Preparation Method and Application of a Modified Sodium Vanadium Phosphate Composite Material

Abstract

The invention discloses a preparation method and application of a modified sodium vanadium phosphate composite material, which belongs to the technical field of sodium ion battery electrode material preparation. A chain carbon source, a vanadium source, an ammonium phosphate salt, an ammonium sulfate salt, and a sodium source are added to deionized water for heating reaction, aging, and spray drying to generate Na3V2(PO4) 3‑x (SO4) x Precursor material, then Na3V2(PO4) 3‑x (SO4) x The precursor material, ammonia water, and liquid titanium source were placed in ethanol, reacted, filtered, washed, and dried to obtain a powder material, which was calcined in an Ar-H2 mixed atmosphere to obtain a modified sodium vanadium phosphate composite material. The modified sodium vanadium phosphate composite material was used in sodium ion batteries and released 102.67 mAhg at a current density of 20C in a rate test. ‑1 The specific capacity of the battery is significantly improved in the field of fast charge and discharge applications. After 2300 cycles at a current density of 0.5C, the discharge specific capacity can still be maintained at 100.59 mAhg ‑1 The Coulombic efficiency is 99.84%, and the cycle capacity attenuation rate is as low as 0.005%.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing electrode materials for sodium-ion batteries, and particularly relates to a preparation method and application of a modified sodium vanadium phosphate composite material. Background Art

[0002] The demand for and dependence on energy by human development have been increasing year by year. A large amount of coal-fired power generation releases a large amount of carbon dioxide, which causes an obvious greenhouse effect on the global human living environment and has a serious negative impact on the ecological balance of the earth. Therefore, there is a contradiction of imbalance between supply and demand. In order to balance the urgent demand for energy and the sustainable development of the ecological environment, researchers have proposed various energy storage methods to store intermittent green and renewable energy such as wind energy and solar energy. Electrochemical energy storage is further divided into various energy storage methods such as lithium battery energy storage, sodium battery energy storage, lead-acid battery energy storage, all-vanadium redox flow battery energy storage, and iron-chromium redox flow battery energy storage.

[0003] Sodium-ion batteries, due to their rich reserves and global average distribution of resources, effectively avoid the problem of resource restrictions by other countries. Sodium-ion batteries have a high capacity release rate at both high and low temperatures, and energy storage and two-wheeled electric vehicles will become the main application scenarios of sodium-ion batteries. The main technical routes for the positive electrode materials of sodium-ion batteries are: layered metal oxides, Prussian blue-based, and polyanion-based three major technical routes. Among the polyanion materials, sodium vanadium phosphate has advantages such as good thermal stability, strong cycle stability, and mild storage conditions, which have attracted more research by scholars and enterprises. However, the problem of poor conductivity seriously affects the release of the material's capacity, and it needs to be effectively modified.

[0004] The Chinese patent document with the publication number CN 114156453 B discloses a double-site doped modified sodium vanadium phosphate positive electrode material, which uses alkali metals to simultaneously replace the Na site and the V site to adjust the local chemical bond and electron distribution, and improve the electronic and ionic conductivity. However, replacing the Na and V sites with other elements will reduce the specific capacity, and the cycle stability of this invention is poor.

[0005] The Chinese patent document with the publication number CN 115995546 B discloses a sodium vanadium phosphate material with a three-dimensional carbon framework, its preparation method and application. Carbon nanotubes, carbon materials, and various carbon materials such as ZIF-8 are introduced to form an NVP-ZIF / CNTs / C three-dimensional carbon framework to enhance the electronic conductivity of sodium vanadium phosphate. However, too much carbon material is introduced into this material, and the cycle capacity attenuation rate is large.

[0006] The Chinese patent document with the publication number CN 114944479 B discloses a composite material of graphene composite potassium and silicon co-doped sodium vanadium phosphate, its preparation and application. Partially replace the Na site in sodium vanadium phosphate with K + and replace the Na site in sodium vanadium phosphate with Si 4+Partially replace the P site in sodium vanadium phosphate to achieve double doping of sodium vanadium phosphate, thereby improving the conductivity of sodium vanadium phosphate. The specific capacity released in the rate performance at a current density of 20C is 86 mAhg -1 , and there is still room for improvement. Summary of the Invention

[0007] The purpose of the method of the present invention is to provide a preparation method and application of a modified sodium vanadium phosphate composite material. The modified sodium vanadium phosphate composite material is prepared by a method of multivalent anion substitution combined with defective titanium dioxide coating, so as to improve the electronic conductivity and sodium ion diffusion kinetics of the material and optimize its electrochemical performance.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] On the one hand, the present invention provides a preparation method of a modified sodium vanadium phosphate composite material, including the following steps:

[0010] (1) Add a chain carbon source, a vanadium source, an ammonium phosphate salt, and an ammonium sulfate salt to deionized water, stir and heat for reaction; add a sodium source to the reacted solution and stir until dissolved to form a homogeneous solution. After aging the homogeneous solution, perform spray drying to obtain a Na3V2(PO4) 3-x (SO4) x precursor material;

[0011] (2) Add the Na3V2(PO4) 3-x (SO4) x precursor material and ammonia water to ethanol, ultrasonically disperse, and dropwise add a liquid titanium source to form a mixed solution. Heat and stir the mixed solution for reaction to obtain a suspension. Filter, wash, and dry the suspension to obtain a powder material; calcine the powder material in an Ar-H2 mixed atmosphere to obtain a modified sodium vanadium phosphate composite material (Na3V2(PO4) 3-x (SO4) x @H-TiO2).

[0012] Further, in the step (1), the chain carbon source is one of ascorbic acid, glucose, sucrose, and citric acid; the vanadium source is one of ammonium metavanadate, sodium metavanadate, and hexacarbonylvanadium; the ammonium phosphate salt is one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium hydrogen phosphate; the ammonium sulfate salt is ammonium bisulfate or ammonium sulfate; the sodium source is one of sodium carbonate, sodium oxalate, and sodium citrate; In the sodium source The molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphate radical in the ammonium phosphate salt, and sulfate radical in the ammonium sulfate salt is 3:2:3 - x:x , 0.03 ≤ x ≤ 0.17; the molar volume ratio of the chain carbon source to deionized water is 0.05~0.1 mol:2 L; the aging duration is 5~10 h; the spray drying temperature is 110~200 °C; the flow rate is 200~300 mLh -1 .

[0013] Further, in the step (2), the liquid titanium source is one of tetrabutyl titanate, titanium isopropoxide, and titanium chloride; Na3V2(PO4) 3-x (SO4) x The mass-volume ratio of the precursor material to the liquid titanium source is 0.3 g to 1.0 g: 0.3 mL; the concentration of ammonia water is 25 to 28 wt%; the volume ratio of ammonia water to ethanol is 0.2 mL to 0.3 mL: 50 mL; the heating temperature is 45°C to 65°C, and the stirring duration is 10 h to 15 h; the calcination is two-stage calcination, the first-stage calcination temperature is 350°C to 450°C, and the duration is 2 h to 4 h; the second-stage calcination temperature is 700°C to 900°C, and the duration is 6 h to 10 h;

[0014] On the other hand, the present invention also provides an application of the modified sodium vanadium phosphate composite material prepared by the above method, and uses the modified sodium vanadium phosphate composite material as a cathode material for sodium ion batteries.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0016] In the prior art, other elements are usually used to replace the Na and V sites in the electrode material. However, since Na and V elements are capacity-contributing elements, replacing them has a certain impact on the theoretical specific capacity. Compared with the prior art, the technical solution of the present invention uses SO4 radicals with a similar tetrahedral structure to dope and replace part of the PO4 radicals, which can make SO4 radicals and PO4 radicals coexist in the material framework structure to form a defect structure and generate a local current, effectively improving the conductivity of the material without affecting the theoretical specific capacity of the electrode material and the stability of the framework structure of the material itself; compared with the modification method of using single atoms such as F and Cl to replace PO4 radicals, the modification method of using SO4 radicals to replace part of the PO4 radicals has more definite substitution sites, which is convenient for precise regulation.

[0017] The technical solution of the present invention dissolves the Na3V2(PO4) 3-x (SO4) x precursor material, ammonia water, and liquid titanium source in ethanol to form solution A, so that the Na3V2(PO4) 3-x (SO4) x precursor material and the titanium source are in liquid-phase contact, improving the diffusion efficiency and compatibility of molecules between the two liquid phases of the Na3V2(PO4) 3-x (SO4) x precursor dispersion liquid and the titanium source liquid. Using ethanol as a solvent and adding the liquid titanium source drop by drop can reduce the hydrolysis rate of the titanium source, and make the titanium compound uniformly coated on the Na3V2(PO4) 3-x (SO4) xSurface of the precursor material; Compared with solid-phase contact coating, the liquid-phase contact coating adopted in the technical solution of the present invention has the following advantages. First, the amount of titanium compound coated and the thickness of the titanium coating layer are controllable, improving the consistency of the target material and stabilizing the electrochemical performance of the product. Second, the uniformity of the titanium compound coating is improved, effectively avoiding problems such as material agglomeration and sintering during the calcination process. Moreover, the uniformly coated surface layer can effectively reduce the loss of active transition metals and avoid side reactions such as electrolyte decomposition, improving the cycle stability of the material.

