodiments, the ratio of the volume of the first dispersion to the volume of the second dispersion is 1:(0.1-10), for example, it can be 1:0.1, 1:0.2, 1:0.5, 1:1, 1:3, 1:5, 1:6, 1:9, or any ratio between 1:0.1 and 1:10.

[0147] In some embodiments, the first reaction temperature can be 5 degrees Celsius to 100 degrees Celsius, for example, 10 degrees Celsius, 15 degrees Celsius, 20 degrees Celsius, 25 degrees Celsius, 40 degrees Celsius, 50 degrees Celsius, 60 degrees Celsius, 70 degrees Celsius, 80 degrees Celsius, 90 degrees Celsius, or any temperature value between 5 degrees Celsius and 100 degrees Celsius.

[0148] In certain embodiments, the first stirring time can be 12 hours to 72 hours, for example, can be 18 hours, 24 hours, 36 hours, 40 hours, 48 ​​hours, 56 hours, 60 hours, 64 hours or any time value between 12 hours to 72 hours.During the first stirring time, the mixture can be fully reacted by stirring to realize.The stirring speed of the mixture can be 100rpm to 1500rpm, for example, can be 200rpm, 300rpm, 500rpm, 600rpm, 800rpm, 1000rpm, 1200rpm, 1300rpm, 1400rpm or any stirring speed between 100rpm to 1500rpm.

[0149] In some embodiments, the first standing time can be 12 hours to 36 hours, for example, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, or any time value between 12 hours and 36 hours.

[0150] In some embodiments, the solid precipitate can be separated and obtained by common solid-liquid separation methods, such as suction filtration, filtration, etc.

[0151] In some embodiments, step S200 includes:

[0152] S210, washing the solid precipitate with a first detergent to obtain a product to be dried;

[0153] S220, drying the product to be dried to obtain the Prussian blue positive electrode material.

[0154] In some embodiments, the first detergent can be selected from deionized water and / or anhydrous ethanol. The solid precipitate can be washed with the first detergent once or multiple times (e.g., twice, three times, etc.) to obtain the product to be dried. When the first detergent is selected from deionized water and anhydrous ethanol, the solid precipitate is washed with deionized water and anhydrous ethanol, respectively.

[0155] In some embodiments, the drying process can be carried out by conventional drying methods, for example, vacuum drying. In some embodiments, vacuum drying can be carried out at a temperature of 60 to 120 degrees Celsius, for example, 65, 70, 75, 80, 85, 90, 95, 98, 100, 102, 105, 108, or any temperature between 90 and 110 degrees Celsius; the vacuum drying time is greater than 2 hours, and further, the vacuum drying time can be 12 to 36 hours, for example, 16, 20, 24, 28, 32, or any time between 12 and 36 hours.

[0156] In some embodiments, when the first dispersion includes a carbonaceous material, the carbonaceous material is at least partially attached to the surface of the Prussian blue compound crystals. That is, the Prussian blue positive electrode material includes the Prussian blue compound and the carbonaceous material at least partially attached to the surface of the Prussian blue compound crystals.

[0157] The preparation method of the Prussian blue positive electrode material provided in an embodiment of the present invention is to obtain the Prussian blue positive electrode material by co-precipitating a Prussian blue compound by mixing a ferrocyanide source, a first sodium source and a divalent iron source, wherein the addition of a complexing agent forms a strong complexation with the ferrous ions provided by the divalent iron source, which is beneficial to controlling the generation rate of the Prussian blue compound, reducing the defects of the Prussian blue compound and increasing the yield of the Prussian blue compound, thereby improving the performance of the Prussian blue positive electrode material, and is beneficial to improving the cycle stability, specific capacity, coulombic efficiency, rate performance and other properties of the sodium ion battery using the prepared Prussian blue positive electrode material.

[0158] An embodiment of the present invention further provides a positive electrode plate, which includes the Prussian blue positive electrode material as described above; or, the positive electrode plate includes the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above.

