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

Abstract

A doped coated sodium battery positive electrode material, and a preparation method therefor and the use thereof. The doped coated sodium battery positive electrode material comprises a core and a shell, wherein the chemical general formula of the core is NabNixTiyMnzMkO2, where 0.6≤b≤1.2, x+y+z+k=1, 0.1≤x≤0.5, 0.01≤y≤0.10, 0.2≤z≤0.6, 0.1≤k≤0.5, and M comprises a transition metal element; and the shell comprises a transition metal oxide. As for the sodium battery positive electrode material, by means of doping, the stability of oxygen in the material is improved, and oxygen vacancies and structural recession are inhibited; and by means of being coated with a metal oxide shell, metal ions are prevented from being dissolved out, thereby improving the air stability and cycle performance of the material, such that the capacity retention rate of a battery can still reach 80% or above after 4000 cycles.

Description

A doped and coated sodium battery cathode material, its preparation method and application Technical Field

[0001] This application belongs to the field of battery technology and relates to a doped and coated sodium battery cathode material, its preparation method and application. Background Art

[0002] With the popularization of renewable energy and electric vehicles, the global demand for energy storage technologies is increasing day by day, and it has become crucial to efficiently store and regulate energy. Lithium-ion batteries have shown great promise in the energy storage field due to their high energy density, long life and excellent rate performance, and have been widely used in fields such as electric vehicles and portable devices. However, the scarcity of lithium resources limits its sustainable development, and the price fluctuations and unstable supply of other materials further increase the uncertainty of battery costs. Due to the rich reserves of sodium resources and their similar chemical properties to lithium, sodium-ion batteries have attracted much attention and are expected to reduce the dependence on scarce lithium resources.

[0003] Among them, layered metal oxide-type sodium battery cathode materials (Na x TMO2, TM = transition metals such as Co, Fe, Mn, Ni, 0 < x < 1), due to their low cost, low toxicity and high theoretical specific capacity, have become one of the potential candidate materials for sodium battery cathodes. However, at the end of the discharge process, this material will exhibit the Jahn-Teller effect and phase transformation of Mn 3+ , resulting in capacity decay during the charge and discharge process of the battery. In addition, the air stability of layered metal oxides is poor, and they are prone to react with water and carbon dioxide in the air, promoting the generation of alkaline substances, which further exacerbates the attenuation of the cell performance. In order to improve its performance and address these problems, doping and coating and other means are usually used to modify it.

[0004] For example, CN 114300658A discloses a doped and coated sodium battery cathode material and its preparation method. Coating MS2 on the surface of the vanadium-aluminum doped sodium battery cathode material effectively eliminates the active oxygen formed during the charge and discharge process of the sodium battery cathode material, inhibits the oxidation and decomposition of the electrolyte to produce gas, and can also form a stable coating layer to prevent it from contacting the electrolyte, improving the cycle performance and stability.

[0005] For example, CN 116417590A discloses a sodium ion battery positive electrode material coated with anion and cation co-doping and a preparation method thereof. The outer layered transition metal oxide formed by the co-doping of anion and cations is coated with an inner layered transition metal oxide to form a ternary material, which improves the air stability and reduces the contact area between the inner layered transition metal oxide and the electrolyte, thereby slowing down the occurrence of interfacial side reactions and improving the cyclic stability of the material; and the doped cations help to reduce the effective coordination of O atoms, enhance the TM-O bond strength and narrow the TMO2 layer. At the same time, the anions form a covalent bond with oxygen. This synergistic modification and regulation of the crystal structure mechanism of the material by anion and cations expands the sodium layer spacing, which is beneficial to sodium ion transmission and reduces the loss of lattice oxygen. It can not only improve the structural stability and expand the voltage window, but also improve its specific capacity, high first efficiency and cyclic stability.

[0006] However, although the layered oxide positive electrode materials for sodium ion batteries in the existing technology have good gram capacity, their air stability is poor and their cycle performance is not ideal (usually between 1000 and 2000 cycles), which cannot meet the application of sodium ion batteries in the energy storage field.

[0007] Based on the above research, it is necessary to provide a doped and coated sodium battery positive electrode material, which can inhibit oxygen vacancies and structural degradation and has extremely excellent air stability and cycle performance.

[0008] Summary of the Invention

[0009] 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.

