Positive electrode material for sodium batteries, its manufacturing method and applications

Abstract

The present invention provides a sodium battery positive electrode material, the chemical formula of the sodium battery positive electrode material is xNaMBO3.yNa2Ti3O7.zNa3V2(BO3)3 / C, where the molar ratio of x, y and z is 0.94-0.96:0.02-0.03:0.02-0.03, M is Fe and Mn, the molar ratio of Fe and Mn is 8-9:1-2, and the mass fraction of carbon in the sodium battery positive electrode material is 1.2%-1.5%. The sodium battery positive electrode material provided by the present invention has high capacity, high voltage platform, stable structure, high cycle performance, and its manufacturing method is simple, low cost, and short process flow.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to a Chinese patent application filed with the China Patent Office on July 29, 2022, bearing application number 202210907322.9 and entitled "Positive electrode material for sodium battery, manufacturing method thereof and application thereof," the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of sodium battery technology, and more particularly to a positive electrode material for sodium batteries, and its manufacturing method and application. [Background technology]

[0003] With the daily depletion of fossil fuels and the rapid development of clean energy such as wind and solar energy, the global energy consumption mode is gradually shifting from fossil fuels to new energy sources, which largely depends on advanced large-scale energy storage technology.

[0004] Among the various energy storage technologies currently available, commercialized lithium-ion batteries are a relatively mature energy storage technology, with advantages such as high energy density, low self-discharge rate, long life, ease of integration and management, etc. Sodium-ion batteries first appeared in the 1980s, and research into sodium-ion batteries subsequently stalled due to the superior performance of lithium-ion batteries.

[0005] After 2010, the ever-increasing demand for power batteries led to a shortage of lithium-ion battery materials, which prompted a resumption of research into room-temperature sodium-ion batteries. According to application scenarios, sodium-ion batteries can be divided into two main categories: power and energy storage. Compared to the mature commercialization of lithium-ion batteries, the commercialization of sodium-ion batteries is still in its infancy, with only a small number of companies achieving initial commercialization of sodium-ion batteries and no fully developed industrial chain.

[0006] In recent years, sodium-ion battery technology has gained renewed popularity among researchers due to its advantages, such as abundant global sodium resource reserves, low cost, and similar energy storage principles and process technologies to lithium-ion batteries, and has developed into an energy storage technology with great application potential.

[0007] Although sodium-ion batteries have the potential advantage of low cost, their cycle life and rechargeability cannot meet the demands of current large-scale energy storage technology. As a medium for electrochemical reactions, the electrolyte is an important factor that determines the thermodynamic and kinetic processes of the electrode material interface reaction, thereby affecting the cycle stability, rechargeability, etc. of sodium-ion batteries. Although the properties of sodium and lithium are similar, Na + Li + The specific phase change process, storage mechanism, and interface process of the insertion and desorption into the electrode material are well understood. + Therefore, the advantage of sodium battery materials is their low cost, but current conventional sodium battery materials all have drawbacks such as instability and low capacity. Therefore, there is a strong demand for the development of materials that are structurally stable, have high capacity, and are low cost. Summary of the Invention [Problem to be solved by the invention]

[0008] In view of this, the technical problem to be solved by the present invention is to provide a positive electrode material for a sodium battery, a manufacturing method thereof, and applications thereof. The positive electrode material for a sodium battery provided by the present invention has a stable structure, a high capacity, and a low cost. [Means for solving the problem]

[0009] The present invention provides a positive electrode material for a sodium battery, the chemical formula of the positive electrode material for the sodium battery being: xNaMBO3.yNa2Ti3O7.zNa3V2(BO3)3 / C, Here, the ratio of the number of moles of x, y, and z is 0.94 to 0.96:0.02 to 0.03:0.02 to 0.03, M is Fe and Mn, and the molar ratio of Fe to Mn is 8-9:1-2; The mass fraction of carbon in the positive electrode material of the sodium battery is 1.2% to 1.5%.

[0010] Preferably, the positive electrode material of the sodium battery includes a core material and a first coating layer and a second coating layer sequentially coated on the surface of the core material, wherein the core material is NaMBO, the first coating layer includes NaTiO and NaV(BO), and the second coating layer is amorphous carbon.

[0011] Preferably, the particle size of the core material is 200 to 500 nm, the thickness of the first coating layer is 10 to 20 nm, and the thickness of the second coating layer is 1.5 to 3.5 nm.

[0012] The present invention further provides a method for producing the positive electrode material of the sodium battery, Mixing a ferrous salt, a manganese salt and water to obtain an iron-manganese mixed solution; A) mixing the iron-manganese mixed solution with an ammonium bicarbonate solution to react with each other and obtain a reaction product; B) adding the reaction product to a hydrazine hydrate solution to form a slurry, and then adding the reaction product to an oxalic acid solution to precipitate the product, and adjusting the pH of the solution to obtain ferrous manganese oxalate; Step C) of mixing the manganese iron oxalate with sodium borate and sodium bicarbonate, adding a sodium hexametaphosphate solution to form a slurry, grinding the slurry, and spray-drying the slurry. The resulting material is fired in an inert atmosphere to obtain a first fired material. and D) mixing sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcined material with water, grinding and spray drying, and then performing a second calcination, and sieving the calcined product to remove iron, thereby obtaining a positive electrode material for a sodium battery.

[0013] Preferably, in step A), the ferrous salt is selected from ferrous sulfate crystals, the manganese salt is selected from manganese sulfate crystals; The concentration of the ammonium bicarbonate solution is 1.5 to 1.8 mol / L, the ratio of the molar amount of the ammonium hydrogen carbonate to the total molar amount of manganese and iron in the ferrous salt and manganese salt is 2.2 to 2.5:1; After mixing the iron-manganese mixed solution and the ammonium bicarbonate solution, an acid-base regulator is added to adjust the pH of the slurry to 7.3-7.5, and the stirring speed throughout the process is 300-500 r / min.

[0014] Preferably, in step B), the concentration of the hydrazine hydrate solution is 0.05 to 0.1 mol / L; the mass ratio of the reaction product to hydrazine hydrate is 1:1.5 to 2; The concentration of the oxalic acid solution is 0.2 to 0.5 mol / L, Adjust the solution pH to 4-5.

