A method for preparing a positive electrode material for a polyanion sodium ion battery

Abstract

The present invention relates to a method for preparing a positive electrode material for a polyanion sodium ion battery. The method comprises the following steps: (1) mixing raw materials and a carbon source; (2) spray drying; (3) coating the precursor surface with a sodium supplementation layer; and (4) microwave sintering. The present invention improves the intrinsic conductivity and ion deintercalation rate of the positive electrode material by doping with transition metal elements to replace vanadium sites; improves the electronic conductivity of the positive electrode material by coating with a carbon layer, thereby improving the cycle performance and rate performance of the battery; and coating the surface with a sodium supplementation layer not only reduces side reactions between the positive electrode material and the electrolyte, but also effectively solves the problem of irreversible sodium consumption in sodium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for preparing a positive electrode material for a polyanion sodium ion battery. Background Art

[0002] With the rapid development of new energy devices, secondary batteries with excellent performance have attracted the attention of researchers. Lithium-ion batteries (LIBs) have played a leading role as secondary batteries in the past few decades and are the main power source of choice for portable and mobile devices. However, with the excessive growth of demand for energy storage, lithium reserves have become increasingly scarce, and the search for alternative lithium reserves has become more urgent. Sodium batteries (SIBs) have the advantages of low cost, high sodium abundance, high sodium ion utilization, and the same working mode as LIBs, which makes SIBs show excellent potential in energy storage systems. Due to the different radii of sodium ions in SIBs and lithium ions in LIBs, cathode materials that can be used for LIBs cannot be directly used as cathode materials for SIBs. Therefore, the development of cathode materials suitable for sodium-ion batteries is of great significance.

[0003] Polyanion-type sodium-ion battery cathode Na3V2(PO4)3(NVP) has high sodium ion mobility, a high operating voltage platform (approximately 3.4V), and a stable structure, making it a very competitive and promising sodium-ion battery cathode material. However, polyanion-type sodium-ion battery cathode Na3V2(PO4)3 has poor conductivity, and the radius of sodium ions is larger than that of lithium ions, making sodium deintercalation more difficult than lithium deintercalation. This results in a low actual discharge capacity and poor rate performance. Summary of the Invention

[0004] The present invention is mainly aimed at overcoming the problems of poor conductivity of the positive electrode of polyanion sodium ion battery and irreversible consumption of anode sodium ions, which reduce the coulombic efficiency, full battery capacity, energy density and the like, and provides a method for preparing the positive electrode material of polyanion sodium ion battery.

[0005] To achieve the above object, the present invention provides a method for preparing a polyanion sodium ion battery positive electrode material, comprising the following steps:

[0006] (1) weighing a sodium source, a vanadium source, and a transition metal source in a desired stoichiometric ratio, adding them to deionized water, and stirring to obtain a first solution; weighing a phosphorus source according to the stoichiometric ratio of sodium and phosphorus, and adding the phosphorus source and a carbon source to the first solution, performing ultrasonic dispersion to obtain a second solution; heating and fully stirring to obtain a uniformly mixed precursor solution;

[0007] (2) placing the precursor solution into a spray drying device for spray drying to obtain a carbon-coated precursor powder;

[0008] (3) adding the carbon-coated precursor powder and the sodium supplement agent to a solvent, performing ultrasonic treatment and fully stirring and mixing, and then vacuum evaporating, grinding and screening to obtain a precursor powder compositely coated with carbon and sodium supplement layer;

[0009] (4) The precursor powder coated with the carbon and sodium supplement layer is microwave sintered under an inert atmosphere, and then ground and sieved to obtain a sodium ion battery positive electrode material coated with the carbon and sodium supplement layer.

[0010] Preferably, the chemical formula of the sodium ion battery positive electrode material is Na3V 2-x M x (PO4)3, where M is a transition metal element and x is in the range of 0.005-1.

