Prussian blue-based positive electrode material and preparation method and application thereof

Abstract

The application discloses a Prussian blue type positive material and a preparation method and application thereof. The preparation method mainly comprises the following steps: sequentially adding a manganese source, a nickel source, an iron source and a reducing agent into a sodium ferrocyanide solution, and heating to obtain the Prussian blue type positive material; wherein the sodium ferrocyanide solution comprises Na4Fe[CN]6 slow-release tablets and / or Na4Fe[CN]6 capsules. Through tabletting or surface coating of the raw material Na4Fe[CN]6 capsules, and by utilizing the difference in solubility product between manganese, nickel, iron and ferrocyanide, the adding sequence of the reaction raw materials is adjusted, the production efficiency of the Prussian blue type positive material is improved, and the prepared Prussian blue type positive material has excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to a Prussian blue-based cathode material, its preparation method, and its application. Background Technology

[0002] With the advancement of science and technology, the excessive consumption of fossil fuels such as coal and oil has led to increasingly serious problems such as energy shortages and environmental pollution. Clean energy sources such as solar, wind, and tidal power also suffer from intermittency and are constrained by natural and geographical conditions. Therefore, developing efficient energy storage technologies has become a key factor in the development of clean energy. In recent years, lithium-ion batteries have been widely used in various fields due to their excellent electrochemical performance. However, the scarcity and uneven distribution of lithium resources result in high costs for lithium-ion batteries, hindering their widespread application in large-scale energy storage. Sodium, which has similar physicochemical properties to lithium, is abundant in the Earth's crust, widely distributed, and inexpensive. Therefore, developing sodium-ion batteries is of great significance for large-scale energy storage.

[0003] Because sodium ions have a larger radius than lithium ions, their diffusion within the crystal lattice is more difficult, and their insertion into the crystal more easily causes changes in material volume. Therefore, analogues of cathode materials that exhibit excellent performance in lithium-ion battery systems often display poor electrochemical performance when applied to sodium-ion batteries, such as low operating voltage and poor cycle life. Thus, developing suitable cathode materials for sodium-ion batteries has become a key research focus and challenge. Common sodium-ion battery cathode materials mainly include layered oxides, polyanionic compounds, and Prussian blue analogues (PBA). Among these, Prussian white (with all transition metals in a divalent valence state and a white color), as a Prussian blue analogue, possesses an open framework and porous structure compared to other cathode materials, allowing for the free and rapid insertion and extraction of sodium ions, thereby effectively improving the electrochemical performance of sodium-ion batteries. In addition, this type of material has advantages such as inexpensive and readily available raw materials, environmental friendliness and non-toxicity, and mild synthesis conditions, making it a promising candidate for large-scale synthesis and thus a relatively ideal sodium-ion cathode material.

[0004] However, these materials also face the problem of low cycle stability. The main reasons are as follows: 1. Coprecipitation is one of the main methods for synthesizing these materials. Prussian blue and its analogues have a large solubility product, which causes excessively rapid nucleation during the reaction. This results in a large amount of water of crystallization being trapped within the precipitate. This water of crystallization decomposes during the charge-discharge process, destroying the open framework structure, reducing reversibility during charge-discharge, and causing a sharp capacity decay. 2. Because these materials contain Fe... 2+ It is easily oxidized in air, therefore a certain amount of Fe will be produced during the synthesis process. 2+ Oxidation results in a low actual sodium content in the material, which in turn leads to a low actual specific capacity of the product.

[0005] To overcome the above problems, Prussian blue (PBA) cathode materials typically employ techniques such as adding complexing agents and altering reaction temperatures during synthesis to suppress precipitation rates and reduce the amount of water of crystallization trapped in the precipitated crystals. This aims to improve the integrity of the crystal structure and ultimately enhance the specific capacity and cycle performance of the product. Existing PBA material preparation technologies often rely on low precursor concentrations, low dropping rates, and small-volume reaction devices to control reaction rates, making the synthesis processes and performance evaluations difficult to apply in actual production.

[0006] The impact of moisture on cycling performance can be reduced by extreme dehydration of the prepared PBA material. However, PBA contains two types of water molecules: zeolite water and crystal water. While the removal of zeolite water does not affect the crystal structure, the removal of crystal water can easily cause distortion and even structural damage. Therefore, strict control of the dehydration process conditions is necessary. In general, improving PBA performance through extreme dehydration is not only energy-intensive (requiring heating) and environmentally demanding (requiring a vacuum environment), but also requires high-level process control, making it unsuitable for large-scale PBA production. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome the shortcomings of existing Prussian blue cathode materials, such as poor specific capacity and cycle performance, and the high process requirements of their preparation methods, making them unsuitable for large-scale production. This invention provides a Prussian blue cathode material, its preparation method, and its applications. By pressing or surface-coating the raw material Na4Fe[CN]6 into tablets, and utilizing the difference in solubility products between manganese, nickel, and iron elements and ferrocyanide ions, the order of addition of the reactants is adjusted, thereby improving the production efficiency of Prussian blue cathode materials. The resulting Prussian blue cathode material exhibits excellent electrochemical performance.

