Prussian blue cathode material, method for producing the same, cathode sheet, and sodium ion battery

Abstract

The present invention provides a Prussian blue cathode material, a method for manufacturing the same, a cathode sheet, and a sodium ion battery. The Prussian blue cathode material contains a Prussian blue compound represented by the chemical general formula Na x Fe[Fe(CN)6] y ·nH2O. The Prussian blue cathode material according to the present invention has a simple synthesis method, low raw material cost, and is advantageous for improving the characteristics of sodium ion batteries in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability when used in sodium ion batteries.

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on June 27, 2023, with an application number of 202310772356.6 and an application title of "Prussian Blue Cathode Material, Its Manufacturing Method, and Its Use", and all of its contents are incorporated herein by reference.

[0002] The present invention belongs to the technical field of batteries and electrochemical energy storage, and particularly relates to Prussian blue cathode materials and their manufacturing methods, cathode sheets, and sodium-ion batteries.

Background Art

[0003] In modern society, energy storage has become an important issue in order to utilize renewable energy and promote smart grids. Room-temperature sodium-ion batteries (SIBs) operating under the same chemical conditions as lithium-ion batteries (LIBs) are promising candidates for energy storage systems (ESSs) because sodium is abundant and low-cost worldwide. Rechargeable sodium-ion batteries (SIBs) have emerged as promising candidates for large-scale energy storage system applications due to their abundant resources and controllable costs. Prussian blue (PB) and its analogs (PBA) are considered potential cathodes and are attracting increasing attention due to their unique rigid open framework, large interstitial sodium storage sites, high theoretical capacity, and non-toxic properties. Furthermore, the convenient synthesis process and low cost of PBA are also very attractive for potential large-scale applications. However, PBA has low electronic conductivity and defects in the PBA framework, resulting in poor rate performance and cycle stability.

[0004] In a typical PB framework, depending on whether the iron atom is located on the carbon side or the nitrogen side of the cyanide ligand, the iron center exists in a low-spin (Fe LS (C)) or high-spin (Fe HS (N)) structure. Fe 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 both Fe sites is equal in the complete PB framework. However, existing literature shows that the capacity contribution of the Fe LS (C) redox reaction pair is much lower compared to the Fe HS (N) redox reaction pair. Furthermore, this insufficiently activated low-spin Fe LS (C) redox pair is electrochemically active at a higher potential, thus inevitably lowering the average potential platform of the PBA-based cathode. Although the activation of the Fe LS (C) redox pair by reduction with water or incorporation of other transition metals has been reported, the cycle stability is optimized while the capacity is sacrificed. Therefore, to maximize the potential of PBA-based cathode materials, this problem needs to be solved urgently, and satisfactory rate performance is another issue for the commercialization of PBA materials.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above, an object of the present invention is to provide a Prussian blue cathode material with high rate performance and excellent cycle stability, a manufacturing method thereof, and its use, in order to solve the problem of causing capacity degradation when using a conventional Prussian blue material in a sodium-ion battery to optimize cycle stability.

[0006] In view of the above, an object of the present invention is to provide a Prussian blue cathode material with high rate performance and excellent cycle stability, a manufacturing method thereof, and its use, in order to solve the problem of the conventional Prussian blue material causing capacity degradation to optimize cycle stability.

Means for Solving the Problems

[0007] In a first aspect, the present invention provides a Prussian blue cathode material having the following chemical general formula. Nax Fe[Fe(CN)]6·nH2O of Formula I, (In Formula I, x is 0.01 to 3, n is 0.01 to 3.)

[0008] In the examples of the present invention, x may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5. When x < 1.5, the obtained Prussian blue cathode material has better cycle stability, a lower sodium ion content, a sodium-deficient state, a faster reaction rate, fewer lattice defects and water content, and thus better properties. n may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, and both x and n are molar ratios.)

[0009] The Prussian blue cathode material according to the present invention has a block structure.)

[0010] In the examples of the present invention, the size of the nanocubes of the Prussian blue cathode material is 500 nm to 2000 nm.)

[0011] In a second aspect, the present invention provides a step of mixing Solution A and Solution B to obtain a solid precipitate, and a step of washing and drying the solid precipitate to obtain a Prussian blue cathode material, wherein Solution A contains a carbonaceous material, sodium ferrocyanide, and a first solvent, and Solution B contains an iron salt, sodium citrate, and a second solvent, and provides a method for producing a Prussian blue cathode material.)

[0012] In the examples of the present invention, the carbonaceous material may be selected from conductive carbon black, activated carbon, etc. For example, Ketjen black may be used.)

[0013] In the embodiments of the present invention, the first solvent may contain water and solvent A. The water may be selected from deionized water, and the solvent A may be one or more selected from ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol, for example, it may be ethylene glycol. The volume ratio of water to solvent A may be selected from 1:(0.01 - 100), for example, 1:(0.05 - 90), 1:(0.1 - 80), 1:(0.5 - 70), 1:(1 - 60), 1:(5 - 50), 1:(10 - 40), 1:(20 - 30). In the embodiments of the present invention, the manufacturing method of the first solvent may include the step of uniformly mixing water and solvent A. The mixing is carried out while stirring, and the stirring time may be selected from 1 min to 100 min, for example, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min.

[0014] In the embodiments of the present invention, the concentration of sodium ferrocyanide in solution A may be selected from 0.1 g / L to 100 g / L, for example, 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, 90 g / L.

[0015] In the embodiments of the present invention, the manufacturing method of solution A may include the steps of dispersing the carbonaceous material in the first solvent to obtain a dispersion, and then dissolving sodium ferrocyanide in the dispersion to obtain solution A.

[0016] In the embodiments of the present invention, ultrasonic stirring may be used for the dispersion.

[0017] In the embodiments of the present invention, the iron salt may be one or more selected from divalent iron salts, for example, FeSO4·7H2O, Fe(NO3)2, FeCl2·4H2O.

[0018] In the embodiments of the present invention, the sodium citrate may be one or more selected from anhydrous sodium citrate, sodium citrate dihydrate, and sodium citrate pentahydrate.

[0019] In an embodiment of the present invention, the second solvent may contain water and solvent B. The water may be selected from deionized water, and solvent B may be one or more selected from ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol. For example, it is 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), 1:(20~30). In an embodiment of the present invention, the manufacturing method of the second solvent may include the step of uniformly mixing water and solvent B. The mixing is carried out while stirring, and the stirring time may be selected from 1 min to 100 min, such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min.

[0020] In an embodiment of the present invention, the manufacturing method of solution B is It may include the step of dissolving iron salt and sodium citrate in the second solvent to obtain solution B.

[0021] In an embodiment of the present invention, a uniform solution B may be obtained by stirring and dissolving.

[0022] In an embodiment of the present invention, the molar ratio of the carbonaceous material to sodium ferrocyanide may 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 to iron salt may be selected from 1:(1~3), for example, 1:2. The molar ratio of iron salt to sodium citrate may 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 to solution B may 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).

[0023] In the embodiments of the present invention, both solvent A and solvent B are solvents in which sodium ferrocyanide is difficult to dissolve. By adjusting the solubility to control the reaction rate, it plays a role in suppressing the generation of defects during crystal growth.