[0159] The positive electrode plate provided in an embodiment of the present invention includes the Prussian blue positive electrode material as described above or the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above, so when applied to a sodium ion battery, it is beneficial to improve the performance of the sodium ion battery in terms of specific capacity, coulombic efficiency, rate performance and long-cycle stability.

[0160] An embodiment of the present invention further provides a sodium ion battery, comprising the Prussian blue positive electrode material as described above, or the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above, or the positive electrode plate as described above.

[0161] The sodium ion battery provided by the embodiment of the present invention, by including the Prussian blue positive electrode material as described above or the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material as described above, or the positive electrode plate as described above, has improved performance in terms of specific capacity, coulombic efficiency, rate performance and long-cycle stability.

[0162] In some embodiments, the sodium ion battery includes: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0163] In some embodiments, a method for preparing a positive electrode sheet may include:

[0164] mixing a Prussian blue positive electrode material, a binder, a conductive agent and a solvent to obtain a slurry;

[0165] The slurry is coated on an aluminum foil and then dried to obtain a positive electrode sheet.

[0166] In some embodiments, the positive electrode material is the Prussian blue positive electrode material as described above; the binder can be selected from polyvinylidene fluoride (PVDF); the conductive agent can be selected from Super P (conductive carbon black); the mass ratio of the positive electrode material, the binder and the conductive agent can be selected from (6-8): (1-3): (0.5-1.5), or can be selected from (6.5-7.5): (1.5-2.5): (0.8-1.2), or can be selected from 7:2:1; the solvent is selected from dimethylpyrrolidone.

[0167] In some embodiments, the negative electrode can be selected from metallic sodium; the separator can be selected from a glass fiber membrane; and the electrolyte can be selected from 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroacetate) (the volume ratio of EC:PC:FEC is 0.45:0.45:0.05).

[0168] In some embodiments, the positive electrode, negative electrode, separator, and electrolyte can be assembled into a CR2032 button cell in a glove box.

[0169] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications were used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

[0170] Example 1

[0171] 100 mg of Ketjen black was added to 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 3:1) and ultrasonically stirred for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Subsequently, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was added thereto and stirred for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, 5 g of anhydrous sodium citrate and 0.834 g of ferrous sulfate (FeSO4·7H2O) were dissolved in 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 3:1) and stirred to dissolve to obtain a transparent mixed metal salt solution.

[0172] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion through a constant pressure funnel at 25°C at a dropping rate of 3.33 mL / min. After the addition was completed, the mixture was stirred at 500 rpm at 25°C for 4 hours, and then allowed to stand for 24 hours. After the end of the standing period, the blue Prussian blue precipitate was filtered off to obtain;

[0173] The obtained Prussian blue precipitate was washed alternately with water and ethanol, wherein the water washing was performed twice and the ethanol washing was performed once, until the impurities were completely removed; and then the precipitate was placed in a vacuum dryer at 100°C for 24 hours to obtain a Prussian blue positive electrode material for sodium ion batteries, wherein the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 □ 0.07 2.6H2O (XRD was used to determine the molecular formula), that is, the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ·2.6H2O.

[0174] Example 2

[0175] 200 mg of Ketjen black was added to 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 2:1) and ultrasonically stirred for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Subsequently, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was added thereto and stirred for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, 5 g of anhydrous sodium citrate and 0.834 g of ferrous sulfate (FeSO4·7H2O) were dissolved in 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 2:1) and stirred to dissolve to obtain a transparent mixed metal salt solution.

[0176] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion through a constant pressure funnel at 25°C at a dropping rate of 3.33 mL / min. After the addition was completed, the mixture was stirred at 500 rpm at 25°C for 4 hours, and then allowed to stand for 24 hours. After the end of the standing period, the blue Prussian blue precipitate was filtered off to obtain;

[0177] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, wherein the water was washed twice and the ethanol was washed once until the impurities were completely removed; then it was placed in a vacuum dryer at 100°C for 24 hours to obtain a Prussian blue positive electrode material for sodium ion batteries, wherein the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 □ 0.07 2.6H2O, that is, the chemical formula of Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ·2.6H2O.

