A modified sodium ion battery layer oxygen high iron positive electrode material and its preparation method

Abstract

The present invention discloses a modified sodium ion battery layer oxygen high iron positive electrode material and a preparation method thereof, which belongs to the technical field of sodium ion battery preparation. The modified high iron layer oxygen positive electrode material prepared by the present invention through the above measures is coated with a layer of relatively stable conventional system in the precursor, doped with a specific proportion of transition metals, halogens, rare elements, etc. during the sintering process, and finally coated with core-shell materials to effectively improve the rate and cycle performance. Combined with the low nickel and high iron component design of the material itself, it takes into account multiple indicators such as cost capacity and performance, which has great advantages for the application of sodium electric materials in fields such as two-wheeled vehicles that are sensitive to cost requirements. At a current density of 0.1C (voltage window 2‑4V), the first-cycle discharge specific capacity can reach 142mAh / g. At a current density of 1C, the capacity can reach 130mAh / g, and after 50 cycles of charge and discharge, there is still a capacity retention rate of 94.5%, showing excellent long cycle life and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery preparation, and specifically relates to a modified sodium ion battery layered oxygen high-iron positive electrode material and a preparation method thereof. Background Art

[0002] With the increasing global attention to environmental protection and sustainable development, new energy vehicles and energy storage systems, as key technologies for reducing carbon emissions and promoting energy structure transformation, are experiencing unprecedented rapid development. Against this backdrop, battery technology, as a core component of energy storage, especially the widespread application of lithium-ion batteries, has achieved remarkable results. However, its limited resources (such as uneven distribution of lithium resources and rising costs) and safety issues have gradually become prominent, prompting the scientific research community and industry to actively explore new battery systems. Sodium-ion batteries, as a potential alternative to lithium-ion batteries, have become a research hotspot in recent years due to their abundant sodium resource reserves, lower cost advantages, and similar electrochemical working mechanisms.

[0003] The performance of sodium-ion batteries depends largely on the properties of their cathode materials. Ideal cathode materials should possess high specific capacity, long cycle life, good rate capability, and structural stability. However, research on cathode materials for sodium-ion batteries is still in its early stages and faces numerous challenges, the most critical of which is balancing cost, capacity, and cycle stability.

[0004] Among the many cathode materials, layered oxygen materials (such as Na x Ni y Mn z Fe 1-y-z O2, where x, y, and z are stoichiometric numbers) has attracted much attention due to its adjustable composition, high specific capacity, and relatively good cycle performance. By adjusting the ratio of nickel, manganese, and iron in the material, precise control of the material properties can be achieved. In particular, reducing the nickel content and increasing the content of low-priced metal elements such as iron is considered an effective cost-cutting and efficiency-enhancing strategy. This strategy not only reduces material costs, but also is expected to increase the energy density of the overall battery due to the high theoretical specific capacity of iron (compared to nickel and manganese).

[0005] However, as the iron content increases, a series of problems also arise. First, positive electrode materials with high iron content are prone to iron ion dissolution during the charging and discharging process, which not only leads to the loss of active materials, but may also cause contamination of the electrolyte, thereby affecting the cycle life and safety performance of the battery. Secondly, when the iron content exceeds a certain threshold (such as 33%), clustering of Fe atoms begins to appear in the material. During the charging process, when the Fe ions are oxidized to +4 valence, these clusters trigger the Jan-Taylor effect, resulting in the migration and phase change of adjacent Fe ions. This phase change is often irreversible, which destroys the crystal structure of the material, resulting in a significant attenuation of the discharge capacity and deterioration of the cycle performance.

[0006] There are several solutions to these problems. For example, surface coating modification can be used to coat the cathode material with a stable oxide or phosphate layer to inhibit the dissolution of iron ions and improve the material's cycling stability. Furthermore, by fine-tuning synthesis conditions, a uniform distribution of iron, manganese, and nickel in the layered oxide material can be achieved, reducing the formation of iron clusters and mitigating the adverse effects of the Jan-Taylor effect on material performance.

