Preparation method of positive pole piece of Prussian blue sodium-ion battery, pole piece and battery
By employing a three-step synergistic dehydration strategy, the water content of the Prussian blue sodium-ion battery cathode material was reduced, solving the problem of the material's susceptibility to water absorption in the air and improving the battery's electrochemical stability and cycle performance.
Patent Information
- Application Number
- CN202511046507.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-29
- Publication Date
- 2025-11-14
AI Technical Summary
In existing technologies, the Prussian blue sodium-ion battery cathode material has a high water content, which affects the battery's electrochemical performance. Furthermore, the material is prone to absorbing water from the air, leading to battery swelling, reduced cycle stability, and enhanced interfacial side reactions.
A three-step synergistic water removal strategy was adopted: a co-precipitation reaction was carried out under inert gas protection, followed by centrifugal washing and vacuum drying, then high-temperature treatment in reducing gas, and finally secondary heat treatment in inert gas to prepare sodium-ion battery positive electrode sheets, thereby reducing the content of lattice water and adsorbed water in the material.
It effectively reduces the water content of Prussian blue materials, improves electrochemical stability, and enhances cycle stability. The material retains more than 95% of its capacity after 100 cycles at a 0.5C rate.
Smart Images
Figure CN120955091A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of sodium-ion battery technology, specifically to a method for preparing a Prussian blue sodium-ion battery positive electrode, the electrode, and the battery. Background Technology
[0002] In recent years, with the rapid development of electric vehicles, large-scale energy storage power stations, and smart grids, the demand for energy storage equipment has been increasing. Compared with lithium-ion batteries, sodium-ion batteries are considered a low-cost supplement or competitor to lithium-ion batteries in large-scale power storage applications due to their advantages in storage capacity and cost. Prussian blue compounds, as common cathode materials for sodium-ion batteries, have become a research hotspot due to their unique open-framework structure, abundant redox sites, low cost, and high safety.
[0003] Prussian blue materials are generally synthesized using a solution co-precipitation method. Due to the rapid reaction during synthesis, the lattice integrity of the material is poor, resulting in a high content of lattice water and interstitial water in the product. The lattice integrity and water content significantly affect the electrochemical performance of the material, and Prussian blue materials are also prone to absorbing water from the air. Therefore, the preparation of Prussian blue materials with low defects and low water content is currently a key research focus for Prussian blue sodium-ion battery cathode materials.
[0004] It should be noted that the information disclosed in the background section of this application is intended only to enhance the understanding of the general background of this application, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention
[0005] In view of this, this application provides a method for preparing a positive electrode sheet of Prussian blue sodium-ion battery, the electrode sheet and the battery, so as to solve the problem that the high water content of the positive electrode material of Prussian blue sodium-ion battery affects the electrochemical performance of the battery in the prior art.
[0006] In a first aspect, embodiments of this application provide a method for preparing a positive electrode sheet for a Prussian blue sodium-ion battery, comprising:
[0007] Under inert gas protection, solution A containing ferrous salt and chelating agent, and solution B containing sodium ferrocyanide and reducing agent are simultaneously added dropwise to solution C containing auxiliary salt and surfactant. The reaction is carried out at 25℃~40℃ for 12~48h. After centrifugation and washing, the solution is dried under vacuum at 130-160℃ to obtain primary Prussian blue material.
[0008] The primary Prussian blue material was heat-treated in a reducing gas at 130-160°C to obtain the Prussian blue material.
[0009] The Prussian blue material is used to make a positive electrode sheet for a sodium-ion battery, and then subjected to a second heat treatment at 130-160°C in an inert gas to make the water content of the positive electrode sheet ≤100ppm.
[0010] In one possible implementation, the molar ratio of the ferrous salt in solution A to the sodium ferrocyanide in solution B is 0.8 to 1.5, and the volume ratio of solution A to solution B is 0.8 to 1.2.
[0011] In one possible implementation, the concentration of the ferrous salt is 0.1–0.5 mol / L, the concentration of the chelating agent is 0.1–1.5 mol / L, the concentration of the sodium ferrocyanide is 0.1–0.5 mol / L, and the concentration of the reducing agent is 1–2 mol / L.
