An iron-based Prussian blue cathode material, its preparation method and application

Abstract

The present invention belongs to the technical field of sodium-ion batteries, and discloses an iron-based Prussian blue cathode material, a preparation method thereof and an application. The preparation method comprises the following steps: mixing a ferrous salt, an acid and water to obtain a first solution; mixing a cyanide source, a sodium supplement agent and water to obtain a second solution; mixing a water scavenger and water to obtain a third solution; mixing the first solution, the second solution and the third solution, and aging to obtain the iron-based Prussian blue cathode material. The iron-based Prussian blue cathode material prepared by the method of the present invention has high specific capacity, high Coulomb efficiency and high capacity retention rate at high rates, and exhibits good rate performance and cycle performance when used as the cathode material of a sodium-ion battery, providing a broad application prospect for low-cost and high-performance sodium-ion batteries in the field of large-scale energy storage.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to an iron-based Prussian blue cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the advanced electrochemical energy storage systems, lithium-ion batteries are widely used in various portable electronic devices. However, lithium-ion batteries face serious problems such as a severe shortage of lithium resources. Sodium and lithium are in the same group and have similar chemical properties. At the same time, sodium resources are rich in reserves and widely distributed, so sodium-ion batteries are considered to be a powerful supplement to lithium-ion batteries. Among them, the sodium cathode material, as a key component of the sodium-ion battery, is a key factor affecting the energy density, power density, and safety of the sodium-ion battery. Iron-based Prussian blue materials have become highly competitive and mass-producible cathode materials due to their open three-dimensional framework structure, large interstitial space and ion diffusion channels, as well as their low cost and simple synthesis steps.

[0003] Currently, the common preparation of highly crystalline Prussian blue-based materials mainly uses the co-precipitation method. However, during co-precipitation in an aqueous solution, the reaction rate between metal salts and sodium ferrocyanide is very fast, causing water molecules to enter the interstitial positions to form crystal water, which leads to a decline in the electrochemical performance of Prussian blue cathode materials. To improve the crystal water problem, the commonly used method is to add a complexing agent to slow down the reaction rate between metal salts and sodium ferrocyanide and reduce the generation of defects. Additionally, by regulating the co-precipitation reaction solution system, the entry of crystal water into the interstices during the reaction can be reduced, thereby improving the crystallinity of Prussian blue materials. For example, in Chinese Patent Application CN119018911A, a cobalt salt solution and a ferrocyanide salt solution are subjected to a solvothermal reaction in a mixed solution of water and an organic solvent. During the reaction, the organic solvent will embed into the crystal interior of the Prussian blue analogue, replacing the water molecules in the original positions, thus reducing the water content. Another example is Chinese Patent Application CN116605887A, which dissolves a cyanide source, a metal source, an antioxidant, and a complexing agent in a polar organic solvent, and through microwave synthesis means, the Prussian blue complexation that cannot occur in a non-aqueous solvent can be rapidly synthesized. Still another example is Chinese Patent Application CN116598484A, which uses a solvent in which sodium ferrocyanide is poorly soluble as the reaction solution system, adjusts the solubility to control the reaction rate, and thereby controls the generation of defects during the crystal growth process. In summary, the currently disclosed methods for regulating the solvent system all directly dissolve a cyanide source, a metal source, a complexing agent, etc. in an organic solvent system for co-precipitation reaction. However, the solubility of the above-mentioned salt substances in the organic solvent system is not high, resulting in layering or precipitation of salts during dissolution, and even making the reaction system present a solid-liquid two-phase state, causing the reaction to occur only at the interface, seriously affecting the homogeneity of the reaction solution system and the product quality, and reducing the preparation efficiency. In order to increase the solubility of salt substances in the organic solvent system, the solvothermal or microwave heating used will increase the operation complexity and energy consumption, which is not conducive to large-scale rapid batch preparation. Summary of the Invention

[0004] The purpose of the present invention is to provide an iron-based Prussian blue cathode material, which solves the problems of complex operation and high energy consumption in the preparation methods of existing iron-based Prussian blue-based materials, and significantly improves the rate performance and cycling performance of Prussian blue-based materials.

