Doped and coated sodium-ion positive electrode material, preparation method therefor and use thereof

Abstract

Provided are a doped and coated sodium-ion positive electrode material, a preparation method therefor and a use thereof. The doped and coated sodium-ion positive electrode material comprises a core and a coating layer located on the surface of the core; the core comprises a nickel-iron-manganese sodium-ion positive electrode matrix and a titanium element doped in the nickel-iron-manganese sodium-ion positive electrode matrix; and the coating layer comprises a titanium-containing oxide. According to the provided sodium-ion positive electrode material, by synergistically combining bulk doping of titanium in the core with a titanium-containing oxide surface coating, the voltage decay is mitigated while the capacity is increased.

Description

Doped coated sodium ion positive electrode material and preparation method and use thereof Technical Field

[0001] The present application belongs to the technical field of sodium ion batteries and relates to a doped and coated sodium ion positive electrode material and a preparation method and use thereof. Background Art

[0002] In response to the shortage of lithium resources, people have begun to shift their attention to other battery systems with more abundant raw material reserves. Among them, sodium-ion batteries have the following advantages: (1) The raw material reserves are abundant and low in price, which greatly reduces the cost of batteries; (2) Due to the characteristics of sodium salts, low-concentration electrolytes can be used, reducing costs; (3) Sodium ions do not form alloys with aluminum, and aluminum foil can be used as the negative electrode current collector, which can further reduce costs and weight. However, because sodium ions are larger than lithium ions, more energy is required to drive the movement of ions, which makes the commercial application of sodium-ion batteries difficult. At the same time, sodium ions cannot use graphite as the negative electrode material for sodium ions, which hinders the large-scale application of sodium-ion batteries.

[0003] Research on sodium-ion batteries began around the 1980s. However, due to the inability to find suitable electrode materials, its development has been slow. Therefore, finding suitable sodium-ion electrode materials is one of the keys to the practical application of sodium-ion energy storage batteries. In recent years, a series of positive and negative electrode materials have been developed based on the characteristics of sodium-ion batteries, achieving significant improvements in specific capacity and cycle life. The positive electrode uses polyanions, Prussian blue, oxide materials, especially layered Na x MO2 (M = Fe, Mn, Co, V, Ti) materials exhibit excellent charge and discharge specific capacity and cycle stability, and the negative electrode uses hard carbon, transition metal sulfides, selenides, etc. to achieve matching with the positive electrode capacity.

[0004] However, the capacity and operating voltage of sodium-ion batteries are significantly inferior to those of lithium-ion batteries. Although sodium-ion layered transition metal oxides have the advantage of high capacity, they are prone to phase change during charging and discharging, resulting in capacity and voltage attenuation.

[0005] Therefore, how to effectively improve the capacity of sodium-ion batteries and slow down their voltage decay is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] To address the shortcomings of the existing technology, the present application aims to provide a doped and coated sodium-ion cathode material, its preparation method, and its use. The sodium-ion cathode material provided in this application improves capacity while slowing voltage decay by bulk-doping titanium in the core and synergizing with a titanium oxide-containing surface coating.

[0009] To achieve this goal, this application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a doped coated sodium ion positive electrode material, wherein the doped coated sodium ion positive electrode material comprises a core and a coating layer located on the surface of the core;

[0011] The core comprises a nickel-iron-manganese-sodium ion positive electrode matrix and titanium doped in the nickel-iron-manganese-sodium ion positive electrode matrix;

[0012] The coating layer includes a titanium-containing oxide.

[0013] The sodium ion positive electrode material provided in the present application improves the discharge voltage of the sodium ion battery by bulk doping titanium in the core, thereby increasing the capacity of the battery; at the same time, it cooperates with the surface coating containing titanium oxide to slow down the voltage decay, thereby simultaneously improving the capacity and cycle performance of the sodium ion battery.