[0007] However, there is currently no relevant research on the above two solutions. Summary of the Invention

[0008] Based on this, the present invention provides a modified sodium-ion battery layered iron cathode material and its preparation method. This method involves coating during the precursor synthesis phase, followed by element doping and re-coating during the cathode material sintering phase. This effectively reduces the adverse effects of increased iron content, such as ion dissolution and phase change, caused by increased iron content. Because this material offers high capacity, low cost, and stable cycling performance, it can be applied to the second-wheel vehicle market and other fields after being fabricated into battery cells and modules.

[0009] The present invention provides a modified sodium ion battery layered oxygen high iron positive electrode material, comprising a substrate and a precursor coating, a positive electrode doping and a second coating.

[0010] The matrix material is Na x (Ni a Fe b Mn c )X d Y e Z f O2; 0.85≤x<1, 0≤a<0.33, 0.33≤b<0.5, 0≤c<0.33, 0.01≤d<0.05, e=1-abc, 0.01≤f<0.05, X is nickel-iron-manganese oxide, Y is one or more elements such as Al, Y, Mg, Ca, Ce, Cu, Ti, and Z is a core-shell structured sodium-based polymer.

[0011] The present invention provides a method for preparing a modified sodium ion battery layered oxygen high iron cathode material, comprising the following steps:

[0012] (1) mixing a nickel source, an iron source, and a manganese source according to a first molar ratio of nickel, iron, and manganese elements to obtain a layered oxygen salt solution 1, and adding the layered oxygen salt solution 1, an alkaline solution, and a complexing agent to a bottom liquid in parallel for a coprecipitation reaction to obtain a layered oxygen precursor;

[0013] (2) mixing a nickel source, an iron source, and a manganese source according to a second molar ratio of nickel, iron, and manganese elements to obtain a layered oxygen salt solution 2, mixing the layered oxygen salt solution 2, an alkaline solution, a complexing agent, and the layered oxygen precursor in step (1), and coating the layered oxygen precursor to obtain the sodium ion battery layered oxygen high iron positive electrode material precursor;

[0014] (3) uniformly mixing the sodium ion battery layered oxygen high iron positive electrode material precursor with a sodium source and a metal compound and then calcining the mixture to obtain a multi-element doped sodium ion battery layered oxygen high iron positive electrode material;

[0015] (4) introducing an inert gas into the solvent, adding polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate and zirconium acetate to fully disperse, adding a multi-element doped sodium ion battery layered oxygen high iron positive electrode material, adding an initiator to initiate a polymerization reaction, and obtaining a core-shell structured sodium-based polymer;

[0016] (5) calcining the core-shell structure sodium-based polymer to obtain the modified sodium ion battery layered oxygen high iron positive electrode material;

[0017] The molar ratio of the iron element in the first molar ratio is higher than or equal to the molar ratio of the iron element in the second molar ratio.

[0018] Specifically, the nickel source is a compound containing nickel, and at least one of nickel sulfate, nickel acetate and nickel nitrate can be preferably selected.

[0019] The manganese source is a compound containing manganese, and preferably at least one of manganese sulfate, manganese acetate and manganese nitrate can be selected.

[0020] The iron source is an iron-containing compound, and preferably at least one of ferrous sulfate, ferrous oxalate and ferrous nitrate can be selected.

[0021] The concentrations of the layer oxygen salt solution 1 and the layer oxygen salt solution 2 are both 1.0-5.0 mol / L;

[0022] The alkali solution is a sodium hydroxide solution, and the concentration of the alkali solution is 2.0-4.0 mol / L.

[0023] The complexing agent is ammonia water, EDTA or sodium citrate, and the concentration of the complexing agent is 1.0-5.0 mol / L.

[0024] Preferably, in step (1), the first molar ratio of nickel, iron and manganese elements is 0.1-0.33:0.33-0.5:0.2-0.35; more preferably, in the embodiment of the present invention, the first molar ratio of nickel, iron and manganese elements is 20-25:45-50:25-30 as an example;

[0025] In step (2), the second molar ratio of nickel, iron and manganese elements is g:h:i, wherein g+h+i=1, h<1 / 3:

[0026] The mass ratio of the layer oxygen salt solution 1 to the layer oxygen salt solution 2 is 1:0.01-0.05.