[0005] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method for an iron-based Prussian blue cathode material, comprising the following steps:

[0007] Mix a ferrous salt, an acid, and water to obtain a first solution;

[0008] Mix a cyanide source, a sodium supplement agent, and water to obtain a second solution;

[0009] Mix the water capturer with water to obtain a third solution;

[0010] Mix the first solution, the second solution and the third solution, and age them to obtain an iron-based Prussian blue cathode material;

[0011] Among them, the water capturer is an acidic or neutral organic solvent having a functional group capable of forming hydrogen bonds and being miscible with water in any proportion; the functional group capable of forming hydrogen bonds should have both a hydrogen bond donor and a hydrogen bond acceptor.

[0012] Preferably, in the preparation method, the ferrous salt includes ferrous chloride or ferrous sulfate;

[0013] In the first solution, the molar amount of the ferrous salt to the volume of the water is 1 mmol: 3-7 mL.

[0014] Preferably, in the preparation method, the acid includes hydrochloric acid and / or acetic acid, and the mass concentration of the acid is 36-38%;

[0015] In the first solution, the volume ratio of the acid to the water is 1: 10-40.

[0016] Preferably, in the preparation method, the cyanide source includes sodium ferrocyanide; the sodium supplementing agent includes one or more of sodium chloride, sodium acetate, and sodium oxalate;

[0017] The molar ratio of the cyanide source to the sodium supplementing agent is 1: 2-8;

[0018] In the second solution, the molar amount of the cyanide source to the volume of the water is 1 mmol: 3-7 mL.

[0019] Preferably, in the preparation method, the water capturer includes one or more of methanol, formic acid, formamide, ethanol, acetic acid, ethylene glycol, propanol, propionic acid, propylene glycol, glycerol, and isopropanol;

[0020] The concentration of the functional group capable of forming hydrogen bonds in the water capturer in the third solution is 0.92-1.28 mol / L.

[0021] Preferably, in the preparation method, the molar ratio of the ferrous salt to the cyanide source is 1: 0.5-2;

[0022] The volume ratio of the water in the first solution to the third solution is 1: 2-6.

[0023] Preferably, in the preparation method, the method of mixing the first solution, the second solution and the third solution is: simultaneously drop the first solution and the second solution into the third solution for dispersion;

[0024] The rate at which the first solution is added to the third solution and the rate at which the second solution is added to the third solution are independently 0.5 to 5 mL / min, and the temperature of the addition is room temperature;

[0025] The dispersion time is 2 to 8 h.

[0026] Preferably, in the preparation method, the aging temperature is room temperature, and the aging time is 8 to 48 h.

[0027] The present invention also provides an iron-based Prussian blue cathode material prepared by the above preparation method.

[0028] The present invention also provides an application of the iron-based Prussian blue cathode material in a sodium ion battery.

[0029] Through the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention adopts a method of first dissolving salt substances such as iron source and cyanide source in water, and then mixing the two salt solutions in a third-phase water scavenger solution, which improves the solubility of the salt substances, prevents the problems of insoluble and layered precipitation of the salt substances in the organic phase solution, simplifies the operation process, and improves the uniformity of subsequent reactions and the quality of products.