[0011] Preferably, in step (1), the sodium source is selected from at least one of sodium carbonate, sodium citrate, sodium acetate, sodium oxalate, and sodium dihydrogen phosphate; the vanadium source is selected from at least one of ammonium metavanadate, sodium metavanadate, vanadium oxalate, and vanadyl hydroxide; the transition metal is at least one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, and Ru, and the transition metal source is at least one of the carbonate, oxalate, and acetate of the corresponding transition metal; the phosphorus source is selected from at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phosphoric acid, metaphosphoric acid, and sodium metaphosphate; and the carbon source is selected from at least one of glucose, fructose, sucrose, starch, cellulose, carbon nanotubes, hexadecyltrimethylammonium bromide, polyethylene glycol octylphenyl ether, sodium dodecylbenzenesulfonate, polyvinyl pyrrolidone, sodium polyacrylate, and polyacrylic acid.

[0012] Preferably, the solubility of the precursor solution in step (1) is 0.05-1.5 mol / L.

[0013] Preferably, the spray drying in step (2) is carried out in a pressure-type or centrifugal-type spraying manner; the air inlet temperature is 150-250°C, and the outlet temperature is 50-120°C.

[0014] Preferably, the carbon source in step (1) is 0.1-5 wt% of the total mass of the positive electrode material; and the sodium supplement in step (3) is 1-8 wt% of the carbon-coated precursor powder.

[0015] Preferably, the sodium supplement in step (3) is selected from at least one of Na2C3O3, Na2C4O4, Na2C5O5, Na2C6O6, Na2C2O4, Na2C3O5, Na2C4O6, Na2C5O7, Na2C6O8, and sodium citrate.

[0016] Preferably, the solvent in step (3) is any one of deionized water, methanol, ethanol, isopropanol, acetonitrile, N-methylformamide, and dimethyl sulfoxide.

[0017] Preferably, the grinding and screening in steps (3) and (4) are performed by grinding with an agate mortar and then screening with a sieve of 100-200 mesh.

[0018] Preferably, the specific operation of microwave sintering in step (4) is: placing the precursor powder compositely coated with carbon and sodium-filled layer in a corundum boat, sending it into a microwave sintering furnace, heating it from room temperature to 300-500°C at a heating rate of 0.5°C / min-10°C / min for pre-sintering for 3-8h, and then sintering it at a high temperature of 600°C-950°C for 4-20 hours and then cooling it naturally.

[0019] Preferably, the stirring in step (1) is carried out by magnetic stirring, with a rotation speed of 1000-1500 rpm and a stirring time of 1-2 hours; the stirring in step (3) is carried out by magnetic stirring, with a rotation speed of 1000-1500 rpm, a stirring temperature of 25-60°C and a stirring time of 2-6 hours.

[0020] Preferably, the ultrasonic treatment temperature in steps (1) and (3) is 25-50° C., and the ultrasonic treatment time is 0.5-2 h.

[0021] Preferably, the heating in step (1) is performed in a water bath at 50-90° C. for 0.5-2 h.

[0022] Preferably, the vacuum evaporation temperature in step (3) is 80-180° C., and the evaporation time is 1-10 h.

[0023] Preferably, the inert atmosphere in step (4) comprises one of pure argon, nitrogen, and a nitrogen-argon mixture.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0025] (1) The sodium ion battery positive electrode Na3V prepared by the present invention 2-x M x (PO4)3, compared with the positive electrode of sodium ion battery Na3V2(PO4)3, Na3V 2-x M x The (PO4)3 positive electrode material is doped with transition metal elements to replace vanadium sites to improve the intrinsic conductivity and ion deintercalation rate of the positive electrode material, solving the problems of poor cycle performance and rate performance of polyanion sodium ion batteries; at the same time, the cost and toxicity are further reduced by replacing doping.

[0026] (2) The present invention prepares the sodium ion battery positive electrode by a spray drying method, which has a single crystal morphology and a small particle size. The smaller positive electrode particle size can shorten the diffusion path of ions in the particles and improve the structural stability during the sodium ion embedding and de-embedding process.

[0027] (3) The present invention further improves the ion / electron transport at the interface between the positive electrode active material and the electrolyte / electrolyte by carbon-coating the positive electrode material of the sodium ion battery, thereby further improving the cycle stability and high-rate performance of the battery.

