Vanadium-manganese-sodium phosphate composite material, preparation method thereof and application of vanadium-manganese-sodium phosphate composite material in sodium-ion battery

Abstract

The invention discloses a vanadium-manganese-sodium phosphate composite material, a preparation method thereof and application of the vanadium-manganese-sodium phosphate composite material in a sodium-ion battery, and belongs to the technical field of sodium-ion batteries. The problems of non-uniform carbon coating, porosity, low nitrogen doping efficiency, complex process and the like in the existing method for coating the modified positive electrode material are solved. The method comprises the following steps: taking a sodium source, a manganese source, a vanadium source and a phosphorus source according to a molar ratio of Na: Mn: V: P of 3: 1: 1: 3, carrying out ball milling, uniformly mixing, and drying to obtain a precursor; then calcining in air to obtain a pre-sintered material; finally, under the protection of inert atmosphere, carbonization is conducted, the vanadium manganese sodium phosphate composite material is obtained, and ball milling liquid is absolute ethyl alcohol containing 3-amino-2-naphthol and boric acid. The vanadium manganese sodium phosphate composite material prepared by the invention has more compact carbon layer coating, lower battery internal resistance, more excellent rate capability and more stable capacity retention ratio, and can be applied as a sodium ion battery positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium vanadium manganese phosphate composite material, its preparation method and its application in sodium-ion batteries, and particularly to the application of the sodium vanadium manganese phosphate composite material with a nitrogen-doped carbon coating in the preparation of sodium-ion battery cathode materials. Background Technology

[0002] Sodium and lithium belong to the same group in the periodic table, have similar chemical properties, and are abundant in the Earth's crust. Therefore, with the continuous growth of energy demand, sodium-ion batteries (SIBs) have become a hot topic of interest for professionals worldwide as ideal candidates for large-scale energy storage systems (ESSs). Developing SIBs with higher performance to meet the requirements of ESSs is crucial. However, compared to lithium, sodium has a higher relative atomic mass, higher electrode potential, and larger ionic radius. SIBs also face challenges such as slow kinetics, insufficient specific power, low specific energy, and rapid capacity decay. These problems significantly limit the practical application of SIBs. To overcome these shortcomings, it is urgent to find sodium-ion battery electrode materials with excellent structure and electrochemical performance.

[0003] Sodium vanadium phosphate (Na3V2(PO4)3, abbreviated as NVP) is one of the most popular sodium superionic conductors (NASICON) materials currently available, due to its excellent Na+ properties. + Storage capacity, high theoretical capacity (117mAh g) -1 Vanadium (NVP) has been extensively studied due to its rapid sodium ion migration rate and excellent thermal and cycling stability. However, despite its excellence, NVP has only a 3.4V voltage platform, and vanadium is relatively expensive, increasing the manufacturing cost of ESSs. Furthermore, its toxicity is harmful to human health and the environment, failing to meet current environmental protection requirements. Replacing V with other low-cost elements that have higher voltage platforms and are more abundant would help increase operating voltage and reduce costs.

[0004] Manganese is widely used in energy storage systems due to its environmental friendliness, abundant resources, and low cost. More importantly, many manganese-based materials have proven to be the electrochemically active host in energy storage blocks (SIBs) and have exhibited excellent electrochemical performance. In 2016, Goodenough's team prepared Na₄MnV(PO₄)₃ (NMVP) by replacing some of the V with Mn. NMVP achieved a satisfactory theoretical capacity of 111 mAh g⁻¹. -1 Based on Mn 3+ / Mn 2+ and Mn 4+ / Mn 3+The redox pair of manganese exhibits a high redox potential of 3.6V, is environmentally friendly, and offers the advantage of low cost, showing broad application prospects. However, its intrinsic electronic conductivity is extremely low (<10). -9 The redox reaction plays a crucial role in improving the working voltage and actual specific capacity of the cathode material, making it difficult to achieve the theoretical capacity, resulting in insufficient utilization of active materials (low initial coulombic efficiency), poor rate performance, and limited cycle life.

