A sodium vanadium oxyfluorophosphate composite material, a preparation method thereof and a sodium ion battery
By constructing mesocrystalline sodium fluorophosphate nanocrystal units and coating them with carbon, the problems of poor electronic conductivity and slow ion transport of sodium fluorophosphate composite materials were solved, thus achieving a high-efficiency improvement in sodium-ion battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2026-03-18
- Publication Date
- 2026-06-19
AI Technical Summary
Existing sodium fluorophosphate composite materials suffer from poor electronic conductivity and long ion transport distance due to large single crystal particles, which leads to increased polarization and decreased efficiency in sodium-ion batteries. Furthermore, the cathode material is prone to volume changes and secondary particle breakage and shedding during cycling.
A composite material consisting of single-crystal sodium fluorophosphate nanocrystal units self-assembled and carbon-coated on the surface of the nanocrystals by low molecular weight ligands, combined with high-temperature annealing in-situ carbon coating, is constructed.
It improves the electronic conductivity and ion transport rate of the material, reduces the specific surface area, enhances the structural stability of the material, improves the overall electrochemical performance of the electrode material, and increases the capacity and cycle stability of sodium-ion batteries.
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Figure CN122246089A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of sodium-ion battery cathode materials technology, and in particular to a sodium fluorophosphate vanadium oxyvanadium composite material, its preparation method, and a sodium-ion battery. Background Technology
[0002] In recent years, electrochemical energy storage technology, due to its high power characteristics, has shown great application potential in military fields such as high-energy microwaves, high-energy lasers, electromagnetic guns, and electromagnetic catapults. Sodium-ion batteries, due to their similarity to lithium-ion batteries in structure, charging and discharging principles, and manufacturing processes, as well as their abundant and inexpensive raw material sources, good safety, and excellent low-temperature performance, have received strong support from industrial capital and are currently being applied in areas such as two-wheeled electric vehicles, low-speed electric vehicles, home energy storage, and commercial energy storage. At the same time, sodium-ion batteries have demonstrated unique advantages in high-power applications, simultaneously achieving high safety, high energy density, and low cost.
[0003] Among current sodium-ion battery cathode materials, the NASICON-structured polyanionic sodium vanadium fluorophosphate cathode material has attracted widespread attention due to its high operating voltage and theoretical specific capacity, high energy density, good structural stability, and ion transport efficiency. Single-crystal polyanionic cathode materials can further improve the structural stability and cycle performance under high-power charge-discharge conditions. However, the larger the single-crystal particle volume in polyanionic cathode materials, the longer the distance electrons and ions travel within the crystal, leading to a significant decrease in the material's ionic and electronic conductivity. This results in a substantial drop in the overall ion transport efficiency of the battery and an increase in polarization voltage, causing a significant decline in the capacity, rate capability, and cycle performance of sodium-ion batteries.
[0004] Therefore, there is an urgent need to design and develop new high-performance single-crystal sodium vanadium fluorophosphate cathode materials. Summary of the Invention
[0005] This application provides a sodium vanadium fluorophosphate composite material, its preparation method, and a sodium-ion battery, aiming to solve the problems of increased polarization and decreased efficiency of existing sodium vanadium fluorophosphate composite materials due to poor electronic conductivity of large single crystal particles and long ion transport distance, as well as the problem of secondary particle breakage and shedding caused by easy volume changes of the positive electrode material during sodium-ion battery cycling.
[0006] To achieve the above objectives, the present application adopts the following technical solution.
[0007] A first aspect of this application provides a sodium fluorophosphate oxyvanadium composite material, comprising a mesocrystalline sodium fluorophosphate oxyvanadium and an amorphous carbon layer coating the outer layer of the sodium fluorophosphate oxyvanadium.
[0008] The mesocrystalline sodium fluorophosphate is formed by the self-assembly of small sodium fluorophosphate nanocrystal units coated with multiple low molecular weight ligands. After annealing, the low molecular weight ligands form carbon coating on the surface of the nanocrystal units.