[0024] In the embodiments of the present invention, for the mixing, solution A may be dropped into solution B, or solution B may be dropped into solution A. The dropping rate may be selected from 0.1 mL / min to 100 mL / min, for example, 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, 90 mL / min.

[0025] In the embodiments of the present invention, the mixing of solution A and solution B plays a role in adjusting the dissolution rate to control the reaction rate.

[0026] In the embodiments of the present invention, the mixing may be a reaction. The temperature of the mixing may be selected from 5°C to 100°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C. The mixing may be carried out with stirring, and the stirring speed may be selected from 100 rpm to 1500 rpm, for example, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm. The mixing time may be selected from 12 to 72 h, for example, 24 h, 36 h, 48 h, 60 h.

[0027] In the embodiments of the present invention, the cleaning reagent may be selected from water or ethanol. The water may be selected from deionized water, and the ethanol may be selected from absolute ethanol. The cleaning may be alternately performed using water and ethanol. The number of times of cleaning with water may be 2, and the number of times of cleaning with ethanol may be 1.

[0028] In the embodiments of the present invention, the drying temperature may be selected from 60°C to 120°C, such as 70°C, 80°C, 90°C, 100°C, 110°C, and the drying time may exceed 2 h.

[0029] In the embodiments of the present invention, the method for manufacturing the Prussian blue cathode material is as follows. Deionized water and ethylene glycol are stirred for 10 minutes to 60 minutes at a volume ratio of 1:(0.01 - 50) for uniform mixing. Next, Ketjen black is added to the mixed solution and ultrasonic stirring is performed until uniform dispersion. Then, the raw material sodium ferrocyanide (Na4Fe(CN)6·10H2O) is added to the dispersion and stirred for 30 minutes to obtain a sodium ferrocyanide dispersion with a concentration of 5 g / L to 50 g / L. Weigh divalent iron salt and sodium citrate so that the molar ratio of divalent iron salt to sodium citrate is 1:(0.01 - 100), and the molar ratio of sodium ferrocyanide to total metal salt is 1:(1 - 2). Add them to a mixed solution of deionized water and ethylene glycol with a predetermined volume, and make the volume ratio of the sodium ferrocyanide dispersion to the mixed metal salt solution 1:(0.1 - 10). After sufficient stirring and dissolution, a transparent mixed metal salt solution is obtained. The mixed solution obtained above is slowly dropped into another mixed solution by a constant-pressure funnel or a peristaltic pump at a dropping rate of 1 mL / min to 100 mL / min, and reacted at a reaction temperature of 5°C to 100°C and a stirring speed of 100 rpm to 1500 rpm for 12 h to 72 h. Then, filtration or centrifugation is performed to obtain a blue Prussian blue precipitate. The Prussian blue precipitate obtained above is washed with a cleaning agent, and then placed in a vacuum oven at 60°C to 120°C for drying for more than 2 h to obtain the Prussian blue cathode material for sodium-ion batteries in the present invention. It may include the above steps.

[0030] In the embodiments of the present invention, the divalent iron salt is one or more selected from FeSO4·7H2O, Fe(NO3)2, or FeCl2·4H2O, the sodium citrate is one or more selected from anhydrous sodium citrate, sodium citrate dihydrate, and sodium citrate pentahydrate, and the cleaning agent is selected from deionized water or absolute ethanol.

[0031] The present invention also provides a Prussian blue cathode material containing a Prussian blue compound represented by the following chemical general formula.

[0032] 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.)

[0033] When the Prussian blue cathode material according to the present invention is used in a sodium-ion battery, it is advantageous for improving the characteristics of the sodium-ion battery in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability.

[0034] The present invention also provides a step of mixing the first dispersion liquid and the second dispersion liquid to obtain a solid precipitate, and a step of washing and drying the solid precipitate to obtain a Prussian blue cathode material, and provides a method for manufacturing a Prussian blue cathode material.

[0035] The first dispersion liquid contains a ferrocyanide source, a first sodium source, and a first dispersant, and the second dispersion liquid contains a divalent iron source, a complexing agent, and a second dispersant.

[0036] In the method for manufacturing a Prussian blue positive electrode material according to the present invention, a ferrocyanide source, a first sodium source, and a divalent iron source are mixed and co-precipitated to generate a Prussian blue compound, whereby a Prussian blue positive electrode material is obtained. The complexing agent and the divalent iron source added cause a strong complexing action on the ferrous ions, which controls the generation rate of the Prussian blue compound, reduces the defects of the Prussian blue compound, improves the yield of the Prussian blue compound, and is advantageous for improving the properties of the Prussian blue positive electrode material. It is advantageous for improving the properties such as cycle stability, specific capacity, Coulomb efficiency, and rate characteristics of a sodium ion battery using the manufactured Prussian blue positive electrode material.

[0037] The present invention also provides a positive electrode sheet including the Prussian blue positive electrode material or the Prussian blue positive electrode material obtained by the method for manufacturing the Prussian blue positive electrode material.

[0038] The positive electrode sheet according to an embodiment of the present invention includes the Prussian blue positive electrode material or the Prussian blue positive electrode material obtained by the method for manufacturing the Prussian blue positive electrode material. When used in a sodium ion battery, it is advantageous for improving the properties of the sodium ion battery in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability.

[0039] The present invention provides a sodium ion battery including the Prussian blue positive electrode material described in the above technical solution, or the Prussian blue positive electrode material manufactured by the method described in the above technical solution, or the positive electrode sheet described in the above technical solution.

[0040] In an embodiment of the present invention, the sodium ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0041] In an embodiment of the present invention, the method for manufacturing the positive electrode is mixing a positive electrode material, a binder, a conductive agent, and a solvent to obtain a slurry The step of applying the slurry onto an aluminum foil and drying it to obtain a positive electrode may be included.

[0042] 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 adhesive may be selected from polyvinylidene fluoride (PVDF), the conductive agent may be selected from Super P, and the mass ratio of the positive electrode material, the adhesive, and the conductive agent may be selected from (6 - 8):(1 - 3):(0.5 - 1.5), may be selected from (6.5 - 7.5):(1.5 - 2.5):(0.8 - 1.2), may be 7:2:1, and the solvent is selected from dimethylpyrrolidone.

[0043] In an embodiment of the present invention, the negative electrode may be selected from metallic sodium, the separator may be selected from a glass fiber membrane, and the electrolyte may be selected from 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroethylene carbonate) (EC:PC:FEC = 0.45:0.45:0.05, vol).

[0044] In an embodiment of the present invention, the positive electrode, the negative electrode, the separator, and the electrolyte may be assembled in a glove box to obtain a CR2032 button battery.

[0045] The present invention provides a high-capacity and high-rate Prussian blue positive electrode material for a sodium-ion battery. The positive electrode material has a chemical composition of Na x Fe[Fe(CN)]6·nH2O, has a stable and highly dispersed hierarchical structure (it can be observed by a scanning electron microscope that the Prussian blue material is not in the form of regular cubes but in the form of quasi-cubes formed by stacking layers), has high rate performance, and excellent cycle stability. The manufacturing method of the Prussian blue positive electrode material for a sodium-ion battery according to the present invention has low raw material costs, a simple manufacturing process, easy control, low energy consumption, and is suitable for industrialization.