[0008] This invention provides a method for preparing Prussian blue-based cathode materials, which mainly includes the following steps: adding a manganese source, a nickel source, an iron source and a reducing agent sequentially to a sodium ferrocyanide solution, heating, and obtaining the Prussian blue-based cathode material; wherein, the sodium ferrocyanide solution includes Na4Fe[CN]6 sustained-release tablets and / or Na4Fe[CN]6 capsules.

[0009] In this invention, the manganese salt in the manganese source can be of the conventional type in the art, preferably one or more of manganese sulfate, manganese chloride, manganese carbonate and manganese nitrate, such as manganese sulfate.

[0010] In this invention, the concentration of manganese salt in the manganese source can be 0.05-0.15 mol / L, for example 0.1 mol / L.

[0011] In this invention, the raw material of the manganese source may also include a complexing agent.

[0012] The complexing agent may be one or more of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate (Na2EDTA), sodium gluconate, trisodium aminotriacetate, sodium tartrate, and sodium acetate, such as disodium ethylenediaminetetraacetate (Na2EDTA).

[0013] The molar ratio of the manganese salt to the complexing agent can be 1:(1-3), for example, 1:2.

[0014] In some preferred embodiments, the manganese source is prepared by dissolving the manganese salt in a solvent, and after complete dissolution, adding the complexing agent; or, the manganese salt and the complexing agent are directly dissolved in a solvent.

[0015] In this invention, the nickel salt in the nickel source can be of the conventional type in the art, preferably one or more of nickel acetate tetrahydrate, nickel chloride, nickel nitrate and nickel sulfate, such as nickel sulfate.

[0016] In this invention, the concentration of nickel salt in the nickel source can be 0.05-0.15 mol / L, for example 0.1 mol / L.

[0017] In this invention, the raw materials of the nickel source may also include a complexing agent.

[0018] The complexing agent may be one or more of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate (Na2EDTA), sodium gluconate, trisodium aminotriacetate, sodium tartrate, and sodium acetate, such as disodium ethylenediaminetetraacetate (Na2EDTA).

[0019] The molar ratio of the nickel salt to the complexing agent can be 1:(1-3), for example, 1:2.

[0020] In some preferred embodiments, the nickel source is prepared by dissolving the nickel salt in a solvent, and after complete dissolution, adding the complexing agent; or, the nickel salt and the complexing agent are directly dissolved in a solvent.

[0021] In this invention, the iron source may contain one or more of the following iron salts: ferrous ammonium sulfate, ferrous sulfate, ferrous chloride, and ferrous acetate, such as ferrous ammonium sulfate and / or ferrous sulfate.

[0022] In this invention, the raw materials of the iron source may also include ammonium sulfate.

[0023] The molar ratio of the iron salt to the ammonium sulfate can be 1:(1-3), for example, 1:1.

[0024] In this invention, the iron source can be prepared by adding iron filings to a mixed solution of ammonium sulfate and the iron salt, and stirring.

[0025] The iron filings may be in excess.

[0026] The stirring time can be 1-2 hours, for example, 2 hours. During the stirring process, ferric ions in the solution react with iron filings and are converted into ferrous ions.

[0027] The stirring process may further include a filtration operation. After filtering the solution to remove iron filings, the iron source for the prepared product is obtained.

[0028] In this invention, the concentration of iron salt in the iron source can be 0.05-0.15 mol / L, for example, 0.1137 mol / L. The concentration of the iron source can be obtained by the following method: the iron filings obtained by filtration are washed three times with deionized water, washed once with acetone, dried in an oven for 2 hours, and weighed. The mass difference of the iron filings before and after adding them to the solution is the amount of elemental iron reacting with ferric ions, from which the true concentration of ferrous ions in the purified iron source can be calculated. The conversion relationship above satisfies that for every 1 mol of metallic iron consumed, 2 mol of ferric ions can be reduced, and the final increase in the iron ion concentration in the solution is 1 mol.

[0029] Since the purity of commercially available ferrous salts cannot reach battery-grade purity, mainly due to the presence of ferric salts, the present invention employs the above steps to simultaneously perform reduction and impurity removal treatment, thereby achieving the purification of the ferrous salt raw material solution.

[0030] In this invention, preferably, the manganese salt, the nickel salt, and the iron salt are all sulfates. Choosing sulfates effectively prevents the introduction of anions, such as chloride ions and nitrate ions, that could affect subsequent electrochemical performance from the raw materials.

[0031] In this invention, the solvent used in the manganese source, the nickel source, and the iron source can all be deionized water.