[0012] In one possible implementation, the ferrous salt is any one or a combination of ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous chloride tetrahydrate, ferrous sulfate heptahydrate, ferrous nitrate hexahydrate, and ferrous acetate tetrahydrate.
[0013] The chelating agent is any one or a combination of sodium citrate, ethylenediaminetetraacetic acid, and sodium carboxymethyl cellulose.
[0014] The reducing agent is ascorbic acid;
[0015] The auxiliary salt is sodium chloride;
[0016] The surfactant is polyvinylpyrrolidone.
[0017] In one possible implementation, the centrifugal washing includes:
[0018] The sample was washed multiple times by centrifugation with deionized water and anhydrous ethanol. The centrifugation speed with deionized water was 10,000-12,000 rpm, and the centrifugation speed with anhydrous ethanol was 7,000-8,000 rpm.
[0019] In one possible implementation, the step of fabricating the Prussian blue material into a sodium-ion battery positive electrode includes:
[0020] A positive electrode slurry comprising the Prussian blue material, a conductive agent, and a binder is coated onto a positive electrode current collector and then dried in a vacuum drying oven to obtain a sodium-ion battery positive electrode sheet.
[0021] In one possible implementation, the conductive agent is one or a mixture of at least two of carbon black, Ketjen black, and conductive carbon black; the binder is one or a mixture of at least two of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.
[0022] In one possible implementation, the mass ratio of the Prussian blue material, the conductive agent, and the binder is 7:2:1.
[0023] Secondly, embodiments of this application provide a Prussian blue sodium-ion battery positive electrode sheet, which is prepared by the method described in any one of the first aspects, wherein the lattice water content is ≤5wt%, the adsorbed water content is ≤5wt%, and the electrode sheet water content is ≤100ppm.
[0024] Thirdly, embodiments of this application provide a sodium-ion battery comprising the positive electrode sheet described in the second aspect.
[0025] The multi-step dehydration method provided in this application can effectively reduce the water content in Prussian blue materials, reduce lattice defects in the system, and increase sodium content. Furthermore, the Prussian blue material prepared by the multi-step dehydration method exhibits excellent electrochemical stability when applied as a cathode material in sodium-ion batteries. Attached Figure Description
[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of a method for preparing a positive electrode sheet of a Prussian blue sodium-ion battery according to an embodiment of this application.
[0028] Figure 2 A diagram of the experimental apparatus for preparing Prussian blue provided in the embodiments of this application;
[0029] Figure 3 SEM images of Prussian blue materials from Example 1 and Comparative Example 1 provided for embodiments of this application;
[0030] Figure 4 The thermogravimetric curve of Example 1 provided in this application;
[0031] Figure 5 The thermogravimetric curve of Comparative Example 1 provided in the embodiments of this application.
[0032] Figure 6 The cycling performance of the battery assembled in Example 1 and Comparative Example 1 provided for the embodiments of this application at 0.5C (1C = 170mAh / g) is shown in the graph. Detailed Implementation
[0033] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.
[0034] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.
[0035] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.
[0036] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.
[0037] Prussian blue materials, due to their open framework structure, readily adsorb large amounts of water. The presence of crystalline water (occupying lattice vacancies) and adsorbed water (attached to the surface) can cause three major problems: 1. Deterioration of electrochemical performance: Water electrolysis produces gas, leading to battery expansion and a sharp drop in cycle stability; 2. Destruction of structural integrity: Water molecules react with Fe... 2+ Coordination induces lattice distortion, accelerating the dissolution of transition metals; 3. Interfacial side reactions surge: Aqueous materials react with electrolyte to generate HF, which corrodes the electrode interface.
[0038] Traditional coprecipitation methods result in high defect structures and water content due to rapid nucleation, while high-temperature dehydration alone oxidizes Fe. 2+ This leads to a structural phase transition. To address the aforementioned challenges, embodiments of this application provide a three-step synergistic water removal strategy:
[0039] 1. Removal of primary lattice water: Under inert gas protection, the nucleation rate is controlled by a chelating agent to achieve low-defect co-precipitation, thereby reducing the crystal water content to ≤5wt%.
[0040] 2. Secondary adsorption water removal: Heat treatment in a reducing atmosphere (H2 / Ar) selectively breaks down water molecules and Fe. 2+ Hydrogen bonds are formed to avoid changes in the oxidation state, and the residual adsorbed water is ≤5wt%.