[0015] Preferably, in step C), the molar ratio of manganese iron oxalate to sodium borate to sodium hydrogen carbonate is 4:1.02-1.03:2.02-2.04; The mass of the sodium hexametaphosphate solution is 2 to 2.5 times the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate, The concentration of the sodium hexametaphosphate solution is 0.02 to 0.05 mol / L. Polish until the particle size of the slurry becomes 0.2 to 0.3 μm. During the spray drying process, the particle size of the final spray-dried material is maintained at 10-30 μm and the moisture content is maintained at less than 1 wt%. During the firing process, the firing atmosphere is at least one of carbon dioxide, nitrogen, and argon, and the temperature is raised to 450-500°C at a heating rate of 80-100°C / h and fired for 3-5 hours. Then, the temperature is lowered at a rate of 100-150°C / h until the temperature of the material reaches 50°C or less, after which the material is discharged and the first fired product is placed in a nitrogen environment, sealed, and stored.

[0016] Preferably, in step D), the molar ratio of the first calcined material, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate is 0.94-0.96:0.04-0.06:0.015-0.0225:0.06-0.09:0.03-0.045.

[0017] The titanium dioxide is nano-titanium dioxide, the primary particle size is 15 to 50 nm, and the BET is 20 to 40 nm. 2 / g and the purity is ≧99 wt%.

[0018] Preferably, in step D), the mixing method is as follows: Sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry, to obtain a mixed slurry, and the solid content of the mixed slurry is 1 wt% to 3 wt%. Next, a first calcined material is added and mixed to obtain a mixed slurry; The polishing is performed until the grain size of the material becomes 200 to 250 nm, During the spray drying process, the moisture content of the final spray-dried material is kept below 0.5 wt% and the particle size is kept between 3 and 10 μm. The secondary firing process is as follows: the sintering atmosphere is nitrogen or argon, the temperature rise rate is 50-80°C / h, the heat retention temperature is 650-700°C, and the heat retention time is 4-8 hours. The firing process is performed using a roller hearth kiln, which is connected to an inverter intake fan and the furnace pressure inside the roller hearth kiln is controlled to be 60-100 Pa higher than the external atmospheric pressure. The humidity in the heat retention stage is controlled to be 5% or less, and the temperature drop rate in the temperature drop stage is controlled to be 100-150°C / h. The sieving and de-ironizing is performed by electromagnetic de-ironizing, and the de-ironizing is stopped after the magnetic substance content of the product is reduced to 300 ppb or less. A sieve of 100 to 150 mesh is used for the sieving.

[0019] After the sieving and iron removal, the product is further vacuum packed. The vacuum packing process is carried out in a temperature and humidity controlled room at a temperature of 15 to 25°C and a humidity of 5 to 10%.

[0020] The present invention further provides a sodium battery, which includes the above-described sodium battery positive electrode material. [Effects of the Invention]

[0021] Compared with the prior art, the present invention provides a sodium battery positive electrode material, and the chemical formula of the sodium battery positive electrode material is xNaMBO3.yNa2Ti3O7.zNa3V2(BO3)3 / C, where the molar ratio of x to y to z is 0.94-0.96:0.02-0.03:0.02-0.03, M is Fe and Mn, and the molar ratio of Fe to Mn is 8-9:1-2, and the mass fraction of carbon in the sodium battery positive electrode material is 1.2-1.5%.

[0022] The positive electrode material for sodium batteries provided by the present invention has high capacity, high voltage platform, stable structure, high cycle performance, and its manufacturing method is simple, low cost, and short process flow.

[0023] The present invention uses borate as the anion, which has the advantage of being cheaper than phosphate. The price of sodium borate is about 3,000 yuan / ton, while the price of sodium phosphate is more than 6,000 yuan / ton. Moreover, the number of moles of boric acid groups is smaller than that of phosphate groups. Therefore, in terms of the theoretical capacity of the final manufactured product, the theoretical capacity of the borate-type positive electrode material is higher than that of the phosphate-type positive electrode material.

[0024] The present invention uses Na2Ti3O7 and Na3V2(BO3)3 coated on the surface of NaMBO3, and C coated on the surface of Na2Ti3O7 and Na3V2(BO3)3, where the carbon is amorphous carbon. The main problem with borate-based positive electrode materials is that in air or in an environment with a small amount of moisture, iron and manganese are rapidly oxidized, which causes the deterioration of the electrical performance of the material. However, the present invention uses Na2Ti3O7 and Na3V2(BO3)3 coated on the surface of NaMBO3, which can isolate Na(Mn,Fe)BO3. This avoids rapid degradation of the capacity of the material, and the price of the product of the present invention is low because the prices of manganese and iron are much lower than those of elements such as vanadium. The surface-coated materials of the present invention are Na2Ti3O7 and Na3V2(BO3)3, which can greatly improve the oxidation resistance and moisture resistance of the material and further improve the ionic conductivity of the product. A carbon coating layer is also introduced to improve the electronic conductivity and serve as a second protective layer, further improving the stability of the material. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is an SEM image of the washed and dried material produced in Example 1 of the present invention. [Figure 2] FIG. 1 is an SEM image of ferromanganese oxalate produced in Example 1 of the present invention. [Figure 3] FIG. 2 is an SEM image of a first fired material produced according to Example 1 of the present invention. [Figure 4]FIG. 1 is an SEM image of a positive electrode material for a sodium battery produced according to Example 1 of the present invention. [Figure 5] FIG. 1 is a transmission electron microscope image of a positive electrode material for a sodium battery produced according to Example 1 of the present invention. [Figure 6] FIG. 2 is a charge / discharge curve diagram of the positive electrode material of a sodium battery produced according to Example 1 of the present invention. [Figure 7] 1 shows the cycle performance test results of a battery assembled with the positive electrode material for a sodium battery obtained by manufacturing according to Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention provides a positive electrode material for a sodium battery, the chemical formula of the positive electrode material for the sodium battery being: xNaMBO3.yNa2Ti3O7.zNa3V2(BO3)3 / C, Here, the ratio of the number of moles of x, y, and z is 0.94 to 0.96:0.02 to 0.03:0.02 to 0.03, M is Fe and Mn, and the molar ratio of Fe to Mn is 8-9:1-2; The mass fraction of carbon in the positive electrode material of the sodium battery is 1.2% to 1.5%.