[0027] Specifically, in step (1), the coprecipitation temperature is 40-60°C;

[0028] In step (2), the particle size D50 of the sodium ion battery layered oxygen high iron positive electrode material precursor is 3.5-10 μm.

[0029] Specifically, in step (3), the sodium source is sodium carbonate, sodium nitrate or sodium hydroxide,

[0030] The metal compound is one or more of aluminum compounds, copper compounds, calcium compounds, cerium nitrate, titanium compounds, yttrium oxide, and magnesium oxide;

[0031] The aluminum compound is aluminum oxide or aluminum nitrate, the copper compound is copper oxide or copper sulfate, the calcium compound is calcium carbonate or calcium nitrate, and the titanium compound is titanium dioxide or titanium tetrachloride;

[0032] The molar ratio of the sodium ion battery layered oxygen high iron cathode material precursor to the sodium source and the metal compound is 1:0.9-1.1:0.01-0.05.

[0033] Preferably, the calcination treatment conditions are: calcination temperature is 830-950° C., and calcination time is 10-20 hours.

[0034] Preferably, in step (4), the mass ratio of the multi-element doped sodium ion battery layered oxygen high iron positive electrode material to polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, zirconium acetate and solvent (water or ethanol can be selected) is 100-120:0.2-2:5-9:15-21:2-5:0.2-2:0.1-2:1000-1200;

[0035] The initiator is azobisisobutyronitrile;

[0036] The polymerization reaction conditions are: reaction at 60° C. for 6 hours.

[0037] Specifically, the calcination treatment conditions are: calcination temperature is 450-650° C., and calcination time is 5-10 hours.

[0038] The present invention also provides a modified sodium ion battery layered oxygen high iron positive electrode material prepared by the preparation method.

[0039] The present invention also provides a sodium ion battery comprising a positive electrode, a separator and a negative electrode, wherein the positive electrode comprises the modified sodium ion battery layered oxygen high iron positive electrode material.

[0040] The modified high-iron layered oxygen cathode material prepared by the above measures is prepared by coating a relatively stable conventional system in the precursor, doping a specific proportion of transition metals, halogens, rare elements, etc. during the sintering process, and finally coating the core-shell material to effectively improve the rate and cycle performance. Combined with the low-nickel and high-iron component design of the material itself, it takes into account multiple indicators such as cost capacity and performance, which has great advantages for the application of sodium battery materials in cost-sensitive fields such as the second-wheel.

[0041] At a current density of 0.1C (voltage window 2-4V), the first-cycle discharge capacity reached 142mAh / g. At a current density of 1C, the capacity reached 130mAh / g. After 50 cycles of charge and discharge, the battery maintained a 94.9% capacity retention rate, demonstrating excellent long cycle life and stability. This experimental method is simple and easy to implement, with low material costs, and can be expanded to synthesize other energy storage materials, thereby improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Ni obtained in Example 2 of the present invention 0.25 Fe 0.50 Mn 0.25 SEM images of (OH)2 precursor materials;

[0043] Figure 2 This is a SEM image of the positive electrode material obtained in Example 2 of the present invention;

[0044] Figure 3 This is a SEM image of the positive electrode material obtained in Example 3 of the present invention;

[0045] Figure 4 This is a 0.1C charge-discharge curve of the positive electrode material obtained in Example 2 of the present invention;

[0046] Figure 5 This is a capacity diagram of the positive electrode material obtained in Example 2 of the present invention after 50 cycles at a current density of 1C. DETAILED DESCRIPTION

[0047] Example 1

[0048] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 500 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:50:25) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 2.0 mol / L ammonia water and 4 mol / L NaOH solution. The reaction pH was adjusted to 10 for co-precipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L to react, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.05.

[0049] The final precipitate was washed with deionized water and dried at 120 °C to obtain the coated Ni 0.25 Fe 0.5 Mn 0.25 (OH)2 precursor powder, particle size D50 = 6 μm.

[0050] Synthesis of positive electrode materials: According to the molar ratio of M:Na:Ca:Cu:Ti=1:0.94:0.03:0.005:0.005, the coated Ni 0.2S Fe 0.5 Mn 0.25 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, copper oxide and titanium dioxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 900°C and sintered for 15 hours in an air atmosphere to obtain a sodium-ion battery positive electrode material uniformly doped with calcium, copper and titanium.