[0032] In this invention, preferably, the amount of raw materials used is such that the chemical formula of the product is Na₂Mn. (1-x) Ni x Fe y [Fe(CN)6].

[0033] Preferably, the stoichiometric ratio of the added nickel salt in the product is controlled to be between 0 and 0.1, for example, 0.05 or 0.1. This corresponds to the x value in the chemical formula.

[0034] Preferably, the stoichiometric ratio of the added iron salt in the product is controlled to be between 0 and 0.1, for example, 0.05 or 0.1. This corresponds to the y-value in the chemical formula.

[0035] In this invention, the manganese source, the nickel source, and the iron source can be added to the sodium ferrocyanide solution by means of a peristaltic pump injection.

[0036] In this invention, the reducing agent is preferably hydrazine.

[0037] In this invention, the molar ratio of the reducing agent to Na₄Fe[CN]₆ in the sodium ferrocyanide solution can be 1:(8-12), for example, 1:10. In this invention, the addition of the reducing agent can prevent the conversion of ferrous iron to ferric iron during heating and aging, thus avoiding reversible capacity loss; only a small amount needs to be added.

[0038] In this invention, the Na4Fe[CN]6 sustained-release tablets or capsules may include Na4Fe[CN]6, sodium stearate, and a film-forming material. In this invention, the Na4Fe[CN]6 sustained-release tablets and capsules serve as sustained-release feedstocks in the system, achieving the goal of maintaining the Na4Fe[CN]6 feedstock concentration in the reactor at a low level. The concentration can be maintained within a stable range by continuously adding capsules during the reaction. This method can increase the yield of a single reactor reaction.

[0039] The sodium stearate can improve the mechanical properties of sustained-release tablets or capsules and increase their stability.

[0040] The mass ratio of Na4Fe[CN]6 to sodium stearate can be 1:(2-4), for example 1:3.

[0041] The film-forming material may be one or more of cellulose acetate, ethyl cellulose, cellulose propionate, polyvinyl chloride, and polycarbonate, such as ethyl cellulose.

[0042] The film-forming material may include film-forming material A and film-forming material B.

[0043] The mass ratio of the film-forming material A to the sodium stearate can be 1:(2-4), for example, 1:1.

[0044] The mass ratio of the film-forming material B to the Na4Fe[CN]6 can be 1-8%.

[0045] In this invention, the Na4Fe[CN]6 sustained-release tablets can be prepared by the following steps: mixing Na4Fe[CN]6 with sodium stearate and film-forming material A evenly, pressing it into tablets, and then performing surface coating treatment to prepare sustained-release tablets; in the coating treatment, the coating solution includes film-forming material B and solvent.

[0046] The solvent may be anhydrous ethanol.

[0047] The mass ratio of the film-forming material B to the solvent can be 1:(9-11), for example, 1:10.

[0048] Preferably, the surface coating treatment is performed using a high-efficiency coating machine conventional in the art.

[0049] The surface coating treatment may further include a drying process. The drying temperature can be conventional in the art, such as 60°C.

[0050] In this invention, the Na4Fe[CN]6 capsule can be prepared by the following steps: mixing Na4Fe[CN]6 and sodium stearate evenly, filling the mixture into a capsule, and sealing the capsule opening; the capsule is made of the film-forming material.

[0051] Preferably, the Na4Fe[CN]6 capsules can be prepared using a fully automated capsule filling machine, which is conventional in the art.

[0052] In this invention, the sodium ferrocyanide solution is prepared by mixing ferrocyanide raw material with deionized water; wherein the ferrocyanide raw material is the Na4Fe[CN]6 sustained-release tablet or the Na4Fe[CN]6 capsule.

[0053] During the mixing process, the coating material or capsules on the surface of the ferrocyanide raw material begin to swell, gradually releasing Na4Fe[CN]6 into the deionized water to form a sodium ferrocyanide reaction solution. The ferrocyanide raw material conforms to a zero-order release model after being added to the deionized water.

[0054] In this invention, the sodium ferrocyanide solution may further include sodium citrate and / or sodium sulfate. The sodium citrate and / or sodium sulfate can serve as additives in the reaction medium to increase the sodium ion concentration and provide complexing ions.

[0055] The molar ratio of the ferrocyanide raw material to the sodium citrate can be 1:(10-20), for example, 1:15.

[0056] When the sodium ferrocyanide solution includes sodium citrate and sodium sulfate, the molar ratio of sodium citrate to sodium sulfate can be 1:(0.5-1.5), for example, 1:1.

[0057] In this invention, stirring may be included before adding the reducing agent.

[0058] The stirring time can be 1-2 hours.

[0059] In this invention, the heating temperature can be 60-120℃, for example 90℃.

[0060] In this invention, the heating time can be 2-12 hours, for example, 2 hours.

[0061] In this invention, preferably, the reaction device is kept in a sealed state during heating.