[0010] The purpose of the present application is to provide a doped and coated sodium cathode material, a preparation method and an application thereof. The sodium cathode material improves the stability of oxygen in the material by doping, inhibits oxygen vacancies and structural decay, thereby improving the stability of the material in the electrochemical cycle. By coating with a metal oxide shell, metal ion dissolution is avoided, the air stability and cycle performance of the material are improved, and the capacity retention rate of the battery can still reach more than 80% after 4000 cycles.

[0011] To achieve this goal, this application adopts the following technical solutions:

[0012] In the first aspect, the present application provides a doped coated sodium positive electrode material, the doped coated sodium positive electrode material comprises a core and a shell, the chemical formula of the core is Na b Ni x Ti y Mn z M kO2, wherein 0.6≤b≤1.2, x+y+z+k=1, 0.1≤x≤0.5, 0.01≤y≤0.10, 0.2≤z≤0.6, 0.1≤k≤0.5, M includes a transition metal element, and the outer shell includes a transition metal oxide.

[0013] The present invention improves the conductivity of the material by uniformly doping inactive metal titanium and M elements in the interior of the sodium positive electrode material. At the same time, the surface spinel structure is conducive to Na + transmission, thereby improving the capacity of the battery. In addition, the Ti-O bond provided by titanium doping improves the stability of oxygen, thereby inhibiting oxygen vacancies and structural decay, and therefore maintains better stability during the electrochemical cycle. At the same time, the present application coats the surface of the positive electrode material with a transition metal oxide shell, thereby avoiding the dissolution of transition metal ions during long-term cycling, thereby achieving the purpose of improving the electrochemical performance.

[0014] The 0.6≤b≤1.2 may be, for example, 0.6, 0.8, 1.0 or 1.2, x+y+z+k=1, 0.1≤x≤0.5 may be, for example, 0.15, 0.2, 0.4 or 0.5, 0.01≤y≤0.10 may be, for example, 0.01, 0.03, 0.05, 0.07 or 0.09, 0.2≤z≤0.6 may be, for example, 0.3, 0.5 or 0.6, 0.1≤k≤0.5 may be, for example, 0.15, 0.2, 0.4 or 0.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0015] In one embodiment, the M includes any one or a combination of at least two of Co, Cu or Fe.

[0016] In one embodiment, the shell comprises V2O5.

[0017] The shell of this application is vanadium pentoxide, which acts as a coating to provide sodium ion channels during the charge and discharge process, improving ionic conductivity. Furthermore, the V2O5 coating provides a protective outer shell, inhibiting structural changes in the positive electrode material during charge and discharge. Furthermore, the surface V2O5 coating exhibits excellent stability in both air and electrolyte, effectively isolating the CO2 / H2O in the air from the electrolyte, significantly improving the material's stability in both air and electrolyte.

[0018] In one embodiment, the mass ratio of the core to the shell is (20-100):1, for example, 30:1, 50:1, 70:1, 90:1 or 100:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In a second aspect, the present application provides a method for preparing the doped and coated sodium cathode material as described in the first aspect, the preparation method comprising the following steps:

[0020] (1) mixing and sintering the doped precursor material and the sodium source to obtain a cathode material intermediate;

[0021] (2) Mixing a transition metal source, a solvent and the cathode material intermediate of step (1), drying and calcining to obtain the doped and coated sodium cathode material.

[0022] In one embodiment, the cathode material intermediate in step (1) is washed and dried before step (2).

[0023] In one embodiment, the washing liquid used in the washing comprises deionized water.

[0024] The positive electrode material intermediate of the present application is washed with water before being coated, which can improve the bonding strength between the coating layer and the coated material, thereby avoiding the pulverization and shedding of the coating layer. Therefore, the air stability and cycle performance of the sodium battery positive electrode material of the present application can be significantly improved.

[0025] In one embodiment, the mass ratio of the positive electrode material intermediate to the washing liquid in step (1) is 1:(20-30), for example, it can be 1:20, 1:23, 1:25, 1:27, 1:29 or 1:30, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] The mass ratio of the positive electrode material intermediate to the washing liquid in this application will affect the washing effect and the stability of the positive electrode material. If the amount of washing liquid is too small, the contact interface between the coating layer and the positive electrode material will be unstable during the coating process, causing the coating layer to pulverize or fall off. Therefore, the amount of detergent should be increased appropriately during the washing process. Although excessive detergent can achieve the desired effect, it will cause unnecessary material loss.