[0005] Currently, methods for modifying cathode materials mainly include element doping, particle size optimization, and carbon coating. Element doping is an effective method to improve the electrochemical performance of batteries by introducing new elements to change the material composition. Existing polyanion cathode materials mainly involve doping with transition metal elements, including single-atom and multi-atom doping. Particle size optimization affects the electrochemical performance and ion diffusion by changing the morphology and crystal orientation of the electrode material. This can be achieved by altering its structural characterization through different processes or raw materials, thereby affecting its electrochemical performance. Carbon coating is a widely used modification method in polyanion phosphate electrode materials. Carbon is the most abundant material in nature, environmentally friendly, and inexpensive. Coating the surface of the active material not only enhances the material's conductivity but also promotes sodium ion transport and increases the diffusion rate.

[0006] Existing carbon coating technologies mainly use carbon sources such as glucose, citric acid, and sucrose, which are mixed through ball milling and high-temperature pyrolysis to achieve coating, thereby increasing the electronic conductivity to 10. -3 The performance is on the order of S / cm. However, it has two major drawbacks: poor coating uniformity and insufficient interfacial transport kinetics. Uneven coating leads to inconsistent performance. Although the carbon layer improves electronic conductivity, an excessively thick or loose carbon layer may become a physical barrier to the diffusion of sodium ions at the electrode / electrolyte interface, increasing interfacial impedance, especially during high-rate charge and discharge. This may result in insufficient capacity utilization and increased polarization.

[0007] Current nitrogen-doped carbon coating technology mainly involves stepwise doping processes, using composite sources such as glucose and urea or polyvinylpyrrolidone (PVP) and melamine, to alter the spline concentration of the carbon layer through nitrogen atoms. 2 The hybrid structure introduces a pseudocapacitive effect. However, it suffers from low nitrogen doping efficiency and a porous coating layer structure.

[0008] The fundamental flaw of existing carbon / nitrogen source doping systems is the mismatch between decomposition products and the target carbon / nitrogen structure (uncontrollable chemical composition): This is because most organic carbon sources undergo complex chemical reactions (cracking, condensation, cyclization, dehydrogenation, removal of heteroatoms, etc.) during pyrolysis and carbonization, and these reaction pathways are difficult to control precisely; the decomposition process produces harmful / difficult-to-treat byproducts: organic precursors inevitably produce a large number of gaseous or volatile small molecule byproducts under high-temperature pyrolysis (usually in an inert atmosphere). For example, externally doped nitrogen sources (such as urea) are mainly physically adsorbed, and easily escape in the form of NH3 at high temperatures; the process window is narrow and the thermodynamic / kinetic mismatch exists: the ideal coating process requires the carbon / nitrogen source to decompose at a lower temperature and form a uniform coating layer, and this temperature must be lower than the temperature at which the cathode material undergoes an unfavorable phase transition or decomposition. Meanwhile, the coating process requires good interaction (wetting, adsorption) with the surface of the cathode particles; under conventional mixing-pyrolysis processes, the decomposition, carbonization, and deposition processes of existing precursor systems are significantly affected by factors such as diffusion, concentration gradient, and local temperature differences, making it difficult to achieve uniform, dense, and thin-layer coating. Summary of the Invention

[0009] This invention addresses the technical problems of uneven carbon coating, porosity, low nitrogen doping efficiency, and complex processes in existing methods for coating modified cathode materials. It provides a sodium vanadium manganese phosphate composite material, its preparation method, and its application in sodium-ion batteries.

[0010] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows.

[0011] In a first aspect, the present invention provides a method for preparing a sodium manganese vanadium phosphate composite material, comprising the following steps: 1) Sodium source, manganese source, vanadium source and phosphorus source were taken according to the molar ratio of Na:Mn:V:P 3:1:1:3, ball-milled and mixed evenly, and dried to obtain the precursor; Therefore, the ball milling fluid used is anhydrous ethanol containing 3-amino-2-naphthol and boric acid. The ratio of the volume of the ball milling fluid to the total mass of the sodium, manganese, vanadium, and phosphorus sources is (2.5~5.0) mL:1g. The concentration of 3-amino-2-naphthol in the ball milling fluid is 0.1~0.2 mol / L, and the concentration of boric acid is 0.03~0.05 mol / L. 2) The precursor is calcined in air at 300~400℃ for 2~5 hours to obtain the pre-sintered material; 3) Under an inert atmosphere, the pre-sintered material is carbonized at 700~800℃ for 6~12h, and then ground into powder to obtain sodium manganese vanadium phosphate composite material (Na3MnV(PO4)3@C / N).