[0062] In this invention, the heating process may further include an aging process.

[0063] The aging temperature can be room temperature, which is the room temperature conventionally understood in the art, such as 15-30°C.

[0064] The aging time can be 4-12 hours, for example, 12 hours.

[0065] In this invention, a double-layered co-precipitation reactor is used for the reaction. The outer layer of the double-layered co-precipitation reactor can be heated or pressurized in a sealed environment. The aging process can be carried out under sealed heating conditions, further promoting the recrystallization of the PBA product and forming crystals with larger particle sizes, reducing crystal structure defects and minimizing encapsulated water molecules.

[0066] In this invention, after the reaction is completed, washing and drying operations may also be included.

[0067] The washing process can be carried out by centrifugal separation and sedimentation.

[0068] The washing solvent may be one or more of sodium chloride, deionized water, and acetone.

[0069] Preferably, the product PBA is first washed with sodium chloride, followed by washing with deionized water or acetone. This washing sequence prevents the loss of sodium ions from the product PBA during the removal of impurities.

[0070] The drying temperature can be 100-120℃, for example 105℃ or 120℃.

[0071] The drying time can be 12-24 hours, for example, 24 hours.

[0072] In this invention, after the reaction is completed, grinding and sieving operations may also be included.

[0073] The sieving process can be performed using a 200-mesh sieve.

[0074] The present invention also provides a Prussian blue-based cathode material, which is prepared by the above-described preparation method.

[0075] The present invention also provides an application of the above-mentioned Prussian blue cathode material in sodium-ion batteries.

[0076] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0077] The reagents and raw materials used in this invention are all commercially available.

[0078] The positive and progressive effects of this invention are as follows:

[0079] (1) This invention prepares a sodium-rich Prussian blue cathode material with excellent electrochemical performance by optimizing the order of adding the reaction raw materials. Furthermore, this invention modifies the reaction raw materials to further improve the electrochemical performance of the product. Moreover, the concentration of Na4Fe[CN]6 in the reaction vessel is controlled by controlling the rate and amount of addition of this raw material during the subsequent preparation of the Prussian blue sodium ion formulation material.

[0080] (2) This invention utilizes the difference in solubility products between manganese, nickel, and iron and ferrocyanide to adjust the order of addition of reactants, thereby obtaining a high-performance Prussian blue-based cathode material. A small amount of nickel doping can sacrifice a small amount of theoretical capacity to suppress the Jan Taylor effect caused by manganese ion distortion in the Mn-PBA crystal, stabilize the crystal structure, and improve cycle life. Since nickel has no electrochemical activity in the material and only improves structural stability, ferrous iron, which has better capacity, is also doped to compensate for the capacity loss. Because the solubility product of iron is much higher than that of manganese, a small amount of iron can replace manganese on the crystal surface, inhibiting manganese dissolution.

[0081] (3) By compressing the raw material Na4Fe[CN]6 into tablets or coating it with capsules, the raw material can be fed into the reactor in a solid state. Due to the binding of the coating material or capsule, it is slowly released into the reactor, keeping the Na4Fe[CN]6 concentration in the reactor at a low level. Moreover, because it is a solid feed, the yield can be increased compared to liquid feed.

[0082] (4) The present invention can improve the production efficiency of Prussian blue cathode materials, and the product obtained has better specific capacity and cycle life. Attached Figure Description

[0083] Figure 1 This is a schematic diagram of the preparation process in Example 1.

[0084] Figure 2 The first charge-discharge curve of the cathode material prepared in Example 1 is shown.

[0085] Figure 3 The first charge-discharge curve of the cathode material prepared in Comparative Example 1 is shown. Detailed Implementation

[0086] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0087] Example 1

[0088] 1. Analytical grade Na4Fe[CN]6 was mixed with sodium stearate and ethyl cellulose at a mass ratio of 6:2:2 and then compressed into Na4Fe[CN]6 tablets. Ethyl cellulose and anhydrous ethanol were mixed at a mass ratio of 1:10 to prepare a coating raw material solution. The compressed Na4Fe[CN]6 tablets were then coated using a high-efficiency coating machine and dried in a vacuum drying oven at 60°C to produce Na4Fe[CN]6 sustained-release tablets.

[0089] 2. Accurately weigh 0.1 mol of analytical grade manganese sulfate and 0.2 mol of Na2EDTA salt, add them to deionized water and stir to dissolve. Then, dilute to 1 L in a volumetric flask to prepare a 0.1 mol / L manganese salt raw material solution.

[0090] 3. Accurately weigh 0.1 mol of analytical grade nickel sulfate and dissolve it in deionized water. After it is completely dissolved, add 0.2 mol of Na2EDTA salt, stir to dissolve, and prepare a 0.1 mol / L nickel salt raw material solution.