[0178] Example 3

[0179] 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed and added to a mixed solution of 100 mL of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 1:1), and stirred for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. 5 g of anhydrous sodium citrate and 0.834 g of ferrous sulfate (FeSO4·7H2O) were weighed and dissolved in a mixed solution of 100 mL of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol was 1:1), stirred and dissolved to obtain a transparent mixed metal salt solution.

[0180] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion through a constant pressure funnel at 25°C at a dropping rate of 3.33 mL / min. After the addition was completed, the mixture was stirred at 500 rpm at 25°C for 4 hours, and then allowed to stand for 24 hours. After the end of the standing period, the blue Prussian blue precipitate was filtered off to obtain;

[0181] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, wherein the water was washed twice and the ethanol was washed once until the impurities were completely removed; then it was placed in a vacuum dryer at 100°C for 24 hours to obtain a Prussian blue positive electrode material for sodium ion batteries, wherein the chemical formula of the Prussian blue compound is Na 0.517 Fe[Fe(CN)6] 0.85 □ 0.15 3.15H2O, that is, the chemical formula of Prussian blue compound is Na 0.517 Fe[Fe(CN)6] 0.85 ·3.15H2O.

[0182] Comparative Example 1

[0183] 100 mg of Ketjen black was weighed and added to 100 mL of deionized water and ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Subsequently, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed and added thereto and stirred for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. 5 g of anhydrous sodium citrate and 0.834 g of ferrous sulfate (FeSO4·7H2O) were weighed and dissolved in 100 mL of deionized water and stirred to dissolve to obtain a transparent mixed metal salt solution.

[0184] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion through a constant pressure funnel at 25°C at a dropping rate of 3.33 mL / min. After the addition was completed, the mixture was stirred at 500 rpm at 25°C for 4 hours, and then allowed to stand for 24 hours. After the end of the standing period, the blue Prussian blue precipitate was filtered off to obtain;

[0185] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, until all impurities were removed; it was then vacuum dried at 100° C. for 24 hours to obtain a Prussian blue positive electrode material for sodium ion batteries.

[0186] Comparative Example 2

[0187] 200 mg of Ketjen black was weighed and added to 100 mL of deionized water and ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Subsequently, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed and added thereto and stirred for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. 5 g of anhydrous sodium citrate and 0.834 g of ferrous sulfate (FeSO4·7H2O) were weighed and dissolved in 100 mL of deionized water and stirred to dissolve to obtain a transparent mixed metal salt solution.

[0188] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion through a constant pressure funnel at 25°C at a dropping rate of 3.33 mL / min. After the addition was completed, the mixture was stirred at 500 rpm at 25°C for 4 hours, and then allowed to stand for 24 hours. After the end of the standing period, the blue Prussian blue precipitate was filtered off to obtain;

[0189] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, until all impurities were removed; it was then vacuum dried at 100° C. for 24 hours to obtain a Prussian blue positive electrode material for sodium ion batteries.

[0190] Performance testing

[0191] (1) X-ray diffraction (XRD) test:

[0192] Testing was performed using a Bruker D8 Focus X-ray powder diffractometer from Germany, using a Cu-Kα radiation source with a wavelength of 1.5046λ. A Ni filter was used, with a tube current of 40 mA and a tube voltage of 40 kV. The scanning range was 5° to 90°, the scanning speed was 5° / min, and the step size was 0.05°. The cathode materials prepared in the examples and comparative examples were placed on a glass slide, flattened, and then the slide was inserted into the center of the instrument's experimental chamber for testing. Phase identification and crystal structure information were analyzed using JADE 6.0 software.

[0193] (2) Scanning electron microscopy characterization:

[0194] The morphology of the material was observed using a SU-3500 scanning electron microscope produced by HITACHI with an accelerating voltage of 15 kV.

