Magnesium-based O / P composite phase coated sodium ion battery positive electrode additive and preparation method thereof

Abstract

The invention provides a magnesium-based O / P composite phase coated sodium ion battery positive electrode additive and a preparation method thereof.The preparation method comprises the steps that firstly, nickel manganese hydroxide, a sodium source and an iron source serve as raw materials, and after grinding and mixing, high-temperature roasting is conducted in an air atmosphere through a muffle furnace; and after calcining, cooling the material to room temperature to obtain the core positive electrode material with the O / P composite phase. Dissolving and mixing a magnesium source and the core positive electrode material, adding phosphoric acid to enable the residual sodium source on the surface of the composite phase to fully react with the phosphoric acid to generate a sodium-containing coating layer, and finally performing high-temperature calcination to obtain a final product. The sodium-ion battery positive electrode material prepared by matching the magnesium-based O / P composite phase coated sodium-ion battery positive electrode additive has relatively high charge-discharge efficiency and cycling stability, and an effective strategy is provided for improving the comprehensive performance of the sodium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery materials, and particularly to a magnesium-based O / P composite phase-coated additive for sodium-ion battery cathodes and a preparation method thereof. Background Art

[0002] In the context of the ever-increasing energy demand today, efficient and environmentally friendly energy storage devices have become a research hotspot. Sodium-ion batteries are regarded as one of the most promising energy storage systems due to their advantages of abundant resources, low cost, and environmental friendliness. However, the cathode materials of sodium-ion batteries face a series of challenges in terms of performance and stability, which largely limit their development in practical applications. Current research mainly focuses on cathode materials with different structures such as layered, spinel, and olivine. Although these materials have good electrochemical performance, during the actual application process, the cathode materials will experience repeated volume expansion and contraction during charge and discharge. This volume change may lead to the gradual destruction of the material structure, thereby affecting the overall performance and cycle life of the battery. In addition, the diffusion rate of sodium ions in the cathode material is relatively slow, which directly limits the charge and discharge rate of the battery and affects its energy density, that is, the amount of energy stored per unit volume or mass. These problems of structural stability and ion transport rate not only affect the charge and discharge efficiency of sodium-ion batteries but also reduce their application potential in high-performance energy storage devices. Therefore, solving the problems of cathode materials in terms of performance and stability is the key to promoting the maturity and marketization of sodium-ion battery technology.

[0003] To overcome these difficulties, researchers have tried to develop new cathode materials and optimize the preparation process. Adding sodium that can be predictably and inevitably lost in the sodium-ion battery cathode in advance as an effective improvement method has attracted wide attention. Sodium-ion battery cathode additives can increase the structural stability of the cathode material, improve the ion transport rate, and enhance the battery performance. However, they also have the disadvantage of possibly introducing new impurities that affect safety, and the addition amount of some sodium-ion battery cathode additives is large, resulting in an increase in cost. Summary of the Invention

[0004] To overcome the limitations of existing sodium-ion battery cathode additives, the present invention provides a magnesium-based O / P composite phase-coated additive for sodium-ion battery cathodes and a preparation method thereof. The magnesium-based O / P composite phase-coated material not only has the advantage of high capacity of O3-type layered oxides but also has good structural retention of P2 fixed materials, which is beneficial to alleviating the defect of poor stability during charge and discharge when used as a cathode additive. In addition, the outer-coated magnesium phosphate effectively neutralizes the residual alkali on the surface of the core material, preventing these residual alkalis from decomposing to produce carbon dioxide gas under high pressure, which may cause the battery to bulge and generate serious sodium ions.

[0005] To achieve the above object, the present invention provides a preparation method of a magnesium-based O / P composite phase-coated sodium battery cathode additive, comprising the following steps:

[0006] (1) First, a sodium source, a lithium source, a nickel source, an iron source, and a manganese source are put into a mortar and ground and mixed in a certain proportion, then transferred to a ball mill for ball milling, and then transferred to a tubular furnace for high-temperature calcination to obtain a core cathode material of the O / P composite phase; the molar ratio of the sodium source, the lithium source, the nickel source, the iron source, and the manganese source is 1-1.15:0.05-0.2:0.3-0.6:0.2-0.5:0.1-0.3;

[0007] (2) Weigh a certain mass ratio of a magnesium source and dissolve it in absolute ethanol, then add a certain mass of the core cathode material, and finally dropwise add an appropriate amount of phosphoric acid; place the mixed solution in an oil bath and stir until the solvent evaporates to dryness;

[0008] (3) Collect the powder dried in step (2) into a crucible and calcine it at a high temperature in a muffle furnace to obtain the final product.