[0091] 4. Accurately weigh 0.1 mol of ferrous sulfate and 0.1 mol of analytical grade ammonium sulfate, add them to deionized water, stir until completely dissolved, then add 5.0000 g of pure iron filings. After stirring for 2 hours, the ferric ions in the solution react with metallic iron and are converted into ferrous ions. Filter the solution to remove the iron filings, then dilute to 1 L in a volumetric flask to use as the raw material solution for preparing the iron salt product. Wash the filtered iron filings three times with deionized water, wash once with acetone, and dry in an oven for 2 hours. The weight is 4.2330 g. The mass difference of the iron filings before and after adding them to the solution is the mass of elemental iron that reacted with the ferric ions. The actual concentration of ferrous ions in the purified iron salt raw material can be calculated to be 0.1137 mol / L.

[0092] 5. Add 1.5 mol of analytical grade sodium citrate and 1.5 mol of analytical grade sodium sulfate to the reaction vessel, add deionized water, start the stirring device and continue stirring until completely dissolved. Add Na4Fe[CN]6 sustained-release tablets (containing 0.1 mol Na4Fe[CN]6) to the reaction vessel. The coating material on the surface of the Na4Fe[CN]6 sustained-release tablets gradually begins to swell, gradually dissolving the sodium ferrocyanide Na4Fe[CN]6 and slowly releasing it into the deionized water to form a sodium ferrocyanide reaction solution.

[0093] 6. Slowly inject the above two manganese salt raw materials into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will react with sodium ferrocyanide to form a precipitation reaction. Stop adding manganese salt raw materials when the amount added is 0.08 mol.

[0094] 7. Slowly inject the above 3 nickel salt raw materials into the reactor using a peristaltic pump, and continue stirring. Stop adding the nickel salt when the amount added is 0.01 mol.

[0095] 8. Slowly inject the above 4 iron salt raw materials into the reaction vessel using a peristaltic pump, and continue stirring. Stop adding iron salt when the amount added is 0.01 mol.

[0096] 9. After thoroughly stirring the above suspension for 2 hours, add 0.01 mol of hydrazine as a reducing agent, stir evenly, heat the reaction vessel to 90 degrees Celsius, and keep the reaction vessel sealed. Continue heating and stirring for 2 hours, then stop heating and stirring. Let it stand for 12 hours to allow the precipitate to age.

[0097] 10. Transfer the reaction product after settling from the reactor to a centrifuge and centrifuge to separate the precipitate. Wash the precipitate with 5% sodium chloride solution and centrifuge again. Repeat the washing process three times. Then wash the precipitate with deionized water and centrifuge again. Repeat this process three times. Finally, wash the precipitate with acetone. After the acetone dries, vacuum dry at 120°C for 24 hours to remove residual moisture.

[0098] This yielded FeNi-doped Mn-PBA with a monoclinic crystal structure, which, after being ground through a 200-mesh sieve, was used for the preparation and testing of sodium-ion battery cathodes. The chemical formula of the product is Na₂Mn. 0.8 Ni 0.1 Fe 0.1 [Fe(CN)6]. The sample is designated as MnNiFe@PBA-1.

[0099] Preparation schematic diagram as shown Figure 1 As shown.

[0100] Example 2

[0101] The raw material pretreatment is the same as steps 1-5 in Example 1.

[0102] The above two manganese salt raw materials are slowly injected into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will undergo a precipitation reaction with sodium ferrocyanide. The addition is stopped when the amount of manganese salt raw material added is 0.09 mol.

[0103] The above-mentioned nickel salt raw materials were slowly injected into the reactor using a peristaltic pump, and the mixture was continuously stirred. The addition was stopped when the amount of nickel salt added was 0.005 mol.

[0104] The above four iron salt raw materials were slowly injected into the reactor using a peristaltic pump, and the mixture was continuously stirred. The addition was stopped when the amount of iron salt added was 0.005 mol.

[0105] The subsequent processing is the same as steps 9-10 in Example 1. The chemical formula of the product is Na₂Mn. 0.9 Ni 0.05 Fe 0.05 [Fe(CN)6], sample denoted as MnNiFe@PBA-2.

[0106] Comparative Example 1

[0107] 1. Accurately weigh 0.1 mol of analytical grade Na₄Fe[CN]₆ into a reaction vessel as the reaction raw material. Then add 1.5 mol of sodium citrate and 1.5 mol of sodium sulfate to the reaction raw material solution, add deionized water, stir until completely dissolved, and then make up to 1 L for later use.

[0108] 2. Accurately weigh 0.1 mol of analytical grade manganese sulfate and 0.2 mol of Na2EDTA salt, add them to deionized water and stir to dissolve. Then, dilute to 1 L in a volumetric flask to prepare a 0.1 mol / L manganese salt raw material solution.