[0014] In the present application, the bulk doping of titanium and the coating containing titanium oxide must work together and neither can be missing. If only the bulk doping of titanium is performed, the positive electrode material will be gradually eroded during the charge and discharge process, causing the cycle performance and capacity to gradually decay. If only the coating containing titanium oxide is performed, the disadvantage of poor lattice stability cannot be solved. Doping can increase the cutoff voltage, thereby increasing the specific capacity and energy density.

[0015] The bulk doping of titanium in this application means that titanium is doped during the precursor preparation stage.

[0016] In one embodiment, the core has the general chemical formula Na x Ni a Fe b Mn c Ti d O2, where 0.67≤x≤1, 0<a<1, 0<b<1, 0<c<1, 0 <d<0.2,a+b+c+d=1。

[0017] For example, the x may be 0.67, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1, etc.; the a may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.; the b may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.; the c may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.; the d may be 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18 or 0.19, etc.

[0018] In one embodiment, the titanium-containing oxide comprises titanium dioxide.

[0019] In one embodiment, the mass of the titanium-containing oxide is 0.01-5% of the mass of the sodium ion positive electrode material, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%.

[0020] In the present application, the doping amount of titanium (i.e., its stoichiometric ratio in the core) and the coating amount of titanium oxide are coordinated to better improve the battery capacity and cycle performance.

[0021] In a second aspect, the present application provides a method for preparing the doped coated sodium ion positive electrode material as described in the first aspect, the preparation method comprising the following steps:

[0022] Adding a nickel-iron-manganese mixed salt solution, a titanium source solution, a precipitant solution, and a complexing agent solution in parallel to perform a coprecipitation reaction to obtain a sodium ion precursor material;

[0023] Mixing the sodium ion precursor material with the sodium source and sintering once to obtain the positive electrode material to be coated;

[0024] The positive electrode material to be coated is mixed with the coating titanium source solution in liquid phase and sintered twice to obtain a doped and coated sodium ion positive electrode material.

[0025] The preparation method provided in the present application performs bulk doping of titanium in the precursor stage to achieve uniform doping of titanium (obtaining a nickel-iron-manganese-titanium precursor material), and further performs coating with a titanium-containing oxide to obtain a doped-coated sodium ion positive electrode material; the preparation method is simple to operate, does not require complex processing procedures, and is suitable for large-scale production.

[0026] In the present application, if titanium doping is not performed in the precursor preparation stage but the titanium-containing compound is doped in a single sintering process, uniform doping of the titanium source cannot be achieved, thereby affecting the battery performance.

[0027] In one embodiment, the titanium source solution comprises a titanyl sulfate solution.

[0028] In one embodiment, the reaction temperature of the coprecipitation reaction is 40-100°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0029] In one embodiment, the stirring rate of the coprecipitation reaction is 150-600 rpm, for example, 150 rpm, 230 rpm, 250 rpm, 300 rpm, 400 rpm, 500 rpm or 600 rpm.

[0030] In one embodiment, the pH value of the coprecipitation reaction is 8 to 13, for example, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13.

[0031] In one embodiment, the D50 of the sodium ion precursor material is 2 to 20 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, etc.

[0032] In one embodiment, the primary sintering is performed in an oxygen-containing atmosphere.

[0033] In the present application, the oxygen-containing atmosphere includes air atmosphere and oxygen atmosphere. Those skilled in the art can adaptively select the sintering atmosphere according to specific needs.

[0034] In one embodiment, the primary sintering temperature is 600-1200°C, for example, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0035] In one embodiment, the primary sintering time is 3 to 15 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours.

[0036] In one embodiment, the coating titanium source solution includes a tetraisopropyl titanate solution.

[0037] In this application, tetraisopropyl titanate solution is used to coat and sinter the positive electrode material, which can better improve the coating effect and coating uniformity, thereby better improving the performance.

[0038] In one embodiment, after the liquid phases are mixed, solid-liquid separation and drying are performed.

[0039] In one embodiment, the secondary sintering is performed in an oxygen-containing atmosphere.

[0040] In one embodiment, the secondary sintering temperature is 400-1200°C, for example, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0041] In one embodiment, the secondary sintering time is 3 to 15 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours.