[0046] The present invention provides a pure-phase Prussian blue cathode material for sodium-ion batteries. The cathode material in the present invention is an Fe-based Prussian blue material with a general chemical formula of Na x Fe[Fe(CN)]6·nH2O. Based on the characteristics that sodium ferrocyanide is difficult to dissolve in the organic solvent used and easy to dissolve in water, there is a difference in the solubility of sodium ferrocyanide in mixed solvents with different volume ratios of organic solution and water, and the reaction system shows two phases of solid phase and liquid phase, and the present invention utilizes a new synthesis mechanism of forming Prussian blue. Since there is an organic solvent in the reaction system, the reaction rate between ions is slowed down to a certain extent. Excessive sodium citrate not only plays a strong complexing role with ferrous ions, but also effectively increases the content of sodium ions in the solution, significantly slows down the precipitation rate, and effectively increases the content of sodium ions in the elemental composition of the precipitate. Combining the above characteristics, the reaction mechanism of the present invention can effectively control the formation rate of Prussian blue and effectively improve the yield. Therefore, the Prussian blue produced by the method according to the present invention has fewer defects and a higher yield.

[0047] The reaction mechanism of the Prussian blue cathode material for sodium-ion batteries in the present invention is as follows. First, a small amount of solid-phase sodium ferrocyanide is partially dissolved in the organic solvent to generate Na + and [Fe(CN)6] 4- ions. Next, Na + and [Fe(CN)6] 4- are combined with water-soluble Fe 2It undergoes a coprecipitation reaction in the liquid phase. The new synthesis mechanism of Prussian blue in the two-phase synthesis process helps slow down the reaction rate, control the crystal growth process, and makes it easier to grow on the surface of the precipitate formed during the formation of Prussian blue crystals. Therefore, the produced Prussian blue is a stable, highly dispersed hierarchical micro-nano structure self-assembled by micron cubes, with characteristics such as appropriate crystal grain size, large specific surface area, and fast sodium ion migration rate, ensuring high-rate performance and good cycle stability. In the research according to specific examples, the battery obtained in the present invention has a specific capacity exceeding 100 mA g -1 after 200 cycles and a specific capacity exceeding 84 mA g -1 after 800 cycles. In the present invention, by adding a certain amount of Ketjen black to the Prussian blue cathode material for sodium-ion batteries, the drawback of poor conductivity of the Prussian blue alone cathode material is greatly improved. Since Ketjen black is a common conductive carbon black, it is easily available and the cost can be controlled. The raw materials used in the method of the present invention are inexpensive and easily available, the synthesis process is safe and controllable, the energy consumption is low, and it is not difficult to recover the waste liquid generated in the reaction system, so it has high production capacity.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0049] Hereinafter, the technical solution in the embodiments of the present invention will be clearly and completely described. However, it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present invention.

[0050] The embodiments of the present invention provide a Prussian blue positive electrode material containing a Prussian blue compound represented by the following chemical general formula.

[0051] 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.)

[0052] When used in a sodium-ion battery, the Prussian blue positive electrode material according to the present invention is advantageous for improving the characteristics of the sodium-ion battery in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability.

[0053] In some embodiments, x may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, or any numerical value between 0.01 and 3. Preferably, x < 1.5. In this case, the Na ion content is low, a sodium-deficient state is obtained, the reaction rate is fast, which is advantageous for reducing the lattice defects and moisture content of the Prussian blue compound, thereby achieving better characteristics and being advantageous for improving the characteristics such as cycle stability, specific capacity, Coulomb efficiency, and rate characteristics of the sodium-ion battery using the Prussian blue positive electrode material. More preferably, x < 1. In this case, the Prussian blue compound is in a further sodium-deficient state, the reaction rate is further increased, the lattice defects and moisture content of the Prussian blue compound are reduced, which is advantageous for further improving the characteristics such as cycle stability, specific capacity, Coulomb efficiency, and rate characteristics of the sodium-ion battery using the Prussian blue positive electrode material. Also, when x > 0.5, the sodium ion content of the Prussian blue compound is controlled within a more appropriate range, thereby being more advantageous for improving the characteristics such as cycle stability, specific capacity, Coulomb efficiency, and rate characteristics of the sodium-ion battery using the Prussian blue positive electrode material.

[0054] In some embodiments, n may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.1, 3.2, or any numerical value between 0.01 and 3.5. Thereby, the water content of the Prussian blue compound can be controlled to obtain more excellent characteristics, which is advantageous for improving the characteristics such as cycle stability, specific capacity, Coulomb efficiency, and rate characteristics of the sodium-ion battery using the Prussian blue positive electrode material.

[0055] In some embodiments, 0 < y < 1, and y may be selected from any value between greater than 0 and less than 1, such as 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 0.

[0056] In some embodiments, y may be expressed as y = 1 - δ, where δ represents the content of vacancies of ferrocyanide ions. Here, 0 < δ < 1, and δ may 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.

[0057] Preferably, 0.8 < y < 1, that is, 0 < δ < 0.2. Thereby, the lattice defects of the Prussian blue compound are controlled to be in a state with few defects, the properties of the Prussian blue compound are improved, and it is advantageous for improving properties such as the cycle stability, specific capacity, Coulomb efficiency, and rate performance of the sodium-ion battery using the Prussian blue positive electrode material.

[0058] In some embodiments, when y is expressed as y = 1 - δ, the chemical general formula of the Prussian blue compound may be expressed as follows.

[0059] Na x Fe[Fe(CN)6] 1-δ □ δ ·nH2O Formula II Here, □ represents the vacancy of ferrocyanide ions. The value ranges of x, n, and δ are as described above.

[0060] In some embodiments, at least a part of the crystal of the Prussian blue compound is quasi-cubic, that is, when the crystal of the Prussian blue compound is observed with a scanning electron microscope, the crystal of the Prussian blue compound shows an obvious cubic structure, provided that the intersection of the edges of the crystal of the Prussian blue compound is arc-shaped.

[0061]

[0061] In some embodiments, at least a part of the crystals of the Prussian blue compound is substantially spherical. Compared with the quasi-cubic crystals of the Prussian blue compound, when observed with a scanning electron microscope, the crystals of the substantially spherical Prussian blue compound have arc-shaped crystal edges.

[0062] In some embodiments, the size of the crystals of the Prussian blue compound is 0.1 μm or more and 2.5 μm or less, for example, 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 value between 0.1 μm and 2.5 μm.

[0063] In some embodiments, the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 0.93 ·2.6H2O, and Na 0.517 Fe[Fe(CN)6] 0.85 0.85 ·3.15H2O, and is at least one selected therefrom. Thereby, a Prussian blue compound having more excellent properties is obtained, which is advantageous for improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery using the Prussian blue positive electrode material.

[0064] In some embodiments, the Prussian blue positive electrode material further includes a carbonaceous material, and at least a part of the carbonaceous material adheres to the surface of the crystals of the Prussian blue compound. The addition of the carbonaceous material suppresses the generation of defects in the manufacturing process of the Prussian blue compound, is advantageous for improving the conductivity of the Prussian blue positive electrode material, and is advantageous for improving the properties such as cycle stability, specific capacity, Coulomb efficiency, and rate performance of the sodium ion battery using the Prussian blue positive electrode material.