[0109] 3. Slowly inject the above two manganese salt raw materials into the reaction vessel using a peristaltic pump while maintaining continuous stirring. The manganese ions will react with sodium ferrocyanide to form a precipitation reaction. After the amount of manganese salt raw material added is 0.1 mol, turn off the peristaltic pump.

[0110] 4. After stirring the above suspension thoroughly for 2 hours, let it stand for 12 hours to allow it to settle and age.

[0111] 5. Transfer the reaction product after settling from the reactor to a centrifuge and centrifuge to separate the precipitate. Wash the precipitate with deionized water and centrifuge again, repeating this process three times. Finally, wash the precipitate with acetone, and after drying with acetone, vacuum dry at 120°C for 24 hours to remove residual moisture. This yields Mn-PBA with the chemical formula Na2Mn[Fe(CN)6]. After grinding and passing through a 200-mesh sieve, it is used for testing the preparation of a sodium-ion battery cathode.

[0112] Comparative Example 2

[0113] The raw material pretreatment is the same as steps 1-5 in Example 1.

[0114] The above two manganese salt raw materials are slowly injected into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will undergo a precipitation reaction with sodium ferrocyanide. The addition is stopped when the amount of manganese salt raw material added is 0.09 mol.

[0115] The above three nickel salt raw materials were slowly injected into the reactor using a peristaltic pump, and stirring was continued. The addition was stopped when the amount of nickel salt added was 0.01 mol.

[0116] The subsequent processing is the same as steps 9-10 in Example 1. The chemical formula of the product is Na₂Mn. 0.9 Ni 0.1 [Fe(CN)6], sample denoted as MnNiFe@PBA-3.

[0117] Comparative Example 3

[0118] The raw material pretreatment is the same as steps 1-5 in Example 1.

[0119] The above two manganese salt raw materials are slowly injected into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will undergo a precipitation reaction with sodium ferrocyanide. The addition is stopped when the amount of manganese salt raw material added is 0.09 mol.

[0120] The above four iron salt raw materials were slowly injected into the reactor using a peristaltic pump, and the mixture was continuously stirred. The addition was stopped when the amount of iron salt added was 0.01 mol.

[0121] The subsequent processing is the same as steps 9-10 in Example 1. The chemical formula of the product is Na₂Mn. 0.9 Fe 0.1 [Fe(CN)6], sample denoted as MnNiFe@PBA-4.

[0122] Comparative Example 4

[0123] The raw material pretreatment is the same as steps 1-5 in Example 1.

[0124] The above three nickel salt raw materials were slowly injected into the reactor using a peristaltic pump, and stirring was continued. The addition was stopped when the amount of nickel salt added was 0.01 mol.

[0125] The above four iron salt raw materials were slowly injected into the reactor using a peristaltic pump, and the mixture was continuously stirred. The addition was stopped when the amount of iron salt added was 0.01 mol.

[0126] The above two manganese salt raw materials are slowly injected into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will undergo a precipitation reaction with sodium ferrocyanide. The addition is stopped when the amount of manganese salt raw material added is 0.08 mol.

[0127] The subsequent processing is the same as steps 9-10 in Example 1. The chemical formula of the product is Na₂Mn. 0.8 Ni 0.1 Fe 0.1 [Fe(CN)6], sample denoted as MnNiFe@PBA-5.

[0128] Comparative Example 5

[0129] The raw material pretreatment is the same as steps 1-5 in Example 1.

[0130] The above four iron salt raw materials were slowly injected into the reactor using a peristaltic pump, and the mixture was continuously stirred. The addition was stopped when the amount of iron salt added was 0.01 mol.

[0131] The above three nickel salt raw materials were slowly injected into the reactor using a peristaltic pump, and stirring was continued. The addition was stopped when the amount of nickel salt added was 0.01 mol.

[0132] The above two manganese salt raw materials are slowly injected into the reactor using a peristaltic pump while maintaining continuous stirring. The manganese ions will undergo a precipitation reaction with sodium ferrocyanide. The addition is stopped when the amount of manganese salt raw material added is 0.08 mol.

[0133] The subsequent processing is the same as steps 9-10 in Example 1. The chemical formula of the product is Na₂Mn. 0.8 Ni 0.1 Fe 0.1 [Fe(CN)6], sample denoted as MnNiFe@PBA-6.

[0134] Example 1

[0135] Assemble button half-cells based on the cathode material prepared above. Weigh and mix the cathode material, conductive carbon black (SP), and binder (PVDF) at a mass ratio of 80:15:5. Add N-methylpyrrolidone as a solvent and stir thoroughly to form a uniform slurry. Coat the slurry onto aluminum foil using a doctor blade, then transfer the aluminum foil to an oven and dry at 80°C for 2 hours, followed by drying in a vacuum drying oven at 105°C for 12 hours. After drying, compact the aluminum foil with a rolling mill, cut it into 10mm circular electrode sheets, weigh them, and quickly transfer them to a glove box for later use. In the glove box, stack the electrode sheets, separator, and sodium sheet in the following order, add commercial sodium-ion battery electrolyte, and then encapsulate the battery (2032 type button cell).

