Prussian blue positive electrode material and its manufacturing method, positive electrode 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 priority to a Chinese patent application bearing application number 202310772356.6 and entitled "Prussian blue positive electrode material, its manufacturing method and its use," filed with the China Intellectual Property Office on June 27, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of batteries and electrochemical energy storage, and in particular to a Prussian blue cathode material and its manufacturing method, a cathode sheet and a sodium ion battery. [Background technology]

[0003] Energy storage has become a key issue in modern society to harness renewable energy and promote smart grids. Room-temperature sodium-ion batteries (SIBs), which operate under chemical conditions similar to those of lithium-ion batteries (LIBs), are promising candidates for energy storage systems (ESSs) due to the abundance and low cost of sodium worldwide. Rechargeable sodium-ion batteries (SIBs) have emerged as promising candidates for large-scale energy storage systems due to their abundant resources and controllable 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 framework, large interstitial sodium storage sites, high theoretical capacity, and non-toxic properties. Furthermore, the convenient synthesis process and low cost of PBAs make them very attractive for potential large-scale applications. However, PBAs suffer from poor rate capability and cycling stability due to their low electronic conductivity and defects in the PBA framework.

[0004] In a typical PB framework, the iron center can be either low-spin (Fe LS (C)) or high spin (Fe HS (N) structure. LS (C) and Fe HS(N) participates in the redox reaction of sodium storage at different potentials, and in a perfect PB framework, the number of both Fe sites is equal, so theoretically, it provides the same number of coulombs. However, existing literature suggests that Fe LS (C) The capacity contribution of the redox reaction couple is Fe HS (N) redox couple. Furthermore, this low-spin Fe LS (C) Redox couples are electrochemically active at higher potentials, which inevitably lowers the average potential platform of PBA-based cathodes. Fe reduction by water or incorporation of other transition metals LS (C) Activation of the redox couple has been reported, which optimizes cycling stability but sacrifices capacity. Therefore, to realize the full potential of PBA-based cathode materials, this issue needs to be resolved urgently, and satisfactory rate performance is another challenge for the commercialization of PBA materials. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, an object of the present invention is to provide a Prussian blue positive electrode material having high rate capability and excellent cycle stability, a method for producing the same, and uses thereof, in order to solve the problem that when conventional Prussian blue materials are used in sodium ion batteries, capacity degradation occurs in order to optimize cycle stability.

[0006] In view of the above, an object of the present invention is to provide a Prussian blue positive electrode material having high rate capability and excellent cycle stability, a method for producing the same, and use thereof, in order to solve the problem of conventional Prussian blue materials that cause capacity degradation in order to optimize cycle stability. [Means for solving the problem]

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

[0008] In the present embodiment, x may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5. When x<1.5, the resulting Prussian blue cathode material has better cycle stability, a low Na ion content, a sodium deficiency state, a fast reaction rate, and fewer lattice defects and water content, thereby providing better performance. n may be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5. 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 embodiment 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 method for producing a pharmaceutical composition comprising: mixing solution A and solution B to obtain a solid precipitate; washing and drying the solid precipitate to obtain a Prussian blue cathode material; Solution A includes a carbonaceous material, sodium ferrocyanide, and a first solvent; The solution B includes an iron salt, sodium citrate, and a second solvent.

[0012] In an embodiment of the present invention, the carbonaceous material may be selected from conductive carbon black, activated carbon, etc., and for example, Ketjen black may be used.

[0013] In an embodiment of the present invention, the first solvent may comprise water and solvent A, where water may be selected from deionized water, and solvent A may be one or more selected from ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol, such as ethylene glycol, and 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), and 1:(20-30). In an embodiment of the present invention, the method for preparing the first solvent may include a step of uniformly mixing water and solvent A, where the mixing is performed under 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, and 90 min.

[0014] In an embodiment 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, and 90 g / L.

[0015] In an embodiment of the present invention, the method for preparing solution A comprises: The method may include the steps of dispersing the carbonaceous material in a first solvent to obtain a dispersion, and then dissolving sodium ferrocyanide in the dispersion to obtain solution A.

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

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

[0018] In 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 comprise water and solvent B, where 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, such as ethylene glycol, and the volume ratio of water to solvent B 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), and 1:(20-30). In an embodiment of the present invention, the method for preparing the second solvent may include a step of uniformly mixing water and solvent B, where the mixing is performed under 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, and 90 min.

[0020] In an embodiment of the present invention, the method for preparing solution B comprises: The method may include dissolving an iron salt and sodium citrate in a second solvent to obtain solution B.

[0021] In the embodiment of the present invention, a homogeneous 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), for example, 1:(5-90), 1:(10-80), 1:(20-70), 1:(30-60), 1:(40-50), the molar ratio of the sodium ferrocyanide to the iron salt may be selected from 1:(1-3), for example, 1:2, and the molar ratio of the iron salt to citric acid may be selected from 1:(1-3), for example, 1:2. The molar ratio of sodium may be selected from 1:(1 to 100), for example, 1:(5 to 90), 1:(10 to 80), 1:(20 to 70), 1:(30 to 60), and 1:(40 to 50), and the volume ratio of solution A to solution B may be selected from 1:(0.1 to 10), for example, 1:(0.5 to 9), 1:(1 to 8), 1:(2 to 7), 1:(3 to 6), and 1:(4 to 5).

[0023] In the embodiment of the present invention, both solvent A and solvent B are solvents that are difficult to dissolve sodium ferrocyanide, and they play a role in suppressing the generation of defects during crystal growth by adjusting the solubility and controlling the reaction rate.

[0024] In an embodiment of the present invention, the mixing may be performed by adding solution A dropwise to solution B, or by adding solution B dropwise to solution A, and 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, and 90 mL / min.

[0025] In the present embodiment, the mixing of solution A and solution B serves to regulate the dissolution rate and thereby control the reaction rate.