[0018] The modified sodium iron pyrophosphate phosphate composite material formed by calcining the powder material in an Ar-H2 mixed atmosphere according to the technical solution of the present invention. H2 can not only prevent the presence of multiple valence states of iron ions from affecting the purity and specific capacity of the target material, but also dope H elements into titanium dioxide during the calcination process to form a defect-hydrogen doped titanium dioxide coating layer on the material surface, and there is a part of Ti 4+ and Ti 2+ , and local charge flow is formed between ions of different valence states; the material has a carbon network structure inside the bulk phase and a defective titanium dioxide layer on the surface layer, which can effectively improve the conductivity of the material.

[0019] Under the dual strategies of adopting bulk-phase doping of SO4 radicals and external coating of defective titanium dioxide, the technical solution of the present invention effectively improves the reaction kinetics of the modified sodium vanadium phosphate composite material, achieving the effect of optimizing the electrochemical performance of the material.

[0020] The technical solution of the present invention uses spray drying to obtain the Na3V2(PO4) 3-x (SO4) x precursor material, and spherical precursors are obtained under low energy consumption conditions by adjusting the temperature and flow rate, avoiding problems such as insufficient drying of the powder and nozzle blockage due to too fast flow rate, and low production efficiency due to too slow flow rate.

[0021] The calcination of the powder material in an Ar-H2 mixed atmosphere according to the technical solution of the present invention includes two-stage calcination. The first stage is calcined at 350°C to 450°C to stabilize the material structure and shape the material morphology. The second stage is high-temperature calcination at 700°C to 900°C to further improve the crystallinity of the material on the premise of ensuring the material structure.

[0022] When the modified sodium vanadium phosphate composite material is applied to a sodium-ion battery, at a current density of 20C in the rate test, the battery releases a specific capacity of 102.67 mAhg -1 , and after 2300 cycles at a current density of 0.5C, the discharge specific capacity can still remain at 100.59 mAhg -1 , and the Coulomb efficiency is 99.84%. Description of the Drawings

[0023] Figure 1The Na3V2(PO4) obtained in Example 1 3-x (SO4) x SEM morphology diagram of the precursor material at a magnification of 882 times;

[0024] Figure 2 The modified sodium vanadium phosphate composite material (Na3V2(PO4) 2.91 (SO4) 0.08 @H-TiO2) SEM morphology diagram at a magnification of 7510 times under scanning electron microscopy;

[0025] Figure 3 The modified sodium vanadium phosphate composite material (Na3V2(PO4) 2.91 (SO4) 0.08 @H-TiO2) XRD diffraction pattern;

[0026] Figure 4 The modified sodium vanadium phosphate composite material (Na3V2(PO4) 2.91 (SO4) 0.08 @H-TiO2) As a cathode material applied in a sodium-ion battery, rate performance at different current densities;

[0027] Figure 5 The modified sodium vanadium phosphate composite material (Na3V2(PO4) 2.91 (SO4) 0.08 @H-TiO2) As a cathode material applied in a sodium-ion battery, cycling performance at a current density of 0.5C. Detailed implementation manners

[0028] The present invention will be further described in detail below in conjunction with the embodiments. The accompanying drawings of the specification and the embodiments are only used to explain the present invention and do not constitute an improper limitation to the present invention. It should be noted that the ammonia water used in the following various examples is a commercially available reagent with an ammonia content of 25 - 28 wt%. Example 1

[0029] (1) Add 0.05 mol of citric acid, 1.2 mol of ammonium metavanadate, 1.75 mol of ammonium dihydrogen phosphate, and 0.05 mol of ammonium bisulfate to 2 L of deionized water, and stir and heat the reaction at 60 °C; add 0.9 mol of sodium carbonate to the reacted solution and stir until dissolved to form a homogeneous solution. After aging at 80 °C for 10 h, spray drying is carried out at 110 °C and 200 mL / h -1 to obtain the Na3V2(PO4) 2.91 (SO4) 0.08 precursor material;

[0030] (2) Add 0.3 g of Na3V2(PO4)2.91 (SO4) 0.08 The precursor material and 0.2 mL of 25 - 28 wt% ammonia water were added to 50 mL of ethanol, ultrasonically dispersed for 15 min, and 0.3 mL of tetrabutyl titanate was added dropwise. The mixture was heated and stirred at 45 °C for 15 h to obtain a suspension. The suspension was filtered, washed, and dried to obtain a powder material; the powder material was calcined in an Ar - H2 mixed atmosphere, first calcined at 350 °C for 4 h, and then calcined at 800 °C for 8 h to finally obtain Na3V2(PO4) 2.91 (SO4) 0.08 @H - TiO2 composite material, namely modified sodium vanadium phosphate composite material.