[0027] In one embodiment, the transition metal source in step (2) includes a vanadium source.

[0028] In one embodiment, the solid-liquid ratio of the vanadium source to the solvent in step (2) is (0.13-0.65) g:90 mL, for example, 0.15 g:90 mL, 0.3 g:90 mL, 0.5 g:90 mL or 0.6 g:90 mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] In one embodiment, the mass ratio of the vanadium source to the positive electrode material intermediate of step (1) is (0.013-0.065):1, for example, it can be 0.015:1, 0.03:1, 0.05:1 or 0.065:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In one embodiment, the calcination atmosphere in step (2) includes an oxygen-containing atmosphere, the temperature is 500-700°C, for example, 550°C, 600°C, 650°C or 700°C, and the time is 2-5h, for example, 3h, 4h or 5h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In one embodiment, the sintering atmosphere in step (1) includes an oxygen-containing atmosphere, the temperature is 800-1400°C, for example, it can be 900°C, 1100°C, 1300°C or 1400°C, and the time is 10-25h, for example, it can be 12h, 15h, 20h or 25h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In one embodiment, the doped precursor material in step (1) is prepared by the following method:

[0033] Mixing the mixed metal salt solution, the precipitant solution and the complexing agent solution to perform a coprecipitation reaction to obtain the doped precursor material;

[0034] The mixed metal salt solution includes nickel salt, titanium salt, manganese salt and M salt.

[0035] In one embodiment, the total metal ion concentration in the mixed metal salt solution is 0.5-5 mol / L, for example, 1 mol / L, 3 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] In one embodiment, the feed rate of the mixed metal salt solution is 4-100 L / h, for example, 10 L / h, 30 L / h, 50 L / h, 70 L / h, 90 L / h or 100 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In one embodiment, the concentration of the precipitant solution is 2-15 mol / L, for example, 3 mol / L, 5 mol / L, 10 mol / L or 15 mol / L, and the feed rate is 1-20 L / h, for example, 5 L / h, 10 L / h, 15 L / h or 20 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In one embodiment, the concentration of the complexing agent solution is 4-12 mol / L, for example, 5 mol / L, 8 mol / L, 10 mol / L or 12 mol / L, and the feed rate is 0.5-10 L / h, for example, 3 L / h, 5 L / h, 8 L / h or 10 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In one embodiment, the temperature of the coprecipitation reaction is 20-70°C, for example, 30°C, 50°C or 70°C, and the pH is maintained in the range of 8-12, which means that the minimum pH of the coprecipitation reaction is above 8, for example, 8, 8.25, 8.5, 8.75 or 9, and the maximum pH is below 12, for example, 12, 11.8, 11.6, 11.4 or 11, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In one embodiment, the mixed metal salt solution, precipitant solution and complexing agent solution are simultaneously introduced into the base liquid to carry out a coprecipitation reaction. The pH of the base liquid is 8-12, for example, 8, 9, 10, 11 or 12, and the concentration of the complexing agent is 0-2 mol / L, for example, 0 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] As an optional technical solution of the preparation method described in this application, the preparation method comprises the following steps:

[0042] (1) introducing a mixed metal salt solution, a precipitant solution, and a complexing agent solution into a base solution in parallel to perform a coprecipitation reaction, wherein the coprecipitation reaction temperature is 20-70° C. and the pH is maintained in the range of 8-12 to obtain the doped precursor material;

[0043] The mixed metal salt solution includes nickel salt, titanium salt, manganese salt and M salt, the total metal ion concentration of the mixed metal salt solution is 0.5-5 mol / L, and the feed rate is 4-100 L / h;

[0044] (2) mixing the doped precursor material with a sodium source, and then sintering the mixture in an oxygen-containing atmosphere at a temperature of 800-1400° C. for 10-25 hours to obtain a cathode material intermediate;

[0045] (3) washing and drying the positive electrode material intermediate of step (2), wherein the mass ratio of the positive electrode material intermediate of step (2) to the washing liquid is 1:(20-30), to obtain a washed positive electrode material intermediate;

[0046] The vanadium source, the solvent and the washed positive electrode material intermediate are mixed and dried, and then calcined at a temperature of 500-700° C. for 2-5 hours in an oxygen-containing atmosphere to obtain the doped and coated sodium positive electrode material.

[0047] In a third aspect, the present application provides a sodium ion battery, which includes the doped and coated sodium cathode material as described in the first aspect.