[0026] In an embodiment of the present invention, the mixing may be a reaction, and the mixing temperature 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, and 90°C. The mixing may be performed 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, and 1400 rpm. The mixing time may be selected from 12 to 72 hours, for example, 24 hours, 36 hours, 48 ​​hours, and 60 hours.

[0027] In an embodiment 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; cleaning may be performed alternately with water and ethanol, the number of times of cleaning with water may be two, and the number of times of cleaning with ethanol may be one.

[0028] In the embodiment of the present invention, the drying temperature may be selected from 60°C to 120°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C, and the drying time may be more than 2 hours.

[0029] In an embodiment of the present invention, the method for producing the Prussian blue cathode material comprises: Deionized water and ethylene glycol are mixed in a volume ratio of 1:(0.01-50) and stirred for 10-60 minutes to be uniformly mixed, then Ketjen black is added to the mixture and ultrasonically stirred until uniformly dispersed, then raw material sodium ferrocyanide (NaFe(CN)10H0) is added to the dispersion and stirred for 30 minutes to obtain a 5g / L-50g / L sodium ferrocyanide dispersion, and divalent iron salt and sodium citrate are weighed out so that the mass ratio of divalent iron salt to sodium citrate is 1:(0.01-100) and the mass ratio of sodium ferrocyanide to total metal salt is 1:(1-2), and these are added to a predetermined volume of a mixed solution of deionized water and ethylene glycol to make the volume ratio of the sodium ferrocyanide dispersion to the mixed metal salt solution 1:(0.1-10), and the mixture is thoroughly stirred and dissolved to obtain a transparent mixed metal salt solution. the mixed solution obtained above is slowly added dropwise to another mixed solution at a rate of 1 mL / min to 100 mL / min using a constant pressure funnel or a peristaltic pump, and the mixture is reacted at a reaction temperature of 5°C to 100°C and at a stirring speed of 100 rpm to 1500 rpm for 12 hours to 72 hours, and then filtered or centrifuged to obtain a blue Prussian blue precipitate; The method may include a step of washing the Prussian blue precipitate obtained above with a detergent, and then drying it in a vacuum oven at 60°C to 120°C for more than 2 hours to obtain the Prussian blue positive electrode material for sodium ion batteries of the present invention.

[0030] In an embodiment 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 comprising a Prussian blue compound having the general chemical formula shown below:

[0032] Na x Fe[Fe(CN)6] y nH2O Formula I, (In Formula I, x is 0.01 to 3, and 0 <y<1であり、 n is 0.01 to 3.5.

[0033] When used in a sodium ion battery, the Prussian blue positive electrode material according to the present invention is advantageous in improving the properties of the sodium ion battery in terms of specific capacity, coulombic efficiency, rate capability, and long cycle stability.

[0034] The present invention also provides mixing the first dispersion and the second dispersion to obtain a solid precipitate; and washing and drying the solid precipitate to obtain a Prussian blue cathode material.

[0035] the first dispersion comprises a ferrocyanide source, a sodium source, and a first dispersant; The second dispersion includes a divalent iron source, a complexing agent, and a second dispersing agent.

[0036] In the method for producing a Prussian blue positive electrode material according to the present invention, a ferrocyanide source, a sodium source, and a divalent iron source are mixed and co-precipitated to produce a Prussian blue compound, thereby obtaining the Prussian blue positive electrode material. The ferrous ions from the added complexing agent and the divalent iron source exert a strong complexing effect, which is advantageous for controlling the rate of production of the Prussian blue compound, reducing defects in the Prussian blue compound, increasing the yield of the Prussian blue compound, and improving the properties of the Prussian blue positive electrode material. This is advantageous for improving the cycle stability, specific capacity, Coulombic efficiency, rate capability, and other properties of sodium-ion batteries using the produced Prussian blue positive electrode material.

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

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

[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 produced 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, a sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0041] In an embodiment of the present invention, a method for manufacturing a positive electrode includes the steps of: Mixing a positive electrode material, an adhesive, a conductive agent, and a solvent to obtain a slurry; The method may include a step of applying the slurry onto an aluminum foil and drying it to obtain a positive electrode.

[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, 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), or 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, a CR2032 button cell battery may be obtained by assembling a positive electrode, a negative electrode, a separator, and an electrolyte in a glove box.

[0045] The present invention provides a high-capacity, high-rate Prussian blue cathode material for sodium-ion batteries, the cathode material having a chemical composition of Na x The material is Fe[Fe(CN)]6·nH2O, and has a stable, highly dispersed hierarchical structure (scanning electron microscopy has revealed that the Prussian blue material is not a regular cube, but rather a quasi-cubic structure formed by stacking layers), with high rate capability and excellent cycle stability. The method for producing Prussian blue positive electrode material for sodium-ion batteries according to the present invention has low raw material costs, a simple and easy-to-control manufacturing process, 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 has the general chemical formula Na x The Fe-based Prussian blue material is Fe[Fe(CN)]6·nH2O. The present invention utilizes a novel synthesis mechanism: sodium ferrocyanide is poorly soluble in organic solvents but highly soluble in water. This leads to differences in the solubility of sodium ferrocyanide in mixed solvents with different volume ratios of organic solution to water, resulting in a two-phase reaction system (solid and liquid) that forms Prussian blue. The presence of organic solvent in the reaction system slows the reaction rate between ions to a certain extent. Excess sodium citrate not only provides strong complexing with ferrous ions, but also effectively increases the sodium ion content in the solution, significantly slowing the formation rate of the precipitate and increasing the sodium ion content in the elemental composition of the precipitate. Combining these features, the reaction mechanism of the present invention effectively controls the formation rate of Prussian blue and improves yield. Therefore, the Prussian blue produced by the method of 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 sodium ferrocyanide is partially dissolved in an organic solvent, and then Na + and [Fe(CN)6] 4- ions, then Na + and [Fe(CN)6] 4- Water-soluble Fe 2The Prussian blue undergoes a co-precipitation reaction in the liquid phase. The new synthesis mechanism of Prussian blue in the two-phase synthesis process slows down the reaction rate and helps control the crystal growth process, making it easier for the crystals to grow on the surface of the precipitates formed during the formation of Prussian blue crystals. Therefore, the produced Prussian blue has a stable, highly dispersed hierarchical micro-nano structure in which microcubes are self-assembled, and is characterized by appropriate crystal grain size, a large specific surface area, and a fast sodium ion migration rate, ensuring high-rate performance and good cycle stability. In a study using specific examples, the battery obtained by the present invention had a specific capacity of 100 mA g after 200 cycles. -1 and a specific capacity of 84 mA g after 800 cycles. -1 The results show that the conductivity exceeds 100%. In the present invention, by adding a certain amount of Ketjen Black to a Prussian blue cathode material for sodium-ion batteries, the drawback of Prussian blue alone, which has poor conductivity, is significantly improved. Ketjen Black is a common conductive carbon black, so it is easy to obtain and the cost can be controlled. The raw materials used in the method of the present invention are inexpensive and easy to obtain, the synthesis process is safe and controllable, consumes little energy, and the waste liquid generated in the reaction system can be easily recovered, resulting in high production capacity. [Brief explanation of the drawings]