[0195] The test results are as follows:

[0196] Figure 1 (a) is an X-ray diffraction pattern of the spherical Prussian blue positive electrode material for sodium ion batteries prepared in Example 1, wherein the X-axis is the X-ray scanning angle 2θ, and the ordinate is the intensity of the X-ray. It can be seen from Figure 1 that the Prussian blue positive electrode material has a characteristic peak on the (200) crystal plane at a scanning angle of 16.92°, a characteristic peak on the (220) crystal plane at a scanning angle of 24.12°, a characteristic peak on the (400) crystal plane at a scanning angle of 34.18°, and a characteristic peak on the (400) crystal plane at a scanning angle of 16.92°. There is a characteristic peak on the (420) crystal plane at an angle of 38.56°, a characteristic peak on the (422) crystal plane at a scanning angle of 42.46°, a characteristic peak on the (440) crystal plane at a scanning angle of 49.39°, a characteristic peak on the (600) crystal plane at a scanning angle of 52.78°, and a characteristic peak on the (620) crystal plane at a scanning angle of 55.77°. It belongs to the Fm-3m space group and there are no impurity peaks in the X-ray diffraction pattern, indicating that the positive electrode material is a pure phase substance.

[0197] Figure 1 (b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 1. It can be observed that the Prussian blue positive electrode material is a cubic block structure composed of nano-scale cubic grains, and the size of the nanocube is ∼2 μm.

[0198] Figure 2 (a) is an X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 2, wherein the X-axis is the X-ray scanning angle 2θ, and the ordinate is the intensity of the X-ray. It can be seen that the Prussian blue positive electrode material has a characteristic peak on the (200) crystal plane at a scanning angle of 16.88°, a characteristic peak on the (220) crystal plane at a scanning angle of 24.06°, a characteristic peak on the (400) crystal plane at a scanning angle of 34.1°, and a characteristic peak on the (400) crystal plane at a scanning angle of 3 There is a characteristic peak on the (420) crystal plane at a scanning angle of 8.42°, a characteristic peak on the (422) crystal plane at a scanning angle of 42.38°, a characteristic peak on the (440) crystal plane at a scanning angle of 49.4°, a characteristic peak on the (600) crystal plane at a scanning angle of 52.62°, and a characteristic peak on the (620) crystal plane at a scanning angle of 55.67°, which belongs to the Fm-3m space group. There are no impurity peaks in the X-ray diffraction pattern, indicating that the positive electrode material is a pure phase substance.

[0199] (b) in Figure 2 is a scanning electron microscope image of the Prussian blue positive electrode material for sodium ion batteries obtained in Example 2. It can be observed that the Prussian blue material is a porous hierarchical spherical structure composed of nanocubes. The size of the nanocube is ~100nm, the hierarchical spherical size is ~2μm, and the dispersion is good.

[0200] Figure 3 (a) is an X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 3, wherein the X-axis is the X-ray scanning angle 2θ, and the ordinate is the intensity of the X-ray. It can be seen that the Prussian blue positive electrode material has a characteristic peak on the (200) crystal plane at a scanning angle of 17.48°, a characteristic peak on the (220) crystal plane at a scanning angle of 24.84°, a characteristic peak on the (400) crystal plane at a scanning angle of 34.44°, and a characteristic peak on the (400) crystal plane at a scanning angle of 3 There is a characteristic peak on the (420) crystal plane at a scanning angle of 8.53°, a characteristic peak on the (422) crystal plane at a scanning angle of 42.03°, a characteristic peak on the (440) crystal plane at a scanning angle of 49.61°, a characteristic peak on the (600) crystal plane at a scanning angle of 50.94°, and a characteristic peak on the (620) crystal plane at a scanning angle of 55.67°, which belongs to the Fm-3m space group. There are no impurity peaks in the X-ray diffraction pattern, indicating that the positive electrode material is a pure phase substance.

[0201] FIG3 (b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 3. It can be observed that the Prussian blue material is composed of nanocubic particles, but some of them are broken. The size of the nanocubic particles is 500 nanometers.