[0048] Compared with the prior art, this application has the following beneficial effects:

[0049] The present application improves the electrical conductivity of the material by doping metal elements, and the Ti-O bonds provided by titanium doping improve the stability of oxygen, thereby inhibiting oxygen vacancies and structural decay, and thus maintaining better stability during the electrochemical cycle; at the same time, the present application coats the surface of the positive electrode material with a transition metal oxide shell, avoiding the dissolution of transition metal ions during long-term cycling, thereby achieving the purpose of improving electrochemical performance.

[0050] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] 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.

[0052] FIG1 is a SEM image of the doped precursor material described in Example 1 of the present application;

[0053] FIG2 is an SEM image of the doped and coated sodium cathode material described in Example 1 of the present application. DETAILED DESCRIPTION

[0054] 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.

[0055] Example 1

[0056] This embodiment provides a doped coated sodium cathode material, the doped coated sodium cathode material comprises a core and an outer shell, the chemical formula of the core is Na[Ni 0.4 Ti 0.1 Mn 0.4 Co 0.1 ]O2, the outer shell is V2O5, and the mass ratio of the inner core to the outer shell is 60:1;

[0057] The preparation method of the doped and coated sodium cathode material comprises the following steps:

[0058] (1) Sulfate solutions of nickel, titanium, manganese, and cobalt were mixed in proportion at a molar ratio of 0.40:0.10:0.40:0.10 to obtain a mixed metal salt solution, and the mixed metal salt solution with a total metal ion concentration of 2 mol / L, a sodium hydroxide solution with a concentration of 10 mol / L, and an ammonia solution with a concentration of 8 mol / L were added concurrently to a base solution with a pH of 12.4 and an ammonia concentration of 1 mol / L, and a coprecipitation reaction was carried out at 50° C. After the reaction was completed, the solution was centrifuged and washed, and dried at 120° C. to obtain the doped precursor material. The SEM image of the doped precursor material is shown in FIG1 ;

[0059] The mixed metal salt solution was fed at a rate of 40 L / h, and the pH of the reaction system was controlled between 11.3 and 11.5, and the ammonia concentration was controlled between 0.9 and 1.1 mol / L by adjusting the flow rates of the sodium hydroxide solution and aqueous ammonia. The coprecipitation reaction was stopped when the average particle size of the product reached 8 μm.

[0060] (2) mixing the doped precursor material and sodium carbonate at a metal ion molar ratio of 1:1.08, and then sintering at 1400° C. for 16 h in an air atmosphere to obtain a positive electrode material intermediate;

[0061] (3) mixing the cathode material intermediate of step (2) with deionized water at a mass ratio of 1:30, stirring and washing, and then drying to obtain a washed cathode material intermediate;

[0062] Dissolving ammonium metavanadate in a 50° C. aqueous solution to form an ammonium metavanadate aqueous solution, then adding the washed positive electrode material intermediate to the ammonium metavanadate aqueous solution, followed by drying, and finally calcining at 600° C. for 3 h in an air atmosphere, cooling to room temperature, and grinding and sieving to obtain the doped and coated sodium positive electrode material. The SEM image of the doped and coated sodium positive electrode material is shown in FIG2 ;

[0063] In the ammonium metavanadate aqueous solution, the solid-liquid ratio of ammonium metavanadate to water is 0.4 g:90 mL, and the mass ratio of the ammonium metavanadate to the washed positive electrode material intermediate is 0.04:1.

[0064] Example 2

[0065] This embodiment provides a doped coated sodium cathode material, the doped coated sodium cathode material comprises a core and an outer shell, the chemical formula of the core is Na[Ni 0.30 Ti 0.05 Mn 0.45 Fe 0.20 ]O2, the outer shell is V2O5, and the mass ratio of the inner core to the outer shell is 20:1;

[0066] The preparation method of the doped and coated sodium cathode material comprises the following steps:

[0067] (1) mixing sulfate solutions of nickel, titanium, manganese, and iron in a molar ratio of 0.30:0.05:0.45:0.20 to obtain a mixed metal salt solution, adding the mixed metal salt solution with a total metal ion concentration of 1.5 mol / L, a sodium hydroxide solution with a concentration of 12 mol / L, and ammonia water with a concentration of 10 mol / L to a base liquid with a pH of 12 and an ammonia concentration of 0.8 mol / L in parallel, and performing a coprecipitation reaction at 45° C. After the reaction is completed, centrifugation and washing are performed, and drying is performed at 150° C. to obtain the doped precursor material;

[0068] The mixed metal salt solution was fed at a rate of 10 L / h, and the pH of the reaction system was controlled between 11.0 and 11.5, and the ammonia concentration was controlled between 0.7 and 0.9 mol / L by adjusting the flow rates of the sodium hydroxide solution and aqueous ammonia. The coprecipitation reaction was stopped when the average particle size of the product reached 8 μm.