[0012] Preferably, in step 1), the sodium source is one or more of sodium carbonate (Na2CO3), sodium acetate, sodium bicarbonate, and sodium dihydrogen phosphate; the manganese source is one or more of manganese acetate tetrahydrate (Mn(CH3COO)2•4H2O), manganese carbonate, and manganese nitrate hexahydrate; the vanadium source is one or more of ammonium metavanadate (NH4VO3) and vanadium pentoxide; and the phosphorus source is one or more of sodium dihydrogen phosphate, ammonium dihydrogen phosphate (NH4H2PO4), and diammonium hydrogen phosphate.

[0013] Preferably, in step 1), the drying temperature is 60~80℃ and the drying time is 6~8h.

[0014] Preferably, in step 1), the ball milling speed is 300~500 rpm, the time is 6~12 h, and the ball-to-material ratio is 10:1; more preferably, the ball milling time is 9~11 h.

[0015] Preferably, in step 1), the ball milling slurry is prepared by mixing 3-amino-2-naphthol, boric acid and anhydrous ethanol evenly to obtain a ball milling slurry (yellow-green in color). More preferably, the method of achieving uniform mixing is ultrasonic stirring, magnetic stirring, vortex stirring, or bubble stirring. Preferably, 3-amino-2-naphthol, boric acid and anhydrous ethanol are ultrasonically mixed for 8-10 minutes until homogeneous.

[0016] Preferably, in step 1), the amount of sodium source is replaced with an excess of 2-5 wt%.

[0017] Preferably, in step 2), the temperature is increased to 300-400°C at a heating rate of 3-6°C / min.

[0018] Preferably, in step 2), the calcination time is 2-4 hours.

[0019] Preferably, in step 3), the inert atmosphere is argon, and the flow rate of the inert atmosphere is 70~90 mL / min.

[0020] Preferably, in step 3), the temperature is increased to 700-800°C at a heating rate of 1-5°C / min; More preferably, the temperature is increased to 700-800°C at a heating rate of 1-3°C / min.

[0021] Preferably, in step 3), the carbonization time is 7-9 hours.

[0022] Preferably, in step 3), after grinding into powder, the powder is passed through a 200-400 mesh sieve.

[0023] Secondly, the present invention also provides a sodium vanadium manganese phosphate composite material prepared by the above-mentioned method for preparing sodium vanadium manganese phosphate composite material.

[0024] Thirdly, the present invention also provides the application of the above-mentioned sodium vanadium manganese phosphate composite material in the cathode material of sodium-ion batteries.

[0025] The principle of this invention is as follows: the preparation method of this invention achieves the preparation of sodium manganese phosphate composite material through the synergistic effect of molecular design (3-amino-2-naphthol) and process improvement (pre-sintering + carbonization); Among them, the amino group (-NH2) of 3-amino-2-naphthol is conjugated with the naphthalene ring, and preferentially forms pyridine nitrogen during pyrolysis, which significantly improves high-temperature stability. Furthermore, the nitrogen element is fixed by boric acid. During pre-sintering, the fixed nitrogen element undergoes an oxidative cross-linking reaction in air to generate a nitrogen-containing fused ring polymer, which inhibits the escape of HCN and achieves intramolecular self-locking of nitrogen. In addition, the -OH group in the 3-amino-2-naphthol molecule binds to oxygen vacancies on the surface of the precursor, and atomic-level dispersion is achieved by utilizing the hydroxyl anchoring effect; Furthermore, by forming inorganic / organic core-shell microparticles (with sodium manganese vanadium phosphate as the core and nitrogen-doped carbon as the coating layer) through ball milling, a nanoscale precursor design is achieved, resulting in high electronic / ionic conductivity and lower battery internal resistance, as well as high capacity retention over long cycles. This provides a high-performance cathode material for the industrialization of sodium-ion batteries in the energy storage field.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the sodium manganese vanadium phosphate composite material of the present invention achieves high-efficiency nitrogen doping through the synergistic effect of intramolecular carbon-nitrogen synergy of 3-amino-2-naphthol and process innovation (pre-sintering + carbonization), and forms an ultra-thin, highly adhesive carbon layer through hydrogen bonding.