[0031] (2) The water scavenger used in the present invention acts on water molecules through a hydrogen bond donor (a hydrogen atom covalently bonded to an electronegative atom, such as a hydrogen atom in a hydroxyl group or an amine group) and a hydrogen bond acceptor (an electronegative atom with a lone pair of electrons, such as an oxygen atom in a carbonyl group and a hydroxyl group), forming a bulk hydrogen bond network, thereby binding the water molecules in the solution, weakening the movement and reactivity of free water molecules, increasing the solution viscosity, and inhibiting the entry of water molecules into the Prussian blue interstices. In addition, it reduces the diffusion rate of reactants in the solution, provides a certain degree of control over the growth directionality of crystals, thereby playing a role in inducing the growth of ordered crystals and increasing the stability of crystals, and reducing the defects of iron-based Prussian blue crystals under the combined action with an acid. Taking hydrochloric acid as an example, the H + ions in hydrochloric acid cooperate with the water scavenger to adjust the charge distribution in the solution, and this adjustment will affect the charge state on the surface of the Prussian blue crystal, making the deposition of the crystal more orderly. The Cl - in hydrochloric acid may exist as weakly adsorbed ions on the crystal surface, further inhibiting disordered aggregation. At the same time, the loss of the water scavenger is small, and it can be recycled, reducing costs and saving raw materials.

[0032] (3) In the solution of the present invention, a sodium supplement is further added. The sodium ions of the sodium supplement can fill the vacancy defects, stabilize the crystal framework structure of Prussian blue, enhance the ionic conduction performance. At the same time, a high sodium ion concentration helps to inhibit the rapid precipitation of crystals, forming more uniform and regular crystals. The present invention does not require additional addition of complexing agents, further simplifies the preparation process, and reduces the production cost.

[0033] (4) The iron-based Prussian blue cathode material prepared by the method of the present invention has high specific capacity, high Coulomb efficiency and high capacity retention rate at high rates. When used as the cathode material of a sodium-ion battery, it exhibits good rate performance and cycling performance, providing a bright prospect for low-cost and high-performance sodium-ion batteries for large-scale energy storage applications.

[0034] (5) The synthesis method of the present invention selects sodium ferrocyanide, ferrous sulfate and a water scavenger of a specific type and concentration for coprecipitation in an aqueous phase, and strictly controls the proportion of the water scavenger and the synthesis time, regulating the hydrogen bond density and the system viscosity. It not only ensures the efficient dissolution of salts in the solvent system, but also restricts the embedding of water molecules at the gaps, obtaining an iron-based Prussian blue cathode material with a low-defect crystal structure. The raw materials are simple and easy to obtain, the process operation is simple, the energy consumption is low, the experimental repeatability is good, and it is easy to industrialize. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art.

[0036] Figure 1 XRD pattern of the iron-based Prussian blue cathode material for Example 1;

[0037] Figure 2 SEM image of the iron-based Prussian blue cathode material for Example 1;

[0038] Figure 3 SEM image of the iron-based Prussian blue cathode material for Comparative Example 1;

[0039] Figure 4 Charge and discharge data of the sodium-ion batteries for Application Examples 1-2 and Comparative Application Examples 1-3 in the first 500 cycles at a current of 10C;

[0040] Figure 5 Rate performance graph of the sodium-ion batteries for Application Examples 1-2 and Comparative Application Examples 1-3;

[0041] Figure 6 Charge and discharge curve graph of the sodium-ion battery for Application Example 1 in the first three weeks at a current of 0.1C. Detailed Description of the Embodiments

[0042] The present invention provides a method for preparing an iron-based Prussian blue cathode material, comprising the following steps:

[0043] Mix a ferrous salt, an acid and water to obtain a first solution;

[0044] Mix a cyanide source, a sodium supplement agent and water to obtain a second solution;

[0045] Mix a water scavenger and water to obtain a third solution;

[0046] Mix the first solution, the second solution and the third solution, and age to obtain the iron-based Prussian blue cathode material;

[0047] Wherein, the water scavenger is an acidic or neutral organic solvent having a functional group capable of forming hydrogen bonds and being miscible with water in any proportion; the functional group capable of forming hydrogen bonds should have both a hydrogen bond donor and a hydrogen bond acceptor.

[0048] In the present invention, the ferrous salt preferably includes ferrous chloride or ferrous sulfate, and more preferably ferrous sulfate.