[0009] Preferably, in step (1), the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate, and sodium acetate; the lithium source is selected from at least one of lithium carbonate, lithium bicarbonate, lithium citrate, lithium oxalate, and lithium acetate; the nickel source is selected from at least one of nickel oxide, nickel oxalate, and nickel acetate; the iron source is selected from at least one of iron oxide, iron acetate, and magnetite; the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese sesquioxide.

[0010] Preferably, in step (1), the ball milling speed is 500-900 rpm, and the ball milling time is 6-10 h.

[0011] Preferably, in step (1), the calcination temperature is 700-1000 °C, the calcination time is 12-24 h, and the atmosphere in the tubular furnace is argon.

[0012] Preferably, in step (2), the magnesium source is selected from at least one of magnesium acetate, magnesium citrate, and magnesium oxalate.

[0013] Preferably, in step (2), the proportion of the magnesium source in the total mass of the O / P composite phase material ranges from 1% to 5%.

[0014] Preferably, in step (2), the temperature of the oil bath is 60 °C, the stirring speed is 200-500 rpm, and the stirring time is 10-12 h.

[0015] Preferably, in step (2), the calcination temperature is 700-900 °C, the calcination time is 5-9 h, and the heating and cooling rate is 1 °C / min.

[0016] The present invention also provides a sodium - ion battery cathode additive coated with a magnesium - based O / P composite phase obtained by the above - mentioned method. The chemical formula of the sodium - ion battery cathode additive is Na a Li b Ni c Fe x Mn y O 2 @NaMgPO 4 , where 0.5 < a < 1.5, 0 < b < 1, 0 < c < 1, and a + b + c = 1; 0.05 < x < 0.1, 0.05 < y < 0.15, and x + y = 0.67.

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) The magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive of the present invention not only has the advantage of high capacity of O3 - type layered oxides but also has good structural retention of P2 - type materials, which helps to improve the transmission rate of sodium ions. The existence of the coating layer further promotes the diffusion of ions in the cathode material, thus accelerating the ion transport during the charge - discharge process.

[0019] (2) The magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive of the present invention can effectively compensate for sodium loss, thus significantly improving the structural stability of the cathode material. This additive can neutralize the residual alkali on the surface of the cathode material and reduce its volume expansion and contraction during the charge - discharge process. This structural improvement not only enhances the cycle stability of the battery but also extends the service life of the battery, providing a reliable guarantee for the performance improvement of sodium - ion batteries in practical applications. Description of the Drawings

[0020] Figure 1 is the XRD pattern of the magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive prepared in Example 1 of the present invention;

[0021] Figure 2 is the SEM image of the magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive prepared in Example 1 of the present invention;

[0022] Figure 3 is the half - cell cycle performance graph of the magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive prepared in cooperation with Example 1 of the present invention;

[0023] Figure 4 is the XRD pattern of the magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive prepared in Example 2 of the present invention;

[0024] Figure 5 is the SEM image of the magnesium - based O / P composite - phase - coated sodium - ion battery cathode additive prepared in Example 2 of the present invention;

[0025] Figure 6 It is the first charge-discharge curve in the half-cell prepared with the sodium battery cathode additive coated with magnesium-based O / P composite phase prepared in accordance with Example 1 of the present invention;

[0026] Figure 7 It is the half-cell cycle performance diagram of the sodium battery cathode additive coated with magnesium-based O / P composite phase prepared in Comparative Example 1;

[0027] Figure 8 It is the SEM diagram of the core cathode material prepared in Comparative Example 2;

[0028] Figure 9 It is the half-cell cycle performance diagram of the core cathode material prepared in Comparative Example 2;

[0029] Figure 10 It is the half-cell cycle performance diagram of the cathode material prepared in Comparative Example 3;

[0030] Figure 11 It is the half-cell cycle performance diagram of the cathode material prepared in Comparative Example 3. Detailed implementation manners

[0031] To better illustrate the purpose, technical solution and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0032] Example 1

[0033] (1) First, weigh 1.26 grams of sodium carbonate, 0.16 grams of lithium carbonate, 1.49 grams of nickel oxide, 1.52 grams of iron oxide, and 0.53 grams of manganese dioxide, put them into a mortar for grinding and mixing, and then transfer them to a ball mill, and ball mill at a speed of 700 rmp for 8 hours. Respectively take 2.5 g of the ball-milled mixture and calcine it in a tube furnace under a nitrogen atmosphere at 800 °C for 18 hours, and cool it to room temperature to obtain the core cathode material.