[0009] A second aspect of this application provides a method for preparing the above-mentioned sodium vanadium fluorophosphate composite material, comprising:
[0010] S1, add vanadium source, reducing agent, and low molecular weight ligand to deionized water, heat and stir to obtain solution A; dissolve sodium source, phosphorus source and fluorine source in water to obtain solution B;
[0011] S2, mix solution B and solution A thoroughly, and then carry out a hydrothermal reaction to obtain sodium vanadium fluorophosphate powder with a mesocrystalline structure;
[0012] S3, the sodium fluorophosphate oxyvanadium powder and carbon source are wet-mixed and dried, and the resulting mixture is calcined under an inert atmosphere to obtain sodium fluorophosphate oxyvanadium composite material.
[0013] Preferably, the low molecular weight ligand is at least one of formic acid / formate, acetic acid / acetate, propionic acid, butyric acid, benzoic acid / benzoate, ethylamine, propylamine, butylamine, hexylamine, ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, gluconic acid, malonic acid, succinic acid, phthalic acid, catechol, dopamine, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), hexamethylenetetramine (HMTA), glycine, alanine, aspartic acid, glutamic acid, lysine, or dodecylphenoxy polyoxyethylene ether.
[0014] Preferably, the reducing agent includes at least one of oxalic acid, malic acid, tartaric acid, or citric acid;
[0015] The vanadium source includes at least one of vanadium pentoxide, ammonium metavanadate, vanadium tetroxide, vanadium trioxide, vanadium tetrahydroxide, vanadium oxalate, vanadium oxysulfate, vanadium oxalate, vanadium trichloride, vanadium acetylacetonate, or vanadium acetylacetonate.
[0016] The sodium source includes at least one of sodium fluoride, sodium chloride, sodium carbonate, sodium hydroxide, sodium sulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or sodium nitrate.
[0017] The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or ammonium phosphate.
[0018] The fluorine source is at least one or more of sodium fluoride, calcium fluoride, ammonium fluoride, potassium fluoride, and magnesium fluoride;
[0019] The carbon source includes at least one of sucrose, ascorbic acid, glucose, citric acid, fructose, pitch, acetylene black, carbon nanotubes, graphene, carbon fibers, mesophase carbon microspheres, resin, or starch.
[0020] Preferably, the amounts of vanadium source, sodium source, phosphorus source and fluorine source in S1 are in the atomic ratio of Na:V:P:F=3:x:2:1, where 1.5<x<2.
[0021] Preferably, the amount of the low molecular weight ligand added is 0.1 to 30 wt% of the total amount of vanadium source, sodium source, phosphorus source and fluorine source.
[0022] Preferably, the amount of carbon source used is 0.1% to 20 wt% of the mass of sodium fluorophosphate.
[0023] Preferably, the heating temperature in S1 is 40~90°C;
[0024] The hydrothermal reaction described in S2 is carried out at a temperature of 100~250℃ for a time of 1~36 h;
[0025] The calcination temperature described in S3 is 350℃~800℃, and the calcination time is 1min~20h.
[0026] A third aspect of this application provides a positive electrode material for sodium-ion batteries, comprising the above-described sodium fluorophosphate oxyvanadium composite material or the sodium fluorophosphate oxyvanadium composite material prepared by the above-described preparation method.
[0027] In a fourth aspect, this application provides a sodium-ion battery, wherein the positive electrode material is the aforementioned positive electrode material.
[0028] Compared with the prior art, the beneficial effects of this application are as follows:
[0029] This application obtains a superlattice mesocrystalline sodium fluorophosphate oxyvanadium material assembled from nano-single crystals via a hydrothermal method, and combines it with a high-temperature annealing in-situ carbon coating method to obtain a sodium fluorophosphate oxyvanadium composite material with single-crystal unit carbon coating and large-particle mesocrystalline secondary carbon coating. The preparation process is simple, easy to scale up, and the product has excellent performance.