[0027] The preparation method of the sodium manganese vanadium phosphate composite material of the present invention mainly adopts the wet ball milling-pre-sintering-high temperature carbonization method. It utilizes the unique molecular structure of 3-amino-2-naphthol, in which the amino group and naphthalene ring are conjugated in the molecule and pre-sintering forms a cross-linked nitrogen-fixing structure. Boric acid is added to assist in the formation of BN bonds, thereby achieving efficient nitrogen doping. Furthermore, through pre-sintering and carbonization, the naphthalene ring in the molecule is carbonized to form a high-density coating layer, thereby achieving "one molecule with dual functions".

[0028] The preparation method of the sodium manganese phosphate composite material of the present invention is simple.

[0029] The sodium manganese vanadium phosphate composite material of the present invention has a special molecular structure. The high nitrogen content carbon layer is uniformly coated, which improves electronic conductivity (N doping), increases interfacial active sites (providing pseudocapacitance), strengthens interfacial bonding (forming chemical bonds), and the tight bonding between the core and the shell can effectively suppress side reactions and metal dissolution, provide a buffer layer, alleviate volume changes, and maintain structural integrity.

[0030] The sodium manganese phosphate composite material of the present invention has a denser carbon layer coating, lower battery internal resistance, better rate performance, and more stable capacity retention.

[0031] The sodium vanadium manganese phosphate composite material of this invention possesses a high nitrogen content and a synergistic carbon-nitrogen coating structure. When used as a positive electrode material in sodium-ion batteries, its unique molecular structure design enhances the wettability of the electrolyte on the positive electrode, reduces the film resistance of the positive electrode, improves ionic conductivity, promotes rapid electron / ion migration, reduces sodium ion consumption during SEI film formation, decreases the internal resistance of the sodium-ion battery, and improves its cycle stability. This provides strong support for the further development of sodium-ion batteries in terms of high performance and safety, and also offers a reference for improving the safety of other related electrochemical energy storage devices. Attached Figure Description

[0032] Figure 1 The diagram shows the room temperature cycling capacity retention rates of Examples 1-3 and Comparative Examples 1-2 of the present invention. Figure 2 This is a schematic diagram of the process flow for preparing the sodium manganese phosphate composite material in Example 1 of the present invention. Detailed Implementation

[0033] To further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0034] The preparation method of sodium vanadium manganese phosphate composite material of the present invention is the first to apply the bifunctionality of 3-amino-2-naphthol to sodium ion cathode material. Its technical essence is to utilize the conjugation effect of the fused ring skeleton (carbon source) and the ortho-amino group (nitrogen source) in the 3-amino-2-naphthol molecule to achieve carbon and nitrogen atomic-level synergistic doping; the pre-sintering-carbonization synergistic process eliminates the phenomenon of impurity phase and nitrogen escape; and the carbon content is stabilized by forming BN bonds with the assistance of air pre-sintering and boric acid, thereby constructing a cross-linked nitrogen-fixing structure, and finally realizing the preparation of high-performance sodium vanadium manganese phosphate composite material.

[0035] The preparation method of the sodium manganese phosphate composite material of the present invention includes the following steps: 1) Ball milling mixing: Sodium, manganese, vanadium and phosphorus sources were taken in a Na:Mn:V:P molar ratio of 3:1:1:3, ball-milled and mixed evenly, and dried to obtain the precursor. Therefore, the ball milling fluid used is anhydrous ethanol containing 3-amino-2-naphthol and boric acid. The ratio of the volume of the ball milling fluid to the total mass of the sodium, manganese, vanadium, and phosphorus sources is (2.5~5.0) mL:1g. The concentration of 3-amino-2-naphthol in the ball milling fluid is 0.1~0.2 mol / L, and the concentration of boric acid is 0.03~0.05 mol / L. 2) Pre-sintering: The precursor is calcined in air at 300-400℃ for 2-5 hours to obtain a pre-sintered material; 3) High-temperature carbonization: Under an inert atmosphere, the pre-sintered material was carbonized at 700~800℃ for 6~12h, and then ground into powder to obtain sodium manganese vanadium phosphate composite material (Na3MnV(PO4)3@C / N).