[0034] (2) Weigh 0.25 grams of magnesium acetate and dissolve it in absolute ethanol, then add 2.5 g of the core cathode material, and finally drop 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 70 °C and stir it at a speed of 1400 rpm for 11 hours.

[0035] (3) Place the collected material in a muffle furnace and sinter it at 800 °C for 7 hours, and cool it to 150 °C to obtain the final product - the cathode additive.

[0036] Analyze the final product of this example by X-ray powder diffraction, and the results are as Figure 1 shown. Its phase exists in P phase, O phase, and NaMgPO 4 , indicating that the coating of magnesium-based O / P composite phase is successful.

[0037] The final product of this example was scanned using a scanning electron microscope, and the results are as follows Figure 2 As shown, the optimized O3 layered oxide cathode material exhibits an irregular spherical morphology, which are "secondary particles" or "aggregates", with heterogeneous surface characteristics and size distribution. There is a thin coating layer on the surface of its irregular spherical aggregate morphology, indicating that the coating is effective.

[0038] To distinguish from the effect of our cathode additive on the performance of sodium-ion batteries, a single sodium-ion battery cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ) was selected for experimental comparative testing. Weigh 0.02 g of the final product prepared in the above step three, 0.08 g of the cathode material, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder). After thorough grinding, add 0.6 mL of NMP and disperse and mix them. After uniform slurry adjustment, draw the slurry on an aluminum foil to make a film. After drying in a blast at 85 °C, cut it into a disc with a diameter of 12 mm, and assemble it in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, 1 M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) as the electrolyte, and use glass fiber (Grade GF / F) as the separator to assemble a CR2032 type coin cell.

[0039] Figure 3 The cycling performance graph in -1 shows that when the product is subjected to constant current charge-discharge testing between 2-4.0 V at a rate of 1 A g -1 at 25 °C, the initial discharge specific capacity of the product is 122.6 mA h g -1 , and the discharge specific capacity after 100 cycles is 77.2 mA h g

[0040] Example 2

[0041] (1) First, weigh 1.51 grams of sodium bicarbonate, 0.18 grams of lithium citrate, 1.29 grams of nickel oxalate, 1.25 grams of iron oxide, and 0.86 grams of manganese oxalate and grind and mix them in a mortar. Then transfer them to a ball mill and ball mill for 9 h at a speed of 800 rmp. Take 2.5 g of the ball-milled mixture and calcine it in two tubular furnaces under an argon atmosphere at 900 °C for 20 h, and cool it to room temperature to collect the core cathode material.

[0042] (2) Weigh 0.18 grams of magnesium acetate and dissolve it in absolute ethanol. Then add 2.5 g of the core cathode material and finally drop 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 60 °C and stir it at a speed of 300 rpm for 10 h.

[0043] (3) Place the collected materials in a muffle furnace and sinter at 750 °C for 6 h. Cool down to 150 °C and collect to obtain the final product.

[0044] Analyze the product of this example by X-ray powder diffraction. The results are as Figure 4 shown. Its phases include P phase, O phase, and NaMgPO 4 , indicating successful coating of the magnesium-based O / P composite phase.

[0045] Scan the product of this example using a scanning electron microscope. The results are as Figure 5 shown. Similar to Example 1, it has an irregular secondary spherical morphology and the surface coating layer is relatively smooth, indicating effective removal of residual alkali on the surface.

[0046] Weigh 0.02 g of the product prepared above, 0.08 g of the cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ), 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder). After thorough grinding, add 0.6 mL of NMP and disperse and mix them. After uniformly adjusting the slurry, draw the slurry on an aluminum foil to make a film. After drying at 85 °C with air blowing, cut it into a disc with a diameter of 12 mm, and assemble it in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, 1 M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) as the electrolyte, and use glass fiber (Grade GF / F) as the separator to assemble a CR2032 type button cell.