[0030] This application improves the electronic conductivity of both the individual nanocrystal surfaces and the large mesocrystalline particles by simultaneously constructing a sodium vanadium fluorophosphate composite material with carbon coating on single-crystal nanounits and secondary carbon coating on large mesocrystalline particles. It also reduces the specific surface area of the material, forming rapid ion transport channels within the single crystals and effectively improving the overall electrochemical performance of the electrode material. First, under the action of a low-molecular-weight ligand, this application achieves the self-assembly of nanocrystals of the same shape to form a mesocrystalline superlattice structure. The ligand coordinated on the surface of the nanocrystals forms a carbon-coated structure on the nanocrystal surface after annealing, constructing orderly electron and ion transport channels within the superlattice structure, achieving rapid electron and ion transport within the mesocrystalline structure and effectively improving the ion dynamics characteristics of the material. Second, this application uses a low-molecular-weight ligand to control the size and morphology of the nanocrystal units during synthesis, thereby adjusting the electron / ion transport distance and effectively improving the ion dynamics characteristics of the material. Third, the sodium vanadium fluorophosphate nanocrystal particles of this application exhibit small volume changes during charge and discharge, avoiding the breakage and shedding phenomena that occur during the cycling of polycrystalline materials, effectively improving the structural stability of the material. Fourth, the well-defined grain boundary channels of the sodium vanadium fluorophosphate composite material synthesized in this application only transport electrons and ions, preventing electrolyte from entering, thus effectively reducing the specific surface area of the material and the formation of the positive electrode side reaction CEI film. Attached Figure Description
[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0032] Figure 1 SEM image of the sodium vanadium fluorophosphate composite material prepared in Example 1;
[0033] Figure 2 SEM image of the sodium vanadium fluorophosphate composite material prepared in Example 2;
[0034] Figure 3 SEM image of the bulk single-crystal sodium vanadium fluorophosphate prepared for comparison;
[0035] Figure 4 The TEM cross-sectional view of the sodium vanadium fluorophosphate composite material prepared in Example 2;
[0036] Figure 5 The images show a comparison of the XRD patterns of the sodium fluorophosphate oxyvanadium composite materials prepared in Examples 1-4 and the bulk single-crystal sodium fluorophosphate oxyvanadium composite materials prepared in the comparative examples. Detailed Implementation
[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0038] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.
[0039] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.
[0040] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.
[0041] 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" and "the" as 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.
[0042] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0043] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0044] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0045] This application provides a sodium fluorophosphate oxyvanadium composite material, which includes a mesocrystalline sodium fluorophosphate oxyvanadium and an amorphous carbon layer covering the outer layer of the sodium fluorophosphate oxyvanadium.
[0046] The mesocrystalline sodium fluorophosphate is formed by the self-assembly of multiple carbon-coated small sodium fluorophosphate nanocrystal units.
[0047] This application utilizes low molecular weight ligands to control crystal growth and form nano-single crystal units, constructing a sodium vanadium fluorophosphate composite material with single-crystal unit carbon coating and large-particle mesocrystalline secondary carbon coating. This improves the electronic conductivity of the surface of individual nanocrystals and large-particle mesocrystalline particles, reduces the specific surface area of the material, and forms a rapid ion transport channel inside the single crystal, effectively improving the comprehensive electrochemical performance of the electrode material.
[0048] This application obtains a superstructured mesocrystalline sodium fluorophosphate oxyvanadium material assembled from nanocrystals via a hydrothermal method, and combines this with a high-temperature annealing in-situ carbon coating method to obtain a sodium fluorophosphate oxyvanadium composite material with single-crystal unit carbon coating and large-particle mesocrystalline secondary carbon coating. It features a carbon-coated nanocrystal self-assembled structure, where the nanocrystals are single-particle columnar or plate-like sodium fluorophosphate oxyvanadium crystals, the outer shell of the nanocrystals is amorphous carbon, and the ordered arrangement of the nanocrystals forms a mesocrystalline superlattice structure, coated with an amorphous carbon layer. The preparation process is simple, easily scalable, and the product exhibits superior performance. The specific preparation method includes:
[0049] S1, add vanadium source, reducing agent, and low molecular weight ligand to deionized water, heat and stir at 40~90℃ for 10~60 min to obtain solution A; dissolve sodium source, phosphorus source and fluorine source in water to obtain solution B;
[0050] In this application, the vanadium source is selected from at least one of vanadium pentoxide, ammonium metavanadate, vanadium tetroxide, vanadium trioxide, vanadium tetrahydroxide, vanadium oxalate, vanadium oxysulfate, vanadium oxalate, vanadium trichloride, vanadium acetylacetonate, or vanadium acetylacetonate.