[0036] In step 1) of this invention, the preferred sodium source is one or more of sodium carbonate (Na2CO3), sodium acetate, sodium bicarbonate, and sodium dihydrogen phosphate; the preferred manganese source is one or more of manganese acetate tetrahydrate (Mn(CH3COO)2•4H2O), manganese carbonate, and manganese nitrate hexahydrate; the preferred vanadium source is one or more of ammonium metavanadate (NH4VO3) and vanadium pentoxide; and the preferred phosphorus source is one or more of sodium dihydrogen phosphate, ammonium dihydrogen phosphate (NH4H2PO4), and diammonium hydrogen phosphate. It should be noted that when using a substance containing multiple elements from sodium, manganese, vanadium, and phosphorus as a raw material, it can be used as a multi-source raw material simultaneously. For example, sodium dihydrogen phosphate can be used as both a sodium source and a phosphorus source. Preferably, the amount of sodium source used is 2-5 wt% excess to compensate for volatilization losses during calcination and carbonization.

[0037] In step 1) of the present invention, the drying is preferably carried out in a vacuum oven at a temperature of 60-80°C for 6-8 hours.

[0038] In step 1) of this invention, ball milling preferably uses a ball milling jar, and the grinding balls are zirconia balls or agate balls. Preferably, the ball milling speed is 300-500 rpm, the time is 6-12 h, and the ball-to-material ratio is 10:1; more preferably, the ball milling time is 9-11 h. The ball milling fluid used in this invention is anhydrous ethanol containing 3-amino-2-naphthol and boric acid. The concentration of 3-amino-2-naphthol in the ball milling fluid of this invention is 0.1-0.2 mol / L. For example, in some embodiments, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, and 0.2 mol / L are used. The concentration of boric acid is 0.03~0.05 mol / L, such as in some embodiments 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, and 0.05 mol / L. The ball milling slurry is prepared by mixing 3-amino-2-naphthol, boric acid, and anhydrous ethanol evenly to obtain a ball milling slurry (yellow-green in color). The mixing method can be ultrasonic stirring, magnetic stirring, vortex stirring, or bubble stirring; there are no particular limitations. Ultrasonic mixing for 8~10 minutes is preferred. This invention utilizes 3-amino-2-naphthol. The amino group (-NH2) of 3-amino-2-naphthol is conjugated with the naphthalene ring (carbon source), achieving atomic-level co-doping of carbon and nitrogen. During pyrolysis, pyridine nitrogen is preferentially formed, significantly improving high-temperature stability. Boric acid forms a BN bond with the amino group, pre-locking the nitrogen element. During pre-sintering, the fixed nitrogen element undergoes an oxidative cross-linking reaction in air, generating a nitrogen-containing fused-ring polymer, inhibiting HCN escape and achieving intramolecular self-locking of nitrogen. The -OH group in the 3-amino-2-naphthol molecule binds to oxygen vacancies on the precursor surface, utilizing the hydroxyl anchoring effect to achieve atomic-level dispersion. Ball milling forms inorganic / organic core-shell microparticles, enabling nanoscale precursor design, achieving high electronic / ionic conductivity and lower battery internal resistance, and achieving high capacity retention over long cycles. In this invention, the amount of 3-amino-2-naphthol is preferably calculated based on the target carbon coating amount. Considering its large molecular weight, sufficient carbon content must be ensured. The actual amount added needs to take into account the carbon loss during the pre-sintering stage and the residual rate of high-temperature carbonization. The theoretical amount added = required carbon amount / (carbon element fraction × residual rate), and the actual amount added = empirical coefficient (due to the carbon loss during the pre-sintering stage). Theoretical addition amount.

[0039] In step 2) of this invention, the temperature is preferably increased to 300-400°C at a heating rate of 3-6°C / min. The calcination time is preferably 2-4 hours. Calcination is usually carried out in a muffle furnace.