[0041] 3. Elimination of micro-moisture in electrode sheets: After the electrode sheets are formed, they undergo a second heat treatment in an inert atmosphere to completely eliminate moisture reabsorption during the coating process, resulting in an electrode sheet moisture content of ≤100ppm.
[0042] This method overcomes the contradiction between "water removal and structural stability" in Prussian blue materials. The resulting cathode material retains >95% capacity after 100 cycles at 0.5C, solving the long-standing industry pain points of difficult water removal and performance degradation after water removal. The process is simple and safe, possessing industrial-scale application value. A detailed introduction follows.
[0043] See Figure 1 This is a schematic flowchart illustrating a method for preparing a Prussian blue sodium-ion battery positive electrode sheet according to an embodiment of this application. Figure 1 As shown, it mainly includes the following steps.
[0044] Step S101: Under inert gas protection, solution A containing ferrous salt and chelating agent, and solution B containing sodium ferrocyanide and reducing agent are simultaneously added dropwise to solution C containing auxiliary salt and surfactant. The reaction is carried out at 25℃~40℃ for 12~48h. After centrifugation and washing, the solution is dried under vacuum at 130-160℃ to obtain primary Prussian blue material.
[0045] Specifically, ferrous salt and chelating agent are added, and the mixture is stirred for a certain time to form solution A; sodium ferrocyanide and reducing agent are added, and the mixture is stirred for a certain time to form solution B; auxiliary salt and surfactant are added, and the mixture is stirred for a certain time to form solution C. Solutions A and B are slowly added dropwise to solution C using a peristaltic pump, while stirring under continuous inert gas protection. After the addition of solutions A and B is complete, stirring continues under inert gas protection for a certain time to complete the reaction. Figure 2 As shown.
[0046] In the embodiments of this application, the inert gas can be nitrogen or argon, or a combination thereof. The vacuum drying temperature after centrifugal washing can be any value between 130-160°C. For example, 130°C, 140°C, 150°C, 160°C, etc. The applicant has found through research that when the vacuum drying temperature after centrifugal washing is less than 130°C, the removal rate of water of crystallization is less than 50%; when the vacuum drying temperature after centrifugal washing is greater than 160°C, it will lead to the oxidation of Fe2+. Therefore, the vacuum drying temperature after centrifugal washing is limited to the above-mentioned value range.
[0047] In one possible implementation, the molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B is 0.8–1.5, and the volume ratio of solution A to solution B is 0.8–1.2. Those skilled in the art can select any value within the above range according to actual needs. For example, the molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B is 1, and the volume ratio of solution A to solution B is 1. The applicant has found through research that if the molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B is too small, or the volume ratio of solution A to solution B is too small, the reaction may be incomplete; if the molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B is too large, or the volume ratio of solution A to solution B is too large, nucleation may be accelerated, leading to defects. Therefore, the molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B, and the volume ratio of solution A to solution B, are limited to the above-mentioned range.
[0048] In one possible implementation, the concentration of the ferrous salt is 0.1–0.5 mol / L, the concentration of the chelating agent is 1–1.5 mol / L, the concentration of sodium ferrocyanide is 0.1–0.5 mol / L, and the concentration of the reducing agent is 1–2 mol / L. Those skilled in the art can select any values within the above range according to actual needs.
[0049] In one possible implementation, the ferrous salt is any one or a combination of ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous chloride tetrahydrate, ferrous sulfate heptahydrate, ferrous nitrate hexahydrate, and ferrous acetate tetrahydrate; the chelating agent is any one or a combination of sodium citrate, ethylenediaminetetraacetic acid, and sodium carboxymethyl cellulose; the reducing agent is ascorbic acid; the auxiliary salt is sodium chloride; and the surfactant is polyvinylpyrrolidone (PVP). For example, solution A contains 0.1 mol / L ferrous salt and 0.25 mol / L sodium citrate; solution B contains 0.1 mol / L sodium ferrocyanide and 10 g / L ascorbic acid; and solution C contains 30 g / L sodium chloride and 10 g / L polyvinylpyrrolidone.