[0051] The reducing agent is selected from at least one of oxalic acid, malic acid, tartaric acid, or citric acid.
[0052] The low molecular weight ligand is at least one of formic acid / formate, acetic acid / acetate, propionic acid, butyric acid, benzoic acid / benzoate, ethylamine, propylamine, butylamine, hexylamine, ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, gluconic acid, malonic acid, succinic acid, phthalic acid, catechol, dopamine, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), hexamethylenetetramine (HMTA), glycine, alanine, aspartic acid, glutamic acid, lysine, or dodecylphenoxy polyoxyethylene ether.
[0053] The sodium source includes at least one of sodium fluoride, sodium chloride, sodium carbonate, sodium hydroxide, sodium sulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or sodium nitrate.
[0054] The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or ammonium phosphate.
[0055] The fluorine source is at least one or more of sodium fluoride, calcium fluoride, ammonium fluoride, potassium fluoride, and magnesium fluoride.
[0056] In this application, the amounts of the vanadium source, sodium source, phosphorus source and fluorine source are in the atomic ratio of Na:V:P:F=3:x:2:1, where 1.5 < x < 2; the amount of the low molecular weight ligand added accounts for 0.1~30 wt% of the total amount of the vanadium source, sodium source, phosphorus source and fluorine source.
[0057] S2, mix solution B and solution A thoroughly, and then carry out a hydrothermal reaction at 100~250℃ for 1~36h to obtain sodium vanadium fluorophosphate powder with mesocrystalline structure;
[0058] S3, the sodium fluorophosphate oxyvanadium powder and carbon source are wet-mixed and dried, and the resulting mixture is calcined at 350℃~800℃ for 1min~20h under an inert atmosphere to obtain sodium fluorophosphate oxyvanadium composite material.
[0059] In this application, the carbon source includes at least one of sucrose, ascorbic acid, glucose, citric acid, fructose, pitch, acetylene black, carbon nanotubes, graphene, carbon fibers, mesophase carbon microspheres, resin, or starch. The amount of carbon source used is 0.1% to 20 wt% of the mass of sodium vanadium fluorophosphate.
[0060] The sodium fluorophosphate oxyvanadium composite material prepared in this application achieves the self-assembly of identical-shaped nanocrystals into a mesocrystalline superlattice structure under the action of a low-molecular-weight ligand. The ligand coordinated on the surface of the nanocrystals forms a carbon-coated structure on the surface of the nanocrystals after annealing, constructing regular and ordered electron and ion transport channels within the superlattice structure. This enables rapid electron and ion transport within the mesocrystalline structure, effectively improving the ion dynamics characteristics of the material. By controlling the size and morphology of the nanocrystal units during synthesis using a low-molecular-weight ligand, and thus adjusting the electron / ion transport distance, the ion dynamics characteristics of the material can be effectively improved. The sodium fluorophosphate oxyvanadium nanocrystal particles of this application exhibit small volume changes during charge and discharge, avoiding the breakage and shedding phenomena that occur during the cycling of polycrystalline materials, effectively improving the structural stability of the material. Furthermore, the regular grain boundary channels of the sodium fluorophosphate oxyvanadium composite material synthesized in this application only transport electrons and ions, preventing electrolyte entry and effectively reducing the specific surface area of the material and the formation of the positive electrode side reaction CEI film. Based on these excellent properties, the sodium fluorophosphate oxyvanadium composite material of this application can be used as a positive electrode material for sodium-ion batteries.