[0040] In step 3) of this invention, the inert atmosphere is preferably argon, and the flow rate of the inert atmosphere is 70-90 mL / min. The temperature is preferably increased to 700-800°C at a rate of 1-5°C / min; more preferably, it is increased to 700-800°C at a rate of 1-3°C / min. The carbonization time is preferably 7-9 hours. The powder is preferably passed through a 200-400 mesh sieve. Carbonization is typically carried out in a tube furnace.

[0041] The pre-sintering and carbonization of the present invention promote the carbonization of the naphthalene ring in the 3-amino-2-naphthol molecule to form a high-density coating layer.

[0042] The method for preparing sodium vanadium manganese phosphate composite material of the present invention produces a sodium vanadium manganese phosphate composite material that is an inorganic / organic core-shell microparticle with sodium vanadium manganese phosphate as the core and nitrogen-doped carbon as the coating layer. It exhibits a denser carbon layer coating, lower battery internal resistance, superior rate performance, and more stable capacity retention. It can be used to prepare cathode materials for sodium-ion batteries. There are no special limitations on its application method; reference can be made to existing methods for using sodium vanadium manganese phosphate materials in the preparation of cathode materials for sodium-ion batteries.

[0043] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to embodiments.

[0044] In the following examples and comparative examples, the various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, apparatus, instruments, equipment, etc., used in the following examples and comparative examples are commercially available.

[0045] Example 1 like Figure 2 As shown, the preparation method of sodium manganese phosphate composite material includes the following steps: 1) Ball milling and mixing: Weigh 1.63g sodium carbonate, 2.45g manganese acetate tetrahydrate, 1.17g ammonium metavanadate and 3.45g ammonium dihydrogen phosphate and mix them, then add them to the ball mill jar; Add 1.02 g of 3-amino-2-naphthol and 0.1 g of boric acid to 40 mL of anhydrous ethanol, and sonicate for 10 min until completely dissolved to obtain... The ball milling slurry, which is yellowish-green, contains 0.16 mol / L of 3-amino-2-naphthol and 0.04 mol / L of boric acid. The slurry is then added to the ball milling jar. Zirconia balls were added to a ball milling jar at a ball-to-material ratio of 10:1. The ball milling speed was 400 rpm and the milling time was 10 h. The resulting mixture was dried in a vacuum oven at 70 °C for 7 h to obtain the precursor. 2) Pre-sintering: The obtained precursor is transferred to a muffle furnace and calcined in air atmosphere at a temperature of 350℃ for 3 hours and a heating rate of 5℃ / min to obtain pre-sintered material. 3) High-temperature carbonization: The pre-sintered material is added to a tube furnace and carbonized under the protection of argon (flow rate of 80 mL / min). The carbonization temperature is 750℃, the carbonization time is 8 h, and the heating rate is 2℃ / min. After grinding, it is passed through a 200-mesh sieve to obtain sodium manganese vanadium phosphate composite material, denoted as Na3MnV(PO4)3@C / N.

[0046] Example 2 The amount of 3-amino-2-naphthol added in Example 1 was replaced with 1.28 g, and the corresponding molar concentration was 0.20 mol / L. Other operations were the same as in Example 1.

[0047] Example 3 The amount of 3-amino-2-naphthol added in Example 1 was replaced with 0.77 g, and the corresponding molar concentration was 0.12 mol / L. Other operations were the same as in Example 1.

[0048] Comparative Example 1 Preparation method of sodium manganese vanadium phosphate composite material (coating achieved by existing stepwise solid-state method): 1) Weigh out 1.63g sodium carbonate, 2.45g manganese acetate tetrahydrate, 1.17g ammonium metavanadate and 3.45g ammonium dihydrogen phosphate, mix them and add them to a ball mill jar; Add 30 mL of ethanol to the ball mill jar; Zirconia balls were added to a ball milling jar at a ball-to-material ratio of 10:1. The ball milling speed was 300 rpm and the milling time was 6 h. The first mixture was dried in a vacuum oven at 80 °C for 2 h and then transferred to a tube furnace for calcination in an air atmosphere at a calcination temperature of 350 °C for 4 h and a heating rate of 5 °C / min to obtain the precursor. 2) Add the precursor obtained in step 1), 0.72g of glucose and 0.36g of urea (replacing 3-amino-2-naphthol (equal carbon and nitrogen content)) into a ball mill jar. Add zirconia balls to the ball mill jar at a ball-to-material ratio of 10:1. The ball milling speed is 300 rpm and the ball milling time is 3h. Then bake the obtained powder in a vacuum oven at 60℃ for 12h to obtain the second mixture. 3) The second mixture was added to a tube furnace and carbonized under nitrogen protection (flow rate of 50 mL / min). The carbonization temperature was 750℃, the carbonization time was 10 h, and the heating rate was 5℃ / min. After grinding, the mixture was passed through a 200-mesh sieve to obtain sodium manganese vanadium phosphate composite material, denoted as Na3MnV(PO4)3@C / N.