[0048] [Figure 1] 1(a) is an X-ray diffraction pattern of the positive electrode material produced in Example 1. FIG. 1(b) is a scanning electron microscope image of the positive electrode material produced in Example 1. [Figure 2] 1(a) is an X-ray diffraction pattern of the positive electrode material produced in Example 2. FIG. 1(b) is a scanning electron microscope image of the positive electrode material produced in Example 2. [Figure 3] 1(a) is an X-ray diffraction pattern of the positive electrode material produced in Example 3. FIG. 1(b) is a scanning electron microscope image of the positive electrode material produced in Example 3. [Figure 4]1(a) is an X-ray diffraction pattern of the positive electrode material produced in Comparative Example 1. FIG. 1(b) is a scanning electron microscope image of the positive electrode material produced in Comparative Example 1. [Figure 5] 1(a) is an X-ray diffraction pattern of the positive electrode material produced in Comparative Example 2. FIG. 1(b) is a scanning electron microscope image of the positive electrode material produced in Comparative Example 2. [Figure 6] FIG. 2 is a graph showing the charge-discharge performance of the positive electrode material produced in Example 1. [Figure 7] 1(a) is a graph showing the charge-discharge performance of the positive electrode material produced in Example 2. FIG. 1(b) is a graph showing the rate characteristics of the positive electrode material produced in Example 2. FIG. 1(c) is a graph showing the cycle characteristics of the positive electrode material produced in Example 2. [Figure 8] FIG. 10 is a graph showing the charge-discharge performance of the positive electrode material produced in Example 3. [Figure 9] FIG. 1 is a graph showing the charge-discharge performance of the positive electrode material produced in Comparative Example 1. [Figure 10] FIG. 10 is a graph showing the charge-discharge performance of the positive electrode material produced in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0049] The following provides a clear and complete description of the technical solutions in the embodiments of the present invention, but it is clear that the described embodiments are only a part of the embodiments of the present invention, and do not represent all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present invention.

[0050] An embodiment of the present invention provides a Prussian blue cathode material comprising a Prussian blue compound having the general chemical formula shown below:

[0051] Na x Fe[Fe(CN)6] y nH2O Formula I (In Formula I, x is 0.01 to 3, and 0 <y<1であり、 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 in improving the properties of the sodium ion battery in terms of specific capacity, coulombic efficiency, rate capability, 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 number between 0.01 and 3. Preferably, x<1.5, which results in a low Na ion content, a sodium-deficient state, a fast reaction rate, and advantageously reduces the lattice defects and water content of the Prussian blue compound, thereby achieving better performance and advantageously improving the cycle stability, specific capacity, Coulombic efficiency, rate performance, and other properties of a sodium-ion battery using the Prussian blue positive electrode material. More preferably, x<1, which results in a further sodium-deficient state of the Prussian blue compound, further accelerating the reaction rate, reducing the lattice defects and water content of the Prussian blue compound, and advantageously further improving the cycle stability, specific capacity, Coulombic efficiency, rate performance, and other properties of a sodium-ion battery using the Prussian blue positive electrode material. Furthermore, when x>0.5, the sodium ion content of the Prussian blue compound is controlled within a more appropriate range, which is advantageous in improving the cycle stability, specific capacity, coulombic efficiency, rate characteristics, and other properties of a 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 number between 0.01 and 3.5, thereby controlling the water content of the Prussian blue compound to obtain better properties, which is advantageous for improving the properties of a sodium-ion battery using the Prussian blue positive electrode material, such as cycle stability, specific capacity, coulombic efficiency, and rate capability.

[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, which is advantageous for improving properties such as the cycle stability, specific capacity, Coulomb efficiency, rate performance, etc. 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<{0000023}>Fe[Fe(CN)6]<{0000024}>□<{0000025}>·nH2O Formula II Here, □ represents the vacancy of ferrocyanide ions. The ranges of the values of x, n, and δ are as described above.

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

[0061] In some embodiments, at least a portion of the crystals of the Prussian blue compound are approximately spherical, and compared to the quasi-cubic crystals of the Prussian blue compound, the approximately spherical crystals of the Prussian blue compound have arc-shaped crystal edges when observed under a scanning electron microscope.

[0062] In some embodiments, the size of the crystals of the Prussian blue compound may be 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 2.6H2O and Na 0.517 Fe[Fe(CN)6] 0.85 3.15H2O. This provides a Prussian blue compound with superior properties, which is advantageous for improving the cycle stability, specific capacity, coulombic efficiency, rate characteristics, etc. of a sodium-ion battery using the Prussian blue positive electrode material.

[0064] In some embodiments, the Prussian blue positive electrode material further comprises a carbonaceous material, at least a portion of which is attached to the surface of the crystal of the Prussian blue compound. The addition of the carbonaceous material is advantageous in suppressing the occurrence of defects in the manufacturing process of the Prussian blue compound and improving the conductivity of the Prussian blue positive electrode material, which is advantageous in improving the properties of a sodium-ion battery using the Prussian blue positive electrode material, such as cycle stability, specific capacity, Coulombic efficiency, and rate characteristics.