[0031] As Figure 1 shown, the technical solution of Example 1 uses SO4 radicals with a similar tetrahedral structure to dope and replace part of the PO4 radicals. Without affecting the theoretical specific capacity of the electrode material and the stability of the framework structure of the material itself, SO4 radicals and PO4 radicals can co - exist in the material framework structure, forming a defect structure and forming a local current, effectively improving the conductivity of the material. The Na3V2(PO4) 2.91 (SO4) 0.08 The precursor material is a micron - scale spherical material. The amount of coated titanium compound and the thickness of the titanium coating layer are controllable, improving the consistency and coating uniformity of the target material. The obtained modified sodium vanadium phosphate composite material is calcined to obtain the material as Figure 2 shown. As confirmed by XRD test as Figure 3 shown, the successful synthesis of the modified sodium vanadium phosphate composite material is verified. The dual strategies of bulk doping and external coating of defective titanium dioxide not only effectively avoid the problems of material agglomeration and sintering during the calcination process, but also the uniform surface coating layer can effectively reduce the loss of active transition metals and avoid side reactions such as electrolyte decomposition, improving the cycle stability of the material. The technical solution of the present invention effectively improves the reaction kinetics of the modified sodium vanadium phosphate composite material and achieves the effect of optimizing the electrochemical performance of the material by adopting the dual strategies of bulk doping with SO4 radicals and external coating of defective titanium dioxide. The modified sodium vanadium phosphate composite material prepared in Example 1 was used as the positive electrode in a sodium - ion battery for rate performance tests at different current densities as Figure 4 shown. The cycle performance at a current density of 0.5C is as Figure 5 shown. After 2300 cycles, the discharge specific capacity can still remain at 100.59 mAhg -1 , the Coulomb efficiency is 99.84%, and the cycle capacity attenuation rate is as low as 0.005%. Example 2

[0032] (1) Add 0.1 mol of ascorbic acid, 1.2 mol of sodium metavanadate, 1.78 mol of diammonium hydrogen phosphate, and 0.02 mol of ammonium sulfate to 2 L of deionized water, and stir and heat the reaction at 60 °C; add 0.9 mol of sodium oxalate to the reacted solution and stir until dissolved to form a homogeneous solution. After aging at 80 °C for 8 h, spray drying is carried out at 150 °C and 300 mL / h -1 to obtain the Na3V2(PO4) 2.97 (SO4) 0.03 precursor material;

[0033] (2) Add 0.5 g of the Na3V2(PO4) 2.97 (SO4) 0.03 precursor material and 0.2 mL of 25 - 28 wt% ammonia water to 50 mL of ethanol, ultrasonically disperse for 15 min, and dropwise add 0.3 mL of titanium isopropoxide. Stir and heat at 65 °C for 10 h to obtain a suspension. Filter, wash, and dry the suspension to obtain a powder material; calcine the powder material in an Ar - H2 mixed atmosphere, first calcine at 400 °C for 2 h, and then calcine at 900 °C for 6 h to finally obtain the Na3V2(PO4) 2.97 (SO4) 0.03 @H - TiO2 composite material, that is, the modified sodium vanadium phosphate composite material. Example 3

[0034] (1) Add 0.05 mol of glucose, 1.2 mol of hexacarbonylvanadium, 1.7 mol of ammonium hydrogen phosphate, and 0.1 mol of ammonium sulfate to 2 L of deionized water, and stir and heat the reaction at 60 °C; add 0.6 mol of sodium citrate to the reacted solution and stir until dissolved to form a homogeneous solution. After aging at 80 °C for 5 h, spray drying is carried out at 180 °C and 200 mL / h -1 to obtain the Na3V2(PO4) 2.83 (SO4) 0.17 precursor material;

[0035] (2) Add 0.5 g of the Na3V2(PO4) 2.83 (SO4) 0.17 precursor material and 0.3 mL of 25 - 28 wt% ammonia water to 50 mL of ethanol, ultrasonically disperse for 15 min, and dropwise add 0.3 mL of titanium chloride. Stir and heat at 55 °C for 13 h to obtain a suspension. Filter, wash, and dry the suspension to obtain a powder material; calcine the powder material in an Ar - H2 mixed atmosphere, first calcine at 350 °C for 4 h, and then calcine at 800 °C for 8 h to finally obtain the Na3V2(PO4) 2.83 (SO4) 0.17@H-TiO2 composite material, namely modified sodium vanadium phosphate composite material. Example 4