[0049] Comparative Example 2 Replace the amount of 3-amino-2-naphthol added in Example 1 with 0g, and perform the other operations as in Example 1.

[0050] Sodium-ion batteries were prepared using the sodium manganese phosphate composite materials prepared in Examples 1-3 and Comparative Examples 1-2 as the positive electrode material. The preparation method of the sodium-ion battery is as follows: 1) Dissolve 100g of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), then add positive electrode material and conductive carbon black and mix evenly to obtain sodium-ion battery positive electrode slurry. In the sodium-ion battery positive electrode slurry, the mass ratio of positive electrode material:PVDF:conductive carbon black:NMP is 58.8:0.6:0.6:40. 2) Dissolve 100g of sodium carboxymethyl cellulose (CMC) in deionized water, then add the negative electrode material hard carbon, the conductive agent conductive carbon black, the binder polyacrylic acid (PAA), and styrene-butadiene rubber (SBR), and mix evenly to obtain a sodium-ion battery negative electrode slurry. In the sodium-ion battery negative electrode slurry, the mass ratio of hard carbon: conductive carbon black: PAA: CMC: SBR: deionized water is 48:1:0.25:0.25:0.5:50. 3) The sodium-ion battery positive electrode slurry is coated onto an aluminum foil current collector, and then rolled, slit, die-cut and baked to obtain the positive electrode sheet; 4) The sodium-ion battery negative electrode slurry is coated onto an aluminum foil current collector, and then rolled, slit, die-cut and baked to obtain the negative electrode sheet; 5) Assemble the positive electrode, negative electrode, 16µm PP separator, electrolyte (a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, with the addition of 1mol / L NaPF6 and 5vol% fluoroethylene carbonate) and casing into a sodium-ion battery.

[0051] The specific surface area, internal resistance, 3C rate discharge, room temperature cycle retention rate, and high temperature cycle retention rate of sodium-ion batteries prepared using sodium manganese phosphate composite materials of Examples 1-3 and Comparative Examples 1-2 as positive electrode materials were tested.

[0052] Test method: Specific surface area according to national standard GB / T 30835-2014. Battery internal resistance, 3C rate discharge, room temperature cycle and high temperature cycle voltage range: 2.0~4.0V, room temperature cycle and high temperature cycle current: 1C.

[0053] The test results are shown in Table 1 and Figure 1 As shown.

[0054] Table 1. Electrochemical performance of sodium-ion batteries prepared using the composite materials of Examples 1-3 and Comparative Examples 1-2 as cathode materials.

[0055] From Table 1 and Figure 1 It can be seen that the sodium-ion batteries of Examples 1-3 exhibit higher performance than Comparative Examples 1 and 2 in several test items, including specific surface area, internal resistance, 3C rate discharge, room temperature cycle retention, and high temperature cycle retention. Example 1 shows the best performance. This indicates that Examples 1-3, using 3-amino-2-naphthol as the carbon and nitrogen source for coating sodium vanadium manganese phosphate, demonstrate superior electrochemical performance compared to Comparative Example 1, which uses existing carbon and nitrogen sources.