[0136] After standing for 12 hours, the battery was connected to the battery testing system and subjected to charge-discharge cycle tests at a rate of 1C with a voltage between 2-4V. The results are shown in Table 1. The first charge-discharge curves of the positive electrode materials prepared in Example 1 and Comparative Example 1 are shown in Table 1. Figure 2 and Figure 3 As shown.

[0137] Table 1

[0138] Reversible capacity at 1C rate (mAh / g) 500-week capacity retention at 1C rate Example 1 135.6 80％ Example 2 138.5 76％ Comparative Example 1 80.5 43％ Comparative Example 2 123.8 86％ Comparative Example 3 140.5 62％ Comparative Example 4 133.2 60％ Comparative Example 5 130.6 55％

[0139] As shown in the table above, the cathode material prepared by the method of the present invention has excellent reversible capacity (up to 135 mAh / g or more) and capacity retention rate (up to 75% or more) when applied to batteries.

[0140] Comparative Example 1 directly used Na4Fe[CN]6 as the reaction raw material, and its reversible capacity and capacity retention rate were significantly reduced.

[0141] Comparative Example 2 lacks an iron source compared to Example 2, resulting in a decrease in its reversible capacity. This is presumably due to the occurrence of manganese dissolution, which is caused by the presence of manganese on the crystal surface.

[0142] Comparative Example 3, lacking a nickel source compared to Example 2, exhibited excellent reversible capacity but significantly lower capacity retention. This demonstrates that the addition of a nickel source in this invention significantly improves cycle performance while sacrificing a small amount of capacity.

[0143] Comparative Examples 4 and 5 adjusted the order of adding manganese, nickel, and iron sources, resulting in significantly reduced cycle performance and lower reversible capacity compared to the present invention.

Claims

1. A method for preparing a Prussian blue-based cathode material, characterized in that, The main steps include: sequentially adding manganese, nickel, iron, and reducing agents to a sodium ferrocyanide solution and heating to obtain a Prussian blue-based cathode material; wherein the sodium ferrocyanide solution includes Na4Fe[CN]6 sustained-release tablets and / or Na4Fe[CN]6 capsules; the amount of raw materials used is sufficient to maintain the chemical formula of the product as Na2Mn. (1-x) Ni x Fe y [Fe(CN)6]; the stoichiometric ratio of nickel salt in the added nickel source in the product is controlled to be 0-0.1; the stoichiometric ratio of iron salt in the added iron source in the product is controlled to be 0-0.

1.

2. The method for preparing Prussian blue-based cathode materials as described in claim 1, characterized in that, The manganese source contains one or more manganese salts selected from manganese sulfate, manganese chloride, manganese carbonate, and manganese nitrate. And / or, in the manganese source, the concentration of manganese salt is 0.05-0.15 mol / L; And / or, the raw materials of the manganese source also include a complexing agent; And / or, in the nickel source, the nickel salt is one or more of nickel acetate tetrahydrate, nickel chloride, nickel nitrate and nickel sulfate; And / or, in the nickel source, the concentration of nickel salt is 0.05-0.15 mol / L; And / or, the raw materials of the nickel source also include a complexing agent; And / or, in the iron source, the type of iron salt is one or more of ferrous ammonium sulfate, ferrous sulfate, ferrous chloride and ferrous acetate; And / or, in the iron source, the concentration of iron salt is 0.05-0.15 mol / L; And / or, the raw materials of the iron source also include ammonium sulfate; And / or, control the stoichiometric ratio of the added nickel salt in the product to be 0.05 or 0.1; And / or, control the stoichiometric ratio of the added iron salt in the product to be 0.05 or 0.

1.

3. The method for preparing Prussian blue-based cathode materials as described in claim 2, characterized in that, The manganese source contains manganese sulfate as the type of manganese salt. And / or, in the nickel source, the type of nickel salt is nickel sulfate; And / or, in the iron source, the type of iron salt is ferrous ammonium sulfate and / or ferrous sulfate; And / or, in the iron source, the concentration of iron salt is 0.1 mol / L or 0.1137 mol / L.

4. The method for preparing Prussian blue-based cathode materials as described in claim 2, characterized in that, The manganese salt, the nickel salt, and the iron salt are all sulfates; And / or, the solvent used in the manganese source, the nickel source, and the iron source is deionized water; And / or, in the manganese source or the nickel source, the complexing agent is selected from one or more of sodium citrate, sodium oxalate, disodium ethylenediaminetetraacetate (Na2EDTA), sodium gluconate, trisodium aminotriacetate, sodium tartrate, and sodium acetate. And / or, the molar ratio of the manganese salt to the complexing agent is 1:(1-3); And / or, the molar ratio of the nickel salt to the complexing agent is 1:(1-3); And / or, the molar ratio of the iron salt to the ammonium sulfate is 1:(1-3).