[0047] Figure 6 The first charge-discharge curve in -1 shows that when the product is subjected to a constant current charge-discharge test at a rate of 1 A g -1 between 2 - 4.0 V at 25 °C, the first discharge capacity of the product is 120.6 mA h g

[0048] Use a scanning electron microscope to scan the morphology of the product after cycling 100 times at a rate of 1 A g -1 and under the conditions of 2 - 4.0 V. The results are as Figure 7 shown. After optimization, the degree of internal structure splitting and expansion of the material during cycling is relatively small. Specifically, the intergranular cracks and the distortion of the layered structure are not obvious, indicating that the material maintains high structural stability, confirming that our material has lower volume expansion and contraction during charge and discharge.

[0049] Example 3

[0050] (1) First, weigh 2.61 g of sodium citrate, 0.23 g of lithium oxalate, 0.97 g of nickel acetate, 0.85 g of ferric acetate and 0.64 g of manganese trioxide, put them into a mortar and grind them, then transfer them to a ball mill and mill them at 850 rpm for 7 h. Take 2.5 g of the ball-milled mixture and calcine it at 850 ° C for 22 h in two tube furnaces under helium atmosphere, and cool it to room temperature to obtain the core positive electrode material.

[0051] (2) Weigh 0.76 g of magnesium citrate and dissolve it in anhydrous ethanol, then add 2.5 g of the core positive electrode material, and finally drop 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 65° C. and stir at 500 rpm for 9 hours.

[0052] (3) The collected material was placed in a muffle furnace and sintered at 850°C for 8 h, then cooled to 150°C to obtain the final product.

[0053] Weigh 0.02 g of the product prepared above, the positive electrode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 )0.08g, acetylene black (conductive agent)0.01g, PVDF (HSV900, binder)0.01g, after fully grinding, add 0.6mL NMP to disperse and mix, slurry is evenly mixed, and slurry is drawn on aluminum foil to make sheets, and after being dried at 85℃ with air blowing, it is cut into discs with a diameter of 12mm, and assembled in a glove box with argon atmosphere, with metal sodium sheet as the counter electrode, 1M NaPF 6 The solution (solvent EC:DEC volume ratio of 1:1) was used as the electrolyte, and glass fiber (Grade GF / F) was used as the separator to assemble a CR2032 button cell. -1 When the constant current charge and discharge test was carried out at a rate between 2-4.0V, the first discharge capacity of the product was 120.5mA hg -1 After 100 cycles, the discharge capacity is 75.9 mA h g -1 , the capacity retention rate is 62.98%.

[0054] Example 4

[0055] (1) First, 1.76 g of sodium oxalate, 0.29 g of lithium acetate, 0.91 g of nickel oxide, 0.76 g of iron oxide and 0.45 g of manganese dioxide were weighed and ground into a mortar, then moved into a ball mill and milled at 900 rpm for 10 h. 2.5 g of the milled mixture was taken and calcined at 1000 ° C for 24 h in two tube furnaces under nitrogen atmosphere, and then cooled to room temperature to obtain the core positive electrode material.

[0056] (2) Weigh 0.31 g of magnesium oxalate and dissolve it in absolute ethanol. Then add 2.5 g of the core cathode material, and finally dropwise add 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 75 °C and stir it at a speed of 200 rpm for 12 h.

[0057] (3) Place the collected material in a muffle furnace and sinter it at 900 °C for 5 h. Cool it down to 150 °C and collect the final product.

[0058] Weigh 0.02 g of the product prepared above, 0.08 g of the cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ), 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder). After fully grinding, add 0.6 mL of NMP and disperse and mix them. After making the slurry uniform, draw the slurry on an aluminum foil to make a film. After drying in a blast at 85 °C, cut it into a circle with a diameter of 12 mm, and assemble it in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, 1 M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) as the electrolyte, and use glass fiber (Grade GF / F) as the separator to assemble a CR2032 type button cell. At 25 °C, when performing a constant current charge-discharge test at a rate of 1 A g -1 between 2 - 4.0 V, the initial charge capacity of the product is 123.4 mA h g -1 , and the charge specific capacity after 100 cycles is 78.9 mA h g -1 , and the capacity retention rate is 64.1%.