[0050] In one possible implementation, centrifugal washing includes multiple washes using deionized water and anhydrous ethanol, with the deionized water centrifugation speed at 10,000-12,000 rpm and the anhydrous ethanol centrifugation speed at 7,000-8,000 rpm. The applicant's research found that if the centrifugation speed using deionized water is below 10,000 rpm or the anhydrous ethanol centrifugation speed is below 7,000 rpm, the material and the cleaning solution cannot be completely separated; if the centrifugation speed using deionized water is above 12,000 rpm or the anhydrous ethanol centrifugation speed is above 8,000 rpm, the material and the centrifuge tube wall are difficult to separate. Therefore, the centrifugation speed is limited to the above-mentioned range.
[0051] In one possible implementation, the peristaltic pumps for adding solutions A and B drop at a rate of 10–50 mL / h. Solution C is stirred mechanically at a speed of 200–300 r / min.
[0052] In one possible implementation, the volume ratio of solution A, solution B, and solution C is 1:1:2. The solvents for solutions A, B, and C can be N-methylpyrrolidone (NMP) or water.
[0053] Step S102: Heat-treat the primary Prussian blue material in a reducing gas at 130-160℃ to obtain the Prussian blue material.
[0054] In this embodiment, the reducing gas can be an argon-hydrogen mixture. The H2 concentration in the argon-hydrogen mixture ranges from 5% to 10%. Those skilled in the art can select any value within this range according to actual needs. For example, 5%, 6%, 7%, 8%, 9%, 10%, etc. The applicant has discovered through research that an H2 concentration < 5% leads to insufficient reduction, while an H2 concentration > 10% triggers material decomposition. Therefore, the H2 concentration is limited to the aforementioned range.
[0055] In the embodiments of this application, the heat treatment temperature of the primary Prussian blue material in a reducing gas can be any value between 130-160°C. For example, 130°C, 140°C, 150°C, 160°C, etc. The applicant has found through research that when the heat treatment temperature is below 130°C, the adsorbed water residue is greater than 3 wt%; when the heat treatment temperature is above 160°C, it leads to lattice collapse. Therefore, the heat treatment temperature is limited to the above-mentioned range.
[0056] The Prussian blue material prepared by this step has a lattice water content of ≤5wt% and an adsorbed water content of ≤5wt%.
[0057] Step S103: Prussian blue material is used to make the positive electrode sheet for sodium-ion batteries, and then subjected to a second heat treatment at 130-160℃ in an inert gas to make the water content of the positive electrode sheet for sodium-ion batteries ≤100ppm.
[0058] Specifically, a positive electrode slurry comprising Prussian blue material, a conductive agent, and a binder is coated onto a positive electrode current collector and dried in a vacuum drying oven to obtain a sodium-ion battery positive electrode sheet. The conductive agent is one or a mixture of at least two of carbon black, Ketjen black, and conductive carbon black; the binder is one or a mixture of at least two of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.
[0059] In one possible implementation, the mass ratio of Prussian blue material, conductive agent, and binder is 7:2:1. It is understood that those skilled in the art can adjust the mass ratio of Prussian blue material, conductive agent, and binder appropriately according to actual needs, and the embodiments of this application do not impose specific limitations in this regard.
[0060] In this embodiment, the inert gas can be nitrogen or argon, or a combination thereof. The temperature for the secondary heat treatment in the inert gas can be any value between 130-160°C, such as 130°C, 140°C, 150°C, or 160°C. The applicant has found that when the secondary heat treatment temperature is below 130°C, the electrode contains excessive moisture; when the temperature is above 160°C, the binder carbonizes. Therefore, the temperature for the secondary heat treatment is limited to the above-mentioned range. The sodium-ion battery positive electrode prepared using this step has a moisture content ≤100ppm.