[0065] In some embodiments, the carbonaceous material is selected from conductive carbon black materials and may be, for example, Ketjen black. The conductive carbon black material is a common conductive carbon black material, which is advantageous for suppressing the generation of defects in the production process of the Prussian blue compound, improving the conductivity of the Prussian blue cathode material, and reducing costs.

[0066] Embodiments of the present invention also include Step S100 of mixing the first dispersion liquid and the second dispersion liquid to obtain a solid precipitate, and step S200 of washing and drying the solid precipitate to obtain a Prussian blue cathode material, and provide a method for manufacturing a Prussian blue cathode material.

[0067] The first dispersion liquid includes a ferrocyanide source, a first sodium source, and a first dispersant, and the second dispersion liquid includes a divalent iron source, a complexing agent, and a second dispersant.

[0068] In the method for manufacturing a Prussian blue cathode material according to the present invention, a Prussian blue cathode material is obtained by mixing a ferrocyanide source, a first sodium source, and a divalent iron source and co-precipitating to generate a Prussian blue compound. The first iron ions from the added complexing agent and the divalent iron source exert a strong complexing effect, which is advantageous for controlling the generation rate of the Prussian blue compound, reducing the defects of the Prussian blue compound, improving the yield of the Prussian blue compound, and improving the properties of the Prussian blue cathode material, and is advantageous for improving the properties such as cycle stability, specific capacity, Coulomb efficiency, and rate performance of a sodium ion battery using the manufactured Prussian blue cathode material.

[0069] In some embodiments, the Prussian blue cathode material manufactured by the method for manufacturing a Prussian blue cathode material is as described above.

[0070] In some embodiments, step S100 includes Step S110 of dispersing a ferrocyanide source and a first sodium source in the first dispersant to obtain a first dispersion liquid; Step S120 of dispersing a divalent iron source and a complexing agent in the second dispersant to obtain a second dispersion liquid; Including step S130 of mixing the first dispersion liquid and the second dispersion liquid to obtain a solid precipitate.

[0071] In some embodiments, the order of steps S110 and S120 is not limited. Step S110 may be performed before step S120, step S120 may be performed before step S110, or steps S110 and S120 may be performed simultaneously.

[0072] In some embodiments, the ferrocyanide source and the first sodium source may be dispersed in the first dispersant by stirring. The stirring time may be controlled to be 5 minutes to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any value between 5 minutes and 30 minutes.

[0073] 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.

[0074] In some embodiments, sodium ferrocyanide may be Na4Fe(CN) 6· 10H2O.

[0075] In some embodiments, the concentration of sodium ferrocyanide in the first dispersant may 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 value between 5 g / L and 50 g / L.

[0076] In some embodiments, the first dispersant contains deionized water and a first solvent, and the ferrocyanide source is poorly soluble in the first solvent. When the ferrocyanide source is derived from sodium ferrocyanide, the first solvent is selected from solvents that are poorly soluble in sodium ferrocyanide. By using a solvent that is poorly soluble in sodium ferrocyanide, the solubility of the ferrocyanide source in the mixed solvent is different, so the reaction system exhibits two phases: a solid phase and a liquid phase. Since the first solvent is an organic solvent, the reaction rate is slowed down, which is advantageous for controlling the formation rate of the Prussian blue compound, reducing the defects of the formed Prussian blue compound, and improving the yield of the Prussian blue compound.

[0077] In some embodiments, the first solvent is one or more selected from ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

[0078] 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 value between 1:0.01 and 1:100.

[0079] In some embodiments, the deionized water and the first solvent in the first dispersant may be uniformly mixed by stirring to obtain the first dispersant. The stirring time after mixing the deionized water and the first solvent in the first dispersant may be controlled to be 1 minute to 100 minutes. For example, it can be 2 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, or any value between 1 minute and 100 minutes.

[0080] In some embodiments, the first dispersion further includes a carbonaceous material. The carbonaceous material is selected from conductive carbon black materials and may be, for example, Ketjen black. The conductive carbon black material is a common conductive carbonaceous material, which is advantageous for suppressing the generation of defects in the manufacturing process of the Prussian blue compound, improving the conductivity of the Prussian blue cathode material, and reducing costs. When the first dispersion further includes a carbonaceous material, step S110 includes step S111 of dispersing the carbonaceous material in the first dispersant, and step S112 of dispersing the ferrocyanide source and the first sodium source in the first dispersant.

[0081] In some embodiments, when the first dispersion includes the carbonaceous material, the first solvent is preferably ethylene glycol, which is advantageous for uniformly dispersing the carbonaceous material in the first dispersant.

[0082] 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 value between 0.1 g / L and 10 g / L.

[0083] In some embodiments, the carbonaceous material may be uniformly dispersed in the first dispersant by ultrasonic dispersion. The time of ultrasonic dispersion is 5 minutes to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any value between 5 minutes and 30 minutes.

[0084] In some embodiments, the ratio of the amount of substance of the carbonaceous material to the amount of substance of the ferrocyanide source is selected from 1:(0.01 to 100). For example, the ratio of the amount of substance of the carbonaceous material to the amount of substance of the ferrocyanide source may 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 value between 1:0.01 and 1:100.

[0085] In some embodiments, the divalent iron source and the complexing agent may be dispersed in the second dispersant by stirring. The stirring time may be controlled to be 5 minutes to 30 minutes. For example, it may be 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any value between 5 minutes and 30 minutes.

[0086] In some embodiments, the divalent iron is derived from a divalent iron salt, and the divalent iron salt is one or more selected from FeSO4·7H2O, Fe(NO3)2, and FeCl2·4H2O.

[0087] In some embodiments, the complexing agent is one or more selected from sodium citrate anhydrous, sodium citrate dihydrate, sodium citrate pentahydrate, sodium oxalate, sodium tartrate, and sodium malate. The divalent iron ions from the complexing agent and the divalent iron source have a strong complexing effect. Also, when the complexing agent is selected from the above compounds, the complexing agent also functions as a second sodium source, effectively improving the concentration of sodium ions in the solution after mixing the first dispersion and the second dispersion, controlling the formation rate of the Prussian blue compound, effectively improving the sodium ion content in the Prussian blue compound, reducing the defects of the Prussian blue compound, improving the yield of the Prussian blue compound, and being advantageous for improving the properties of the Prussian blue cathode material, which is advantageous for improving the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. of the sodium ion battery using the manufactured Prussian blue cathode material.

[0088] In some embodiments, the ratio of the amount of substance of the ferrous iron source to the amount of substance of the complexing agent is selected from 1:(1 to 100). For example, the ratio of the amount of substance of the ferrous iron source to the amount of substance of the complexing agent may be 1:2, 1:4, 1:5, 1:10, 1:20, 1:50, 1:60, 1:80, 1:90, or any value between 1:1 and 1:100.