[0059] Example 5

[0060] (1) First, weigh 2.53 g of sodium carbonate, 0.11 g of lithium carbonate, 0.99 g of nickel oxide, 0.66 g of iron oxide, 0.33 g of manganese dioxide, and 0.33 g of magnesium acetate and put them into a mortar for grinding and mixing. Then transfer them to a ball mill and ball mill them at a speed of 500 rmp for 6 h. Take 2.5 g of the ball-milled mixture respectively and calcine it in two tubular furnaces under an argon atmosphere at 700 °C for 12 h. Cool it to room temperature and collect the core cathode material.

[0061] (2) Weigh 0.33 g of magnesium acetate and dissolve it in absolute ethanol. Then add 2.5 g of the core cathode material, and finally dropwise add 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 80 °C and stir it at a speed of 300 rpm for 10 h.

[0062] (3) Place the collected material in a muffle furnace and sinter it at 700 °C for 9 h. Cool it down to 150 °C and collect the final product.

[0063] Weigh 0.02 g of the product prepared above, 0.08 g of the cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ), 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder). After thoroughly grinding, add 0.6 mL of NMP for dispersion and mixing. After the slurry is evenly adjusted, draw the slurry on an aluminum foil to make a film. After drying in a blast at 85 °C, cut it into a disc with a diameter of 12 mm, and assemble it in a glove box under an argon atmosphere. Use a sodium metal sheet as the counter electrode, 1 M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) as the electrolyte, and use glass fiber (Grade GF / F) as the separator to assemble a CR2032 type button cell. At 25 °C, when performing a constant current charge-discharge test at a rate of 1 A g -1 between 2 - 4.0 V, the initial charge capacity of the product is 122.2 mA h g -1 , and the charge specific capacity after 100 cycles is 77.6 mA h g -1 , and the capacity retention rate is 63.5%.

[0064] Example 6

[0065] (1) First, weigh 1.65 g of sodium bicarbonate, 0.19 g of lithium citrate, 1.42 g of nickel oxalate, 1.12 g of iron oxide, and 0.63 g of manganese oxalate and put them into a mortar for grinding and mixing. Then transfer them to a ball mill and ball mill at a speed of 850 rmp for 7 h. Take 2.5 g of the ball-milled mixture and calcine it in two tubular furnaces under a helium atmosphere at 850 °C for 22 h, and cool it to room temperature to collect the core cathode material.

[0066] (2) Weigh 0.47 g of magnesium acetate and dissolve it in absolute ethanol. Then add 2.5 g of the core cathode material, and finally add 5 ml of phosphoric acid dropwise. Place the mixed solution in an oil bath at 65 °C and stir it at a speed of 500 rpm for 9 h.

[0067] (3) Place the collected material in a muffle furnace and sinter it at 850 °C for 8 h, and cool it to 150 °C to collect the final product.

[0068] Weigh 0.02 g of the product prepared above, 0.08 g of the cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2)0.08 g, 0.01 g of acetylene black (conductive agent), 0.01 g of PVDF (HSV900, binder), after thoroughly grinding, 0.6 mL of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was spread on aluminum foil to make a film. After drying in a blast at 85 °C, it was cut into discs with a diameter of 12 mm and assembled in a glove box under an argon atmosphere. Using a sodium metal sheet as the counter electrode, 1 M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) as the electrolyte, and using glass fiber (Grade GF / F) as the separator, a CR2032 type button cell was assembled. At 25 °C, at a rate of 1 A g -1 during the constant current charge-discharge test between 2 - 4.0 V, the initial charge capacity of the product was 121.4 mA h g -1 , and the charge specific capacity after 100 cycles was 74.54 mA h g -1 , and the capacity retention rate was 61.4%.

[0069] Example 7

[0070] (1) First, weigh 2.5 grams of sodium citrate, 0.23 grams of lithium oxalate, 0.82 grams of nickel acetate, 0.7 grams of iron acetate, and 0.58 grams of manganese(III) oxide and put them in a mortar for grinding and mixing. Then transfer them to a ball mill and ball mill at a speed of 800 rmp. Take 2.5 g of the ball-milled mixture and calcine it in a tube furnace under a nitrogen atmosphere at 800 °C for 18 h, and cool to room temperature to collect the core cathode material.

[0071] (2) Weigh 0.35 grams of magnesium citrate and dissolve it in absolute ethanol, then add 2.5 g of the core cathode material, and finally add 5 ml of phosphoric acid dropwise. The mixed solution was placed in an oil bath at 70 °C and stirred at a speed of 100 rpm for 11 h.