[0061] This application embodiment reduces the water content of the Prussian blue sodium-ion battery positive electrode sheet through a multi-step dehydration method. The first step uses an improved co-precipitation method that introduces an inert gas during the preparation process to prepare primary Prussian blue material. By isolating the material from air, the Fe content during the synthesis process is reduced. 2+ The degree of oxidation decreases, reducing the hydrophilicity of the metal center and weakening its coordination ability with water molecules. This also causes lattice contraction, reducing the sites occupied by water molecules and thus lowering the lattice water content introduced during the synthesis process. The second step, dehydration, involves using a tube furnace to introduce reducing gas for high-temperature treatment of the Prussian blue primary material. The reducing gas reacts with the Fe in the material... 3+ Redox reaction 2Fe 3+ +H2→2Fe 2+ +2H + H + OH groups - reaction Fe 3+ -OH - +H + →Fe 3+ +H2O, the generated water molecules are more easily evaporated at high temperatures, while Fe 3+ Reduced to Fe 2+Afterward, it no longer requires additional water molecules to meet its coordination number requirements, further reducing the water content in the Prussian blue material. The third step of dehydration involves high-temperature treatment of the positive electrode sheet under an inert gas atmosphere to reduce the water content on the electrode sheet. The principle is to remove adsorbed water from the electrode surface a second time by high-temperature treatment while keeping the positive electrode material in an oxygen-free and anhydrous environment in its unchanged oxidation state. The three steps of dehydration are performed in the order of material synthesis-electrode preparation. Compared with traditionally prepared Prussian blue materials, which inevitably contain lattice water and adsorbed water, resulting in low specific capacity, poor rate performance, and poor cycle stability, the multi-step dehydration method disclosed in this application can effectively reduce the water content in the Prussian blue material, reduce lattice defects in the system, and increase sodium content. The Prussian blue material prepared by the multi-step dehydration method exhibits excellent electrochemical stability when applied as a positive electrode material for sodium-ion batteries.
[0062] Corresponding to the above embodiments, this application also provides a Prussian blue sodium-ion battery positive electrode sheet, which is prepared by the above method, wherein the lattice water content is ≤5wt%, the adsorbed water content is ≤5wt%, and the electrode sheet water content is ≤100ppm.
[0063] It should be noted that the specific details of the embodiments of this application can be found in the description above, and will not be repeated here for the sake of brevity.
[0064] Corresponding to the above embodiments, this application also provides a sodium-ion battery, which includes the above-mentioned positive electrode sheet.
[0065] It should be noted that the specific details of the embodiments of this application can be found in the description above, and will not be repeated here for the sake of brevity.
[0066] To facilitate understanding, the technical solutions provided in this application will be described in detail below with reference to some specific embodiments.
[0067] Example 1
[0068] Add 1.4041g FeSO4·7H2O and 3.731g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 1.5g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h. -1 The solutions A and B were added dropwise to the solution C at a certain rate. The mixture was stirred for 12 hours and allowed to stand for 24 hours. The resulting product was centrifuged, washed three times with deionized water and anhydrous ethanol, and then vacuum dried at 130°C for 24 hours.
[0069] The obtained initial dehydrated sample was treated with reducing gas at 130°C in a tube furnace to obtain dehydrated sample 1.
[0070] After dehydration, sample 1, conductive carbon black (Superp), and polyvinylidene fluoride (PVDF) binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 130°C for 12 hours to obtain the positive electrode sheet.
[0071] The obtained electrode was treated at 130℃ under an inert gas atmosphere to obtain a dehydrated electrode. A coin cell was assembled using a sodium metal sheet as the negative electrode, GradeGF / A glass fiber as the separator, and 1 mol / L NaClO4 / EC+DEC (EC:DEC = 1:1) containing 5 wt% additive FEC as the electrolyte. Constant current charge-discharge tests were conducted, with a test voltage range of 2-4.2V.
[0072] Example 2
[0073] Add 1.4041g FeSO4·7H2O and 3.731g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 1.5g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h. -1 The solutions A and B were added dropwise to the solution C at a certain rate. The mixture was stirred for 12 hours and allowed to stand for 24 hours. The resulting product was centrifuged, washed three times with deionized water and anhydrous ethanol, and then vacuum dried at 130°C for 24 hours.
[0074] The obtained preliminary dehydrated sample was subjected to high-temperature treatment at 140°C by passing reducing gas through a tube furnace to obtain dehydrated sample 2.
[0075] After dehydration, sample 2, Superp and polyvinylidene fluoride binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 130℃ for 12 hours to obtain the positive electrode sheet.
[0076] The obtained electrode sheets were treated at high temperature under an inert gas atmosphere to obtain dehydrated electrode sheets. Using sodium metal sheets as the negative electrode, GradeGF / A glass fiber as the separator, and 1 mol / L NaClO4 / EC+DEC (EC:DEC = 1:1) containing 5 wt% additive FEC as the electrolyte, coin cells were assembled and subjected to constant current charge-discharge tests. The test voltage range was 2-4.2V.