[0089] In some embodiments, the ratio of the amount of substance of the ferrocyanide source to the amount of substance of the ferrous iron source is selected from 1:(1 to 3). For example, the ratio of the amount of substance of the ferrocyanide source to the amount of substance of the ferrous iron source may be 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, or any value between 1:1 and 1:3.

[0090] In some embodiments, the second dispersant includes deionized water and a second solvent, and the ferrocyanide source is poorly soluble in the second solvent. When the ferrocyanide source is derived from sodium ferrocyanide, the second solvent is selected from solvents in which sodium ferrocyanide is poorly soluble. By using a poorly soluble solvent as the ferrocyanide source, the solubility of the ferrocyanide source in the solvent after mixing the first dispersion liquid and the second dispersion liquid is different, and the reaction system shows two phases, a solid phase and a liquid phase. Also, by using an organic solvent as the second solvent, the reaction rate is slowed down, the generation rate of the Prussian blue compound is controlled, the defects of the generated Prussian blue compound are reduced, and it is advantageous to improve the yield of the Prussian blue compound.

[0091] In some embodiments, the second solvent is one or more selected from ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

[0092] In some embodiments, the volume ratio of deionized water to the second solvent in the second dispersant is selected from 1:(0.01 to 100). For example, the volume ratio of deionized water to the second solvent in the second dispersant may 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 value between 1:0.01 and 1:100.

[0093] In some embodiments, the first solvent and the second solvent are the same, which is advantageous for reducing the types of solvents used in the manufacturing process and reducing the process cost.

[0094] In some embodiments, step S130 includes step S131 of mixing the first dispersion liquid and the second dispersion liquid to obtain a mixture, and step S132 of stirring the mixture at the first reaction temperature for the first hour and then allowing it to stand for the first standing time to obtain the solid precipitate.

[0095] In some embodiments, the first dispersion liquid and the second dispersion liquid may be mixed by dropping. For example, the mixing may be performed by dropping the first dispersion liquid into the second dispersion liquid or dropping the second dispersion liquid into the first dispersion liquid. Here, a constant-pressure funnel or a peristaltic pump may be used for dropping. The dropping rate may be 1 mL / min to 100 mL / min. For example, it may be 2 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 50 mL / min, 60 mL / min, 75 mL / min, 80 mL / min, 90 mL / min, or any value between 1 mL / min and 100 mL / min.

[0096] In some embodiments, the ratio of the volume of the first dispersion liquid to the volume of the second dispersion liquid is 1:(0.1 to 10). For example, it may be 1:0.1, 1:0.2, 1:0.5, 1:1, 1:3, 1:5, 1:6, 1:9, or any value between 1:0.1 and 1:10.

[0097] In some embodiments, the first reaction temperature is 5°C to 100°C, for example, 10°C, 15°C, 20°C, 25°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or any value between 5°C and 100°C.

[0098] In some embodiments, the first stirring time is 12 hours to 72 hours, for example, 18 hours, 24 hours, 36 hours, 40 hours, 48 hours, 56 hours, 60 hours, 64 hours, or any value between 12 hours and 72 hours. During the first stirring time, the mixture may be sufficiently reacted by stirring. The stirring speed of the mixture is 100 rpm to 1500 rpm, for example, 200 rpm, 300 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1300 rpm, 1400 rpm, or any stirring speed between 100 rpm and 1500 rpm.

[0099] In some embodiments, the first standing time is 12 hours to 36 hours, for example, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, or any value between 12 hours and 36 hours.

[0100] In some embodiments, the solid precipitate may be separated by common solid-liquid separation means, such as suction filtration, filtration and other means.

[0101] In some embodiments, step S200 includes step S210 of washing the solid precipitate with a first cleaning agent to obtain a product to be dried, and step S220 of drying the product to be dried to obtain the Prussian blue cathode material.

[0102] In some embodiments, the first cleaning agent may be selected from deionized water and / or absolute ethanol. The solid precipitate may be cleaned one or more times (for example, 2 times, 3 times, etc.) with the first cleaning agent to obtain the product to be dried. When the first cleaning agent is selected from deionized water and absolute ethanol, the solid precipitate is cleaned with each of deionized water and absolute ethanol.

[0103] In some embodiments, drying may employ common drying means, such as vacuum drying. In some embodiments, the vacuum drying may be performed at a temperature of 60°C to 120°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 98°C, 100°C, 102°C, 105°C, 108°C, or any temperature between 90°C and 110°C. The time of vacuum drying exceeds 2 hours. Further, the time of vacuum drying may be 12 hours to 36 hours, for example, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, or any value between 12 hours and 36 hours.

[0104] In some embodiments, when the first dispersion contains a carbonaceous material, at least a part of the carbonaceous material adheres to the surface of the crystal of the Prussian blue compound. That is, the Prussian blue positive electrode material contains a Prussian blue compound and the carbonaceous material at least a part of which adheres to the surface of the crystal of the Prussian blue compound.

[0105] In the method for manufacturing a Prussian blue positive electrode material according to an embodiment of the present invention, a ferrocyanide source, a first sodium source, and a divalent iron source are mixed and co-precipitated to generate a Prussian blue compound, whereby a Prussian blue positive electrode material is obtained. The first iron ions from the added complexing agent and the divalent iron source have a strong complexing effect, which controls the formation rate of the Prussian blue compound, reduces the defects of the Prussian blue compound, improves the yield of the Prussian blue compound, and is advantageous for improving the properties of the Prussian blue positive electrode material. It is advantageous for improving the properties such as cycle stability, specific capacity, Coulomb efficiency, and rate performance of a sodium ion battery using the manufactured Prussian blue positive electrode material.

[0106] Embodiments of the present invention also provide a positive electrode sheet including the Prussian blue positive electrode material or the Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material.

[0107] The positive electrode sheet according to the embodiments of the present invention includes the Prussian blue positive electrode material or the Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material, and is advantageous for improving the characteristics of a sodium ion battery in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability when used in a sodium ion battery.

[0108] Embodiments of the present invention also provide a sodium ion battery including the Prussian blue positive electrode material, the Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material, or the positive electrode sheet.

[0109] The sodium ion battery according to the embodiments of the present invention includes the Prussian blue positive electrode material, the Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material, or the positive electrode sheet, thereby improving the characteristics in terms of specific capacity, Coulomb efficiency, rate characteristics, and long cycle stability.

[0110] In some embodiments, the sodium ion battery includes a positive electrode sheet, a negative electrode plate, a separator, and an electrolyte.

[0111] In some embodiments, the method for manufacturing the positive electrode sheet is as follows: mixing a Prussian blue positive electrode material, a binder, a conductive agent, and a solvent to obtain a slurry; coating the slurry on an aluminum foil and drying it to obtain a positive electrode sheet.

[0112] In some embodiments, the positive electrode material is the Prussian blue positive electrode material, the binder may be selected from polyvinylidene fluoride (PVDF), the conductive agent may be selected from Super P (conductive carbon black), and the mass ratio of the positive electrode material, the binder, and the conductive agent may be selected from (6-8):(1-3):(0.5-1.5), may be selected from (6.5-7.5):(1.5-2.5):(0.8-1.2), or may be 7:2:1, and the solvent is selected from dimethylpyrrolidone.