[0028] (4) The present invention coats the positive electrode material of the sodium ion battery with a sodium supplement, which can compensate for the irreversible consumption of sodium ions at the anode, solves the problem of structural collapse that is prone to occur during the cycle of the positive electrode material, and thus improves the coulombic efficiency, energy density and cycle stability; at the same time, compared with adding the positive electrode sodium supplement to the positive electrode slurry, the surface coating of the sodium supplement can increase the usage of the positive electrode active material, further improving the energy density and battery capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an SEM image of the sodium ion battery positive electrode material compositely coated with carbon and sodium supplement layer prepared in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention.

[0031] Example 1:

[0032] Sodium acetate, vanadium hydroxide and manganese acetate were weighed in a stoichiometric ratio of 3:1:1 of the molar ratio of Na, V and Mn, and added to 2L of deionized water. The mixture was stirred at 1200 rpm for 30 min by magnetic stirring to obtain a first solution. Phosphoric acid was weighed according to the ratio of Na:P=1:1, and glucose accounting for 1 wt% of the total mass of the positive electrode was weighed. All of the solution was finally added to the first solution. The solution was ultrasonicated at 25°C for 1 h to obtain a second solution, which was placed in a water bath at 80°C and heated with stirring for 1 h to obtain a 0.5 mol / L precursor solution. The precursor solution was placed in a spray drying device for spray drying under the conditions of an air inlet temperature of 220°C and an outlet temperature of 100°C. The gas inlet temperature is 95°C to obtain a carbon-coated precursor powder; 2g of the carbon-coated precursor powder and 20mg of Na2C4O4 are added to ethanol, fully stirred for 1h and ultrasonicated for 30min, and then vacuum evaporated at 90°C for 2h, ground for 15min and sieved with a 200-mesh sieve to obtain a precursor powder compositely coated with a carbon and sodium-supplementing layer; the above-mentioned precursor powder is placed in a corundum boat, and in an argon environment, pre-sintered at 400°C for 5h at a heating rate of 3°C / min, and then sintered at 800°C for 8 hours and naturally cooled, and ground and sieved to obtain a sodium ion battery positive electrode material compositely coated with a carbon and sodium-supplementing layer.

[0033] Figure 1 This is a SEM image of the carbon-and-sodium-supplementing layer composite-coated sodium-ion battery cathode material prepared in Example 1. The SEM image shows that the sample prepared in Example 1 has a particle size of approximately 0.5-1 micron. A smaller particle size shortens the diffusion path of ions within the particles, thereby improving the conductivity of the cathode material. The particles have a distinct coating layer on their surface, which can reduce side reactions during battery cycling, thereby increasing the battery's cycle life.

[0034] Example 2:

[0035] Sodium oxalate, vanadium oxalate, and titanium oxalate were weighed in a stoichiometric ratio of 3:1:1 of Na, V, and Ti, and added to 2 L of deionized water. The mixture was stirred at 1400 rpm for 1 h by magnetic stirring to obtain a first solution. Metaphosphoric acid and 2 wt% of the total mass of the positive electrode were weighed and finally added to the first solution. The mixture was ultrasonicated at 40°C for 1 h to obtain a second solution, which was placed in a 90°C water bath and heated with stirring for 1 h to obtain a 0.8 mol / L precursor solution. The precursor solution was placed in a spray drying device for spray drying under the condition that the air inlet temperature was 230°C. The outlet temperature is 105°C to obtain a carbon-coated precursor powder; 2g of the carbon-coated precursor powder and 40mg of Na2C2O4 are added to isopropanol, fully stirred for 1h and ultrasonicated for 30min, and then vacuum evaporated at 90°C for 2h, ground for 15min and sieved with a 200-mesh sieve to obtain a precursor powder compositely coated with a carbon and sodium-supplementing layer; the above-mentioned precursor powder is placed in a corundum boat, and in a nitrogen environment, pre-sintered at 450°C for 4h at a heating rate of 3°C / min, and then sintered at a high temperature of 820°C for 8 hours and naturally cooled, and ground and sieved to obtain a sodium ion battery positive electrode material compositely coated with a carbon and sodium-supplementing layer.