[0061] This application also provides a sodium-ion battery, the positive electrode material of which is the sodium vanadium fluorophosphate composite material of this application. Based on the high conductivity, fast electron and ion transport, and high structural stability of the sodium vanadium fluorophosphate composite material of this application, the sodium-ion battery of this application exhibits high efficiency and high cycle stability.
[0062] The present application will be further illustrated by the following examples.
[0063] Example 1
[0064] This embodiment provides a sodium vanadium fluorophosphate composite material, the preparation method of which includes:
[0065] S1, weigh 0.004 mol of ammonium metavanadate and 0.002 mol of citric acid, add them to 50 ml of deionized water, and stir at 400 rpm for 1 h in an 80 °C water bath; then add 0.0004 mol of ethylenediaminetetraacetic acid to obtain solution A;
[0066] 0.002 mol of sodium fluoride and 0.004 mol of sodium dihydrogen phosphate were weighed and added to 30 ml of deionized water. The solution was obtained by magnetic stirring at a rotor speed of 400 r / min.
[0067] S2, mix solutions A and B, stir at room temperature for 1 hour to obtain a precursor solution; transfer the precursor solution to a hydrothermal reactor, use water as a solvent, heat to 160℃ and hold at that temperature for 10 hours, then cool naturally to room temperature to obtain superlattice mesocrystalline sodium fluorophosphate vanadium oxyfluoride (Na3V2O2(PO4)2F) assembled from lamellar grain units.
[0068] S3: The mesocrystalline sodium fluorophosphate crystals of S2 and 3 wt% glucose were mixed in a ball mill and then dried in an oven. The mixture was heated to 550°C at a heating rate of 10°C / min under a nitrogen atmosphere, held at the temperature for 30 min, and then naturally cooled to room temperature to obtain the sodium fluorophosphate composite material, which is a superlattice mesocrystalline sodium fluorophosphate / carbon composite material formed by the self-assembly of amorphous carbon-coated lamellar crystalline units.
[0069] Example 2
[0070] This embodiment provides a sodium vanadium fluorophosphate composite material, the preparation method of which includes:
[0071] S1, weigh 0.0015 mol of vanadium pentoxide and 0.015 mol of oxalic acid, add them to 50 ml of deionized water, and stir in an 80 °C water bath at 400 rpm for 1 h; then add 0.0003 mol of sodium benzoate to obtain solution A;
[0072] 0.002 mol of sodium fluoride and 0.004 mol of sodium dihydrogen phosphate were weighed and added to 30 ml of deionized water. The solution was obtained by magnetic stirring at a rotor speed of 400 r / min.
[0073] S2, mix solutions A and B, stir at room temperature for 1 hour to obtain a precursor solution; transfer the precursor solution to a hydrothermal reactor, use water as a solvent, heat to 250℃ and hold at that temperature for 1 hour, then cool naturally to room temperature to obtain superlattice mesocrystalline sodium vanadium fluorophosphate (Na3V2O2(PO4)2F) assembled from lamellar grain units.
[0074] S3: The mesocrystalline sodium fluorophosphate crystals of S2 and citric acid at 1 wt% of their mass are mixed in a ball mill and then dried in an oven. The mixture is heated to 750°C at a heating rate of 2°C / min under a nitrogen atmosphere, held at the temperature for 1 min, and then naturally cooled to room temperature to obtain the sodium fluorophosphate composite material, which is a superlattice mesocrystalline sodium fluorophosphate / carbon composite material formed by the self-assembly of amorphous carbon-coated lamellar grain units.
[0075] Example 3
[0076] This embodiment provides a sodium vanadium fluorophosphate composite material, the preparation method of which includes:
[0077] S1, weigh 0.0035 mol of acetylacetone vanadium oxide and 0.00175 mol of malic acid, add them to 50 ml of deionized water, and stir at 300 rpm for 1 h in an 80 °C water bath; then add 0.0003 mol of gluconic acid to obtain solution A.