[0027] Preferably, the ratio of the number of moles of x, y, and z is 0.94:0.03:0.03, 0.95:0.025:0.025, 0.96:0.02:0.02, or any value between 0.94-0.96:0.02-0.03:0.02-0.03.

[0028] The molar ratio of Fe to Mn is 8:2, 8.5:1.5, 9:1, or any value between 8 to 9:1 and 9:2.

[0029] The mass fraction of carbon in the positive electrode material of the sodium battery is 1.2%, 1.3%, 1.4%, 1.5%, or any value between 1.2% and 1.5%.

[0030] In the present invention, the positive electrode material of the sodium battery includes a core material and a first coating layer and a second coating layer sequentially coated on the surface of the core material, the core material being NaMBO3, the first coating layer including Na2Ti3O7 and Na3V2(BO3)3, and the second coating layer being amorphous carbon.

[0031] In some specific embodiments of the present invention, the particle size of the core material is 200 to 500 nm, preferably 200, 300, 400, 500, or any value between 200 and 500 nm; the thickness of the first coating layer is 10 to 20 nm, preferably 10, 12, 14, 16, 18, 20, or any value between 10 and 20 nm; and the thickness of the second coating layer is 1.5 to 3.5 nm, preferably 1.5, 2.0, 2.5, 3.0, 3.5, or any value between 1.5 and 3.5 nm.

[0032] The present invention further provides a method for producing the positive electrode material of the sodium battery, Mixing a ferrous salt, a manganese salt and water to obtain an iron-manganese mixed solution; A) mixing the iron-manganese mixed solution with an ammonium bicarbonate solution to react with each other and obtain a reaction product; B) adding the reaction product to a hydrazine hydrate solution to form a slurry, and then adding the reaction product to an oxalic acid solution to precipitate the product, and adjusting the pH of the solution to obtain ferrous manganese oxalate; Step C) of mixing the manganese iron oxalate with sodium borate and sodium bicarbonate, adding a sodium hexametaphosphate solution to form a slurry, grinding the slurry, and spray-drying the slurry. The resulting material is fired in an inert atmosphere to obtain a first fired material. and D) mixing sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcined material with water, grinding and spray drying, and then performing a second calcination, and sieving the calcined product to remove iron, thereby obtaining a positive electrode material for a sodium battery.

[0033] Specifically, in the present invention, first, a ferrous salt and a manganese salt are added to pure water and dissolved by stirring to obtain an iron-manganese mixed solution.

[0034] Here, the ferrous salt is selected from ferrous sulfate crystals, and the manganese salt is selected from manganese sulfate crystals.

[0035] An ammonium bicarbonate solution having a concentration of 1.5 to 1.8 mol / L is prepared, where the concentration of the ammonium bicarbonate solution is preferably 1.5, 1.6, 1.7, 1.8, or any value between 1.5 and 1.8 mol / L.

[0036] The order of preparing the iron-manganese mixed solution and the ammonium hydrogen carbonate solution is not particularly limited.

[0037] The iron-manganese mixed solution is added to the reaction vessel together with the ammonium bicarbonate solution over a period of 60 to 90 minutes, preferably 60, 70, 80, 90, or any value between 60 and 90 minutes. The reaction temperature during addition of the materials is 35 to 45°C, preferably 35, 38, 40, 42, 45, or any value between 35 and 45°C.

[0038] The molar ratio of the ammonium hydrogen carbonate to the total molar amount of manganese and iron in the ferrous salt and manganese salt is 2.2 to 2.5:1, and preferably 2.2:1, 2.3:1, 2.4:1, 2.5:1, or any value between 2.2 and 2.5:1.

[0039] After adding the materials, add an acid-base regulator to adjust the pH of the slurry to 7.3-7.5, preferably 7.3, 7.4, 7.5, or any value between 7.3 and 7.5. The temperature of the slurry is raised to 60-65°C, preferably 60, 61, 62, 63, 64, 65, or any value between 60-65°C, and the reaction is continued for 15-30 minutes to obtain the reactant.

[0040] The reaction material is filtered and washed to obtain a washed material, i.e., a reaction product. The present invention does not particularly limit the filtering and washing methods, and any methods known to those skilled in the art may be used.

[0041] Next, in the present invention, the reaction product is added to a hydrazine hydrate solution and stirred to form a slurry, wherein the concentration of the hydrazine hydrate solution is 0.05 to 0.1 mol / L, and preferably 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any value between 0.05 and 0.1 mol / L, and the mass ratio of the reaction product to hydrazine hydrate is 1:1.5 to 2, and preferably 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, or any value between 1:1.5 and 2.

[0042] Next, an oxalic acid solution is added, the temperature of the solution is maintained at 40-50°C, and the pH of the solution is adjusted to 4-5, preferably 4, 4.2, 4.4, 4.6, 4.8, 5, or any value between 4 and 5. The addition of oxalic acid is then stopped, and the reaction is continued with stirring for 15-30 minutes. The precipitate is then filtered and washed to obtain a precipitate, which is then dried to obtain manganese iron oxalate. The concentration of the oxalic acid solution is 0.2-0.5 mol / L, preferably 0.2, 0.3, 0.4, 0.5, or any value between 0.2-0.5 mol / L.

[0043] After obtaining the manganese iron oxalate, the manganese iron oxalate is mixed with sodium borate and sodium bicarbonate, and a sodium hexametaphosphate solution is added to form a slurry, which is then polished and spray-dried. The resulting material is fired in an inert atmosphere to obtain a first fired material; Here, the molar ratio of manganese iron oxalate, sodium borate, and sodium hydrogen carbonate is 4:1.02 to 1.03:2.02 to 2.04, and preferably 4:1.02:2.02, 4:1.03:2.04, 4:1.025:2.03, or any value between 4:1.02 to 1.03:2.02 to 2.04, The concentration of the sodium hexametaphosphate solution is 0.02 to 0.05 mol / L, and preferably 0.02, 0.03, 0.04, 0.05, or any value between 0.02 and 0.05 mol / L.