[0065] In some embodiments, the carbonaceous material may be selected from conductive carbon black materials, such as Ketjen black, which is a common conductive carbon black material and is advantageous in improving the conductivity of the Prussian blue cathode material and reducing costs while suppressing the occurrence of defects in the manufacturing process of the Prussian blue compound.

[0066] An embodiment of the present invention also comprises: Step S100: mixing the first dispersion and the second dispersion to obtain a solid precipitate; and step S200 of washing and drying the solid precipitate to obtain a Prussian blue positive electrode material.

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

[0068] In the method for producing a Prussian blue positive electrode material according to the present invention, a ferrocyanide source, a sodium source, and a ferrous iron source are mixed and co-precipitated to form a Prussian blue compound, thereby obtaining the Prussian blue positive electrode material. The ferrous ions from the added complexing agent and the ferrous iron source exert a strong complexing effect, which is advantageous in controlling the rate of formation of the Prussian blue compound, reducing defects in the Prussian blue compound, increasing the yield of the Prussian blue compound, and improving the properties of the Prussian blue positive electrode material. This is advantageous in improving the cycle stability, specific capacity, coulombic efficiency, rate capability, and other properties of sodium-ion batteries using the produced Prussian blue positive electrode material.

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

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

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

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

[0073] In some embodiments, the ferrocyanide source and the first sodium source are derived from sodium ferrocyanide, i.e., sodium ferrocyanide provides both ferrocyanide ions and sodium ions.

[0074] In some embodiments, sodium ferrocyanide is NaFe(CN) 6· It may also be 10H2O.

[0075] In some embodiments, the concentration of sodium ferrocyanide in the first dispersant can be from 5 g / L to 50 g / L, e.g., 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 includes 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 reaction system exhibits two phases, a solid phase and a liquid phase, due to the different solubilities of the ferrocyanide source in the mixed solvent. Because the first solvent is an organic solvent, the reaction rate is slowed, which is advantageous for controlling the production rate of the Prussian blue compound, reducing defects in the produced 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 to 100), for example, the volume ratio of deionized water to the first solvent in the first 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.

[0079] In some embodiments, the deionized water in the first dispersant and the first solvent may be uniformly mixed by stirring to obtain the first dispersant. The stirring time after mixing the deionized water in the first dispersant and the first solvent may be controlled to be 1 minute to 100 minutes, and may be, 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 value between 1 minute and 100 minutes.

[0080] In some embodiments, the first dispersion liquid further includes a carbonaceous material. The carbonaceous material may be selected from conductive carbon black materials, such as Ketjen black. Conductive carbon black materials are common conductive carbonaceous materials and are advantageous for improving the conductivity of the Prussian blue positive electrode material and reducing costs while suppressing the occurrence of defects in the manufacturing process of the Prussian blue compound. When the first dispersion liquid further includes a carbonaceous material, step S110 includes: A step S111 of dispersing a carbonaceous material in the first dispersant; and step S112 of dispersing a ferrocyanide source and a first sodium source in the first dispersant.

[0081] In some embodiments, when the first dispersion liquid 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 may be 0.1 g / L to 10 g / L, e.g., 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, and the ultrasonic dispersion time may be 5 to 30 minutes, such as 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 the carbonaceous material to the amount of the ferrocyanide source is selected from 1:(0.01 to 100), for example, the ratio of the amount of the carbonaceous material to the amount 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 5 to 30 minutes, for example, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or any value between 5 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 the group consisting of anhydrous sodium citrate, sodium citrate dihydrate, sodium citrate pentahydrate, sodium oxalate, sodium tartrate, and sodium malate. The complexing agent and the ferrous iron source exert a strong complexing effect. When the complexing agent is selected from the above compounds, the complexing agent also functions as a sodium source, effectively increasing the concentration of sodium ions in the solution obtained after mixing the first dispersion and the second dispersion. This effectively controls the production rate of the Prussian blue compound, effectively increases the sodium ion content in the Prussian blue compound, reduces defects in the Prussian blue compound, improves the yield of the Prussian blue compound, and improves the properties of the Prussian blue positive electrode material. This is beneficial for improving the cycle stability, specific capacity, Coulombic efficiency, rate capability, and other properties of a sodium-ion battery using the produced Prussian blue positive electrode material.

[0088] In some embodiments, the ratio of the amount of the divalent iron source to the amount of the complexing agent is selected from 1:(1 to 100), for example, the ratio of the amount of the divalent iron source to the amount 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 the ferrocyanide source to the amount of the divalent 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 divalent 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 dispersion includes deionized water and a second solvent, and the ferrocyanide source is sparingly 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 sparingly soluble. By using a solvent in which the ferrocyanide source is sparingly soluble, the solubility of the ferrocyanide source in the solvent differs after mixing the first dispersion and the second dispersion, and the reaction system exhibits two phases: a solid phase and a liquid phase. Furthermore, using an organic solvent as the second solvent is advantageous in slowing the reaction rate, controlling the production rate of the Prussian blue compound, reducing defects in the produced Prussian blue compound, and improving 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, thereby advantageously reducing the number of solvents used in the manufacturing process and reducing process costs.

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

[0095] In some embodiments, the first dispersion and the second dispersion may be mixed by dropwise addition. For example, mixing may be performed by adding the first dispersion dropwise to the second dispersion, or adding the second dispersion dropwise to the first dispersion. Here, a constant pressure funnel or a peristaltic pump may be used for the dropping. The dropping rate may be 1 mL / min to 100 mL / min, for example, 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 to the volume of the second dispersion may be 1:(0.1-10), for example, 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 may be between 5°C and 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 may be 12 to 72 hours, for example, 18 hours, 24 hours, 36 hours, 40 hours, 48 ​​hours, 56 hours, 60 hours, or 64 hours, or any value between 12 and 72 hours. During the first stirring time, the mixture may be sufficiently reacted by stirring. The stirring speed of the mixture may be 100 rpm to 1500 rpm, for example, 200 rpm, 300 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1300 rpm, or 1400 rpm, or any stirring speed between 100 rpm and 1500 rpm.