[0042] As an optional technical solution, the preparation method includes the following steps:

[0043] Adding a nickel-iron-manganese mixed salt solution, a titanium source solution, a precipitant solution, and a complexing agent solution in parallel, maintaining a pH value of 8 to 13, and performing a coprecipitation reaction at a temperature of 40 to 100° C. and a stirring rate of 150 to 600 rpm to obtain a sodium ion precursor material with a D50 of 2 to 20 μm;

[0044] Mixing a sodium ion precursor material with a sodium source, and sintering the mixture at a sintering temperature of 600 to 1200° C. for 3 to 15 hours in an oxygen-containing atmosphere to obtain a positive electrode material to be coated;

[0045] The positive electrode material to be coated is mixed with tetraisopropyl titanate in liquid phase, solid-liquid separated, dried, and secondary sintered at 400-1200° C. for 3-15 hours to obtain a doped and coated sodium ion positive electrode material.

[0046] It should be noted that in the preparation process provided in this application, the concentration of the solution, the feed flow rate, the mass ratio of the coating, etc. are not limited, and those skilled in the art can make adaptive adjustments based on the doping amount and the coating amount.

[0047] Meanwhile, during the co-precipitation process, a conventional base liquid (such as a mixed solution of water, ammonia water and alkali solution) can be added to the reactor in advance; and the entire co-precipitation process is carried out under a protective atmosphere.

[0048] The precipitant solution and complexing agent solution in this application are both selected according to conventional technology. For example, this application provides several types of precipitants and complexing agents:

[0049] Optionally, the precipitant includes but is not limited to sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate, etc.

[0050] Optionally, the complexing agent includes but is not limited to ammonia water or sodium citrate.

[0051] Depending on the different precipitants, hydroxide precursor materials or carbonate precursor materials can be obtained accordingly.

[0052] In a third aspect, the present application also provides a sodium ion battery, which includes the doped and coated sodium ion positive electrode material as described in the first aspect.

[0053] Compared with the prior art, this application has the following beneficial effects:

[0054] The sodium ion positive electrode material provided in the present application improves the discharge voltage of the sodium ion battery by bulk doping titanium in the core, thereby increasing the capacity of the battery; at the same time, it cooperates with the surface coating containing titanium oxide to slow down the voltage decay, thereby simultaneously improving the capacity and cycle performance of the sodium ion battery.

[0055] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0057] FIG1 is a SEM image of the precursor material provided in Example 1. DETAILED DESCRIPTION

[0058] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0059] Example 1

[0060] This embodiment provides a doped coated sodium ion layered oxide positive electrode material, the doped coated sodium ion layered oxide positive electrode material comprises a core and a coating layer located on the surface of the core; the core comprises a nickel iron manganese sodium ion positive electrode matrix and titanium element NaNi doped in the nickel iron manganese sodium ion positive electrode matrix. 0.32 Fe 0.32 Mn 0.32 Ti 0.04 O2; the coating layer includes titanium dioxide (the coating mass ratio is 0.05%).

[0061] The preparation method of the positive electrode material is as follows:

[0062] Step 1, preparing solution B containing nickel, iron and manganese and having a total ion concentration of 2 mol / L, wherein the nickel, iron and manganese element ratio is 1:1:1, preparing 2 mol / L titanyl sulfate solution C; preparing industrial liquid caustic soda with a concentration of 10 mol / L as a precipitant solution, and preparing 9 mol / L ammonia water as a complexing agent solution;

[0063] Step 2: A base solution A containing a certain precipitant solution and a complexing agent solution is prepared in a reactor, wherein the pH of A is controlled at 10, the ammonia concentration of A is 5 g / L, and the temperature of A is 40° C.; nitrogen is introduced as a protective gas, and a mixed salt solution B, a titanium solution C, a precipitant solution, and a complexing agent solution are added to the reactor in parallel, and a coprecipitation reaction is carried out with a conventional stirring blade at a speed of 300 rpm. The reaction temperature during the reaction is 40° C., and seed particles with a target particle size D50 of 4 μm are obtained;

[0064] Step 3: centrifuging, washing, drying, and removing magnetic foreign matter from the obtained spherical nickel-iron-manganese-titanium precursor to obtain spherical precursor particles;

[0065] Step 4: Washing and drying: The reacted material is centrifuged and washed, and then dried at 200°C.