[0078] 0.002 mol of sodium fluoride, 0.004 mol of ammonium dihydrogen phosphate and 0.002 mol of sodium carbonate were added to 30 ml of deionized water and the mixture was magnetically stirred to obtain solution B, wherein the rotor speed was 400 r / min.
[0079] S2, mix solutions A and B, stir at room temperature for 1 hour to obtain a precursor solution; transfer the precursor solution to a hydrothermal reactor, use water as a solvent, heat to 120℃ and hold at that temperature for 1 hour, then cool naturally to room temperature to obtain superlattice mesocrystalline sodium vanadium fluorophosphate (Na3V2O2(PO4)2F) assembled from lamellar grain units.
[0080] S3: The mesocrystalline sodium fluorophosphate oxyvanadium crystals of S2 and 0.1 wt% of graphene were mixed in a ball mill and then dried in an oven. The mixture was heated to 600°C at a heating rate of 4°C / min under a nitrogen atmosphere, held at the temperature for 1 hour, and then naturally cooled to room temperature to obtain the sodium fluorophosphate oxyvanadium composite material, which is a superlattice mesocrystalline sodium fluorophosphate oxyvanadium / carbon composite material formed by the self-assembly of amorphous carbon-coated lamellar crystalline units.
[0081] Example 4
[0082] This embodiment provides a sodium vanadium fluorophosphate composite material, the preparation method of which includes:
[0083] S1, weigh 0.004 mol of vanadium oxalate and 0.002 mol of tartaric acid, add them to 50 ml of deionized water, and stir in an 80°C water bath at 400 rpm for 1 h; then add 0.0004 mol of alanine to obtain solution A.
[0084] Weigh out 0.002 mol of ammonium fluoride, 0.002 mol of sodium dihydrogen phosphate, and 0.002 mol of disodium hydrogen phosphate and add them to 30 ml of deionized water. Stir the mixture magnetically to obtain solution B, where the rotor speed is 400 r / min.
[0085] S2, mix solutions A and B, stir at room temperature for 1 hour to obtain a precursor solution; transfer the precursor solution to a hydrothermal reactor, use water as a solvent, heat to 100℃ and hold at that temperature for 10 hours, then cool naturally to room temperature to obtain superlattice mesocrystalline sodium vanadium fluorophosphate (Na3V2O2(PO4)2F) assembled from lamellar grain units.
[0086] S3: The mesocrystalline sodium fluorophosphate oxyvanadium crystals of S2 and 20 wt% of pitch are mixed in a ball mill and then dried in an oven. The mixture is heated to 400°C at a heating rate of 1°C / min under a nitrogen atmosphere, held at the temperature for 10 h, and then naturally cooled to room temperature to obtain the sodium fluorophosphate oxyvanadium composite material, which is a superlattice mesocrystalline sodium fluorophosphate oxyvanadium / carbon composite material formed by the self-assembly of amorphous carbon-coated lamellar crystalline units.
[0087] Comparative Example
[0088] A comparative example provides a bulk single-crystal sodium fluorophosphate oxyvanadium material, the preparation method of which includes:
[0089] 0.004 mol ammonium metavanadate and 0.005 mol citric acid were added to 80 ml of deionized water and stirred in a 60 °C water bath at 400 rpm for 0.5 h to obtain a light green solution. 0.006 mol sodium fluoride and 0.004 mol phosphoric acid were added to the light green solution and stirred for another 0.5 h to obtain the precursor solution.
[0090] The precursor solution was transferred to a hydrothermal reactor, and water was used as the solvent. The temperature was raised to 200℃ and held for 10 hours. The solution was then naturally cooled to room temperature to obtain sodium vanadium fluorophosphate single crystal powder (Na3V2O2(PO4)2F).