[0113] In some embodiments, the negative electrode may be selected from metallic sodium, the separator may be selected from a glass fiber membrane, and the electrolyte may be selected from 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroethylene carbonate) (the volume ratio of EC:PC:FEC is 0.45:0.45:0.05).

[0114] In some embodiments, the positive electrode, the negative electrode, the separator, and the electrolyte may be assembled in a glove box to obtain a CR2032 button battery.

[0115] Note that several specific embodiments are listed below. The embodiments described below are illustrative and are only used for interpreting the present application and are not to be understood as limiting the present application. When specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications shall be followed. The reagents or instruments used are all ordinary products that can be obtained through commercial channels when the manufacturer is not specified.

[0116] Example 1 Weigh 100 mg of Ketjen black and add it to 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 3:1), and perform ultrasonic stirring for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Next, weigh 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) and add it to this dispersion, and stir for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, weigh 5 g of sodium citrate anhydrous and 0.834 g of ferrous sulfate (FeSO4·7H2O) and dissolve them in 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 3:1), and stir to dissolve to obtain a transparent mixed metal salt solution.

[0117] The mixed metal salt solution obtained above was slowly dropped into the sodium ferrocyanide dispersion at a dropping rate of 3.33 mL / min at 25°C using a constant pressure funnel. After the dropping was completed, it was stirred at 25°C and 500 rpm for 4 h, then left standing for 24 h. After the standing was completed, it was suction filtered to obtain a blue Prussian blue precipitate.

[0118] The obtained Prussian blue precipitate was washed alternately with water and ethanol. Here, it was washed twice with water and once with ethanol to completely remove impurities. Next, it was vacuum dried at 100°C for 24 h to obtain a Prussian blue cathode material for sodium ion batteries. Here, the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ( 0.07 ·2.6H2O (the molecular formula was determined using XRD detection), that is, the chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ·2.6H2O.

[0119] Example 2 Weigh 200 mg of Ketjen black and add it to 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 2:1), and perform ultrasonic stirring for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Next, weigh 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) and add it to this dispersion, and stir for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, weigh 5 g of sodium citrate anhydrous and 0.834 g of ferrous sulfate (FeSO4·7H2O) and dissolve them in 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 2:1), and stir to dissolve to obtain a transparent mixed metal salt solution.

[0120] The mixed metal salt solution obtained above was slowly dropped into the sodium ferrocyanide dispersion at a dropping rate of 3.33 mL / min at 25°C using a constant pressure funnel. After the dropping was completed, it was stirred at 25°C and 500 rpm for 4 h, then left standing for 24 h. After the standing was completed, it was suction filtered to obtain a blue Prussian blue precipitate.

[0121] The Prussian blue precipitate obtained above was washed alternately with water and ethanol. Here, it was washed twice with water and once with ethanol to completely remove impurities. Next, it was vacuum dried at 100°C for 24 h to obtain a Prussian blue cathode material for sodium ion batteries. Here, 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 the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ·2.6H2O.

[0122] Example 3 Weigh 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O), add it to 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 1:1), stir for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, weigh 5 g of sodium citrate anhydrous and 0.834 g of ferrous sulfate (FeSO4·7H2O), dissolve them in 100 mL of a mixed solution of deionized water and ethylene glycol (the volume ratio of deionized water to ethylene glycol is 1:1), stir to dissolve to obtain a transparent mixed metal salt solution.

[0123] Slowly drop the above-obtained mixed metal salt solution into the sodium ferrocyanide dispersion at a dropping rate of 3.33 mL / min at 25 °C using a constant pressure funnel. After the dropping is completed, stir at 25 °C and 500 rpm for 4 h, then let it stand for 24 h. After standing, perform suction filtration to obtain a blue Prussian blue precipitate.

[0124] Wash the above-obtained Prussian blue precipitate alternately with water and ethanol. Here, wash it twice with water and once with ethanol to completely remove impurities. Next, dry it under vacuum at 100 °C for 24 h to obtain a Prussian blue cathode material for sodium-ion batteries. Here, 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 the Prussian blue compound is Na 0.517 Fe[Fe(CN)6] 0.85 ·3.15H2O.

[0125] Comparative Example 1 Weigh 100 mg of Ketjen black and add it to 100 mL of deionized water. Stir it with ultrasonic waves for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Next, weigh 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) and add it to this dispersion. Stir it for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, weigh 5 g of sodium citrate anhydrous and 0.834 g of ferrous sulfate (FeSO4·7H2O), dissolve them in 100 mL of deionized water, and stir to dissolve to obtain a transparent mixed metal salt solution.

[0126] At 25°C, slowly drop the above-obtained mixed metal salt solution into the sodium ferrocyanide dispersion with a dropping funnel at a dropping rate of 3.33 mL / min. After the dropping is completed, stir it at 25°C and 500 rpm for 4 h, then let it stand for 24 h. After the standing is completed, perform suction filtration to obtain a blue Prussian blue precipitate.

[0127] Wash the above-obtained Prussian blue precipitate alternately with water and ethanol. Here, wash it twice with water and once with ethanol to completely remove impurities. Next, dry it under vacuum at 100°C for 24 h to obtain a Prussian blue cathode material for sodium-ion batteries.

[0128] Comparative Example 2 Weigh 200 mg of Ketjen black and add it to 100 mL of deionized water. Stir it with ultrasonic waves for 5 to 30 minutes to obtain a uniformly dispersed dispersion. Next, weigh 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) and add it to this dispersion. Stir it for 5 to 30 minutes to obtain a 9.68 g / L sodium ferrocyanide dispersion. Separately, weigh 5 g of sodium citrate anhydrous and 0.834 g of ferrous sulfate (FeSO4·7H2O), dissolve them in 100 mL of deionized water, and stir to dissolve to obtain a transparent mixed metal salt solution.

[0129] The mixed metal salt solution obtained above was slowly dropped into the sodium ferrocyanide dispersion at a dropping rate of 3.33 mL / min at 25°C using a constant pressure funnel. After the dropping was completed, it was stirred at 25°C and 500 rpm for 4 h, then left standing for 24 h. After the standing was completed, it was suction filtered to obtain a blue Prussian blue precipitate.

[0130] The Prussian blue precipitate obtained above was washed alternately with water and ethanol. Here, it was washed twice with water and once with ethanol to completely remove impurities. Next, it was vacuum dried at 100°C for 24 h to obtain a Prussian blue positive electrode material for sodium ion batteries.

[0131] Detection of properties

[0132] (1) X-ray diffraction (XRD) test A D8 Focus X-ray powder diffractometer manufactured by Bruker in Germany was used for the test, and Cu-Kα was used as the radiation source with a wavelength of 1.5046λ. A Ni filter was used, the tube flow rate was 40 mA, the tube pressure was 40 KV, the scanning range was 5° to 90°, the scanning speed was 5° / min, and the step size was 0.05°. The positive electrode materials manufactured in the examples and comparative examples were placed on a slide glass and flattened, and this slide glass was embedded in the center of the experimental tank of the instrument for testing, and phase identification and crystal structure information were analyzed by JADE6.0 software.