[0066] Step 5, solid phase sintering reaction: the precursor powder and Na2CO3 powder were uniformly mixed in a molar ratio of 1:1.02, and calcined at 800°C in air atmosphere for 6 hours to obtain a sintered material NNFMTO;

[0067] Step 6: Add 89 g of tetraisopropyl titanate to 30 L of anhydrous ethanol solution and mix evenly, then add 5 kg of NNFMTO and stir for 1.5 h. After heating and evaporating to dryness, calcinate the material at 500 ° C for 8 h to obtain a doped coated positive electrode material.

[0068] Example 2

[0069] This embodiment provides a doped coated sodium ion layered oxide positive electrode material, the doped coated sodium ion layered oxide positive electrode material comprises a core and a coating layer located on the surface of the core; the core comprises a nickel iron manganese sodium ion positive electrode matrix and titanium element NaNi doped in the nickel iron manganese sodium ion positive electrode matrix. 0.32 Fe 0.32 Mn 0.32 Ti 0.04 O2; the coating layer includes titanium dioxide (the coating mass ratio is 0.01%).

[0070] The preparation method of the positive electrode material is as follows:

[0071] Step 1, preparing solution B containing nickel, iron and manganese and having a total ion concentration of 2 mol / L, wherein the nickel, iron and manganese element ratio is 1:1:1, preparing 2 mol / L titanyl sulfate solution C; preparing industrial liquid caustic soda with a concentration of 10 mol / L as a precipitant solution, and preparing 9 mol / L ammonia water as a complexing agent solution;

[0072] Step 2: A base solution A containing a certain precipitant solution and a complexing agent solution is prepared in a reactor, wherein the pH of A is controlled at 10.8, the ammonia concentration of A is 8 g / L, and the temperature of A is 50° C.; nitrogen is introduced as a protective gas, and a mixed salt solution B, a titanium solution C, a precipitant solution, and a complexing agent solution are added to the reactor in parallel, and a co-precipitation reaction is carried out using a conventional stirring blade at a speed of 380 rpm. The reaction temperature during the reaction is 50° C. to obtain seed particles with a target particle size D50 of 8 μm;

[0073] Step 3: centrifuging, washing, drying, and removing magnetic foreign matter from the obtained spherical nickel-iron-manganese-titanium precursor to obtain spherical precursor particles;

[0074] Step 4: Washing and drying: The reacted material is centrifuged and washed, and then dried at 200°C.

[0075] Step 5, solid phase sintering reaction: the precursor powder and Na2CO3 powder were uniformly mixed in a molar ratio of 1:1.02, and calcined at 800°C in air atmosphere for 6 hours to obtain a sintered material NNFMTO;

[0076] Step 6: Add 3.56 g of tetraisopropyl titanate to 5 L of anhydrous ethanol solution and mix evenly, then add 5 kg of NNFMTO and stir for 1.5 h. After heating and evaporating to dryness, calcinate the material at 500 ° C for 8 h to obtain a doped coated positive electrode material.

[0077] Example 3

[0078] This embodiment provides a doped coated sodium ion layered oxide positive electrode material, the doped coated sodium ion layered oxide positive electrode material comprises a core and a coating layer located on the surface of the core; the core comprises a nickel iron manganese sodium ion positive electrode matrix and titanium element NaNi doped in the nickel iron manganese sodium ion positive electrode matrix. 0.3 Fe 0.32 Mn 0.32 Ti 0.06 O2; the coating layer includes titanium dioxide (the coating mass ratio is 0.3%).