[0051] Nitrogen was bubbled into water, and polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, and zirconium acetate were added and thoroughly dispersed. The calcined sodium oxide cathode material was then added, and azobisisobutyronitrile was added as an initiator. The mixture was heated and stirred at 70°C for 6 hours. The mixture was filtered, dried, and ground to obtain a core-shell sodium-based polymer. The mass ratio of the cathode material: polyvinyl alcohol: sodium benzenesulfonate: styrene: magnesium acrylate: zirconium acetate: initiator: water was 110:1.5:5:18:3.5:0.8:0.8:1000.

[0052] The sodium-based polymer was sintered in a kiln at 500°C for 8 hours to obtain the final coated sodium battery positive electrode material.

[0053] Example 2

[0054] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 700 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:45:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 5.0 mol / L EDTA and 5.0 mol / L NaOH solution. The reaction pH was adjusted to 10 for co-precipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L and the reaction was carried out, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.01.

[0055] The final precipitate was washed with deionized water and dried at 120 °C to obtain the coated Ni 0.25 Fe 0.45 Mn 0.30 (OH)2 precursor powder, particle size D50 = 7.2 μm, its SEM image is as follows Figure 1 As shown, there is a certain coating on the surface of the ball.

[0056] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Al: Ce = 1: 0.90: 0.02: 0.005: 0.005, the coated Ni 0.25 Fe 0.45 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, aluminum oxide, and cerium nitrate using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 870°C for 15 hours in an air atmosphere to obtain a uniformly doped sodium-ion high-iron cathode material. The SEM image is shown in FIG. Figure 2 Shown is a polycrystalline structure.

[0057] Nitrogen was bubbled into water, and polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, and zirconium acetate were thoroughly dispersed. A calcined sodium oxide cathode material was added, along with azobisisobutyronitrile as an initiator. The mixture was heated and stirred for 6 hours, filtered, dried, and ground to obtain a core-shell sodium-based polymer. The mass ratio of cathode material: polyvinyl alcohol: sodium benzenesulfonate: styrene: magnesium acrylate: zirconium acetate: initiator: water was 100:1:3:13:3:0.5:0.8:1200.

[0058] The sodium-based polymer was sintered in a kiln at 550°C for 10 hours to obtain the final coated sodium battery positive electrode material.

[0059] Example 3

[0060] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 550 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=20:50:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 3.0 mol / L sodium citrate and 8 mol / L NaOH solution. The reaction pH was adjusted to 10 for co-precipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L to react, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.03.

[0061] The final precipitate was washed with deionized water and dried at 120 °C to obtain the coated Ni 0.20 Fe 0.5 Mn 0.30 (OH)2 precursor powder, material particle size D 50 =4.1μm.

[0062] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Y: B: Ti = 1: 0.94: 0.02: 0.01: 0.015: 0.01, the coated Ni 0.20 Fe 0.5 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, yttrium oxide, boric acid and titanium dioxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 980°C for 15 hours in an air atmosphere to obtain a uniformly doped single-crystal sodium-ion high-iron cathode material. The SEM image is as follows: Figure 3 Shown is the single crystal morphology.

[0063] Nitrogen was bubbled into water, and polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, and zirconium acetate were added and thoroughly dispersed. The calcined sodium oxide cathode material was then added, along with azobisisobutyronitrile as an initiator. The mixture was heated and stirred at 70°C for 6 hours. The mixture was filtered, dried, and ground to obtain a core-shell sodium-based polymer. The mass ratio of the cathode material: polyvinyl alcohol: sodium benzenesulfonate: styrene: magnesium acrylate: zirconium acetate: initiator: water was 120:2:4.5:15:4:1:0.8:1200.

[0064] The sodium-based polymer was sintered in a kiln at 600°C for 10 hours to obtain the final coated sodium battery positive electrode material.

[0065] Example 4

[0066] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was kept at a constant temperature of 50 ° C and stirred at a speed of 500 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:45:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 4.0 mol / L ammonia solution and 5.0 mol / L NaOH solution. The reaction pH was adjusted to 10 for coprecipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L and the reaction was carried out, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.05.