[0044] The mass of the sodium hexametaphosphate solution is 2 to 2.5 times the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate, and is preferably 2, 2.1, 2.2, 2.3, 2.4, 2.5, or any value between 2 and 2.5 times; The polishing is performed until the particle size of the slurry becomes 0.2 to 0.3 μm, preferably 0.2, 0.25, 0.3, or any value between 0.2 and 0.3 μm; During the spray drying process, the particle size of the final spray-dried material is maintained at 10 to 30 μm, preferably 10, 15, 20, 25, 30, or any value between 10 and 30 μm, and the moisture content is maintained at less than 1 wt%; During the firing process, the firing atmosphere is at least one of carbon dioxide, nitrogen, and argon, and the temperature is raised to 450-500°C at a heating rate of 80-100°C / h and fired for 3-5 hours. Then, the temperature is lowered at a rate of 100-150°C / h until the temperature of the material reaches 50°C or less, after which the material is discharged and the first fired product is placed in a nitrogen environment, sealed, and stored.

[0045] Here, the temperature increase rate is preferably 80, 85, 90, 95, 100, or any value between 80 and 100°C / h, the firing temperature is preferably 450, 460, 470, 480, 490, 500, or any value between 450 and 500°C, the firing time is preferably 3, 4, 5, or any value between 3 and 5 hours, and the temperature decrease rate is 100, 110, 120, 130, 140, 150, or any value between 100 and 150°C / h.

[0046] Finally, sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcination material and water are mixed, polished and spray-dried, and then the secondary calcination is carried out. The calcined product is sieved to remove iron, and the positive electrode material for sodium batteries is obtained.

[0047] Specifically, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry to obtain a mixed slurry, and the solid content of the mixed slurry is 1 wt% to 3 wt%, preferably 1 wt%, 2 wt%, 3 wt%, or any value between 1 wt% and 3 wt%, Next, the first calcined material is added and mixed to obtain a mixed slurry.

[0048] Here, the molar ratio of the first calcined material, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate is 0.94-0.96:0.04-0.06:0.015-0.0225:0.06-0.09:0.03-0.045, preferably 0.95:0.05:0.02:0.08:0.04, 0.94:0.06:0.015:0.06:0.03, 0.96:0.04:0.0225:0.09:0.045, or any value between 0.94-0.96:0.04-0.06:0.015-0.0225:0.06-0.09:0.03-0.045.

[0049] The titanium dioxide is nano-titanium dioxide, and the primary particle size is 15 to 50 nm, preferably 15, 20, 30, 40, 50, or any value between 15 and 50 nm, and the BET is 20 to 40 nm. 2 / g, preferably 20, 30, 40, or 20 to 40 m 2 / g and the purity is ≧99 wt%.

[0050] After obtaining the mixed slurry, the material is ground until the particle size is 200 to 250 nm, preferably 200, 210, 220, 230, 240, 250, or any value between 200 and 250 nm.

[0051] Subsequently, spray drying is carried out to obtain a spray-dried material. During the spray drying process, the moisture content of the final spray-dried material is maintained at less than 0.5 wt% and the particle size is maintained at 3 to 10 μm, preferably 3, 5, 5.8, 8, 10, or any value between 3 and 10 μm; Next, the spray-dried material is subjected to secondary firing. The secondary firing process is as follows: the sintering atmosphere is nitrogen or argon, the temperature rise rate is 50 to 80°C / h, preferably 50, 60, 70, 80 or 50 to 80°C / h, the temperature is 650 to 700°C, preferably 650, 660, 670, 680, 690, 700 or any value between 650 and 700°C, and the temperature holding time is 4 to 8 hours, preferably 4, 5, 6, 7, 8 or 4 to 8 hours. the firing process is performed using a roller hearth kiln, and the roller hearth kiln is connected to an inverter intake fan, and the furnace pressure inside the roller hearth kiln is controlled to be 60 to 100 Pa higher than the external atmospheric pressure; the humidity in the heat retention stage is controlled to 5% or less; and the temperature reduction rate in the temperature reduction stage is controlled to 100 to 150°C / h, preferably 100, 110, 120, 130, 140, 150, or any value between 100 and 150°C / h; After secondary firing, the material is sieved to remove iron and then vacuum-packaged to obtain a positive electrode material for sodium batteries. The sieving and demagnetization is performed by electromagnetic demagnetization, with the demagnetization stopped after the magnetic substance content of the product reaches 300 ppb or less. A 100-150 mesh sieve is used for sieving. The sieving and demagnetization is followed by vacuum packaging, which is carried out in a temperature- and humidity-controlled room at a temperature of 15-25°C and a humidity of 5-10%.

[0052] The present invention first prepares Na(Mn,Fe)BO3 and then uses oxalate to prepare it. Ferrous oxalate has high stability, and relatively pure Na(Mn,Fe)BO3 can be obtained. In this step, no carbon coating layer is added. The main purpose is to prepare for subsequent coating. If a carbon coating layer is added in this step, it will prevent Na2Ti3O7 and Na3V2(BO3)3 from being coated by Na(Mn,Fe)BO3. The carbon layer has the effect of preventing inter-particle growth. Therefore, in the first sintering step of the present invention, Na2Ti3O7 and Na3V2(BO3)3 can be successfully grown by Na(Mn,Fe)BO3 without adding a carbon layer.

[0053] In the second step, the present invention uses nano-polishing to nano-size Na(Mn,Fe)BO3 and use it as a nucleus. Furthermore, water-soluble raw materials such as sodium metavanadate, sodium borate, and sodium stearate are introduced. The water-soluble raw materials are then crystallized and deposited by spray drying to coat the surface of the solid particles. Furthermore, the sodium salt of the present invention incorporates organic carbon chains, which can be thermally decomposed and carbonized in an inert atmosphere to form a carbon coating layer.

[0054] By adopting this method, the present invention can better form a stable and uniform coating layer, and this coating layer of the present invention still has a certain capacity performance. Subsequently, a carbon coating layer is formed on the outer surface, and the resulting structure can greatly improve the stability of the material, and also has a high capacity performance. It also uses cheap raw materials, further reducing costs.

[0055] The present invention further provides a sodium battery, which includes the above-described sodium battery positive electrode material.