[0036] Example 3:

[0037] Sodium carbonate, ammonium metavanadate, and nickel acetate were weighed in a stoichiometric ratio of 3:1:1 of Na, V, and Ni, and added to 1 L of deionized water. The mixture was stirred at 1500 rpm for 30 min by magnetic stirring to obtain a first solution. Then, diammonium hydrogen phosphate was weighed in a ratio of Na:P=1:1, and polyvinyl pyrrolidone (3 wt% of the total mass of the positive electrode) was weighed. The whole solution was finally added to the first solution, and ultrasonicated at 50°C for 1 h to obtain a second solution. The solution was placed in a water bath at 90°C and heated with stirring for 1 h to obtain a 1 mol / L precursor solution. The precursor solution was placed in a spray drying device for spray drying under the condition that the air inlet temperature was 240°C. The outlet temperature is 110°C to obtain a carbon-coated precursor powder; 2g of the carbon-coated precursor powder and 60mg of Na2C4O6 are added to acetonitrile, fully stirred for 1h and ultrasonicated for 30min, and then vacuum evaporated at 150°C for 3h, ground for 15min and sieved with a 200-mesh sieve to obtain a precursor powder compositely coated with a carbon and sodium-supplementing layer; the above-mentioned precursor powder is placed in a corundum boat, and in an argon environment, pre-sintered at 500°C for 4h at a heating rate of 3°C / min, and then sintered at a high temperature of 850°C for 6 hours and naturally cooled, and ground and sieved to obtain a sodium ion battery positive electrode material compositely coated with a carbon and sodium-supplementing layer.

[0038] Example 4:

[0039] Sodium citrate, vanadyl hydroxide and ferric acetate were weighed in a stoichiometric ratio of 3:1:1 of the molar ratio of Na, V and Fe and added to 2L of deionized water. The mixture was stirred at 1500 rpm for 1 hour by magnetic stirring to obtain a first solution. Ammonium dihydrogen phosphate was weighed according to the ratio of Na:P=1:1, and sodium polyacrylate was weighed as the carbon source, which was 4 wt% of the total mass of the positive electrode. All of the solution was finally added to the first solution. The solution was ultrasonicated at 50°C for 1 hour to obtain a second solution. The solution was placed in a water bath at 90°C and heated with stirring for 1 hour to obtain a 1 mol / L precursor solution. The precursor solution was placed in a spray drying device for spray drying under the conditions of an inlet temperature of 250 ℃, the outlet temperature is 120℃, and a carbon-coated precursor is obtained; 2g of carbon-coated precursor powder and 80mg of sodium citrate are added to ethanol, fully stirred for 1h and ultrasonicated for 30min, and then vacuum evaporated at 90℃ for 2h, ground for 15min and sieved with a 200-mesh sieve to obtain a precursor powder compositely coated with a carbon and sodium-supplementing layer; the above-mentioned precursor powder is placed in a corundum boat, and in an argon environment, it is pre-sintered at 350℃ for 8h at a heating rate of 3℃ / min, and then sintered at a high temperature of 780℃ for 12 hours and then naturally cooled, and ground and sieved to obtain a sodium ion battery positive electrode material compositely coated with a carbon and sodium-supplementing layer.

[0040] Comparative Example 1: The preparation steps are the same as those in Example 1, except that no transition metal source is added for doping and substitution during the preparation process to obtain a Na3V2(PO4)3 positive electrode material compositely coated with a carbon and sodium-supplementing layer.

[0041] Comparative Example 2: The preparation steps are the same as those of Example 1, except that no carbon source is added for carbon coating during the preparation process, and a Na3VMn(PO4)3 positive electrode material coated with a sodium supplement layer is obtained.

[0042] Comparative Example 3: The preparation steps are the same as those of Example 1, except that no sodium-supplementing layer coating modification is performed, and the carbon-coated Na3VMn(PO4)3 positive electrode material is directly obtained.

[0043] Performance Testing

[0044] The sodium ion positive electrode materials prepared in Example 1 and Comparative Examples 1-3 were made into 2032 button batteries and tested. The specific performance is shown in Table 1 below:

[0045] Table 1 Performance data of button batteries made of positive electrode materials of Example 1 and Comparative Examples 1-3

[0046]

[0047] From Table 1, it can be seen that the 5C gram capacity of the material in Example 1 is much higher than that in Comparative Examples 1-3, indicating that the present method is very effective in improving the discharge performance of polyanion sodium ion batteries under large currents; compared with Comparative Example 1, the rate performance and cycle performance of the material doped with transition metal ions in Example 1 are much better than those of the undoped material; compared with Comparative Example 2, the cycle performance and rate performance of the positive electrode with carbon coating in Example 1 are better than those of the positive electrode without carbon coating; compared with Comparative Example 3, the capacity retention rate of the positive electrode material coated with the sodium supplement layer in Example 1 is higher, thanks to the fact that the sodium supplement layer supplements the irreversible consumption of sodium ions at the anode during the battery cycle.