[0049] In the present invention, in the first solution, the molar amount of the ferrous salt to the volume of the water is preferably 1 mmol: 3-7 mL, more preferably 1 mmol: 4-6 mL, and still more preferably 1 mmol: 5 mL.

[0050] In the present invention, the acid preferably includes hydrochloric acid and / or acetic acid, and more preferably hydrochloric acid.

[0051] In the present invention, the mass concentration of the acid is preferably 36-38%, more preferably 36-37%, and still more preferably 36%.

[0052] In the present invention, in the first solution, the volume ratio of the acid to the water is preferably 1: 10-40, more preferably 1: 20-30, and still more preferably 1: 25.

[0053] In the present invention, the cyanide source preferably includes sodium ferrocyanide.

[0054] In the present invention, in the second solution, the molar amount of the cyanide source to the volume of the water is preferably 1 mmol: 3-7 mL, more preferably 1 mmol: 4-6 mL, and still more preferably 1 mmol: 5 mL.

[0055] In the present invention, the sodium supplement agent preferably includes one or more of sodium chloride, sodium acetate, and sodium oxalate, more preferably includes sodium chloride, sodium acetate or sodium oxalate, and still more preferably sodium chloride.

[0056] In the present invention, the molar ratio of the cyanide source to the sodium supplementing agent is preferably 1:2 to 8, more preferably 1:3 to 6, and still more preferably 1:5 to 5.2.

[0057] In the present invention, the functional group capable of forming hydrogen bonds preferably includes one or more of a hydroxyl group, an amide group, and a carboxyl group, more preferably includes a hydroxyl group and / or a carboxyl group, and still more preferably is a hydroxyl group.

[0058] In the present invention, the water scavenger preferably includes one or more of methanol, formic acid, formamide, ethanol, acetic acid, ethylene glycol, propanol, propionic acid, propylene glycol, glycerol, and isopropanol, more preferably includes ethylene glycol, propylene glycol, or glycerol, and still more preferably is ethylene glycol.

[0059] In the present invention, the concentration of the functional group capable of forming hydrogen bonds in the water scavenger in the third solution is preferably 0.92 to 1.28 mol / L, more preferably 1 to 1.2 mol / L, and still more preferably 1.1 mol / L.

[0060] In the present invention, the molar ratio of the ferrous salt to the cyanide source is preferably 1:0.5 to 2, more preferably 1:0.5 to 1.5, and still more preferably 1:1.

[0061] In the present invention, the volume ratio of the water in the first solution to the third solution is preferably 1:2 to 6, more preferably 1:3 to 5, and still more preferably 1:4.

[0062] In the present invention, the method of mixing the first solution, the second solution, and the third solution is preferably: simultaneously dropping the first solution and the second solution into the third solution for dispersion.

[0063] In the present invention, the rate of dropping the first solution into the third solution and the rate of dropping the second solution into the third solution are each preferably 0.5 to 5 mL / min, more preferably 0.5 to 2 mL / min, and still more preferably 1 mL / min.

[0064] In the present invention, the temperature of dropping is preferably room temperature.

[0065] In the present invention, the dispersion time is preferably 2 to 8 h, more preferably 4 to 6 h, and still more preferably 5 h.

[0066] In the present invention, the aging temperature is preferably room temperature.

[0067] In the present invention, the aging time is preferably 8 to 48 h, more preferably 16 to 36 h, and still more preferably 24 h.

[0068] In the present invention, after aging, it preferably further includes: successively performing centrifugal washing and vacuum drying.

[0069] In the present invention, the reagent for centrifugal washing is preferably water.

[0070] In the present invention, the centrifugal speed for centrifugal washing is preferably 3000 - 6000 rpm, more preferably 3500 - 4500 rpm, and even more preferably 4000 rpm.

[0071] In the present invention, the number of times of centrifugal washing is preferably 2 - 5 times, more preferably 3 - 4 times, and even more preferably 3 times.