[0202] (a) in FIG4 is an X-ray diffraction pattern of the cubic Prussian blue positive electrode material for sodium ion batteries prepared in Comparative Example 1, wherein the X-axis is the X-ray scanning angle 2θ, and the ordinate is the intensity of the X-ray; it can be seen that the Prussian blue positive electrode material has a characteristic peak on the (200) crystal plane at a scanning angle of 16.94°, a characteristic peak on the (220) crystal plane at a scanning angle of 24.08°, a characteristic peak on the (400) crystal plane at a scanning angle of 34.34°, and a characteristic peak on the (500) crystal plane at a scanning angle of 16.94°. There is a characteristic peak on the (420) crystal plane at a scanning angle of 38.56°, a characteristic peak on the (422) crystal plane at a scanning angle of 42.38°, a characteristic peak on the (440) crystal plane at a scanning angle of 49.4°, a characteristic peak on the (600) crystal plane at a scanning angle of 52.36°, and a characteristic peak on the (620) crystal plane at a scanning angle of 55.67°, which belongs to the Fm-3m space group. There are no impurity peaks in the X-ray diffraction pattern, indicating that the positive electrode material is a pure phase substance.

[0203] (b) in Figure 4 is a scanning electron microscope image of the cubic Prussian blue positive electrode material for sodium ion batteries prepared in Comparative Example 1. It can be observed that the morphology of the Prussian blue material is a cubic morphology composed of agglomerated nanoparticles, wherein the size of the nanoparticles is 1 micron.

[0204] Figure 5 (a) is an X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion battery prepared in Comparative Example 2, wherein the X-axis is the X-ray scanning angle 2θ, and the ordinate is the intensity of the X-ray; it can be seen that the Prussian blue positive electrode material has a characteristic peak on the (200) crystal plane at a scanning angle of 16.82°, a characteristic peak on the (220) crystal plane at a scanning angle of 23.96°, a characteristic peak on the (400) crystal plane at a scanning angle of 34.1°, and a characteristic peak on the (400) crystal plane at a scanning angle of 3 There is a characteristic peak on the (420) crystal plane at a scanning angle of 8.35°, a characteristic peak on the (422) crystal plane at a scanning angle of 42.19°, a characteristic peak on the (440) crystal plane at a scanning angle of 49.17°, a characteristic peak on the (600) crystal plane at a scanning angle of 52.26°, and a characteristic peak on the (620) crystal plane at a scanning angle of 55.42°, which belongs to the Fm-3m space group. There are no impurity peaks in the X-ray diffraction pattern, indicating that the positive electrode material is a pure phase substance.

[0205] (b) in FIG5 is a scanning electron microscope image of the Prussian blue positive electrode material for sodium ion batteries prepared in Comparative Example 2. It can be observed that the Prussian blue material is a cubic block structure composed of nanocubic particles with a size of 1 μm.

[0206] It can be seen from the XRD diffraction results of the embodiment and the comparative example that the diffraction peak intensity of the Prussian blue material prepared in the embodiment is stronger than that of the comparative example, and the crystallinity of the material prepared in the embodiment is higher and the quality is better.

[0207] At the same time, the small particulate matter attached to the surface of the Prussian blue compound shown in (b) in Figure 1 and (b) in Figure 2 indicates that the Ketjen black added in Example 1 and Example 2 is at least partially attached to the surface of the Prussian blue compound in the prepared Prussian blue positive electrode material.

[0208] The Prussian blue positive electrode material for sodium ion batteries prepared in the examples and comparative examples was used as the positive electrode active material for the sodium ion battery. The positive electrode active material was mixed with a binder (polyvinylidene fluoride PVDF) and a conductive agent (Super P) in a mass ratio of 7:2:1, and dimethylpyrrolidone (NMP) was added as a solvent and stirred to form a uniform slurry; the slurry was evenly applied on an aluminum foil, dried and cut into thin sheets as the positive electrode, metallic sodium was used as the negative electrode, a glass fiber membrane was used as a separator, 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroacetate) (EC: PC: FEC = 0.45:0.45:0.05, vol) was used as the electrolyte, and CR2032 button batteries were assembled in an argon glove box.