[0091] Sodium fluorophosphate oxyvanadium crystals and 5 wt% glucose were mixed in a ball mill and then dried in an oven. The mixture was heated to 600°C at a heating rate of 4°C / min under a nitrogen atmosphere, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain amorphous carbon-coated blocky sodium fluorophosphate oxyvanadium single crystal (sodium fluorophosphate oxyvanadium / carbon) cathode material.
[0092] The morphology and composition of the sodium vanadium fluorophosphate composite materials prepared in the embodiments and comparative examples of this application were characterized as follows:
[0093] 1. Morphological characteristics
[0094] Figure 1 and Figure 2 SEM images of the sodium vanadium fluorophosphate composite materials prepared in Examples 1 and 2, respectively. Figure 1 and Figure 2 It can be seen that the lamellar grain units grow in a stepwise manner along the material surface, indicating that the prepared material forms a self-assembled structure of lamellar grain units, that is, sodium vanadium fluorophosphate with a mesocrystalline structure.
[0095] Figure 3 SEM images of bulk single-crystal sodium vanadium fluorophosphate material prepared for comparison. From... Figure 3It can be seen that the surface structure of the grain is smooth, indicating that without the addition of a low molecular weight ligand, a bulk single crystal structure obtained by conventional crystal growth mode is obtained.
[0096] Figure 4 This is a TEM cross-sectional image of the sodium vanadium fluorophosphate composite material prepared in Example 2. From... Figure 4 The TEM cross-sectional image shows that the material is composed of stacked layered nano-single crystal particles with obvious gaps between the particles, forming a regular and orderly electron and ion transport channel.
[0097] 2. Structural Characterization
[0098] Figure 5 The images show a comparison of the XRD patterns of the sodium fluorophosphate oxyvanadium composite materials prepared in Examples 1-4 and the bulk single-crystal sodium fluorophosphate oxyvanadium composite material prepared in the comparative examples. Figure 5 It can be seen that the sodium vanadium fluorophosphate materials prepared in the examples and comparative examples all exhibit good crystallinity.
[0099] Sodium fluorophosphate vanadium oxyphosphate composite materials prepared in the examples and comparative examples were assembled into sodium-ion batteries, and their electrochemical performance was tested.
[0100] The specific method is as follows: The sodium vanadium fluorophosphate composite materials prepared in Examples 1-4 and the comparative example are mixed with the conductive agent Super P and the binder CMC in an equal mass ratio of 8:1:1 and dissolved in ultrapure water. The slurry is coated onto aluminum foil, dried, rolled, and cut into sheets to serve as the positive electrode. A sodium metal sheet is used as the negative electrode, a glass fiber membrane as the separator, and an aluminum foil as the current collector to assemble a CR2016 coin cell sodium-ion battery. The above CR2016 coin cell sodium-ion battery was subjected to constant current charge-discharge tests at 0.2, 1, and 20C rates, as well as a 1C cycle test. The results are shown in Table 1.
[0101] Table 1 Performance test results of the assembled batteries in the examples and comparative examples
[0102]
[0103] As shown in Table 1, the sodium-ion batteries of Examples 1-4 significantly outperformed the comparative examples in terms of capacity, efficiency, rate capability, and cycle life. Specifically, the sodium-ion battery of Example 1 achieved specific capacities of 125.6, 125.1, and 112.7 mAh / g at 0.2, 1, and 10C rates, respectively, far exceeding the 113.4, 108.6, and 85.6 mAh / g of Comparative Example 1. This fully demonstrates that the shortened electron-ion transport distance of the mesocrystalline sodium fluorophosphate composite material of this invention results in superior rate performance. After 1000 cycles at 1C rate, the capacity retention rate of the sodium-ion batteries of Examples 1-4 was all above 95%, significantly better than the comparative examples. This indicates that the mesocrystalline structure can significantly mitigate crystal volume changes during charging and discharging, maintaining the structural stability of large-particle mesocrystalline crystals.
[0104] This application employs superlattice self-assembly technology to shorten the transport distance of electrons and ions in the lattice while ensuring a low specific surface area of the material. This effectively improves the electronic / ionic conductivity and structural stability of the material, and significantly enhances the capacity and rate performance of sodium vanadium fluorophosphate. This is of great significance for promoting the application of sodium-ion batteries in high-power scenarios.