[0072] In the present invention, the temperature for vacuum drying is preferably 80 - 120 °C, more preferably 100 - 120 °C, and even more preferably 110 °C.

[0073] In the present invention, the time for vacuum drying is preferably 8 - 24 h, more preferably 10 - 18 h, and even more preferably 12 h.

[0074] The present invention also provides an iron-based Prussian blue cathode material prepared by the above preparation method.

[0075] The present invention also provides an application of the iron-based Prussian blue cathode material in a sodium-ion battery.

[0076] In the present invention, the method for the above application is not limited, and a scheme well-known to those skilled in the art can be adopted.

[0077] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0078] In the embodiments and comparative examples of the present invention, ferrous sulfate is ferrous sulfate heptahydrate (FeSO 4 ·7H 2 O), ferrous chloride is FeCl 2 , sodium ferrocyanide is Na 4 Fe(CN) 6 , and sodium chloride is NaCl.

[0079] Example 1

[0080] This example provides a preparation method of an iron-based Prussian blue cathode material, including the following steps:

[0081] Dissolve 5 mmol of FeSO 4 ·7H 2O and 1 mL of concentrated hydrochloric acid (mass concentration 36%) were dissolved in 25 mL of deionized water, stirred evenly to obtain the first solution;

[0082] 5 mmol of Na 4 Fe(CN) 6 (with a mass of 1.52 g) and 1.5 g of NaCl (molar amount 25.67 mmol) were dissolved in 25 mL of deionized water, stirred evenly to obtain the second solution;

[0083] 100 mL of 0.55 mol / L ethylene glycol - aqueous solution was used as the third solution, in which the molar concentration of hydroxyl groups was 1.10 mol / L;

[0084] Under the condition of stirring at room temperature, the first solution and the second solution were simultaneously added to the third solution through a peristaltic pump at a rate of 1 mL / min. After the dropping was completed, the solution became a blue suspension; stirring was continued for 5 h, and finally, it was aged at room temperature for 24 h; after pouring off the supernatant, the obtained blue precipitate was centrifugally washed 3 times with deionized water at a centrifugal speed of 4000 rpm, and then vacuum - dried at 110 °C for 12 h to obtain the iron - based Prussian blue cathode material, denoted as EG - PBA.

[0085] Example 2

[0086] 5 mmol of FeSO 4 ·7H 2 O and 1 mL of concentrated hydrochloric acid (mass concentration 36%) were dissolved in 25 mL of deionized water, stirred evenly to obtain the first solution;

[0087] 5 mmol of Na 4 Fe(CN) 6 (with a mass of 1.52 g) and 1.5 g of NaCl (25.67 mmol) were dissolved in 25 mL of deionized water, stirred evenly to obtain the second solution;

[0088] 100 mL of 0.37 mol / L glycerol - aqueous solution was used as the third solution, in which the molar concentration of hydroxyl groups was 1.10 mol / L;

[0089] Under the condition of stirring at room temperature, the first solution and the second solution were simultaneously added to the third solution through a peristaltic pump at a rate of 1 mL / min. After the dropping was completed, the solution became a blue suspension; stirring was continued for 5 h, and finally, it was aged at room temperature for 24 h; after pouring off the supernatant, the obtained blue precipitate was centrifugally washed 3 times with deionized water at a centrifugal speed of 4000 rpm, and then vacuum - dried at 110 °C for 24 h to obtain the iron - based Prussian blue cathode material, denoted as Gl - PBA.