5. The method for preparing Prussian blue-based cathode materials as described in claim 4, characterized in that, In the manganese source or the nickel source, the complexing agent is disodium ethylenediaminetetraacetate (Na2EDTA).

6. The method for preparing Prussian blue-based cathode materials as described in claim 2, characterized in that, The manganese source is prepared by the following method: the manganese salt is dissolved in a solvent, and after complete dissolution, the complexing agent is added; or, the manganese salt and the complexing agent are directly dissolved in a solvent. And / or, the nickel source is prepared by the following method: the nickel salt is dissolved in a solvent, and after complete dissolution, the complexing agent is added; or, the nickel salt and the complexing agent are directly dissolved in a solvent; And / or, the iron source is prepared by adding iron filings to a mixed solution of the ammonium sulfate and the iron salt and stirring.

7. The method for preparing Prussian blue-based cathode material as described in claim 6, characterized in that, The stirring time is 1-2 hours; And / or, the stirring process may also include a filtering operation.

8. The method for preparing Prussian blue-based cathode material as described in claim 1, characterized in that, The reducing agent is hydrazine; And / or, the molar ratio of the reducing agent to Na4Fe[CN]6 in the sodium ferrocyanide solution is 1:(8-12); And / or, the Na4Fe[CN]6 sustained-release tablets or the Na4Fe[CN]6 capsules include Na4Fe[CN]6, sodium stearate and film-forming material.

9. The method for preparing the Prussian blue-type cathode material as described in claim 8, characterized in that, The mass ratio of Na4Fe[CN]6 to sodium stearate is 1:(2-4); And / or, the film-forming material is one or more of cellulose acetate, ethyl cellulose, cellulose propionate, polyvinyl chloride, and polycarbonate; And / or, the film-forming material includes film-forming material A and film-forming material B; wherein, The mass ratio of film-forming material A to sodium stearate is 1:(2-4); the mass ratio of film-forming material B to Na4Fe[CN]6 is 1-8%.

10. The method for preparing the Prussian blue-based cathode material as described in claim 9, characterized in that, The film-forming material is ethyl cellulose.

11. The method for preparing Prussian blue-based cathode material as described in claim 9, characterized in that, The Na4Fe[CN]6 sustained-release tablets are prepared by the following steps: Na4Fe[CN]6 is mixed evenly with sodium stearate and film-forming material A, pressed into tablets, and then surface-coated to form sustained-release tablets; in the coating process, the coating solution includes film-forming material B and solvent; And / or, the Na4Fe[CN]6 capsule is prepared by the following steps: mixing the Na4Fe[CN]6 with the sodium stearate evenly, filling the mixture into capsules, and sealing the capsule opening; the capsule is made of the film-forming material; And / or, the sodium ferrocyanide solution is prepared by mixing ferrocyanide raw material with deionized water; wherein, the ferrocyanide raw material is the Na4Fe[CN]6 sustained-release tablet or the Na4Fe[CN]6 capsule; And / or, the sodium ferrocyanide solution further includes sodium citrate and / or sodium sulfate; wherein, when the sodium ferrocyanide solution includes sodium citrate and sodium sulfate, the molar ratio of sodium citrate to sodium sulfate is 1:(0.5-1.5).

12. The method for preparing the Prussian blue-based cathode material as described in claim 11, characterized in that, The solvent is anhydrous ethanol; And / or, the mass ratio of the film-forming material B to the solvent is 1:(9-11); And / or, the surface coating treatment further includes a drying operation; And / or, the molar ratio of the ferrocyanide raw material to the sodium citrate is 1:(10-20).

13. The method for preparing Prussian blue-based cathode material as described in claim 1, characterized in that, The process of adding the reducing agent also includes stirring. And / or, the heating temperature is 60-120°C; And / or, the heating time is 2-12 hours; And / or, during the heating, the reaction apparatus is kept in a sealed state; And / or, after heating, the process also includes an aging process; And / or, after the reaction is complete, washing and drying operations are also included; And / or, after the reaction is complete, grinding and sieving operations are also included.

14. The method for preparing Prussian blue-based cathode material as described in claim 13, characterized in that, The stirring time is 1-2 hours; And / or, the aging temperature is room temperature; And / or, the aging time is 4-12 hours; And / or, the solvent for washing is one or more of sodium chloride solution, deionized water, and acetone.

15. The method for preparing the Prussian blue-type cathode material as described in claim 14, characterized in that, The washing process involves first washing with a sodium chloride solution, followed by washing with deionized water or acetone.

16. A Prussian blue-based cathode material, characterized in that, It is prepared by any one of the preparation methods as described in claims 1-15.

17. The application of the Prussian blue cathode material as described in claim 16 in a sodium-ion battery.

Images