[0056] The sodium battery cathode material provided by the present invention has high capacity, a high voltage platform, a stable structure, and excellent cycle performance, and its manufacturing method is simple, low cost, and short process flow. The present invention uses borate as the anion, which has the advantage of being cheaper than phosphate (the price of sodium borate is about 3,000 yuan / ton, while the price of sodium phosphate is more than 6,000 yuan / ton). Moreover, the molar number of boric acid groups is smaller than that of phosphate groups, so that the theoretical capacity of the final product is higher for the borate-type cathode material than for the phosphate-type cathode material.

[0057] The present invention uses Na2Ti3O7 and Na3V2(BO3)3 coated on the surface of NaMBO3, and C coated on the surface of Na2Ti3O7 and Na3V2(BO3)3, where the carbon is amorphous carbon. The main problem with borate-based positive electrode materials is that in air or in an environment with a small amount of moisture, iron and manganese are rapidly oxidized, which causes the deterioration of the electrical performance of the material. However, the present invention uses Na2Ti3O7 and Na3V2(BO3)3 coated on the surface of NaMBO3, which can isolate Na(Mn,Fe)BO3. This avoids rapid degradation of the capacity of the material, and the price of the product of the present invention is low because the prices of manganese and iron are much lower than those of elements such as vanadium. The surface-coated materials of the present invention are Na2Ti3O7 and Na3V2(BO3)3, which can greatly improve the oxidation resistance and moisture resistance of the material and further improve the ionic conductivity of the product. A carbon coating layer is also introduced to improve the electronic conductivity and serve as a second protective layer, further improving the stability of the material.

[0058] In order to further understand the present invention, the positive electrode material for sodium batteries provided by the present invention and its manufacturing method and application will be described below with reference to examples, and the protection scope of the present invention is not limited to the following examples.

[0059] Example 1 The cathode material for high performance sodium batteries has the following structure:

[0060] 0.95Na(Fe 0.85 ,Mn 0.15 )BO3·0.025Na2Ti3O7·0.025Na3V2(BO3)3 / C, Here, the mass fraction of the carbon content is 1.4%.

[0061] Na2Ti3O7 and Na3V2(BO3)3 are coated on the surface of NaMBO3, C is coated on the surface of Na2Ti3O7 and Na3V2(BO3)3, and the carbon is amorphous carbon.

[0062] The manufacturing method is as follows.

[0063] 1) Battery-grade ferrous sulfate crystals and manganese sulfate crystals are added to pure water and dissolved by stirring to obtain an iron-manganese mixed solution, in which the molar ratio of iron to manganese in the mixed solution is 0.857:0.143 and the pH is 2.15; Next, prepare a 1.72 mol / L ammonium bicarbonate solution, add the iron-manganese mixed solution together with the ammonium bicarbonate solution into the reactor, add for 85 minutes, the ratio of the moles of ammonium bicarbonate added to the total moles of manganese iron is 2.4:1, the reaction temperature during the addition of the materials is 42±1.5°C, the stirring speed throughout the process is 400±20 r / min, after the addition is complete, the pH of the solution is 7.25, add sodium carbonate to adjust the pH of the slurry to 7.35, and heat to 62±1°C, continue the reaction for 25 minutes to obtain the reactants, The reaction material was sampled and the particle size was detected, and the obtained particle sizes were D10: 1.75 μm, D50: 6.59 μm, and D90: 15.43 μm.

[0064] The reaction material was filtered and washed to obtain the washed material, which was dried in a vacuum drying box and then crushed. The data were detected, and the results are shown in Table 1.

[0065] [Table 1]

[0066] Please refer to FIG. 1, which is an SEM image of the washed and dried material obtained by manufacturing according to Example 1 of the present invention.

[0067] 2) Add the cleaning agent to the hydrazine hydrate solution, the mass ratio of the cleaning agent to the hydrazine hydrate solution is 1:1.83, and the concentration of the hydrazine hydrate solution added is 0.072 mol / L. Stir to form a slurry, then add oxalic acid solution, the concentration of the added oxalic acid solution is 0.37 mol / L, maintain the temperature of the solution at 46±1°C, adjust the pH of the solution to 4.38, then stop adding oxalic acid, continue stirring and react for 20 minutes, then filter and wash to obtain a precipitate, which is dried to obtain manganese ferrous oxalate, the SEM of which is shown in Figure 2, which is the SEM image of the manganese ferrous oxalate prepared in Example 1 of the present invention.

[0068] The manganese iron oxalate was detected, and the results are shown in Table 2.

[0069] [Table 2]

[0070] 3) Manganese iron oxalate was mixed with sodium borate and sodium bicarbonate, and then a sodium hexametaphosphate solution was added to form a slurry. The molar ratio of manganese iron oxalate, sodium borate, and sodium bicarbonate was 4:1.025:2.03, and the mass of the added sodium hexametaphosphate solution was 2.3 times the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate. The concentration of the sodium hexametaphosphate solution was 0.03 mol / L. After grinding, the mixture was spray-dried to form a slurry. The particle size of the powder was polished to 0.253 μm. During the spray drying process, the particle size of the final spray-dried material was maintained at 17.8 μm and the moisture content was 0.35 wt%. The resulting material was calcined in an inert atmosphere at a temperature of 480 ° C for 4 hours, and then removed to obtain the first calcined material. During the calcination process, the heating rate was 90 ° C / h, the calcination atmosphere was nitrogen, and the cooling rate in the cooling stage was 145 ° C / h. After the material temperature was cooled to 50 ° C or less, the material was discharged to obtain the first calcined material. The discharged material was sealed and stored in a nitrogen environment. Please refer to FIG. 3, which is an SEM image of the first fired material produced in Example 1 of the present invention.

[0071] The first fired material was detected, and the results are shown in Table 3.