[0069] (2) mixing the doped precursor material and sodium carbonate at a metal ion molar ratio of 1:1.07, and then sintering at 1100° C. for 12 h in an air atmosphere to obtain a positive electrode material intermediate;

[0070] (3) mixing the cathode material intermediate of step (2) with deionized water at a mass ratio of 1:20, stirring and washing, and then drying to obtain a washed cathode material intermediate;

[0071] dissolving ammonium metavanadate in an aqueous solution at 50° C. to form an ammonium metavanadate aqueous solution, then adding the washed positive electrode material intermediate to the ammonium metavanadate aqueous solution, drying, and finally calcining at 500° C. for 5 hours in an air atmosphere, cooling to room temperature, and grinding and sieving to obtain the doped and coated sodium positive electrode material;

[0072] In the ammonium metavanadate aqueous solution, the solid-liquid ratio of ammonium metavanadate to water is 0.13 g:90 mL, and the mass ratio of the ammonium metavanadate to the washed positive electrode material intermediate is 0.013:1.

[0073] Example 3

[0074] This embodiment provides a doped coated sodium cathode material, the doped coated sodium cathode material comprises a core and an outer shell, the chemical formula of the core is Na[Ni 0.4 Ti 0.1 Mn 0.4 Co 0.1]O2, the shell is V2O5, and the mass ratio of the core to the shell is 100:1;

[0075] The preparation method of the doped and coated sodium cathode material comprises the following steps:

[0076] (1) mixing sulfate solutions of nickel, titanium, manganese, and cobalt in a molar ratio of 0.40:0.10:0.40:0.10 to obtain a mixed metal salt solution, adding the mixed metal salt solution with a total metal ion concentration of 4 mol / L, a sodium hydroxide solution with a concentration of 15 mol / L, and ammonia water with a concentration of 12 mol / L to a base liquid with a pH of 9 and an ammonia concentration of 2 mol / L in parallel, and performing a coprecipitation reaction at 70° C. After the reaction is completed, centrifugation and washing are performed, and drying is performed at 120° C. to obtain the doped precursor material;

[0077] The mixed metal salt solution was fed at a rate of 5 L / h, and the pH of the reaction system was controlled between 11.3 and 11.5, and the ammonia concentration was controlled between 0.9 and 1.1 mol / L by adjusting the flow rates of the sodium hydroxide solution and aqueous ammonia. The coprecipitation reaction was stopped when the average particle size of the product reached 8 μm.

[0078] (2) mixing the doped precursor material and sodium carbonate at a metal ion molar ratio of 1:1.08, and then sintering at 800° C. for 25 h in an air atmosphere to obtain a positive electrode material intermediate;

[0079] (3) mixing the cathode material intermediate of step (2) with deionized water at a mass ratio of 1:30, stirring and washing, and then drying to obtain a washed cathode material intermediate;

[0080] Dissolving ammonium metavanadate in a 50° C. aqueous solution to form an ammonium metavanadate aqueous solution, then adding the washed positive electrode material intermediate to the ammonium metavanadate aqueous solution, followed by drying, and finally calcining at 700° C. for 2 hours in an air atmosphere, cooling to room temperature, and grinding and sieving to obtain the doped and coated sodium positive electrode material;

[0081] In the ammonium metavanadate aqueous solution, the solid-liquid ratio of ammonium metavanadate to water is 0.65 g:90 mL, and the mass ratio of the ammonium metavanadate to the washed positive electrode material intermediate is 0.065:1.

[0082] Example 4

[0083] This embodiment provides a doped and coated sodium cathode material. The doped and coated sodium cathode material is the same as that of embodiment 1 except that the outer shell is Al2O3.

[0084] The preparation method of the doped and coated sodium cathode material is the same as that of Example 1, except that the solid-liquid ratio of the ammonium metavanadate aqueous solution in step (3) is replaced by an aluminum nitrate solution.