[0077] Example 3
[0078] Add 1.4041g FeSO4·7H2O and 3.731g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 1.5g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h. -1 The solutions A and B were added dropwise to the solution C at a certain rate. The mixture was stirred for 12 hours and allowed to stand for 24 hours. The resulting product was centrifuged, washed three times with deionized water and anhydrous ethanol, and then vacuum dried at 130°C for 24 hours.
[0079] The obtained preliminary dehydrated sample was subjected to high-temperature treatment at 150°C by passing reducing gas through a tube furnace to obtain dehydrated sample 3.
[0080] After dehydration, sample 3, Superp, and polyvinylidene fluoride binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 150°C for 12 hours to obtain the positive electrode sheet.
[0081] The obtained electrode sheets were treated at high temperature under an inert gas atmosphere to obtain dehydrated electrode sheets. Using sodium metal sheets as the negative electrode, GradeGF / A glass fiber as the separator, and 1 mol / L NaClO4 / EC+DEC (EC:DEC = 1:1) containing 5 wt% additive FEC as the electrolyte, coin cells were assembled and subjected to constant current charge-discharge tests. The test voltage range was 2-4.2V.
[0082] Example 4
[0083] Add 1.4041g FeSO4·7H2O and 3.731g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 1.5g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h. -1 The solutions A and B were added dropwise to the solution C at a certain rate. The mixture was stirred for 12 hours and allowed to stand for 24 hours. The resulting product was centrifuged, washed three times with deionized water and anhydrous ethanol, and then vacuum dried at 130°C for 24 hours.
[0084] The obtained preliminary dehydrated sample was treated with reducing gas at 130°C in a tube furnace to obtain dehydrated sample 4.
[0085] After dehydration, sample 4, Superp, and polyvinylidene fluoride binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 130°C for 12 hours to obtain the positive electrode sheet.
[0086] The obtained electrode was treated at 140°C under an inert gas atmosphere to obtain a dehydrated electrode. A coin cell was assembled using a sodium metal sheet as the negative electrode, GradeGF / A glass fiber as the separator, and a 1 mol / L NaClO4 / EC+DEC electrolyte containing 5 wt% additive FEC (EC:DEC = 1:1) for constant current charge-discharge testing. The test voltage range was 2-4.2V.
[0087] Comparative Example 1
[0088] Add 1.4041g FeSO4·7H2O and 3.2631g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 3g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h. -1 Solutions A and B were added dropwise to solution C at a certain rate, stirred for 12 hours, allowed to stand for 24 hours, and the resulting product was centrifuged, washed three times each with deionized water and anhydrous ethanol, and then vacuum dried at 130°C for 24 hours. Comparative sample 1 was obtained.
[0089] After dehydration, the control sample 1, Superp and polyvinylidene fluoride binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 130℃ for 12 hours to obtain the positive electrode sheet.
[0090] A coin cell was assembled using sodium metal sheet as the negative electrode, GradeGF / A glass fiber as the separator, and 1mol / L NaClO4 / EC+DEC (EC:DEC = 1:1) containing 5wt% additive FEC as the electrolyte. Constant current charge-discharge tests were conducted, with the test voltage range being 2-4.2V.
[0091] Comparative Example 2
[0092] Add 1.4041g FeSO4·7H2O and 3.2631g Na3C6H5O7·2H2O to 50mL of deionized water and stir at 25℃ for 2h to obtain solution A. Add 2.4447g Na4Fe(CN)6·10H2O and 1g ascorbic acid to 50mL of deionized water and stir at 25℃ for 2h to obtain solution B. Add 3g NaCl and 1g polyvinylpyridinium to 100mL of deionized water to obtain solution C. Dissolve the solutions using a peristaltic pump at a rate of 10mL / h.-1 Solutions A and B were added dropwise to solution C at a certain rate, stirred for 12 hours, allowed to stand for 24 hours, and the resulting product was centrifuged, washed three times each with deionized water and anhydrous ethanol, and then vacuum dried at 140°C for 24 hours. This yielded control sample 2.
[0093] After dehydration, the control sample 2, Superp and polyvinylidene fluoride binder were mixed in a ratio of 7:2:1 to form a slurry, which was then coated onto aluminum foil and vacuum dried in a vacuum oven at 140℃ for 12 hours to obtain the positive electrode sheet.