Claims

1. A method for preparing a polyanion sodium ion battery positive electrode material, characterized in that: The following steps are involved: (1) weighing a sodium source, a vanadium source, and a transition metal source according to a desired stoichiometric ratio, adding them to deionized water, and stirring to obtain a first solution; weighing a phosphorus source according to a stoichiometric ratio of sodium to phosphorus, and adding the phosphorus source and a carbon source to the first solution, performing ultrasonic dispersion to obtain a second solution; heating and fully stirring to obtain a uniformly mixed precursor solution; (2) placing the precursor solution into a spray drying device for spray drying to obtain a carbon-coated precursor powder; (3) adding the carbon-coated precursor powder and the sodium supplement agent into a solvent, performing ultrasonic treatment and fully stirring and mixing, and then vacuum evaporating, grinding and screening to obtain the precursor powder composite-coated with the carbon and sodium supplement layer; (4) subjecting the precursor powder coated with the carbon and sodium-supplementing layer to microwave sintering under an inert atmosphere, and grinding and screening to obtain a sodium-ion battery positive electrode material coated with the carbon and sodium-supplementing layer; The carbon source in step (1) is 0.1-5 wt% of the total mass of the prepared positive electrode material; and the sodium supplement in step (3) is 1-8 wt% of the carbon-coated precursor powder.

2. The method according to claim 1, characterized in that The chemical formula of the sodium ion battery positive electrode material is Na3V 2-x M x (PO4)3, where M is a transition metal element and x is in the range of 0.005-1.

3. The method according to claim 1, characterized in that In the step (1), the sodium source is selected from at least one of sodium carbonate, sodium citrate, sodium acetate, sodium oxalate, and sodium dihydrogen phosphate; the vanadium source is selected from at least one of ammonium metavanadate, sodium metavanadate, vanadium oxalate, and vanadyl hydroxide; the transition metal is at least one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, and Ru, and the transition metal source is at least one of carbonates, oxalates, and acetates of the corresponding transition metals; the phosphorus source is selected from at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phosphoric acid, metaphosphoric acid, and sodium metaphosphate; and the carbon source is selected from at least one of glucose, fructose, sucrose, starch, cellulose, carbon nanotubes, hexadecyltrimethylammonium bromide, polyethylene glycol octylphenyl ether, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, sodium polyacrylate, and polyacrylic acid.

4. The method according to claim 1, wherein The solubility of the precursor solution in step (1) is 0.05-1.5 mol / L.

5. The method according to claim 1, wherein The spray drying in step (2) is carried out in a pressure-type or centrifugal-type spraying manner; the air inlet temperature is 150-250°C, and the outlet temperature is 50-120°C.

6. The method according to claim 1, characterized in that The sodium supplement in step (3) is selected from at least one of Na2C3O3, Na2C4O4, Na2C5O5, Na2C6O6, Na2C2O4, Na2C3O5, Na2C4O6, Na2C5O7, Na2C6O8, and sodium citrate.

7. The method according to claim 1, characterized in that The solvent in step (3) is any one of deionized water, methanol, ethanol, isopropanol, acetonitrile, N-methylformamide, and dimethyl sulfoxide.

8. The method according to claim 1, characterized in that The grinding and screening in steps (3) and (4) are performed by grinding with an agate mortar and then screening with a sieve of 100-200 mesh.

9. The method according to claim 1, characterized in that The specific operation of microwave sintering in step (4) is as follows: placing the precursor powder coated with carbon and sodium-filled layer in a corundum boat, sending it into a microwave sintering furnace, heating it from room temperature to 300-500°C at a heating rate of 0.5°C / min-10°C / min for pre-sintering for 3-8 hours, and then sintering it at a high temperature of 600°C-950°C for 4-20 hours and then cooling it naturally.

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