[0067] The final precipitate was washed with deionized water and dried at 120 °C to obtain the coated Ni 0.25 Fe 0.45 Mn 0.30 (OH)2 precursor powder, particle size D50 = 10 μm.

[0068] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Cu: Mg = 1: 0.91: 0.02: 0.01: 0.005, the coated Ni 0.25 Fe 0.45 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, copper oxide and magnesium oxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 850°C and sintered for 15 hours in an air atmosphere to obtain a sodium-ion battery high-iron positive electrode material uniformly doped with calcium, copper and titanium.

[0069] Nitrogen was bubbled into water, and polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, and zirconium acetate were added and thoroughly dispersed. The calcined sodium oxide cathode material was then added, along with azobisisobutyronitrile as an initiator. The mixture was heated and stirred at 70°C for 6 hours. The mixture was filtered, dried, and ground to obtain a core-shell sodium-based polymer. The mass ratio of the cathode material: polyvinyl alcohol: sodium benzenesulfonate: styrene: magnesium acrylate: zirconium acetate: initiator: water was 100:1:3:13:3:0.5:0.8:1100.

[0070] The sodium-based polymer was sintered in a kiln at 450°C for 10 hours to obtain the final coated sodium battery positive electrode material.

[0071] Example 5

[0072] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 500 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:45:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 7 mol / L ammonia solution and 5 mol / L NaOH solution. The reaction pH was adjusted to 10 for co-precipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L to react, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.05.

[0073] The final precipitate was washed with deionized water and dried at 120 °C to obtain the coated Ni 0.25 Fe 0.45 Mn 0.30 (OH)2 precursor powder, particle size D50 = 5.1 μm.

[0074] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Cu: Mg = 1: 0.91: 0.02: 0.01: 0.005, the coated Ni 0.25 Fe 0.45 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, copper oxide and magnesium oxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 850°C and sintered for 15 hours in an air atmosphere to obtain a sodium-ion battery high-iron positive electrode material uniformly doped with calcium, copper and titanium.

[0075] Nitrogen was bubbled into water, and polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, and zirconium acetate were thoroughly dispersed. The calcined sodium oxide cathode material was added, and azobisisobutyronitrile was added as an initiator. The mixture was heated and stirred at 70°C for 6 hours. The mixture was filtered, dried, and ground to obtain a core-shell sodium-based polymer. The mass ratio of the cathode material: polyvinyl alcohol: sodium benzenesulfonate: styrene: magnesium acrylate: zirconium acetate: initiator: water was 100:1:3:13:3:0.5:0.8:1200.

[0076] The sodium-based polymer was sintered in a kiln at 550°C for 10 hours to obtain the final coated sodium battery positive electrode material.

[0077] Comparative Example 1

[0078] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 500 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:45:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 2.0 mol / L EDTA and 4 mol / L NaOH solution. The reaction pH was adjusted to 10 and a co-precipitation reaction was carried out. After the feeding was completed, the precipitate was washed with deionized water and dried at 120 ° C to obtain Ni 0.25 Fe 0.45 Mn 0.30 (OH)2 precursor powder.

[0079] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Cu: Ti = 1: 0.91: 0.02: 0.01: 0.005, the coated Ni 0.25 Fe 0.45 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, copper oxide and magnesium oxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 850°C and sintered for 15 hours in an air atmosphere to obtain a sodium-ion battery high-iron positive electrode material uniformly doped with calcium, copper and titanium.

[0080] Comparative Example 2

[0081] Synthesis of the precursor: 1 L of pure water was added to a 5 L reactor, and sodium hydroxide and ammonia solution were added to adjust the pH to 11. The mixture was stirred at a constant temperature of 50 ° C and a speed of 600 r / min. A mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=25:45:30) with a total concentration of 2.0 mol / L was added to the reactor in parallel with 10.0 mol / L ammonia water and 5.0 mol / L NaOH solution. The reaction pH was adjusted to 10 for co-precipitation reaction. After the feeding was completed, the salt was replaced with a mixed salt solution of NiSO4.6H2O, MnSO4·H2O and FeSO4·7H2O (Ni:Fe:Mn=1:1:1) with a total concentration of 1.0 mol / L to react, keeping the temperature and pH unchanged. The mass ratio of the added amount of the two batches of salt was 1:0.05.