[0079] The preparation method of the positive electrode material is as follows:

[0080] Step 1, preparing solution B containing nickel, iron and manganese and having a total ion concentration of 2 mol / L, wherein the nickel, iron and manganese element ratio is 1:1:1, preparing 2 mol / L titanyl sulfate solution C; preparing industrial liquid caustic soda with a concentration of 10 mol / L as a precipitant solution, and preparing 9 mol / L ammonia water as a complexing agent solution;

[0081] Step 2: A base solution A containing a certain precipitant solution and a complexing agent solution is prepared in a reactor, wherein the pH of A is controlled at 10, the ammonia concentration of A is 5 g / L, and the temperature of A is 40° C.; nitrogen is introduced as a protective gas, and a mixed salt solution B, a titanium solution C, a precipitant solution, and a complexing agent solution are added to the reactor in parallel, and a coprecipitation reaction is carried out with a conventional stirring blade at a speed of 300 rpm. The reaction temperature during the reaction is 40° C., and seed particles with a target particle size D50 of 12 μm are obtained;

[0082] Step 3: centrifuging, washing, drying, and removing magnetic foreign matter from the obtained spherical nickel-iron-manganese-titanium precursor to obtain spherical precursor particles;

[0083] Step 4: Washing and drying: The reacted material is centrifuged and washed, and then dried at 200°C.

[0084] Step 5, solid phase sintering reaction: the precursor powder and Na2CO3 powder were uniformly mixed in a molar ratio of 1:1.02, and calcined at 800°C in air atmosphere for 6 hours to obtain a sintered material NNFMTO;

[0085] Step 6: Add 267 g of tetraisopropyl titanate to 100 L of anhydrous ethanol solution and mix evenly, then add 5 kg of NNFMTO and stir for 1.5 h. After heating and evaporating to dryness, calcinate the material at 500 ° C for 8 h to obtain a doped coated positive electrode material.

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 is that the doping amount of titanium in this embodiment is NaNi 0.3 Fe 0.1 Mn 0.3 Ti 0.2 O2.

[0088] In the preparation method, the amount of titanium source added is adaptively adjusted.

[0089] The rest of the preparation methods and parameters were the same as those in Example 1.

[0090] Example 5

[0091] The difference between this embodiment and embodiment 1 is that the coating mass ratio of titanium dioxide in this embodiment is 0.005%.

[0092] In the preparation method, the amount of titanium dioxide added as the coating raw material is adaptively adjusted.

[0093] The rest of the preparation methods and parameters were the same as those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 1 is that the coating mass ratio of titanium dioxide in this embodiment is 6%.

[0096] In the preparation method, the amount of titanium dioxide added as the coating raw material is adaptively adjusted.

[0097] The rest of the preparation methods and parameters were the same as those in Example 1.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that titanium is not doped in this comparative example.

[0100] The rest of the preparation methods and parameters were the same as those in Example 1.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that the positive electrode material provided in this example is a core, that is, no titanium dioxide coating is performed.

[0103] In the preparation method, the titanium dioxide coating and sintering process is not carried out.

[0104] The rest of the preparation methods and parameters were the same as those in Example 1.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is that in this comparative example, the nickel source, iron source, manganese source, and titanium source are mixed and ball-milled and sintered to obtain a doped precursor, and the subsequent steps are consistent with Example 1.

[0107] The rest of the preparation methods and parameters were the same as those in Example 1.

[0108] The positive electrode materials, acetylene black and polyvinylidene fluoride provided in Examples 1-6 and Comparative Examples 1-3 were mixed in a mass ratio of 8:1:1, and added to N-methyl-2-pyridine to obtain a positive electrode slurry. The positive electrode slurry was evenly applied on an aluminum foil, dried, and punched into a thin sheet to obtain a positive electrode sheet; the positive electrode sheet, elemental sodium sheet, glass fiber separator, electrolyte (sodium salt is NaClO4) gasket, shrapnel and battery shell were assembled into a button battery in an Ar gas glove box.

[0109] The positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-3 were used to prepare button-type batteries, and electrochemical performance test data were performed at a charge and discharge voltage of 2.0 to 4.0 V. The test results are shown in Table 1.

[0110] Table 1

[0111] From the data results of Example 1 and Examples 4-6, it can be seen that in the present application, the synergistic combination of the titanium doping amount and the titanium oxide coating amount can better improve the battery capacity and cycle performance.