[0085] Example 5

[0086] This embodiment provides a doped and coated sodium cathode material. The doped and coated sodium cathode material is the same as that of embodiment 1 except that the outer shell is ZnO.

[0087] The preparation method of the doped and coated sodium cathode material is the same as that of Example 1, except that the solid-liquid ratio of the ammonium metavanadate aqueous solution in step (3) is replaced by a zinc nitrate solution.

[0088] Example 6

[0089] This embodiment provides a doped and coated sodium cathode material. The doped and coated sodium cathode material is the same as that in Example 1 except that in the preparation method thereof, step (3) is not washed with water, and the cathode material intermediate described in step (2) is directly used for coating, so that the obtained doped and coated sodium cathode material is changed accordingly.

[0090] Example 7

[0091] This embodiment provides a doped and coated sodium cathode material. The doped and coated sodium cathode material is the same as that in Example 1 except that, in the preparation method, the cathode material intermediate described in step (2) is mixed, stirred and washed with deionized water at a mass ratio of 1:10 to change the obtained doped and coated sodium cathode material accordingly.

[0092] Example 8

[0093] This embodiment provides a doped and coated sodium cathode material. The doped and coated sodium cathode material is the same as that in Example 1 except that in its preparation method, the cathode material intermediate described in step (2) is mixed, stirred and washed with deionized water at a mass ratio of 1:40 to make the obtained doped and coated sodium cathode material change accordingly.

[0094] Comparative Example 1

[0095] This comparative example provides a sodium cathode material. The sodium cathode material is the same as Example 1 except that in the preparation method thereof, titanium is not doped when preparing the precursor material in step (1), and the molar ratio of nickel, manganese, and cobalt is 0.40:0.40:0.1, so that the adaptability of the obtained sodium cathode material is changed.

[0096] Comparative Example 2

[0097] This comparative example provides a sodium battery positive electrode material, which is the same as Example 1 except that it does not include a shell;

[0098] The method for preparing the sodium cathode material is the same as that of Example 1 except that step (3) is not performed.

[0099] Comparative Example 3

[0100] This comparative example provides a sodium cathode material. The sodium cathode material is the same as Example 1 except that in its preparation method, titanium is not doped when preparing the precursor material in step (1), the molar ratio of nickel, manganese and cobalt is 0.40:0.40:0.1, and the coating step in step (3) is not performed to adapt the obtained sodium cathode material.

[0101] At 25°C, the sodium cathode materials prepared in the above examples and comparative examples were used as the main cathode materials, and the sodium metal sheet was used as the negative electrode to assemble a CR2032 button battery. Then, the discharge current density was 20 mA g in the voltage range of 1.5-4.1 V. -1 The electrochemical performance test was carried out under the following conditions. The test results of the capacity retention rate after 4000 cycles are shown in the following table:

[0102] Table 1

[0103] From Table 1 we can see that:

[0104] It can be seen from Example 1 and Comparative Examples 1-3 that the present application significantly improves the cycle performance of the sodium ion battery by doping and coating, and can still achieve a capacity retention rate of more than 80% after up to 4000 cycles; it can be seen from Example 1 and Examples 4-5 that the specific vanadium pentoxide coating of the present application can further improve the battery cycle performance; it can be seen from Example 1 and Examples 6-8 that the present application is first washed with water before coating, and the specific amount of detergent ensures the washing effect, improves the bonding strength between the coating layer and the coated material, thereby avoiding the powdering and falling off of the coating layer, thereby further improving the cycle performance of the battery.

[0105] In summary, the present application provides a doped and coated sodium cathode material, a preparation method and an application thereof. The sodium cathode material improves the stability of oxygen in the material by doping, inhibits oxygen vacancies and structural decay, thereby improving the stability of the material in the electrochemical cycle. By coating with a metal oxide shell, the dissolution of metal ions is avoided, the air stability and cycle performance of the material are improved, and the capacity retention rate of the battery can still reach more than 80% after 4,000 cycles.

[0106] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A doped-coated sodium battery cathode material, comprising a core and a shell, and the chemical general formula of the core is Na b Ni x Ti y Mn z M k O 2 , Among them, 0.6 ≤ b ≤ 1.2, x + y + z + k = 1, 0.1 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.10, 0.2 ≤ z ≤ 0.6, 0.1 ≤ k ≤ 0.5, M includes transition metal elements, and the shell includes transition metal oxides.