[0105] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.
Claims
1. A sodium oxyvanadophosphate composite material, characterized in that, It includes sodium vanadium fluorophosphate with a mesocrystalline structure, and an amorphous carbon layer covering the outer layer of the sodium vanadium fluorophosphate; The mesocrystalline sodium fluorophosphate is formed by the self-assembly of multiple carbon-coated small sodium fluorophosphate nanocrystal units.
2. The method for preparing the sodium oxyvanadofluorophosphate composite material according to claim 1, characterized in that, include: S1, add vanadium source, reducing agent, and low molecular weight ligand to deionized water, heat and stir to obtain solution A; dissolve sodium source, phosphorus source and fluorine source in water to obtain solution B; S2, mix solution B and solution A thoroughly, and then carry out a hydrothermal reaction to obtain sodium vanadium fluorophosphate powder with a mesocrystalline structure; S3, the sodium fluorophosphate oxyvanadium powder and carbon source are wet-mixed and dried, and the resulting mixture is calcined under an inert atmosphere to obtain sodium fluorophosphate oxyvanadium composite material.
3. The production method according to claim 2, characterized by, The low molecular weight ligand is at least one of formic acid / formate, acetic acid / acetate, propionic acid, butyric acid, benzoic acid / benzoate, ethylamine, propylamine, butylamine, hexylamine, ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, gluconic acid, malonic acid, succinic acid, phthalic acid, catechol, dopamine, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), hexamethylenetetramine (HMTA), glycine, alanine, aspartic acid, glutamic acid, lysine, or dodecylphenoxy polyoxyethylene ether.
4. The preparation method according to claim 2, characterized in that, The reducing agent includes at least one of oxalic acid, malic acid, tartaric acid or citric acid; The vanadium source includes at least one of vanadium pentoxide, ammonium metavanadate, vanadium tetroxide, vanadium trioxide, vanadium tetrahydroxide, vanadium oxalate, vanadium oxysulfate, vanadium oxalate, vanadium trichloride, vanadium acetylacetonate, or vanadium acetylacetonate. The sodium source includes at least one of sodium fluoride, sodium chloride, sodium carbonate, sodium hydroxide, sodium sulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or sodium nitrate. The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, or ammonium phosphate. The fluorine source is at least one or more of sodium fluoride, calcium fluoride, ammonium fluoride, potassium fluoride, and magnesium fluoride; The carbon source includes at least one of sucrose, ascorbic acid, glucose, citric acid, fructose, pitch, acetylene black, carbon nanotubes, graphene, carbon fibers, mesophase carbon microspheres, resin, or starch.
5. The preparation method according to claim 2, characterized in that, The amounts of vanadium, sodium, phosphorus and fluorine sources in S1 are in the atomic ratio of Na:V:P:F=3:x:2:1, where 1.5 < x < 2.
6. The preparation method according to claim 2, characterized in that, The amount of the low molecular weight ligand added is 0.1 to 30 wt% of the total amount of vanadium source, sodium source, phosphorus source and fluorine source.
7. The preparation method according to claim 2, characterized in that, The amount of carbon source used is 0.1% to 20 wt% of the mass of sodium fluorophosphate.
8. The preparation method according to claim 2, characterized in that, The heating temperature described in S1 is 40~90℃; The hydrothermal reaction described in S2 is carried out at a temperature of 100~250℃ for a time of 1~36 h; The calcination temperature described in S3 is 350℃~800℃, and the calcination time is 1min~20h.
9. A positive electrode material for sodium-ion batteries, characterized in that, It includes the sodium fluorophosphate oxyvanadium composite material according to claim 1 or the sodium fluorophosphate oxyvanadium composite material prepared by the preparation method according to any one of claims 2-8.
10. A sodium-ion battery, characterized in that, Its positive electrode material is the positive electrode material as described in claim 9.