[0072] [Table 3]

[0073] 4) Sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry, resulting in a solid content of 1.7 wt%. A first calcined material is added, and the molar ratio of the first calcined material to sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate is 0.95:0.05:0.02:0.08:0.04. The material is then ground until the particle size is 230 nm, and then spray-dried. During the spray-drying process, the moisture content of the final spray-dried material is maintained at less than 0.5 wt% and the particle size is 5.8 μm. The spray-dried material is placed in a roller hearth kiln for secondary firing. During the secondary firing process, the sintering atmosphere is nitrogen, the temperature rise rate is 75°C / h, the temperature is kept at 680°C, and the temperature is kept at 6 hours. The firing process is carried out using a roller hearth kiln, and the roller hearth kiln is connected to an inverter intake fan. The furnace pressure in the roller hearth kiln is controlled to be 80 Pa higher than the external atmospheric pressure. The humidity in the temperature keeping stage is controlled to be below 5%, and the temperature drop rate in the temperature drop stage is controlled to be 120°C / h. After sintering, the material is sieved to remove iron and then vacuum-packaged. The vacuum packaging process is carried out in a constant temperature and humidity room at a temperature of 20±1°C and a humidity of 8.1%. Before vacuum packaging, the sieved material needs to be subjected to electromagnetic demagnetization. Demagnetization is stopped when the magnetic substance of the product reaches 215 ppb. A 150 mesh sieve is used for sieving to obtain a sodium battery positive electrode material. See FIGS. 4 and 5, where FIG. 4 is an SEM image of the sodium battery positive electrode material obtained by manufacturing according to Example 1 of the present invention.

[0074] Figure 5 is a transmission electron microscope image of the positive electrode material for a sodium battery produced in Example 1 of the present invention. As can be seen from Figure 5, a carbon coating layer with a thickness of 2.5±1 nm was formed on the surface of the positive electrode material for a sodium battery produced in Example 1.

[0075] The titanium dioxide is nano-titanium dioxide, the primary particle size is 30 nm, and the BET is 31.5 m 2 / g and the purity was 99.53 wt%.

[0076] The positive electrode material of the sodium battery was detected, and the results are shown in Table 4.

[0077] [Table 4]

[0078] The charge and discharge curve of the obtained sodium battery positive electrode material product is shown in Figure 6, which is a diagram of the charge and discharge curve of the sodium battery positive electrode material obtained in Example 1 of the present invention. An electric shock test was performed. The negative electrode was sodium sheet, the positive electrode composition was sodium battery positive electrode material:PVDF:SP in a mass ratio of 85:5:10, the electrolyte in the electrolyte solution was sodium hexafluorophosphate, the solvent was EC+DMC+EMC in a mass ratio of 5:2:3, and the concentration of sodium hexafluorophosphate was 0.45mol / L. Three electric shock tests were made using the same batch of material and were charged and discharged at a rate of 0.1C.

[0079] As can be seen from FIG. 6, the charge capacity reaches 146.9 mAh / g, and the discharge capacity reaches 142.1 mAh / g, which is close to the electrochemical performance of lithium iron phosphate. The 1C discharge capacity is 139.8 mAh / g, which is already equivalent to conventional lithium iron phosphate. The electrical performance is excellent, and the charge / discharge curve shows a very gentle discharge platform with small polarization.

[0080] The cycle performance of the obtained sodium battery positive electrode material product was tested, and four cells were made using the same material. Specifically, the positive electrode material produced in Example 1 was used as the positive electrode active material, and a positive electrode sheet was made with a sodium battery positive electrode active material:PVDF:SP mass ratio of 85:5:10. Hard carbon was used as the negative electrode, and a negative electrode sheet was made. Sodium hexafluorophosphate was used as the electrolyte, and the solvent was EC+DMC+EMC, with a mass ratio of 5:2:3. The concentration of sodium hexafluorophosphate was 0.45 mol / L, and pouch cells were assembled.

[0081] The cycle performance was measured at a capacity of 1 Ah, a temperature of 25°C, and a current of 1C. The results are shown in Figure 7, which shows the cycle performance test results for a battery assembled with the sodium battery positive electrode material obtained in Example 1 of the present invention. As can be seen from Figure 7, after 250 cycles, the room temperature cycle capacity retention rate was higher than 95%, demonstrating excellent cycle performance.

[0082] Based on current prices (lithium carbonate is 485,000 RMB / ton), the cost price of lithium iron phosphate is about 150,000 RMB / ton, while the cost price of the material of the present invention is only 35,000 RMB / ton, which is a very high price-performance ratio, with a capacity 20-40 mAh / g higher than other polyanion materials such as sodium iron sulfate and sodium iron phosphate. Furthermore, this material has excellent cycle performance and low-temperature performance.

[0083] Example 2 A) Mixing a ferrous salt, a manganese salt and water to obtain an iron-manganese mixed solution; The iron-manganese mixed solution and the ammonium bicarbonate solution are mixed and reacted to obtain a reaction product; B) The reaction product is successively added to a hydrazine hydrate solution to form a slurry, and then added to an oxalic acid solution to precipitate, and the pH of the solution is adjusted to obtain manganese iron oxalate; C) Mixing the manganese iron oxalate with sodium borate and sodium bicarbonate, adding a sodium hexametaphosphate solution to form a slurry, grinding the slurry, and spray-drying the slurry. The resulting material is fired in an inert atmosphere to obtain a first fired material. D) Sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcined material and water were mixed, polished and spray-dried, and then the second calcination was carried out. The calcined product was sieved to remove iron, and then a positive electrode material for a sodium battery was obtained.

[0084] In step A), the ferrous salt is selected from ferrous sulfate crystals, the manganese salt is selected from manganese sulfate crystals; The concentration of the ammonium bicarbonate solution is 1.5 mol / L. the ratio of the molar amount of ammonium bicarbonate to the total molar amount of manganese and iron in the ferrous salt and manganese salt is 2.2:1; After mixing the iron-manganese mixed solution and the ammonium bicarbonate solution, an acid-base regulator was added to adjust the pH of the slurry to 7.3, and the stirring speed throughout the entire process was 300 r / min.

[0085] In step B), the concentration of the hydrazine hydrate solution is 0.05 mol / L; the mass ratio of the reaction product to hydrazine hydrate is 1:1.5; The concentration of the oxalic acid solution is 0.2 mol / L; The solution pH was adjusted to 4.