2. The doped and coated sodium battery cathode material according to claim 1, Among them, the M includes any one or a combination of at least two of Co, Cu or Fe; Optionally, the housing includes V 2 O 5 ; Optionally, the mass ratio of the core to the shell is (20 - 100):

1.

3. A method for preparing the doped and coated sodium battery cathode material according to claim 1 or 2, comprising the following steps: (1) Mix and sinter the doped precursor material with a sodium source to obtain a cathode material intermediate; (2) Mix, dry and calcine the transition metal source, the solvent and the cathode material intermediate obtained in step (1) to obtain the doped and coated sodium battery cathode material.

4. According to the preparation method described in claim 3, Among them, before performing step (2), the cathode material intermediate obtained in step (1) is first washed and dried; Optionally, the washing liquid used for washing includes deionized water; Optionally, the mass ratio of the cathode material intermediate obtained in step (1) to the washing liquid is 1:(20 - 30).

5. According to the preparation method described in claim 3 or 4, Among them, the transition metal source in step (2) includes a vanadium source; Optionally, the solid-liquid ratio of the vanadium source to the solvent in step (2) is (0.13 - 0.65) g:90 mL; Optionally, the mass ratio of the vanadium source to the cathode material intermediate obtained in step (1) is (0.013 - 0.065):

1.

6. According to the preparation method described in any one of claims 3 - 5, Among them, the atmosphere of the calcination in step (2) includes an oxygen-containing atmosphere, the temperature is 500 - 700 °C, and the time is 2 - 5 h; Optionally, the atmosphere of the sintering in step (1) includes an oxygen-containing atmosphere, the temperature is 800 - 1400 °C, and the time is 10 - 25 h.

7. According to the preparation method described in any one of claims 3 - 6, Among them, the doped precursor material in step (1) is prepared by the following method: Mix the mixed metal salt solution, the precipitant solution and the complexing agent solution, and perform a coprecipitation reaction to obtain the doped precursor material; the mixed metal salt solution includes nickel salt, titanium salt, manganese salt and M salt; Optionally, the total metal ion concentration in the mixed metal salt solution is 0.5 - 5 mol / L; Optionally, the feeding rate of the mixed metal salt solution is 4 - 100 L / h.

8. According to the preparation method described in claim 7, Among them, the concentration of the precipitant solution is 2 - 15 mol / L, and the feeding rate is 1 - 20 L / h; Optionally, the concentration of the complexing agent solution is 4 - 12 mol / L, and the feeding rate is 0.5 - 10 L / h; Optionally, the temperature of the coprecipitation reaction is 20 - 70 °C, and the pH is maintained in the range of 8 - 12; Optionally, the mixed metal salt solution, precipitating agent solution, and complexing agent solution are simultaneously introduced into the bottom liquid for coprecipitation reaction. The pH of the bottom liquid is 8 - 12, and the concentration of the complexing agent is 0 - 2 mol / L.

9. The preparation method according to any one of claims 3 - 8, wherein, the preparation method comprises the following steps: (1) Simultaneously introduce the mixed metal salt solution, precipitating agent solution, and complexing agent solution into the bottom liquid for coprecipitation reaction. The temperature of the coprecipitation reaction is 20 - 70 °C, and the pH is maintained within the range of 8 - 12 to obtain the doped precursor material; The mixed metal salt solution includes nickel salt, titanium salt, manganese salt, and M salt. The total metal ion concentration of the mixed metal salt solution is 0.5 - 5 mol / L, and the feeding rate is 4 - 100 L / h; (2) Mix the doped precursor material with a sodium source, and then in an oxygen-containing atmosphere, at a temperature of 800 - 1400 °C, sinter for 10 - 25 h to obtain the cathode material intermediate; (3) Wash and dry the cathode material intermediate obtained in step (2). Among them, the mass ratio of the cathode material intermediate obtained in step (2) to the washing liquid is 1:(20 - 30) to obtain the washed cathode material intermediate; Mix and dry the vanadium source, solvent, and the washed cathode material intermediate, and then calcine at a temperature of 500 - 700 °C for 2 - 5 h in an oxygen-containing atmosphere to obtain the doped and coated sodium battery cathode material.

10. A sodium ion battery comprising the doped and coated sodium battery cathode material according to claim 1 or 2.

Images