[0099] In some embodiments, the first standing time may be between 12 hours and 36 hours, such as 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 conventional solid-liquid separation means, such as suction filtration, filtration, and the like.

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

[0102] In some embodiments, the first cleaning agent may be selected from deionized water and / or absolute ethanol. The solid precipitate may be washed with the first cleaning agent one or more times (e.g., two times, three times, etc.) to obtain the dried product. When the first cleaning agent is selected from deionized water and absolute ethanol, the solid precipitate is washed with deionized water and absolute ethanol, respectively.

[0103] In some embodiments, drying may be performed using common drying methods, such as vacuum drying. In some embodiments, vacuum drying may be performed at a temperature of 60° C. to 120° C., such as 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., and the vacuum drying time may be greater than 2 hours, and may be 12 hours to 36 hours, such as 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 liquid contains a carbonaceous material, at least a portion of the carbonaceous material is attached to the surface of the crystals of the Prussian blue compound, i.e., the Prussian blue positive electrode material contains a Prussian blue compound and the carbonaceous material, at least a portion of which is attached to the surface of the crystals of the Prussian blue compound.

[0105] In a method for producing a Prussian blue positive electrode material according to an embodiment of the present invention, a ferrocyanide source, a sodium source, and a divalent iron source are mixed and co-precipitated to form a Prussian blue compound, thereby obtaining a Prussian blue positive electrode material. The ferrous ions from the added complexing agent and the divalent iron source exert a strong complexing effect, which is advantageous for controlling the rate of formation of the Prussian blue compound, reducing defects in the Prussian blue compound, increasing the yield of the Prussian blue compound, and improving the properties of the Prussian blue positive electrode material. This is advantageous for improving the cycle stability, specific capacity, Coulombic efficiency, rate capability, and other properties of a sodium-ion battery using the produced Prussian blue positive electrode material.

[0106] An embodiment of the present invention also provides a positive electrode sheet including the Prussian blue positive electrode material or a 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 embodiment of the present invention contains the Prussian blue positive electrode material or a Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material, and when used in a sodium ion battery, is advantageous in improving the properties of the sodium ion battery in terms of specific capacity, coulombic efficiency, rate characteristics, long cycle stability, etc.

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

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

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

[0111] In some embodiments, a method for producing a positive electrode sheet includes: Mixing a Prussian blue positive electrode material, an adhesive, a conductive agent, and a solvent to obtain a slurry; and applying the slurry onto 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 adhesive may be selected from polyvinylidene fluoride (PVDF), the conductive agent may be selected from Super P (conductive carbon black), 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), (6.5-7.5):(1.5-2.5):(0.8-1.2), or 7:2:1, and the solvent is selected from dimethylpyrrolidone.

[0113] In some examples, 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) (volume ratio of EC:PC:FEC is 0.45:0.45:0.05).

[0114] In some embodiments, a CR2032 button cell battery may be obtained by assembling the positive electrode, negative electrode, separator, and electrolyte in a glove box.

[0115] Although several specific examples are listed below, the examples described below are illustrative and are used only to interpret the present application and are not to be understood as limiting the present application. Unless specific techniques or conditions are specified in the examples, they should be carried out in accordance with the techniques or conditions described in the literature in the field or in accordance with the product instructions. Unless the manufacturer of the reagents or instruments used is specified, they are all ordinary products available commercially.

[0116] Example 1 100 mg of Ketjen Black was weighed and added to 100 mL of a mixture of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 3:1). The mixture was ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Next, 0.968 g of sodium ferrocyanide (NaFe(CN)10H0) was weighed and added to the dispersion. The mixture was 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 (FeSO7H0) were weighed and dissolved in 100 mL of a mixture of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 3:1). The mixture was stirred to obtain a clear mixed metal salt solution.

[0117] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion at 25°C using a constant pressure funnel at a rate of 3.33 mL / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 4 hours and then allowed to stand for 24 hours. After the standing period was over, the mixture was subjected to suction filtration to obtain a blue Prussian blue precipitate.

[0118] The resulting Prussian blue precipitate was washed alternately with water and ethanol, twice with water and once with ethanol, to completely remove impurities. It was then dried in a vacuum at 100°C for 24 hours to obtain a Prussian blue cathode material for sodium-ion batteries. The chemical formula of the Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 ( 0.07 2.6H2O (determining the molecular formula using XRD detection), i.e., the chemical formula of Prussian blue compound is Na 0.647 Fe[Fe(CN)6] 0.93 2.6H2O.

[0119] Example 2 200 mg of Ketjen Black was weighed and added to 100 mL of a mixture of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 2:1). The mixture was ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Next, 0.968 g of sodium ferrocyanide (NaFe(CN)10H0) was weighed and added to the dispersion. The mixture was 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 (FeSO7H0) were weighed and dissolved in 100 mL of a mixture of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 2:1). The mixture was stirred to obtain a clear mixed metal salt solution.

[0120] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion at 25°C using a constant pressure funnel at a rate of 3.33 mL / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 4 hours and then allowed to stand for 24 hours. After the standing period was over, the mixture was subjected to suction filtration to obtain a blue Prussian blue precipitate.

[0121] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, to completely remove impurities. It was then dried in a vacuum at 100°C for 24 hours to obtain a Prussian blue cathode material for sodium-ion batteries. 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.

[0122] Example 3 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed out and added to 100 mL of a mixed solution of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 1:1), 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 weighed out and dissolved in 100 mL of a mixed solution of deionized water and ethylene glycol (volume ratio of deionized water to ethylene glycol: 1:1), and stirred to dissolve, obtaining a clear mixed metal salt solution.