[0090] Comparative Example 1

[0091] This comparative example provides a method for preparing an iron-based Prussian blue cathode material, including the following steps:

[0092] Dissolve 5 mmol of FeSO 4 ·7H 2 O and 1 mL of concentrated hydrochloric acid (mass concentration 36%) in 25 mL of deionized water, stir evenly to obtain a first solution;

[0093] Dissolve 5 mmol of Na 4 Fe(CN) 6 (with a mass of 1.52 g) and 1.5 g of NaCl (25.67 mmol) in 25 mL of deionized water, stir evenly to obtain a second solution;

[0094] Take 100 mL of deionized water as the third solution;

[0095] Under the condition of stirring at room temperature, add the first solution and the second solution to the third solution simultaneously through a peristaltic pump at a rate of 1 mL / min. After the dropping is completed, the solution becomes a blue suspension; continue to stir for 5 h, and finally age at room temperature for 24 h; after pouring off the supernatant, wash the obtained blue precipitate 3 times with deionized water by centrifugation at a centrifugal speed of 4000 rpm, and then vacuum dry at 110 °C for 24 h to obtain the iron-based Prussian blue cathode material.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing an iron-based Prussian blue cathode material, including the following steps:

[0098] Dissolve 5 mmol of FeSO 4 ·7H 2 O and 1 mL of concentrated hydrochloric acid (mass concentration 36%) in 25 mL of deionized water, stir evenly to obtain a first solution;

[0099] Dissolve 5 mmol of Na 4 Fe(CN) 6 (with a mass of 1.52 g) and 1.5 g of NaCl (25.67 mmol) in 25 mL of deionized water, stir evenly to obtain a second solution;

[0100] Take 100 mL of 0.90 mol / L ethylene glycol-aqueous solution as the third solution, in which the molar concentration of hydroxyl groups is 1.80 mol / L;

[0101] Under the condition of stirring at room temperature, the first solution and the second solution were simultaneously added to the third solution through a peristaltic pump at a rate of 1 mL / min. After the dropping was completed, the solution became a blue suspension; stirring was continued for 5 h, and finally, it was aged at room temperature for 24 h; after pouring off the supernatant, the obtained blue precipitate was centrifugally washed 3 times with deionized water at a centrifugal speed of 4000 rpm, and then vacuum dried at 120 °C for 24 h to obtain the iron-based Prussian blue cathode material.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing an iron-based Prussian blue cathode material, including the following steps:

[0104] Dissolve 5 mmol of FeSO 4 ·7H 2 O and 1 mL of concentrated hydrochloric acid (mass concentration 36%) in 25 mL of deionized water, stir evenly to obtain the first solution;

[0105] Dissolve 5 mmol of Na 4 Fe(CN) 6 (mass 1.52 g) and 1.5 g of NaCl (25.67 mmol) in 25 mL of deionized water, stir evenly to obtain the second solution;

[0106] Take 100 mL of 0.55 mol / L ethyl acetate-aqueous solution as the third solution;

[0107] Under the condition of stirring at room temperature, the first solution and the second solution were simultaneously added to the third solution through a peristaltic pump at a rate of 1 mL / min. After the dropping was completed, the solution became a blue suspension; stirring was continued for 5 h, and finally, it was aged at room temperature for 24 h; after pouring off the supernatant, the obtained blue precipitate was centrifugally washed 3 times with deionized water at a centrifugal speed of 4000 rpm, and then vacuum dried at 120 °C for 24 h to obtain the iron-based Prussian blue cathode material.

[0108] The phase analysis of the iron-based Prussian blue cathode material prepared in Example 1 was carried out using an X-ray powder diffractometer. Using Cu-k as the radiation source, the wavelength was 1.5406, a Ni filter was used, the tube current was 40 mA, the tube voltage was 40 kV, the scanning range was 10~90°, the scanning speed was 8° / min, and the step size was 0.02°. The identification of the phase and the crystal structure information were analyzed by JADE 6.0 software. The results are as Figure 1 shown.

[0109] It can be Figure 1 seen that the EG-PBA in Example 1 has good crystallinity, and each diffraction peak basically coincides with the standard card (JCPDS, NO.52-1907).

[0110] Using a scanning electron microscopy tester of model S-4800 with an acceleration voltage of 20 kV, the microscopic morphologies of the iron-based Prussian blue cathode materials prepared in Example 1 and Comparative Example 1 were observed. The results are respectively as Figure 2 and Figure 3 shown.