[0056] The above experiments demonstrate that in existing technologies, the pyrolysis of carbon sources (such as glucose) produces gas that creates pores, resulting in a loose carbon layer. Physical mixing also leads to uneven carbon source dispersion. Furthermore, the high-temperature decomposition of nitrogen sources (such as urea) releases NH3 / HCN, resulting in low nitrogen doping efficiency, poor interfacial dynamics, and insufficient electronic conduction. Simultaneously, volumetric strain causes particle breakage, leading to insufficient cycle stability. In contrast, this invention utilizes 3-amino-2-naphthol, which exhibits superior performance due to its unique molecular structure. The -OH groups in the molecule form hydrogen bonds with the precursor, and wet ball milling achieves nanoscale pre-assembly with coating, enabling hydroxyl-assisted directional adsorption for more uniform coating. The conjugation of the amino group and naphthalene ring enhances thermal stability, and pre-sintering (300-400℃ in air) forms a cross-linked nitrogen-fixing structure. Boric acid is added to assist in the formation of BN bonds, creating intramolecular nitrogen lock, thereby improving nitrogen doping efficiency. Nitrogen doping constructs fast ion channels, allowing pyridine nitrogen to adsorb Na. + The reduction of desolvation energy improves the interfacial ion transport rate, and its dense carbon layer can buffer structural stress. Mainly, the carbonization of naphthalene rings forms a highly elastic coating layer, which effectively improves its cycling performance.

[0057] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a sodium manganese vanadium phosphate composite material, characterized in that, Includes the following steps: 1) Sodium source, manganese source, vanadium source and phosphorus source were taken according to the molar ratio of Na:Mn:V:P 3:1:1:3, ball-milled and mixed evenly, and dried to obtain the precursor; Therefore, the ball milling fluid used is anhydrous ethanol containing 3-amino-2-naphthol and boric acid. The ratio of the volume of the ball milling fluid to the total mass of the sodium, manganese, vanadium, and phosphorus sources is (2.5~5.0) mL:1g. The concentration of 3-amino-2-naphthol in the ball milling fluid is 0.1~0.2 mol / L, and the concentration of boric acid is 0.03~0.05 mol / L. 2) The precursor is calcined in air at 300~400℃ for 2~5 hours to obtain the pre-sintered material; 3) Under an inert atmosphere, the pre-sintered material is carbonized at 700~800℃ for 6~12h, then ground into powder to obtain sodium manganese vanadium phosphate composite material.

2. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 1, characterized in that, In step 1), the sodium source is one or more of sodium carbonate, sodium acetate, sodium bicarbonate, and sodium dihydrogen phosphate; the manganese source is one or more of manganese acetate tetrahydrate, manganese carbonate, and manganese nitrate hexahydrate; the vanadium source is one or more of ammonium metavanadate and vanadium pentoxide; and the phosphorus source is one or more of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

3. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 1, characterized in that, In step 1), the drying temperature is 60~80℃ and the drying time is 6~8h.

4. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 1, characterized in that, In step 1), one or more of the following characteristics are present: The ball mill operates at a speed of 300-500 rpm for 6-12 hours, with a ball-to-material ratio of 10:

1. The ball milling slurry is prepared by mixing 3-amino-2-naphthol, boric acid and anhydrous ethanol evenly to obtain the ball milling slurry.

5. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 4, characterized in that, Mix 3-amino-2-naphthol, boric acid and anhydrous ethanol by sonication for 8-10 minutes until homogeneous.

6. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 1, characterized in that, In step 1), the amount of sodium source is replaced with an excess of 2-5 wt%.

7. The method for preparing the sodium manganese phosphate composite material according to claim 1, characterized in that, In step 2), one or more of the following characteristics are present: Heating to 300-400℃ at a heating rate of 3-6℃ / min; The calcination time is 2-4 hours.

8. The method for preparing the sodium manganese vanadium phosphate composite material according to claim 1, characterized in that, In step 3), one or more of the following characteristics are present: The inert atmosphere is argon, and the flow rate of the inert atmosphere is 70~90 mL / min; Heating to 700-800℃ at a heating rate of 1-5℃ / min; The carbonization time is 7-9 hours; After being ground into powder, it is passed through a 200-400 mesh sieve.

9. The sodium vanadium manganese phosphate composite material prepared by the preparation method of the sodium vanadium manganese phosphate composite material according to any one of claims 1 to 8.

10. The application of the sodium vanadium manganese phosphate composite material according to claim 9 in the preparation of sodium-ion battery cathode materials.

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