[0123] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion at 25°C using a constant pressure funnel at a rate of 3.33 mL / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 4 hours and then allowed to stand for 24 hours. After the standing period was over, the mixture was subjected to suction filtration to obtain a blue Prussian blue precipitate.

[0124] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, to completely remove impurities. It was then dried in a vacuum at 100°C for 24 hours to obtain a Prussian blue cathode material for sodium-ion batteries. The chemical formula of the Prussian blue compound is Na 0.517 Fe[Fe(CN)6] 0.85 ( 0.15 3.15H2O, i.e., the chemical formula of Prussian blue compound is Na 0.517 Fe[Fe(CN)6] 0.85 3.15H2O.

[0125] Comparative Example 1 100 mg of Ketjen Black was weighed out and added to 100 mL of deionized water. The mixture was ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Next, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed out and added to the dispersion. The mixture was 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 weighed out and dissolved in 100 mL of deionized water. The mixture was stirred to obtain a clear mixed metal salt solution.

[0126] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion at 25°C using a constant pressure funnel at a rate of 3.33 mL / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 4 hours and then allowed to stand for 24 hours. After the standing period was over, the mixture was subjected to suction filtration to obtain a blue Prussian blue precipitate.

[0127] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, to completely remove impurities, and then vacuum dried at 100°C for 24 hours to obtain a Prussian blue cathode material for sodium-ion batteries.

[0128] Comparative Example 2 200 mg of Ketjen Black was weighed out and added to 100 mL of deionized water, and the mixture was ultrasonically stirred for 5 to 30 minutes to obtain a uniform dispersion. Next, 0.968 g of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was weighed out and added to this dispersion, and the mixture was 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 weighed out and dissolved in 100 mL of deionized water, and the mixture was stirred to obtain a clear mixed metal salt solution.

[0129] The mixed metal salt solution obtained above was slowly added dropwise to the sodium ferrocyanide dispersion at 25°C using a constant pressure funnel at a rate of 3.33 mL / min. After the addition was complete, the mixture was stirred at 25°C and 500 rpm for 4 hours and then allowed to stand for 24 hours. After the standing period was over, the mixture was subjected to suction filtration to obtain a blue Prussian blue precipitate.

[0130] The Prussian blue precipitate obtained above was washed alternately with water and ethanol, twice with water and once with ethanol, to completely remove impurities, and then vacuum dried at 100°C for 24 hours to obtain a Prussian blue cathode material for sodium-ion batteries.

[0131] Detecting Characteristics

[0132] (1) X-ray diffraction (XRD) test A D8 Focus X-ray powder diffractometer manufactured by Bruker GmbH, Germany, was used for the tests, with a Cu-Kα radiation source at a wavelength of 1.5046λ. A Ni filter was used, with a tube flow rate of 40 mA, tube pressure of 40 kV, a scan range of 5° to 90°, a scan rate of 5° / min, and a step size of 0.05°. The positive electrode materials prepared in the examples and comparative examples were placed on flat glass slides and embedded in the center of the experimental chamber. Phase identification and crystal structure information were analyzed using JADE 6.0 software.

[0133] (2) Characterization by scanning electron microscope The morphology of the material was observed using a scanning electron microscope tester, model SU-3500, manufactured by Hitachi Co., Ltd., at an accelerating voltage of 15 KV.

[0134] Detection Results FIG. 1(a) is an X-ray diffraction pattern of the approximately spherical Prussian blue positive electrode material for a sodium-ion battery prepared in Example 1, where the X-axis is the X-ray scan angle 2θ and the ordinate is the X-ray intensity. As shown in Figure 1, this Prussian blue cathode material exhibits a characteristic peak for the (200) crystal plane at a scan angle of 16.92°, a characteristic peak for the (220) crystal plane at a scan angle of 24.12°, a characteristic peak for the (400) crystal plane at a scan angle of 34.18°, a characteristic peak for the (420) crystal plane at a scan angle of 38.56°, a characteristic peak for the (422) crystal plane at a scan angle of 42.46°, a characteristic peak for the (440) crystal plane at a scan angle of 49.39°, a characteristic peak for the (600) crystal plane at a scan angle of 52.78°, and a characteristic peak for the (620) crystal plane at a scan angle of 55.77°. This indicates that the cathode material belongs to the Fm-3m space group and has no impurity peaks in the X-ray diffraction pattern. This confirms that this cathode material is a pure-phase material.

[0135] FIG. 1(b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium-ion batteries prepared in Example 1. Upon inspection, the Prussian blue positive electrode material has a cubic structure composed of nanoscale cubic crystal grains, with the size of the nanocubes being approximately 2 μm.

[0136] FIG. 2(a) is the X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 2, where the X-axis is the X-ray scan angle 2θ and the ordinate is the X-ray intensity. The Prussian blue cathode material exhibited a characteristic peak for the (200) crystal plane at a scan angle of 16.88°, a characteristic peak for the (220) crystal plane at a scan angle of 24.06°, a characteristic peak for the (400) crystal plane at a scan angle of 34.1°, a characteristic peak for the (420) crystal plane at a scan angle of 38.42°, a characteristic peak for the (422) crystal plane at a scan angle of 42.38°, a characteristic peak for the (440) crystal plane at a scan angle of 49.4°, a characteristic peak for the (600) crystal plane at a scan angle of 52.62°, and a characteristic peak for the (620) crystal plane at a scan angle of 55.67°. It was determined that the cathode material belonged to the Fm-3m space group and had no impurity peaks in the X-ray diffraction pattern. This confirmed that the cathode material was a pure phase material.

[0137] FIG. 2(b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium-ion batteries obtained in Example 2. The Prussian blue material has a porous hierarchical spherical structure composed of nanocubes, with the size of the nanocubes being approximately 100 nm and the size of the hierarchical spheres being approximately 2 μm, and is found to have good dispersibility.