[0133] (2) Property evaluation by scanning electron microscope Using a SU-3500 model scanning electron microscope tester manufactured by HITACHI, the morphology of the material was observed at an acceleration voltage of 15 KV.

[0134] Results of detection Figure 1(a) is the X-ray diffraction pattern of the substantially spherical Prussian blue cathode material for a sodium-ion battery manufactured in Example 1. Here, the X-axis is the X-ray scanning angle 2θ, and the vertical coordinate is the intensity of the X-ray. From Figure 1, in this Prussian blue cathode material, there is a characteristic peak of the (200) crystal plane at a scanning angle of 16.92°, a characteristic peak of the (220) crystal plane at a scanning angle of 24.12°, a characteristic peak of the (400) crystal plane at a scanning angle of 34.18°, a characteristic peak of the (420) crystal plane at a scanning angle of 38.56°, a characteristic peak of the (422) crystal plane at a scanning angle of 42.46°, a characteristic peak of the (440) crystal plane at a scanning angle of 49.39°, a characteristic peak of the (600) crystal plane at a scanning angle of 52.78°, and a characteristic peak of the (620) crystal plane at a scanning angle of 55.77°. It was found that this belongs to the Fm-3m space group and there are no impurity peaks in the X-ray diffraction pattern. From this, it became clear that this cathode material is a pure-phase substance.

[0135] Figure 1(b) is a scanning electron microscope image of the Prussian blue cathode material for a sodium-ion battery manufactured in Example 1. As a result of inspection, the Prussian blue cathode material has a cubic structure composed of nanoscale cubic crystal grains, and the size of the nanocubes is about 2 μm.

[0136] Figure 2(a) shows the X-ray diffraction pattern of the Prussian blue cathode material for sodium-ion batteries manufactured in Example 2. Here, the X-axis is the X-ray scanning angle 2θ, and the vertical coordinate is the intensity of the X-ray. In this Prussian blue cathode material, there is a characteristic peak of the (200) crystal plane at a scanning angle of 16.88°, a characteristic peak of the (220) crystal plane at a scanning angle of 24.06°, a characteristic peak of the (400) crystal plane at a scanning angle of 34.1°, a characteristic peak of the (420) crystal plane at a scanning angle of 38.42°, a characteristic peak of the (422) crystal plane at a scanning angle of 42.38°, a characteristic peak of the (440) crystal plane at a scanning angle of 49.4°, a characteristic peak of the (600) crystal plane at a scanning angle of 52.62°, and a characteristic peak of the (620) crystal plane at a scanning angle of 55.67°. It was found that this belongs to the Fm-3m space group and there are no impurity peaks in the X-ray diffraction pattern. From this, it became clear that this cathode material is a pure-phase substance.

[0137] Figure 2(b) shows the scanning electron microscope image of the Prussian blue cathode material for sodium-ion batteries obtained in Example 2. This Prussian blue material has a porous hierarchical spherical structure composed of nanocubes. The size of the nanocubes is about 100 nm, the size of the hierarchical spheres is about 2 μm, and it was confirmed that the dispersibility is good.

[0138] Figure 3(a) shows the X-ray diffraction pattern of the Prussian blue cathode material for sodium-ion batteries manufactured in Example 3. Here, the X-axis represents the X-ray scanning angle 2θ, and the vertical axis represents the intensity of the X-ray. In this Prussian blue cathode material, there is a characteristic peak of the (200) crystal plane at a scanning angle of 17.48°, a characteristic peak of the (220) crystal plane at a scanning angle of 24.84°, a characteristic peak of the (400) crystal plane at a scanning angle of 34.44°, a characteristic peak of the (420) crystal plane at a scanning angle of 38.53°, a characteristic peak of the (422) crystal plane at a scanning angle of 42.03°, a characteristic peak of the (440) crystal plane at a scanning angle of 49.61°, a characteristic peak of the (600) crystal plane at a scanning angle of 50.94°, and a characteristic peak of the (620) crystal plane at a scanning angle of 55.67°. It belongs to the Fm-3m space group, and it was found that there are no impurity peaks in the X-ray diffraction pattern. From this, it became clear that this cathode material is a pure-phase substance.

[0139] Figure 3(b) shows the scanning electron microscope image of the Prussian blue cathode material for sodium-ion batteries manufactured in Example 3. As a result of the observation, the Prussian blue material has a structure composed of nano-cubic particles, but it is somewhat damaged, and the size of the nano-cubic particles is 500 nm.

[0140] Fig. 4(a) shows the X-ray diffraction pattern of the cubic Prussian blue cathode material for sodium-ion batteries manufactured in Comparative Example 1. Here, the X-axis is the X-ray scanning angle 2θ, and the vertical coordinate is the intensity of the X-ray. In this Prussian blue cathode material, there is a characteristic peak of the (200) crystal plane at a scanning angle of 16.94°, a characteristic peak of the (220) crystal plane at a scanning angle of 24.08°, a characteristic peak of the (400) crystal plane at a scanning angle of 34.34°, a characteristic peak of the (420) crystal plane at a scanning angle of 38.56°, a characteristic peak of the (422) crystal plane at a scanning angle of 42.38°, a characteristic peak of the (440) crystal plane at a scanning angle of 49.4°, a characteristic peak of the (600) crystal plane at a scanning angle of 52.36°, and a characteristic peak of the (620) crystal plane at a scanning angle of 55.67°. It was found that this belongs to the Fm-3m space group and there are no impurity peaks in the X-ray diffraction pattern. From this, it became clear that this cathode material is a pure-phase substance.

[0141] Fig. 4(b) shows the scanning electron microscope image of the cubic Prussian blue cathode material for sodium-ion batteries manufactured in Comparative Example 1. As a result of the observation, this Prussian blue material has a cubic morphology in which nanoparticles are aggregated, and the size of the nanoparticles is about 1 μm.

[0142] FIG. 5(a) is an X-ray diffraction pattern of the Prussian blue cathode material for a sodium ion battery manufactured in Comparative Example 2. Here, the X-axis is the X-ray scanning angle 2θ, and the vertical coordinate is the intensity of the X-ray. In the Prussian blue cathode material, there is a characteristic peak of the (200) crystal plane at a scanning angle of 16.82°, a characteristic peak of the (220) crystal plane at a scanning angle of 23.96°, a characteristic peak of the (400) crystal plane at a scanning angle of 34.1°, a characteristic peak of the (420) crystal plane at a scanning angle of 38.35°, a characteristic peak of the (422) crystal plane at a scanning angle of 42.19°, a characteristic peak of the (440) crystal plane at a scanning angle of 49.17°, a characteristic peak of the (600) crystal plane at a scanning angle of 52.26°, and a characteristic peak of the (620) crystal plane at a scanning angle of 55.42°. It was found that this belongs to the Fm-3m space group and there are no impurity peaks in the X-ray diffraction pattern. From this, it became clear that this cathode material is a pure phase substance.

[0143] FIG. 5(b) is a scanning electron microscope image of the Prussian blue cathode material for a sodium ion battery manufactured in Comparative Example 2. As a result of observation, the Prussian blue material has a cubic structure composed of nano-cubic particles, and the size of the nano-cubic particles is about 1 μm.