[0082] The final precipitate was washed with deionized water and dried at 120 °C to obtain Ni 0.25 Fe 0.45 Mn 0.30 (OH)2 precursor powder.

[0083] Synthesis of positive electrode materials: According to the molar ratio of M: Na: Ca: Cu: Ti = 1: 0.90: 0.02: 0.01: 0.005, the coated Ni 0.25 Fe 0.45 Mn 0.30 The (OH)2 precursor powder is fully mixed with Na2CO3, calcium carbonate, copper oxide and magnesium oxide using a high-speed mixer, and then the mixture is sintered in a kiln at a sintering temperature of 850°C and sintered for 15 hours in an air atmosphere to obtain a sodium-ion battery high-iron positive electrode material uniformly doped with calcium, copper and titanium.

[0084] Test Example 1

[0085] Preparation of battery electrodes: Active material, conductive agent (SP), and binder (PVDF) are weighed in a mass ratio of 90:5:5. First, 45mg of the weighed active material is dissolved in a certain amount of NMP solvent and stirred continuously until the active material is completely dissolved. Then, PVDF is added to the active material solution. After the PVDF and active material are mixed, the conductive agent is added and stirred continuously. After the active material, SP, and PVDF are mixed, the slurry is evenly applied to aluminum foil using an applicator. The coated copper foil is transferred to a vacuum drying oven and dried at 120°C for 12 hours. Finally, the dried electrode sheet is cut into circular electrode sheets with a diameter of 14mm using a cutting machine. The cut electrode sheets are weighed.

[0086] CR2032 coin cell assembly: In an argon-filled glove box, the positive electrode casing, negative electrode sheet, electrolyte, separator, electrolyte, sodium metal sheet, gasket, spring, and negative electrode casing were stacked in this order. The cells were then pressed into a button cell using a sealing machine and left to activate for 12 hours before testing. The electrolyte was 1M NaPF6 / (PC + 5% FEC); the separator was Whatman glass fiber, and the battery test voltage window was set to 2-4V.

[0087] The test results are shown in Table 1. The 0.1C charge-discharge curve of the positive electrode material obtained in Example 2 is shown in Table 1. Figure 4 The capacity diagram of the positive electrode material obtained in Example 2 of the present invention after 50 cycles at a current density of 1C is shown in FIG. Figure 5 shown.

[0088] When the capacity of the present invention is tested by cycling 50 times at a current density of 1C, the battery is first cycled once at current densities of 0.1C, 0.2C, and 0.5C, and then cycled 50 times at a current density of 1C.

[0089] Table 1 First cycle discharge capacity at 0.1C current density and capacity retention rate of 50 cycles at 1C current density of the examples and comparative examples

[0090]

[0091] From Table 1 and Figure 5 The results show that at a current density of 0.1C (voltage window 2-4V), the battery prepared with the cathode material obtained in Example 2 has an initial discharge capacity of 142mAh / g. At a current density of 1C, the capacity is 130mAh / g. After 50 charge and discharge cycles, the capacity retention rate is still 94.9%, demonstrating excellent long cycle life and stability.