[0112] From the data results of Example 1 and Comparative Examples 1-3, it can be seen that the present application must achieve the simultaneous improvement of cycle performance and capacity through the coordinated cooperation of bulk doping of titanium and surface coating containing titanium oxide.

[0113] In summary, the sodium ion positive electrode material provided by the present application increases the discharge voltage of the sodium ion battery by bulk doping titanium in the core, thereby increasing the capacity of the battery; at the same time, it cooperates with the titanium oxide-containing surface coating to slow down the voltage decay, thereby simultaneously improving the capacity and cycle performance of the sodium ion battery.

[0114] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A doped and coated sodium ion cathode material, comprising a core and a coating layer on the surface of the core; The core includes a nickel-iron-manganese sodium ion cathode matrix and titanium elements doped in the nickel-iron-manganese sodium ion cathode matrix; The coating layer includes titanium-containing oxides.

2. The doped and coated sodium ion cathode material according to claim 1, wherein, The chemical general formula of the core is Na x Ni a Fe b Mn c Ti d O 2 , where 0.67 ≤ x ≤ 1, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 0.2, and a + b + c + d = 1.

3. The doped and coated sodium ion cathode material according to claim 1 or 2, wherein, The titanium-containing oxides include titanium dioxide; Optionally, the mass of the titanium-containing oxides is 0.01-5% of the mass of the sodium ion cathode material.

4. A preparation method of the doped and coated sodium ion cathode material according to any one of claims 1-3, comprising the following steps: Adding a nickel-iron-manganese mixed salt solution, a titanium source solution, a precipitant solution and a complexing agent solution in parallel flow to carry out a coprecipitation reaction to obtain a sodium ion precursor material; Mixing the sodium ion precursor material with a sodium source and sintering once to obtain a cathode material to be coated; Mixing the cathode material to be coated with a coating titanium source solution in a liquid phase and sintering twice to obtain the doped and coated sodium ion cathode material.

5. The preparation method according to claim 4, wherein, The titanium source solution includes a titanyl sulfate solution; Optionally, the reaction temperature of the coprecipitation reaction is 40-100 °C; Optionally, the stirring rate of the coprecipitation reaction is 150-600 rpm; Optionally, the pH value of the coprecipitation reaction is 8-13.

6. The preparation method according to claim 4 or 5, wherein, The D50 of the sodium ion precursor material is 2-20 μm.

7. The preparation method according to any one of claims 4-6, wherein, The first sintering is carried out in an oxygen-containing atmosphere; Optionally, the temperature of the first sintering is 600-1200 °C; Optionally, the time of the first sintering is 3-15 h.

8. The preparation method according to any one of claims 4-7, wherein, The coating titanium source solution includes a tetra-isopropyl titanate solution; Optionally, after the liquid phase mixing, solid-liquid separation and drying are carried out; Optionally, the second sintering is carried out in an oxygen-containing atmosphere; Optionally, the temperature of the second sintering is 400-1200 °C; Optionally, the time of the second sintering is 3-15 h.

9. The preparation method according to any one of claims 4-8, wherein, The preparation method includes the following steps: Adding a nickel-iron-manganese mixed salt solution, a titanium source solution, a precipitant solution and a complexing agent solution in parallel flow, maintaining the pH value at 8-13, and carrying out a coprecipitation reaction at a temperature of 40-100 °C and a stirring rate of 150-600 rpm to obtain a sodium ion precursor material with a D50 of 2-20 μm; Mixing the sodium ion precursor material with a sodium source and carrying out the first sintering at a sintering temperature of 600-1200 °C for 3-15 h in an oxygen-containing atmosphere to obtain a cathode material to be coated; Mixing the cathode material to be coated with tetra-isopropyl titanate in a liquid phase, carrying out solid-liquid separation, drying, and carrying out the second sintering at 400-1200 °C for 3-15 h to obtain the doped and coated sodium ion cathode material.

10. A sodium-ion battery comprising the doped-coated sodium-ion cathode material according to any one of claims 1-3.

Images