[0144] From the XRD diffraction results of the examples and comparative examples, it was found that the diffraction peak intensity of the Prussian blue material manufactured in the examples was stronger than that of the materials in the comparative examples, and the crystals of the materials manufactured in the examples had higher crystallinity and higher quality.

[0145] Also, from the small particle substances adhering to the surface of the Prussian blue compound shown in FIGS. 1(b) and 2(b), the Ketjen black added in Example 1 and Example 2 is at least partially adhered to the surface of the Prussian blue cathode material manufactured.

[0146] The Prussian blue cathode material for sodium-ion batteries produced in the examples and comparative examples was used as the cathode active material of the sodium-ion battery. The cathode active material, binder (polyvinylidene fluoride PVDF), and conductive agent (Super P) were mixed at a mass ratio of 7:2:1, and dimethylpyrrolidone (NMP) was added as a solvent, followed by mixing and stirring to obtain a uniform slurry. The slurry was uniformly coated on an aluminum foil, dried, cut into sheets to form a cathode, metallic sodium was used as the anode, a glass fiber membrane was used as the separator, and 1.0 mol / L NaClO4 / EC (ethylene carbonate) + PC (polycarbonate) + FEC (fluoroethylene carbonate) (EC:PC:FEC = 0.45:0.45:0.05, vol) was used as the electrolyte, and a CR2032 button battery was assembled in an argon glove box.

[0147] The button battery assembled above was tested with a Land battery tester manufactured by Wuhan Jinnuo Electronics Co., Ltd. The test conditions and results are as follows. A constant current charge-discharge test was performed on the button battery, and the charge-discharge voltage range was set to 2V - 4.2V. In Examples 1 - 3, the Prussian blue electrode manufactured with the cathode material of Example 2 had the most excellent electrochemical properties. At a current density of 100 mA / g, the initial charge specific capacity and initial discharge specific capacity of the battery were 113.3 mAh / g and 137 mAh / g respectively, and the discharge specific capacity retention rate after 200 cycles was 87.1%. On the other hand, the capacities of Comparative Example 1 and Comparative Example 2 after 200 cycles were only 42% and 30% respectively. Furthermore, the Prussian blue electrode manufactured using the cathode material of Example 2 still had a discharge specific capacity retention rate of 77% after 800 cycles, and the Coulombic efficiency of each cycle was close to 99%. The detection results are as follows (see Table 1 and Figures 6 - 10).

[0148]

Table 1

[0149] Combining the results of FIGS. 6 to 10 and Table 1, the Prussian blue positive electrode material obtained in the examples of the present invention exhibits excellent characteristics in terms of cycle stability, charge-discharge specific capacity, Coulomb efficiency, rate characteristics, etc. of the sodium-ion battery when used in a sodium-ion battery.

[0150] In the present invention, it was observed from the scanning electron microscope image that Prussian blue and Ketjen black were uniformly distributed, and sodium ferrocyanide was dissolved in the ethylene glycol solution. When an organic solvent is introduced into the reaction system, a mixed phase is formed, and ferrous sulfate and sodium citrate are insoluble in the organic solvent. However, since water is required for the reaction, the introduction of the organic solvent further controls the reaction rate, thereby controlling the growth process of Prussian blue crystals and reducing the defects of aged Prussian blue. The addition of Ketjen black can improve the problem that the conductivity of Prussian blue is inferior. When Ketjen black is introduced, the conductivity of the composite material of Prussian blue and Ketjen black is significantly improved. By introducing ethylene glycol as the organic solvent in the present invention, two phases exist in the reaction system, and the sodium ion concentration in the aqueous reaction system further increases. The organic solution introduced in the present invention does not participate in the reaction, only achieves the purpose of controlling the reaction rate, and can realize recycling and reuse after the reaction is completed, without waste. The recovery method may be vacuum distillation at 80 °C, which is environmentally friendly and safe.

[0151] The present invention has been described with reference to specific embodiments of the present invention, but these descriptions and explanations do not limit the present invention. Those skilled in the art can clearly understand that various changes can be made without departing from the true spirit and scope of the present invention defined by the appended claims in order to adapt a specific situation, material, composition of matter, substance, method or process to the purpose, spirit and scope of the present application. It is intended that all such changes be within the scope of the appended claims. The methods disclosed in this specification are described with reference to specific operations performed in a specific order, but it should be understood that these operations can be combined, subdivided, or the order changed to form equivalent methods without departing from the teachings of the present invention. Therefore, unless specifically indicated herein, the order and grouping of operations do not limit the present application.

Claims

1. A Prussian blue cathode material, characterized by comprising a Prussian blue compound having the following chemical general formula. Na ｘ Fe[Fe(CN) ６ ｙ ｙ ·nH ２ ２ O 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 cathode material according to Claim 1, wherein 0.5 < x < 1.5 and 0.8 < y < 1.

3. The Prussian blue cathode material according to Claim 2, wherein 0.5 < x < 1.

4. The Prussian blue cathode material according to any one of Claims 1 to 3, wherein at least a part of the crystals of the Prussian blue compound has a quasi-cubic shape.

5. The Prussian blue cathode material according to Claim 1, wherein the size of the crystals of the Prussian blue compound is 0.1 μm or more, and the size of the crystals of the Prussian blue compound is 2.5 μm or less.

6. The chemical formula of the Prussian blue compound is Na ０．６４７ Fe[Fe(CN) ６ < ０．９３ >・2.6H ２ 2O and Na ０．５１７ Fe[Fe(CN) ６ < ０．８５ >・3.15H ２ 2O, and is at least one selected therefrom. The Prussian blue positive electrode material according to claim 1, characterized in that.

7. The Prussian blue cathode material according to Claim 1, further comprising a carbonaceous material, and at least a part of the carbonaceous material adheres to the surface of the crystals of the Prussian blue compound.

8. The Prussian blue cathode material according to Claim 7, wherein the carbonaceous material is selected from conductive carbon black materials.

9. Mixing a first dispersion liquid and a second dispersion liquid to obtain a solid precipitate; Washing and drying the solid precipitate to obtain a Prussian blue cathode material, The first dispersion liquid contains a ferrocyanide source, a first sodium source, and a first dispersant, The second dispersion liquid contains a divalent iron source, a complexing agent, and a second dispersant, and a method for manufacturing a Prussian blue cathode material.

10. The ferrocyanide source and the first sodium source are derived from sodium ferrocyanide, and / or The divalent iron source is derived from a divalent iron salt, and the divalent iron salt is FeSO ４ ·7H ２ O, Fe(NO ３ ) ２ , FeCl ２ ·4H ２ O, and is one or more selected therefrom, and / or The method for manufacturing a Prussian blue cathode material according to Claim 9, wherein the complexing agent is one or more selected from sodium citrate anhydrous, sodium citrate dihydrate, sodium citrate pentahydrate, sodium oxalate, sodium tartrate, and sodium malate.

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

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

13. The method for manufacturing a Prussian blue positive electrode material according to any one of claims 9 to 12, wherein the first dispersion liquid further contains a carbonaceous material.

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

15. A positive electrode sheet 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 method for manufacturing a 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, the Prussian blue positive electrode material obtained by the method for manufacturing a 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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