[0072] (3) Place the collected material in a muffle furnace and sinter it at 800 °C for 7 h, and cool to 150 °C to collect the final product.

[0073] Weigh 0.02 g of the product prepared above, 0.08 g of the cathode material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 ), 0.01 g of acetylene black (conductive agent), 0.01 g of PVDF (HSV900, binder), after thoroughly grinding, 0.6 mL of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was spread on aluminum foil to make a film. After drying in a blast at 85 °C, it was cut into discs with a diameter of 12 mm and assembled in a glove box under an argon atmosphere. Using a sodium metal sheet as the counter electrode, 1 M NaPF 6The solution (solvent EC:DEC volume ratio of 1:1) was used as the electrolyte, and glass fiber (Grade GF / F) was used as the separator to assemble a CR2032 button cell. -1 When the constant current charge and discharge test was carried out at a rate between 2-4.0V, the initial charge capacity of the product was 122.08mA hg -1 After 100 cycles, the charge capacity is 77.4 mA h g -1 , the capacity retention rate is 63.4%.

[0074] Comparative Example 1

[0075] (1) First, 1.26 g of sodium carbonate, 0.16 g of lithium carbonate, 1.49 g of nickel oxide, 1.52 g of iron oxide and 0.53 g of manganese dioxide were weighed and ground into a mortar, then moved into a ball mill and milled for 8 h at 700 rpm. 2.5 g of the ball-milled mixture was taken and calcined at 800 ° C for 18 h in two tube furnaces under nitrogen atmosphere, and then cooled to room temperature to obtain the core positive electrode material.

[0076] (2) Weigh 0.25 g of magnesium acetate and dissolve it in anhydrous ethanol, then add 2.5 g of the core positive electrode material, and finally drop 5 ml of phosphoric acid. Place the mixed solution in an oil bath at 70°C and stir at 1400 rpm for 11 hours.

[0077] (3) The collected material was placed in a muffle furnace and sintered at 800°C for 7 h, then cooled to 150°C to obtain the final product.

[0078] Weigh 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder), grind them thoroughly, add 0.6 mL of NMP to disperse and mix, slurry them evenly, and then draw them on aluminum foil to make sheets. After drying at 85 °C with air blowing, cut them into discs with a diameter of 12 mm, and assemble them in a glove box with an argon atmosphere. Use a metal sodium sheet as the counter electrode and 1 M NaPF 6 The solution (solvent EC:DEC volume ratio of 1:1) was used as the electrolyte, and glass fiber (Grade GF / F) was used as the separator to assemble into a CR2032 button cell. Figure 8 The cycling performance diagram in the figure shows that at 25°C, the -1 When the constant current charge and discharge test was carried out at a rate between 2-4.0V, the first discharge capacity of the product was 109.2mA hg -1 After 100 cycles, the charge capacity is 62.3 mA h g -1 The capacity retention rate is 57.05%. The first three steps are exactly the same as those in Example 1.

[0079] Comparative Example 2

[0080] Compared with Example 5, first, 1.26 g of sodium carbonate, 0.16 g of lithium carbonate, 1.49 g of nickel oxide, 1.52 g of iron oxide, and 0.53 g of manganese dioxide were weighed and ground and mixed in a mortar, and then transferred to a ball mill and ball-milled at 700 rmp for 8 h. 2.5 g of the ball-milled mixture was taken and calcined in a tubular furnace under a nitrogen atmosphere at 800 °C for 18 h, and then cooled to room temperature to obtain the core cathode material.

[0081] The product of this example was scanned using a scanning electron microscope, and the results are as Figure 9 shown. It has an irregular secondary spherical morphology, with different secondary spherical shapes, uneven particle size distribution, and a large number of residual alkali particles attached to the surface.

[0082] 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder) were weighed, thoroughly ground, and then 0.6 mL of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was spread on an aluminum foil to make a film. After drying in a blast at 85 °C, it was cut into a 12 mm diameter disc and assembled in a glove box under an argon atmosphere. A sodium metal sheet was used as the counter electrode, and 1 M NaPF 6 solution (solvent EC:DEC volume ratio of 1:1) was used as the electrolyte, and a glass fiber (Grade GF / F) was used as the separator to assemble a CR2032 type button cell. Figure 10 The cyclic performance diagram in -1 shows that at 25 °C, when a constant current charge-discharge test was carried out between 2 - 4.0 V at a rate of 1 A g -1 , the initial discharge specific capacity of the product was 114.9 mA h g -1 , and the charge specific capacity after 100 cycles was 40.1 mA h g