[0138] FIG. 3(a) is the X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion batteries prepared in Example 3, where the X-axis is the X-ray scanning angle 2θ and the ordinate is the X-ray intensity. The Prussian blue cathode material exhibited a characteristic peak for the (200) crystal plane at a scan angle of 17.48°, a characteristic peak for the (220) crystal plane at a scan angle of 24.84°, a characteristic peak for the (400) crystal plane at a scan angle of 34.44°, a characteristic peak for the (420) crystal plane at a scan angle of 38.53°, a characteristic peak for the (422) crystal plane at a scan angle of 42.03°, a characteristic peak for the (440) crystal plane at a scan angle of 49.61°, a characteristic peak for the (600) crystal plane at a scan angle of 50.94°, and a characteristic peak for the (620) crystal plane at a scan angle of 55.67°. It was determined that the cathode material belonged to the Fm-3m space group and had no impurity peaks in the X-ray diffraction pattern. This confirmed that the cathode material was a pure phase material.

[0139] FIG. 3(b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium-ion batteries prepared in Example 3. Observation revealed that the Prussian blue material has a structure composed of nanocubic particles, but they are somewhat broken, and the size of the nanocubic particles is 500 nm.

[0140] FIG. 4(a) shows the X-ray diffraction pattern of the cubic Prussian blue positive electrode material for sodium ion batteries prepared in Comparative Example 1, where the X-axis represents the X-ray scanning angle 2θ and the ordinate represents the X-ray intensity. The Prussian blue cathode material exhibited a characteristic peak for the (200) crystal plane at a scan angle of 16.94°, a characteristic peak for the (220) crystal plane at a scan angle of 24.08°, a characteristic peak for the (400) crystal plane at a scan angle of 34.34°, a characteristic peak for the (420) crystal plane at a scan angle of 38.56°, a characteristic peak for the (422) crystal plane at a scan angle of 42.38°, a characteristic peak for the (440) crystal plane at a scan angle of 49.4°, a characteristic peak for the (600) crystal plane at a scan angle of 52.36°, and a characteristic peak for the (620) crystal plane at a scan angle of 55.67°. It was determined that the cathode material belonged to the Fm-3m space group and had no impurity peaks in the X-ray diffraction pattern. This confirmed that the cathode material was a pure phase material.

[0141] FIG. 4(b) is a scanning electron microscope image of the cubic Prussian blue positive electrode material for sodium-ion batteries produced in Comparative Example 1. Observation revealed that the Prussian blue material had a cubic shape composed of aggregated nanoparticles, with the nanoparticles measuring approximately 1 μm in size.

[0142] FIG. 5(a) is the X-ray diffraction pattern of the Prussian blue positive electrode material for sodium ion batteries prepared in Comparative Example 2, where the X-axis is the X-ray scanning angle 2θ and the ordinate is the X-ray intensity. The Prussian blue cathode material exhibited a characteristic peak for the (200) crystal plane at a scan angle of 16.82°, a characteristic peak for the (220) crystal plane at a scan angle of 23.96°, a characteristic peak for the (400) crystal plane at a scan angle of 34.1°, a characteristic peak for the (420) crystal plane at a scan angle of 38.35°, a characteristic peak for the (422) crystal plane at a scan angle of 42.19°, a characteristic peak for the (440) crystal plane at a scan angle of 49.17°, a characteristic peak for the (600) crystal plane at a scan angle of 52.26°, and a characteristic peak for the (620) crystal plane at a scan angle of 55.42°. It was determined that the cathode material belonged to the Fm-3m space group and had no impurity peaks in the X-ray diffraction pattern. This confirmed that the cathode material was a pure phase material.

[0143] FIG. 5(b) is a scanning electron microscope image of the Prussian blue positive electrode material for sodium-ion batteries produced in Comparative Example 2. Observation revealed that the Prussian blue material has a cubic structure composed of nanocubic particles, with the size of the nanocubic particles being approximately 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 produced in the Examples was stronger than that of the material in the Comparative Examples, and the crystals of the material produced in the Examples were of higher crystallinity and higher quality.

[0145] Furthermore, from the small particulate matter adhering to the surface of the Prussian blue compound shown in Figures 1(b) and 2(b), it can be seen that at least a portion of the Ketjen Black added in Examples 1 and 2 is adhered to the surface of the Prussian blue compound in the produced Prussian blue positive electrode materials.

[0146] The Prussian blue cathode material for sodium-ion batteries prepared in the Examples and Comparative Examples was used as the cathode active material for sodium-ion batteries. The cathode active material, binder (polyvinylidene fluoride (PVDF)), and conductive agent (Super P) were mixed in a mass ratio of 7:2:1, and then mixed and stirred with dimethylpyrrolidone (NMP) as a solvent to form a uniform slurry. The slurry was uniformly coated on aluminum foil, dried, and cut into a sheet to form the cathode. CR2032 button batteries were assembled in an argon glove box using metallic sodium as the anode, a glass fiber membrane 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) as the electrolyte.

[0147] The button batteries assembled as described above were tested using 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 conducted on the button batteries, with a charge / discharge voltage range of 2 V to 4.2 V. Among Examples 1 to 3, the Prussian blue electrode fabricated with the positive electrode material of Example 2 exhibited the best 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%. In contrast, the capacities of Comparative Examples 1 and 2 after 200 cycles were only 42% and 30%, respectively. Furthermore, the Prussian blue electrode fabricated with the positive electrode material of Example 2 maintained a discharge specific capacity retention rate of 77% even 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 to 10).

[0148] [Table 1] 6 is a schematic diagram showing the results of the discharge specific capacity in the first to third charge / discharge cycles of the Prussian blue positive electrode material produced in Example 1. FIGS. 7(a) to 7(c) are schematic diagrams showing the charge / discharge performance of the Prussian blue positive electrode material produced in Example 2. FIG. 7(a) is a schematic diagram showing the results of the charge / discharge specific capacity in the first to fifth cycles of the Prussian blue positive electrode material produced in Example 2. FIGS. 7(b) and 7(c) are schematic diagrams showing the results of the rate characteristics and cycle characteristics, respectively, of the Prussian blue positive electrode material produced in Example 2. FIG. 8 is a schematic diagram showing the results of the discharge specific capacity in the first to fourth charge / discharge cycles of the Prussian blue positive electrode material produced in Example 3. FIG. 9 is a schematic diagram showing the results of the discharge specific capacity in the first to third charge / discharge cycles of the positive electrode material produced in Comparative Example 1. FIG. 10 is a schematic diagram showing the results of the discharge specific capacity in the first to third charge / discharge cycles of the positive electrode material produced in Comparative Example 2.