[0094] A coin cell was assembled using sodium metal sheet as the negative electrode, GradeGF / A glass fiber as the separator, and 1mol / L NaClO4 / EC+DEC (EC:DEC = 1:1) containing 5wt% additive FEC as the electrolyte. Constant current charge-discharge tests were conducted, with the test voltage range being 2-4.2V.
[0095] The prepared materials of the examples and comparative examples were characterized and analyzed respectively. Figure 3 Scanning electron microscopy results showed that the material after water removal had a small size, indicating a large specific surface area and good diffusion capacity. Figure 4 , 5 The thermogravimetric analysis results of the examples and comparative examples show that the water content of the Prussian blue material was significantly reduced after water removal. Sodium-ion batteries were assembled using the examples and comparative examples as cathode materials, and the electrochemical test results are attached. Figure 6 As shown, it is evident that the embodiments exhibit good stability, demonstrating that this application has successfully prepared a dehydrated Prussian blue cathode material.
[0096] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.
Claims
1. A method for preparing a positive electrode sheet for a Prussian blue sodium-ion battery, characterized in that, include: Under inert gas protection, solution A containing ferrous salt and chelating agent, and solution B containing sodium ferrocyanide and reducing agent are simultaneously added dropwise to solution C containing auxiliary salt and surfactant. The reaction is carried out at 25℃~40℃ for 12~48h. After centrifugation and washing, the solution is dried under vacuum at 130-160℃ to obtain primary Prussian blue material. The primary Prussian blue material was heat-treated in a reducing gas at 130-160°C to obtain the Prussian blue material. The Prussian blue material is used to make a positive electrode sheet for a sodium-ion battery, and then subjected to a second heat treatment at 130-160°C in an inert gas to make the water content of the positive electrode sheet ≤100ppm.
2. The method according to claim 1, characterized in that, The molar ratio of ferrous salt in solution A to sodium ferrocyanide in solution B is 0.8–1.5, and the volume ratio of solution A to solution B is 0.8–1.
2.
3. The method according to claim 1, characterized in that, The concentration of the ferrous salt is 0.1–0.5 mol / L, the concentration of the chelating agent is 0.1–1.5 mol / L, the concentration of the sodium ferrocyanide is 0.1–0.5 mol / L, and the concentration of the reducing agent is 1–2 mol / L.
4. The method according to claim 1, characterized in that, The ferrous salt is any one or a combination of ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous chloride tetrahydrate, ferrous sulfate heptahydrate, ferrous nitrate hexahydrate, and ferrous acetate tetrahydrate. The chelating agent is any one or a combination of sodium citrate, ethylenediaminetetraacetic acid, and sodium carboxymethyl cellulose. The reducing agent is ascorbic acid; The auxiliary salt is sodium chloride; The surfactant is polyvinylpyrrolidone.
5. The method according to claim 1, characterized in that, The centrifugal washing includes: The sample was washed multiple times by centrifugation with deionized water and anhydrous ethanol. The centrifugation speed with deionized water was 10,000-12,000 rpm, and the centrifugation speed with anhydrous ethanol was 7,000-8,000 rpm.
6. The method according to claim 1, characterized in that, The process of fabricating the Prussian blue material into a positive electrode sheet for a sodium-ion battery includes: A positive electrode slurry comprising the Prussian blue material, a conductive agent, and a binder is coated onto a positive electrode current collector and dried in a vacuum drying oven to obtain a sodium-ion battery positive electrode sheet.
7. The method according to claim 6, characterized in that, The conductive agent is one or a mixture of at least two of carbon black, Ketjen black, and conductive carbon black; the binder is one or a mixture of at least two of polyvinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.
8. The method according to claim 6, characterized in that, The mass ratio of the Prussian blue material, the conductive agent, and the binder is 7:2:
1.
9. A Prussian blue sodium-ion battery positive electrode, characterized in that, Prepared by the method according to any one of claims 1-8, wherein the lattice water content is ≤5wt%, the adsorbed water content is ≤5wt%, and the electrode water content is ≤100ppm.
10. A sodium-ion battery, characterized in that, It includes the positive electrode sheet as described in claim 9.