[0209] The above-assembled button cells were tested using a Land battery tester produced by Wuhan Jinnuo Electronics Co., Ltd. The test conditions and results are as follows: the button cells were subjected to constant current charge and discharge tests with a charge and discharge voltage range of 2V to 4.2V. Among Examples 1 to 3, the Prussian blue electrode prepared from the positive electrode material in Example 2 had the best electrochemical performance. At a current density of 100mA / g, the initial charge and discharge specific capacities of the battery were 113.3mAh / g and 137mAh / g, respectively. The discharge specific capacity retention rate after 200 cycles was 87.1%, while the capacity of Comparative Example 1 and Comparative Example 2 after 200 cycles was only 42% and 30%. In addition, the discharge specific capacity retention rate of the Prussian blue electrode prepared from the positive electrode material in Example 2 was still 77% after 800 cycles, and the coulombic efficiency of each cycle was close to 99%. The test results are as follows (as shown in Table 1 and Figures 6 to 10):

[0210] Table 1

[0211] Among them, Figure 6 is a schematic diagram of the first to third charge and discharge specific capacity results of the Prussian blue positive electrode material prepared in Example 1; Figures 7 (a) to 7 (c) are schematic diagrams of the charge and discharge performance of the Prussian blue positive electrode material prepared in Example 2, Figure 7 (a) is a schematic diagram of the first to fifth charge and discharge specific capacity results of the Prussian blue positive electrode material prepared in Example 2, Figures 7 (b) and 7 (c) are schematic diagrams of the rate performance and cycle performance results of the Prussian blue positive electrode material prepared in Example 2, respectively; Figure 8 is a schematic diagram of the first to fourth charge and discharge specific capacity results of the Prussian blue positive electrode material prepared in Example 3; Figure 9 is a schematic diagram of the first to third charge and discharge specific capacity results of the positive electrode material prepared in Comparative Example 1; Figure 10 is a schematic diagram of the first to third charge and discharge specific capacity results of the positive electrode material prepared in Comparative Example 2.

[0212] From the results in Figures 6 to 10 and Table 1, it can be seen that the Prussian blue positive electrode material obtained in the embodiment of the present invention, when applied to sodium ion batteries, makes the sodium ion batteries perform better in terms of cycle stability, charge and discharge specific capacity, coulombic efficiency, and rate performance.

[0213] The present invention observes that Prussian blue and Ketjen black are evenly distributed by scanning electron microscopy, sodium ferrocyanide can be dissolved in ethylene glycol solution, and when the reaction system introduces an organic solvent, a mixed phase is formed, because ferrous sulfate and sodium citrate are insoluble in organic solvents, but the reaction must be carried out with the participation of water, so the introduction of an organic solvent can further control the reaction rate and thus control the growth process of Prussian blue crystals, making the aged Prussian blue defect less, and the addition of Ketjen black can improve the problem of poor conductivity of Prussian blue. After Ketjen black is introduced, the conductivity of the composite material of Prussian blue and Ketjen black can be greatly improved. The introduction of the organic solvent ethylene glycol in the present invention causes two phases to exist in the reaction system, and further increases the concentration of sodium ions in the reaction system of the aqueous phase. The organic solution introduced in the present invention does not participate in the reaction, but only realizes the purpose of controlling the reaction rate. The present invention is that after the reaction is completed, closed-loop recycling can be fully realized, without waste, and the recycling method can be distilled under reduced pressure at 80°C, which is green and safe.

[0214] Although the present invention has been described and illustrated with reference to specific embodiments of the present invention, these descriptions and illustrations do not limit the present invention. It will be clearly understood by those skilled in the art that, without departing from the true spirit and scope of the present invention as defined by the appended claims, various changes may be made to make specific circumstances, materials, compositions of matter, substances, methods or processes suitable for the object, spirit and scope of the present application. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it will be understood that these operations may be combined, subdivided or reordered to form equivalent methods without departing from the teachings of the present invention. Therefore, unless otherwise indicated herein, the order and grouping of operations are not limitations of the present application.

Claims

1. A Prussian blue positive electrode material, characterized in that: The Prussian blue positive electrode material includes a Prussian blue compound, and the chemical formula of the Prussian blue compound is: Na x Fe[Fe(CN)6] y nH2O Formula I, In formula I, x is 0.01 to 3, 0 <y<1, n is 0.01 to 3.