[0111] Figure 2 Figure SEM of the iron-based Prussian blue cathode material of Example 1. It can be seen from Figure 2 that the iron-based Prussian blue cathode material obtained in Example 1 shows a relatively regular cubic phase, has a more regular morphology, and the particles are relatively dispersed with less particle agglomeration. In this way, the interstitial water in the particles will be less, and it shows more sufficient sodium deintercalation / insertion in the subsequent electrochemical performance.

[0112] Figure 3 Figure SEM of the iron-based Prussian blue cathode material of Comparative Example 1. It can be seen from Figure 3 that the iron-based Prussian blue cathode material obtained in Comparative Example 1 has a larger particle size and serious agglomeration phenomenon. The sodium ions cannot be smoothly inserted / extracted, resulting in hindrance during the charge and discharge process in the subsequent electrochemical performance test, affecting the capacity of the cathode material.

[0113] Application Examples 1-2, Comparative Application Examples 1-3

[0114] The iron-based Prussian blue cathode materials of Examples 1-2 or Comparative Examples 1-3, conductive carbon black (Timcal, model Super P Li), and polyvinylidene fluoride (PVDF, molecular weight 1 million) were respectively mixed according to a mass ratio of 7:2:1, and solvent N-methylpyrrolidone (NMP) was added to mix into a slurry; the uniformly mixed slurry was respectively coated on aluminum foil, and the coating amount of the iron-based Prussian blue cathode material on the aluminum foil was 2 mg / cm 2 ; after drying, it was cut into circular pieces with a diameter of 10 mm as the positive electrode;

[0115] A metal sodium sheet with a diameter of 10 mm was used as the negative electrode;

[0116] Glass fiber (manufacturer Whatman, model GF / D, grade No. 1823-090) was used as the separator;

[0117] The electrolyte was prepared from NaClO 4 , EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate); the concentration of NaClO 4 was 1.0 mol / L, the volume ratio of EC to DEC was 1:1, and the mass fraction of FEC in the electrolyte was 5%;

[0118] A sodium-ion battery was assembled in an argon glove box.

[0119] The sodium-ion batteries assembled in Application Examples 1-2 and Comparative Application Examples 1-3 were tested using a LAND battery tester at a test voltage of 2.0-4.0 V.

[0120] Figure 4 The charge and discharge data of the sodium-ion batteries in Application Examples 1-2 and Comparative Application Examples 1-3 at a current of 10C (1C = 170 mAh·g -1 ) for the first 500 cycles. From Figure 4 It can be seen that the sodium-ion batteries assembled in Application Examples 1-2 can provide high specific capacities of 66.7 mAh·g -1 and 61.1 mAh·g -1 respectively at a high rate of 10C; and after 500 cycles, they have high capacity retention rates of 90.97% and 99.00% respectively. While the sodium-ion batteries assembled in Comparative Application Examples 1-3 can only provide specific capacities of 12.2 mAh·g -1 , 20.1 mAh·g -1 and 40.2 mAh·g -1 respectively at a high rate of 10C. In addition, after 500 cycles, the Coulombic efficiencies of the sodium-ion batteries assembled in Application Examples 1-2 and Comparative Application Examples 1-3 both remain at about 99%, and the difference is not obvious.

[0121] Figure 5 The rate performance graphs of the sodium-ion batteries assembled in Application Examples 1-2 and Comparative Application Examples 1-3 at 0.1 / 0.2 / 0.5 / 1 / 2 / 5 / 10 / 0.1C (1C = 170 mAh·g -1 ). From Figure 5 It can be seen that the batteries assembled in Application Examples 1-2 have good rate performance and can provide specific capacities of 93.9 mAh·g -1 and 82.0 mAh·g -1 respectively at a current of 5C, and can provide specific capacities of 83.4 mAh·g -1 and 68.6 mAh·g -1 respectively at a current of 10C. After restoring to 0.1C, the capacity retention rates are 97.95% and 96.81%. While the batteries assembled in Comparative Application Examples 1-3 are significantly lower than those in Application Examples 1-2 at each rate. In addition, the Coulombic efficiencies of the batteries assembled in Application Examples 1-2 and Comparative Application Examples 1 and 3 remain at about 99% at different currents, while the Coulombic efficiency of the battery assembled in Comparative Application Example 2 is relatively low, only about 80%.