[0083] At 25 °C, we tested the electrochemical performance of the materials before and after coating. The material before coating showed a high specific capacity of 114.9 mA h g -1 during the first discharge, but after 100 cycles, the charge specific capacity decreased to 40.1 mAh g -1 , and the capacity retention rate was only 34.81%, indicating that the material suffered relatively serious capacity decay during the cycling process. In contrast, although the initial discharge specific capacity of the coated material was slightly lower, at 109.2 mA h g -1 , its cyclic performance was significantly improved, and the charge specific capacity after 100 cycles was 62.3 mA h g -1, the capacity retention rate reaches 57.05%. This improvement indicates that the introduction of the coating layer effectively inhibits the interfacial reaction and the dissolution of transition metal ions, improves the structural stability and cycle life of the material, and thus enhances the overall performance of the sodium-ion battery.

[0084] The residual alkali on the surface of the cathode material has a significant negative impact on the performance of the sodium-ion battery. It mainly causes interfacial reactions and promotes the dissolution of transition metal ions, leading to the deterioration of the interfacial properties and the loss of active substances, thereby shortening the battery cycle life and reducing the discharge specific capacity. The capacity retention rate of the untreated battery is only 34.81% after 100 cycles, while it can be increased to more than 57.05% after treatment. The treatment of surface residual alkali is crucial for improving the cycle performance of the battery and can effectively improve the stability and energy storage capacity of the battery.

[0085] In a sodium-ion battery, when the battery operates at high voltage or there is residual alkali on the surface of the cathode material, the residual alkali will decompose to generate carbon dioxide gas. If the space inside the battery is limited, the generation of gas will cause an increase in the internal pressure of the battery, which will in turn cause the battery to bulge. After the battery bulges, the contact area between the electrode material and the electrolyte inside the battery decreases, resulting in a reduction in the efficiency of the electrochemical reaction. In addition, the bulge may also cause damage to the battery structure, making it impossible for sodium ions to be effectively inserted and extracted during charge and discharge, thus causing the loss of sodium ions. The relationship between the two can be summarized as: the generation of gas causes the battery to bulge, and the battery bulge further leads to the loss of sodium ions. This is because after the battery bulges, the effective capacity of the battery decreases and the utilization rate of sodium ions decreases, thus affecting the overall performance of the battery.

[0086] Therefore, through the magnesium-based O / P composite phase coating material in the present invention, the residual alkali on the surface of the cathode material can be effectively neutralized, the generation of carbon dioxide gas can be reduced, the battery bulge can be prevented, and further the loss of sodium ions can be reduced, improving the stability and life of the battery. We carried out SEM analysis on the cycled materials. The SEM images clearly show that the optimized materials have relatively less internal structure splitting and swelling during the cycling process. Specifically, the intergranular cracks and the distortion of the layered structure are not obvious, indicating that the materials maintain a high structural stability, confirming that our materials have lower volume expansion and contraction during charge and discharge, which is crucial for improving the cycle performance and extending the service life of sodium-ion batteries.

[0087] Comparative Example 3

[0088] To distinguish from the effect of our cathode additive on the performance of sodium-ion batteries, a single sodium-ion battery cathode material was selected for experimental comparative testing. Referring to Example 5 and Comparative Example 2, first, 1.8 g of sodium carbonate, 1.25 g of nickel oxide, 1.25 g of iron oxide, and 0.57 g of manganese dioxide were weighed and ground in a mortar, and then transferred to a ball mill and ball milled at 500 rmp for 6 h. 2.5 g of the ball-milled mixture was taken and calcined in a tube furnace under a nitrogen atmosphere at 750 °C for 12 h, and the cathode material was obtained after cooling to room temperature.