[0149] Combining the results of Figures 6 to 10 and Table 1, when used in sodium ion batteries, the Prussian blue positive electrode materials obtained in the examples of the present invention exhibit excellent properties in terms of the cycle stability, charge / discharge specific capacity, coulombic efficiency, rate characteristics, etc. of the sodium ion battery.

[0150] In the present invention, scanning electron microscope images showed that Prussian blue and Ketjen black were uniformly distributed, and sodium ferrocyanide was dissolved in the ethylene glycol solution. When an organic solvent was added to the reaction system, a mixed phase was formed. Because ferrous sulfate and sodium citrate are insoluble in organic solvents but require water for the reaction, adding an organic solvent further controls the reaction rate, thereby controlling the Prussian blue crystal growth process and reducing defects in the aged Prussian blue. The addition of Ketjen black alleviates the problem of Prussian blue's poor conductivity. The addition of Ketjen black significantly improves the conductivity of Prussian blue / Ketjen black composites. The addition of the organic solvent ethylene glycol in the present invention creates a two-phase reaction system, further increasing the sodium ion concentration in the aqueous phase. The organic solution introduced in the present invention does not participate in the reaction; it only serves to control the reaction rate. It can be recycled and reused after the reaction is complete, eliminating waste. The recovery method, which can be vacuum distillation at 80°C, is environmentally friendly and safe.

[0151] While the present invention has been described with reference to specific embodiments thereof, these descriptions and illustrations are not intended to limit the invention. Those skilled in the art will readily recognize that various modifications may be made to adapt a particular situation, material, composition of matter, substance, method, or process to the objective, spirit, and scope of the present application without departing from the true spirit and scope of the invention as defined by the appended claims. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein are described with reference to specific operations performed in a particular order, it should be understood that these operations may be combined, sub-divided, or reordered to form equivalent methods without departing from the teachings of the present invention. Accordingly, unless otherwise indicated herein, the order and grouping of operations is not intended to be limiting.

Claims

1. It comprises a Prussian blue compound having the general chemical formula: Na ｘ Fe[Fe(CN) ６ ] ｙ ・nH ２ O Formula I (In Formula I, 0.5<x<1, 0.8<y<1, n is 0.01 to 3.

5. A Prussian blue positive electrode material, further comprising a carbonaceous material, at least a portion of which is attached to a surface of the crystal of the Prussian blue compound.

2. 2. The Prussian blue positive electrode material according to claim 1, wherein at least a portion of the crystals of the Prussian blue compound have a quasi-cubic shape.

3. 2. The Prussian blue positive electrode material according to claim 1, wherein the crystal size of the Prussian blue compound is 0.1 μm or more and the crystal size of the Prussian blue compound is 2.5 μm or less.

4. The chemical formula of the Prussian blue compound is Na ０．６４７ Fe[Fe(CN) ６ ] ０．９３ ・2.6H ２ O and Na ０．５１７ Fe[Fe(CN) ６ ] ０．８５ ・3.15H ２ 2. The Prussian blue positive electrode material according to claim 1, wherein the Prussian blue positive electrode material is at least one selected from the group consisting of fluorine, fluorine, iodine, fluor ...

5. 2. The Prussian blue cathode material of claim 1, wherein the carbonaceous material is selected from conductive carbon black materials.

6. mixing the first dispersion and the second dispersion to obtain a solid precipitate; washing and drying the solid precipitate to obtain a Prussian blue cathode material; the first dispersion comprises a ferrocyanide source, a sodium source, and a first dispersant; the second dispersion liquid comprises a divalent iron source, a complexing agent, and a second dispersing agent; 2. The method for producing a Prussian blue cathode material according to claim 1, wherein the first dispersion further contains a carbonaceous material.

7. 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 and / or one or more selected from 7. The method for producing a Prussian blue positive electrode material according to claim 6, wherein the complexing agent is one or more selected from the group consisting of anhydrous sodium citrate, sodium citrate dihydrate, sodium citrate pentahydrate, sodium oxalate, sodium tartrate, and sodium malate.

8. the first dispersant comprises deionized water and a first solvent, and the ferrocyanide source is sparingly soluble in the first solvent; and / or the second dispersion comprises deionized water and a second solvent, and the ferrocyanide source is sparingly soluble in the second solvent; and / or 7. The method for producing a Prussian blue positive electrode material according to claim 6, wherein the first solvent and the second solvent are each independently one or more solvents selected from the group consisting of ethylene glycol, N,N-dimethylformamide, ethanol, and glycerol.

9. The volume ratio of deionized water to the first solvent in the first dispersant is selected from the range of 1:(0.01 to 100), and / or 9. The method for producing a Prussian blue positive electrode material according to claim 8, wherein the volume ratio of deionized water to the second solvent in the second dispersant is selected from the range of 1:(0.01 to 100).

10. 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), and / or The ratio of the amount of molar of the ferrocyanide source to the amount of molar of the divalent iron source is selected from 1:(1 to 3), and / or 7. The method for producing a Prussian blue positive electrode material according to claim 6, 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 the range of 1:(1 to 100).

11. A positive electrode sheet comprising the Prussian blue positive electrode material according to claim 1 or a Prussian blue positive electrode material obtained by the method for producing a Prussian blue positive electrode material according to claim 6.

12. A sodium ion battery comprising the Prussian blue positive electrode material according to claim 1 or a Prussian blue positive electrode material obtained by the method for producing the Prussian blue positive electrode material according to claim 6.

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