[0086] In step C), the molar ratio of ferric manganese oxalate to sodium borate to sodium bicarbonate is 4:1.02:2.02; The mass of the sodium hexametaphosphate solution is twice the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate. The concentration of the sodium hexametaphosphate solution is 0.02 mol / L. Polish until the particle size of the slurry becomes 0.2 μm. During the spray drying process, the particle size of the final spray-dried material is maintained at 10 μm and the moisture content is maintained at less than 1 wt%. During the firing process, the firing atmosphere was at least one of carbon dioxide, nitrogen, and argon. The temperature was increased to 450°C at a heating rate of 80°C / h and fired for 3 hours. The material was then cooled at a cooling rate of 100°C / h until the temperature of the material reached 50°C or less, after which the material was discharged and the first fired product was placed in a nitrogen environment, sealed, and stored.

[0087] In step D), the molar ratio of the first calcined material, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate was 0.94:0.04:0.015:0.06:0.03.

[0088] The titanium dioxide is nano-titanium dioxide, the primary particle size is 15 nm, and the BET is 20 m 2 / g and the purity was ≧99 wt%.

[0089] In step D), the mixing method is as follows: Sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry, and a mixed slurry is obtained, and the solid content of the mixed slurry is 1 wt %. Next, a first calcined material is added and mixed to obtain a mixed slurry; The polishing is performed until the grain size of the material is 200 nm, During the spray drying process, the moisture content of the final spray-dried material is kept below 0.5 wt% and the particle size is kept at 3 μm. The secondary firing process is as follows: the sintering atmosphere is nitrogen or argon, the temperature rise rate is 50°C / h, the temperature retention temperature is 650°C, and the temperature retention time is 4h. The firing process is performed using a roller hearth kiln, and the roller hearth kiln is connected to an inverter intake fan. The furnace pressure inside the roller hearth kiln is controlled to be 60 Pa higher than the external atmospheric pressure. The humidity during the temperature retention stage is controlled to be below 5%, and the temperature reduction rate during the temperature reduction stage is controlled to be 100°C / h. The sieving and de-ironizing process is performed by electromagnetic de-ironizing, and the de-ironizing process is stopped when the magnetic substance content of the product is reduced to 300 ppb or less. A 100 mesh sieve is used for the sieving.

[0090] After the sieving and iron removal, the product was further vacuum packed. The vacuum packing process was carried out in a temperature and humidity controlled room, with the temperature at 15°C and the humidity at 5%.

[0091] Example 3 A) Mixing a ferrous salt, a manganese salt and water to obtain an iron-manganese mixed solution; The iron-manganese mixed solution and the ammonium bicarbonate solution are mixed and reacted to obtain a reaction product; B) The reaction product is successively added to a hydrazine hydrate solution to form a slurry, and then added to an oxalic acid solution to precipitate, and the pH of the solution is adjusted to obtain manganese iron oxalate; C) Mixing the manganese iron oxalate with sodium borate and sodium bicarbonate, adding a sodium hexametaphosphate solution to form a slurry, grinding the slurry, and spray-drying the slurry. The resulting material is fired in an inert atmosphere to obtain a first fired material. D) Sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcined material and water were mixed, polished and spray-dried, and then the second calcination was carried out. The calcined product was sieved to remove iron, and then a positive electrode material for a sodium battery was obtained.

[0092] In step A), the ferrous salt is selected from ferrous sulfate crystals, the manganese salt is selected from manganese sulfate crystals; The concentration of the ammonium bicarbonate solution is 1.8 mol / L, the ratio of the molar amount of ammonium bicarbonate to the total molar amount of manganese and iron in the ferrous salt and manganese salt is 2.5:1; After mixing the iron-manganese mixed solution and the ammonium bicarbonate solution, an acid-base regulator was added to adjust the pH of the slurry to 7.5, and the stirring speed throughout the entire process was 500 r / min.

[0093] In step B), the concentration of the hydrazine hydrate solution is 0.1 mol / L; the mass ratio of the reaction product to hydrazine hydrate is 1:2; The concentration of the oxalic acid solution is 0.5 mol / L; The solution pH was adjusted to 5.

[0094] In step C), the molar ratio of ferric manganese oxalate to sodium borate to sodium bicarbonate is 4:1.03:2.04; The mass of the sodium hexametaphosphate solution is 2.5 times the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate. The concentration of the sodium hexametaphosphate solution is 0.05 mol / L. Polish until the particle size of the slurry becomes 0.3 μm. During the spray drying process, the particle size of the final spray-dried material is maintained at 30 μm and the moisture content is maintained at less than 1 wt%. During the firing process, the firing atmosphere was at least one of carbon dioxide, nitrogen, and argon. The temperature was increased to 500°C at a heating rate of 100°C / h and fired for 5 hours. The temperature was then decreased at a cooling rate of 150°C / h until the temperature of the material reached 50°C or less. The material was then discharged, and the first fired product was placed in a nitrogen environment, sealed, and stored.

[0095] In step D), the molar ratio of the first calcined material, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate was 0.96:0.06:0.0225:0.09:0.045.

[0096] The titanium dioxide is nano-titanium dioxide, the primary particle size is 50 nm, and the BET is 40 m 2 / g and the purity was ≧99 wt%.

[0097] In step D), the mixing method is as follows: Sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry, and the solid content of the mixed slurry is 3 wt %. Next, a first calcined material is added and mixed to obtain a mixed slurry; The polishing is performed until the grain size of the material is 250 nm, During the spray drying process, the moisture content of the final spray-dried material is kept below 0.5 wt% and the particle size is kept at 10 μm. The secondary firing process is as follows: the sintering atmosphere is nitrogen or argon, the temperature rise rate is 80°C / h, the temperature retention temperature is 700°C, and the temperature retention time is 8h. The firing process is performed using a roller hearth kiln, and the roller hearth kiln is connected to an inverter intake fan. The furnace pressure inside the roller hearth kiln is controlled to be 100Pa higher than the external atmospheric pressure. The humidity during the temperature retention stage is controlled to be below 5%, and the temperature reduction rate during the temperature reduction stage is controlled to be 150°C / h. The sieving and de-ironizing process employs electromagnetic de-ironizing, and stops de-ironizing when the magnetic substance content of the product is below 300 ppb. A 150 mesh sieve is used for the sieving.

[0098] After the sieving and iron removal, the product was further vacuum-packaged. The vacuum-packaging process was carried out in a temperature- and humidity-controlled room at a temperature of 25° C. and a humidity of 10%.