5.

2. The Prussian blue positive electrode material according to claim 1, characterized in that 0.5 <x<1.5,0.8<y<1。 3. The Prussian blue positive electrode material according to claim 2, characterized in that 0.5<x<1。 4. The Prussian blue positive electrode material according to any one of claims 1 to 3, characterized in that At least part of the crystals of the Prussian blue compound are in a cubic shape.

5. The Prussian blue positive electrode material according to claim 1, characterized in that The size of the crystal of the Prussian blue compound is greater than or equal to 0.1 micrometer, and the size of the crystal of the Prussian blue compound is less than or equal to 2.5 micrometer.

6. The Prussian blue positive electrode material according to claim 1, characterized in that The chemical formula of the Prussian blue compound is selected from Na 0.647 Fe[Fe(CN)6] 0.93 2.6H2O and Na 0.517 Fe[Fe(CN)6] 0.85 · At least one of 3.15H2O.

7. The Prussian blue positive electrode material according to claim 1, characterized in that The Prussian blue positive electrode material further includes a carbonaceous material, and the carbonaceous material is at least partially attached to the surface of the crystal of the Prussian blue compound.

8. The Prussian blue positive electrode material according to claim 7, characterized in that The carbonaceous material is selected from conductive carbon black materials.

9. A method for preparing a Prussian blue positive electrode material, characterized in that: include: mixing the first dispersion and the second dispersion to obtain a solid precipitate; The solid precipitate is washed and dried to obtain a Prussian blue positive electrode material; Wherein, the first dispersion liquid comprises: a ferrocyanide source, a first sodium source and a first dispersant; The second dispersion includes: a divalent iron source, a complexing agent and a second dispersant.

10. The method for preparing the Prussian blue positive electrode material according to claim 9, characterized in that: The ferrocyanide source and the first sodium source are from sodium ferrocyanide; or / and, The ferrous iron source comes from a ferrous iron salt, and the ferrous iron salt is selected from one or more of FeSO4·7H2O, Fe(NO3)2, and FeCl2·4H2O; or / and, The complexing agent is selected from one or more of anhydrous sodium citrate, dihydrate sodium citrate, pentahydrate sodium citrate, sodium oxalate, sodium tartrate and sodium malate.

11. The method for preparing the Prussian blue positive electrode material according to claim 9, characterized in that: The first dispersant comprises: deionized water and a first solvent, wherein the ferrocyanide source is poorly soluble in the first solvent; or / and, The second dispersant comprises: deionized water and a second solvent, wherein the ferrocyanide source is poorly soluble in the second solvent; or / and, The first solvent and the second solvent are independently selected from one or more of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

12. The method for preparing the Prussian blue positive electrode material according to claim 11, characterized in that: The volume ratio of the deionized water and the first solvent in the first dispersant is selected from 1:(0.01-100); or / and, The volume ratio of the deionized water and the second solvent in the second dispersant is selected from 1:(0.01-100).

13. The method for preparing the Prussian blue positive electrode material according to any one of claims 9 to 12, characterized in that: The first dispersion also includes a carbonaceous material.

14. The method for preparing the Prussian blue positive electrode material according to claim 13, characterized in that: The ratio of the amount of the carbonaceous material to the amount of the ferrocyanide source is selected from 1:(0.01-100); or / and, The ratio of the amount of the ferrocyanide source to the amount of the ferrous iron source is selected from 1:(1-3); or / and, The ratio of the amount of the divalent iron source to the amount of the complexing agent is selected from 1: (1 to 100).

15. A positive electrode sheet, characterized in that: The positive electrode plate comprises the Prussian blue positive electrode material according to any one of claims 1 to 8; or, the positive electrode plate comprises the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material according to any one of claims 9 to 14.

16. A sodium ion battery comprising: The Prussian blue positive electrode material according to any one of claims 1 to 8, or the Prussian blue positive electrode material obtained by the preparation method of the Prussian blue positive electrode material according to any one of claims 9 to 14, or the positive electrode sheet according to claim 15.

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