[0036] (1) Add 0.1 mol of sucrose, 2.4 mol of hexacarbonylvanadium, 3.4 mol of ammonium hydrogen phosphate, and 0.2 mol of ammonium sulfate into 2 L of deionized water, stir and heat the reaction at 60 °C; add 1.2 mol of sodium citrate to the reacted solution and stir until dissolved to form a homogeneous solution. After aging at 80 °C for 10 h, spray drying is carried out at 200 °C and 200 mL / h -1 to obtain the Na3V2(PO4) 2.83 (SO4) 0.17 precursor material;

[0037] (2) Add 1.0 g of Na3V2(PO4) 2.83 (SO4) 0.17 precursor material and 0.3 mL of 25 - 28 wt% ammonia water into 50 mL of ethanol, ultrasonically disperse for 15 min, and dropwise add 0.3 mL of titanium chloride. Heat and stir at 65 °C for 10 h to obtain a suspension. Filter, wash, and dry the suspension to obtain a powder material; calcine the powder material in an Ar-H2 mixed atmosphere, first calcine at 450 °C for 3 h, and then calcine at 700 °C for 10 h to finally obtain Na3V2(PO4) 2.83 (SO4) 0.17 @H-TiO2 composite material, namely modified sodium vanadium phosphate composite material.

[0038]

[0039] Prepare the electrode sheets and assemble the sodium-ion batteries for the materials obtained in each example, and the test data are shown in Table 1. From the result comparison, under the experimental conditions of Example 1, when doping sulfate to form Na3V2(PO4) 2.91 (SO4) 0.08 the charge-discharge specific capacity and cycle performance of the battery are the best.

Claims

1. A preparation method of a modified sodium vanadium phosphate composite material, characterized in that, It includes the following steps: (1) Add the chain carbon source, vanadium source, ammonium phosphate salt and ammonium sulfate salt into deionized water, stir and heat for reaction. Add the sodium source to the reacted solution and stir until dissolved to form a homogeneous solution. After aging the homogeneous solution, perform spray drying to obtain the Na3V2(PO4) 3-x (SO4) x precursor material; the molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphate radical in the ammonium phosphate salt, and sulfate radical in the ammonium sulfate salt is 3:2:3 - x:x, where 0.03 ≤ x ≤ 0.17; (2) Add Na3V2(PO4) 3-x (SO4) x precursor material and ammonia water into ethanol, ultrasonically disperse them, and dropwise add the liquid titanium source to reduce the hydrolysis rate of the titanium source and uniformly coat the titanium compound on the surface of the Na3V2(PO4) 3-x (SO4) x precursor material; form a mixed solution, heat and stir the mixed solution for reaction to obtain a suspension, filter, wash, and dry the suspension to obtain a powder material; calcine the powder material in an Ar-H2 mixed atmosphere to obtain a modified sodium vanadium phosphate composite material; In the step (1), the chain carbon source is one of ascorbic acid, glucose, sucrose, and citric acid; the vanadium source is one of ammonium metavanadate, sodium metavanadate, and hexacarbonylvanadium; the ammonium phosphate salt is one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium hydrogen phosphate; the ammonium sulfate salt is ammonium bisulfate or ammonium sulfate; the sodium source is one of sodium carbonate, sodium oxalate, and sodium citrate; the molar volume ratio of the chain carbon source to deionized water is 0.05 - 0.1 mol: 2 L; the aging duration is 5 - 10 h; the spray drying temperature is 110 - 200 °C; the flow rate is 200 - 300 mL / h -1 ; In the step (2), the liquid titanium source is one of tetrabutyl titanate, titanium isopropoxide, and titanium chloride; Na3V2(PO4) 3-x (SO4) x The mass-volume ratio of the precursor material to the liquid titanium source is 0.3 g to 1.0 g: 0.3 mL; the concentration of ammonia water is 25 to 28 wt%; the volume ratio of ammonia water to ethanol is 0.2 mL to 0.3 mL: 50 mL; the heating temperature is 45°C to 65°C, and the stirring duration is 10 h to 15 h; the calcination is two-stage calcination, the temperature of the first-stage calcination is 350°C to 450°C, and the duration is 2 h to 4 h; the temperature of the second-stage calcination is 700°C to 900°C, and the duration is 6 h to 10 h.

2. Use of a modified sodium vanadium phosphate composite material prepared by the method according to claim 1, characterized in that, Use the modified sodium vanadium phosphate composite material as the cathode material for a sodium-ion battery.

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