[0099] The above description is only a preferred embodiment of the present invention, and those skilled in the art may make some improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be regarded as within the protection scope of the present invention.

Claims

1. A positive electrode material for a sodium battery, comprising: The chemical formula of the positive electrode material of the sodium battery is: xNaMBO ３ .yNa ２ Ti ３ O ７ .zNa ３ V ２ (BO) ３ ) ３ / Cであり、 wherein the ratio of the number of moles of x, y, and z is 0.94 to 0.96:0.02 to 0.03:0.02 to 0.03; M is Fe and Mn, and the molar ratio of Fe to Mn is 8-9:1-2; the mass fraction of carbon in the positive electrode material of the sodium battery is 1.2% to 1.5%; The positive electrode material for the sodium battery includes a core material and a first coating layer and a second coating layer sequentially coated on the surface of the core material, the core material being NaMBO 3 , the first coating layer including Na 2 Ti 3 O 7 and Na 3 V 2 (BO 3 ) 3 , and the second coating layer being amorphous carbon. Cathode material for sodium batteries.

2. The particle size of the core material is 200 to 500 nm, the thickness of the first coating layer is 10 to 20 nm, and the thickness of the second coating layer is 1.5 to 3.5 nm. The positive electrode material for a sodium battery according to claim 1.

3. Mixing a ferrous salt, a manganese salt and water to obtain an iron-manganese mixed solution; A) mixing the iron-manganese mixed solution with an ammonium bicarbonate solution to react with each other and obtain a reaction product; B) adding the reaction product to a hydrazine hydrate solution to form a slurry, and then adding the reaction product to an oxalic acid solution to precipitate the product, and adjusting the pH of the solution to obtain ferrous manganese oxalate; Step C) of mixing the manganese iron oxalate with sodium borate and sodium bicarbonate, adding a sodium hexametaphosphate solution to form a slurry, grinding the slurry, and spray-drying the slurry. The resulting material is fired in an inert atmosphere to obtain a first fired material. D) mixing sodium metavanadate, sodium borate, titanium dioxide, sodium stearate, the first calcined material and water, grinding and spray drying the mixture, and then performing a second calcination; and sieving the calcined product to remove iron, thereby obtaining a positive electrode material for a sodium battery. A method for producing the positive electrode material for a sodium battery according to claim 1 or 2.

4. In step A), the ferrous salt is selected from ferrous sulfate crystals; the manganese salt is selected from manganese sulfate crystals; The concentration of the ammonium bicarbonate solution is 1.5 to 1.8 mol / L, the ratio of the molar amount of the ammonium bicarbonate to the total molar amount of manganese and iron in the ferrous salt and manganese salt is 2.2 to 2.5:1; After mixing the iron-manganese mixed solution and the ammonium bicarbonate solution, an acid-base regulator is added to adjust the pH of the slurry to 7.3-7.5, and the stirring speed throughout the process is 300-500 r / min. The method of claim 3.

5. In step B), the concentration of the hydrazine hydrate solution is 0.05 to 0.1 mol / L; the mass ratio of the reaction product to hydrazine hydrate is 1:1.5 to 2; The concentration of the oxalic acid solution is 0.2 to 0.5 mol / L, Adjust the solution pH to 4-5; The method of claim 3.

6. In step C), the molar ratio of manganese iron oxalate to sodium borate to sodium bicarbonate is 4:1.02-1.03:2.02-2.04; The mass of the sodium hexametaphosphate solution is 2 to 2.5 times the total mass of the added manganese iron oxalate, sodium borate, and sodium bicarbonate, The concentration of the sodium hexametaphosphate solution is 0.02 to 0.05 mol / L, Polishing is performed until the particle size of the slurry becomes 0.2 to 0.3 μm. During the spray drying process, the particle size of the final spray-dried material is maintained at 10-30 μm and the moisture content is maintained at less than 1 wt %; In the firing process, the firing atmosphere is at least one of carbon dioxide, nitrogen, and argon, and the temperature is increased to 450-500°C at a temperature increase rate of 80-100°C / h and fired for 3-5 hours. Then, the temperature is decreased at a temperature decrease rate of 100-150°C / h until the temperature of the material is 50°C or less, after which the material is discharged, and the first fired product is stored in a nitrogen environment and sealed. The method of claim 3.

7. In step D), the molar ratio of the first calcined material, sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate is 0.94 to 0.96: 0.04 to 0.06: 0.015 to 0.0225: 0.06 to 0.09: 0.03 to 0.045; The titanium dioxide is nano-titanium dioxide, with a primary particle size of 15-50 nm, a BET of 20-40 m / g, and a purity of 99 wt% or more. The method of claim 3.

8. In step D), the mixing method is as follows: Sodium metavanadate, sodium borate, titanium dioxide, and sodium stearate are mixed, and then water is added to form a slurry, to obtain a mixed slurry, and the solid content of the mixed slurry is 1 wt% to 3 wt%. Next, a first calcined material is added and mixed to obtain a mixed slurry, The polishing is performed until the grain size of the material is 200 to 250 nm, During the spray drying process, the moisture content of the final spray-dried material is maintained at less than 0.5 wt% and the particle size is maintained at 3-10 μm; The secondary firing process is as follows: the sintering atmosphere is nitrogen or argon, the temperature rise rate is 50-80°C / h, the heat retention temperature is 650-700°C, and the heat retention time is 4-8h. The firing process is performed using a roller hearth kiln, which is connected to an inverter intake fan and the furnace pressure inside the roller hearth kiln is controlled to be 60-100 Pa higher than the external atmospheric pressure. The humidity in the heat retention stage is controlled to be 5% or less, and the temperature drop rate in the temperature drop stage is controlled to be 100-150°C / h. The sieving and de-ironizing step uses electromagnetic de-ironizing, and stops de-ironizing when the magnetic substance content of the product is below 300 ppb. The sieving step uses a 100-150 mesh sieve. After the sieving and iron removal, the product is further vacuum-packaged. The vacuum-packaging process is carried out in a temperature- and humidity-controlled room at a temperature of 15-25°C and a humidity of 5-10%. The method of claim 3.

9. The sodium battery positive electrode material according to claim 1 or 2, Sodium battery.

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