Claims

1. A method for preparing a modified sodium ion battery layered oxygen high iron cathode material, characterized in that: The following steps are involved: (1) mixing a nickel source, an iron source, and a manganese source according to a first molar ratio of nickel, iron, and manganese elements to obtain a layered oxygen salt solution 1, and adding the layered oxygen salt solution 1, an alkali solution, and a complexing agent to a bottom liquid in parallel for a coprecipitation reaction to obtain a layered oxygen precursor; (2) mixing a nickel source, an iron source, and a manganese source according to a second molar ratio of nickel, iron, and manganese elements to obtain a layered oxygen salt solution 2, mixing the layered oxygen salt solution 2, an alkaline solution, a complexing agent, and the layered oxygen precursor in step (1), and coating the layered oxygen precursor to obtain the sodium ion battery layered oxygen high iron positive electrode material precursor; (3) uniformly mixing the sodium ion battery layered oxygen high iron cathode material precursor with a sodium source and a metal compound and then calcining the mixture to obtain a multi-element doped sodium ion battery layered oxygen high iron cathode material; (4) Inert gas is introduced into the solvent, polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate and zirconium acetate are added and fully dispersed, multi-element doped sodium ion battery layered oxygen high iron positive electrode material is added, and an initiator is added to cause polymerization reaction to obtain a core-shell structured sodium-based polymer; (5) calcining the core-shell structured sodium-based polymer to obtain the modified sodium ion battery layered oxygen high iron positive electrode material; wherein the molar ratio of the iron element in the first molar ratio is higher than the molar ratio of the iron element in the second molar ratio; The mass ratio of the salt in the layer oxygen salt solution 1 to the salt in the layer oxygen salt solution 2 is 1:0.01-0.05; In step (1), the first molar ratio of nickel, iron and manganese elements is 20-25:45-50:25-30; In step (2), the second molar ratio of nickel, iron and manganese elements is 1:1:

1.

2. The method for preparing the modified sodium ion battery layered oxygen high iron positive electrode material according to claim 1, characterized in that: The nickel source is at least one of nickel sulfate, nickel acetate and nickel nitrate, The manganese source is at least one of manganese sulfate, manganese acetate and manganese nitrate, The iron source is at least one of ferrous sulfate, ferrous oxalate and ferrous nitrate, The concentrations of the layer oxygen salt solution 1 and the layer oxygen salt solution 2 are both 1.0-5.0 mol / L; The alkali solution is a sodium hydroxide solution, and the concentration of the alkali solution is 2.0-8.0 mol / L. The complexing agent is ammonia water, EDTA or sodium citrate, and the concentration of the complexing agent is 1.0-10.0 mol / L.

3. The method for preparing the modified sodium ion battery layered oxygen high iron positive electrode material according to claim 1, characterized in that: In step (1), the coprecipitation temperature is 40-60°C; In step (2), the particle size D of the precursor of the sodium ion battery layered oxygen high iron positive electrode material is 50 =3.5-10μm.

4. The method for preparing the modified sodium ion battery layered oxygen high iron positive electrode material according to claim 1, characterized in that: In step (3), the sodium source is sodium carbonate, sodium nitrate or sodium hydroxide, The metal compound is one or more of aluminum compounds, copper compounds, calcium compounds, cerium nitrate, titanium compounds, yttrium oxide, and magnesium oxide; The aluminum compound is aluminum oxide or aluminum nitrate, the copper compound is copper oxide or copper sulfate, the calcium compound is calcium carbonate or calcium nitrate, and the titanium compound is titanium dioxide or titanium tetrachloride; The molar ratio of the sodium ion battery layered oxygen high iron cathode material precursor to the sodium source and the metal compound is 1:0.9-1.1:0.01-0.

05.

5. The method for preparing the modified sodium ion battery layered oxygen high iron positive electrode material according to claim 4, characterized in that: The calcination treatment conditions are: calcination temperature is 830-950° C., and calcination time is 10-20 hours.

6. The method for preparing the modified sodium ion battery layered oxygen high iron cathode material according to claim 1, characterized in that: In step (4), the mass ratio of the multi-element doped sodium ion battery layered oxygen high iron positive electrode material to polyvinyl alcohol, sodium benzenesulfonate, styrene, magnesium acrylate, zirconium acetate and solvent is 100-120: 0.2-2: 5-9: 15-21: 2-5: 0.2-2: 0.1-2: 1000-1200; The initiator is azobisisobutyronitrile; The polymerization reaction conditions are: reaction at 60° C. for 6 h.

7. The method for preparing the modified sodium ion battery layered oxygen high iron cathode material according to claim 1, characterized in that: The calcination treatment conditions are: calcination temperature is 450-650° C., and calcination time is 5-10 hours.

8. A modified sodium ion battery layered oxygen high iron positive electrode material prepared by the preparation method according to any one of claims 1 to 7.

9. A sodium ion battery comprising a positive electrode, a separator and a negative electrode, characterized in that: The positive electrode comprises the modified sodium ion battery layered oxygen high iron positive electrode material according to claim 8.

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