[0089] 0.08 g of the product prepared above, 0.01 g of acetylene black (conductive agent), and 0.01 g of PVDF (HSV900, binder) were weighed, thoroughly ground, then 0.6 mL of NMP was added for dispersion and mixing. After the slurry was evenly adjusted, it was pasted on an aluminum foil and made into a film. After drying at 85 °C in a blast oven, it was cut into a disc with a diameter of 12 mm and assembled in a glove box under an argon atmosphere. A sodium metal sheet was used as the counter electrode, and 1M NaPF 6 solution (the volume ratio of the solvent EC:DEC is 1:1) was used as the electrolyte, and glass fiber (Grade GF / F) was used as the separator to assemble a CR2032-type button battery. Figure 11 The cycling performance graph in -1 shows that at 25 °C, when a constant current charge-discharge test was carried out between 2 - 4.0 V at a rate of 1 A g -1 , the initial charge capacity of the product was 124.02 mA h g -1 , and the charge specific capacity after 100 cycles was 61.9 mA h g -1 , and the capacity retention rate was 49.91%. By comparing the performance data of sodium-ion batteries containing sodium-ion battery cathode additives and pure cathode materials, we can see the significant effect of the additives on battery performance. For the battery with the sodium-ion battery cathode additive added, its initial discharge specific capacity was 122.6 mA h g -1 , and the discharge specific capacity after 100 cycles was 77.2 mA h g -1 , and the capacity retention rate reached 63.11%. For the battery without the additive added, the initial discharge specific capacity was 124.02 mA h g -1 , but the discharge specific capacity after 100 cycles decreased to 61.9 mA h g

[0090] , and the capacity retention rate was 49.91%. The data shows that although the additive slightly reduces the initial discharge specific capacity, it significantly improves the cycling performance of the battery. During the cycling process, the battery with the additive added shows a higher capacity retention rate, indicating that the additive can effectively inhibit the attenuation of active substances and improve the cycling stability and service life of the battery.Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a magnesium-based O / P composite phase-coated sodium positive electrode additive, characterized in that: The following steps are involved: (1) First, a sodium source, a lithium source, a nickel source, an iron source and a manganese source are put into a mortar in a certain proportion and ground and mixed, then moved to a ball mill for ball milling, and then transferred to a tube furnace for high-temperature calcination to obtain a core positive electrode material of an O / P composite phase; the molar ratio of the sodium source, the lithium source, the nickel source, the iron source and the manganese source is 1-1.15:0.05-0.2:0.3-0.6:0.2-0.5:0.1-0.3; (2) Weigh a certain mass ratio of magnesium source and dissolve it in anhydrous ethanol, then add a certain mass of core positive electrode material, and finally drop an appropriate amount of phosphoric acid; place the mixed solution in an oil bath and stir until the solvent evaporates; (3) collecting the powder evaporated in step (2) into a dry pot, and calcining at high temperature in a muffle furnace to obtain a final product.

2. The preparation method according to claim 1, characterized in that: In step (1), the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate, and sodium acetate; the lithium source is selected from at least one of lithium carbonate, lithium bicarbonate, lithium citrate, lithium oxalate, and lithium acetate; the nickel source is selected from at least one of nickel oxide, nickel oxalate, and nickel acetate; the iron source is selected from at least one of iron oxide, iron acetate, and ferroferric oxide; and the manganese source is selected from at least one of manganese dioxide, manganese acetate, manganese oxalate, and manganese trioxide.

3. The preparation method according to claim 1, characterized in that: In step (1), the ball milling speed is 500-900 rpm, and the ball milling time is 6-10 h.

4. The preparation method according to claim 1, characterized in that: In step (1), the calcination temperature is 700-1000° C., the calcination time is 12-24 hours, and the atmosphere of the tubular furnace is argon.

5. The preparation method according to claim 1, characterized in that: In step (2), the magnesium source is selected from at least one of magnesium acetate, magnesium acetate, magnesium citrate and magnesium oxalate.

6. The preparation method according to claim 1, characterized in that: In step (2), the ratio of the magnesium source to the total mass of the O / P composite phase material is in the range of 1% to 5%.

7. The preparation method according to claim 1, characterized in that: In step (2), the temperature of the oil bath is 60° C., the stirring speed is 200-500 rpm, and the stirring time is 10-12 h.

8. The preparation method according to claim 1, characterized in that: In step (2), the calcination temperature is 700-900°C, the calcination time is 5-9h, and the heating and cooling rate is 1°C / min.

9. A magnesium-based O / P composite phase coated sodium positive electrode additive obtained by the method according to any one of claims 1 to 8, characterized in that: The chemical formula of the sodium positive electrode additive is Na a Li b Ni c Fe x Mn y O2@NaMgPO4, where 0.5<a<1.5, 0<b<1, 0<c<1, a+b+c=1; 0.05<x<0.1, 0.05<y<0.15, x+y=0.67.

Images