[0122] Figure 6 The charge and discharge curves of the sodium-ion battery of Application Example 1 at a current of 0.1C (1C = 170 mAh·g -1 ) for the first three cycles. From Figure 6It can be known that Application Example 1 has two plateaus at 2.6V - 3.0V and 3.3V - 3.6V during both charging and discharging: during charging, the longer plateau at 2.6V and the shorter plateau above 3.3V respectively correspond to the oxidation of high-spin Fe 2+ and low-spin Fe 2+ , while the two discharging plateaus correspond to the reduction of two Fe 3+ to Fe 2+ . At the same time, since some of the iron in the initial state Prussian blue structure is trivalent, the first charging capacity is lower than the subsequent charging capacities. The first discharge specific capacity is 114.97 mAh·g -1 .

[0123] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing an iron-based Prussian blue positive electrode material, characterized in that: The following steps are involved: Mixing ferrous salt, acid and water to obtain a first solution; mixing a cyanide source, a sodium supplement and water to obtain a second solution; mixing the water-capturing agent with water to obtain a third solution; The first solution, the second solution and the third solution are mixed and aged to obtain an iron-based Prussian blue positive electrode material; Wherein, the sodium supplement includes one or more of sodium chloride, sodium acetate, and sodium oxalate, and the molar ratio of the cyanide source to the sodium supplement is 1:2-8; The water-capturing agent is an acidic or neutral organic solvent having a functional group capable of forming hydrogen bonds and being miscible with water in any proportion; the functional group capable of forming hydrogen bonds should have both a hydrogen bond donor and a hydrogen bond acceptor; The water-capturing agent includes one or more of methanol, formic acid, formamide, ethanol, acetic acid, ethylene glycol, propanol, propionic acid, propylene glycol, glycerol, and isopropanol; The concentration of the functional groups capable of forming hydrogen bonds in the water-capping agent in the third solution is 0.92-1.28 mol / L.

2. The preparation method according to claim 1, characterized in that: The ferrous salt includes ferrous chloride or ferrous sulfate; In the first solution, the ratio of the molar amount of the ferrous salt to the volume of the water is 1 mmol: 3-7 mL.

3. The preparation method according to claim 1 or 2, characterized in that: The acid includes hydrochloric acid and / or acetic acid, and the mass concentration of the acid is 36-38%; In the first solution, the volume ratio of the acid to the water is 1:10-40.

4. The preparation method according to claim 3, characterized in that: The cyanide source includes sodium ferrocyanide; In the second solution, the ratio of the molar amount of the cyanide source to the volume of the water is 1 mmol: 3-7 mL.

5. The preparation method according to claim 1, characterized in that: The molar ratio of the ferrous salt to the cyanide source is 1:0.5-2; The volume ratio of water in the first solution to the third solution is 1:2-6.

6. The preparation method according to claim 1 or 5, characterized in that: The method of mixing the first solution, the second solution and the third solution is: simultaneously dropping the first solution and the second solution into the third solution to disperse; The rate at which the first solution is added dropwise to the third solution is independently 0.5 to 5 mL / min and the temperature of the addition is room temperature; The dispersion time is 2 to 8 hours.

7. The preparation method according to claim 1, characterized in that: The aging temperature is room temperature, and the aging time is 8 to 48 hours.

8. The iron-based Prussian blue positive electrode material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the iron-based Prussian blue positive electrode material according to claim 8 in sodium ion batteries.

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